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Chilled-Water System Variations
SYS-APM001-EN Chiller System Design and Control 75
Sidestream heat recovery
A similar situation occurs if a heat-recovery chiller is placed in this
sidestream position
24
(see Figure 46). This chiller may be equipped with a
heat recovery condenser or it could be a standard, single-condenser chiller
operating as a heat pump in a heating control mode. The chiller may not be
capable of cooling water to the system supply temperature. That is
unimportant with this configuration. Think of the machine as a heater instead
of a chiller. Its primary function is heating, and cooling is a beneficial by-
product. The passing return-chilled-water stream appears as an infinite heat
source to the heat recovery chiller. The chiller only cools its evaporator water
enough to satisfy the heating demand. This avoids the control predicament
of deciding how to reject surplus condenser heat when the cooling and
heating loads of a chiller do not strike a perfect heat balance.
Figure 46. Heat recovery chiller in sidestream position
Sidestream with alternative fuels or absorption
An absorption chiller may be applied in a sidestream location. This allows the
chiller to be loaded whenever utility rates make it beneficial. It also ensures
that the absorption water chiller receives the warmest entering-water
temperature, allowing it to operate more efficiently and produce more
cooling.
Referred to as “distribution sidestream,”
an alternative location is to apply the
chiller at the air handler that requires
reheat. The heat recovery chiller can
cool either the supply or return chilled
water. If only a small amount of heating
is needed, this may be accomplished
with a water-to-water heat pump.
Off
50.2°F
[10.1°C]
40°F
[4.4°C]
Chilled
Water
Production
Chilled
Water
Distribution
900 gpm [56.8 L/s]
40°F [4.4°C] 75 gpm
Bypass Line
42.7°F [5.9°C]
51.2°F
[10.7°C]
56°F
[13.3°C]
300 gpm [18.9 L/s]
Heat
Recovery
Chiller
825 gpm
[52 L/s]