SiBE121123_A
Function of Thermistor
Function and Control
90
(4) Indoor Heat
Exchanger
Thermistor
1. The indoor heat exchanger thermistor is used for controlling target discharge pipe
temperature. The system sets the target discharge pipe temperature according to the
outdoor and indoor heat exchanger temperature, and controls the outdoor electronic
expansion valve opening so that the target discharge pipe temperature can be obtained.
2. In cooling operation, the indoor heat exchanger thermistor is used for freeze-up protection
control. If the indoor heat exchanger temperature drops abnormally, the operating frequency
becomes lower or the operation halts.
3. In cooling operation, the indoor heat exchanger thermistor is used for anti-icing function. If
any of the following conditions are met in the room where operation halts, it is assumed as
icing.
The conditions are
Tc
≤
– 1° C
Ta – Tc
≥
10° C
where Ta is the room thermistor temperature and Tc is the indoor heat exchanger
temperature.
4. In heating operation, the indoor heat exchanger thermistor is used for heating peak-cut
control. If the indoor heat exchanger temperature rises abnormally, the operating frequency
becomes lower or the operation halts.
5. In heating operation, the indoor heat exchanger thermistor is used for detecting
disconnection of the discharge pipe thermistor. When the discharge pipe temperature drops
below the highest indoor heat exchanger temperature by more than a certain value, the
discharge pipe thermistor is judged as disconnected.
6. When only one indoor unit is operating, the indoor heat exchanger thermistor is used for
subcooling control. The actual subcool is calculated with the liquid pipe temperature and the
indoor heat exchanger temperature. The system controls outdoor electronic expansion valve
openings to obtain the target subcool.
(5) Liquid Pipe
Thermistor
1. When only one indoor unit is in heating, the liquid pipe thermistor is used for subcooling
control. The actual subcool is calculated with the liquid pipe temperature and the maximum
indoor heat exchanger temperature. The system controls outdoor electronic expansion valve
openings to obtain the target subcool.
2. In heating operation, the liquid pipe thermistor is used for liquid pipes isothermal control. The
system controls outdoor electronic expansion valve opening so that the liquid pipe
temperatures in each room becomes equal.
(6) Radiant Panel
Thermistors
1. The radiant panel thermistors are used for calculating radiant panel surface temperature.
Due to structural and manufactural restrictions, the radiant panel surface temperature
cannot be controlled directly with a thermistor. Thermistors are mounted on the radiant panel
piping in order to calculate the radiant panel surface temperature.
The indoor electronic expansion valve is controlled according to the radiant panel surface
temperature.
2. The radiant panel thermistors are used for detecting malfunction of the indoor electronic
expansion valve.
