Menu Outdoor Unit / 13.7 – EEV Control

In standard and fully featured refrigeration circuits, the EEV (Electronic Expansion Valve) is controlled based on the actual refrigerant superheat after the evaporator. To calculate it accurately, it is necessary to know the evaporation temperature (obtained from pressure) and the refrigerant vapor temperature at the evaporator outlet.

However, control units of typical air conditioners often do not include pressure sensors. Therefore, they use an indirect, simplified EEV control based on the compressor discharge temperature (the refrigerant temperature at the outlet). Based on this temperature, the system attempts to estimate superheat so that the circuit operates relatively safely and efficiently.

This approach is optimized only for a narrow range of operating conditions when cooling or heating air. A problem arises when such an air conditioner is used (or modified) for water heating. The original logic almost always attempts to keep the compressor discharge temperature within a fixed range of 60–80 °C, which leads to two major problems:

In warm weather and with low water temperature: This target range is too high. The system restricts the refrigerant flow, resulting in unnecessarily high superheat and a significant decrease in efficiency (COP).
At low outdoor temperatures during DHW heating (Domestic Hot Water): If the water temperature rises toward 55–60 °C, the condensing temperature becomes even higher. Forcing a discharge temperature of 60–80 °C at this moment is physically incorrect. The system gradually opens the EEV to cool the compressor, which reduces superheat to zero and may damage the compressor due to liquid refrigerant entering the suction.

The EEV Control function takes over the EEV regulation. Compared to the original control integrated in the outdoor unit logic, it uses dynamic targeting of the refrigerant vapor discharge temperature based on current conditions (outdoor temperature, water temperature, and frequency). At the same time, it adjusts the EEV value more quickly so that the correct superheat is achieved as fast as possible.
This function is available only for regulation types PID / FF.

Calibration

– The calculated target refrigerant discharge temperature can be adjusted to decrease or increase the refrigerant superheat.

Minimum Value

– The EEV value below which the valve will not be set (some air conditioners have their own internal limit, e.g. around 70, and cannot go below this value regardless of the setting).

Startup Value

– After the compressor starts, the EEV always begins regulating from the startup position. This value can be adjusted if needed to achieve faster stabilization at the optimal value. Most air conditioners start respecting this parameter only about 3 minutes after compressor startup; until then they use their predefined startup value.

In most cases, this function provides more efficient and safer EEV control than the function built into the outdoor unit. Nevertheless, we recommend monitoring the behavior of the outdoor unit during the first few days of operation and disabling this function if any anomalies occur.
The EEV control function limits the compressor discharge temperature to approximately 90 °C (small overshoots above this temperature may occasionally occur).

13.6 Defrost trigger

14.1 Firmware upgrade