Trane SYS-APM001-EN manual Condenser-Water Temperatures, Chilled- and Condenser-Water Flow Rates

System Design Options

Condenser-Water Temperatures

Today’s chillers can run at various entering condenser-water temperatures, from design temperature to the lowest-allowable temperature for that particular chiller design. However, many existing older chillers are limited in their allowable condenser-water temperatures. Contact the chiller manufacturer for these limits. Optimal condenser-water temperature control is discussed in the section, “System Controls” on page 87.

Chilled- and Condenser-Water Flow Rates

The selection of chilled-water and condenser-water flow rates is a powerful tool that designers have at their disposal. Kelly and Chan10, and Schwedler and Nordeen11, found that reducing flow rates can reduce the costs of chilled-water system installation and/or operation. The ASHRAE GreenGuide8 states, “Reducing chilled- and condenser-water flow rates (conversely, increasing the ΔTs) can not only reduce operating cost, but, more important, can free funds from being applied to the less efficient infrastructure and allow them to be applied toward increasing overall efficiency elsewhere.”

Standard rating flow conditions

Presently, the standard-rating-condition flow rates for electric chillers in ARI 550/590 are:

•2.4 gpm/ton [0.043 L/s/kW] for evaporator

•3.0 gpm/ton [0.054 L/s/kW] for condenser

This evaporator flow rate corresponds to a 10°F [5.6°C] temperature difference. Depending on the compressor efficiency, the corresponding condenser temperature difference is 9.1°F to 10°F [5.1°C to 5.6°C].

Absorption chillers are rated using ARI Standard 560–2000, Absorption Water Chiller and Water Heating Packages 9. The evaporator flow rates are the same as those used in ARI 550/590; however, condenser (often called cooling water) flow rates differ depending on the absorption chiller design. Table 3 shows the standard rating conditions for various absorption chillers.

Table 3. Standard rating conditions for absorption chillers

		Condenser Flow Rate
Absorption Chiller Type		gpm/ton	L/s/kW
Single Effect		3.60	0.065
Double Effect	Steam or hot water	4.00	0.072
	Direct fired	4.00	0.081

SYS-APM001-EN Chiller System Design and Control 29