| Work Detail |
Austrian researchers have developed a new heat pump system for residential applications that achieves a coefficient of performance between 2.82 and 3.11 at an outdoor air temperature of 10ºC and 20ºC, respectively. They also verified that the system was capable of offering comfort conditions at all the outdoor temperatures tested.
A group of researchers from the University of Innsbruck (Austria) has designed a façade-integrated split-type heat pump (HP) for the production of domestic hot water (DHW) that is reportedly minimally invasive, compact, modular and silent.
The scientists explained that split-type HP integrated into the façade can be a viable alternative to gas boilers in rehabilitated buildings when installation space is limited. “Due to the possibility of carrying out works outside the premises, prefabricated modular facades not only work better from the point of view of construction physics, but also guarantee a considerably shorter construction time,” they added.
The research team explained that they designed the system using a holistic approach consisting of simulations and laboratory work to evaluate components, refrigerant cycles, and system configuration. Their analysis took into account the fluid dynamics and performance of the outdoor unit, as well as its noise emissions and dynamic interaction with the DHW user.
The system has a nominal heat output of 15 kW and uses propane (R290) as a refrigerant. It consists of an outdoor unit and an indoor unit with a 200-liter domestic hot water storage tank. The system also includes a compressor, condenser, and split ductwork.
“The choice of a square non-pressurized tank was adopted to improve the compactness of the interior unit and allow some flexibility in its design,” the academics noted. “With the current system configuration, it was possible to achieve a minimum air temperature in the cold room of 10°C. For this reason, the measurements were carried out at 10, 15 and 20 ºC of cold air temperature, while the ambient temperature of the chamber was kept constant at 20 ºC.”
The system also uses a 2-way solenoid valve for water extraction, three Pt100 temperature sensors to measure the temperature of the water tank and four axial fans with low consumption and noise emissions.
The researchers carried out a series of simulations and tests with MATLAB and Simulink programs. The analysis showed that the system can satisfy the DHW demand of a small home already at -7 ºC outdoor air temperature with a set temperature of 45 ºC. They also found that the ideal tank capacity is between 90 L and 110 L.
“In cases where the compactness of the DHW is the highest priority, a 90-liter tank could be opted for, even if some post-heating is required at lower outside air temperatures,” they specified. “On the other hand, to increase flexibility and depend less on user behavior, the optimal choice is a larger storage volume (e.g. 120 L).”
The scientists also verified that the system presents an air flow pattern in the evaporator that approaches a completely homogeneous one. In addition, they verified that it can supply the necessary hot water in an outdoor air temperature range of 10 ºC to 20 ºC, with a COP of the system obtained of 2.82 and 3.11, respectively. “The functional model developed was capable of providing comfort conditions at all tested outdoor temperatures,” they added.
They described the prototype in the article “ Simulation-assisted design of a silent façade- integrated R290 mini-split heat pump ,” published in Applied Thermal Engineering . “The proposed façade-integrated HP R290 mini-split is to be installed in a demonstration project of a multi-family building renovation in Vienna, where it will be compared with centralized and semi-centralized HP concepts based on simulations and monitoring data,” they concluded. |
