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An environmentally friendly heat pump for all requirements

A new type of heat pump can both heat and cool buildings and uses propane as a refrigerant. ZHAW researchers have been measuring the efficiency of the machine for two years. The project was supported by the Swiss Federal Office of Energy.

It heats in winter and cools in summer: the switchable heat pump.

The heat pump is regarded as a future-oriented heating system: it extracts thermal energy from the environment and raises it to a higher temperature level supported by an electrical source. Thus, the environmental heat can be used to heat buildings. A great advantage is that a lot of heating energy is supplied with relatively little electrical energy. A component of every heat pump is the internal refrigerant circuit, in which climate-damaging gases are often used because of their good thermal properties. These refrigerants have a global warming potential up to 2000 times higher than CO2, which is why they are gradually being banned by regulatory measures. In addition, society is increasingly demanding air conditioning in summer, which means that houses and especially office buildings are more and more being equipped with refrigeration machines. They function in the same way as a heat pump, but the heat is extracted from the building and released into the environment by means of electrical energy.

A new approach

The heat pump measured by the ZHAW Institute of Energy Systems and Fluid Engineering (IEFE) covers two needs with one machine: It is switchable, so that the same device can be used for both cooling and heating. A machine that can do both is cheaper to buy than two machines with only one operating mode each. Similar switchable machines are already available. However, since these are often optimized for heating operation, they can only be run inefficiently in cooling mode. The device developed and built by Scheco AG does not have this disadvantage. The switchover from heating to cooling mode and vice versa takes place in the machine instead of in the building. This means that both operating modes run at their optimum. Since houses always have an environmentally dependent heating and cooling requirement, the machine was the first of its kind to be equipped with a continuously variable output control.

In addition, the switchable heat pump uses propane as a refrigerant. As a flammable, colorless and odorless gas, it poses certain risks. Special safety measures must therefore be taken when handling it. With a global warming potential similar to CO2, propane is also much more environmentally friendly than conventional refrigerants. In addition, its favorable thermal properties enable an extremely high heat pump efficiency. It will therefore remain one of the few approved refrigerants in the long term and is regarded as an operating medium of the future.