Consulting Specifying Engineer July August 2026

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Decarbonization in HVAC design

NEWS &BUSINESS

5 | Integrated building systems need more than technology to succeed MEP engineers are being asked to do more than ever with integrated building systems.

BUILDING SOLUTIONS

6 | How decarbonization achieves resilience in HVAC design

For long-term resilience in HVAC, decarbonization and risk management go hand in hand.

12 | Decarbonization in HVAC design: A phased approach

Decarbonization is best achieved through an approach that reduces building energy demand and electrifies equipment.

18 | Tips for operating room AHU energy efficiency and controls

Learn some practical control strategies for OR air handling units.

24 | How to achieve ASHRAE 62.1 compliance for VAV system design

Meeting ASHRAE 62.1 requirements for variable air volume systems presents unique challenges.

30 | Case study: How one museum modernized its electrical system

New electrical systems include a vault upgrade and generators to support modern power demands.

ENGINEERING INSIGHTS

36 | How to design industrial facilities for future-ready service

Learn how industrial facility engineers address electrification, automation and supply chain pressures.

AMARA ROZGUS, Editor-in-Chief ARozgus@WTWHMedia.com

FRANCES RICHARDS, Associate Editor FRichards@WTWHMedia.com

AMANDA PELLICCIONE, Marketing Research Manager APelliccione@WTWHMedia.com

MICHAEL SMITH, Art Director MSmith@WTWHMedia.com

EDITORIAL ADVISORY BOARD

DARREN BRUCE, PE, LEED AP BD+C, Director of Strategic Planning, Mid-Atlantic Region, NV5, Arlington, Va.

MICHAEL CHOW, PE, CEM, CXA, LEED AP BD+C, Principal, Metro CD Engineering LLC, Columbus, Ohio

CINDY COGIL, PE, FASHRAE, Vice President, SmithGroup, Chicago

TOM DIVINE, PE, Senior Electrical Engineer, Johnston, LLC, Houston

CORY DUGGIN, PE, LEED AP BD+C, BEMP, Energy Modeling Wizard, TLC Engineering Solutions, Brentwood, Tenn.

PAUL ERICKSON, LEED AP BD+C Principal, Affiliated Engineers Inc., Madison, Wis.

ROBERT J. GARRA JR., PE, CDT, Vice President, Electrical Engineer, CannonDesign, Grand Island, N.Y.

JASON GERKE, PE, LEED AP BD+C, CXA, Senior Design Phase Manager, JP Cullen, Milwaukee

JOSHUA D. GREENE, PE, Associate Principal, Simpson Gumpertz & Heger, Waltham, Mass.

RAYMOND GRILL, PE, FSFPE, LEED AP, Principal, Ray Grill Consulting, PLLC, Clifton, Va.

WILLIAM KOFFEL, PE, FSFPE, President, Koffel Associates Inc., Columbia, Md.

WILLIAM KOSIK, PE, CEM, LEGACY LEED AP BD+C, Associate Principal, Sector Leader, HED, Chicago

KENNETH KUTSMEDA, PE, LEED AP, Engineering Manager, Jacobs, Philadelphia

DAVID LOWREY, Chief Fire Marshal, Boulder (Colo.) Fire Rescue

JASON MAJERUS, PE, CEM, LEED AP, Principal, DLR Group, Cleveland

CALEB MARVIN, PE, Senior Associate, Associate Partner, Certus Consulting Engineers, Dallas

JUSTIN MILNE, PE, PMP, Senior Engineer, Southcentral Region, Jensen Hughes, Allen, Texas

SPENCER PERRY, PE, Senior Vice President/Regional Team Leader, CDM Smith Inc., Maitland, Fla.

CRAIG ROBERTS, CEM, Account Executive, National Technical Services, McKinstry, Powell, Tenn.

SUNONDO ROY, PE, LEED AP, Director, Design Group, Romeoville, Ill.

JONATHAN SAJDAK, PE, Senior Associate/Fire Protection Engineer, Page, Houston

RANDY SCHRECENGOST, PE, CEM, Austin Operations Group Manager/Senior Mechanical Engineer, Stanley Consultants, Austin, Texas

MATT SHORT, PE, Project Manager/Mechanical Engineer, Smith Seckman Reid, Houston

RICHARD VEDVIK, PE, Senior Electrical Engineer and Acoustics Engineer, IMEG Corp., Rock Island, Ill.

TOBY WHITE, PE, LEED AP, Associate, Boston Fire & Life Safety Leader, Arup, Boston

APRIL WOODS, PE, LEED AP BD+C, Vice President, WSP USA, Orlando, Fla.

JOHN YOON, PE, LEED AP ID+C, Lead Electrical Engineer, McGuire Engineers Inc., Chicago

Integrated building systems need more than technology to succeed

Mechanical, electrical, plumbing (MEP) and fire protection engineers are being asked to do more with integrated building systems as the profession is under internal pressure. This year’s State of Integrated Building Systems findings make that point: Owners are requesting integrated systems more often, with survey respondents indicating a 14% increase over last year’s results. At the same time, respondents indicate that barriers to successful integration are becoming more human and organizational, not just technical.

Amara Rozgus, Editor-in-Chief

This is where artificial intelligence (AI) joins the conversation, not as a replacement for engineering judgment, but as a force multiplier. AI can help firms organize and interpret operational data, identify patterns in building performance, support fault detection and improve the speed and quality of analysis tied to integrated systems. In an environment where experienced leaders may be stretched thin and younger staff need faster development, AI can help close part of the gap by making complex operating information more accessible and actionable.

Two findings stand out: Limited employee skills and knowledge to operate technology rose 10 percentage points from last year, reaching 40%. At the same time, the share of respondents who said building owners and consulting engineers need better alignment around ongoing support and training climbed 11 points to 55%.

That concern should resonate across MEP engineering firms, especially as they navigate succession planning and knowledge transfer. The survey did not measure workforce age directly, but the broader industry context is hard to ignore.

Across engineering, firms have been contending with retirements and the challenge of moving long-standing knowledge to the next generation quickly enough to meet demand. With integrated building systems, that knowledge is not limited to design fundamentals.

But AI will not solve the workforce problem on its own. Firms still need to invest in training, mentorship and hands-on development. They need to give younger engineers exposure to real integration challenges, not just design documents. They need senior professionals to transfer practical knowledge before it leaves the organization.

We are seeing an important shift in this market. Integrated building systems are no longer just about connecting technologies. They are about bridging generations of expertise, translating data into value and preparing engineering leaders in a more intelligent building environment. If the profession wants to meet growing client expectations, workforce development must be the center of the conversation. cse

BUILDING SOLUTIONS

Grace Turner, EIT, SmithGroup, Chicago, and Nancy Kohout, PE, LEED AP, Buro Happold, Chicago

Improved ways decarbonization achieves resilience in HVAC design

When considering long-term resilience in heating, ventilation and air conditioning, decarbonization and risk management go hand in hand.

Risk aris es from uncertainty and heating, ventilation and air conditioning (HVAC) systems are exposed to uncertainty from many directions. Consider something as simple and integral to HVAC design as outdoor design conditions: Cooling systems must meet demand during the warmest outdoor conditions, yet no weather forecast can accurately predict the temperature over the lifetime of the equipment. Unless equipment is severely oversized, there remains a risk that the highest temperature is beyond what a building can accommodate.

Mechanical designers weigh many risks in the design process: the potential for unforeseen maintenance snafus, changes in municipal code, supply chain issues and even natural disasters all impact the approach to good mechanical design. The list of catastrophes to consider — and strategies to avoid them — can become dizzying. While decarbonization is not synonymous with risk avoidance, it provides a framework to approach longer-term risks.

Courtesy: SmithGroup

Emissions measurement

Combustion systems, such as those that burn natural gas, coal or oil, play many roles in the built environment. When fuel is burned to generate heat, power the electric grid or move vehicles, waste gases are also generated, which are exhausted from the system. The waste gases, typically carbon dioxide (CO2), nitrogen dioxide and methane, enter the atmosphere and impact the way radiation from the sun warms the planet, trapping heat like windows of a greenhouse.

Global scientific consensus ties these atmospheric changes to warming ocean temperatures, glacial melt resulting in rising sea levels and more extreme temperatures and weather events. Per research from RMI, buildings make up 40% of global energy greenhouse gas (GHG) emissions, with mechanical systems contributing a significant amount to overall operational emissions.

Common language is key to understanding the impact that mechanical strategies have on decarbonization. As sustainable design becomes a fixture in the built environment, the industry has adopted standardized language to discuss decarbonization. Key terms for mechanical designers to be familiar with are explained below.

Global warming potential (GWP): Different gases emitted have different impacts on the greenhouse properties of Earth’s atmosphere. The GWP of an emitted gas is the impact that it has relative to CO2, which has a potential of one. This provides a consistent metric for understanding the impact of all gases emitted from a process.

The Intergovernmental Panel on Climate Change quantifies the global warming potential for seven main GHGs.

FIGURE 1: Decarbonization strategies can be broken into three pillars, which each have risk management benefits.

Scope emissions: The GHG Protocol established scope emissions as a standard framework for carbon accounting. The three scopes break down where emissions originate across a value chain:

• Scope 1 emissions are direct emissions from on-site installations, such as from fuel burned by a natural gas steam boiler.

• Scope 2 emissions are indirect emissions associated with energy purchased from off-site, in the form of electricity, heat or steam, such as from a coal-fired powerplant generating electricity supplied to a building.

• Scope 3 emissions are other indirect emissions associated with the production, transportation and disposal of purchased materials, such as from a diesel truck delivering construction materials to a site.

Embodied versus operational emissions: This is another framework, often used in conjunction with the GHG Protocol’s scopes, to address how a building’s emissions are reflected over the course of its entire lifetime.

Operational emissions refer to emissions associated with the energy a building needs to operate, such as those tied to the electricity and natural gas that keep the lights on and the boiler running. For most buildings, emissions associated with mechanical system operation makes up a significant portion of operational emissions.

Embodied emissions (also referred to as embodied carbon) are the emissions generated from manufacturing, transporting, constructing, maintaining and disposing of building materials. Mechanical, electrical and plumbing (MEP) systems can account for more than half of a building’s embodied emissions. Total operational emissions over the course of a building’s lifetime plus its embodied emissions make up “whole life carbon.”

Decarbonization as a risk management strategy

The consequences of choices made regarding the environment will be felt for generations. While the future remains opaque, scientists connect the actively occurring phenomena of droughts and wildfires across the Western U.S., increased hurricanes and flooding across the Eastern U.S. and record temperature highs across the continent to human-caused atmospheric changes. The World Health Organization expects climate change to contribute to at least 250,000 additional deaths per year — with 3.6 billion people living in areas currently susceptible to climate change.

Engineers have an ethical imperative to design systems that hold paramount the safety, health and welfare of the public; as such, engineers have a responsibility to consider how their designs contribute to this ongoing crisis. Engineers also have a responsibility to their clients. Decarbonization strategies continue to be highly sought after, even as regulatory barriers in the U.S. have increased with the rollbacks of Inflation Reduction Act (IRA)

FIGURE 2: Rooftop view from DC Water Headquarters, which uses an innovative wastewater thermal recovery system to decrease total energy use. Courtesy: SmithGroup

Objectives Learningu

• Understand the key decarbonization concepts and terminology used throughout the industry.

• Know the common risks facing HVAC systems and how decarbonization strategies can help mitigate them.

• Consider a holistic decarbonization framework when designing systems for both sustainability and low risk.

BUILDING SOLUTIONS

‘Regardless of where the building is located, it will be subject to changing regulations.’

credits and complex permitting processes.

Setting aside several motivators, the power of decarbonization extends beyond industry goals and client wishes into the fundamentals of good design: Decarbonization strategies are also risk management strategies. When considering the lifetime of mechanical systems, decarbonization can be a framework to build toward resiliency against unknown changes to come.

Climate risk

Decarbonization strategies can be separated into three fundamental pillars: reducing the energy used, managing energy sources and considering materials. As these strategies support decarbonization goals, they also support risk management goals.

