Three things decide a heat pump's environmental impact: how the electricity it uses is generated, how efficient the unit is, and the refrigerant circulating inside it. A heat pump burns no fuel. It collects heat from the outdoor air and moves it into the building, typically delivering three to four units of heat for every unit of electricity. That is why, in most cases, it produces the same heat with less CO₂ than a gas or coal boiler, and there is no flue gas at the building at all. On the refrigerant side the figure that matters is the global warming potential (GWP); natural refrigerants such as R290 bring that impact close to zero.
Compared with a boiler: a worked example
The easiest way to see the difference is a simple calculation. The values below are assumptions for illustration; the figures for your own building and region will differ.
- Let the building's annual heat demand be 10,000 kWh.
- Burning natural gas releases about 0.20 kg of CO₂ for every kWh of heat it produces; this figure comes from the chemistry of the fuel. With a boiler efficiency of 90%, each kWh of heat delivered to the building accounts for 0.22 kg of CO₂. Annual total: about 2,220 kg.
- Take a seasonal efficiency (SCOP) of 3.5 for the heat pump. 10,000 kWh of heat then needs about 2,860 kWh of electricity.
- Assume the grid releases 0.45 kg of CO₂ for every kWh of electricity generated. The heat pump's annual share comes to about 1,290 kg.
For the same heat, the boiler releases about 2,220 kg of CO₂ and the heat pump about 1,290 kg. Under these assumptions the two systems break even on a grid that emits about 0.78 kg of CO₂ per kWh, which means the heat pump stays ahead unless almost all of the electricity comes from coal-fired power stations. Against a coal boiler the gap is wider still: coal releases considerably more CO₂ than gas for the same heat.
There is one more gain that the CO₂ calculation leaves out: local air quality. Besides CO₂, a boiler's flue releases nitrogen oxides, and with coal also sulphur dioxide and particulate matter, straight into the air around the building. A heat pump burns nothing, so there is no flue gas in the street where the building stands. In densely built cities, this difference shows directly in the air people breathe in winter.
Where does the electricity come from?
A boiler burns the same fuel throughout its life; fifteen years on, it runs with the same emissions as on its first day. A heat pump's emissions change with the grid. As the share of wind, solar and hydropower in electricity generation grows, the same unit causes a little less CO₂ every year without any change to the unit itself.
If the building has solar panels on its roof, the effect is immediate: electricity generated during the day powers the heat pump. We cover how such a system is set up, and at which hours it pays to use the electricity, in our article on solar energy with a heat pump.
The unit's efficiency matters at least as much as the source of its electricity. Consumption falls as the flow temperature drops and as the inverter compressor runs only as hard as needed; for the building in the example, a SCOP of 4 instead of 3 cuts the electricity needed from about 3,330 kWh to 2,500 kWh a year, and emissions fall in the same proportion. We go through these levers in detail in our article on heat pump electricity consumption.
Refrigerants and GWP
As long as the refrigerant stays inside the sealed circuit, it does no harm to the environment. Its impact appears during charging, in a leak during the unit's life, or at the end of its life if it is not recovered properly.
That impact is measured as global warming potential (GWP): the warming caused by 1 kg of the refrigerant in the atmosphere over 100 years, relative to the warming caused by 1 kg of CO₂. Using the 100-year values from the IPCC's Fourth Assessment Report:
- R410A: 2,088
- R134a: 1,430
- R32: 675
- R290 (propane): 3
To put the numbers in context: releasing 1 kg of R410A into the atmosphere is equivalent to emitting about 2 tonnes of CO₂. That is more than one and a half years of the heat pump's electricity-related emissions in the example above. The same amount of R32 is equivalent to 675 kg, and of R290 to just 3 kg.
The risk of a leak depends on the circuit as much as on the refrigerant. In monobloc units the refrigerant circuit is sealed at the factory and no refrigerant connections are made on site; in split systems, the workmanship of the pipe joints between the indoor and outdoor units has a direct effect on the risk of leaks. That is why, in a split system, the leak-tightness test after installation matters at least as much as the choice of refrigerant.
The ozone layer is a separate issue. The CFCs and HCFCs that damage ozone (R22 is one of them) have been phased out under the Montreal Protocol. R410A, R32 and R290 have no effect on ozone; the difference between them lies in their climate impact. High-GWP HFCs are now being cut back step by step as well, under the 2016 Kigali Amendment and the European Union's F-gas regulation. We summarise the history of this shift in our article on the history of the heat pump.
Refrigerant choice in the AD series
We chose the refrigerant for each series according to the climate and the required water temperature:
- The Poyraz and Boran series run on R290.
- In the Ayaz series two circuits work in cascade: the first stage, which takes heat from the outdoor air, uses R290, and the second stage, which raises the water to 75 °C, uses R134a.
- The Vaha series, designed for coastal climates, uses R32, which keeps its cooling efficiency in hot weather.
- The commercial V and W series outdoor units use R410A.
We built our residential series around R290 for two reasons. The first is climate: its GWP is 3 and it has no effect on ozone. The second is thermodynamics: the critical temperature of propane is about 97 °C, compared with about 78 °C for R32 and about 71 °C for R410A. A refrigerant with a high critical temperature holds its efficiency better at high water temperatures. Alongside the vapour-injection compressor circuit, this property is part of why the Boran can produce 65 °C water at an outdoor temperature of −25 °C.
R290 comes with a condition: it is flammable, with safety class A3. The refrigerant charge, the design of the unit and the installation location are therefore set according to the rules of the relevant standards. For comparison, R32 is mildly flammable (A2L) and R410A is non-flammable (A1). A leak-tight circuit and an installation that follows the rules are what make R290 safe to use.
From manufacture to recycling
A unit's environmental footprint does not end with its use. Most of a heat pump's body is steel, copper and aluminium, all of them recyclable metals. Electronic boards and compressor oil are collected separately. When a unit reaches the end of its life, the most important step is recovering the refrigerant instead of letting it escape into the atmosphere. With high-GWP refrigerants, this single step noticeably changes the unit's lifetime climate impact.
A long service life is an environmental gain too: every unit that does not need replacing is a unit that does not need to be manufactured again. In the V and W series outdoor units, the condenser is made of epoxy-coated copper tubes and resists the corrosion caused by salt, humidity and dust on the coast and in industrial areas. We design our heat pumps to the European Union's ErP (Ecodesign) and energy labelling directives.
In short
- Emissions are decided by the source of the electricity and the unit's seasonal efficiency; as the grid gets cleaner, the heat pump's advantage grows.
- A refrigerant's GWP shows how much harm a possible leak would do; in this respect R290 is among the lowest-risk options.
- The right capacity, a low flow temperature and a leak-tight circuit turn the environmental gain on paper into a real one.
You can read our full approach on our sustainability page. If you would like to know which series suits your building and climate zone, write to us through the quote form.
