Retro-Greening: Bringing sustainability to your existing facility

Chris Carter

Office Manager ESA, A Terracon Company Round Rock, Texas

uilding owners have a plethora of choices when it comes to classifying their future renovation as “green”: LEED, CHPS, and Energy Star to name a few. The requirements vary for each program but they all originated from a common idea—to facilitate the incorporation of sustainable, efficient equipment and practices into existing buildings where they do not currently exist.

Sustainability is defined many ways, but it most often refers to minimizing or eliminating the carbon footprint that a building leaves on its environment. Energy efficiency is producing the necessary building conditions or manufactured product with as little energy use and cost as possible. Retrofitting existing buildings with systems that produce renewable energy and incorporating equipment and strategies that reduce wasted energy is referred to as “RetroGreening.”

Energy and sustainability retrofits can be accomplished in many different systems in an existing facility. This article illustrates a few examples of typical projects.

Renewable Energy

ESA, A Terracon Company, assisted with the installation of a 101kW solar photovoltaic system on the roof of an existing parking garage to offset peak demand and consumption charges for a city hall. The system also offered the added benefit of providing additional shaded parking to the top level of the garage. The city has considered utilizing a larger system at the wastewater treatment plant that would supply renewable power to the smaller distribution pumps, aerators and building lighting sources that operate throughout the day.

Lighting

Many of our facilities were constructed with the intent to utilize daylighting strategies to limit the need for light fixtures to operate during the day, but the controls and equipment for implementing those strategies have been abandoned or were value engineered out of the original construction. There have been significant gains in the technology and reliability of daylighting controls and the incorporation, or reincorporation, of these controls into the existing lighting systems is typically a relatively easy task. We find a number of areas in almost every building we survey that have an abundance of natural daylight supplied by windows, skylights or light wells, but operate all of the existing light fixtures in the space during the daytime. The introduction of a photocell into an existing lighting circuit that serves fixtures located in these areas will automatically control the fixtures so that they turn on when the ambient light is not sufficient, but more importantly, they turn off when the natural daylight satisfies the lighting requirements of the space.

It is not uncommon to find light fixtures operating throughout the day in an area designed to utilize energy saving daylighting strategies.

Hot Water and Steam Production

Many facilities utilize large boilers to produce process or space conditioning steam or hot water for the needs of the business or the facility. One retrofit possibility is replacing the large existing steam boiler with smaller point-of-use steam generators that produce steam for only those loads that require steam (such as sterilizers and humidifiers) and satisfying the remainder of the heating requirements with smaller, hot water-producing equipment located close to the site of the actual hot water consumption. As most energy loss within a hot water or steam system occurs through the distribution piping, steam traps and condensate return pumps, utilizing high efficiency condensing boilers or instantaneous hot water generators located close to the source of use will generally consume significantly less energy than larger single systems that must distribute heat energy over long distances. The turndown ratio on larger heating systems is frequently unable to stage its operation to match load conditions as well as smaller systems designed to closely match the heating requirements with the existing loads. The maintenance required for each unit increases as more pieces of equipment are introduced into the system, but the overall maintenance for the system decreases as the distribution piping network is shortened or eliminated. Additionally, supplying the process or space conditioning energy from multiple zoned sources creates a naturally redundant system and results in a more dependable and more efficient system.

Thermal Storage

As deregulation becomes the norm for many of our states’ electricity markets, and even in areas that are not deregulated and still offer time-of-use rate schedules, thermal storage remains a viable option to reduce energy costs. We find many facilities in Texas that simply abandoned their thermal storage systems after deregulation eliminated the time-of-use rate schedules within the deregulated region of the state, thinking that the systems offered little benefit without a “free energy” period in which to recharge the system. We have found that the thermal storage system remains viable as a means of demand limitation. By operating one chiller in a multiple chiller system overnight and charging the thermal storage tank, that reserve chilled water can be utilized throughout the day in conjunction with chillers in the system so that the chilled water requirement can be satisfied with one less chiller during the day than would have been required without the thermal storage supplement. There are no consumption savings generated with this strategy; the reduction in demand charges, however, results in a significantly lowered utility bill and with proper lead/lag chiller operating strategies can lead to improved longevity for the chillers within the system.

Heat Recovery

Another effective energy retrofit is to install waste heat recovery equipment to capture and reuse waste heat that normally escapes the building through the flues of combustion process heat generation equipment. The waste heat is captured and utilized to pre-heat the boiler or generator make-up water supply and reduce the overall load requirements of the system.

Variable Frequency Drives (VFDs)

We still survey buildings that have large hydronic system distribution pumps and cooling tower fans that do not utilize VFDs. In the case of adding VFDs to chilled or hot water pumps, it is important to know that the installation of a VFD may require the facility to replace three-way valves located at the air handlers and terminal units with two-way valves. Also, a differential pressure sensor will need to be installed at the correct location within the distribution piping to signal the drive when to throttle the pump up or down. For cooling tower fans, the installation is easier as the fan throttles based on condenser water return temperature to the chiller. VFDs have an added benefit in both situations of serving as a soft-starter for the pump or fan and, in addition to the energy savings produced, should extend the service life of the equipment.

Improving energy efficiency and reducing a building’s impact on the environment is not limited solely to new construction or high-cost equipment and system retrofits. There are many opportunities to green-up your facility with much of the infrastructure that you already have in place.

Installing variable frequency drives on existing driveless cooling tower fans can be an excellent opportunity for energy savings at an existing facility.

Chris Carter is the office manager for the Round Rock, Texas, location of ESA, A Terracon Company. He can be reached at (512) 258-0547 or ccarter@ esa-engineers.com. Terracon is an employee-owned engineering consulting firm with more than 2,700 employees providing geotechnical, environmental, construction materials and facilities services from more than 130 offices in 39 states nationwide.