Weather in the 2020s has been different than weather in the 1990s. Weather is getting both warmer and more extreme. More catastrophic weather events are being recorded, with droughts on the western side of the U.S. and hurricanes in the eastern U.S. While exact changes are difficult to predict, major shifts to climatic conditions are likely to continue to occur.

Outdoor conditions are integral to mechanical engineering: From a purely psychrometric point of view, changes in climatic conditions will impact sizing and performance of systems and viability of passive strategies. While exact trends in future temperatures are unpredictable, the ASHRAE Handbook of Fundamentals urges the consideration of projected future data as a design exercise.

Catastrophic weather events threaten energy systems even more directly. Hurricanes, flooding, wildfires and tornados can cause power outages

lasting anywhere from minutes to days. For many buildings, a power outage is a major inconvenience. For some, outages can present crippling expenses or significant safety hazards. Sensitive buildings such as laboratories or hospitals often cannot afford to be subject to power outages.

Regulatory risk

Buildings continue to exist through political and regulatory changes. For example, 2025 saw many changes regarding federal support of sustainability initiatives, including the freezing of Department of Energy (DOE) loans and a rollback of some IRA tax credits.

Other changes are happening at the state and municipal levels. Twenty-three states have a policy establishing climate action plans, while eight states released new or updated climate plans in 2025. All of these plans incorporate building energy performance standards and many include energy codes, appliance efficiency standards and benchmarking or reporting requirements. Twelve states have fasttracked renewable siting and permitting.

Globally, regulations are also changing. The United Kingdom has strengthened building codes and net-zero mandates, Australia has implemented climate reporting regulations and France has implemented strict building regulations for both operational and embodied emissions.

Regardless of where the building is located, it will be subject to changing regulations. Throughout the lifetime of an HVAC system, it is likely to be held to increasingly higher standards.

Financial risk

Financial uncertainty is perhaps the easiest risk to quantify yet the hardest to predict.

In October 1973, text across a full-page ad in a Maine newspaper voiced a fear many Americans were facing at the time: “Will there be enough oil to keep us warm this winter?” The price of oil had just quadrupled, from $2.90 to $11.65 a barrel because of the 1973 OPEC oil embargo and subsequent energy crisis. Many homeowners attempted to reduce energy bills by turning down their thermostats and installing better insulation. Woodstoves, a fading alternative to heating oil, skyrocketed in popularity as residents sought ways to stay warm. While price spikes have yet to be as drastic as

CASE STUDY:

Learn three ways a campus building approached sustainability

THIS CASE STUDY EXAMINES strategies for reducing building-related carbon emissions through energy-efficient and sustainable design solutions in the built environment.

Decarbonization can be a powerful way to approach risk management. Strategies that support decarbonization can be separated into three fundamental pillars: reducing the energy used, managing energy sources and considering materials. As these approaches support decarbonization goals, they also support risk management goals. Learn how these strategies were applied to an educational project at the University of Michigan (U-M) Edward and Rosalie Ginsberg Building.

The building is a deeply impactful community center designed to support civic engagement between students, community organizations and U-M. The building is a hub for meaningful social change and the design reflects this: It is universally accessible, with spaces designed for conversation and collaboration and it visually complements the surrounding neighborhood. It is also one of U-M’s first carbon-neutral buildings.

The building is a model of sustainable performance and is on track to achieve LEED v4 Gold BD+C Certification. This aligns with U-M’s priorities of climate justice and the decarbonization strategies play into good design beyond helping meet campus goals. Strategies used to achieve this and how they relate to risk management include:

Pillar 1: Reduced energy use

• High COP equipment: More efficient mechanical, electrical and plumbing equipment means less energy used and reduced electric demand from the utility. This can result in smaller utility bills, more manageable transmission infrastructure and lower time-of-use costs.

• Geothermal boreholes (500 feet deep): The stable temperature of the earth insulates the connected ground source heat pump from dramatic fluctuations in outdoor temperature.

those of the 1973 oil crisis, the cost of oil continues to fluctuate unpredictably. As geopolitical conflict raised the cost of gas in March 2026, some people turned to electric vehicles to insulate themselves from unpredictable budgets.

Electricity is also subject to these fluctuations. The U.S. Bureau of Labor Statistics reports that electricity has risen roughly twice as fast as overall inflation since the pandemic. This can be attribut-

3: The Edward and Rosalie Ginsberg Building is all-electric and uses decarbonization strategies like high-COP equipment, geothermal loops and a highly effective envelope. Courtesy: SmithGroup

Pillar 2: Strategic energy sources

• All-electric system: The building is conditioned with a watersource heat pump connected to geothermal boreholes. By relying entirely on electricity, building operation is insulated from fluctuations in prices of other fuels and could potentially be attached to independent renewable generation or electric storage in the future. This building will continue to have a smaller carbon footprint as Michigan’s electric grid incorporates more renewables.

Pillar 3: Intentional material choice

• High-performance envelope: The high-performance exterior has an insulation value 50% greater than required by code, preserving interior conditions for longer and reducing wasted energy.

• Limited, intentional glazing: A small number of triple-glazed, high-performance glass windows promote daylighting while reducing envelope losses.

• Hybrid timber construction and low-carbon concrete: By using innovative, low-carbon materials, the building’s embodied footprint is 23% less than similar buildings. These materials also foster a healthy space that visually complements its surroundings.

ed to an aging electric grid as well as an unprecedented rise in demand, much of it attributed to data centers serving artificial intelligence. As utilities attempt to manage peaks, time-of-use demand charges are driving utility costs.

A strategy for decarbonization

Decarbonization strategies will vary by building and location, but all can be sorted into three pillars.

FIGURE

BUILDING SOLUTIONS

‘Considering material sourcing and required maintenance reduces a project’s embodied emissions.’

1. Use less energy: A building that uses less energy contributes fewer operational emissions to the environment. It is also less sensitive to shocks to the energy system. A building that requires less energy to operate will spend less on utility bills if there is a spike in gas or electricity costs and will reach smaller peaks during extreme weather events. It will be easier to store enough energy to weather gaps in supply and if energy supply is short, will allow more buildings to operate.

Decarbonization strategies for using less energy:

• Choose efficient equipment: Designing around equipment with a higher coefficient of performance (COP), such as geothermal heat pumps, will help the same amount of energy result in more heat or cooling.

• Right-size equipment: Improperly sized equipment will run less efficiently.

• Improve the building envelope: Consider where equipment is located as well as penetrations in the envelope to keep the energy that was already used.

• Capture waste energy: Technology such as heat recovery chillers can reuse energy that would otherwise be exhausted, which can reduce overall consumption when deployed properly.

• Use economizers: Outdoor air can be levered to an advantage, helping meet a building’s internal load when conditions are appropriate.

2. Consider energy sources: A building that designs around a reliable energy source or generates its own energy is insulated from many shocks. Independent energy sources are becoming easier, greener and cheaper to install locally and when directly attached to a project can help reduce energy bills and withstand outages.

Decarbonization strategies for energy sourcing:

• Electrification: Buildings that burn fossil fuels on site will always generate the same emissions. Buildings attached to an electric grid will automatically become greener as more renewable energy sources continue to be installed.

• Design for time of use: Electricity drawn from the grid during hours of peak generation, especially from intermittent renewables like solar, results in fewer Scope 2 emissions and fewer demand charges.

• Energy storage: Thermal storage or electric storage can help systems undergo outages or shift usage times.

• Renewable generation: Solar panels, connected wind and even micronuclear generation can remove a project’s reliance on outside energy sources.

3. Manage material sourcing: Considering material sourcing and required maintenance reduces a project’s embodied emissions. It can also be a key strategy for reducing construction and maintenance costs and avoiding supply chain issues. Decarbonization strategies for materials:

• Adaptive reuse: When feasible, renovating existing buildings can avoid the material cost — and embodied emissions — of building from scratch.

• Sustainable refrigerants: High-GWP refrigerants can contribute significantly to a building’s embodied emissions and leaks over time can potentially compound this impact. Lower-GWP refrigerants avoid this risk. As regulations and guidance around refrigerants shift, systems that depend on refrigerants with high GWPs will face more restrictions and be harder to maintain.

• Local sourcing: Emissions associated with material transportation and risks associated with complicated supply chains can be reduced by sourcing local materials where possible.

The art of decarbonization

Mechanical design is called design for a reason: Good engineering requires creativity. Many strategies for decarbonization and risk management can be contradictory and different engineers will arrive at different solutions. Refrigerants provide a fantastic example: Some sustainable refrigerants may make the system cheaper to maintain and easier to dispose of — and may also make the system operate at a lower COP, raising operational energy costs and exposing a system to fluctuations in energy pricing.

Costs, regulations and equipment constraints complicate the puzzle. It falls to the engineer to determine the appropriate balance of efficiency and lower embodied emissions. Looking into the future and considering the risks that the system will be exposed to can provide clarity. One project may prioritize a more efficient system, while another may choose a more sustainable refrigerant, while a third may consider a combination that prioritizes reducing whole-life carbon.

While no project can implement every single decarbonization strategy, every project will find benefit in considering tools for a greener design. The role that decarbonization plays in design will change depending on the project, client and geographic region. Weighing decarbonization from a risk management perspective can reframe the process of mechanical design from an immediate-cost perspective to a long-term, future-proof one.

Mechanical engineers have a unique opportunity and responsibility to build systems for a greener and safer future. cse

Grace Turner, EIT, is a building performance analyst on SmithGroup’s Integrated Multidisciplinary Performance-Analytics Climate Action Team.

Nancy Kohout, PE, LEED AP, is a Principal and MEP Engineering Leader at Buro Happold, serves on the Executive Committee of ASHRAE’s Center of Excellence for Building Decarbonization and is a founder of the Women in ASHRAE Leadership Symposium.

csemag.com

Decarbonization insights

uBuildings account for nearly 40% of global carbon emissions, pushing engineers to prioritize decarbonization, energy efficiency and resilient building systems.

uOwners and designers are increasingly seeking integrated solutions that balance sustainability goals with long-term operational performance and occupant needs.

26_003825_Consulting_Specifying_Engineer_JUL Mod: April 24, 2026 4:50 PM Print: 05/15/26 page 1 v2.5

COLUMBUS

BUILDING SOLUTIONS

Jaclyn Kinson, PE, CDM Smith, Boston, and Matthew Goss, PE, PMP, CEM, CEA, CDSM, LEED AP, CDM Smith, Albany, New York

Decarbonization in HVAC design: A phased process approach

Decarbonization is best achieved through a phased, systems-level approach that reduces building energy demand, electrifies HVAC equipment and integrates clean energy sources to minimize operational carbon emissions.

Decarb onization is a strategic and systematic effort aimed at reducing and removing fossil fuels and their associated carbon emissions from the environment. Decarbonization is aimed at creating a cleaner, healthier and safer environment for current and future generations.

According to the International Energy Agency (IEA), building operations account for 26% of global carbon dioxide (CO2) emissions and 30% of global energy consumption (see Figure 1). Direct emissions from buildings account for 8% of global CO2 emissions, while indirect emissions from the production of electricity and heat used

FIGURE 1: According to the International Energy Agency, building operations account for 26% of global carbon dioxide (CO2) emissions. Direct emissions from buildings account for 8% of global CO2 emissions, while indirect emissions from the production of electricity and heat used in buildings account for 18%. Courtesy: CDM Smith

in buildings account for 18%. Buildings are a major contributor to global and United States greenhouse gas emissions, even more than transportation or agriculture. According to the U.S. Environmental Protection Agency (EPA), the building sector accounts for 31% of emissions in the United States.

Building decarbonization must target both embodied carbon and operational carbon. As defined by the ASHRAE Center of Excellence for Building Decarbonization, embodied carbon is the amount of carbon emitted over a building’s life cycle, from construction through end of life, including raw materials and refrigerants. Operational carbon is the amount of carbon emitted from the building during operation, including emissions from energy and water consumption.

