The client’s initial goal was achieving 500,000 kWh in annual electrical savings and 3,000 therms in natural gas savings. GBA identified 11 potential energy conservation measures (ECMs), and Motorola elected to implement six. The client’s goal was greatly exceeded, with verified electrical energy savings of 941,051 kWh/year ($99,751) and gas energy savings of 13,865 therms/year ($5,823). The simple payback for implemented measures was only about six months.
The implemented ECMs included:
- Schedule three air-handling units. Three AHUs had previously been set to operate 24/7. The implemented schedules vary slightly based on area served, but in general result in units operating during the day and shutting off on evenings and weekends. Scheduling of AHU S-1, which serves core areas of nine floors of the Tower, resulted in the largest energy savings among all measures: nearly 548,000 kWh ($58,000) and 20,100 therms ($8,400). Scheduling also provided significant energy savings for AHU S-4 (more than 147,000 kWh and 1,500 therms, for a combined annual total of more than $16,000 in savings).
- Use a variable frequency drive for the AHU S-4 supply fan. This fan had been operating at constant speed because its VFD was broken. A new VFD, which once again allows the fan speed to modulate according to a static pressure setpoint, was installed.
- Repair/replace dampers. AHU S-5, which serves common areas on the first floor of the annex (including food service) as well as basement areas, was found to have nonfunctional outside air and return air dampers. Both were replaced, allowing the dampers to modulate to meet minimum outside air requirements and provide more efficient mixed air temperature control.
- Reset duct static pressure. This measure affected three AHUs as well as a rooftop unit. At baseline, static pressure setpoints on all units were held constant. The implemented ECM allows the setpoint to reset when appropriate, based on polling of the zone terminal units. Energy savings from this ECM exceeded 143,000 kWh (about $15,170 annually).
To gain additional savings from another ECM, implementation of a follow-up RCx project to optimize the free cooling heat exchanger was completed in 2021. Control was modified for the transitions between chiller and heat exchanger operation, along with inclusion of an automatic cooling tower defrost sequence. Annual savings were approximately 180,000 kWh and $19,000.