It is likely that in sector of heat pumps under 12 kW, in the future propane will establish itself as main refrigerant, a gas that features excellent thermodynamic properties and a low GWP value, therefore offering a great potential to satisfy the sector decarbonization requirements. The drawback is its flammability. To minimize this inconvenient, the charge reduction to less than 150 g is a promising approach.
LC150: record efficiencies
In Germany, the Institute Fraunhofer, in collaboration with some manufacturers and suppliers of heat pumps, has just accomplished the LC150 research project (“low charge 150 g”), funded by the German Federal Ministry for Economy and Climate Protection (BMWi), whose goal was developing a standardized refrigeration circuit with low refrigerant content, with propane as work fluid.
The results obtained are exceptional: the best of the various brine-to-water heat pumps prototypes manufactured during the project has a heating capacity of 12.8 kilowatts (and of about 10kW of cooling) obtained with only 124 grams of propane. This results in a specific refrigerant charge of around 10 g/kW where the project target was decreasing the specific refrigerant charge to 15-30 grams/kilowatt, goal widely exceeded. We can better understand the exceptionality of this result if we consider that the best devices on the market have a capacity ranging from 60 to 80 grams/kW. «The one indicated is the best result achieved, but we have also implemented some prototypes with capacity of 8-9 kW with 150 grams, which is anyway always an excellent result» states Clemens Dankwerth, Project Manager of LC150 together with his colleagues Lena Schnabel and Katharina Morawietz.
How have these results been reached? «Due to the collaboration with manufacturing companies, we have considered all available components on the market and we have assembled them in the most various plant engineering configurations, measuring the efficiency of each of them. We have invented nothing new and we have not manufactured specific components precisely because they wanted to start from what available on the market today».
Change of perspective
What characterizes the configuration of the most efficient prototype? Oil reduction, compact circuit, compressor at the highest admissible revolutions, asymmetric exchangers are the ingredients that have allowed reaching this efficiency.
From the laboratory to the field
What is the destiny of this prototype? «The companies that have taken part in the project can use these prototypes and the competences deriving from the project as they prefer, to be able to manufacture their own machines that then they will release on the market». The question is whether these so exceptional efficiencies, reached in laboratory, will be obtained on the field, too. Dankwerth affirms: «For the best prototype, we have used an automotive compressor and we have always made it operate at 120-140 Hertz. This is not possible in the reality, where we can reach 8-9 kW with 150 grams, which is anyway always much better than what available on the market nowadays». Moreover, the one manufactured in the LC150 project is a brine-to-water heat pump that can be implemented in a very compact manner and needs less refrigerant than an air-water heat pump but at the same time it involves a more difficult installation because the thermal energy source – water – is not always available. «If we had to build an air-water heat pump we should clearly increase the refrigerant charge»
Foe what uses?
The heat pump developed in the LC150 project is a brine-to-water pump for heating and cooling. «It is perfectly suitable for satisfying the requirements of a single-family cottage or condominium apartments. In this case, the problem might eventually be to find water as thermal energy source, as it is not always and everywhere at disposal».
However, if we want to carry out a real decarbonization of the European residential sector, it is necessary to proceed to equipping with heat pumps also buildings with apartments where water is not necessarily present.
Propane in the future of the building industry
The main message issued by the LC150 project is that with 150 grams of propane maximum it is possible to satisfy the heating (and cooling) requirements of each single house and of apartments in condominiums.
If we consider legislative and technological developments, we can state that the propane will become an increasingly diffused refrigerant in the European building sector.
