The decision to activate an air-side economizer is typically based on a comparison of the outdoor and return air enthalpy of the two airstreams; the stream utilized is the one with the lowest enthalpy. For data centers that comply with the high supply air conditions recommended in ASHRAE’s Thermal Guidelines for Data Processing Environments (ASHRAE 2004a); however, conditioning the return air typically only requires sensible cooling. If the outdoor air with low enthalpy but high dew point is utilized, a dehumidification process is needed in addition to a sensible cooling process. This dehumidification process (desiccant or otherwise) will have a COP different from sensible cooling, which will affect the range of psychrometric conditions suitable for economizer use. The purpose of this paper is to look at the efficiency of the dehumidification process (mechanical refrigeration vs. desiccant) needed to utilize this high dew point outdoor air to allow for air-side economizer operation.

Units: Dual