Daikin DCC048 SERIES, Руководство по установке

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13
HEAT PUMP OPERATION
C
OOLING
C
YCLE
When the heat pump is in the cooling cycle, it operates exactly as
a Summer Air Conditioner unit. In this mode, all the charts and
data for service that apply to summer air conditioning apply to
the heat pump. Most apply on the heating cycle except that “con-
denser” becomes “evaporator”, “evaporator” becomes “con-
denser”, “cooling” becomes “heating”.
H
EATING
C
YCLE
The heat pump operates in the heating cycle by redirecting refrig-
erant flow through the refrigerant circuit external to the compres-
sor. This is accomplished through the reversing valve. Hot discharge
vapor from the compressor is directed to the indoor coil (evapora-
tor on the cooling cycle) where the heat is removed, and the va-
por condenses to liquid. It then goes through the expansion de-
vice to the outdoor coil (condenser on the cooling cycle) where
the liquid is evaporated, and the vapor goes to the compressor.
When the solenoid valve coil is operated either from heating to
cooling or vice versa, the piston in the reversing valve to the low
pressure (high pressure) reverse positions in the reversing valve.
The following figures show a schematic of a heat pump on the
cooling cycle and the heating cycle. In addition to a reversing valve,
a heat pump is equipped with an expansion device and check valve
for the indoor coil, and similar equipment for the outdoor coil. It
is also provided with a defrost control system.
The expansion devices are flowrator distributors and perform the
same function on the heating cycle as on the cooling cycle. The
flowrator distributors also act as check valves to allow for the re-
verse of refrigerant flow.
When the heat pump is on the heating cycle, the outdoor coil is
functioning as an evaporator. The temperature of the refrigerant
in the outdoor coil must be below the temperature of the outdoor
air in order to extract heat from the air. Thus, the greater the
difference in the outdoor temperature and the outdoor coil tem-
perature, the greater the heating capacity of the heat pump. This
phenomenon is a characteristic of a heat pump. It is a good prac-
tice to provide supplementary heat for all heat pump installations
in areas where the temperature drops below 45° F. It is also a
good practice to provide sufficient supplementary heat to handle
the entire heating requirement should there be a component fail-
ure of the heat pump, such as a compressor, or refrigerant leak,
etc.
Since the temperature of the refrigerant in the outdoor coil on the
heating cycle is generally below freezing point, frost forms on the
surfaces of the outdoor coil under certain weather conditions of
temperature and relative humidity. Therefore, it is necessary to
reverse the flow of the refrigerant to provide hot gas in the out-
door coil to melt the frost accumulation. This is accomplished by
reversing the heat pump to the cooling cycle. At the same time,
the outdoor fan stops to hasten the temperature rise of the out-
door coil and lessen the time required for defrosting. The indoor
blower continues to run and the supplementary heaters are ener-
gized.
D
EFROST
C
ONTROL
During operation the power to the circuit board is controlled by a
temperature sensor, which is clamped to a feeder tube entering
the outdoor coil. Defrost timing periods of 30,60 and 90 minutes
may be selected by connecting the circuit board jumper to 30, 60
and 90 respectively. Accumulation of time for the timing period
selected starts when the sensor closes (approximately 31° F), and
when the wall thermostat calls for heat. At the end of the timing
period, the unit’s defrost cycle will be initiated provided the sen-
sor remains closed. When the sensor opens (approximately 75° F),
the defrost cycle is terminated and the timing period is reset. If
the defrost cycle is not terminated due to the sensor tempera-
ture, a ten minute override interrupts the unit’s defrost period.