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The effect of chilled water DP reset on plant pump power consumption varies based on cooling load profile and diversity, plant pump configuration, size and efficiency of the selected pumps. This reduction in DP setpoint is based on cooling load (chilled water valve position s ).

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ДЄ chilled water system may be designed to meet the full (peak) cooling load with 42 В° F chilled water and could be reset between 42 В° F and 48 В° F to optimize chiller energy savings.ДЄ control strategy for reducing chilled water plant pump power consumption for variable flow systems is to reset the chilled water system DP setpoint that controls the chilled water pump speeds. Д¬onversely, if all the high priority valves are open 90% or greater or if the average open position of all of the medium priority valves is 75% or greater, the setpoint will be adjusted down by an adjustable value of 0.5 В° F. If all of the high priority valves are open 70% or less and the average open position of all of the medium priority valves is 50% or less, the CHWST setpoint will be adjusted up by an adjustable value of 0.5 В° F. This strategy requires that all of the chilled water valves be assigned a priority ( l ow, m edium or h igh ) and that every chilled-water valve position be polled at regular intervals, typically 30 minutes, via valve position feedback. Table 1 uses data from actual manufacturerвЂ™s chiller selections to illustrate this. 5% reduction in compressor kilowatt input per degree F ahrenheit of increased CHWST. With the major chiller manufacture r s implementing the latest chiller technology, including falling film evaporators, CHW S T reset can result in 2 % to 2. T his reduction is consistent for water-cooled chillers independent of chiller size and configuration. Increasing the CHWST has a significant impact on chiller compressor power consumption.

The input to the BAS is polling of the AHU chilled water valve position s. One control strategy for reducing chiller power consumption is to increase the CHWST based on cooling load.

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