Experimental thermal performance of a solar source heat-pump system for residential heating in cold climate region Kadir Bakirci a, * , Bedri Yuksel b a Department of Mechanical Engineering, Atatürk University, 25240 Erzurum, Turkey b Department of Mechanical Engineering, Balikesir University, 10569 Balikesir, Turkey article info Article history: Received 21 September 2010 Accepted 20 January 2011 Available online 1 February 2011 Keywords: Solar energy Experimental thermal performance Heat pump Cold climate Turkey abstract Solar source heat pump systems present tremendous environmental benefits when compared to the conventional systems for residential applications. In addition to not exhausting natural resources, their main advantage is, in most cases, total absence of almost any air emissions or waste products. In order to inves- tigate the performance of a solar source and energy stored heat-pump system in the province of Erzurum, an experimental set-up was constructed, which consisted of twelve flat-plate solar collector, a sensible heat energy storage tank, a water-to-water plate heat exchanger, a liquid-to-liquid vapor compression heat pump, water circulating pumps and other measurement equipments. The experiments were carried out from January to June of 2004 and, the collector efficiency (h c ), the heat pump coefficient of performance (COP) and the system performance (COPS) were calculated. In these months performed of the experiments, the outdoor temperature range varies from 10.8  C to 14.6  C. This study shows that the system could be used for residential heating in the province of Erzurum having the coldest climate of Turkey. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In the future the world’s energy supply must become more sustainable. This means that it must meet the basic needs of the poor worldwide without using up in this process the limited natural resources to the detriment of future generations. This can be achieved by a more efficient use of energy and relying on renewable sources of energy, particularly wind, hydropower, solar and geothermal energy [1]. Solar energy arriving on earth is the most fundamental renew- able energy source in nature. Solar energy occupies one of the most important places among various alternative energy sources [2]. Solar energy technologies offer a clean, renewable and domestic energy source, and are essential components of a sustainable energy future [3]. Costing of energy resources remains inequitable, as it does not include subsidies, or environmental and other consequences. Development of renewable energy, and of all energy systems for that matter, is dominated by the highly controlled, cost-unrelated, highly fluctuating and unpredictable conventional energy prices. Fuel and energy consumption in general must be significantly constrained, with due attention to prevention of the rebound effects [4]. Solar energy systems and heat pumps are two promising means of reducing the consumption of fossil energy resources (coal, petroleum etc.), and hopefully, the cost of delivered energy for residential heating. An intelligent extension is to try to combine the two to further reduce the cost of delivered energy. In general, it is widely believed that combined systems will save energy, but what is not often known is the magnitude of the possible energy saving and the value of those savings relative to the additional expense [5]. Although solar space heat is a mature technology and reliable design methods exist, the size and cost of an active solar heating system, which depend not only on the heat collected but also on the storage facilities, affect its successful utilization on a large scale. One attractive way to reduce the collection and storage require- ments is to utilize a solar source heat-pump system for heat supply, including domestic hot water and space heating. The low temper- ature thermal requirement of a heat pump makes it an excellent match for the use of low temperature solar energy and, as such, adds the benefit of a smaller solar energy system, with its lower associated cost [6]. The idea of combining the heat pump and solar energy has been proposed and the performance of these systems has been experimentally analyzed by several researchers in the literature [7e12]. Chaturvedi et al. [13] analyzed two-stage direct expansion solar- assisted heat pump for high temperature applications. Compari- sons between the two-stage and the single-stage direct expansion solar-assisted heat pump systems were performed and presented. * Corresponding author. Tel.: þ90 442 2314846; fax: þ90 442 2360957. E-mail address: abakirci@atauni.edu.tr (K. Bakirci). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2011.01.039 Applied Thermal Engineering 31 (2011) 1508e1518