Daikin VRV – Compressor Capacity Control

In the compressor capacity controller of VRV system, the pressure detected (Pe or Pc) by pressure sensor installed in outdoor unit is converted into equivalent saturation temperature, and the evaporation temperature (Te) while cooling or the condensation temperature (Tc) while heating are so controlled with PI control as to put them close to the target value in order to maintain stable capacity in spite of incessantly varying load. (Refer target value below table.)

*Above all target temperatures mean saturation temperatures on gas sides.

The pressure loss in piping increases depending on connecting piping length and operation
capacity of compressor. In order to compensate capacity lowering caused by the pressure loss
in piping, the following correction are made.

Correction of Target Evaporation Temperature by ?P.

? Target value adjustment can be made through field setting.
Long connection piping at the installation site may increase pressure loss in piping and an inverse installation (outdoor unit is placed lower than indoor unit) may increase liquid pipe inside resistance. In such case, “lower” setting of target evaporation temperature by using field setting will give stable operation.
On the other hand for short connection piping, higher setting will make stable operation easy.

In addition, samplings of evaporation temperature and condensation temperature are so made that pressure detected by every pressure sensors of high/low pressure are read every 20 seconds and calculated. And every time the compressor capacity (INV frequency or STD ON/OFF) is controlled to eliminate deviation from target value.

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