Catalogue

10 RLC-PRC042D-EN
Application Considerations
setpoint. Chiller 1 will finish cooling the leaving water from Chiller 2 down to the system design
setpoint.
Staggering the chiller set points is another control technique that works well for preferentially
loading Chiller 1. If the cooling load is less than 50 percent of the system capacity, Chiller 1 would
be able to satisfy the entire call for cooling. As system loads increase, Chiller 2 is started to meet
any portion of the load that Chiller 1 can not meet.
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 waterbox. 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.
Figure 3. Typical series chiller arrangement
Chiller 2
Setpoint = 42°F (5.6°C)
Chiller 1
Setpoint = 42°F (5.6°C)
Variable
depending
on load
Blending
Valve
58°F
(14.4°C)
42°F (5.6°C)