Multiple studies from ASHRAE, the U.S. Department of Energy (DOE) and IEA show that heating, ventilation and air conditioning (HVAC) systems typically account for approximately 40% or more of total building energy use. HVAC systems are the largest energy end use in buildings, surpassing lighting as lighting efficiency standards have improved more quickly than HVAC efficiency standards. As a result, HVAC decarbonization is a critical pathway for reducing building-related emissions.

Policy drivers for HVAC decarbonization

Several federal, state and local policies have been implemented to drive the acceleration of HVAC decarbonization. At the federal level, the Inflation Reduction Act (IRA) provides long-term financial incentives for HVAC electrification, energy efficiency retrofits and clean energy integration, significantly lowering the cost barrier to building decarbonization. The Commercial Building Energy Efficiency Tax Deduction (Section 179D) provides

support for HVAC, lighting, envelope and water heating upgrades that reduce energy use intensity (EUI). The IRA also includes long-term tax credits for heat pumps, geothermal systems and renewable electricity to support emissions reductions.

At the state and local levels, various governments have enacted stricter policies to accelerate decarbonization, including but not limited to HVAC. Washington State’s Clean Buildings Performance Standard (CBPS) mandates energy performance targets for existing buildings, compelling HVAC system or control upgrades where heating, cooling and ventilation energy use exceeds established EUI thresholds. The CBPS requires compliance with ASHRAE Standard 100: Energy Efficiency in Existing Buildings (2018) energy performance targets.

New York City’s (NYC) Local Law 97 established building-level carbon emissions caps for buildings over 25,000 square feet, starting in 2024, with stricter limits taking effect in 2030. According to NYC Department of Buildings, more than two-thirds of greenhouse gas emissions come from buildings in the city, making HVAC electrification and efficiency upgrades essential for compliance in large commercial and residential buildings.

HVAC decarbonization

It is crucial for HVAC design engineers to consider and implement decarbonization efforts into HVAC design for both new and existing buildings. A building’s average lifespan is typically between 50 and 100 years, with many structures lasting longer when properly maintained. Mechanical systems typically have a lifespan of 25 years and will be replaced several times during a building’s life. Therefore, HVAC systems provide an opportunity to reduce long-term operational carbon emissions in existing buildings.

HVAC decarbonization is most efficiently achieved by following a phased process: Reduce energy demand, electrify systems and integrate clean energy sources (see Figure 2). This progression relies on the premise that the most cost-effective and emissions-friendly unit of energy is the one not currently being used. Once energy efficiency measures have been implemented and system and equipment sizes and performance have been optimized, progression would then lead to electrified replacements, followed by clean energy source integration.

FIGURE 2: Decarbonization in HVAC systems can be achieved by following a phased, systematic approach. First, reduce building energy demand. Second, electrify HVAC systems. Third, integrate clean energy sources. Courtesy: CDM Smith

FIGURE 3: An energy recovery ventilator unit installed at an administration building in Massachusetts. The ventilator exchanges heat between outdoor air and ventilation from occupied spaces. It operates in air economizer mode when the outdoor air temperature is below 60°F and modulates the outside air damper and return air damper to maintain the mixed air temperature set point. Courtesy: CDM Smith

By lowering heating and cooling loads first, energy efficiency measures reduce peak electrical demand and enable smaller and more cost-effective electrified systems. Therefore, the scale of renewable energy and required grid infrastructure is minimized. Without aggressive efficiency measures, electrification alone risks increasing energy costs, straining electrical systems and limiting the feasibility of deeper carbon reductions over the building’s remaining lifetime.

HVAC decarbonization: A phased approach

PHASE 1: Reducing energy demand (energy efficiency)

Often guided by the energy auditing process, identification and implementation of energy efficiency measures is a critical step to cost-effective decarbonization. Energy efficiency reduces heating and cooling loads, minimizes system sizes and improves operational energy usage.

Energy efficiency measures such as passive design strategies, improving building thermal envelopes and optimizing ventilation strategies can be

Learningu

Objectives

• Understand why decarbonizing HVAC systems is important in the context of global and United States energy consumption.

• Learn how to achieve HVAC decarbonization using a phased, systematic approach.

• Understand how integrating clean energy sources such as sewage waste heat recovery can reduce emissions in buildings.

BUILDING SOLUTIONS

FIGURE 4: A split-system airsource heat pump installed at an administration building in Massachusetts. The outdoor condenser unit is on the roof (pictured), with an indoor unit located inside the space. Refrigerant is circulated between the outdoor condensing unit and the indoor evaporator, providing both heat and cooling to the space at high efficiencies. Courtesy: CDM Smith

implemented to reduce a building’s heating and cooling loads.

The Passive House Institute developed the Passive House standard for building performance. To meet the standard, buildings must achieve a 90% reduction of energy needs for heating and cooling and a 75% reduction of overall energy use compared to conventional building construction. Passive design strategies reduce energy loads by shaping the building form and thermal envelope to work with local climate conditions. Strategies such as building orientation, shading, high-performance thermal envelopes, daylighting and natural ventilation limit unwanted heat loss and solar heat gain to passively reduce heating and cooling loads.

The building envelope includes windows, doors, walls and the roof, which have associated heat transfer characteristics that depend on the type of construction material. ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings outlines requirements in Chapter 5, “Building Envelope.” The International Energy Conservation Code (IECC) outlines thermal envelope minimum requirements based on climate zones, as listed in Section C402, “Building Envelope Requirements.” Improving a building’s thermal envelope reduces its cooling, heating and energy loads.

Optimizing ventilation strategies including demand-control ventilation (DCV) and heat recovery can significantly reduce energy consumption without compromising indoor air quality. DCV is implemented by modulating outdoor air intake based on real-time indicators of occupancy such as CO2 sensors. ASHRAE Standard 62.1: Ventilation and Acceptable Indoor Air Quality provides requirements for mechanical and natural ventilation systems including DCV.

Heat recovery is typically integrated through airto-air energy recovery ventilators (ERVs), such as enthalpy wheels and plate heat exchangers (see Figure 3). ERVs exchange heat with leaving exhaust air to preheat or precool outdoor air in the air handling unit (AHU). ERVs that also allow moisture transfer facilitate the transfer of latent energy, reducing humidification loads. Harnessing energy recovery reduces the requirement size for the heating coil and consequently also reduces the amount of energy consumed to operate the unit, as compared to a typical AHU. The IECC outlines requirements for

providing energy recovery for ventilation systems in Section 403.7.4, “Energy Recovery Systems.”

By lowering both peak and annual heating and cooling energy through these measures, HVAC systems can be smaller and operate more efficiently. Energy consumption can be further improved in existing buildings through energy audits targeting operational energy consumption.

Through the energy audit process, a wide range of measures are often identified that can improve system operational efficiency without major capital investment for retro-commissioning. These measures frequently include optimization of temperature, pressure and ventilation setpoints and refinement of control sequences to better align equipment operation with occupancy and load profiles. Correcting set points and building schedules can eliminate unnecessary runtime.

Energy audits also commonly uncover faulty or degraded equipment such as malfunctioning sensors, stuck dampers, failed actuators or improperly operating variable-speed drives, which prevent systems from operating as intended and increase energy consumption. Systems that would benefit from commissioning or retro-commissioning are commonly identified through energy audits. By addressing these operational and control-focused deficiencies, building owners can achieve measurable reductions in energy use while improving occupant comfort and extending equipment life.

Incorporating these energy efficiency strategies reduces energy consumption and supports the transition to fully electric systems.

PHASE 2: Electrifying systems and grid decarbonization

While an existing HVAC system can be replaced with an electrified alternative, doing so may not make fiscal sense unless energy efficiency has been maximized. After system performance has been maximized, if further decarbonization is required, equipment replacement with clean, electricity-driven equipment is warranted.

In commercial buildings, electrification targets space heating and water heating, where combustion equipment drives both energy use and direct on-site emissions. Electrifying HVAC systems replaces on-site fossil fuel combustion such as gas boilers, furnaces and water heaters with electric technologies.

CASE STUDY: Sewage waste heat recovery

THIS CASE STUDY EXPLORES

a thermal energy network using geothermal, waste heat recovery and sewage heat recovery to support low-carbon heating and cooling.

In December 2024, National Grid submitted a proposal for the KeySpan Energy Delivery New York (KEDNY) thermal energy network to the New York Public Service Commission as part of the Utility Thermal Energy Network and Jobs Act (UTENJA). UTENJA aims to support thermal energy networks and promote new jobs in the decarbonization sector for residents.

The project proposes to construct a one-pipe ambient loop to serve the heating and cooling loads for multiple commercial customers and a residential housing development in Brooklyn, New York. The ambient loop would be served by a variety of thermal energy sources, including a geothermal heat exchange borefield, waste heat recovery from a supermarket refrigerant system and sewage waste heat recovery. Due to limited space available for additional boreholes, sewage waste heat recovery was included to provide additional low-carbon heat injection and heat rejection.

A closed-loop SHARC system was proposed to transfer heat between the ambient loop and wastewater from the residential building (see Figure 5). The residential building has two sanitary lines leaving the building, which would be combined into a 12,000-gallon on-site storage tank. The wastewater would be pumped from the holding tank through a skid that includes a macerator to grind the solids in the wastewater before entering a heat exchanger.

The heat exchanger transfers heat between the wastewater and ambient loop. After passing through the heat exchanger, wastewater would be directed back through the sanitary line, where it connects into the main sewer line in the street and is transported to the wastewater treatment facility.

The ambient loop is designed to operate within a temperature range of 40°F to 80°F, and the temperature of the sanitary flow leaving the residential building was assumed to be 68°F. When the temperature of the sanitary flow is warmer than the ambient loop, heat is injected into the ambient loop from the wastewater.

Of the available HVAC electric technologies, heat pumps are one of the most impactful solutions. Heat pumps can deliver the same thermal services at substantially higher efficiencies, especially when operating at part load. Combustion technologies are limited to 80% efficiency, whereas heat pumps can transfer more heat than the electricity they consume; therefore, they are three to five times

FIGURE 5: Process flow diagram of SHARC system for proposed thermal energy network for National Grid KEDNY project. An inline pump on the source side of the heat exchanger pumps fluid from the ambient loop through the heat exchanger. Two solids-handling pumps are in the wastewater holding tank to pump combined wastewater from the holding tank back into the building and through the SHARC skid (macerator, filter and heat exchanger). Wastewater then flows back into the wastewater holding tank. Two sludge pumps are used to pump wastewater from the holding tank back to the sewer.

Courtesy: CDM Smith

Conversely, when the temperature of the sanitary flow is cooler than the ambient loop, heat is rejected from the ambient loop into the wastewater.

The SHARC system’s capacity was limited by the available space inside the building to locate the equipment and the quantity of sanitary flow leaving the building. The project site is near an existing wastewater resource recovery facility and had considered the possibility of using this larger wastewater source.

However, this option was ultimately discarded due to the length of distribution piping required to connect to the system and the need to cross a major throughfare within the area. This option would also require coordination and approval from the New York Department of Environmental Protection, as they owned the wastewater infrastructure in question.

more efficient than traditional gas boilers, according to IEA. The DOE’s Better Buildings’ guidance highlights this as a key decarbonization strategy, although electrification adaptation varies by region, climate, utility rates, existing systems and building conditions (see Figure 4).

Decarbonization of HVAC electrification depends on how electricity is produced in the region where

BUILDING SOLUTIONS

‘Once energy usage has been reduced as much as practical, electrification of HVAC systems can be pursued more effectively.’

the building is located. Electricity produced from traditional fossil fuels, such as coal and oil, will have higher emission rates than cleaner energy resources, such as wind and solar. The EPA publishes emission rates and resource mixes for electricity generation across the United States in the Emissions & Generation Resource Integrated Database (eGRID). Depending on the eGRID subregion and energy resource mix, electrification systems have different emissions reductions. Looking forward, grid emissions will change over time as more clean energy sources are integrated into the energy resource mix.

PHASE

3: Integrating clean energy sources

In addition to reducing energy demand and electrifying equipment, incorporating clean energy sources and technologies is important to achieve overall decarbonization goals. Clean energy generation technologies, such as wind and solar, generate clean electricity for building consumption, but waste heat recovery is also an important strategy for reducing or removing fossil fuel combustion in HVAC applications.

