The Danish Technological Institute (DTI) is collaborating with a number of industry stakeholders, including Danish OEM Fenagy and Danish controls provider Reftronix, in a three-year project to develop a range of CO2 (R744) heat pumps that will offer 20–200kW (5.7–56.9TR) in cooling capacity for residential and commercial use.

However, to produce energy- and cost-efficient heat pumps of this size that use CO2, several components – such as the evaporator and plate heat exchanger – must be redesigned, explains the institute on its website.

“It is not possible to scale down the existing solutions used for larger heat pumps, since the price of the complete system is decisive,” said the DTI. “New components must be designed for the [new] heat pump solution.”

Once developed, Fenagy, a subsidiary of Beijer Ref, will own the final product produced from what is called the Smart CO2 Heat Pump project.

In addition to Reftronix and Fenagy, the DTI will collaborate with Bitzer Electronics, Danfoss, Kelvion, LU-VE, Salling Group, CO2X and Aarhus University on the project, which began in January 2023 and is scheduled to run until 2026.

Gap in the market

The Smart CO2 Heat Pump unit is being developed for multi-family residential buildings, as well as smaller commercial and industrial applications. In addition to installations in new buildings, the air-to-water and water-to-water heat pumps would also be suitable for retrofits, replacing existing fossil fuel-based boiler systems.

For these markets, energy efficiency and cost-competitive pricing are important features, as are the flammability and toxicity of the heat pump’s refrigerant, says the DTI.

“CO2 is therefore a perfect choice,” it adds.

It is also important that the heat pump developed is robust and easy to install and service.

According to the institute, heat pump solutions using “non-flammable and non-toxic natural refrigerants” – e.g., CO2 – do not currently exist in the 20–200kW capacity range. Existing units in this market segment typically using HFO refrigerants, which are flammable and harmful for human and environmental health.

Because of this gap in the market, demand is high, with the possibility of millions of installations across the EU alone, making the market potential of a mid-range CO2 heat pump extensive.

The project team is aiming to achieve a COP of 3 to 5, depending on the operating conditions, and secure energy savings of 31.4% at full load compared to HFO-based heat pumps.

New components

A number of new components will need to be designed to ensure the heat pump can meet the goals of the project.

One of the main elements that will need to be developed is a new type of high-efficiency evaporator using cold-gas defrost, which will help increase efficiency compared to transitional electric defrost.

With cold-gas defrosting, the heat pump produces heat and remains operational during the defrost process, explains the institute on its website. This is not the case with electric defrosting. 

“The evaporator must be an integral part of the heat pump and be divided into at least four sections,” it adds.

Another important element is the plate heat exchanger. “Traditionally, plate heat exchangers for higher pressures are equipped with an additional frame to increase strength, [which] is expensive,” the DTI says. For this project, a new super-efficient plate heat exchanger that does not require an extra frame needs to be developed.

The project team will also need to develop a new refrigerant circuit configuration, a new type of modulating ejector, a new type of expander and a new type of “tube and fin heat exchangers for air.”

Remote monitoring

The smart CO2 heat pump will also require a new type of management platform, which will be provided by Reftronix.

“A particularly innovative element of the project is to connect the heat pump unit to the ‘cloud’ to be able to monitor operating conditions online and use this knowledge to optimize the heat pump’s efficiency, predict maintenance and solve problems caused by broken components until replacement is performed,” says the DTI. “It will thus be possible to keep the heat pump running until service is available.”

Algorithms will be built into the cloud-based solution to help reduce operating costs. The system will monitor real-time electricity prices and then establish the most efficient operating strategy for the heat pump.

“A particularly innovative element of the project is to connect the heat pump unit to the ‘cloud’ to be able to monitor operating conditions online and use this knowledge to optimize the heat pump’s efficiency.”

Danish Technological Institute

The Smart CO2 Heat Pump project is supported by the Energy Technology Development and Demonstration Program (EUDP), a Danish program that uses public funding to co-finance energy technology solutions.

According to Fenagy, the project partners are also working to develop a reversible solution for cooling.

The DTI is also currently working with Danish manufacturer Unic Air and other stakeholders to develop an air-handling unit (AHU) with a reversible CO2 heat pump for office buildings.