As seen in the RSES Journal = Breaking Down the Basics of the Economizer, by Phil Kimble.
Due to internal heat loads associated with people, equipment and lighting, most large commercial buildings require year-round cooling. One tool that helps alleviate this excess heat gain is an economizer system. Since the only energy an economizer uses is for blower operation, an economizer system in conjunction with a traditional HVAC system can significantly reduce energy consumption by drawing in or
pushing out the outdoor air. This “free” cooling the economizer provides can be utilized during
mild and cold weather periods.
Economizer systems have existed for many years, but older systems require several motors and controls along with extensive mechanical linkage. Thousands of older, installed economizer systems are nonfunctional due to improper installation, setup and/or component failure. However, most systems can be upgraded and made fully functional by applying new and more reliable components, and thereby sig
nificantly save energy.
Two types of economizers are in use today. A ventilation-type system operates only when the outside air can be used for cooling, as determined by the enthalpy control, without mechanical cooling. An integrated-type system allows the economizer to provide all or some of the cooling, along with supplementary compressor operation, and requires a multi-stage cooling thermostat.
Determining when outside air is useable for free cooling
The enthalpy sensor used in an economizer system senses the relative humidity and temperature.
The control point for the enthalpy sensor within the selected control point value. Outside air is usable for free cooling as long as the humidity level and temperature are on the control point curve. The enthalpy sensor senses the