R290 Heat Pump
A simplified scheme of the layout of the test rig built for a functional model of the split air-to-water HP for DHW preparation. Extracted from W. Monteleone et al. (2024)

Researchers Develop Façade-Integrated R290 Air-to-Water Heat Pump for Multi-Family Buildings

The heat pump is designed as an alternative to gas-fired and electric boilers to domestic hot water production in renovated buildings.

Researchers from the University of Innsbruck, Austria, have developed a façade-Integrated propane (R290) air-to-water heat pump designed for use in renovated multi-family residential buildings.

The heat pump was designed by William Monteleone, Fabian Ochs, Georgios Dermentzis and Samuel Breuss of the university’s Department of Structural Engineering and Material Sciences’s Unit for Energy Efficiency. The researchers detailed their work in the paper “Simulation-assisted design of a silent façade-integrated R290 mini-split heat pump,” published in the journal Applied Thermal Engineering.

The researchers said that in recent years, space and accessibility limitations had contributed to contractors installing decentralized gas-fired or “inefficient” electrical boilers for domestic hot water (DHW) production in renovated multi-family buildings in urban areas, with the authors noting that this has particularly been the case in Austria. They noted that façade integration can address issues of limited space and that the concept is becoming increasingly popular in multi-family building renovations.

“The trend is toward decentralizing HVAC into prefabricated façade systems so that they can be replaced anytime with minimal disturbances to the tenants and the building core,” the paper said. “Due to the possibility of performing off-site work, prefabricated modular façades not only have a better performance from a building physics perspective but also ensure considerably lower construction times.”

According to the paper, laboratory experiments demonstrated the system’s ability to provide hot water at a setpoint temperature of 45°C (113°F) at an ambient temperature of −7°C (19.4°F) with a COP of 2.5. At an ambient temperature of 10°C (50°F) the COP is 4.5. The heat pump is equipped with a flow-reversing valve for deicing.

The heat pump features a nominal heating capacity of 1.5kW (0.42TR) and is paired with a 200l (52.8gal) hot water storage tank. The researchers state that in situations where conserving space is a top priority, their modeling shows that a 120l (31.7gal) hot water storage tank can meet the needs of a three-person household.

“Currently, the European market does not provide alternatives to gas-fired or electric boilers for DHW preparation, which are minimally invasive, compact, modular and silent,” the study wrote. “Our proposed solution can contribute to the increase of the renovation rate in multi-family buildings and the decarbonisation of the building stock.”

The lab work

The heat pump’s development involved simulations and laboratory experiments conducted at three  levels: the component level, focusing on the outdoor unit design, the refrigerant cycle level and the overall heat pump system level, which includes the storage periphery and control mechanisms.

By employing computational fluid dynamics simulations, the research team was able to design and optimize the outdoor unit for compactness, flow homogeneity and reduced pressure drop, addressing the need for space efficiency and performance.

The functional model was installed in test cells at the University of Innsbruck. A movable external climate chamber enabled the heat pump to be tested at different outdoor temperatures. The sink temperature under those conditions was 30 to 50°C (86 to 122°F), with a nominal air volume flow of 350 m3/h(12,360.1ft3/h). A Coriolis mass flow meter for low-flow applications was installed in the refrigerant cycle to measure the refrigerant cycle accurately.

The researchers said the façade-integrated R290 heat pump will be tested under real-world conditions when it is installed as part of a demonstration project at a multi-family building in Vienna undergoing renovation.

“Currently, the European market does not provide alternatives to gas-fired or electric boilers for DHW preparation, which are minimally invasive, compact, modular and silent. Our proposed solution can contribute to the increase of the renovation rate in multi-family buildings and the decarbonisation of the building stock.”

Researchers from University of Innsbruck, Austria

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