While industrial processes and data centers often provide opportunities for waste heat recovery, these are not thermal sources that are widely available for the general building stock. For residential buildings, sewage waste heat recovery is a viable and widely available option.

mechanical systems are replaced multiple times over their lifespan, design decisions made during each retrofit have long-term implications for energy use, emissions and system performance. Energy efficiency measures to reduce building heating and cooling loads and energy consumption are the foundation of this approach.

Reducing heating and cooling loads through thermal envelope improvements, ventilation optimization and operational refinement enables HVAC systems to be smaller and operate more efficiently. These reductions are particularly important as buildings electrify, as unmanaged load growth can increase peak electrical demand, strain existing electric infrastructure and require carbon-intensive electrical generation.

u

csemag.com

Decarbonization insights

uHVAC systems account for roughly 40% of total building energy use, making HVAC decarbonization one of the most effective pathways to reduce operational carbon emissions in buildings.

u A phased decarbonization strategy that involves improving energy efficiency, electrifying HVAC systems and integrating clean energy sources can help reduce emissions while minimizing strain on electrical infrastructure.

Sanitary streams leaving buildings are typically 55°F to 75°F year-round, offering a stable thermal energy resource for HVAC applications. The temperature can increase depending on processes in the building, such as hospitals with steam loads. Sewer system infrastructure is also an available thermal energy source. Sanitary streams, whether captured behind the meter at the building or directly using larger main sewer lines within the street, can provide domestic hot water for individual buildings with a heat pump or can be used as heat injection and/or heat rejection sources for networked or district thermal systems using heat exchangers.

Benefits of an integrated approach

Achieving meaningful reductions in building operational carbon requires an integrated approach that prioritizes energy efficiency before transitioning to electrified and low-carbon HVAC systems. Because buildings are long-lived assets and

Once energy usage has been reduced as much as practical, electrification of HVAC systems can be pursued more effectively. High-performance heat pump technologies, low-temperature distribution systems and advanced controls are best applied in buildings with reduced loads. Continued improvements in grid decarbonization increase the emissions benefits of electrified systems over time, further reinforcing the importance of early efficiency investments. Commissioning and ongoing performance verification remain critical throughout the process, ensuring that systems operate as designed and continue to deliver energy and emissions savings.

Ultimately, HVAC decarbonization is not a single technology choice but a phased, systems-level strategy that integrates efficiency, electrification and clean energy over time. By focusing first on reducing operational energy demand, design teams can improve comfort, resilience and affordability while creating a clear pathway to low-carbon building operation. This approach aligns near-term economic objectives with long-term climate goals, ensuring that each incremental investment moves the building closer to net-zero performance. cse

Jaclyn Kinson, PE, is a mechanical engineer and climate resilience discipline leader for MEP + Energy at CDM Smith.

Matthew Goss, PE, PMP, CEM, CEA, CDSM, LEED AP, is the infrastructure services group director at CDM Smith.

BUILDING SOLUTIONS

Louis J. Lercara, PE, HFDP, LEED AP, WSP, Dallas

Practical tips for OR AHU energy efficiency and controls

OR AHUs operate under some of the most restrictive environmental requirements in the built environment. Learn practical, efficient control strategies.

EObjectives

• Understand how operating room temperature and humidity requirements influence AHU operating states, economizer viability and discharge air temperature selection.

• Apply temperatureand enthalpy-based economizer logic that avoids unintended increases in cooling or humidification energy.

• Implement discharge air temperature and fan static pressure reset strategies that reduce cooling, reheat and fan energy while preserving OR environmental control.

nerg y conservation has become increasingly important in heating, ventilation and air conditioning (HVAC) design and operation as the industry responds to tighter energy codes, owner sustainability goals and the broader impacts of energy consumption. Healthcare facilities are among the most energy-intensive building types and represent a significant opportunity for energy savings. At the same time, they are one of the most difficult environments in which to pursue energy reductions responsibly because HVAC systems must support occupant safety, infection control, reliability and redundancy and strict environmental control requirements.

Operating rooms (ORs) are a prime example of this complexity. OR HVAC systems must maintain temperature and humidity within a narrow allowable band while delivering high outdoor air rates and high air change rates. While ASHRAE Standard 170: Ventilation of Health Care Facilities permits temperature in an OR to range from 68°F to 75°F, some clinical users prefer a cooling setpoint as low as 62°F and some jurisdictions impose different maximum temperature requirements. Throughout that range, ASHRAE 170 also requires the system to maintain the relative humidity between 30% and 60%.

Meeting both temperature and humidity requirements often increases reheat demand well beyond what is typical in non healthcare systems.

Because the required air change rate is maintained regardless of cooling load, the reheat system must be sized to temper the full supply airflow from the cooling coil leaving condition up to the temperature required to maintain space conditions, particularly following dehumidification during humid outdoor conditions.

Typical OR AHU configuration and why it matters

While OR AHU designs vary by facility, climate and owner preferences, many systems share common elements intended to meet temperature, humidity, filtration and reliability requirements (see Figure 1). A representative OR AHU configuration may include:

• Outdoor air intake section with damper(s), often including:

– A single modulating outdoor air damper that varies between a minimum position to maintain the code-required outdoor air flow rate and a maximum position during economizer operation when outdoor conditions are favorable; or

– A minimum outdoor air damper that maintains the constant required outdoor air flow rate, paired with a separate economizer damper that modulates additional outdoor air during economizer operation.

• Mixing section where outdoor air and return air combine:

– In some designs, a channel blender or mixing device is used to improve air mixing and reduce stratification, which supports stable sensing and control.

• Prefilters and final filters:

– A two stage approach (prefilter and final filter) is common for protecting coils and maintaining air quality; typical arrangements include minimum efficiency reporting value (MERV) 8 to 11 prefilters with MERV 14 to 16 or high-efficiency particulate air final filters, depending on facility requirements.

• Preheat coil (often hot water or steam):

– Used to prevent excessively cold mixed air, avoid coil freezing and reduce discomfort risk during cold weather operation.

• Cooling/dehumidification coil(s):

FIGURE 1: This illustrates a representative operating room air handling unit configuration, including outdoor air and return air dampers, mixing components, filtration stages, preheat, cooling, humidification and supply and return fan systems. Courtesy: WSP

– Depending on humidity requirements, chilled water temperatures and climate, OR AHUs may rely on conventional cooling coil dehumidification and/or enhanced dehumidification strategies such as glycol cooling coils or desiccant wheels.

– A glycol cooling system can be used to support lower chilled water operating temperatures by providing freeze protection, enabling the cooling coil to cool the supply air to the desired dewpoint temperature (e.g., 42°F). Glycol is mixed into a separate chilled water system at a specified concentration (e.g., 30% propylene glycol) to lower the freezing point and protect coils when operating with colder water temperatures (e.g., 32°F supply, 42°F return). This approach enhances latent performance while avoiding coil freezing risk, at the expense of reduced heat transfer efficiency and additional pumping energy.

– A desiccant wheel can also be used to achieve lower dewpoint temperatures. In a common configuration, the desiccant wheel is installed between a primary and secondary cooling coil. The primary cooling coil typically cools the air to approximately 49°F to 52°F, after which the air passes through the

desiccant wheel, where additional moisture is removed to achieve the target dewpoint. The desiccant process adds sensible heat to the air stream, requiring the secondary cooling coil to perform sensible-only cooling to meet the desired supply air temperature. The desiccant wheel is regenerated using the mixed air upstream of the primary cooling coil, preheated if necessary to achieve the required dehumidification performance.

• Humidification system (using central plant steam when available, gas-fired or electric point-of-use steam generators):

– Used to maintain the minimum relative humidity (RH, at 30%) during dry outdoor conditions.

• Supply and return fans and controls (variable frequency drive, or VFD, per fan motor or single VFD for fan array), along with sensors for discharge air temperature and duct static pressure.

OR environmental requirements’ impact on operating states

OR HVAC controls are constrained by three nonnegotiable requirements:

• Ventilation and minimum outdoor air must be maintained.

‘OR HVAC systems must maintain temperature and humidity within a narrow allowable band while delivering high outdoor air rates and high air change rates.’

BUILDING SOLUTIONS

Moisture content can dominate the total energy required to condition air.

• Temperature must be controllable across the required range.

• RH must remain between 30% and 60% across those temperature conditions.

These constraints must be met across a set of major AHU operating states that should be considered explicitly in the sequence of operations:

• Full cooling (often summer and humid shoulder days)

• Economizer with cooling coil (when outdoor air can reduce mechanical cooling energy)

• Free cooling (when outdoor air can meet the full cooling load)

• Preheat (cold weather protection and conditioning)

A common mistake is to treat economizer logic as a standalone “enable” decision based only on outdoor air conditions. For ORs, economizer should be considered in the context of which other

Table 1: Typical OR AHU operating states

STATE 1: Full cooling

STATE 2: Economizer with cooling coil

STATE 3: Free cooling

STATE 4: Preheat

Default state on startup. Entered when outdoor air conditions are not favorable for economizer operation.

Enabled when outdoor air temperature and enthalpy are favorable. Transitions out when outdoor conditions are no longer favorable or cooling demand does not require cooling coil.

Enabled when outdoor air alone can satisfy discharge air temperature setpoint. Transitions out when economizer capacity is no longer sufficient.

Enabled during cold outdoor conditions when cooling is not required.

components are active, especially regarding dehumidification and humidification (see Table 1).

Economizer decisions must consider temperature, enthalpy

Economizer mode is often described as “free cooling,” but that description can be misleading in OR applications because the air must still be conditioned to meet both temperature and RH constraints. In many climates, outdoor temperature alone is a poor indicator of whether economizer operation will save energy. Moisture content can dominate the total energy required to condition air and that moisture contribution is reflected more accurately by enthalpy.

A useful way to conceptualize the importance of moisture is this: it takes roughly three times the cooling energy to reduce the dry bulb temperature of saturated air compared to dry air by the same amount.

For OR AHUs, economizer enable decisions should therefore consider both:

• Outdoor air temperature, and

• Outdoor air enthalpy (relative to return air enthalpy)

Economizer damper is closed. Cooling coil modulates to maintain discharge air temperature.

Economizer damper is open. Cooling coil modulates as needed to maintain discharge air temperature.

Cooling coil closed. Economizer damper modulates to maintain discharge air temperature.

Cooling coil and economizer damper closed. Preheat coil modulates to maintain discharge air temperature.

Cooling coil and humidifier operate as required to maintain discharge air dewpoint within an acceptable range.

Humidity controlled primarily by cooling coil. If discharge air dewpoint drifts out of range, unit should revert to a non economizer state (1 or 4, depending on coil demand).

Air handling unit should only operate in this state while discharge air dewpoint remains within acceptable limits.

Humidifier operates as required to maintain minimum discharge air dewpoint.

TABLE 1: This summarizes common operating states for operating room air handling units, including full cooling, economizer with cooling, free cooling and preheat and highlights the associated temperature control methods and humidity control considerations in each state. Courtesy: WSP

Even that is not always sufficient because economizer can still create downstream impacts (especially humidification demand) that negate savings. However, temperature and enthalpy are the right starting point and are more robust than temperature alone.

In many operating room AHUs, the minimum outdoor air percentage is often 20%, driven by the ASHRAE 170 requirement of four outdoor air changes and 20 total air changes per hour, but may be higher depending on system configuration and space zoning. Economizer operation can significantly increase the outdoor air percentage above minimum, amplifying the impacts of sensible and latent conditioning.

Economizer enable logic

A commissioning-friendly way to document economizer enable logic is to structure it as a set of gates. This makes it easier to explain, test and troubleshoot.

Gate 1: Minimum outdoor air requirement: Minimum outdoor air must always be maintained to satisfy ventilation, infection control and pressurization requirements. Economizer operation is never allowed to reduce outdoor air below this minimum.

