Development of a gas absorption heat pump for residential applications

Thermally Driven Heat Pumps represent an option to reduce the energy consumption for space heating and domestic hot water in hard-to-decarbonize buildings without impacting the electrical grid and utilizing the current and future gaseous energy vectors with high efficiency. Ariston Group and Politecnico di Milano developed a gas absorption heat pump for the residential market, exploiting design and manufacturing solutions to enable large-scale production and introducing technical features to assure high performance over the entire working range. In particular, the use of a variable restrictor setup coupled with a patented solution, called “booster”, can reduce the temperature of the generator at high load and high lift conditions, enabling the heat pump to provide the nominal capacity from -22 °C to +40 °C of outdoor air temperature, with supply temperature up to 70 °C. Moreover, coupled with a specifically designed combustion system, the heat pump can modulate at 1:6 ratio of its nominal capacity. This feature makes it possible to maintain high efficiency also at part load conditions, avoiding the on-off operation and making redundant the installation of inertial buffer. Additionally, an innovative strategy to perform the defrosting of the air-sourced heat exchanger without the need of acting on the thermodynamic cycle has been developed. This allows defrosting operations extremely fast, while offering an almost negligible effect on the heat pump performance and substantially no interruption to the heating service and contributing to the elimination of the need to install an inertial buffer. The thermodynamic core of the appliance was built targeting large scale production. It allows for high specific capacity (kg/kW) and a small footprint (m2/kW) with the ability to serve nominal capacities ranging from 8 to 15 kW based on the configurations. Laboratory test to assess the performances based on the European Standard EN 12309 returned a seasonal gas utilization efficiency on the net calorific of 1.50, a seasonal primary energy ratio of 1.27, and extremely low electrical consumption for the auxiliaries.