Modular low-capacity R-290 Heat Pump water heaters enhanced with compact PCM thermal storage [22]

Almost half of European buildings have boilers installed before 1992. To achieve the EU's climate neutrality targets, the European building market needs a radical shift towards sustainable thermal energy systems.

At the AIT Austrian Institute of Technology GmbH, innovative Heat Pump solutions are developed in collaboration with industrial partners across Europe to replace gas boilers in large multi-family houses, combining ease of installation, modularity, ecological refrigerants, thermal storage and acoustic optimisation.

The “Gasthermenersatz” project together with Ochsner Wärmepumpen GmbH aims to develop and validate an innovative compact Heat Pump concept with refrigeration circuit modules connected in series and in parallel. This compact, decentralised solution is suitable not only for heating and cooling, but also for domestic hot water supply in large residential buildings. The modular design ensures ease of installation and gradual replacement for each flat, without affecting the rest of the flats. The technical solution uses environmental-friendly refrigerants. A “smart” controller enables efficient communication between the heating systems to ensure a maximum degree of efficiency. The acoustics design of the refrigeration circuit module is optimised to minimise sound emissions of the Heat Pump.

In the ongoing European project “HYSTORE” the solution is further developed with focus on a domestic hot water (DHW) booster Heat Pump for multi-family houses. The Heat Pump water heater is enhanced by a compact storage module with a refrigerant-PCM-water heat exchanger and a nominal storage capacity of 6-9 kWh. The innovative integration of a high energy-dense biobased phase change material (PCM) enables a more efficient supply of domestic hot water (DHW) at 50 °C, using the floor heating return flow as a heat source for the Heat Pump. Two modules are built with a 150 g charge of R290 as refrigerant. The design of the high performance PCM storage includes aluminum Micro/Multi Port Extrusion (MPE) tubes for the water and refrigerant sides, and a secondary fresh water circuit to prevent aluminum corrosion when in contact with DHW. The solution is currently under development and will be demonstrated in a multi-family house in St. Barbara (Austria), to replace the gas boiler currently in use.

The projects were respectively funded in the framework of the programme “Stadt der Zukunft” (Gasthermenersatz, No. 886973) and from the European Union Horizon Europe Programme (HYSTORE, No. 101096789).