Gate 2: Temperature and enthalpy conditions: Economizer should be enabled only when outdoor conditions are favorable compared to return air:

• Outdoor air temperature must be lower than return air temperature (or below a defined economizer high-limit temperature); and

• Outdoor air enthalpy must be lower than return air enthalpy (or below a defined economizer high-limit enthalpy)

If either temperature or enthalpy is not favorable, economizer should remain at minimum outdoor air.

Gate 3: Humidification energy: For operating room AHUs that must maintain relative humidity at or above 30%, humidification energy can quickly become the dominant component of total system energy use during dry outdoor conditions. While there are scenarios in which increased outdoor air may provide a modest cooling energy credit, the net benefit depends on both the efficiency of

the cooling system and the energy intensity of the humidification source.

A practical approach is to estimate the cooling energy credit associated with increased outdoor air during economizer operation and compare it against the additional humidification energy required to maintain the minimum 30% RH. This comparison can be used to identify an outdoor condition threshold at which the humidification penalty outweighs the cooling benefit. When that threshold is exceeded, economizer operation should be disabled and the AHU should revert to minimum outdoor air.

Although this balance point will vary by climate, system type and utility rates, explicitly evaluating it allows the economizer strategy to be tailored to the actual system economics rather than relying solely on generic temperature or enthalpy limits.

From an energy standpoint, the least expensive air to condition for an OR is often the air that just returned from that OR.

Discharge air temperature reset

Supply air temperature (SAT) reset is a separate but complementary strategy that can reduce energy use by minimizing unnecessary cooling and reheat. Importantly, SAT reset can be valuable not only in winter but also during shoulder seasons, including periods when humidification may be required and economizer may not be desirable.

SAT reset can significantly reduce reheat energy by avoiding overly cold supply air when space sensible loads are low. A practical SAT reset strategy in variable air volume (VAV) systems is to monitor the cooling demand of all terminal units in the system. One example logic sequence is:

• Raise SAT by 0.5°F if no VAV in the system has a cooling demand greater than 80%, subject to a defined maximum SAT limit.

• Lower SAT by 0.5°F if any VAV in the system has a cooling demand greater than 90%, subject to a defined minimum SAT limit.

This approach can be enhanced by incorporating reheat coil control valve positions for constant volume terminal units:

‘Economizer operation can significantly increase the outdoor air percentage above minimum, amplifying the impacts of sensible and latent conditioning.’

BUILDING SOLUTIONS

‘Some codes and facility standards allow reduced air change rates during defined unoccupied modes.’

• If reheat coil control valve positions are consistently high, SAT may be too cold and raising SAT can reduce reheat energy.

• Conversely, if any reheat coil control valves are fully closed and cooling is still required, SAT may need to be lowered to satisfy cooling demand.

In constant-volume OR systems, SAT reset can be a key way to provide significant energy savings when the mixed air dewpoint is within the target range and the space cooling loads do not require the design SAT. This strategy should be bounded by the need to maintain OR temperature and RH within allowable limits. In practice, owners often set conservative SAT limits and then tune reset rates based on observed OR performance and commissioning feedback.

For OR AHU applications, this approach should be implemented with careful attention to system sensitivity and redundancy. Reset logic should be based on the most open terminal device, rather than an average damper position, to ensure critical spaces are protected. During system balancing, all VAV terminals should be set to their maximum airflow setpoints and the static pressure at which the most open terminal damper is 95% open should be established as the maximum static pressure setpoint.

Likewise, with all VAV terminals set to their minimum airflow setpoints, the static pressure corresponding to a most open damper position of 95% should be established as the minimum static pressure setpoint. The static pressure reset sequence can be structured in a manner like the discharge air temperature reset logic discussed previously, using incremental adjustments based on demand with defined upper and lower limits.

u

OR AHU insights

u An OR AHU in a healthcare setting must balance energy conservation with strict requirements for ventilation, temperature control, humidity control, infection prevention and reliability, making economizer decisions far more complex than in typical commercial systems.

u The most effective OR AHU energy strategy is to maintain minimum outdoor air, enable economizer only when both temperature and enthalpy are favorable, account for humidification penalties and use discharge air temperature reset and static pressure reset to reduce cooling, reheat and fan energy.

Practical takeaway: Even when economizer is locked out due to humidification, SAT reset can still provide meaningful savings by reducing unnecessary cooling and reheat during low-load conditions.

Static pressure reset

In VAV systems serving operating rooms and associated support spaces, duct static pressure reset can provide meaningful fan energy savings when implemented with appropriate safeguards. Rather than maintaining a fixed, conservative static pressure setpoint, reset strategies adjust fan pressure based on actual terminal demand, reducing fan speed and fan energy during periods of low airflow requirement.

A common and effective approach is to reset duct static pressure based on VAV terminal damper positions. When most terminal dampers are operating at relatively closed positions, this indicates that system static pressure is higher than necessary and the supply fan static pressure setpoint can be reduced incrementally. Conversely, when one or more terminals approach their fully open position, static pressure can be increased to ensure adequate airflow is delivered to the most demanding zone.

Some codes and facility standards allow reduced air change rates during defined unoccupied modes, which can further enhance the effectiveness of static pressure reset when permitted. ASHRAE 170 Table 7-1 identifies which space types permit unoccupied turndown. Any such reductions should be carefully coordinated to maintain required pressure relationships to adjoining spaces.

When properly tuned, static pressure reset complements discharge air temperature reset by reducing fan energy during low load conditions without compromising airflow control or room pressurization. Together, these strategies allow OR AHUs to respond dynamically to actual demand rather than operating continuously at worst case design conditions.

Design and controls takeaways

For OR AHUs that must remain within 30% to 60% RH, the most reliable approach is to focus on robust, commissionable control strategies.

These principles strategically limit economizer operation to the periods when it is most likely to deliver true net savings without creating downstream penalties in humidity control. cse

Louis J. Lercara, PE, HFDP, LEED AP, is a mechanical engineer specializing in healthcare HVAC system design and controls, with a focus on energy performance optimization and future ready resiliency.

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BUILDING SOLUTIONS

Autumn Beer and Valerie Lecaros, CDM Smith, Maitland, Florida

How to achieve ASHRAE 62.1 compliance for VAV system design

Meeting ASHRAE 62.1 requirements

in VAV systems presents unique challenges, as fluctuating airflow, varying occupancy loads and system diversity.

Var iable air volume (VAV) systems are among the most widely used air distribution strategies in commercial heating, ventilation and air conditioning (HVAC) design because of their flexibility, energy efficiency and compatibility with modern ventilation standards such as ASHRAE Standard 62.1: Ventilation and Acceptable Indoor Air Quality.

u

Objectives

• Understand the key ASHRAE 62.1 requirements as they apply to variable air volume (VAV) systems, including zone air distribution effectiveness and system ventilation efficiency.

• Identify the challenges VAV systems present for maintaining compliance, such as varying airflow rates, occupancy diversity and their impact on outdoor air delivery.

• Apply strategies to achieve compliance with VAV design, including outdoor air calculation methods and balance techniques to ensure stable ventilation performance.

Understanding how VAV systems are defined and applied, particularly in comparison to constant air volume (CAV) systems, is essential for achieving code-compliant and high-performance designs.

The 2024 ASHRAE Handbook—HVAC Systems and Equipment provides extensive guidance on air distribution approaches. For example, Chapter 2, Section 2.10 “Single-Zone VAV Systems” gives an in-depth discussion of single-zone VAV systems, outlining their advantages and disadvantages, recommended control sequences, terminal unit options and key application considerations.

This foundational material helps designers determine when a VAV approach is appropriate, how it should be integrated with ventilation strategies and which operational characteristics most strongly influence system performance. It also clarifies how single-zone VAV differs from multizone configurations, particularly in terms of controls and energy-saving potential. By establishing these

fundamentals early in the chapter, the handbook provides a framework designers can apply when approaching more advanced VAV system types.

A common misconception is that a VAV system automatically means “VAV boxes.” While VAV boxes are typically in multizone systems, they are not required for all VAV applications. In a single-zone VAV system, one air handling unit (AHU) serves a single thermal zone. Airflow from the AHU is modulated to match the load of the space, with the cooling and heating coil outputs simultaneously adjusted to meet the required thermal conditions. No downstream VAV terminal units are required because only one zone is being controlled.

In this configuration, the AHU’s supply fan speed varies to meet demand, with cooling and heating coil output adjusted accordingly. The system is still considered a VAV system because the airflow changes over time, even though no terminal boxes are present.

In a multizone VAV configuration, a single central AHU serves multiple thermal zones, each equipped with its own terminal unit (VAV box) that independently modulates airflow in response to a space temperature sensor. Manufacturers provide a range of terminal-unit types — including cooling-only boxes, electric or hot-water reheat boxes and fan-powered VAV units — to accommodate different design and comfort requirements.

Additional features to consider are insulation, sound attenuation and control options. This arrangement enables precise zone-level temperature control and represents the most common VAV system configuration used in commercial office buildings, educational facilities and healthcare environments.

The key distinction between VAV and CAV systems is how they respond to load changes. A CAV system delivers a fixed airflow rate to a space. Depending on the design, a CAV system may respond to load changes by modulating the supply air temperature or, in many cases, by cycling the unit on and off. In practice, operating schedules can cycle cooling but not ventilation. The fans continue running and outdoor air (OA) remains at its set level, since it’s not acceptable for ventilation to shut off in commercial spaces.

A typical residential air conditioning unit is a good example of a CAV system: The fan operates at a steady speed and delivers a constant volume of air, while the equipment cycles on and off based on the thermostat — or, in some cases, humidity control — to maintain the desired conditions. Many newer high efficiency residential systems, however, use variable speed fans that modulate airflow.

A VAV system, by contrast, keeps the supply air temperature relatively constant and varies only the airflow rate to meet the space’s changing load. At peak cooling demand, the system delivers maximum airflow; as the load decreases, it reduces the airflow accordingly. This approach offers several advantages, particularly in relation to modern energy codes and ventilation standards. Lowering airflow significantly reduces fan energy consumption, improving overall efficiency.

Referencing the affinity laws, a 25% reduction in airflow (Q) produces a 25% reduction in fan speed (N), which then leads to a 42.2% reduction in overall power consumption (P). In multizone buildings, VAV systems also allow each space to respond independently to its own load profile, which enhances comfort and provides more precise environmental control (see Figure 1).

VAV systems rely on the ability to continuously modulate supply fan speed in response to changing duct static pressure. As VAV dampers open and close, the system pressure profile shifts and the supply fan adjusts its speed to maintain the target setpoint. Traditionally, this modulation was achieved using variable frequency drives (VFDs). Electronically commutated motors now provide the same dynamic speed control without requiring a separate VFD, making fan turndown more efficient and streamlined. By varying fan speed rather than throttling airflow, the system significantly reduces energy use because the fan’s power draw drops sharply as speed decreases. This results in substan-

FIGURE 1: Equations for affinity laws, based on 2024 ASHRAE Handbook, HVAC Systems and Equipment, Chapter 44.8 “Affinity Laws,” Table 1. Courtesy: CDM Smith

FIGURE 2: Schematic of a single-duct variable air volume terminal unit showing the inlet, outlet and damper components. Courtesy: CDM Smith

‘Lowering airflow significantly reduces fan energy consumption, improving overall efficiency.

tial savings during part-load operation, which represents most building operations.

Based on 2025 ASHRAE Handbook Fundamentals, Chapter 14 “Climatic Design Conditions,” HVAC systems are typically sized to meet 1% cooling and 99% heating design conditions, meaning buildings operate below peak load for well over 90% of the year. Due to this, equipment spends most of its life modulating part load rather than running at full capacity, making part-load efficiency far more impactful than peak performance.

In addition to improving energy performance, variable speed operation allows the system to better match outdoor air delivery to actual demand. This stable, demand-driven airflow helps maintain proper ventilation rates across all zones, supporting compliance with ASHRAE 62.1 even as occupancy and thermal loads fluctuate.

In addition to central fan-level control, VAV systems rely on zone-level strategies to maintain comfort and efficiency across the building. In multizone applications, dampers regulate the volume of air delivered to each zone (see Figure 2). Beyond simple flow control, these dampers play a critical role in maintaining proper ventilation rates under varying load conditions.

