Electricity consumption of heat pumps: A little ABC

Want things toasty warm but not so keen on the cold hard shock of a big bill? You’re not the only one. Never more than nowadays, heating energy does not grow on trees. But switching to a heat pump – the Teslas of heating systems - could be one way forward. Instead of releasing energy through combustion, they harness the ambient heat around them to heat and prepare hot water. Quite clever! Even if they, too, need some electricity to get going. Read on as we explain exactly how much they need and how they can help soothe worries over soaring power costs, even in uncertain times.

This is why a heat pump needs power

If you want the greenest possible way to heat your home, you’re spoiled for choice. And in our overview of the 7 most common heating types, the heat pump tops the lot when it comes to environmentally friendly heating systems.

Remember the rule from physics lessons: primary energy is always needed for heating and normally comes from wood, oil, gas or electricity. A heat pump obtains the heat it needs directly from groundwater, the ambient air or the Earth and then has to convert it into a heat yield. Helped on the way, not by magic, but rather a refrigerant circuit.

This is how it works: The heat pump taps heat from the environment and conducts it to a refrigerant. Exposing the refrigerant to the heat causes the former to evaporate, whereupon it is compressed by a compressor. This pushes up the temperature and pressure until the ta-da moment, when a heat yield is produced. A heat exchanger transfers this heat to the heating system, within which the newly heated water, in turn, then warms your house. The process relies on compressors, pumps and fans. These things require electricity to work so like it or not, the heat pump is also going to use up some of your kilowatt hours!

Good to know: BUT, only a quarter of the electricity goes on generating the heat generation, with the remaining 75 percent available to heat your home with free environmental energy. Isn’t that a sly way to save?!

The seasonal energy efficiency ratio (SEER) - a benchmark you can bank on for calculating your home electricity consumption

If we’ve convinced you to get out there and find your dream heat pump, there is a three-letter acronym you’ll want to remember while shopping around, namely COP. This is the Coefficient of Performance, which is a parameter issued by heat pump manufacturers for each model and expresses the efficiency of a heat pump measured in the laboratory under specific operating conditions. Which, needless to say, will differ from those in your house in Switzerland! A more reliable indicator for determining heat pump efficiency - and thus electricity consumption - is the seasonal energy efficiency ratio (SEER). This variable describes the effective coefficient of performance over the entire year under real operation conditions.

What this boils down to: The SEER indicates how many kilowatt hours (kWh) of heat are obtained when one kWh of electricity is consumed. The higher the SEER, the more efficiently the electricity is used and the lower the energy required and vice versa. Make sense? Warning – you’ll need your maths hat here, as well as physics! Thus, using the SEER, one can easily calculate the electricity consumption of one's heat pump if the annual heating capacity in kilowatts is known. The formula is as follows:

Power consumption = (heating capacity in kilowatts / SEER) x number of heating hours

Here’s an example calculation: A heat pump running at an SEER of 3.4 for 2000 hours per year and providing 12 kilowatts (kW) of heating power, requires this much electricity: (12 kW / 3.4) x 2,000 = around 7060 kWh of power per year.

All you need to do to calculate the effective costs is multiply the figure for kWh by the current electricity price, which varies depending on where you live. Want an easy summary? Check this Overview from SRF.

Did you know that your heating bill lists only the total electricity consumption? But break it down and more than likely, you’d like to know how much your heat pump is using. If so, have your electricity supplier install a separate electricity meter for the heat pump.

These heat pumps are available - SEER and power consumption at a glance

As usual, the devil is in the detail – not all heat pumps are alike! The SEER of the various types tends to differ significantly, but these four types have proven themselves:

Air-to-water heat pumps - SEER of around 3.5 The best bit: The air-water heat pump is a breeze to install, which also makes it the most affordable option and it uses the ambient air as a heat source. Compared to other variants, however, this is precisely why it needs the most electricity. In winter, when outside temperatures drop, there is less scope to extract heat from the ambient air, which explains why more power is consumed to achieve the desired temperature.

Brine-water heat pumps with ground collectors - SEER of around 4 These units generate thermal energy from the surface heat of the Earth and, like photovoltaics, require collectors to do so. These are placed horizontally near the Earth's surface (approx. 60 - 80 cm deep). Since the surface temperature of the Earth fluctuates less than the air temperature, brine-water heat pumps with collectors outperform their air-water peers in terms of efficiency.

Brine-water heat pumps with ground probes - SEER of around 4.5 This system extracts energy from deeper down underground. Pipes, known as probes, are laid 30 to 100 m vertically under the home into the Earth's interior. Since the Earth’s temperature never goes below 7 degrees when you drill down 10 m or more, even in winter, brine-water heat pumps with geothermal probes are more efficient than brine-water heat pumps with collectors, which explains the lower electricity costs. However, depending on the location, the deep drilling required to install the geothermal probes may not always be possible.

Water-water heat pumps - SEER of around 5 This is the most efficient heat pump, which gets thermal energy from the groundwater. Since the temperature of groundwater is higher than that of the Earth or ambient air, the energy costs are lower. Conversely, investing in this option is costlier than for other heat pumps and the use of groundwater is not always possible.

These factors also impact on the power consumption of heat pumps

• Insulation: We want to keep heat inside – but that’s only possible in well-insulated houses. To reduce electricity consumption, before replacing the heating system you should definitely invest in insulating. I mean you, too, wouldn’t wear a coat with holes in it in winter, would you?

  your facade

• Regional climate: The colder the climate, the more energy the heat pump needs to heat to the desired temperature. An air-to-water heat pump would be great for the Locarno rustico, but maybe less so for the chalet in Zermatt.

• Flow temperature: This refers to the temperature of the heating water supplied to the radiators. The warmer the heating water has to get to bring the house to the desired temperature, the more electricity it needs.

• Space and house size: It’s not rocket science – a tiny house will need less energy than a villa. The larger the heated area and volume (incl. ceiling height) of the rooms, the more energy you will need to heat them.

• Number of persons in the household: The more people live in your household, the more heat you’ll need for cooking or showering, for example. Ergo: The more hot showers your family take, the higher your electricity consumption!

• Technology and model: Ultimately, the exact power consumption also depends very much on the specific heat pump model you choose.