Let's go into a little more detail about the consumption of the heat pump
A little reminder about the heat pump
General operation of a heat pump
The heat pump is a machine electric. It uses electrical energy made available by the electricity supplier, to run its refrigeration circuit and thus "pump" calories into the natural environment. It is based on the same thermodynamic principle as the refrigerator, and uses a compressor, an expansion valve, a condenser and an evaporator.
NB: if you are in France, Belgiumor Switzerland you can receive 3 free quotes with the tool below.
There are two main consumers of electrical energy in a heat pump:
- First the compressor of the heat pump. It's the motor of the refrigeration cycle that provides you with heating. It needs electricity to operate.
- Then the auxiliary electric heater. Watch out for the latter. In fact, many heat pumps are equipped with them to cope with extreme cold. A heat pump captures less energy when temperatures are cold. If it's only used as a back-up, everything's fine, and it will only add slightly to your bill at the end of the year, depending on how cold your region is.
There are also the fan and other elements such as valves, or pumps. But their power consumption is low overall.
The different types of heat pumps
There are 4 main families of heat pumps for home heating:
- Aerothermal or air/water heat pumps: They draw calories from the outside air, and "send" them back through a refrigeration system to the home's water system.
- Water-to-water heat pumps: They draw calories from a natural water source (a lake, for example) and redistribute this energy to your domestic water network.
- Geothermal or ground/water heat pumps: They draw their heat from the earth via a geothermal probe in your garden (at a depth of between 50 and 200 m, or more depending on the power required). Then, still using the same principle, the heat is transferred to your water system via a condenser that exchanges the energy.
- Air-to-air heat pumps: those units you hang on the wall. They're not recommended for heating, as they're not very efficient. They take energy from the air outside with their outdoor unit, and return it to the air in the room.
Each of these types of heat pump has a different operating and efficiency profile, which inevitably affects consumption. For example, aqua thermal heat pumps (water/water) naturally deliver excellent performance, while air/air heat pumps are less efficient for heating purposes.
In practice, this is reflected in a higher or lower COP for each machine. As a reminder, the COP or coefficient of performance is the ratio between heating energy production in kWh and electricity consumption in kWh. Here are some COP ideas:
- Air-to-air heat pump: COP = 2 to 3 (1 kWh of electricity consumed = 2 or 3 kWh produced to heat you)
- PAC Air Water : COP = 3 to 4
- PAC Sol Eau : COP = 4 to 5+.
- PAC Eau Eau : COP = 5 to 7+.
If you were previously on pure electric heating, you can roughly divide your old bill by the COP value to get an estimate of your new consumption with a heat pump.
Electricity consumption plays an important role in the calculating the final price of a heat pump in Switzerlandor in France. It represents costs that will impact the duration of the return on investment.
To know more how much the CAP will consumewe can use several approximation methods that are all equal.
Heat pump consumption from power input
The principle is simple For example, the heat pump has a power consumption of 2.2 kW, as in the Yutaki Combi S 11 kW.
On average, a heat pump operates :
2300 hours at over 800m altitude for heating alone.
2500 hours at over 800m altitude to provide heating and domestic hot water.
2000 hours at less than 800m altitude for heating alone.
And finally, 2300 hours also at less than 800m altitude to provide heating and domestic hot water.
So all we need to do is multiply the power input in kW by the average operating hours in Hours.
If we live at an altitude of less than 800m and the heat pump provides both heating and hot water, then: 2.2kW x 2300hours = 5060KWh (Kilowatt-hours) will be our heat pump's electricity consumption. This example is valid for underfloor heating, as we have considered the power consumption at 35°C water outlet, as indicated on the above data sheet.
Let's say that the price of the kWh is 16cts €: your bill will be around 810€ per year, or 68€ per month.
This cost can be compared to previous consumption. However, this should not be the only decision criteria.
Do the math with this heat pump electricity consumption calculator to get an estimate of your future electricity consumption.
Power consumption calculator
Heat pump consumption using COP
With this approximation method, the idea is to calculate the consumption of previous years with your old heating system. This is an energy-efficient renovation.
