Specifications

20
4.6 Fluid Coolers - Model DAFC
4.6.1 Fluid-Sensing Thermostats
Fluid cooler fan motors are cycled on and off by individual water-sensing thermostats strapped
to the leaving water header. The fi rst fan motor will only have a thermostat if the unit has an Energy
Saver Coil. Without the optional Energy Saver Coil, the fi rst fan motor runs whenever there is a call
for cooling via an auxiliary signal sent by the indoor evaporator (see Section 3.5).
The water-sensing thermostats have adjustable setpoints which are typically staggered to maintain
water temperature in the 85° to 105° F range. This is generally the desired range for glycol cooled
systems.
A surge tank is standard on all fl uid coolers. This is suffi cient on most applications. However,
an expansion tank should be installed at the highest point in the system and the point of least
pressure.
4.6.2 Energy Saver Cooling
In colder climates, the evaporator will often be equipped with an additional free cooling coil to
take advantage of the colder ambient temperatures. When incoming fl uid falls below the setpoint of
a water-sensing thermostat in the evaporator (typically about 50° F), energy saver cooling becomes
available.
Systems with an Energy Saver Coil should have at least one fl uid-sensing thermostat on the fl uid
cooler set lower to take advantage of colder ambient temperatures. The desired fl uid temperature
for energy saver cooling is 45° F. Field adjustment of fl uid-sensing thermostats is not unusual.
It is desirable to use the energy saver mode as much as possible. However, fl uid temperature
that is too cold can cause excessive dehumidifi cation and coil sweating. Fluid temperature that is
too high can also cause the indoor space temperature to rise. This could cause the evaporator’s
microprocessor control to lock out the energy saver mode for one hour while it reverts back to
compressor (mechanical) cooling. Adjust the setpoints of the thermostats to allow the maximum
free cooling time. Over cooling or under cooling the fl uid should be avoided.
Every application will have a different ambient temperature and indoor heat load/air
distribution profi le. Therefore it is not possible to dictate the exact water-sensing thermostat
setpoints. Field adjustments are typical to allow fi ne-tuning to specifi c conditions.