Solar & Wind Technology Vol. 6, No. 2, pp. 171-176, 1989 0741-983X/89 $3.00+.00 Printed in Great Britain. Pergamon Press pie TECHNICAL NOTE Performance studies of an integrated solar collector-cum-storage water heating system with transparent insulation cover J. PRAKASH Ramjas College, Delhi University, Delhi-110007, India and H. P. GARG, D. S. HRISHIKESAN and RANJANA JHA Centre for Energy Studies, Indian Institute of Technology, New Delhi-1 I0016, India (Received21 June 1988 ; accepted31 August 1988) Abstract--In this paper the effect of transparent insulation on the performance of a 100 dm3 capacity built- in-storage type solar water heater is theoretically investigated. The materials of transparent insulation in covering 1 m E area of the top surface are Honeycomb hexagonal PS, Honeycomb hexagonal PA and Honeycomb square PC as suggested by Pftuger et al. (paper presented at the ISES Solar World Congress, Hamburg, 1987). Performance of the third material is compared with a glass cover with and without night insulation cover. Also, the performance of a similar system with an area of 0.5 m 2 on its top surface but with the same capacity and with transparent insulation on top and on all the side walls is studied. Finite difference forward time step marching technique is used in solving the energy balance equations. A comparison between the three materials shows that the system with Honeycomb square PC presents the best performance, but it is inferior to the system with night insulation cover. NOMENCLATURE AB area of the bottom surface of the collector (m 2) AN area of the plate on the nth side, where n = 1 .... ,5 represent, the top, south, north, west and east respectively (m 2) Cp specific heat of the plate (J/kg °C) Cw specific heat of water (J/kg °C) hewn heat transfer coefficient between nth plate and water (W/m 2 °C) la intensity of diffuse radiation on horizontal (W/m 2) ID intensity of beam radiation on horizontal (W/m 2) Io intensity of global radiation (W/m 2) Mp mass of plate per unit area (kg/m 2) Mw mass of water in the heater (kg) S~(t) flux of total solar radiation incident on the nth side of the collector (W/m 2) t time coordinate (s) T~ instantaneous value of ambient temperature (°C) Tp instantaneous value of plate temperature (°C) Tw instantaneous value of water temperature (°C) U~n overall heat transfer coefficient from the nth wall (W/m 2) Greek letters ~p absorptance of the plate fl tilt angle of the plate average system efficiency p ground reflectance z transmittance of the transparent insulation or glass cover 0t angle of incidence of the beam radiation on the titled surface Oh angle of incidence of the beam radiation on the horizontal INTRODUCTION Although many people are aware of the need for extensive utilization of the alternative sources of energy, the lack of popularity of solar energy devices, may, perhaps, be due to the frequent personal attention needed for their efficient per- formance. In today's fast changing world, one is always on the look out for gadgets which can be handled easily. Thus, if solar energy devices are to catch up with their conventional energy counterparts, it is of utmost importance to design them so that they need minimum user attention for their maintenance and functioning. Since energy demand is out of phase with the sunshine hours, stress is to be laid upon designing simple devices which serve the dual purposes of solar energy collection and thermal energy storage. If these systems are to become popular in the domestic sector, they should be technologically efficient, economically viable and easy to operate. Some such systems were analysed and reported by Prakash et al. [1] and Garg and Rani [2]. Movable insulation (MI) was widely employed for efficient thermal energy storage in these collector-cure- storage systems. However, the personal attention needed by the systems provided with the movable insulation hampers their smooth functioning. Transparent insulation materials make a good alternative to movable insulation and aid efficient performance of integrated collector-cum-storage systems. 171