Efficient heating with environmental energy – the heat pump makes it possible

The heat pump is one of the newest renewable energies that can be used to heat buildings. In addition to solar energy and the environmentally friendly alternatives with biogas and bio fuel oil, the heat pump offers a CO2-neutral option for builders and property owners.

Functionality – how the heat pump works

The heat pump uses the thermal energies already stored in the environment to convert them into usable heat for heating. The special thing about this technology is that nothing is burned here, as with wood, gas or oil heating systems, but a technical process converts the thermal energies into heat. The principle is the same as in a refrigerator. Thermal energy with low temperatures are to be raised to a higher level. With the heat pump it works only the other way round. The environmental heat can therefore not only be used in the heating system, but also to provide hot water for the household.

The energy sources of the heat pump – air, earth & water

The heat pump uses different energy sources to generate heat. The brine-to-water heat pump uses the earth as an energy source, the water-to-water heat pump uses the water as an energy source and the air-to-water heat pump uses the air as an energy source. Which heat pump is best for your property depends on a variety of factors, but especially on the location of the property.

The air-to-water heat pump – thermal energy from the air

The energy source air is the easiest to use by the heat pump. The heat pump works with a simple system that sucks in and blows out the air. For this purpose, the heat pump uses the outside air, which is always available and is therefore one of the renewable energies. But even if the heat pump works with outside air, it can be placed inside the house. It then uses ducts to draw in air from outside. But it is also possible to place the system outside the property. There is no need for ducts as the system directly uses the air that is in the surrounding area. However, it is important with a heat pump that works with air that it is always kept free of frost in winter. Since the system has to work with air temperatures below zero, it becomes increasingly difficult to convert the cold air into usable heat. The colder the air, the more difficult the conversion. To keep the efficiency of the heat pump as high as possible, regularly clear it of frost and make sure it is properly maintained.

The brine-to-water heat pump – Earth as an energy source

Thermal energy is also stored in the ground, which the brine-to-water heat pump uses to generate heat for heating. For this purpose, pipes are installed in the ground in which a mixture of water and antifreeze circulates. The liquid, also called brine, extracts heat from the earth and transports it to the heat pump, which feeds it into the heating system. Each metre of ground provides thermal energy of approximately 50 watts that the brine fluid can extract from it. For a normal building, an average of around 150 metres of depth is required, which can, however, be divided into several boreholes. Depending on the individual circumstances of the property, deep boreholes or shallow collectors can be installed. The deep boreholes go up to 100 metres deep into the ground and therefore require special permits and are also not permitted in every area. With this method, plastic pipes (probes) are then installed in the ground.

If this variant is technically or legally not possible, the variant of flat plate collectors can be used. Here, similar to underfloor heating, pipes are laid at a depth of 1.50 m, which can extract 25 watts per square metre. A modern single-family house needs about 350 square meters of pipes to provide heating. The big advantage over the air-water heat pump is that the heat can be extracted all year round without any loss. This fact increases the efficiency of the heat pump and thus reduces the electricity costs incurred. See also: money guide.

The water-to-water heat pump – thermal energy in groundwater

Thermal energy can also be found in the groundwater, which can be used to generate heat. The water-to-water heat pump has a relatively simple mode of operation, as it has two wells that transport the groundwater to the water-to-water heat pump and back again. The wells must be installed in the direction of flow of the groundwater with a minimum distance to prevent the groundwater, which has already cooled down, from entering the heater again.

However, before installing a water-to-water heat pump, the groundwater must be tested. Good water quality is a prerequisite for installation, because chemical ingredients can put a great strain on the heat exchanger and thus limit efficiency enormously. In addition, the use of groundwater in a water-to-water heat pump is subject to approval and is not permitted everywhere. However, the thermal energy that can be used from groundwater is the most constant throughout the year, as the temperatures in the groundwater are not subject to large fluctuations. The water-to-water heat pump is one of the most effective variants of the heat pump.

The cost of a heat pump – installation, operation and energy source

The costs involved in installing a heat pump are generally divided into three areas. The cost of the energy source, i.e. the extraction of thermal energy from the air, earth or water, the cost of the system itself and the cost of operation and maintenance. Depending on which system is suitable for your property, the costs differ depending on the model and the system.

Costs for the extraction of environmental energy from air, earth or water

The choice of thermal energy from which the heat is to be extracted decisively determines the costs. An air-source heat pump, for example, requires hardly any additional technology, whereas with a brine heat pump, the drilling and additional materials must also be paid for. The cost of one metre of deep drilling is around 60 to 80 euros, while one square metre of surface collector costs 10 to 20 euros. The water heat pump also requires costs for the drilling, because the two wells must be laid to the groundwater and back. The costs here amount to about 5000-6000 euros for both wells. Depending upon condition of the environment and situation of the real estate the prices can deviate however also. An exact offer can only be made by a specialist.

Costs for the heat pump itself

The heat pump itself consists of the same components, regardless of the energy source itself, and can be combined with all three options. Depending on the size, installation costs range from 8000 to 12000 euros. However, the installation of a heat pump can be subsidised by various grants. Again, depending on the size required and individual circumstances of the location, prices may vary. For precise prices, request a quote from a specialist company.

Costs for the operation of the heat pump

All heat pumps operate electrically and require electricity to convert the thermal energy into heat. However, the level of these operating costs is highly variable. They depend on the selected energy source, the energy status of the property and the type of heat transfer to the various rooms. It is therefore not possible to give an exact price here and it must be calculated individually for each property.

Solar collectors – the heart of the solar system

Without the collector, a solar system could not convert the solar energy into usable heat. The collector is therefore the heart of the solar system, which makes it possible to use the renewable energy in the home. Want to learn more about solar systems and the cost? Calculate the cost of your individual solar system with our solar system calculator! But which different models are there among the collectors and which one is the right one for my solar system?

