When it comes to reducing CO2, heat pumps are a clean, efficient solution. The housing industry in particular can benefit from this rediscovered technology. Swiss Life has been using a heat pump at its head office that uses water from Lake Zurich since 2013.
In one of the first lectures on energy technology, a professor asks his students: “If you leave the fridge door open with the fridge still on, will it get colder in the kitchen?” Do you know the answer? Let’s consider the question.
According to the principle of energy conservation, the heat extracted from the inside of the fridge must be transferred somewhere. It is actually released into the ambient air at the back of the fridge. Up to this point, with the fridge door open, it would be a zero-sum game and so we can rule out it getting colder in the kitchen. However, it should be noted that the fridge needs electricity to cool things. The electricity used generates additional heat, which the fridge also releases into the environment. As a result, more heat is released from the back of the fridge than is absorbed inside. This means that the room temperature actually rises instead of falling.
How heat pumps work
Heat pumps make use of this physical process, but the heat generated here is not a “by-product”, rather it is the primary objective of the system. This not only justifies the electricity used, but also actively contributes to the desired goal. A power supply is used to raise the extracted heat to a sensible temperature and make it available as useful heat, meaning the heating process is more efficient and consumes fewer resources.
As with the inside of a fridge, the heat pump is colder on the environmental energy side than on the side where the heat is released. This is due to the physics behind the refrigeration cycle with circulating refrigerants. You could say that the thermal energy is “pumped” to a higher temperature. As we use more calories when climbing a steep hill, the heat pump needs more energy the greater the temperature difference it has to bridge.
Environmental heat becomes heating energy
The heat pump uses freely available environmental heat as an energy source, e.g. from the air, the earth or groundwater.
Heat pumps in the housing industry
If the temperature on the delivery side of the heat pump is low, this leads to reduced power consumption. Heat pumps are therefore ideal for heating systems that work with low flow temperatures, such as underfloor heating. When retrofitting existing buildings with radiators, it is essential to carefully check the dimensions of the radiators to ensure that they can function efficiently at the optimum flow temperatures for heat pumps. The effectiveness of this process depends to a large extent on the quality of a building’s insulation: If a house is well insulated, smaller heating surfaces can be used.
Different structural requirements
The type of heat pump is determined by the medium that supplies the environmental energy and the medium to which the heat is delivered. Here a distinction is made between air-to-water heat pumps, water-to-water heat pumps and brine-to-water heat pumps. Air-to-water heat pumps involve lower investment costs compared to other types of heat pump. However, they take up significantly more space and consume more power, especially in winter when the air as a heat source has a very low temperature level. In addition, air-to-water heat pumps can be quite noisy, which requires sound insulation measures in residential areas.
Water-to-water and brine-to-water heat pumps require additional structural measures to generate environmental energy, such as the installation of water intakes or the drilling of wells or probes, which makes these technologies more expensive. However, they have the advantage of providing environmental energy at a higher temperature than air-based systems, which significantly reduces power consumption. They also require less space and do not pose a problem in terms of noise emissions.
History of heat pumps
Heat pumps operate on the principle of the reverse refrigeration cycle. This means that they were originally developed as a result of people needing to cool things down. Martin Zogg writes in his “History of the Heat Pump” that the first refrigerator was invented in 1850. Fossil fuels were scarce before and during World War II; at the same time, there was plenty of electricity from hydropower. This meant that Switzerland was able to position it-self as a pioneer in the development and implementation of heat pumps. As early as 1938, the first European heat pump entered into operation in Zurich’s town hall, with the required environmental energy sourced directly from the river Limmat. In 1941, another heat pump entered into use in Zurich’s indoor pool. It used the waste heat from a transformer station as well as water from the Schanzengraben as an energy source. Both of these pioneering projects were completed by the industrial company Escher Wyss. Heat pumps to supply the Swiss Life head office and the FIFA Museum – which draw heat directly from Lake Zurich – were installed in 2013.
Because they do not require fossil fuels and, according to Martin Zogg, save up to 80% on electricity compared to conventional electric heating systems, heat pumps are on the rise in times of growing interest in decarbonisation. The Swiss industry association Wärmepumpen Schweiz recorded sales of around 41 200 units in Switzerland in 2022. According to Statista, the number of heat pumps sold in Germany was around 236 000, which corresponds to an impressive annual growth of over 20% and over 50%, respectively.