Effects of Thermal Mass, Window Size and Night-Time Ventilation on Peak Indoor Air Temperature in the Arm-Humid Climate of Kumasi, Ghana; By Samuel Amos-Abanyie

ABSTRACT

There is lack of empirical data and practical advice on thermal performance of building envelope materials used in Ghana in figures readily appreciated by building designers, prospective builders and facility managers. As a result air conditioning is adopted as an immediate and direct response to achieving thermal comfort, without recourse to the potential offered by building design and material selection in maintaining thermal comfort in buildings. There is predominant use of low mass sandcrete blocks and adoption of universal building designs with extensive use of glazing that is characterized by high solar and conductive heat gains. Relatively lower night-time outdoor air temperatures are not harnessed to contribute in maintaining thermal comfort in buildings.

 

Mr. Abanyie defending his PhD thesisThis research aimed at advancing knowledge in passive cooling of buildings in warm-humid climates by exploring the integration of passive and low energy cooling techniques in building design in Ghana to enhance thermal comfort and reduce energy use for space cooling. Adopting building performance simulation and experimental approaches, data on carefully selected parameters including site location and climatic conditions, thermo-physical properties and thermal zone descriptions, and air flow systems were used. An optimization was performed through sensitivity analysis based simulations. The effects of thermal mass, window size and night-time ventilation were evaluated using three variables:  (1) the maximum temperatures, (2) the temperature difference ratio (TDR) and (3) the percentage of overheated hours. Following the simulations, experimental cells were designed and constructed based on the specifications of the best performing simulation models. Measured data from the experiments were used to validate the simulated results and the coefficient of variance of root-mean-squared-error (CV(RMSE)) value and the corresponding root mean square difference (r2) were checked to fall within allowable tolerances. The correlation between temperature difference ratio and window to floor area ratio was used to develop an expression that can be used to predict the peak indoor temperature for a given thermal mass, when the peak outdoor temperature and temperature swings are known.

 

The research revealed that thermal mass, window size and night-time ventilation have varied effects in reducing the peak indoor air temperature. However, the three provided a synergistic effect in reducing the peak indoor air temperature. The findings of the study are expected to guide building designers, prospective builders and facility managers in the selection of building envelope material to enhance thermal performance. With the current leanings towards environmental sustainability of building design, the relevance of these findings to the development of Ghana are immense especially during the current inadequate energy supply and frequent power cuts during peak hours.


Contact: Samuel Amos-Abanyie

 Department of Architecture, KNUST

E-mail: sumwelamos@yahoo.com 

      Tel: +233 244 256 552

       +233 203 325 248

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