Abstract: An air conditioning system includes one outdoor unit and at least one indoor unit connected to each other. The outdoor unit has a variable capacity compressor, a four-way valve, an outdoor heat exchanger, and a refrigerant heater, while the indoor unit has an indoor heat exchanger. A saturation temperature calculator computes the saturation temperature at the refrigerant heater outlet pressure. A refrigerant heater outlet temperature detection circuit detects the refrigerant temperature near the refrigerant heater outlet. A superheating calculator calculates refrigerant superheating at the refrigerant heater outlet based on values supplied thereto from the refrigerant heater outlet temperature detection circuit and saturation temperature calculator. A compressor frequency control circuit then adjusts the compressor frequency so that the calculated refrigerant superheating is maintained at a specific level.

Abstract: A multi-room air conditioning system includes an outdoor unit and a plurality of indoor units connected in parallel to the outdoor unit. A compressor frequency and combustion control calculator reads a load level for each indoor unit from a load coefficient table using a differential temperature calculated by a differential temperature calculator and a rated capacity stored in a rated capacity memory. The compressor frequency and combustion control calculator then multiplies a sum of the load levels by a predetermined constant and adds a compensation value thereto to obtain a frequency value. This value is used to control the compressor. The compressor frequency and combustion control calculator also sets a target combustion level using the frequency value for control of a refrigerant heater mounted in the outdoor unit.