Direct use of solar energy as heat source for a heat pump in comparison to a conventional parallel solar air heat pump system

• Parallel and serial solar HP systems for heating purposes (low energy building).
• Evaluated through transient system simulations (performance figures).
• Heat demand of about 45 kW h/(m2 a) and a gross floor area of 140 m2.
• The combination can be an efficient and attractive solution.
• Solar heat is also used as heat source at the evaporator of the HP.

In this paper different combinations of solar energy and heat pump systems are compared and investigated through transient system simulations. The focus is on a small capacity heat pump (HP) with a heating capacity rate of 5.36 kW. The building (single family house 140 m2) which are considered in this paper have a space heating demand of about 45 kW h/m2 a. Based on a conventional air source HP and a parallel solar air source HP system, serial solutions for the combination of solar-HP systems are defined and analysed. For the consideration and evaluation of different systems through transient system simulations, a semi-physical HP-model is used, which offers the possibility to use two evaporators in series. With a combined parallel solar air source HP system the system performance (SPFSystem = 3.65) can be increased significantly compared to a conventional air source HP system (SPFSystem = 2.55). Unglazed selectively coated absorbers as source for the HP offer the advantage, that the collector can be used as an air heat exchanger. If solar radiation is available, higher temperatures at the evaporator of the HP can be achieved, compared to a conventional air source HP system. By the integration of unglazed solar absorbers as source for the HP the HP performance can be increased significantly (SPFHP increases from 3.25 up to 3.55 compared to a conventional air source HP).