Solar-energy harnessing performances of direct-gain and non-vented Trombe walls under yemeni weather conditions

Abstract

The presented design method shows how the monthly average auxiliary energy demand (which is required in a building incorporating direct-gain and non-vented Trombe walls as passive heating aids) in a hot climate, depends upon the building's characteristic parameters and average monthly meteorological data. For this purpose, a direct-gain ambient-energy recuperation factor has been defined and correlated with the difference between the ‘indoor’ thermostat setting and the ambient environment's air temperature, divided by the total amount of solar radiation transmitted per day into the living space through the glazing. An expression for this factor is obtained by solving a one-dimensional energy-balance equation which involves (i) the total amount of solar and ‘internal’ energy gains, (ii) the average thermal conductance of the house's envelope, and (iii) the storage properties of the constructional materials employed in this envelope. The method facilitates the estimation of the following: the solar contribution to the building's heating requirements; the amount of solar energy captured per day that exceeds the house's daily heating load, and which must therefore be vented to prevent overheating; as well as the variation with time of the temperature within the building. Finally the effects of altering (i) the thermostat set-temperature, (ii) the properties of the thermal-store, and (iii) the collector-to-store areas ratio upon the direct-gain ambient-energy recuperation factor (and consequently on the amount of auxiliary energy needed for heating or cooling) have been investigated.