Handbook of air conditioning and refrigeration / Shan K

7.48 CHAPTER SEVEN
FIGURE 7.20 (Continued)
8. During part-load operation, temperature sensors T5, T6, T7, and T8 and flowmeters F1 and F2
measure the readings which give the produced cooling capacity Qrf and required system cooling
capacity Qsc. If Qrf � Qsc � Qrf,c (one chiller’s cooling capacity, Btu/h), none of the chillers is staging
off. When Qrf � Qs � Qrf,c, one of the chillers is then turned off until Qrf � Qsc � Qsc,c. To turn
off a chiller, the compressor is turned off first, then the chiller pump, condenser pump, and cooling
tower fans corresponding to that chiller.
9. During part-load operation, a constant flow of chilled water is still maintained in the evaporator
of each turned-on chiller. However, the volume flow rate in the plant loop V˙
pt depends on the
number of operating chillers and their associated chiller pumps. The staging on or off of the chillers
and their associated pump causes a variation of chilled water volume flow rate in the plant loop.
The difference between the volume flow rate of chilled water in the plant loop V˙
pt and the volume
flow rate in the building loop V˙
pt � V˙
bg gives the volume flow rate of chilled water in the com-