Filter
Top Products
76 TRG-TRC016-EN
notes
period three
System Variations
A second type of waterside economizer is the plate-and-frame heat
exchanger. In this case, water from the cooling tower is kept separate from
the chilled-water loop by a plate-and-frame heat exchanger. This is a popular
configuration because it can achieve a high heat-transfer efficiency without the
potential for cross-contamination. With the addition of a second condenser-
water pump and proper piping modifications, this heat exchanger can operate
simultaneously with the chiller. As much heat as possible is rejected through
the heat exchanger, while the chiller handles any excess cooling load.
If the plate-and-frame heat exchanger is piped in the sidestream position, it can
be used for more hours in the year because it does not need to maintain a
leaving-chilled-water temperature set point. It can provide some useful cooling
at any time that it can precool the system return water.
If simultaneous free cooling and mechanical cooling are performed, care must
be taken to control the evaporator-to-condenser pressure differential inside the
chiller. When very cold condenser water flows through the chiller condenser for
an extended period of time, operational problems may result due to a low
pressure differential between the evaporator and the condenser. Using a
three-way, modulating bypass valve to mix the warm water leaving the chiller
condenser with the cold water entering the condenser, or a two-way
modulating valve and a variable-speed condenser water pump, can eliminate
this problem. Consult with the chiller manufacturer to determine the limits for
the specific chiller being used. This issue is discussed further in Period Four.
waterside economizer
Plate-and-Frame Heat Exchanger
b
y
p
a
s
s
p
i
p
e
b
y
p
a
s
s
p
i
p
e
distribution
distribution
pump
pump
plate
plate
-
-
and
and
-
-
frame
frame
heat exchanger
heat exchanger
c
o
n
d
e
n
s
e
r
c
o
n
d
e
n
s
e
r
w
a
t
e
r
l
o
o
p
w
a
t
e
r
l
o
o
p
Figure 84