Fall 2020, Vision Issue 11: Covid-19 Systems Design

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VISION ISSUE ELEVEN | FALL 2020

Covid-19 and its Implications for Systems Design HVAC Systems and Air Quality The Covid-19 Pandemic has forced building owners and engineers to take a deeper look at HVAC systems and how spaces are treated for human occupancy in light of the new emphasis on air quality. Air quality improvements, when applied to HVAC systems, are intended to reduce viral transmission rates, decrease instances of indoor mold and bacterial growth, and reduce respiratory infections due to indoor environmental conditions. To achieve these improvements in air quality, spaces should be conditioned, ventilated, humidified, filtered, and virus eradication technologies implemented in some cases. If implemented, these measures will help get us through the current pandemic, as well as improve our health thereafter. This may sound like a major renovation to your HVAC system, but it doesn’t have to be. Let’s dig into each measure. Conditioning Heating and Cooling are basic principles for both human comfort and maintaining strong immune systems. The ANSI/ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy addresses indoor environmental and personal factors and specifies an optimal temperature range to ensure a healthy environment for building occupants. Specifically, the range of 68° to 75° F is desired in the winter, while 75° to 80° F is preferred in the summer months. Cooling has the added benefit of dehumidifying the surrounding air; we will discuss why controlling humidity is important in the next section. Currently in the marketplace, there are retrofit options for residential and smallscale commercial projects to incorporate

combined performance of HEPA filtration, UV air purification, and odor removal in one self-contained unit. For variable refrigerant volume systems (VRV systems), it is recommended to upgrade filters to MERV-13 where possible and ensure effective air seals. For non-ducted indoor VRF units, upgrading existing filters may not be feasible. In these cases, ASHRAE recommends adding portable room cleaners with HEPA filters or filters with a higher MERV rating. Figure 1 - Filtration Installation Options Installation (3 options) Stand-Alone

Duct-Mounted (Bypass)

Added Ducts Joined to ducts with collars

• Increased transmission of some airborne viruses and droplets (COVID-19 still being studied) • Increased survival rate of pathogens • Decreased effectiveness of hand hygiene and surface cleaning due to surface recontamination or drying of disinfectants too quickly Buildings that have cooling systems are dehumidified in the summer months as a result of the cooling process, but most buildings are not provided with humidity control during winter operation. Respiratory viral infections are most common between November and April. Figure 2 Optimum Relative Humidity Range for Minimizing Adverse Health Effects Optimum Zone

Decrease in Bar Width Indicates Decrease in Effect

Bacteria Viruses Fungi

Protective grids on top and bottom

Openings in back of unit

Versatile unit that can be positioned horizontally or vertically

As shown above in Figure 1, standalone HEPA filtration, UV air purification, and odor removal units are available in three options for retrofit applications. Humidity Humidity levels between 40%-60% are the ideal range. Humidity ranges above 60% can lead to bacteria and mold growth, and increase the viral transmission rate; levels below 40% have been linked to the issues below: • Reduction of healthy immune system function (respiratory epithelium, skin, etc.)

ALL TEXT ©2020 KOHLER RONAN, LLC

Mites Respiratory Infections Allergic Rhinitis Chemical Interactions Ozone Production 1 Insuffient Data Above 50% Relative Humidity

0

10 20

30 40 50 60 70 80 Relative Humidity (%)

90

Providing 40% to 60% humidity may not be practical for all buildings as the envelope may not be designed to mitigate condensation. As illustrated in Figure 2, however, some humidification is better continued on page 2

IN THIS ISSUE Covid-19: Systems Design

1

Wireless Access Points

3

Women in Engineering Revit® Corner

4

Project Highlight

7


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Fall 2020, Vision Issue 11: Covid-19 Systems Design by Kohler Ronan - Issuu