A heat pump is a heating mechanism based on exchange heat between the interior and exterior of the house. It works on the principle of drawing heat molecules from outside the house—even when the air is cold—to inject them into the interior. In the other direction, it draws molecules of cold air from inside the house and sends them outside. In other words, it cools down the exterior of the home in order to heat up the interior.
The installation of an efficient heat pump in a home can bring about substantial savings in consumption, and therefore in heating costs, provided that the installation meets certain criteria. The higher the temperature of the heat source, even in the winter, the greater the efficiency. This can be greatly increased if the pump is coupled to a solar energy system.
How does it work?
The pump, driven by an electric compressor, runs a heat exchange circuit. This circuit is made by circulating a synthetic gas, propane or carbon dioxide (CO2) through a pipe, which collects heat from the external environment (water, air, or the ground).
This heat is then transmitted to the domestic heating system, usually water circulating in radiators or underfloor heating. To increase the efficiency of the system, the gas circulating in the piping can be expanded, to better absorb the heat molecules. Then it is compressed to heat itself up and transfer this energy into the house.
How do we measure the efficiency?
The efficiency of a heat pump is measured by comparing the energy produced with that consumed by the operation of the appliance. This gives the “coefficient of performance” (COP), which is measured in kilowatt hours (kWh).
Let us say that the pump consumes 1 kWh to extract from ground at a temperature of zero degrees enough energy to heat water to 35 degrees. Let us say that the energy produced amounts to 4.5 kWh. The energy produced is thus 4.5 times greater than that consumed. We may therefore speak of a coefficient of performance (COP) of 4.5.
The three types of heat pump
There are three kinds of heat pumps: air source, ground source, and water source.
Air source heat pumps
Air source heat pumps draw in the outside air and transfer the energy to the water circuit providing the internal heating system. This system is the cheapest of the three, but it is also the least effective due to the significant variation in air temperature. It is thus frequently used in combination with another heating installation.
Ground source heat pumps
A ground source pump seeks heat in the depths of the ground (geothermal energy): the deeper we drill, the higher the ground temperature. For a medium-sized house, a borehole of 120 to 150 metres is sufficient because it produces a temperature of about 15 degrees which, coupled with the pump, generates enough energy to heat the home. A deeper borehole means a higher temperature, but also increases the costs.
Water source heat pumps
A water source heat pump also uses geothermal energy, but directly seeks hot water in the depths of the ground, either groundwater or an underground river. It introduces it directly to the heating circuit before discarding it, cooled. This system offers the best performance, but the water capture is difficult to implement because it impacts on intact geological layers and can risk altering the temperature of the water collected or introducing sources of contamination.
How can we make a heat pump even more efficient?
A heat pump delivers maximum efficiency in very well-insulated buildings with underfloor heating systems. The energy required to heat the living space is therefore less than that required by conventional water radiators.
The installation of photovoltaic solar panels can produce some of the electricity required for the operation of the heat pump, while solar thermal panels accelerate the heating of the water.
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