Low-GWP refrigerants setting the benchmark in heat pump efficiency


17 February 2022

A White Paper published by The Chemours Company

Meeting Environmental Goals for New Builds and Renovations Driven by environmental regulations such as the F-Gas and the Kigali amendment to the Montreal Protocol, Heat Pump OEMs are seeking alternative refrigerant solutions. While regulations mandate the adoption of low-GWP refrigerants, overall energy efficiency remains a major factor in both the selection of refrigerants, and in Heat Pump system design.

As part of the European Green Deal, the 2030 greenhouse gas emission reduction target, including emissions and removals, was set to at least 55 % of 1990-level emissions. Considering that almost 50 % of end energy consumption in the EU is apportioned to heating and cooling, of which 80 % goes to buildings, Heat Pump technology is poised to be a standard-bearer in achieving these consequential targets.

European Commission: “…the integration of renewable and surplus energy into buildings. … photovoltaic solar panels on the roofs, thermal storage and Heat Pumps reduced energy costs for households.” in: Communication from the Commission to the European Economic and Social Committee and the Committee of the Regions, A Renovation Wave for Europe - greening our buildings, creating jobs, improving lives, COM (2020) 662 final, Brussels, 14.10.2020.

Thomas Nowak (EHPA): “100 % Renewable Energy with Heat Pumps is feasible today.” in: Heat Pumps; Integrating technologies to decarbonize heating and cooling, European Copper Institute, Autumn 2018.

Simon Harvey: “Industrial HPs (Heat Pumps) have an important role to play!” in: The role of Heat Pumps for decarbonization of industrial processes, 12th IEA Heat Pump Conference 2017, Rotterdam

European Commission: “The most cost-effective and beneficial heating or cooling solution can be defined as: (among others) - Heat Pumps,…” in: Annexes to the Commission Recommendation on the content of the comprehensive assessment of the potential for efficient heating and cooling under Article 14 of Directive 2012/27/EU, C(2019) 6625 final, ANNEX-ES 1 to 7, Brussels, 25.9.2019. 2 3 Low-GWP HFO refrigerants such as R-454B and R-454C can aid in increasing system efficiency, expanding operating temperature range and reducing CO2 emissions, while providing notable safety improvements over A3-class refrigerants.

These characteristics position low-GWP refrigerants as the ideal solutions not only for new buildings, but for renovation projects as well. This is particularly important in Europe, as the proportion of building renovations compared with new builds is quite significant. For building renovations, high flow temperatures (for existing radiator-based heating systems) are essential for convenient and cost- and energy-efficient replacements of fossil fuel boilers, eliminating the need for additional electric or fossil-fuel booster heaters during the colder months.

Although there is significant potential for increasing system efficiency by using A2L refrigerants, drop-in tests have shown that utilizing a high-performance refrigerant in a standard Heat Pump system, while possible, does not provide the efficiency gains of a purpose-built system.

For maximum energy economy and environmental benefits, Heat Pump systems should be designed around refrigerants, not in isolation.

Special Considerations for Building Renovation

Heating Capacity Needs

For a typical new Central-European construction, heating requirements are around 35 W/m2. While for existing buildings, depending on the degree of thermal insulation, a relative heating capacity of 100 to 150 W/ m² is estimated (https://www.haustechnikdialog.de/SHKwissen/1410/ Spezifische-Heizlast).

This leads to absolute heating capacity requirements of between 5 to 8 kW for heating systems in new buildings (including sanitary hot water requirements) and of 10 to 15 kW for heating systems in existing buildings, also including sanitary hot water usage.

New buildings versus building renovations in Germany from 2001 to 2019 (Breitkopf, 2020)


Temperature Level Requirements

In residential applications and new buildings, Heat Pumps often operate at 35 °C for underfloor heating and 60 °C for sanitary hot water. In cases of building renovations, higher temperatures are necessary to replace fuel or gas boilers, with about 55 °C for radiator heating and 60 °C for sanitary hot water. The target is to provide univalent solutions so as to avoid efficiency losses due to usage of direct electrical heaters, and to avoid an increase in CO2 emissions due to the adoption of an additional gas boiler at low outside temperatures. This requires a high temperature lift at low environmental temperatures, e.g. from -25 °C to +60 °C. Crucially, this required high temperature lift cannot be provided by all refrigerants.

Performance Comparison of Refrigerants

Comparison of R-410A, R-454B, R-452B, R-454C and R-32 Figure 2 shows the capacity calculation results from the previously mentioned tool for the same compressor displacement. With the exception of R-454C, the capacities are close to R-410A. For R-454C, a larger compressor would be required to achieve the same heating capacity, when compared with R-410A.

