What is the requirement for Heat Balance?

The verification of chilled water plant instrument using the heat balance –substantiating test shall be in accordance to AHRI 550/590. The heat balance shall be conducted over the entire normal operating hours with more than 80% of the computed heat balance within ±5% over the audit period (1 week).

The computation formula is as follows:

For open drive chillers, the Winput shall take into account the motor efficiency provided by the manufacturer. An example is provided as follows:

Input power (measured) = 100kW
Motor rated efficiency (η) = 90%
Adjusted Winput = 100kW x90%
                               = 90kW

In the event where hydraulic losses of pumps constitute a substantial heat gain, these losses have to be properly accounted for. The value shall be determined from pump efficiency values provided by the manufacturer. An example is as follows:

Motor input power (measured) = 30kW (A)
Motor rated efficiency (η) = 90% (B)
Pump rated efficiency (η) = 80% (C)
Hydraulic losses = (A) x (B) x (100%- (C) )
                                              = 30kW x90% x(100%-80%)
                                              = 5.4kW
Adjusted Winput = kWi(chillers) + 5.4kW