Column EnginEEr's notEbook type applications, m is typically in the range -0.2 to 0. * Disable the waterside economizer if it is not reducing the chilled water return temperature by at least 1°F (0.6°C). * Disable chillers when HXLWT is at or below the desired chilled water supply temperature setpoint. * Enable chillers when chilled water supply temperature is greater than desired setpoint. Note that multiple chillers may need to be enabled if the current chilled water flow is well above the design flow of a single chiller. * Run as many tower cells as tower minimum flow limits will allow. * Control condenser water flow to roughly match the current chilled water flow but reduce flow (within tower minimum flow constraints) as needed to maintain a minimum 5°F (2.8°C) range. The lower flow and higher range improves tower efficiency and reduces pump power. Flow can be controlled by staging pumps, modulating speed on variable speed pumps, and/or modulating isolation valves on the heat exchanger. Flow rate can be measured directly with a flow meter (full bore magnetic or ultrasonic type are recommended to prevent fouling) or deduced from heat exchanger pressure drop. * Tower speed control: 1. When waterside economizer is disabled: Control speed to maintain normal condenser water temperatures which should be reset from load or wet-bulb temperature.9 2. When waterside economizer and chillers are enabled: Run tower fans at 100% speed. 3. When chillers are disabled: Control speed to maintain HXLWT at desired chilled water supply temperature setpoint. The only complex sequence above is predicting when the economizer should be enabled. Fortunately, if the prediction calculation is off and the economizer is enabled prematurely, it will shortly be disabled and the plant will see no disruptions in chilled water flow or supply temperature. This contrasts with nonintegrated economizers where switching from economizer to chillers can be disruptive and guessing wrong about www.info.hotims.com/49805-22 J u n e 2014 ashrae.org ASHRAE JouRnAl 35