Energy and economic evaluation of a solar assisted ground source heat pump system for a north Mediterranean city

Abstract

In this study, a PVT based solar assisted ground source heat pump (SAGSHP) system was investigated regarding its energy performance and cost-effectiveness for the city of Thessaloniki (Greece). The SAGSHP system was set to cover the space heating and domestic hot water needs for a low-rise dwelling. A mathematic model formulated in TRNSYS was used with the aim to carry out parametric analysis by varying the number of the PVTs. It is worth noting that, two of the most important components of the employed model, the PVT collector and the geothermal heat exchanger, have already been validated via experimental data. Simulations were conducted and through the results seven energy metrics were estimated, with the objective to examine the system’s energy performance from various perspectives. The SAGSHP system with 16 PVTs was found capable to covering 73% of the heating load and to generate 1.22 times more electricity than that consumed by the system. The electricity yield of PVTs was not affected throughout the parametric analysis, and the maximum specific productivity was estimated at 301.5 kWhe PVT−1 per year. The results suggest that a SAGSHP system equipped with about 14 PVTs can reach energy self-sufficiency. As regards the economics of the SAGSHP system, this was compared with a natural gas boiler system via two methods, the life cycle cost (LCC) and the life cycle savings (LCS). A sensitivity analysis with major economic parameters of the systems was carried out. It was found that the cost-effectiveness of the SAGSHP system is influenced mainly by its capital cost and by the price of the natural gas. Systems equipped with less than 12 PVTs can be cost-competitive by subsiding from 8% up to 42% of their capital cost. Also, system with more than 12 collectors were found of more benefit than the smaller ones, in the case where feed-in-tariff schemes are applied, or the bank loan’s interest rate is low. It can be concluded that, the proposed system can be an attractive monetary solution for covering the heating load in comparable dwellings with a similar climate to Thessaloniki.