For the sake of illustration, let's imagine a previous gas consumption of 2000m3 per year for heating and hot water. This 2000m3 of gas is in fact equivalent to 22,000kWh of electricity, since the calorific value of gas is around 11. This is the intrinsic heating and hot water requirement for the building in question.
However, manufacturers give coefficient of performance (COP) values on their technical data sheets. Let's say we have a COP of 3.5
This means that the heat pump draws 3.5 times more renewable energy (air, water or ground) than it does from the electricity grid.
So if we divide these 22,000kWh by these 3.5, we get the approximate final consumption of the heat pump: 6285kWh in this case.
This would mean a bill, with a cost of 16 cts € per kWh, of about 1000 € per year, or 84€ per year.
Average consumption and concrete examples
It is estimated that the average heating requirement varies between 35 and 50 Watts per m3, depending on climate and insulation. A 120m2 house would therefore need between 4200W and 6000W of heating power. In these examples, we assume that the house is heated by the underfloor heating system (35°C water temperature).
Thus 2 examples of adapted PAC are :
- the Hitachi Yutaki Combi S 2.0 - 6kW
- Atlantic Fujitsu Alféa Extensa Duo A.I. 6 R32 5.5kW
|Home||Device||COP A7/W35||Pabsorbed A7/W35||Conso* kWh/year||bill** € / year|
|House 120m2||Yutaki Combi S 2.0 R32||5.25||0.82kW||1886kWh / year||301€ / year|
|House 120m2||Alféa Extensa Duo AI 6 R32||4.65||1.18kW||2714kWh / year||434€ / year|
|House 200m2||Alféa Extensa Duo AI 10 R32||4.5||2.11kW||4853kWh / year||776€ / year|
*2300 hours of operation of the heat pump, over the 8 months of heating
**16 cts € / kWh
To be verified in reality according to the situation of each one
Variables that influence the electrical consumption of the heat pump
- The first variable that influences the annual consumption is naturally the current year's climate. If winter is harsh and the season lasts, the heat pump will run a little longer. Instead of the average 2300 hours, for example, we'll be in a year where it runs for 2700 hours. This 20% variation will be directly reflected in the electricity bill.
- Then, one of the influencing variables is heat pump water outlet temperature. If you have heating, it will probably be 35°C or less. This is ideal for most heat pumps. However, if you have radiators, then the outlet water temperature needs to be higher, as their exchange surface is smaller. So the machine will run at a different speed to produce these higher temperatures, and the COP will be lower. Instead of 3.5, it will be 2.8, for example (Less COP = more consumption) This 20% variation will be paid directly by you to your electricity supplier.
- The intelligent design of the system also has an impact on heat pump consumption. If, for example, one of the designers decided to fit too large a buffer tank, then the heat pump might be constantly running in an attempt to heat this enormous tank, and all for nothing. This is certainly part of the reason why heat pump certificates and other labels exist, to guarantee that the design is sound. In France, call on RGE or QualiPAC-certified professionals. In Switzerland, it's GSP or PAC Système Module certification.
- Finally we can talk about electrical resistancesIf they're not just for back-up, they can come on without you even knowing it, either because of faulty wiring or because the installer isn't familiar with local standards. This can put your electrical costs into geostationary orbit.
Heat pump consumption by type
You may be wondering which type of heat pump to choose to heat your home properly without consuming too much energy. In fact, depending on the source from which you draw the energy, the efficiency is different and so consumption varies.
Consumption of an air-to-air heat pump
Air is a medium with a lower thermal capacity than water, so the COPs of air-to-air heat pumps are always lower than those of other heat pump models. It's best to avoid heating with an air-to-air heat pump, unless for financial reasons it doesn't make sense to install an air-to-water heat pump, and you don't need heating often during the year.
Consumption of an air-to-water heat pump in kwh
The method(s) presented above allow you to find your consumption in kwh in simple ways. The simplest way is to use power consumption. Air-to-water heat pumps are preferred because it's easier to transfer heat to the water in the hydraulic network, since water has a thermal capacity 4 times greater than air. As a result, COPs are much higher and consumption is lower. However, we're still drawing heat from cold air in winter, which is not optimal. The ideal way to limit consumption is to have a source with a constant or little-variable temperature.
