Panasonic U-72MF2U9 Service Manual page 17

3. Compressor Control
3-6-3. Cooling operation with low ambient temperature
When operating in cooling mode with the ambient temperature less than 69.8°F (21°C), the unit is set in low
ambient temperature cooling mode.
During low ambient temperature cooling mode, the heat exchanger capacity control is performed in addition to the
compressor capacity control. The target condensation temperature (Tc_tgt) is controlled between 73.4°F ~ 77°F
(23°C ~ 25°C).
Thereof, the heat exchanger may sometimes be used by half even if the operation is cooling in all indoor units.
(1) Capacity changes of compressor
Similar to control normal cooling operation
(2) Capacity changes of heat exchanger
* Condensation temperature (Tc) is high
The outdoor heat exchanger capacity is increased, increasing the system condensation capacity and lowering the
condensation temperature (Tc).
* Condensation temperature (Tc) is low
The outdoor heat exchanger capacity is decreased, decreasing the system condensation capacity and raising the
condensation temperature (Tc).
Outdoor Unit Heat Exchanger Control Table
57.2°F (14°C)
A
51.8°F (11°C)
42.8°F (6°C)
B
37.4°F (3°C)
C
26.6°F (-3°C)
3-6-4. Control of condensation temperature and evaporation temperature during mixed cooling/heating operation
During mixed cooling/heating operation, the control maintains a heat balance with a target evaporation temperature
(Te) for the cooling mode indoor units of 37.4°F ~ 42.8°F (3°C ~ 6°C) and a target condensation temperature (Tc)
for the heating mode indoor units of 118.4°F ~ 123.8°F (48°C ~ 51°C).
Heat balance control is performed by varying the compressor capacity and heat discharge (heat intake) of the heat
exchanger.
(1) Increasing/decreasing the compressor capacity
* When evaporation temperature (Te) is high and condensation temperature (Tc) is low.
This occurs when both the cooling capacity (heat intake) and the heating capacity (heat discharge) are low.
The compressor capacity and the circulation flow of refrigerant are increased in order to lower the evaporation
temperature (Te) and raise the condensation temperature (Tc).
* When evaporation temperature (Te) is low and condensation temperature (Tc) is high
This occurs when both the cooling capacity (heat intake) and the heating capacity (heat discharge) are high.
The compressor capacity and the circulation flow of refrigerant are decreased in order to raise the evaporation
temperature (Te) and lower the condensation temperature (Tc).
* Under conditions other than those listed above, the capacity of the outdoor unit heat exchanger is adjusted.
In some cases the heat exchanger capacity may also be adjusted at the same time when the compressor capacity
is varied.
Low ← Condensation Temp. [Tc]
A
DOWN
→
B
C
STAY
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3WAY VRF SYSTEM
Control Functions
High
D
UP
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