Title: A novel underground solar thermal heat storage unit cum heat exchanger for non air-conditioned buildings

Authors: Rakesh Kumar, S.C. Kaushik

Addresses: Centre for Energy Studies, Indian Institute of Technology, New Delhi-110016, India. ' Centre for Energy Studies, Indian Institute of Technology, New Delhi-110016, India

Abstract: A novel passive space conditioning configuration is presented, integrating a Solar Collector System, Underground Storage Tank and Novel Heat Exchanger. This Underground Solar Thermal Heat Exchanger (USTHE) provided improved sensible heating/cooling of air by employing a Novel Heat Exchanger (NHX). The dynamic performance of the storage tank in USTHE is modelled using the finite difference method accounting thermal stratification of water into three nodes (three isothermal segments). Analysis of NHX incorporated thermal heat transfer between water in the load loop of a storage tank and cross flowing air in the heat exchanger. Savings were incorporated in the building code in Matlab using a one-dimensional heat conduction equation. A wide range of experimental data was collected for validating the modelling results. Simulations were performed for several parameters viz. solar collector area (Ac), sizing of the storage tank, mass flow rate of water in collector loop (Wc) and load loop (Wl) in daytime and night operations and air flow rate in novel heat exchanger. The effect of these simulations was predicted in terms of useful energy supplied by USTHE, thermal energy retaining period, collector temperature and averaged stratified temperature. Performance of USTHE is evaluated to give maximum heating potential. Effect of averaged isothermal segment temperature, stratification level and day and night flow rate combinations on heating potential is studied in great depth. USTHE supplied a peak heating potential of 5KWh with a collector water flow rate of 252 Kg/h and load water flow rate of 60 Kg/h and obtained a maximum averaged temperature of stratified tank of 37.1°C. Building heating load savings were 6.98KWh during daytime and 2.92KWh at night on 11 December 2001. Dry bulb temperature of air increased by 10.2°C (peak value at 3.00 p.m.) on 1 January 2002 while water temperature decreased by 4.2°C.

Keywords: heat exchanger; sensible heating; solar collector; underground solar thermal heat exchanger; heat transfer; finite difference method; storage tank modeling; thermal stratification; heat conduction; simulation; thermal energy; water heating; solar energy.

DOI: 10.1504/IJGEI.2003.005304

International Journal of Global Energy Issues, 2003 Vol.20 No.2, pp.208 - 222

Published online: 20 Sep 2004 *

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