The economizer hours in this report represent the number of hours that economizer systems can provide 100% of any required off-season cooling. This data can be used to estimate the potential cost savings to justify the installation of a new economizer system or evaluate the performance of an existing system given a known economizer cooling load. The economizer cooling load is comprised mostly of heat gain from internal sources such as people, lights, equipment, and processes. Figure 2 illustrates the cost savings per ton of economizer cooling load for October using the economizer hours in the report.
Waterside economizer systems typically pump cold condenser water from a cooling tower through a heat exchanger to generate chilled water in lieu of operating chillers. Some systems are designed without a heat exchanger, pumping the tower water directly to the cooling coils. The maximum outdoor wet bulb temperature that would allow for waterside economizer cooling is approximately 40 degrees. Above this wet bulb temperature, it's usually not possible to generate chilled water below 47 degrees given the limited approach to the cooling tower and thermal efficiency heat exchanger losses. The waterside economizer hours in the report are the total number of hours when the outside air wet bulb temperature is less than 40 degrees.