| Application Considerations
Figure A-1 -- Recommended
Piping Components For Typical Evaporator Installation
Typical Water Piping
All building water piping must be flushed prior to making final connections to
the chiller. To reduce heat loss and prevent
condensation, insulation should be installed. Expansion tanks are also usually required
so that chilled water volume changes can be
accommodated. A typical piping arrangement is shown in
Figure A-1.
Short Water Loops
The proper location of the temperature control sensor is in the supply (outlet) water. This location allows the building to
act as a buffer and assures a slowly changing return
water temperature. If there is not a sufficient volume
of water in the system to provide an adequate buffer, temperature control can be lost, resulting in erratic system operation
and excessive compressor cycling. A short water loop
(less than two gallons/nominal ton) has the same
effect as attempting to control from the building return water.
To prevent the effect of a short water loop, the following items should be given careful consideration:
A storage tank or larger header pipe to increase the volume of water in the system and, therefore, reduce the rate of
change of the return water temperature.
Multiple Unit Operation
Whenever two or more units are used on one chilled water loop, Trane recommends
that their operation be controlled from a single
control device, such as a Trane Tracer® system.
1
Series Operation
Some systems require large chilled water temperature drops (16 to 24 F). For those installations, two units with their
evaporators in series are usually required. Control of
the units should be from a common temperature
controller to prevent the separate thermostats fighting one another and continually hunting. It is possible to control from the
two individual unit controls, but a common temperature
controller provides a positive method for preventing control overlap, more closely
matches system load, and simplifies compressor lead-lag
capability.
2
Parallel Operation
Some systems require more capacity or standby capability than a single machine can provide. For those installations,
two units with their evaporators in a parallel
configuration are typical. The only effective way of
controlling two units in parallel is with a single temperature controller. Two
individual temperature controllers are not capable of
providing reliable system control and will often result in unsatisfactory operation and possible compressor failure. |