BUILDING SOLUTIONS

FIGURE 3: Equation to determine corrected outdoor air using zone air distribution effectiveness. Based on ASHRAE Standard 62.12025, Equation 6-2.

Courtesy: CDM Smith

As zone demands fluctuate, the damper position directly influences how much OA is ultimately distributed to each space, making accurate damper operation essential for meeting the minimum ventilation requirements prescribed by ASHRAE 62.1, Chapter 6.2 “Ventilation Rate Procedure.” Properly calibrated and responsive dampers help prevent underventilation during low-load periods, support stable pressurization and ensure that the system’s ventilation strategy remains effective across the full range of VAV operations.

statewide code or more restrictive municipal amendments, typically based on the International Mechanical Code (IMC). Designers often follow the latest ASHRAE guidance for best practice, and compliance is ultimately judged against the version of the mechanical code adopted by the authority having jurisdiction.

FIGURE 4: Equation to determine corrected outdoor air using system ventilation efficiency. Based on ASHRAE Standard 62.1-2025, Equations 6-7 and 6-8.

Courtesy: CDM Smith

Calibration typically includes setting the damper’s minimum and maximum positions to match the required airflow rates verified through testing and balancing. A responsive damper precisely tracks control signals, opening or closing quickly and proportionally, so that commanded airflow changes are delivered without delay.

Codes and standards for mechanical systems

ASHRAE 62.1 sets the technical benchmark, but the mechanical code is what most jurisdictions adopt and enforce for mandatory requirements. Depending on the state, this may be a

5: Simplified control diagram for a multi-zone variable air volume system. Courtesy: CDM Smith

ASHRAE 62.1 defines which spaces require dedicated exhaust and the minimum exhaust rates, as outlined in ASHRAE 62.1, Table 6-2 “Minimum Exhaust Rates.” This standard also establishes the minimum ventilation rates necessary to maintain acceptable indoor air quality (IAQ) in occupied spaces, as expressed in Table 6-1 “Minimum Ventilation Rates in Breathing Zone.”

In the context of ASHRAE 62.1 and mechanical codes, “ventilation” specifically refers to OA brought into the building — not supply, return or exhaust airflow. ASHRAE 62.1 specifies the outdoor airflow that must be delivered to each zone based on both occupancy and floor area, forming the basis of any compliant ventilation design.

Exhaust air serves two primary functions in buildings: removing contaminants at the source and maintaining required pressure relationships. These functions are especially critical between adjacent spaces to prevent cross-contamination — for example, ensuring that laboratory areas do not negatively impact surrounding zones or vice versa.

In VAV systems, these functions become more complex because supply airflow varies with load. As the supply air modulates, the exhaust system must be designed and controlled to ensure that contaminant removal and pressure control remain consistent. Without proper coordination, pressure relationships can shift as the supply airflow turns down, potentially compromising containment.

ASHRAE 62.1 establishes minimum exhaust airflow rates for many space types. These rates are typically expressed as cubic feet per minute (cfm) per square foot, or cfm per unit. For example, toilet rooms generally require 50 to 70 cfm per fixture, while janitor closets require approximately 1.0 cfm per square foot. Maintaining these minimum exhaust rates during the design process is essential to ensure that contaminants are removed at a predictable rate, independent of the supply system’s VAV turndown.

FIGURE

Table 1: Zone air distribution effectiveness values

Table 2: VAV system ventilation requirements and fractions

Table 1: Zone air distribution effectiveness (Ez) values for various well-mixed distribution system types.

Based on ANSI/ASHRAE Standard 62.1-2025, Table 6-4. Courtesy: CDM Smith

In VAV systems, these requirements intersect directly with the system’s variable airflow nature. Because supply airflow modulates in response to changing loads, the ventilation strategy must ensure that every zone continues to receive its required minimum OA under all operating conditions, not only during peak cooling when airflow is highest.

In multizone VAV systems, the AHU must supply enough system-level OA to satisfy the “critical” zone — the zone that, at any given operating condition, requires the highest proportion of OA relative to its supply airflow. As individual zone airflows modulate changing loads, the critical zone can shift throughout the day, directly influencing the OA intake required at the system level.

To manage this variability, designers must calculate each zone’s OA requirement, determine the system’s ventilation efficiency and evaluate performance under both peak and part - load conditions. When implemented correctly, this approach maintains compliance with ASHRAE 62.1 while optimizing energy use, ensuring that IAQ, pressure relationships and overall system performance remain stable even as VAV boxes continually adjust across the building.

Controlling VAV systems: key challenges and solutions

There are challenges associated with both single-zone and multizone variable volume systems. To combat this, different factors must be considered when calculating required airflows throughout the system. Ventilation calculations can be performed with ASHRAE supplied spreadsheets or

Table

2: Example variable air volume system ventilation requirements and fractions. Courtesy: CDM Smith

vendor software, which incorporate ASHRAE 62.1 ventilation standards into overall system sizing. When using vendor software, results should be verified against ASHRAE 62.1. Zone air distribution effectiveness (Ez) is one factor that must be considered for OA requirements. Ez is how well a system will dilute contaminants within a breathing zone.

‘Zone air distribution effectiveness (Ez) is one factor that must be considered for OA requirements.’

ASHRAE 62.1, Section 6 “Procedures” lists various air delivery methods and the corresponding Ez values, depending on how air is distributed to the zones. Three different configuration types are:

• Well-mixed air distribution systems (see Table 1)

• Stratified air distribution systems

• Personalized ventilation systems

The stratified air and personalized ventilation systems both have potential Ez values greater than 1, which in turn reduce the OA requirement. The well-mixed systems will have Ez values less than or equal to 1, which can increase the required OA. As seen in Table 1, the instances that provide Ez values less than 1 are those that return air to the ceiling during heating mode. Removing potential contaminants from the breathing zone is less effective because hot air rises to the top of the space and the air in the breathing zone does not get mixed well due to the supply being provided at the top as well.

BUILDING SOLUTIONS

‘Multizone systems are more of a challenge when it comes to VAV systems, as there may be varying airflow rates required.’

According to ASHRAE 62.1, the breathing zone is a portion of occupiable space located between 3 and 72 inches above the floor and at least 2 feet away from walls or fixed air conditioning equip ment. The most effective way to prevent air from bypassing this zone is to use a floor‑level return.

However, that approach isn’t always practical, especially in buildings without basements, which is common in many Southern regions.

For the OA design, the Ez value must be divid ed by the ASHRAE 62.1 minimum OA require ment (Vbz) and then multiplied by a correction factor for air density (Eρ, see Figure 3), result ing in a corrected OA value (Voz). ASHRAE 62.1, Table 6 5 “Air Density Correction Factor” tab ulates various correction factors for air density depending on how high the OA intake is located above sea level. This equation is how one could potentially get an increased value for well mixed distribution type systems with a ceiling return.

To determine the amount of OA provided to a single zone within a multizone VAV system, the Ez value for each zone is calculated separate ly using Table 1. This will provide a corrected amount of OA required by that individual space. These corrected OA values are then compared against the system’s designed supply air rates to identify the zone with the highest fraction, which will be considered the most critical zone.

The supply air is the peak supply to each VAV box, while the OA values are the minimum required per ASHRAE 62.1 (see Figure 5). Table 2 presents these values with their associated OA fractions.

Zone 3 would be the critical zone, as it has the highest fraction of required OA relative to the supply air (see Table 2). Therefore, the system must be designed to provide at least that fraction of OA to the whole system.

csemag.com

VAV insights

u A VAV system enhances commercial energy efficiency and comfort by modulating airflow to meet specific zone loads while maintaining a constant supply air temperature.

u To remain compliant with ventilation standards, a VAV system must be carefully designed to ensure that minimum outdoor air requirements are met across all zones even as supply volumes fluctuate.

Multizone systems are more of a challenge when it comes to VAV systems, as there may be varying airflow rates required throughout the system due to occupant diversity (D). Occu pant diversity considers how the number of peo ple across zones of a system will vary. This can be due to differences in space type or time of day — for example, the peak people load may not be the same in an office space versus a breakroom at one time. Occupant diversity is then used along side system ventilation efficiency to determine the adjusted OA that is required for the system. Sys tem ventilation efficiency (Ev) is how well a sys tem delivers air to each zone and depends on the occupant diversity (see Figure 4).

Like zone air distribution effectiveness, this Ev value is then divided by the ASHRAE 62.1 ven tilation requirement to ultimately determine the adjusted airflow needed for the system. Higher occupant diversity results in lower corrected OA values, while lower occupant diversity results in higher corrected OA values.

Because multizone VAV systems mix all OA at the unit’s return rather than ducting it separate ly to each space, there is no guarantee that the amount of air required for the critical zone would get there if this OA fraction were not considered. If the OA fraction is potentially too high, this can be reduced by providing more supply air to that individual zone, thereby reducing both the OA fraction and the overall system OA fraction (with the understanding that another zone may then become the new critical zone).

The amount of OA pulled into the system is controlled by motor operated dampers that can be anywhere from fully open to fully closed depending on the zone needs. This, along with other VAV box components, is controlled through a direct digital control system, which helps to automate any functions required to maintain IAQ during occupied times. cse

Autumn Beer is a mechanical engineer at CDM Smith focused on efficient heating, ventilation and air conditioning and plumbing design solutions for wastewater and water treatment plants.

Valerie Lecaros is a mechanical engineer at CDM Smith focused on efficient heating, ventilation and air conditioning and plumbing design solutions for wastewater and water treatment plants.

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Andrew Varilone, PE, and Frank Majewski, AIA, NCARB, SmithGroup

Case study: How one museum modernized its electrical system

New electrical systems included a vault upgrade, updated cables and generators to support modern electrical needs.

The Det roit Institute of Arts (DIA) is a historic institution located in Detroit’s cultural district. This museum has a rich history dating back to its founding in 1885. Established to promote the arts and culture in Detroit, the museum has grown into one of the largest and most significant art collections in the United States. Its original collection began with a donation of paintings and sculptures and over the years, the DIA has expanded to include more than 65,000 works, spanning a diverse array of cultures

and time periods. The museum contains more than 140 galleries, an auditorium, an art reference library, art conservation department and a lecture hall, totaling approximately 658,000 square feet.

The DIA engaged SmithGroup to provide engineering services to upgrade and modernize the electrical services to the museum. At the time of the project initiation the cultural district was still operating on the infrastructure of the now-defunct Public Lighting Department (PLD) of Detroit.

PLD, once a vital municipal entity, faced decline due to a combination of financial troubles, aging infrastructure and the broader economic challenges facing the city. Established in the early 20th century, the PLD was responsible for providing street lighting and power to residents and businesses. However, by the late 20th century, the department struggled with budget deficits and operational inefficiencies. Ultimately, in 2013, the department was dissolved as part of a larger restructuring effort during Detroit’s bankruptcy proceedings, with its responsibilities transferred to a large regional utility company. This shift marked the end of an era for Detroit’s public power services, reflecting the city’s broader challenges and the need for modernization in its utility management.

Electrical system service entrance

Upgrading the electrical systems of the DIA was a multipart project that consisted of upgrading equipment both inside the museum as well as outdoors at the electrical service entrance to the campus. The existing electrical services entered the site

FIGURE 1: A 13.2 kV vacuum circuit breaker switchgear with automatic throwover operation. Courtesy: SmithGroup

from underground manholes containing the utility’s 4.8 kilovolt (kV) circuits. Incoming 4.8 kV utility services used three-conductor medium-voltage cables routed into the building through underground duct banks.

The most common distribution system used by the local utility company for serving its customers is 13.2 Y/7.6 kV. To connect into the utility’s 13.2 kV system, new 15 kV cables were brought from an underground manhole system which was totally independent from the existing 4.8 kV system. New exterior 15 kV class medium-voltage switchgear was required to accept the new 13.2 kV services provided by the utility. The incoming sections of the switchgear consisted of electronically interlocked vacuum circuit breakers (see Figure 1), which normally operated on one of the two 13.2 kV circuits, but can automatically switch to the alternate service upon loss of power.

