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Heat pumps are especially sensitive to suction line condensation
Liquid hammering occurs when you have liquid in your suction gas. This can harm the compressor and lead to expensive repair costs. Heat pumps working at elevated gas temperatures has an increased risk of condensing gas in the suction line. When the capacity changes in the system the pressure might increase, and this leads to condensation on the relatively cold pipe walls – enough to cause liquid hammering.

To avoid this phenomenon there are different levers:
• General increased superheating of the gas
• Insulated suction line and control of pressures.
• Liquid detection using a compressor protection sensor and controlling the process.

A compressor protection sensor is installed just before the compressor and it provides an analog signal for the PLC.
The sensor has been on the market for more than five years and it is typically used on larger systems where it can be difficult to control the liquid content in the gas.

A compressor protection sensor with vapor quality
A compressor protection sensor is a capacitive sensor which measures the liquid content in a gas (Vapor Quality) and reacts instantly. The sensor can be used for controlling the process and provide an alarm when liquid occurs.
The same sensor type is also used for controlling the evaporation process both in direct expansion systems where it controls the expansion valve – and in pump circulated systems where it controls the pump capacity.
The sensor can measure a volumetric liquid content in a gas from 0 to 80 % but it is most sensitive for dry gas and is excellent for detecting the small amounts of liquid like in compressor protection.