DOE-2 Engineers Manual Version 2.1A - DOE-2.com

In the direct cooling mode, RCAP; is set equal to 0.0 for the following
types of chillers:
1. Reciprocating chillers,
2. Chillers with air cooled condensers.
The available capacity is
CAP = OPCAPi * RCAP;,
where OPCAPi is the sum of the design (rated) capacities of this chiller
type operating this hour.
Part load ratio, cycl ing, false loading - When the load on a compression
chiller drops below a certain point, the chiller may need to use some sort of
"false loading" mechanism for further capacity reduction. False loading may
be necessary to ensure a high enough refrigerant flow rate through the compressor
to prevent surging (in the case of centrifugal machines) or to prevent
the evaporator from freezing up. A very common method of false loading a
chiller is to bypass hot condenser gas to the evaporator. This mechanism is
naturally called "hot gas bypass." As the capacity needed is reduced still
further, the compressor may need to start cycling.
The average part load ratio over the hour is
ALOAD
PL = CAP'
where ALOAD is the demand on the machine exclusive of any false loading.
If PL is less than the minimum part load ratio, RMINi, the machine is
cycling on and off. The fraction of the hour the machine is running (FRAC) is
PL
FRAC = RMIN"
If PL is less than the mlnlmUm unloading ratio, RUNLDi, the machine must be
false loading. Consequently, as far as the compressor is concerned, the part
load ratio must be at least RUNLD.
PLR = PL or RUNLDi, whichever is larger.
RUNLDi can be input through the keyword [-J-UNL-RATIO.
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