A new approach to modelling of a horizontal geo-heat exchanger with an internal source term q,qq Sarwo Edhy Sofyan a,b,⇑ , Eric Hu a,⇑ , Andrei Kotousov a a School of Mechanical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia b Department of Mechanical Engineering, Syiah Kuala University, Banda Aceh 2331, Indonesia highlights  A new GHE model with an internal source term approach is presented.  The theoretical results are in a good agreement with the experimental data.  The effects of the technical parameters on the GHE’s performance are investigated. article info Article history: Received 7 November 2014 Received in revised form 9 June 2015 Accepted 10 July 2015 Available online xxxx Keywords: Geo-heat exchanger Thermal modelling Internal source term abstract This paper presents a new approach to considering the effect of seasonal changes in soil temperature on the performance of a horizontal geo heat exchanger. It is different from extant models which consider the seasonal changes in soil temperature by applying a real energy balance on the ground surface. In the new model, the seasonal changes in soil temperature, which are affected by the thermal interaction between the ground and the atmosphere, are expressed as an internal source term. The value of the internal source term depends on the soil density, soil specific heat, soil temperature difference during summer and win- ter, and time period. The simulation results show that the new approach, which takes into account the effect of periodic soil temperature fluctuations on the performance of the horizontal geo heat exchanger, is valid. The validated model is then used to conduct a sensitivity analysis to investigate the effects of the pipe length, fluid flow rate, inlet fluid temperature, and burial depth on the thermal performance of the horizontal geo heat exchanger. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, geo heat exchangers (GHEs) have become attractive from a technical perspective in heating and cooling applications because of their renewable nature. GHEs use the ground/soil as a heat source or heat sink to harness the (renew- able) thermal energy stored in the ground as the ground temperature is normally higher than the ambient air temperature during the winter and lower during the summer. Thus, the ground is a suitable medium to be used to extract/store the heat during the winter/summer. GHEs are usually coupled with heat pump and air conditioning systems to provide one of the most energy efficient ways of generating buildings’ heating and cooling. There are two common configurations of GHEs, namely vertical and horizontal. Horizontal heat exchangers are relatively cheap to install, as they are only laid in a trench at a depth of up to 2 m below the surface. Their performance is affected by the continuous thermal interac- tion between the ground and the atmosphere. The diverse mecha- nisms of heat transfer occurring on the ground surface contribute to the thermal recovery of the ground conditions, especially when there is an imbalance between the heating and cooling operations [1]. There is much literature which discusses the theoretical study of horizontal GHEs, including the modelling of their linear [1– 15], slinky [16–20], and flat-panel [21–23] arrangements. One of the key challenges associated with the theoretical study of the http://dx.doi.org/10.1016/j.apenergy.2015.07.034 0306-2619/Ó 2015 Elsevier Ltd. All rights reserved. q This article is based on a short proceedings paper in Energy Procedia Volume 161 (2014). It has been substantially modified and extended, and has been subject to the normal peer review and revision process of the journal. This paper is included in the Special Issue of ICAE2014 edited by Prof. J Yan, Prof. DJ Lee, Prof. SK Chou, and Prof. U Desideri. qq The short version of the paper was presented at the 6th International Conference on Applied Energy – ICAE2014. This paper is the full paper with significant revision of the previously presented short version at the Conference. ⇑ Corresponding authors at: School of Mechanical Engineering, The University of Adelaide, Adelaide, SA 5005, Australia. E-mail addresses: sarwo.sofyan@adelaide.edu.au (S.E. Sofyan), eric.hu@adelaide. edu.au (E. Hu). Applied Energy xxx (2015) xxx–xxx Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Please cite this article in press as: Sofyan SE et al. A new approach to modelling of a horizontal geo-heat exchanger with an internal source term. Appl Energy (2015), http://dx.doi.org/10.1016/j.apenergy.2015.07.034