New 15 kV cabling was routed from the new switchgear lineup to each of the existing transformer vaults located in the basement of the museum. Initially the intent of the engineering team was to use the existing pathways to route new 15 kV medium-voltage cable into the existing vaults, however upon further investigation it was discovered that the underground conduits were totally collapsed. The existing 4.8 kV cables were operating in the collapsed ducts, however it became clear that these pathways were not in suitable condition to be re-used for new cabling.

Screen wall to conceal electrical systems

While engineers may not mind looking at switchgear lineups, it turns out that the public does not find the grey boxes quite as appealing. The new switchgear lineup presented an opportunity to design a screen wall, which discreetly conceals the switchgear equipment while blending function with aesthetic appeal (see Figure 2).

The final design was selected through a collaborative effort with the DIA core leadership team. Initial design concepts were explored in various workshops with the core team. The chosen design honors the campus’s history by offering a modern interpretation of the original architecture and incorporating DIA branding.

Crafted from durable, weather-resistant materials, the screen wall is built to withstand the elements. It features two vertical planes: the outward-

facing plane is made of perforated aluminum, while the inner plane consists of a galvanized B-deck, supported by galvanized steel tubes.

The screen wall design includes a perforated pattern of the DIA logo, powder-coated glossy white, transforming it from a functional element into an appealing focal point. The second plane, painted in DIA’s signature blue, enhances visual appeal by creating a backdrop that adds depth and interacts with natural daylight.

Existing electrical vault conditions

The existing conditions of the electrical rooms presented the design team with some challenges as well as opportunities. The rooms were built as “transformer vaults” in the true sense of the words as defined by NFPA 70: National Electrical Code (NEC) Article 450, which requires these spaces to have three-hour fire rated construction and sills for oil containment among other requirements. Transformer vaults such as these were typical for mid-20th century buildings in Detroit, as the local utility company typically would install its mineral oil transformers in the vaults to step down the incoming 4,800 V service to the building’s utilization voltage. These rooms were only accessible to utility company personnel.

The existing transformers were single-phase “can” style transformers that we would typically expect to see mounted high on utility poles in mod-

2: Architectural screen wall which shields the new switchgear from view along the adjacent public ways. Courtesy: SmithGroup

Objectives Learningu

• Understand how the Detroit Institute of Arts upgraded its electrical infrastructure from an obsolete 4.8 kV service to a modern 13.2 kV utility system.

• Learn about the design challenges involved in replacing aging transformer vault equipment, routing new medium-voltage cabling and selecting codecompliant transformer solutions for a historic building.

• Examine how the project improved electrical reliability, fire pump service, emergency power capacity and overall safety while minimizing disruption to museum operations.

FIGURE

‘

BUILDING SOLUTIONS

Standard unit substation designs presented a multitude of problems when being considered for this application.

ern applications. To provide three-phase service to the building, three of these single-phase transformers were connected to each other in a delta or wye configuration using exposed cables and terminations.

The other main pieces of equipment found in the existing vaults were oil-insulated medium voltage circuit breakers. These circuit breakers provided a means for the utility to disconnect the transformers and provide overcurrent protection using analog relays. Current transformers were installed on the line side of each switch for metering the power usage on each incoming 4,800 V service.

When evaluating equipment that is 50 years old or greater, it is important to consider the possibility that hazardous materials may be present, as some of the systems may have been installed in a time where the knowledge of the effects of certain materials and chemicals was not yet known.

For this project, the main concerns that were evaluated were whether the insulating oils contained polychlorinated biphenyls (PCBs) and whether the medium-voltage cable outer layer contained asbestos. No PCBs were found in the oil; however, the medium-voltage cables did contain asbestos, requiring specific remediation processes to be followed to properly decommission the cables.

Electrical vault design solutions

Due to the existing conditions, the engineering team was presented with several design challenges to solve.

Topping the list of design constraints was the physical space available for the new electrical equipment in the vaults. The weight and size constraints were not an issue previously because the utility used individual single-phase transformers; however, that was not an option for the new equipment due to the safety hazard associated with open terminations.

Traditionally, when bringing medium-voltage feeders inside a building, engineers use unit substations to step down the voltage to the building equipment’s utilization voltage. Unit substations typically consist of a section of medium-voltage metal-enclosed switchgear with a load break switch close coupled to a medium-voltage transformer.

Dry-type transformers are often specified in indoor applications, however liquid-type transformers are being specified more often now due to the available of less-flammable insulating fluids.

Standard unit substation designs presented a multitude of problems when being considered for this application. First, the amount of floor space required was far greater than was available, especially when considering that ideally this equipment would be installed in phases. A standard 15 kV metal-enclosed load break switch is 3 feet wide and 7 feet tall, while a substation style medium-voltage transformer is 8 feet wide by 9 feet tall. These dimensions were a nonstarter due to the limited floor space and the height of the transformer enclosure.

Another issue that became apparent was the weight of a dry-type substation transformer; the largest size required for the project weighs approximately 15,000 pounds, which exceeded the building’s elevator capacity by 5,000 pounds.

The mounting design constraints with drytype substation transformers led the engineering team to investigate liquid-filled transformer solutions. Liquid-filled transformers are available in indoor substation style configurations, however the dimensions of those were not much of an improvement over the dry-types. Liquid-filled transformers also allow the transformers to be made lighter temporarily by draining the fluid and reinstalling after the unit is set in place; this strategy allowed the transformers to be transported down the elevator without exceeding the capacity.

Pad-mount style transformers offer the most compact footprint when comparing them against their counterparts of the same kVA rating, so the decision was made to use pad-mount transformers for the project. Pad-mount transformers can offer even further flexibility in fitting through tight openings, as some can be specified with a removable termination cabinet and removable radiator fins.

As an additional benefit, liquid-filled transformers enjoy a small bump in efficiency over their dry-type counterparts and the liquid can be sampled in the future as a preventive maintenance diagnostic tool.

Pad-mount transformers are available with standard mineral oil or less-flammable insulating fluids. It would have been code compliant to reinstall mineral oil transformers inside of the existing spac-

es, as they were constructed as three-hour fire rated transformer vaults, however it was determined that the less-flammable insulating fluid was the optimal solution. The engineering team was confident that the small cost adder associated with less flammable fluid was worth it to give the museum’s staff, visitors and artwork the best possible protection against fires.

In addition to the previously mentioned advantages, liquid-filled pad-mount transformers also have the benefit of being able to use their insulating oil to provide disconnecting means and overcurrent protection without any additional external equipment. This feature was a great benefit to the project, as it enabled each transformer to have its own integral load-break switch and fusing.

The integral disconnecting means and overcurrent protection was an important design feature, as it enabled the use of a single medium voltage feeder to be daisy-chained between multiple transformers without the need for additional medium voltage switchgear.

Fire pump electrical system considerations

The electrical upgrades project presented an opportunity for the DIA to also upgrade how its existing fire pump power feed was designed. The existing fire pump was served from a tap off the secondary of one of the 480 V service transformers that would be de-commissioned as part of the scope of work. At the time this was installed, the installation was considered code compliant, as the transformers were owned by the utility company and the tap was made before the downstream service disconnecting means.

However, after completion of the upgrades, this existing configuration of the fire pump power source would not be compliant with NEC 695.3(A), which requires that the fire pump be supplied from a connection located ahead of the service disconnecting means. The new system’s design incorporated a dedicated fire pump tap from the main service switchgear, which then fed a dedicated fire pump disconnecting means and fire pump transformer. The fire pump transformer stepped down the new 13.2 kV service voltage to 480 V to match the voltage of the existing pump.

Generator system upgrades

During the normal power upgrades project, the DIA also decided that its emergency power generator system was in need to modernization. The existing generator was a small 208 Y/120 V generator that was supporting a few select loads such as some security related loads and refrigeration equipment. As is common with most facilities with critical loads, their need for generator capacity expanded over time and it became apparent that additional generator capacity was required.

In addition to expanded data and security loads, the DIA wanted to provide additional resilience to the fire pump system. Although there was now an upgraded fire pump service, the fire pump would still be served from a single power source, which is permitted if the source is considered reliable.

However, even with a reliable utility source, the DIA recognized that the fire pump was a critical part of protecting the museum’s collection against fire loss and increasing fire pump system reliability was a sound investment.

‘The electrical upgrades project presented an opportunity for the DIA to also upgrade how its existing fire pump power feed was designed.’

FIGURE 3: Pad-mounted switchgear and transformers used for temporary power to the museum during construction. Courtesy: SmithGroup

BUILDING SOLUTIONS

‘The new utility services exhibited none of the previous symptoms of poor power quality, allowing the DIA to operate more efficiently and reduce the burden on its staff.’

Because the existing generator was 208 Y/120 V and the fire pump was 480 V, it became clear that the best solution for the generator upgrades was to provide a 480 Y/277 V generator sized to handle the fire pump load and provide a step-down transformer to serve all of the 208 Y/120 V loads. A new automatic transfer switch, transformers and panelboards were also integrated into the design to provide a completely upgraded emergency power system.

The typical method of providing two sources of power to a fire pump is to use a fire pump controller with an integrated automatic transfer switch. Fortunately, the DIA had the foresight to install this type of controller years before when the fire pump was installed. This streamlined the fire pump power upgrade process significantly; the installing contractor simply had to land the new generator power and control conductors in the controller.

Additional electrical system scope

The DIA recognized that the electrical equipment was not the only thing that needed to be upgraded in the electrical vaults. The mechanical systems, sprinkler systems, doors, lighting and paint were all upgraded provide a safe, comfortable space for the facilities staff and maintenance technicians.

One unexpected challenge that arose from installing modern energy-efficient transformers was that there was no longer enough waste heat being generated by transformer losses to adequately heat the electrical vaults during the winter months. Electric unit heaters were installed to supplement the transformer heat loss and keep the vaults at an appropriate minimum temperature.

Completion of electrical system upgrades

csemag.com

Electrical system insights

u The Detroit Institute of Arts modernized its electrical system by replacing obsolete 4.8 kV utility infrastructure with a new 13.2 kV service, new switchgear, upgraded transformer vaults and a more resilient fire pump and generator arrangement.

u The project improved the museum’s electrical system through safer equipment, better power quality, codecompliant fire protection and carefully phased construction that minimized disruption while protecting staff, visitors and the art collection.

Construction process and temporary services

The switchover process to migrate from the existing equipment to the new was a very detailed and precisely planned process that required close coordination between the DIA, the installing contractor, the engineering team and the utility. Most switchover work was performed on days that the museum was closed to the public to minimize the disruption to the museum’s operations and its patrons.

Temporary outdoor pad-mount switches and transformers (see Figure 3) were installed by the utility company; the transformers provided 480 Y/277 V and 208 Y/120 V service directly to existing switchboards, which then permitted the existing 4.8 kV equipment to be decommissioned and removed. This temporary equipment was key in minimizing the amount of downtime needed to perform the switchover when taking the old equipment offline.

Upon the completion of the new electrical equipment installation, the improvements were immediately visible to the DIA facilities team. The new utility services exhibited none of the previous symptoms of poor power quality, allowing the DIA to operate more efficiently and reduce the burden on its staff. Another observable benefit upon completion was the improved safety of the electrical systems in the vaults as all cabling was installed in conduit, leaving no exposed live parts.

The DIA continues to stand as a testament to the city’s rich cultural heritage and artistic legacy. The transformation of its electrical systems reflects not only the museum’s commitment to preserving art but also to adapting to modern technological demands. The engineering challenges faced were met with solutions emphasizing safety, efficiency and protecting the museum’s collection. By embracing advancements in electrical infrastructure, the DIA ensures that it can continue to serve the community and protect its invaluable collections for generations to come. cse

Andrew Varilone, PE, is Senior Principal, Electrical Engineer at SmithGroup.

Frank Majewski, AIA, NCARB, is an architect at SmithGroup.

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ENGINEERING INSIGHTS

How to design industrial facilities for future-ready service

This discussion explores how industrial facility engineers are addressing electrification, automation, AI integration and supply chain pressures.

