Challenge
Richmond SPCA had an inadequate system. The controllers were not working properly; a space sensor would read 72 degrees but the controller would show 90 degrees. This caused it to drive the VAV box to max flow which wasted energy. Resetting the controller fixed the problem, but this issue would reappear within 24 hours.
The controllers had similar issues with duct static air-flow. Duct pressure sensors would read the flow as being too high, but the controller would show 0.2 duct static and drive the fans to 100% speed. The system would also not allow the schedules to be changed from 24/7 operation, wasting more energy.
Solution
ColonialWebb performed a BAS upgrade from their previous system to Distech Controls and performed an air balance on each VAV box. Each AHU features a discharge duct-static reset based on the VAV box damper position to maximize energy savings. The max damper position setpoint for each AHU's set of VAV boxes is programmed to 90%, guaranteeing each space has enough airflow for conditioning while saving energy. If the highest VAV box damper position is above 90%, the fans slow down and speed up if the damper position is below 90%.
A Closer Look
The project cost $110,000 and was completed in February 2015. Working with the customer, the schedules were changed from their 24/7 operation at the end of April of 2015. The schedules are at the VAV box level, only keeping the spaces needed conditioned. Because of this, one AHU shuts down due to no conditioning needed while the other AHU runs much lower speeds at night while still maintaining the spaces.
February through the end of April savings totaled $5,212.73 due to a properly working BAS system. After the schedules were added, the savings from February to August (7 months) total $16,874.33 weather normalized. After April, the savings average $2,900 for each month.