Consumption of an air-to-water heat pump for a 100m2 house
Let's take the example of a typical 100m2 house in France. Consumption depends on the model installed. Let's take a standard case of a 7kW heat pump with an average COP of 3.5, running for 2,300 hours a year. 7 / 3.5 = 2kW absorbed on the electrical network, and this for 2300 hours, i.e. 4600kWh per year of consumption, which gives 800€ with a kWh at 0.174€, i.e. 66€ per month and 2.2€ per day.
Consumption of a water-to-water heat pump
The ideal situation is for heat pumps that draw their heat from water. These sources have a much more stable temperature throughout the year (lake or river, or geothermal probe with glycol). To limit your consumption as much as possible, this is the best solution, but it generally costs a lot more. COP can be as high as 5 or 6, enabling you to produce 6 times more energy than you consume in electricity.
Consumption of a pool heat pump
Heating a swimming pool is a luxury far from any ecological consideration. You'll need to heat a large volume of water for several days to get your 28 degrees in the water. And you'll need to maintain it, as the water will lose between 1 and 3°C per day. So you'll need to keep the heat pump running, at a cost of around €500 a year for a standard pool.
Here is a simulator of electrical consumption for swimming pools: http://www.jcg2.fr/piscine_bilan.php
Heat pump electricity consumption simulator: 3 tools
- The German heat pump manufacturer Watterkotte, acquired by NIBE in 2020, has a nice heat pump electricity consumption simulator for France : http://www.waterkotte.fr/calculez-votre-consommation/
- Here is another simulator of consumption of pac air water or other, in artisanal mode: http://nourtier.net/JoceWanadoo/Bricolage/PAC/calcul_PAC.htm
- And finally, an easy-to-use calculator to estimate your electricity consumption. https://calculette.proxiserve.fr/calculette-economies-energie-PAC
The part of consumption that we don't talk about: to go further.
The gas-fired boiler uses gas extracted from natural reserves and transported to Europe.
The heat pump uses electricity from a production source. However, this production source also has its own output. It may be an oil-fired power station, a hydroelectric dam or a nuclear power station.
The overall performance of electricity production is around 40%. Even though Some Siemens turbines, such as the SGT-8000H, now achieve record efficiencies of over 60%.
So when we say that a COP of 3.5 means 1kWh absorbed from the network for 3.5kWh of heating energy produced, this is not accurate.
Since to produce this 1kWh we needed a power plant with an efficiency of 40%. This 1kWh costs in fact 1/0.4 or 2.5kWh so 2.5 times more.
Let's compare a heat pump and a gas boiler to see the absolute difference.
Let's take a heat pump with an average coefficient of performance of 3.5, and a gas boiler with an annual efficiency of 97%.
At maximum load, a 10 kW heat pump has a COP of 2.3 rather than 3.5 so it will consume 10kW/2.3 = 4.34kW of electricity from the grid.
However, to create these 4.34kW, we needed 2.5 times as much energy in the first place: or 10.85kW of primary energy.
The gas boiler of the same power 10kW, with its efficiency of 95%would consume 10/0.95 or 10.52kW.
We see in this case and with the approximations of the values of COP (depends on the manufacturer), that the gas boiler consumes in absolute a little less than the heat pump.
However, it uses fossil fuels, which are by definition exhaustible, whereas the heat pump uses air, which is renewable.
Let's assume that the electricity from the heat pump is produced in a gas turbine power plant, then in the end almost as much gas is burned on the heat pump side to produce the electricity, as on the gas boiler side to play the role of fuel in the boiler.
It's just a question of shifting the frame of reference: for the boiler, everything is done on site, whereas for the heat pump, part of the energy transformation is done externally and isn't really addressed.
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About the author
Juliena mechanical engineering graduate and specialist in climate engineering since 2009, has become a writer specializing in renewable energies, with expertise in heat pumps and photovoltaic solar panels for individual housing.