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SYS-APM001-EN Chiller System Design and Control 29
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 Chan
10
, and Schwedler
and Nordeen
11
, found that reducing flow rates can reduce the costs of
chilled-water system installation and/or operation. The ASHRAE
GreenGuide
8
states, “Reducing chilled- and condenser-water flow rates
(conversely, increasing the Ts) 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
Absorption Chiller Type
Condenser Flow Rate
gpm/ton
kkkkk 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