Remarks

Optimal Supply Air Temp Set Point for VAV Air Systems

This requires polling individual VAV box air valve position and reheat valve position. This utilizes a fixed temperature for cooling (e.g. 52 degrees F) with no reset at all until polling of individual boxes indicates that most of the boxes are in heating - only then is the SA temperature allowed to gradually be reset upward to 62 degrees F max. The reset is accomplished by polling VAV reheat valve positions and the air temperature is gradually reset upwards until at least one VAV box reheat valve is 90% open, thereby providing optimal air temperature (just warm enough). Simultaneously, VAV damper positions are polled to be sure enough cooling is being provided for any zone still calling for cooling, and cooling will prevail if the two are at odds.

A similar, but less accurate, method uses the supply fan VAV output percent command along with outside air to estimate when most of the VAV boxes are at minimum and in the heating mode, signaling the time to begin resetting supply air temperature. An important feature of this reset schedule is that NO reset occurs during summer months, preserving the basis of VAV savings. A simple reset schedule is used for this method as follows:

SA Fan % Capacity

Outside Air Temp

Supply Air Temp Set point

100%

Any

0 0

Post a comment