Phase change material (PCM) storage for free cooling of buildings—A review Adeel Waqas a,n , Zia Ud Din b a Center for Energy Systems, National University of Sciences and Technology (NUST), H-12 Campus Islamabad, Pakistan b School of Mechanical and Manufacturing Engineering, National University of Sciences and Technology (NUST), H-12 Campus Islamabad, Pakistan article info Article history: Received 17 July 2012 Received in revised form 16 October 2012 Accepted 21 October 2012 Available online 4 December 2012 Keywords: Phase change material (PCM) Energy storage Free cooling abstract Globally, buildings are responsible for 40% of the total world annual energy consumption which is responsible for one-third of green house gas emissions around the world. A significant portion of this energy is used for lighting, heating, cooling, and air conditioning purposes in buildings. Increasing awareness of the environmental impact of green house gas emissions and CFCs triggered a renewed interest in environmentally friendly cooling, and heating technologies for buildings. Free cooling of buildings may be seen as an alternate to compressor based air conditioning systems used for the buildings. In free cooling, nighttime cold is accumulated in storage material and extracted when needed. Latent heat storage using phase change materials (PCMs) can be used for free-cooling purposes due to their high storage density. In free cooling, using PCM as storage material, cool air during night is used to solidify the PCM and the accumulated cold is extracted during the hot day times. In this article a detailed review of work conducted by different researchers on PCM based free cooling is presented. Major challenges being faced in the design of PCM based free cooling system such as phase change materials; their thermo-physical properties and the geometry of encapsulation are elaborated and discussed in detail. Also the parameters effecting the charging and discharging of PCM, effect of phase change temperature and climatic conditions on thermal performance of the free cooling system are also discussed. Potential reduction in CO 2 emissions due to the applicability of free cooling systems in residential and commercial buildings is also discussed in this article. This paper also provides a comprehensive list of the PCMs currently being used and that can be used potentially for free cooling applications. At last, this paper also presents some current problems needed further research in this area. & 2012 Elsevier Ltd. All rights reserved. Contents 1. Introduction ...................................................................................................... 608 1.1. Evaporative cooling .......................................................................................... 608 1.2. Soil cooling ................................................................................................. 608 1.3. Ventilation cooling ........................................................................................... 608 1.4. Free cooling ................................................................................................ 609 2. Free cooling of the buildings during summer season ...................................................................... 609 2.1. Free cooling working principle ................................................................................. 609 2.2. Free cooling published literature ................................................................................ 610 2.3. Theoretical and experimental studies on PCM based free cooling of buildings ............................................ 610 3. Climatic applicability of free cooling of the buildings ..................................................................... 614 4. Economical and environmental feasibility of free cooling systems ........................................................... 614 5. Indicators to access the cooling potential of free cooling systems ........................................................... 614 6. Parameters influencing the thermal performance of free cooling system during charging and discharging process .................... 614 7. PCM melting point selection criteria for free cooling applications ........................................................... 615 8. Types of PCMs and their encapsulation for free cooling applications ......................................................... 615 8.1. Manufacturers of PCMs around the world ........................................................................ 616 8.2. PCM encapsulation techniques for free cooling application ........................................................... 616 Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews 1364-0321/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.rser.2012.10.034 n Corresponding author. Tel.: þ92 51 9085 6059; fax: þ92 51 9085 6002. E-mail address: adeelwaqas@gmail.com (A. Waqas). Renewable and Sustainable Energy Reviews 18 (2013) 607–625