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- PublicationSystem efficiency of PVT-collector driven heat pumpsStandard heat pump (HP) systems with horizontal ground heat exchangers (HGHE) are commonly designed based on arbitrary knowledge gained over time and the use of the rule of thumb. Where an undersizing of the HGHE occurs, the HP efficiencies are lowered. Undersizing could result as a consequence of underestimating the soils thermal conductivity. Therefore, this paper considers the combined photovoltaic and solar thermal (PVT) collectors as an extension to standard HP heating systems with a HGHE in single-family houses with the possibility of improving the COP of the HP at a later stage and effortlessly. With the implemented hydronic scheme, the PVT-collector is also used to regenerate the soil around the ground to increase the temperature level of the heat source resulting in improved performance. However, the efficiency potential of the PV-Cells due to active cooling of the modules is analyzed. The results show an increase of the seasonal performance factor (SPF) of 4.1 % and higher electric energy output of 4.4% due to active cooling of the PV-Cells while energy consumption of the regeneration pump is covered.
- PublicationSystem efficiency of pvt collector-driven heat pumpsThe use of standard heat pump (HP) systems offers an efficient option to replace conventional heating systems (e.g. oil and gas boilers) for space heating and domestic hot water. Due to the higher noise emissions and the lower overall energy efficiency of air-to-water heat pumps, the use of ground-coupled heat pump systems is increasingly in demand. The cost-efficient dimensioning of horizontal ground heat exchanger (HGHE) systems, considering possible solar waste heat potentials to improve regeneration behaviour, is particularly challenging. The reason for this is the complex system and control engineering optimisation possibilities resulting from the dynamic heat transport behaviour of the horizontal ground heat exchanger. Essential influencing variables such as the water content of the soil due to the groundwater level, rainwater infiltration and surface evaporation can only be described with massive effort using the model equations of the unsaturated zones. However, these variables are necessary to obtain a better fundamental understanding of the usable storage potential of solar-coupled systems and to be able to derive targeted optimisations at the system level. Therefore, the waste heat utilisation potential of PVT collectors for the regeneration of heat pump coupled horizontal ground heat exchanger systems are analysed employing simulations. For this purpose, a PVT-collector model and a HGHE model based on a single-family were developed and validated by experimental investigations. Based on this, a system simulation model consisting of the components PVT-collector, heat pump, heat delivery system, HGHE and the corresponding control units were built using TRNSYS. With the help of the simulation model, parameter studies were carried out, and the main factors influencing the overall energy efficiency (COP) of the system and the seasonal performance factors (SPF) were identified. Furthermore, the solar waste heat utilisation potential of the PVT collectors was analysed to increase the efficiency of the heat pump system.
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