Optimisation of Heating System Powered by Air Heat Pump and Gas Condensing Boiler Hybrid Unit

Gas condensing boiler and air to water heat pump hybrid unit is an optimal way to introduce renewable energy resources in existing buildings. Two energy sources (gas & electricity) give hybrid unit higher flexibility in comparison to typical air to water heat pump. In hybrid solution air heat pump can be used in locations with low temperature heating seasons. Hybrid unit can output higher heat carrier temperatures, because of this, it can be used in combination with older radiator heating systems. There are many parameters that can influence the performance of hybrid heating unit. This paper investigates heat terminal type, heat carrier temperature, and outdoor switchover temperature setting (outdoor temperature at which hybrid unit switches from electricity to fossil fuel) influence on air to water heat pump and gas condensing boiler hybrid heating unit performance parameters (total efficiency - ηhybrid and primary energy factor - PEFhhp). Hybrid heating units performance is evaluated by using a computer model created in program IDA ice 4.8. The created computer model represents a real building, located in Latvia, that uses the previously mentioned hybrid heating unit. The model is verified by comparing its results with energy meter data from the real building, for time period from 01.03.2022 to 28.02.2023.The verified model is used to simulate how hybrid heating units performance is influenced by changes in heating terminal type, heat carrier temperature and outdoor switchover temperature setting. According to simulation data, at constant heat carrier temperature, heat terminal type has no influence on hybrid heating unit’s performance parameters. It has been found that increased heating system volume can reduce hybrid heating unit’s run time. In this case replacing panel radiators with floor heating, there is a 33% reduction in unit’s annual running time. In simulated scenarios, heat carrier temperature reduction by 15°C, increases ηhybrid by 8.7% and decreases PEFhhp by 17.5 % (at temperature graph 40/35°C). Switch over temperature increase from -7 to 3°C decreases ηhybrid by 47% and increases PEFhhp 7 %. Switch over temperature increase also reduces ηhybrid and PEFhhp change magnitude, when changing heat carrier temperature graphs. When changing the temperature graph from 40/35 to 55/50 °C the changes are as follows: at switchover temperature setting of -7°C,  drops by 14,33 %, but PEFhhp increases by 23,42%; at switchover temperature setting of -2°C (actual setting),  drops by 8,7 %, but PEFhhp increases by 17,51%; at switchover temperature setting of +3°C,  drops by 1,74 %, but PEFhhp increases by 6,45%.