Air-source heat pumps in extreme cold: what to expect

An air-to-water heat pump takes heat from the outdoor air, even in cold weather. The lower the temperature, the less heat there is in the air and the harder the machine has to work. It is worth knowing what to expect in frost.

Down to what temperature it works

According to its datasheets, the Thermia Elve works at outdoor temperatures from -25 to +45 °C, and the Thermia iTec XTR works down to -25 °C. The iTec XTR datasheet states that at that temperature it still delivers water at 65 °C. These are the machine’s operating limits, not a promise of performance. In practice there are Thermia air-source heat pumps running in very cold parts of Spain, such as Segovia, León or Huesca.

What happens to performance

It drops. The datasheets show it with two different SCOP figures, under EN 14825. With underfloor heating at 35 °C:

• Thermia Elve L: 4.96 in an average climate and 4.46 in a cold climate.
• Thermia iTec XTR S: 5.10 in an average climate and 4.30 in a cold climate.

In other words, in a climate much colder than most of Spain the annual performance falls, but it is still high. The Elve L datasheet gives a heating output of 10.1 kW with air at -7 °C and water at 35 °C.

Defrosting

In cold, damp weather ice forms on the outdoor unit. The machine removes it periodically by reversing the cycle for a few minutes. This is normal, and part of the winter consumption goes on it.

When geothermal is the better option

The ground temperature is nearly constant all year, so geothermal does not lose performance when it freezes. If you live in a very cold area, or have a large building with a high heat demand, it is worth comparing the two. See geothermal and air-source.

To find out what your home would expect in your area, request the feasibility study.

By Ana Girod and Miguel Madero, co-founders of Girod Geotermia.