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Air, brine or water heat pumps?

By comparison!

Outside air

Air-to-water heat pump with ventilation

Although air-to-water heat pumps have a comparatively low coefficient of performance, they can be manufactured at far the least cost.

Air-to-water heat pumps use the ambient air. For this type of “heat acquisition” the cost is very low, for the air is simply aspirated. For this reason these pumps are much cheaper to buy than other heat pump types .

Air-to-water compact heat pumps contain an integrated controlled domestic ventilation system. A clever combination for low heating costs and constantly fresh, filtered air for a healthy room climate.

Air-to-water compact heat pump

The growing demands on the room climate and the trend to compact installation of the heating and ventilation systems close to the living area have given rise to the type of heat pump known as the air-to-water compact heat pump. These pumps are complete system solutions that integrate an electrically driven compression heat pump, storage water heater and ventilation unit with heat recovery, and are not larger than a refrigerator-freezer combination.

Passive houses with up to max. 120 square meters of living space

For the special requirements in passive houses, system solutions were developed that enable use of a heat pump. Passive houses always require controlled domestic ventilation. In compact units, therefore, an exhaust air-to-water heat pump is combined with a controlled domestic ventilation system. The heat pump uses the heat in the exhaust air that was not utilised during heat recovery by the ventilation system. This portion is used to reheat the supply air or for drink water heating.

However, passive house compact units can only serve a heated area of max. 120 square metres - or a volume of around 400 cubic metres.

Passive houses and low-energy houses

When heating needs are greater, compact units with an additional outside air flow for the heat pump are required. In this case our Effiziento HV unit is the best choice up to a heat output of max. 6 kW. The Effiziento HV unit can also serve a good low-energy house completely by itself, which always requires controlled domestic ventilation for protection of the basic structure of the building.

Owing to its compact design, the air-to-water compact heat pump can be accommodated in an area of approx. three square metres - connected ducts of the ventilation system are also included here These systems are also advantageous in that they enable the heat pump and the ventilation system to be installed in a single operation.

A connected solar power plant can support the heating of the drinking water. A fireplace can be integrated for heating support.

Hot water heating, e.g. underfloor heating or radiators, provides for warm rooms, and, in addition, reheating of the supply air can occur simultaneously.

If the demand is for environmentally friendly heating technology, the pleasant advantages of controlled ventilation, e.g. no noise, harmful substances and pollen, and rapid amortisation of the investment, our Effiziento HV unit is the solution. A clever combination for low heating costs and constantly fresh, filtered air for a healthy room climate.

Air-to-water heat pumps

Air-to-water heat pumps can be installed inside and outside. In the case of both installation types, the aspirated ambient air is channelled past a heat exchanger, which is part of the cooling circuit of the heat pump. The rooms are heated with a conventional radiator or underfloor heating.

Only when outside temperatures fall below -7 °C do modern air-to-water heat pumps need additional heater - as a rule this is provided by electric heaters. In central European latitudes, however, this additional heater is only used a few days in the year.

Owing to the low investment costs for the outside air supply, air-to-water heat pumps are much cheaper than other heat pump types.

Air-to-water heat pump, inside installation
Air-to-water heat pump, outside installation

Geothermal heat

The geothermal heat sources can be used at the surface at a depth of 1 to 2 m through the horizontal laying of the heat exchanger tubes, or through vertical earth probes to depths of up to approx. 100 m.

The ground is a good heat accumulator, since the temperatures are relatively constant at 7 to 13 °C (at a depth of 2 m) all year round.

In a closed circuit, with a mixture of water and antifreeze (brine), the heat pump absorbs the heat via a PE pipe anchored horizontally or vertically in the ground and delivers it via a heat exchanger to the cooling circuit of the heat pump.

If a direct evaporation procedure is used, a heat exchanger between the heat sources and the heat pump can be dispensed with. In this process the geothermal heat is harnessed by laying horizontal collectors made of copper tubing through which the refrigerant from the heat pump circulates.

Horizontal collector, system installed outside
Vertical collector (earth probe), system installed inside

Brine-to-water heat pumps with flat collectors

Flat collectors have the advantage of being uncomplicated and cheap to manufacture. However, flat collectors need a lot of space.

As a rule, the area required for the heat sources is one or two times larger than the useful area to be heated. As a rule, the heat requirement of the useful area varies between 30 W/square metre in the case of a low-energy house and 80 W/square metre in the case of an old building with thermal insulation.

In the case of horizontal flat collectors, outputs between 10 and 40 W/square metre are to be expected. They are laid at a depth of 130-200 cm and with a pipe spacing of approx. 50 centimetres. The area required for flat collectors results from the heat requirement of the useful area to be heated, the thermal extraction output of the heat sources, and the coefficient of performance of the heat pump.

Brine-to-water heat pumps with earth probes

Although earth probes can also be used in very small spaces, they are relatively expensive as heat sources. Earth probes are often used as an alternative if the ground area is not large enough for flat collectors.

Depending on the ground a heat output of around 70 W can be achieved per drill metre. A precondition for drilling is accessibility for trucks.

As a rule, earth probes are installed at depths of up to 100 m, and most commonly between 40 and 50 metres.

The office of water management grants authorization for earth probes to a depth of 100 m, and from 100 m the mining office is responsible. In water conservation zones (I and II) earth probes are prohibited.

The costs for drilling including a probe amount to € 30-50/metre depending on the composition of the ground. For a typical low-energy single-family house with a heat output of around 6 kW, this results in costs between 3,000 and 5,000 euros.

The costs for tapping the heat source are considerably higher in the case of brine-to-water heat pumps.

Considering the higher tapping costs and lower operating costs compared to air-to-water heat pumps, amortisation is not possible with outputs up to 15 kW.

With higher outputs the costs for air-to-water heat pumps increase sharply while those for brine-to-water heat pumps rise only slightly. Here it would pay to perform a detailed economic analysis and brine-to-water heat pumps could turn out to be the better alternative.

Water heat

Ground water is the heat source with the highest temperature level. Stream or source water is subject to temperature fluctuations. Owing to the all-year-round availability of water heat in sufficient quantities, water-to-water heat pumps can be operated monovalently, that is, without another heat generator.

As a rule, water-to-water heat pumps achieve the best coefficients of performance, but this requires a permit under the Water Act, which is usually granted for a limited period. Another precondition, of course, is a sufficient quantity of water. A single-family house requires at least two cubic metres of ground water per hour.

Water-to-water heat pumps

In normal cases, extraction and absorption wells have to be drilled. The associated costs are very high and if the wells have to be drilled again amortisation, in contrast to the other types, is not achievable.

If stream or source water can be used, the costs are strongly dependent on local conditions. Here too only a detailed economic analysis can enable a sensible decision to be taken for the right heat pump type.

Installation with suction and injection wells

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