Experimental determination of time lag and decrement factor

Abstract

Buildings consume about 40% of the primary energy in the world. This means that buildings are responsible for the majority of greenhouse gas emissions. It’s time to reduce this energy consumption to limit the environmental impact of buildings. The use of high thermal inertia envelopes could be a solution to reduce energy consumption of the building. The thermal inertia is characterize by time lag and decrement factor. This work deals with the experimental determination of time lag and decrement factor of a building envelope. For this purpose, a test cell of 1 m3 made of stabilized earth brick is built at the Cheikh Anta Diop University of Dakar. Stabilized earth bricks are commonly used in Senegal. The time lag and the decrement factor are calculated using the ambient-air temperature inside a test cell and the outdoor average equivalent temperature. The results show that the time lag of a test cell envelope is about 6 h and the decrement factor about 0.4. This reduces the energy needed to cool the building during warm periods, as fluctuations in the outside temperature are not felt. Keywords: Time lag, Decrement factor, Stabilized earth brick, Thermal inertia