The heat pump gains some three-quarters of the thermal energy produced from its surroundings — and thus free of charge and CO2-neutral. Only a small share of electrical energy is necessary to maintain heat circulation. If electricity from renewable sources is used, the entire heat pump system can be operated without CO2 emissions. The heat pump has therefore been on the rise for many years as a resource-friendly and low-cost alternative to conventional heating systems. Around 70 percent of the newly built detached houses in Switzerland are already equipped with a heat pump and every third house in Norway is heated in this way. In Germany, clients equip just under a quarter of new buildings with this advanced technology.

Principle of Operation

The heat pump extracts heat from the ambient air, ground, ground water, or other heat sources, and pumps it to a higher temperature level for heating purposes. This enables many times more than the amount of electrical input energy used to be extracted in the form of heat energy. The temperature of the heat source used can also be far below the freezing point.

The common principle of operation on which all types of heat pumps are based is a closed circuit connecting the heat source to the space to be heated and transferring the thermal energy from the surrounding environment to the inside of the building. The medium used in this circuit is in liquid form at low pressure. It absorbs the ambient heat, vaporizes, and after being subjected to increased pressure in a compressor discharges the heat again on condensing. The medium is then returned to the vaporizer via a valve and the pressure reduced at the same time. This causes the temperature to drop and the cycle is completed.

Types of Heat Pump

Heat pumps can be divided into air, ground, and water heat pumps according to the source of thermal energy used. The air-water heat pump currently dominates in Germany. More than one-half of the models sold in Germany are based on this technology, which transfers thermal energy from the ambient air to the heating medium water. Increased efficiency through technical improvements and simple installation contribute to the growing popularity of the air-water heat pump.

The ground-source heat pump is also a widely used technology. This extracts the necessary energy from the geothermal energy in the ground via near-surface geothermal collectors laid in the ground or ground probes installed in holes drilled for this purpose. A big advantage of this technology is the relatively uniform storage of the ambient heat in the ground over the whole year. Even in winter, the temperature at a depth of 10 meters is still about 10°C – sufficient energy for heat pump operation. Especially in winter, the heating effect of ground-source heat pumps is therefore higher than that of air heat pumps.

Water-to-water heat pumps extract the heat from the ground water. Like ground-source heat pumps, they also profit from the constantly high temperature of the heat source.

The Role of Heat Pumps

Its long-term cost advantage makes the heat pump a sensible alternative to conventional gas and oil heating for many building clients. It owes its great popularity to the increased interest in environmentally friendly solutions for heat production. More than 54,000 heat pumps were sold throughout Germany last year, which means that approximately every 10th newly installed heat producer is a heat pump. As its potential savings are highest in modern passive and low-energy houses, the heat pump already accounts for more than one-quarter of the heating systems in new buildings, trend rising.

The heat pump is even more popular in neighboring countries and other European states. In Switzerland, one-third more heat pumps were sold in 2010 than gas boilers, a total of about 20,000 heat pumps. In less-populated Norway, the statistics even show more than 80,000 heat pumps sold in each of the past years.

Heat Pumps in Everyday Use

Heat pumps are suitable for energy-saving heating in residential buildings and for use in modern, everyday equipment. Heat pump clothes dryers are more effective than conventional models and use up to 50 percent less energy. Engineers utilize the different heat levels on the two sides of the heat pump: The warm part heats up the dried inlet air, which absorbs the moisture from the washing. The cold part condenses the moisture in the outlet air. The dry air is returned to the drum and completes the air cycle. As these modern dryers no longer discharge moisture and only a little waste heat, they can be installed in any position in the home.

Engineers, meanwhile, also use the heat pump in automotive engineering, because modern diesel engines achieve such high efficiency that the waste heat from the engine alone is often no longer sufficient to heat the interior of the car. Car manufacturers use heat pumps to quickly bring the interior temperature up to a pleasant level in winter. In electric-powered cars, the heat pump provides heating and cools the sensitive batteries at the same time, which extends their lifetime.

Use in Public Buildings

Planners also increasingly decide to use heat pumps in public facilities and in the commercial sector. They enable additional heat sources like waste heat in server rooms or waste water to be incorporated, which helps to cut costs and CO2 emissions. Whereas heat pumps with a power consumption of a few kilowatts ensure a pleasant room climate in the home, more powerful equipment rated at up to several hundred kilowatts are used here.

The savings that can be achieved by heat pumps are illustrated by the example of the Fürth, Germany, city hall, which was built in 1840. The building has been heated by a heat pump since 2010, which saves 130 tons of CO2 and 65 percent of heating energy a year. The complex heat pump system uses the thermal energy stored in the city’s waste water. Heat exchangers absorb the heat from the waste water and the heat pump brings it to the higher temperature level of the heating water.

Cooling and Heating in Supermarkets

Heat pumps are increasingly used in supermarkets, where products are kept at low temperatures in refrigerated display cabinets and heat for heating the supermarket is required at the same time. Cooling and building heating were previously provided by two separate systems, and the waste heat from the supermarket’s own cooling units was not used. At times of rising energy prices, more and more supermarket operators are changing to systems that utilize the heat already available. Heat recovery enables the surplus heat to be fed to the floor heating or to heat exchangers mounted on the ceiling. The heat pump provides both pleasant temperatures in the sales area and reliable temperature control for the refrigerated products. On extremely cold winter days, modern heat pump systems extract extra heat from the ambient air and then transfer this to the interior at a higher temperature level. They can also run in cooling mode to replace the air conditioning system in the summer. The modern supermarket, therefore, manages all year-round without additional heating from fossil fuels.

Heat Pumps in Industrial Applications

Other applications for heat pumps are in agriculture and in the food and chemical industries. They produce useful heat for glasshouses, are used for drying wood, and guarantee the right temperatures for chemical production processes. If they are intelligently coupled, they help to transfer heat within buildings, for example by making use of the heat radiation losses from machinery: With the aid of a heat pump, the heat that would otherwise heat up production buildings can be used to control the temperature of the administration buildings.

Large Heat Pumps for District Heating and Cooling

Suitably rated large heat pump systems can produce sufficient thermal energy to supply whole-district heating grids. The Swedish capital Stockholm uses a 180-MW heat pump for this purpose, which is the world’s biggest heat pump operated by seawater. It absorbs the energy stored in the seawater at 2.5°C and, by coupling six heat circuits, produces hot water at up to 80° for the households connected to the grid.

Common Features

For all the differences between the heat pump applications, they all have common design features, namely their high energy efficiency that makes it possible to extract many times more energy than the energy input. Another advantage: The heat pump can be used continuously and thus, in contrast to other systems for using renewable energy sources, independently of the time of day or night or weather conditions.

Publication date: 1/21/2013