Energy and Buildings 126 (2016) 2–13 Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild Simulation and optimization study on a solar space heating system combined with a low temperature ASHP for single family rural residential houses in Beijing Jie Deng a,b,∗ , Zhiyong Tian b , Jianhua Fan b , Ming Yang a , Simon Furbo b , Zhifeng Wang a a Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, PR China b Department of Civil Engineering, Technical University of Denmark, Brovej 118, Kgs. Lyngby, DK 2800, Denmark a r t i c l e i n f o Article history: Received 26 March 2016 Received in revised form 6 May 2016 Accepted 7 May 2016 Available online 11 May 2016 Keywords: Solar space heating for single family houses Air source heat pump (ASHP) System parameter optimization Economic analysis a b s t r a c t A pilot project of the solar water heating system combined with a low temperature air source heat pump (ASHP) unit was established in 2014 in a detached residential house in the rural region of Beijing, in order to investigate the system application prospect for single family houses via system optimization design and economic analysis. The established system was comprised of the glass heat-pipe based evacuated tube solar collectors with a gross area of 18.8 m 2 and an ASHP with a stated heating power of 8 kW for the space heating of a single family rural house of 81.4 m 2 . The dynamic thermal performance of the pilot system was measured for continuous 20 days under typical cold climate conditions and the test data was used to validate the TRNSYS simulation model established. On the basis of model validation, system optimizations of both the existing pilot household and the typical rural house with good building insulation were undertaken to figure out the system economical efficiency in the rural regions of Beijing. The results show that the payback periods of the solar space heating system combined with the ASHP with the collector areas 15.04–22.56 m 2 are 17.3–22.4 years for the established pilot household on the current electricity price level of 0.5 RMB/kWh, comparing with the reference condition of the fully ASHP space heating. It is further found that the equivalent solar heat price per kWh is too high under the current solar market cost price and collector technology. To put forward the integrated solar space heating for reducing carbon emission, it is suggested that the Beijing municipal government should offer some financial subsidy to compensate the equivalent solar heat price per kWh. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Rural buildings in China account for more than half of the total building energy consumptions of the country in recent years [1]. It is reported that the use of coal and biomass for space heating and cooking may contribute 15–20% of primary PM 2.5 emissions in Beijing [2]. It is therefore an urgent demand to develop building energy conservation and renewable energy utilization for carbon emission reduction in the rural regions of China as the increase of frequently appeared haze days contributing to the environment deterioration. Although the government has been advocating the retrofit of existing residential buildings for energy conservation ∗ Corresponding author at: Institute of Electrical Engineering (IEE), Chinese Academy of Sciences (CAS), No. 6, Beier Alley, Zhongguancun, Haidian District, Bei- jing 100190, PR China. E-mail address: deng-jie2@163.com (J. Deng). since 2005 via plenty of policy supporting projects, there is still a huge potential to push forward energy savings and renewable energy in the rural residential houses due to many obstacles [3]. Solar space heating combined with some auxiliary sources such as the air-source heat pump, biomass boiler is one of the promis- ing ways of developing renewable energy and energy saving in the rural region of northern China. Shan et al. [4] studied the thermal performance of a combined solar heating system integrated with the ASHP in a simulated rural house. They measured the energy supply of the system for space heating in two different running modes under typical cold climate conditions of Beijing. And they successfully reduced 25% electricity consumption of the ASHP by reasonably adjusting the running procedures of the system. How- ever, the economical payback period of the solar space heating system was not considered. The economical efficiency of the solar space heating combined with ASHP, which is a key factor in pro- moting the system application in rural regions of northern China, should be pay more attention on. Li et al. [5] studied an active solar http://dx.doi.org/10.1016/j.enbuild.2016.05.019 0378-7788/© 2016 Elsevier B.V. All rights reserved.