Experimental investigation and numerical simulation analysis on the thermal performance of a building roof incorporating phase change material (PCM) for thermal management Experimental investigation and numerical simulation analysis on the thermal performance of a building roof incorporating phase change material (PCM) for thermal management A. Pasupathy a, L. Athanasius a, R. Velraj a,*, R.V. Seeniraj b a Department of Mechanical Engineering, College of Engineering, Chennai 600 025, India b Department of Mechanical Engineering, Sri Venkateswara College of Engineering, Sriperumpudur, Tamilnadu, India Received 12 December 2006; accepted 24 April 2007 Available online 10 May 2007 Abstract Thermal storage plays a major role in a wide variety of industrial, commercial and residential application when there is a mismatch between the supply and demand of energy. Latent heat storage in a phase change material (PCM) is very attractive, because of its high- energy storage density and its isothermal behavior during the phase change process. Several promising developments are taking place in the field of thermal storage using phase change materials (PCM) in buildings. It has been demonstrated that for the development of a latent heat storage system (LHTS) in a building fabric, the choice of the PCM plays an important role in addition to heat transfer mech- anism in the PCM. Increasing the thermal storage capacity of a building can enhance human comfort by decreasing the frequency of internal air temperature swings, so that the indoor air temperature is closer to the desired temperature for a longer period of time. This paper attempts to study the thermal performance of an inorganic eutectic PCM based thermal storage system for thermal management in a residential building. The system has been analyzed by theoretical and experimental investigation. Experiments are also conducted by circulating water through the tubes kept inside the PCM panel to test its suitability for the summer months. In order to achieve the opti- mum design for the selected location, several simulation runs are made for the average ambient conditions for all the months in a year and for the various other parameters of interest. � 2007 Elsevier Ltd. All rights reserved. Keywords: Latent heat thermal energy storage; Space heating and cooling; Building energy conservation; Phase change material; Encapsulation 1. Introduction Scientists all over the world are in search of new and renewable energy sources. One of the options is to develop energy storage devices, which are as important as develop- ing new sources of energy. Thermal energy storage systems provide the potential to attain energy savings, which in turn reduce the environment impact related to non-renew- able energy use. In fact, these systems provide a valuable solution for correcting the mismatch that is often found between the supply and demand of energy. Latent heat storage is a relatively new area of study although it previ- ously received much attention during the energy crisis of late 1970’s and early 1980’s where it was extensively researched for use in solar heating systems. When the energy crisis subsided, much less emphasis was put on latent heat storage. Although research into latent heat stor- age for solar heating systems continues, recently it is increasingly being considered for waste heat recovery, load leveling for power generation, building energy conservation and air conditioning applications. As demand for air conditioning increased greatly during the last decade, large demands of electric power and limited reserves of fossil fuels have led to a surge in interest with regard to energy efficiency. Electrical energy consumption 1359-4311/$ - see front matter � 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2007.04.016 * Corresponding author. Tel.: +91 44 22203008; fax: +91 44 22300916. E-mail addresses: pasu1967@gmail.com (A. Pasupathy), Athanasius@ sify.com (L. Athanasius), velrajr@annauniv.edu (R. Velraj), seenirajr@ hotmail.com (R.V. Seeniraj). www.elsevier.com/locate/apthermeng Available online at www.sciencedirect.com Applied Thermal Engineering 28 (2008) 556–565 mailto:pasu1967@gmail.com mailto:Athanasius@sify.com mailto:Athanasius@sify.com mailto:velrajr@annauniv.edu mailto:seenirajr@hotmail.com mailto:seenirajr@hotmail.com varies significantly during the day and night according to the demand by industrial, commercial and residential activ- ities. In hot and cold climate countries, the major part of the load variation is due to air conditioning and domestic space heating, respectively. This