A heat pump is a device that exploits free heat present in the environment – outdoor air, rivers, the ground. All bodies, even "cold" ones," contain large amounts of energy, some of which can be extracted. Using a fluid in a thermodynamic cycle, the heat pump extracts heat from the "cold" source side and injects it into the "heat sink" side. This transfer is a forced process, as naturally the heat would migrate from the hot side to the cold side. A compressor provides the heat pump with the necessary energy. Heat pumps are used primarily for heating, but can also provide sanitary hot water, and air conditioning: such heat pumps are called reversible heat pumps.
There are two families of heat pumps:
• Aerothermal heat pumps
Air-air heat pumps have two components. An outdoor unit extracts calories from the air, and a convection fan releases them inside the building, generally for heating, but also for cooling in summer, in the case of a reversible heat pump.
Air-water heat pumps use the calories extracted outside to heat water in a heating circuit, and also to cool the interior in summer, and to produce sanitary hot water (under certain conditions).
This involves a mixed heat pump technology, with a refrigerant circuit to extract heat, and a hot water circuit to distribute it.
There is one constraint: supplementary heating is required in cold climates, as the heat pump will not function at temperatures below -5°C.
• Geothermal heat pumps
Water-water heat pumps extract heat from the ground and return it either directly via a closed-circuit underfloor heating system (direct expansion HP) or indirectly via water circulating in a heat distribution system (mixed HP system).
Two types of coils are used for heat extraction, depending on available outdoor space:
- Horizontal coils: this is the most common system, and the least expensive; coils are placed horizontally at shallow depth, which calls for a space of sufficient size.
- Vertical coils: more expensive, but require less land area; coils are placed vertically in holes drilled beforehand.
This type of installation must be declared to authorities and a permit obtained.
Heat pumps can be reversible: by reversing the thermodynamic cycle of the refrigerant, the heat pump extracts calories inside the building and releases them outdoors. They procure a moderate drop in temperature, between 3 and 4°C cooler than outdoors, meaning that it is a cooling system rather than an air conditioning system. A reversible system consumes electricity all year round for thermal comfort, whereas a heat pump for heating purpose alone is used only in winter.
A heat pump can cover up to 70% of building heating needs. The remaining fraction (depending on the energy source and operating mode) corresponds to the electricity consumed to operate the pump.
Heat pumps require energy (electricity or gas, according to the model) to operate, but their energy consumption is minimal compared to the thermal energy produced, ensuring environmental and economic gains.
The heat pump coefficient of performance (COP) is used to evaluate device efficiency, comparing electricity (or gas) consumption to the amount of thermal energy produced. This COP is on average between 2 and 3, meaning that for 1 kW consumed the heat pump produced 2 to 3 kW of energy.
One advantage of heat pumps is that they can be adapted to practically all existing heating systems (radiators, floor heating, convection fans, wall units or consoles, etc.)
- Study by recognised environmental professionals of the existing installation, and possible installation of a heat pump to replace current equipment
- Examine possibility of combining sanitary hot water production with space heating
- Comparison of cost estimates
- Choice of period for work to avoid disturbing customers
- Establish maintenance contract with installer
Tariffs vary widely, depending on existing system, space to be heated, other technical elements (convection fan, floor heating, hole drilling, etc.).
It is worthwhile analysing potential savings on your energy consumption for each system, to determine payback times.
- free renewable energy if the heat pump is supplied with renewable energy
- reduced greenhouse gases emissions, greater protection of the ozone layer
- lower power consumption, to be evaluated according to the heat pump COP ==> a heat pump with a COP of 3 produces 3 kW of heating for 1 kW of electricity consumed.
- High cost / Payback time approximately 5 years
- Long work time, that must be done when weather is not cold; difficult for seaside hotels to plan work in the middle of the summer season
- Environmental impact of refrigerant gases which are known to contribute to global warming and to destruction of the ozone layer.
French companies Aldes and Sanden have developed and brought to market a revolutionary heat pump; unlike conventional models, this heat pump uses a natural fluid, CO2, that is non-inflammable and non-toxic. If there is leakage, a natural component of the atmosphere is released. Better still, this design does not require backup electricity, and has an excellent environmental performance, providing three times as much "free" energy as traditional solar water heaters.
- Noise levels: heat pumps create background noise, between 50 and 60 decibels at 1 metre, and about 40 dB at 5 metres distance. The heat pump must be placed on a vibration-absorbing "silent block".