For Heat Pump Water Heaters no alternative low GWP refrigerant at this moment fulfils all the requirements at once.
Alternative refrigerants for Heat Pump Water Heaters to the currently used refrigerants (R134a, R410A) are:
- Carbon dioxide (R744) and Propane (R290) are natural refrigerants, which can be used to reach higher output temperatures up to 80°C.
- R152a, R1234yf, R1234ze(E) and Ammonia are interesting alternatives for DHW HP, not yet broadly in use but already tested in R&D projects, while R32 is strongly promoted by a number of manufacturers.
In the choice of refrigerants the condenser configuration exchanging heat with the storage tank and the risks (like flammability) of the refrigerant play an important role. Oak Ridge National Laboratory (ORNL) has done a number of studies in this area and great leap forward with Propane has been achieved with research by Kungliga Tekniska Högskolan (KTH) among others.
GWP versus LCCP
For HPWHs not much focused research is available in which results show which refrigerant is the ‘best solution’. The Global Warming Potential (GWP) can be a useful metric to compare different refrigerants. However, it may overestimate the benefits of low GWP refrigerant to environment, as it does not take into account many other affecting factors. Such factors, like the use of high efficiency components and system design, such as the optimal storage size, stratification and condenser design have a big influence on the overall energy efficiency of the system. Moreover, ensuring proper installation, optimised control and operation, under all common operating and climate conditions are factors not directly related to the technology itself and the choice of refrigerant. In the end, the overall energy use of the installation is an important factor in the calculation of the Life Cycle Climate Performance (LCCP) or the Total Equivalent Warming Impact (TEWI) factor. At the 2019 IIR Conference in Montréal a presentation on this topic was give by dr. Pavel Makhnatch (KTH).
The main policies worldwide focus on banning the use of refrigerants with a high GWP. However this does not necessarily result in lowering climate impact, expressed in term of LCCP value. Thus, LCCP evaluation can be necessary in order to account for the entire climate impact of a system when selecting an alternative refrigerant.
In 2018 the Swedish Kyl & Värmepumpföreningen (SKVP) requested that the Swedish state apply for exemptions from the European Union pursuant to Article 15.4 of the F-Gas Regulation for products listed in the Ecodesign Directive Lot 1 (boilers and heat pumps), as well as Lot2 (water heaters and accumulator tanks). This is to give the heat pump industry access to refrigerants outside the F-Gas Regulation quota system in order to ensure a qualitative and energy efficient transition to new low-GWP refrigerants.
Needed R&D
Although manufacturers are active and well aware of the need to develop new technologies with alternatives, further international collaboration on alteraniteve refrigerants for Heat Pump Water Heaters is of importance. At the 2019 IIR Conference a number of papers were presented, one of these papers focusing on the application of R290 as refrigerant for Heat Pump Water Heaters.
Annex Report on Refrigerants
The Annex has in its collaboration analysed the work done on refrigerants for Heat Pump Water Heaters. The Final Report on this is available and can be downloaded.