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36 TRG-TRC012-EN
notes
period five
Application Considerations
1) The water flow rate through the chiller’s evaporator must stay between the
minimum and maximum evaporator bundle flow rates as specified by the
chiller manufacturer. These limits depend on the specific details of the actual
evaporator bundle, such as the number of tubes, number of passes, and
geometry of the bundle. A method for sensing evaporator water flow through
each chiller is the only way to make sure the water flow rate stays within these
limits.
2) The rate which the evaporator water flow rate changes must be kept below a
specified level, which is dependent on the level of protection desired. For
example, the maximum rate of change in order to maintain chilled water
setpoint is more stringent than the maximum rate of change in order to keep
the chiller on line. There are 3 common levels of protection desired:
maintaining chilled water setpoint control, keeping the chiller on line, and
protecting the chiller from damage.
The limits for these different levels of protection should be obtained from the
chiller manufacturer.
Short Evaporator Water Loops
Proper chilled water temperature control requires that the temperature of the
chilled water returning to the evaporator not change any faster than the chiller
controls can respond. The volume of water in the evaporator loop acts as a
buffer and ensures a slowly changing return water temperature and, therefore,
stable temperature control. If there is not a sufficient volume of water in the
loop to provide an adequate buffer, temperature control can be lost, resulting in
erratic system operation.
The chiller manufacturer should be consulted for volume requirements of the
evaporator water loop.
load
load
chilled
chilled
water
water
pump
pump
evaporator
evaporator
Short Evaporator Water Loops
Figure 52