Multiple Refrigeration Circuits - Daikin R-22 Refrigerant Piping Design Manual

Multiple Refrigeration Circuits

For control and redundancy, many refrigeration systems
include two or more refrigeration circuits. Each circuit must
be kept separate and designed as if it were a single system.
In some cases, a single refrigeration circuit serves multiple
evaporators, but multiple refrigeration circuits should never
be connected to a single evaporator. A common mistake is
to install a two circuit condensing units with a single circuit
evaporator coil.
Figure 11 shows common DX coils that include multiple
circuits. Interlaced is the most common. It is possible to have
individual coils, each with a single circuit, installed in the same
system and connected to a dedicated refrigeration circuit.
While most common air conditioning applications have one
evaporator for each circuit, it is possible to connect multiple
evaporators to a single refrigeration circuit.
Figure 12 shows a single refrigeration circuit serving two
DX coils. Note that each coil has its own solenoid and
thermal expansion valve. There should be one TX valve for
each distributor. Individual solenoids should be used if the
evaporators will be operated independently (i.e. for capacity
control). If both evaporators will operate at the same time, then
a single solenoid valve in a common pipe may be used.
If the two evaporators serve a common airstream, then one
solenoid valve serving both evaporators is sufficiant at point
"X" in Figure 12.
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Figure 11: DX Coils with Multiple Circuits
Refrigerant
(In)
Refrigerant
(Out)
Face Control
Figure 12: Two Evaporators on a Common Refrigeration
Circuit
TX
Valve
Bulb mounted
on horizontal pipe,
close to coil to
avoid mounting
in traps
Slope in direction
of refrigerant flow
15 AG 31-011 • REFRIGERANT PIPING DESIGN
Refrigerant
(In)
Refrigerant Refrigerant
(Out) (Out)
Row Control Interlaced
Filter-
Drier
Liquid
Solenoid
Line
Valve
Sight
Glass
X
External
Equalization
Line
Trap to protect
TX Valve bulb
from liquid
refrigerant
Refrigerant
(In)
Suction
Line