Subcooler Heat Exchanger (Shx 48/50Pg20- -28 Only) - Carrier 48/50PG Series Controls, Start-Up, Operation, Service And Troubleshooting Instructions

BUILDING SUPERVISOR
NETWORK
OPTIONS
REMOTE AUTODIAL
CCN SITE GATEWAY
NON CARRIER
HVAC
EQUIPMENT
COMFORT
CONTROLLER
Subcooler Heat Exchanger
(SHX - - 48/50PG20- -28 Only)
The purpose of the subcooler heat exchanger (SHX) and the
subcooler TXV is to increase the capacity of the evaporator by
sending subcooled liquid refrigerant into the evaporator. Normally,
the condenser subcools the liquid refrigerant by approximately
10_F. The SHX adds another 10_F to 15_F degrees of subcooling
before the refrigerant reaches the evaporator. This allows the
refrigerant to absorb more heat from the mixed air, thereby
providing more cooling capacity.
The subcooler functions by taking a small percentage of the high
pressure, medium temperature liquid refrigerant which exits the
condenser and converting it into a low pressure, low temperature
gas. This is accomplished by using the subcooler TXV. The gas is
then routed through a reverse- -flow heat exchanger (SHX), which
transfers heat from the remaining liquid refrigerant in the liquid
line to the reverse flow gas refrigerant. The moderate temperature
gas is then sent to the compressor to complete the loop and the
cooler liquid refrigerant continues its normal path to the main TXV
and the evaporator. (See Fig. 52.)
CCN BUS
ROOFTOP
UNIT
CL
ROOFTOP
UNIT
CL
TERMINAL
SYSTEM
MANAGER
CL
ROOFTOP
UNIT
AIR DISTRIBUTION-DIGITAL AIR VOLUME CONTROL (DAV)
Fig. 51 - - CCN System Architecture
ROOFTOP
UNIT
CL
ROOFTOP
UNIT
CL
HEATING/COOLING UNITS
TCU TCU
TCU
DAV AIR DAV AIR
TERMINAL
TERMINAL
COND
SUBCOOLER
HX
SUBCOOLER TXV
Fig. 52 - - Subcooler Operation
82
LEGEND
CCN -- Carrier Comfort Networkr
CL -- ComfortLinkt Controls
DAV -- Digital Air Volume
HVAC -- Heating, Ventilation, and
Air Conditoning
TCU -- Terminal Control Unit
TO
ADDITIONAL
TERMINALS
DAV FAN
POWERED
MIXING
BOX
C07030
COMPRESSOR
EVAP
MAIN TXV
C07202