A Dutch study has found that propane (R290) heat pumps are “universally applicable” to space and domestic-water heating in small, medium and large buildings.

The study also reports that heat pumps using natural refrigerants (hydrocarbons, CO2/R744 and ammonia/NH3/R717) deliver COPs equal to, or better than synthetic alternatives for almost every application.

The study was commissioned by the Netherlands Enterprise Agency for the Energy Top Sector at the request of the Dutch-based consortium TKI Urban Energy. René van Gerwen, owner of Dutch consultancy ENTROPYCS (ENTROPY Cooling Solutions), presented findings of the study – which he co-wrote with Charles Geelen, Owner of Dutch manufacturer Infinitus Energy Solutions – at the November 2022 ATMOsphere (ATMO) Europe Summit in Brussels. ATMO Europe was organized by ATMOsphere, publisher of hydrocarbons21.com.

The study, “Natural Refrigerants in Heat Pumps,” covered numerous refrigerants, applicable European and Dutch standards and regulations, and simulations and calculations of performance for a variety of refrigerants in different conditions, said van Gerwen.

Van Gerwen said that R290 heat pumps were “currently in use” and/or had “no significant restrictions” for the following circumstances:

Heating capacity

  • Domestic, less than 12kW (3.4TR)
  • Housing blocks/small utility/apartment buildings, less than 70kW (19.9TR)
  • Residential/large utility buildings, greater than 70kW per unit


  • Low-temperature space heating, 35°C (95°F)
  • Medium-temperature space heating, 55°C (131°F)
  • High-temperature space heating, 75°C (167°F)
  • Domestic hot water, 60 to 80°C (140 to 176°F)


  • Outdoor air, -12 to 15°C (10.4 to 59°F)
  • Ventilation air, 20°C (68°F)
  • Ground source heat exchanger, 0 to 8°C (32 to 46.4°F)
  • Groundwater, 10 to 18°C (50 to 64.4°F)
  • Residual/waste heat (including wastewater heat recovery), 20 to 30°C (68 to 86°F)

“For every condition you have, propane, in particular, is an option,” said van Gerwen. “It is a very generic refrigerant that fits almost everywhere.”

Another hydrocarbon, isobutane (R600a) can be applied to many of the same applications as propane. However, isobutane is described as having “few obvious practical applications” for medium and large building capacities, low- and medium-temperature space heating and outdoor air sources.

In regard to other natural refrigerants, van Gerwen said, “For high supply temperatures, CO2 is a particularly fantastic refrigerant. Ammonia has been the reference refrigerant for industrial applications, but we are also now seeing some small domestic equipment with a tiny amount of ammonia starting to enter the market, particularly in the heat-driven heat pumps.”

The study’s computer simulations compared the COP for various HFC, HFO, and natural refrigerant heat pumps using an outside air source of 7°C (44.6°F) and delivery four different temperature supplies, starting at 35°C (95°F) and ending at 75°C (167°F). “The natural refrigerants all perform equal to or better than any of the non-natural alternatives,” said van Gerwen and indeed the report states that “switching to natural refrigerants leads to equivalent or higher efficiencies.”

“Almost every condition has more than one applicable natural refrigerant option,” said van Gerwen. “That leads to a strong recommendation to use natural refrigerants in heat pumps.” He also suggested doing a study to find the right refrigerant for a particular heat pump purpose. “You can fine-tune and obtain extra performance; extra COPs, for example.”


Even though natural refrigerants supply “good” solutions for heat pumps, “we also have some challenges,” van Gerwen said, “particuarly in variable refrigerant flow (VRF) and large multi-split systems.” Moreover, there remain some safety issues to address, but that also holds true for synthetic refrigerants, including HFOs and R32.

In general, existing heat pumps cannot be converted to natural refrigerants, requiring new heat pumps for decarbonization system upgrades.

The findings in the study were based on the author’s expertise, a literature review and information provided by various experts in the industry. The performance reviews were based on simulations using the computer program CoolTools that were cross-checked against field data.

Van Gerwen used natural refrigerants as an end user on a large scale during his 18 years of work with the company Unilever. In 2016, he started the consulting company ENTROPY Cooling Solutions and is “working to reduce the barriers and accelerate the transition to natural refrigerants globally.”

“For every condition you have, propane, in particular, is an option. It is a very generic refrigerant that fits almost everywhere.”

René van Gerwen, owner, Dutch consultancy ENTROPYCS (ENTROPY Cooling Solutions)