Building Automation Systems: Quick Check
Jean Pullen, P.E., C.E.M., LEED AP
The simplest way to reduce energy consumption and costs is to ensure that things are turned off when not in use. In facilities that use building automation systems for control of heating and air-conditioning systems (HVAC), it is not easy to determine if the automatic controls are programmed for maximum conservation potential. The following is a checklist that you can use in your facility to gauge the effectiveness of scheduling capabilities of the automatic HVAC controls. This checklist applies primarily to central building automation systems that control multiple HVAC systems.
1. Is there someone on-staff who is responsible for changing the scheduled start and stop times of the HVAC systems?
__Yes __No
If the answer to this question is no, then it is highly likely that your systems schedules are set for worst-case conditions. Since HVAC system operation is very energy-intensive, substantial savings can be achieved through active management. If changing the schedule for HVAC systems requires a service call to the controls company, this is a big problem that is easy to fix through training of staff. Building automation schedules are simple to modify; this procedure can generally be done in a few minutes.
2. Does each HVAC system have its own schedule that is separately updated based on daily or weekly coordination with area managers?
__Yes __No
If the answer is no, then develop a plan to coordinate receipt of occupancy schedules for system programming so that only the HVAC systems serving occupied areas are allowed to run. We frequently see buildings with space conditioning enabled throughout even though the facility is only partially occupied. Most chilled-water systems can operate down to 30% of peak load, so there is flexibility in the number of fan systems that must operate to keep the chiller plant online.
3. Are the temperature setpoints during unoccupied periods 55 degrees F or lower in winter and 90 degrees F or higher in summer?
__Yes __No
If the answer is no, then find out why. ASHRAE Standard 90.1 (see footnote), which is the basis for most energy codes, supports these limits. Common problems that impact unoccupied high and low limits can generally be corrected through monitoring of space humidity and by ensuring that during unoccupied periods all outside-air dampers remain closed and exhaust fans serving toilets, etc., are turned off to prevent negative building pressurization.
4. Are the HVAC systems turned on using optimal start versus scheduled start?
__Yes __No
If the answer is no, then ask your control system contractor how to enable optimal start. This is a control strategy that compares the occupied-period setpoints with the actual space temperature and determines how long it will take to recover to setpoint. Optimal start generally reduces fan system operation by about 5-10% while ensuring that space temperatures are at setpoint prior to occupancy. ASHRAE 90.1 mandates optimal start control of all fan systems over 10,000 CFM in capacity.
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1 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., Energy Standard for Buildings Except Low-Rise Residential Buildings, 2004 & 2007.
