Optimize Your Air Handlers

11/30/2012 | By J.R. Howard

Take the time to optimize your air handlers - the savings from year-round monitoring and control justify the effort.

Some people make things happen, some watch what happens, and some wonder what happened.

If you want to create efficiencies in your air handling units (AHUs), keep on reading. A proactive approach to your air handlers can pay off with significant savings.

My facility, a 121,000-square-foot university building in Texas, was opened in 2005. It is equipped with dual-duct AHUs (see diagram). The dampers in the outside air duct and return air duct are controlled by the CO2 setpoint. The fan is controlled by the static pressure in the downstream ducts. The outside-air setpoint operates the valves to the preheat and precool coils. The hot deck setpoint and the cold deck setpoint operate, respectively, the water valves to the hot deck coil and the cold deck coil.

The dual-duct air handlers take 180 degree F. and 42 degree F. water and supply 100 degree F. hot air and 55 degree F. cool air through duct work to a terminal box. The terminal box adjusts the hot and cold dampers to provide sufficient air to reach a room thermostat setpoint.

The most sophisticated part of this facility’s system monitors the terminal box dampers, the room setpoint, and the room temperature. If the room damper exceeds 90%, then the controls lower the AHU supply temperature a few degrees. If this isn’t sufficient, then the AHU static pressure is increased.

Only four water valves, two dampers, and the fan speed can be controlled on the AHUs, but much can be done with them. My main strategy is to operate the system with the least energy while maintaining the warmest room at a maximum of 74 degrees F. The following suggestions assume that your system has digital controls with the ability to change setpoints based on demand and outside air temperature (OAT).

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