CSE: What are some of the biggest trends in industrial and manufacturing facilities that engineers should be aware of?

Jarron Gass: Key trends include the rise of smart factories leveraging artificial intelligence (AI), digital twins and generative design for optimized operations; widespread electrification and decarbonization of process loads; reshoring/nearshoring driven by supply chain resilience; and advanced automation/robotics integrated with internet of things (IoT).

Sustainability mandates and workforce upskilling via alternate reality/virtual reality (AR/VR) tools are also accelerating. Engineers are prioritizing modular construction for scale, edge AI for real-time analytics and cyber-resilient infrastructure to stay competitive. These shifts support an agile, future-ready facility that can be expanded or modified quickly amid growth in advanced manufacturing.

Matthew Merli: Certainly, one of the biggest trends we’re seeing is the elec-

Objectives

• Understand how electrification and decarbonization goals are reshaping industrial facility design.

• Learn how automation, AI and digital tools are influencing manufacturing infrastructure and operations.

• Identify strategies engineers use to improve flexibility, resilience and scalability in industrial projects.

trification of the mechanical systems in these facilities. Many are looking to be fully decarbonized by certain timeframes as part of overall infrastructure master plans. We continue to do a lot of variable refrigerant flow (VRF), heat pumps and other technologies for heating, ventilation and air conditioning (HVAC) systems throughout these facilities.

Darren Rogge: The industrial market has been evolving to accommodate several challenges. Clients are shifting from fossil fuels to all-electric heating systems, requiring higher electrical demand to support increased robotics and automation systems. They are also pushing for net-zero carbon emission solutions or life-cycle carbon reduction.

Michael Walsh: One of the biggest trends is the need to make critical facility decisions earlier, often before the manufacturing process is fully defined. Compressed design and construction schedules are pushing building design ahead of process development, which introduces risk if decisions are made without sufficient data.

To address this, engineers are leveraging AI-driven and automated design tools to evaluate site layouts, utility demands and building configurations in the earliest project phases. These tools allow teams to test multiple scenarios quickly and give owners better information to make informed decisions sooner, resulting in more flexible facilities that can adapt as process requirements evolve while maintaining schedule and budget alignment.

Jacob Weber: Within industrial research and development (R&D) facilities, we are seeing growing demand for specialized applications like electric vehicle (EV) safety testing, hydrogen fuel cell development and hydrogen combustion development. On the manufacturing side, AI and data center growth are driving massive investments in semiconductor manufacturing, while EVs and grid-scale battery energy storage systems (BESS) are driving similar investments in battery plants.

We also see major reinvestment in existing automotive assembly plants as original equipment manufacturers adapt facilities for new products and processes. For such projects, engineers need to gain an early understanding of the process systems and equipment because they ultimately define utility capacity, safety systems, environmental controls and required long-term flexibility.

CSE: What are professionals doing to ensure such projects meet challenges associated with emerging technologies?

Darren Rogge: Emerging technologies present some unique challenges to project design. To help protect clients from having to upgrade systems as these technologies change, designs must include flexible infrastructure such as modular electric rooms, scalable electrical distribution systems or space-protected equipment layouts. This is a crucial element to be discussed during project conception to determine the level

Participants

of risk and cost the client is willing to integrate into their project.

Michael Walsh: To address the pace of emerging technologies, professionals are prioritizing flexibility as a core design principle. This includes planning for expansion zones within the facility and designing “capacity ready” infrastructure, such as electrical, mechanical and utility systems that can support future growth without major rework.

A key challenge is that technologies often evolve between the start of design and construction, requiring teams to make decisions with incomplete information. By building in flexibility through modular layouts, scalable systems and reserved capacity, engineers can help owners adapt to changing process requirements while minimizing future cost, schedule impacts and disruption to operations.

Jacob Weber: Identifying and involving the right stakeholders early is critical to integrating emerging technologies into both new and existing facilities. These technologies can frequently come with challenges like incomplete information, proprietary equipment, limited operating history, evolving safety requirements and

codes and changing design criteria. Input from the owner’s researchers, manufacturing engineers and facilities staff, as well as equipment vendors, is essential to fully understand the process and capture the associated facility requirements.

For existing buildings, there is the added necessity to closely evaluate what the facility can realistically support. This includes floor loading, clear heights, space classifications and utility capacity and distribution. There is an added challenge in making these new processes and equipment operate safely and reliably within existing constraints, rather than a purpose-built environment.

Jarron Gass: Professionals integrate building information modeling (BIM) and digital twins early for simulation and predictive modeling, collaborate cross-functionally with information technology (IT)/operational technology (OT) teams and conduct pilot testing of AI-driven automation and robotics. They perform gap analyses against codes like ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and National Fire Protection Association (NFPA) standards while

Jarron Gass, PE, CFPS

Principal, Fire Protection

Discipline Leader

CDM Smith

Pittsburgh

Matthew R. Merli, PE

Principal/Client Services Director

Fitzemeyer & Tocci Associates Inc.

Woburn, Massachusetts

Principal

Jordan & Skala Engineers Inc.

Norcross, Georgia

Michael P. Walsh, PE, LEED AP

Senior Director of Industrial IMEG

Cincinnati

Jacob Weber, PE

Project Engineer

Affiliated Engineers Inc.

Madison, Wisconsin

using modular/prefabricated mechanical, electrical and plumbing (MEP) systems to accelerate deployment.

Ongoing training in cybersecurity and edge computing addresses interoperability risks. Value engineering and phased retrofits keep existing structures compliant and competitive without full rebuilds. This proactive approach mitigates adoption barriers while delivering resilient, high-performance facilities.

Matthew Merli: Equipment vendors for these systems are changing and rapidly becoming more efficient. Things like a VRF system’s low ambient temperature performance have improved greatly over

Darren Rogge

FIGURE 1: Project Eagle, a 650,000-square-foot sorting facility for a large online retailer. Courtesy: Jordan & Skala Engineers Inc.

ENGINEERING INSIGHTS

the past decade such that they can operate in heating mode even during very cold stretches, which happens frequently in New England, where a decade ago we may not have used that sort of system. Additionally, ongoing refrigerant changes are always something to consider with emerging technologies.

CSE: How are electrification and decarbonization goals reshaping industrial and manufacturing facility design, particularly for process loads?

Jacob Weber: Some owners have shifted from a first-cost decision-making approach to a more holistic evaluation of operational costs, total cost of ownership and emissions impacts. This often includes comparing traditional fossil-fuel-based heating systems against multiple electrified alternatives. Paired with broad societal pressure to reduce carbon emissions, the electrification of processes and HVAC has become more prevalent in industrial facilities. This can create opportunities for technologies

like heat recovery, heat pumps and thermal energy storage to serve simultaneous heating and cooling demands at the temperatures required by processes. The biggest challenge in implementing these strategies is limiting the impact on process reliability, production uptime and operational flexibility.

Jarron Gass: Electrification is shifting process heating from fossil fuels to high-efficiency heat pumps, induction systems and resistive/electrochemical technologies, targeting up to 70% of industrial process heat by 2050. This reduces Scope 1 emissions while demanding upgraded electrical infrastructure, microgrids and energy storage. Decarbonization drives waste-heat recovery, renewable integration and process redesign for variable renewable power. Designs now balance high process loads with grid constraints via smart controls and efficiency measures. The U.S. Department of Energy’s Industrial Decarbonization Roadmap and ASHRAE 90.1 updates guide these changes, improv-

ing long-term operational resilience and sustainability.

Darren Rogge: Increased electrification has been challenging in most markets across the country. The electric utility providers’ infrastructure is inadequate to support the larger electrical demand being requested to serve client needs. The timelines for electric utility providers to upgrade their infrastructure can take up to two years, which makes some project sites unattractive to clients. A solution may be to provide microgrids, on-site generation or energy storage systems, which come at a great cost to the project.

The design can also include renewable energy (solar and wind) and/or implement BESS along with load management systems to help offset peak electrical demand on the utility infrastructure.

Michael Walsh: Electrification and decarbonization goals are significantly increasing facility power demands, particularly as traditional fossil fuel-based processes shift to electric alternatives. At the same time, greater use of automation and advanced manufacturing equipment is further driving up electrical loads. As a result, engineers can no longer rely solely on historical data to size infrastructure.

Instead, there is a greater emphasis on early load modeling, scenario analysis and close coordination with process teams to understand future-state requirements. This often leads to designing more robust and scalable electrical systems, with added capacity and flexibility to accommodate evolving technologies while supporting long-term sustainability and operational goals.

CSE: How are workforce challenges influencing facility design and system selection?

Matthew Merli: Many of our clients on the electronics manufacturing side are turning to automation and robotics on their assembly lines. Previously, we would design lines with people at the stations where we are now seeing robots doing the

FIGURE 2: The 757,750-square-foot Airstream production facility was designed to support large-scale manufacturing operations with flexible production space, integrated material handling systems and high-bay infrastructure optimized for operational efficiency and long-term adaptability. Courtesy: Bella Photographics/IMEG

work. There may be less people, but the advanced electronics and controls are something designers must pay close attention to.

Michael Walsh: Workforce challenges are closely tied to automation, safety and facility performance. Labor shortages are driving increased adoption of automation to maintain productivity, which in turn raises electrical loads and system complexity. As processes become more automated, engineers must carefully consider how people interact with equipment, leading to greater emphasis on safety systems, clear circulation paths and separation between human and robotic operations.

At the same time, more advanced systems require a workforce with different skill sets, influencing how facilities are designed for access, maintenance and training. The result is a more integrated approach where system design, safety and workforce considerations are addressed together rather than independently.

Jarron Gass: Labor shortages and skills gaps are pushing designs toward greater automation, robotics and AI-assisted interfaces that reduce manual tasks and enhance safety. Facilities incorporate intuitive controls, AR/VR training modules and ergonomic layouts to support upskilling. Safety expectations drive redundant systems featuring advanced detection and compliance with the Occupational Safety and Health Administration, NFPA and other industry standards. Modular construction and predictive maintenance analytics are helping minimize on-site labor needs. These choices are thought to improve productivity and lower injury risk while attracting and retaining talent and addressing the projected multimillion jobs gap in manufacturing.

Jacob Weber: Labor shortages in manufacturing are driving changes to process design, including greater reliance on automation. Similarly, shortages in facilities and maintenance staff are influencing facility design and system selection. Owners are prioritizing equipment and systems that provide better maintenance access and easy troubleshooting, use clear control sequences, have intuitive graphics and installation, operation and maintenance procedures and offer strong safety features or a proven operating history. Experienced maintenance staff is difficult to find and retain. Designing systems with health, safety and ease of use in mind can help streamline the training of new staff, reduce the burden on experienced staff and support long-term workforce retention.

CSE: How are you working with IT experts to meet the needs of industrial or manufacturing facilities?

Jarron Gass: Engineers partner with IT experts to converge OT and IT systems via IoT platforms and interoperability standards. Joint teams design secure networks for real-time data flow, enabling predictive maintenance and process optimization. Cybersecurity protocols are embedded from the concept stage. This collaboration ensures scalable digital twins, cloud-edge analytics and seamless integration of smart devices, aligning facility

performance with enterprise goals while meeting emerging technology demands and keeping client digital assets safe.

Michael Walsh: As manufacturing becomes more automated and data-driven, IT systems are now critical to maintaining uptime and operational performance. This has led to much closer coordination between engineering and IT teams, particularly around network infrastructure, data integration and system reliability.

We are collaborating earlier in the design process to align building systems with OT and enterprise platforms, ensuring proper space, power, cooling and redundancy for IT infrastructure. At the same time, increased connectivity brings greater cybersecurity risks, requiring a more intentional approach to network segmentation, system hardening and secure integration of building and process systems to protect operations. cse

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uEngineers are prioritizing modular, scalable infrastructure to accommodate rapidly evolving manufacturing and industrial technologies and future expansion.

uElectrification, automation and reshoring initiatives for industrial buildings are driving higher power demands and increased coordination between engineering, IT and operations teams.

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