Xerox Corporation: Abandoned Air Handler Repurposing
Building 201, which is part of Xerox’s Webster campus, depends on a chilled water system for cooling. The chiller plant consists of two 400 ton water cooled VFD centrifugal chillers, three 20 HP primary chilled water pumps, three 50 HP secondary chilled water pumps, three 30 HP condenser water pumps, and a dual cell cooling tower with two 20 HP fans. As part of Xerox’s sustainability strategy, plant personnel sought to reduce unoccupied base load and although the chiller system was necessary during unoccupied periods, it operated at part-load during such time periods. To address this issue, Xerox made use of an unused air handling unit (AHU), which is now able to serve as a dry cooler during winter months, instead of using the plant’s water-cooled chiller system.More
The repurposed AHU has been integrated into the chilled water system controls such that it only operates as needed. This has allowed for the seasonal shutdown of the plant’s chillers and auxiliary equipment (including chillers, primary & condenser water pumps, and cooling tower) during the months where the outside air temperature is below 40°F. The conversion has resulted in 15% energy cost savings for the facility, yielding annual energy cost savings of $10,000. With a utility rebate equaling the total project cost of roughly $30,000, the project had an immediate simple payback. Xerox actually received a larger rebate than originally anticipated, so the rebate was ultimately capped at total project cost.Less
The opportunity to use “free-cooling” for this system had been identified in previous energy studies, but traditional systems were cost prohibitive to install. “Free-cooling”, also referred to as air cooling or dry cooling, is a process by which heat is exchanged with air, thereby cooling the liquid, in this case chilled water by taking advantage of low ambient temperatures. When possible free-cooling is used in place of chillers, which require greater energy input to provide the cooling effect.More
The plant energy manager continued to evaluate options and the facilities operating engineer identified an abandoned air handling unit. A further study was needed to quantify the ability of the AHU to fit the needs of the system.
After analyzing the underutilized AHU to validate unit functionality, modifications were designed to allow the air handler to be used for free-cooling and be fully integrated into the chiller plant controls. The AHU was already integrated into the Building Management System (BMS). Initial review and testing included the following processes:
- Data loggers were utilized to monitor temperatures.
- BMS instrumentation was utilized to observe that loads were being met and monitor energy consumption.
- Dampers and access doors were manually opened and closed to ensure that cold air was discharged to the atmosphere, as would occur with dry coolers, rather than into the building.
Implementation of the new system took approximately 15 months from initial review to completion. With the modifications made, the system is set to automatically switch to free-cooling when the outside air temperature allows and switch back to mechanical cooling once the temperatures increase past allowable levels. The system will also switch back to mechanical cooling if the free-cooling system is unable to handle the load regardless of outside air temperature.Less
Aside from meeting the expected energy savings, the reduced runtime on the chillers has allowed for additional maintenance time which will extend the life of the chillers. Additionally, had the chiller not been converted, installation of a hot gas bypass would have been needed to allow the chillers to operate under the low load winter conditions. The avoided cost has resulted in additional savings which were considered in overall project payback.
With the success of this project, Xerox is looking into similar conversions in their year-round chiller plants. Free-cooling systems are already installed in several of their buildings and they are looking into how other abandoned assets can be repurposed for additional savings.More