Afjei, Thomas
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Seasonal Performance of a Combined Solar, Heat Pump and Latent Heat Storage System
This paper investigates the seasonal performance of a combined solar, heat pump and latent heat storage system for dwellings. This combination could provide a viable alternative to common brine-water heat pump systems with a borehole heat exchanger (BHX). Since the latent heat storage, or ice storage, is filled with pure water, it can also be used in (but is not limited to) places where a BHX is prohibited, e.g. water protection areas. The aim of this work is to find and evaluate given system configurations for three different annual heat demands that reach seasonal performance factors (SPF) comparable to those of BHX heat pump systems, i.e. SPF ~ 4.0. A simulation study using MATLAB®/SIMULINK® and the CARNOT Blockset is conducted. Technologies considered in the simulation study are a brine-water heat pump, unglazed solar collectors as source for the heat pump and a buried ice storage that serves as alternative source for the heat pump and is regenerated by the collectors. Unglazed collectors use solar irradiation and ambient heat (via convective heat exchange) for heat generation. Additionally, thermal coupling of the ice storage to the surrounding soil which also contributes to the regeneration of the system is considered. The simulation models of this system have been validated with laboratory and field test data. The heat generated by the heat pump is used for space heating and domestic hot water preparation of single family houses with different heat loads which have been defined in the framework of IEA SHC Task 44 / HPP Annex 38 "Solar and heat pump systems". To obtain the desired SPF for each building type the power output of the heat pump with the corresponding size of the collector field is varied. For each building a configuration is found that yields a SPF ~ 4.0. A high SPF can only be reached as long as no backup heating is needed, which means, that the ice storage should never be completely discharged, i.e. completely frozen. This requires significant contributions from the solar collector, especially during the heating period.