Catalogue

CG-PRC017H-EN 9
Application Considerations
microcomputer’s ability to maintain an acceptable supply water temperature range. Furthermore,
full load temperature drops of less than 6°F (3.3°C) may result in inadequate refrigerant superheat
which is critical to long term efficient and reliable operation. Sufficient superheat is always a
primary concern in any refrigerant system and is especially important in a packaged chiller where
the evaporator is closely coupled to the compressor.
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 applied. Expansion tanks are also usually
required so that chilled water volume changes can be accommodated.
Avoidance of Short Water Loops
Adequate chilled water system water volume is an important system design parameter because it
provides for stable chilled water temperature control and helps limit unacceptable short cycling of
chiller compressors.
The chiller’s temperature control sensor is located in the supply (outlet) water connection or pipe.
This location allows the building to act as a buffer to slow the rate of change of the system water
temperature. If there is not a sufficient volume of water in the system to provide an adequate buffer,
temperature control can suffer, resulting in erratic system operation and excessive compressor
cycling.
Typically, a two-minute water loop circulation time is sufficient to prevent short water loop issues.
Therefore, as a guideline, ensure the volume of water in the chilled water loop equals or exceeds
two times the evaporator flow rate. For systems with a rapidly changing load profile the amount
of volume should be increased.
If the installed system volume does not meet the above recommendations, the following items
should be given careful consideration to increase the volume of water in the system and, therefore,
reduce the rate of change of the return water temperature.
• A volume buffer tank located in the return water piping.
• Larger system supply and return header piping (which also reduces system pressure drop and
pump energy use).
Minimum water volume for a process application
If a chiller is attached to an on/off load such as a process load, it may be difficult for the controller
to respond quickly enough to the very rapid change in return solution temperature if the system
has only the minimum water volume recommended. Such systems may cause chiller low
temperature safety trips or in the extreme case evaporator freezing. In this case, it may be
necessary to add or increase the size of the mixing tank in the return line.
Multiple Unit Operation
Whenever two or more units are used on one chilled water loop,Trane recommends that their
operation be coordinated with a higher level system controller for best system efficiency and
reliability.TheTraneTracer system has advanced chilled plant control capabilities designed to
provide such operation.
Ice Storage Operation
An ice storage system uses the chiller to make ice at night when utilities generate electricity more
efficiently and charge less for electricity with lower demand and energy charges.The stored ice
reduces or even replaces mechanical cooling during the day when utility rates are at their highest.
This reduced need for cooling results in significant utility cost savings and source energy savings.