Air side economizer setup

[njnick]

Im in NJ. What is a "typical" enthalpy change-over setpoint for differential enthaply control of an air side economizer?
What about the drybulb override to close the dampers?
At what point is it more efficient to close the dampers and reduce the buildings return air enthalpy instead of exhuasting it.
We are presently using differential enthapy to enable the economizer when the outdoor air is less than 28btu/lb or
70F dry bulb.
I think the current setting are too high and we're wasting fan energy and the cost of filtering the outdoor air in stead of just cooling the recirculated air. Chilled water is already available for other processes.

 

[imok2]

WHEN you use a combination temperature and humidity sensor mounted in both the outside
air and return air ducts to close the outside air damper to a minimum position when the outside air
enthalpy exceeds the return air enthalpy. Enthalpy, in a simplified sense, is nothing more than the total
heat capacity of the air. In humid climates, the enthalpy (or total heat) of the outside air may be greater
than that of the return air even though the dry bulb temperature of the outside air may be lower than
that of the return air. When the outside air enthalpy is less than the return air enthalpy, the outside air
damper, the return air damper, and the cooling valve may be modulated in sequence to provide the
proper supply air temperature. This strategy should be used in climates where the humidity is high or is
not constant.