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COP calculation results from the aforementioned tool. For R-454B and R-452B, the COP at higher ambient temperatures is greater than R-410A, while at lower ambient temperatures, it is slightly lower than R-410A.

The behaviour of R-454B and R-452B is very similar to that of R-410A and the required compressor technology is also similar, if not identical. When using R-32, high flow temperatures can be achieved, but due to the very high discharge temperature, the maximum requested temperature lift (-25 °C to +60 °C) cannot be achieved without added measures to prevent compressor overheating For R-32, the COP drops considerably from high to lower ambient temperature conditions. The only refrigerant performing above the values of R-410A for all operating conditions is R-454C, which also boasts the lowest GWP (148).

For the purposes of this paper, a calculation tool was developed to compare the performance of different refrigerants for Heat Pump applications. The aforementioned tool, developed in Excel®, uses Refprop 10.0 (Reference Fluid Thermodynamic and Transport Properties) for calculating fluid properties. It is based on basic thermodynamic equations linking pressure, temperature, enthalpy and entropy to establish the capacity and coefficient of performance (COP) of a thermodynamic cycle.

Drop-in tests performed on Air to Water (A/W) (R-410A) and Brine to Water (B/W) (R-407C) Heat Pumps by the Fraunhofer ISE Institute demonstrate that simply changing refrigerants without any modification to the Heat Pump system generally does not lead to any performance improvements.

Under some operating conditions, the drop-in refrigerant(s) performed better than the original, whereas under other conditions, the performance worsened. The discrepancies between theoretical performance calculations and actual test results from drop-in trials have been reported by Küpper et. al. (2021). Operating range of R-410A, R-454B, R-452B, R-454C and R-32 (compressor envelopes) Today, R-410A can be taken as a standard reference refrigerant for Heat Pump applications.

With dedicated technologies like enhanced vapor injection or enhanced liquid injection (EVI / ELI) it is possible to achieve the requested temperature lift of between -25 °C to +60 °C. This is sufficient for new buildings, which require 35 °C water temperature for underfloor heating and 60 °C for sanitary hot water. At lower ambient temperatures however, EVI or ELI technology is required to achieve high flow temperature.

Without these additional technologies, only 40 °C to 45 °C would be achievable. Unfortunately, the COP will usually not increase during and due to EVI operation. For renovated buildings at temperate and colder European climate conditions, an additional electrical heater or parallel gas boiler would be necessary to reach the heating capacity and temperature requirements.

. This additional protection is usually detrimental to both the capacity and efficiency of the system. R-454C can be operated with standard one-stage compressors, foregoing EVI or ELI technologies, and still achieve flow temperatures of up to 75 °C, even at very low ambient temperatures.

This makes R-454C an ideal choice for:

• Building renovations, as the existing water radiators often require relatively high flow temperatures for optimum functionality.

• Sanitary hot water production, as the additional legionella controls are not needed

• New buildings as the same compressor can be used for hot water production and space heating.

7 Emissions Impact in Various Countries

Although there is no combustion in a vapor compression cycle Heat Pump, direct emissions caused by leaking refrigerant can cause GWP. Indirect emissions are also a factor, due to the electrical power consumption of the Heat Pump. Both sources of emissions are addressed in the following chapter. Leakage rates of Heat Pumps (direct emissions)

Direct emissions of Heat Pumps can be caused by refrigerant leaks. The decisive factor here is the GWP of the refrigerant and the leakage rate. An analysis of F-Gas logbooks in March 2014 determined that annual leakage rates from Heat Pumps were approximately 3.8 % for nondomestic applications and 3.5 % for domestic applications (Eunomia, 2014).

Based on this annual leakage rate of 3.5 %, the direct emissions over the whole life cycle of the system (assuming a 10-year lifecycle) can be set at 35 % of the initial refrigerant charge. We will consider the emissions for R-410A (GWP 2088), representing the standard industry reference, and for R-454C (GWP 148) representing a long-term solution. In Heat Pumps with a 5 to 10 kW heating capacity, which represent around 60 % of the installed market, the refrigerant charge can be estimated to be between 1.8 to 2 kg.

For Heat Pumps of 10 to 20 kW of heating capacity, which represent about 30 % of the installed market, the refrigerant charge can be estimated to be about 2.5 to 3 kg. As a worst-case scenario, the highest values were used. The lower capacity range (5 to 10 kW) is generally representative of new building applications, while the higher capacity (10 to 20 kW) represents building renovation applications.

For the full paper visit: www.chemours.com