Christoph Trinkl*, Wilfried Zorner*, Vic Hanby**

*Centre of Excellence for Solar Engineering at
Ingolstadt University of Applied Sciences (D)

Esplanade 10, D-85049 Ingolstadt, Tel +49 841 9348-372 Fax +49 841 9348-99372
E-Mail trinkl@fh-ingolstadt. de Internet www. solartechnik-ingolstadt. de

**Institute of Energy and Sustainable Development, De Montfort University Leicester (UK)

Given the finite nature of fossil fuel resources, the increasing pollutant emissions (particu­larly CO2) caused by their combustion and the change of the earth’s climate, innovative technologies for sustaining ecological heat and power generation, especially in the field of solar heating, are gaining more and more importance. Supported by the increase in costs for fossil energy over the last few years, solar heating systems and the use of environ­mental thermal energy have become viable technologies for heating applications. Starting with technologically simple domestic hot water supply, solar space heating with larger col­lector areas and more complex storage units for enlarged solar fraction have become in­creasingly popular. State-of-the-art solar heating systems, however, suffer from the neces­sity for an additional heat source, in most cases based on fossil fuel. The problem derives from the gap between solar radiation availability and thermal energy requirement (day/night and summer/winter shift).

In the course of research in regenerative energy systems for family houses in addition to solar systems, heat pump heating systems have been a focus of researchers for several years. As heat pumps use mechanical energy to transfer ambient energy from a source at a low temperature (o…+15°C) to a sink at a higher temperature (+35…+50°C) they con­sume less primary energy than oil or gas fired systems. For domestic heating systems the sources for a heat pump are mainly ambient air or the ground. The compressor is fre­quently driven by electrical energy. Today this “thermodynamic heating” can use up to 75% of thermal energy for domestic heating from ambient sources, while 25% are electri­cal energy. The coefficient of performance (COP: ratio of heat delivered by the heat pump and the electricity supplied to the compressor) of a heat pump and therewith the fraction of ambient energy depends on the temperature difference between the source and the sink. Apart from the saving of primary energy, heat pumps have the advantage of independence from fossil fuels. The heat pump market has grown steadily in Central Europe for many years.

As both solar heating and heat pumps are sustainable and innovative technologies in the field of domestic heating their combination has often been subject to research in many countries. These so-called “solar heat pump systems” were examined theoretically as well as experimentally in several research laboratories and experimental houses. There are three basic configurations of solar thermal collector and heat pump incorporation for do­mestic heating purposes, as shown in Figure 1. This paper concentrates on the series so­lar heat pump and on the parallel / series combination possibilities as the more innovative and promising options concerning an enhancement of solar fraction for domestic heating and hot water preparation. The basic advantage of the series and combination configura­tions is that the efficiency of the solar collector is enhanced, as it works with low inlet tem­perature which reduces the heat losses to the ambient. This effect was for example shown by Freeman et al. [1] and O’Dell [2] in simulation studies. Apart from that, the heat pump allows collector operation even during low-temperature and low-radiation periods and this extends its utilisation time considerably.