Flat plate collector – the proven model

Flat-plate collectors were the first collectors to be used to harness solar energy. They are therefore still the most widespread model today and form a market share of a proud 70%. Their reputation is probably not entirely unconnected to this, as flat-plate collectors are considered to be very inexpensive, reliable and, above all, they offer a technology that has certainly proven itself over the years.

Structure of a flat plate collector – absorber, housing and the heat transfer fluid

A flat plate collector has two simple components. A housing and a blackened metal sheet that is located inside the housing. This metal sheet is also called an absorber, because the dark coating ensures good absorption of the incident solar radiation. The absorber also efficiently converts the incident solar energy into heat. In order for the heat to be transported, pipes run along the back of the absorber in which heat transfer fluid flows. This flows cold into the collector and leaves it hot. To protect the collector from external conditions, such as the weather, it is covered by a safety glass. This glass is very stable and at the same time highly transparent, so that as little radiation as possible bounces off it. This ensures that as much solar energy as possible reaches the absorber to be converted into heat. To ensure that the housing also contributes effectively to heat generation, it is particularly well insulated and therefore hardly loses any heat energy. The efficiency of the solar system is thus increased.

Differences in flat plate collectors – structure, shape & piping

Even if the flat plate collectors are combined into one model, there are still differences. Different flat plate collectors differ in the housing material, the different connection of the tubes and other features. Depending on the application, the different designs have their advantages and disadvantages.

• Shape of the absorber – The absorber can be made of different materials. There are absorbers made of steel, stainless steel or aluminium sheets. These can be connected in different ways, for example by spot welding or roll bonding. There are also differences in the copper pipes in which the liquid is conducted. They can be pressed in but also soldered.
• Coating of the absorber – The absorber layer has developed further and further in recent years. After all, the layer should be able to absorb as much of the solar energy as possible. Today’s technology provides for highly selective layers that have a particularly high degree of absorption. It also has a low emissivity of the long-wave thermal radiation.
• Laying the heat transfer tubes – The tubes can either be laid in a tube register, where they are parallel side by side and connected at the top and bottom, or they can be laid in a meandering pattern, which means snake-like in one piece.
• Housing material – The material of the housing can also vary depending on the model. The most common are aluminum, stainless steel but also plastic. Even wood would be an option as a housing for a solar collector.

Tube collector – the better thermal insulation ensures higher efficiency

The tube collector came after the flat plate collector and is an alternative to it. Despite different technology and less market share, this model also has its advantages.

Structure of a tube collector – vacuum, heat pipe and the glass tubes

The tube collector model differs from the flat plate collector in one particular point, namely in the insulation. While with the flat plate collector only the housing is insulated, with the tube collector every single absorber is insulated and this in a special way. Here, the absorber is encased in an evacuated glass tube, as vacuum has particularly good thermal insulation properties and allows neither losses through convection nor through heat conduction. Several of the tubes together are connected to a collector and then form a tube collector. Since this way of insulating is much more effective than that of a flat plate collector, the efficiency is much higher here, since less energy is lost. Due to the technology, this model is also called a vacuum tube collector.

Different design of tube collectors – heat pipe, CPC & direct flow

The tube collector models are additionally differentiated into different designs. On the one hand, the direct and the non-direct flow tube collectors – they are also called heat pipes. Another form are the CPC – vacuum tube collectors.

• Direct flow tube collectors – In this design, the heat transfer fluid flows directly through copper tubes into the glass tubes. Here it is heated and when it exits it is combined with the other tubes in the collector. It is then transported to the heat exchanger via the solar circuit. In the event of a defective vacuum, it is not difficult to replace one of the tubes independently of the others.
• Heat-Pipe (non-direct flow) – The heat-pipe uses a thermodynamic process for heat transfer in which a heat pipe ( head-pipe ) passes through the glass tube containing a readily vaporizing liquid, such as water or alcohol. When heated, this liquid evaporates and rises to the head of the glass tube where heat is transferred by condensation of the vapor to the heat transfer fluid passing outside the head. The rest of the liquid flows back to the bottom of the tubes and repeats the process once room temperature is reached. This is sufficient to cause the liquid to condense, as there is a negative pressure in the tubes – the vacuum.
• CPC vacuum tube collector – This design is a variation of the direct flow tube collectors. Here too, the copper tubes run through the glass tubes, but the special feature is that two glass tubes are arranged concentrically and lie in front of a parabolic mirror. The absorbent coating is applied to the inside of the glass tubes. The parabolic mirror helps to make the collector even more efficient, especially at low irradiation. The yields are therefore comparatively higher and the collector works more effectively.

The heat transfer fluid – what needs to be considered

The heat transfer fluid stores the heat and transports it through the solar circuit to the solar storage tank. The heat is then released from the fluid and used to heat tap or heating water. The cooled fluid then flows back and starts its journey all over again. The question that arises, however, is what is suitable as a heat transfer fluid. Here the answer is relatively simple, because normal water is already perfectly suitable for this task. However, as there is a risk of frost, especially in cold months, which could cause irreparable damage to the collector or absorber pipe, the water must be mixed with an antifreeze. But the heat transfer fluid must also be able to withstand high temperatures. Especially in CPC vacuum tube collectors, temperatures of up to 350 °C can occur. To ensure that the viscosity does not suffer due to the antifreeze and such high temperatures, thus reducing the heat capacity, a mixing ratio of 40% propylene glycol and 60% water is usually aimed for. This mixture not only withstands cold temperatures as low as -25°C, but is also suitable for high temperatures. When purchasing the heat transfer fluid, pay particular attention to high temperature stability, good corrosion protection, the lowest possible viscosity, high environmental compatibility and a high heat capacity.