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By Helen Kessler
Energy Efficiency Article Use Policy
The building at 203 N. LaSalle Street is a 650,000-square-foot office structure in downtown Chicago that used the BOMA Experience Exchange as its benchmark — the first step to significant savings. The property manager noticed that its energy cost was about 25 cents per square foot higher than its peers and wanted to see if that cost could be reduced. She requested an energy audit/retrocommissioning study to determine whether there was any low-hanging fruit that could be used to lower the utility bills. Funding for the study came, in part, from a ComEd retrocommissioning incentive program.
During conversations with the building engineers, it became apparent that the building was not able to meet comfort conditions on "normal" summer days. The chief had recommended installing a new $200,000 chiller to increase cooling capacity and comfort, which would be a big capital expense, and it seemed prudent to verify that it was needed. Adding the chiller would also increase utility bills.
In the course of the conversation, it became clear that some damper controls on fan-powered boxes were not working properly, and chilled air was being wasted/dumped into the air plenum. The consultant recommended retrocommissioning to check every VAV box. This was done over a period of several weeks, in the evening, and all controls were fixed.
Rectifying the problem with the fan-powered boxes in the supply air system produced a series of cascading improvements in cooling system performance. There was no longer a need to maximize the output of the chiller to satisfy tenant comfort complaints, which allowed the temperature set point of the chiller to be set back to the design temperature and the maximum chilled water flow to be reverted back to automatic control. As part of the commissioning process, cooling tower controls were recalibrated and a faulty valve was identified and replaced, and outside air damper controls were recalibrated.
The retrocommissioning cost $45,000 in materials (plus consultant fees) but saved the owner more than $150,000 annually (approximately $0.25 per square foot), according to the building manager. Electricity usage was reduced by 2,000 MWh annually. Electricity demand was significantly reduced, because the system now often operates with one chiller, rather than two, which was the previous operating norm. Because the retrocommissioning process brought the operations of the air handling system up to its intended design condition, a new chiller was never required, and the building provided comfortable conditions to the tenants on the hottest day in Chicago's recorded history.
Building management personnel were pleased with the improvements. According to a senior building engineer, "The system has never run better." Tenant comfort improved significantly, resulting in a 60 percent reduction in comfort complaints, increased staff morale, and less time spent troubleshooting comfort problems. Engineering staff now has more time to spend on preventive maintenance and facility improvements and is able to service special tenant requests in-house, generating additional building revenue.
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