variation leads to a differ- ential pricing system for peak and off peak periods of energy use. Better power generation/distribution manage- ment and significant economic benefit can be achieved if some of the peak load could be shifted to the off peak load period. This can be achieved by thermal energy storage for heating and cooling in residential and commercial building establishments. There are several promising developments going on in the field of application of PCMs for heating and cooling of building. Zalba et al. [1] performed a detailed review on thermal energy storage that dealt with phase change materials, heat transfer studies and applications. Farid et al. [2] also presented a review on the analysis of phase change materials, hermetic encapsulation and application of PCMs. Mehling and Hiebler [3] summarized the investi- gations and developments on using PCMs in buildings. Murat Kenisarin1and Khamid Mahkamov [4] presented a review of investigations and developments carried out dur- ing the last 10–15 years in the field of phase change mate- rials, enhancing heat conductivity, available fields of using PCM, and clarifying typical questions. Arkar and Medved [5], Stritih and Novak [6] designed and tested a latent heat storage system used to provide ven- tilation of a building. The results of their work, according to the authors, were very promising. Phase change dry wall or wallboard is an exciting type of building integrated heat storage material. Several authors investigated the various methods of impregnating gypsum and other PCMs [7–12] in wallboards. Limited analytical studies of PCM wall- board have been conducted, but few general rules pertain- ing to the thermal dynamics of PCM wallboard are available. Lee et al. [13] and Hawes et al. [14] presented the ther- mal performance of PCM’s in different types of concrete blocks. They studied and presented the effects of concrete alkalinity, temperature, immersion time and PCM dilution on PCM absorption during the impregnation process. Wood lightweight concrete is a mixture of cement, wood chips or saw dust, which should not exceed 15% by weight, water and additives. This mixture can be applied for building interior and outer wall construction. For inte- gration in wood lightweight concrete, two PCM materials Rubitherm GR40, 1–3 mm and GR 50, 0.2–0.6 mm were investigated by Mehling et al. [15]. Meng Zhang et al. [16] presented the development of a thermally enhanced frame wall that reduces peak air conditioning demand in residential buildings. Ismail et al. [17] proposed a different concept for thermally effective windows using a PCM moving curtain. UniSA (University of South Australia) [18] developed a roof-integrated solar air heating/storage system, which uses existing corrugated iron roof sheets as a solar collector for heating air. Kunping Lina et al. [19] put forward a new kind of under-floor electric heating system with shape-sta- bilized phase change material (PCM) plates. Hed [20] investigated PCM integrated cooling systems for building types where there is an over production of heat during the daytime such as offices, schools and shopping centers. Free cooling was investigated at the University of Zara- goza/Spain by Zalba [21]. The objective of the work was to design and construct an experimental installation to study PCMs with a melting temperature between 20 and 25 �C. Nomenclature C1, C3 specific heat of roof top slab and concrete slab (kJ/kg K) cpl specific heat of liquid PCM (kJ/kg K) cps specific heat of solid PCM (kJ/kg K) f implicit factor GrL Grashof number hi inside heat transfer coefficient (W/m 2 K) ho outside heat transfer coefficient (W/m 2 K) k1, k2, k3 thermal conductivity of roof top slab, PCM panel and bottom concrete slab (W/m K) L1, L2, L3 thickness of roof top slab, PCM panel and bottom concrete slab (m) NuL Nusselt number Pr Prandle number qrad radiation flux (W/m 2) Re Reynolds number T temperature (�C) T1 ambient temperature (�C) T 0i previous time step temperature at ith volume cell (�C) Ti current time step temperature at ith volume cell (�C) Tin initial temperature (�C) Troom room temperature (�C) Ts surface temperature (�C) Tsky sky temperature (�C) a absorptivity 2 emissivity hsl solid–liquid enthalpy change (kJ/kg) r Stefan Boltzmann constant q1, q2, q3 density of roof top slab, PCM panel and bot- tom concrete slab (kg/m3) Dt time step (s) dx1, dx2, dx3 nodal distances (m) Dx1, Dx2, Dx3 control volume length of roof top slab, PCM panel, bottom concrete slab (m) A. 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