Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Research Paper Dynamic modelling and performance evaluation of a direct-expansion solar- assisted heat pump for LPG vaporisation applications Guo-Hua Shi a,b, ⁎ , Lu Aye b , Rui Dai a , Xian-Jun Du c , Jiang-Jiang Wang a a Department of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China b Renewable Energy and Energy Efficiency Group, Department of Infrastructure Engineering Melbourne School of Engineering, The University of Melbourne, Victoria 3010, Australia c College of Electrical and Information Engineering, Lanzhou University of Technology, Lanzhou 730050, China HIGHLIGHTS • An LPG vaporisation system using DX-SAHP with six operating modes is investigated. • A numerical model is developed to estimate the performances of the system. • The system performs well under various weather and gas load conditions. • Weather conditions have significant influences on the operating mode and its running time. • The system has significant energy conservation potential. ARTICLE INFO Keywords: Solar-assisted heat pump LPG vaporisation Operation characteristics Coefficient of performance Collector efficiency ABSTRACT This study investigated a novel LPG vaporisation system utilising direct-expansion solar-assisted heat pump (DX- SAHPV) 1 for supplying residential gas. The DX-SAHPV applies a collector-evaporator to obtain heat energy from both solar radiation and ambient air to produce hot water to vaporise LPG liquid. It can operate in six operating modes depending on the weather and gas load conditions. In this study, a dynamic model and control strategies realising the mode switching were developed to carry out the operating performance evaluation of the system. By applying the typical meteorological year data and the gas load data of a community in Beijing, China, the performance of the DX-SAHPV was evaluated and analysed for the whole year and two selected days. The simulation results show that the system can vaporise adequate LPG liquid for the community throughout the year. The solar energy contribution accounts for approximately 68% of the total heat energy for the water heated vaporisation. It was also found that the DX-SAHP obtains average monthly values of COP ranging from 2.72 to 3.37 and solar collector efficiency varying between 93 and 152%. In addition, which mode the system operates at any time on selected days was predicted and the running time of each mode in each month was discussed. 1. Introduction With the population growth and the increasing requirements on enhancing living conditions, global energy consumption has risen substantially. In 2016, the worldwide energy consumption was about 13.28 billion tonnes oil equivalent with 85.5% from fossil fuels [1]. The combustion of fossil fuels (especially coal and oil) leads to severe en- vironmental issues, such as climate change and haze pollution, which in turn causes public health hazards [2]. Increasing the applications of renewable energy resources has received more and more attention around the world in recent decades. Solar energy, as one of the commonly used renewable energy, can be efficiently converted into thermal energy by integrating solar col- lector with heat pump (i.e. solar assisted heat pump, SAHP). This is because SAHPs can supply energy with temperature above the ambient temperature as heat sources, which contributes to promoting the ther- modynamic performance of heat pumps. SAHPs have a great market potential for low temperature hot-water applications [3], especially integrated with some advanced technologies such as phase change material thermal storage [4], dual-source heat pump [5–7] and https://doi.org/10.1016/j.applthermaleng.2018.12.101 Received 8 July 2018; Received in revised form 12 December 2018; Accepted 15 December 2018 ⁎ Corresponding author at: Department of Energy and Power Engineering, North China Electric Power University, Baoding 071003, China. E-mail address: g.h.shi@ncepu.edu.cn (G.-H. Shi). 1 DX-SAHPV is the abbreviation of “LPG vaporisation system utilizing direct-expansion solar-assisted heat pump”. Applied Thermal Engineering 149 (2019) 757–771 Available online 17 December 2018 1359-4311/ © 2018 Elsevier Ltd. All rights reserved. T