Influence of envelope thickness and solar absorptivity of a test cell on time lag and decrement factor

Abstract

This work deals with the influence of envelope thickness and solar absorption on the time lag and the decrement factor. For this, a test cell of 1 m3 of volume is built with a material commonly used in construction in Senegal, the compressed earth brick stabilized with cement. The ambient-air temperature inside and outside of test cell and solar direct normal irradiance is measured. The test cell is modeled using EnergyPlus software. The comparison of experimental and theoretical ambient-air temperature puts out a great linear showing the reliability of the model. The time lag and the decrement factor are calculated using the air-sol equivalent temperature of the test cell and the inside ambient-air temperature. The time lag and decrement factor of the compressed stabilized earth brick envelope are respectively 0.22 and 6.6 h showing the good thermal inertia of those bricks. A parametric study is performed to determine the effect of envelope thickness and solar absorptivity on the time lag and decrement factor. The results show that the decrement factor decreases with envelope thickness while the time lag increases linearly and that an envelope thickness of 32 cm has a decrement factor of around zero with a maximum time lag of about 12 h for this type of material. The envelope’s solar absorption has a moderate effect on the decrement factor and time lag.

Impact of insulation and wall thickness in compressed earth buildings in hot and dry tropical regions

“…were found only for CEB 0.14 m and CEB 0.20 m where time lag increase a little with values between 4-5 h. However for other simulation cases, time lag values were less than 2 h. In fact, the more the thermal mass or insulation thickness, the less the heat conduction through the building wall. As mentioned [13] beyond 32 cm, the indoor environment is no longer influenced by the outdoor thermal flux through walls. This explains why the effect of thermal mass on thermal lag is more pronounced for thicknesses 0.14 m and 0.22 m; and not 0.35 m and 0.50 m. Because insulation and CEB 0.35 m and CEB 0.50m hinder heat conduction through walls, the low values of thermal lag obtained are related to direct daytime heat gains through the building's other components, especially openings and roof.…”

“…Secondly, when the numerical model precision is acceptable, the sensitivity analysis is performed and the influence of 4 different parameters involved is found with acceptable accuracy. Toure et al [13] investigated the influence of envelope thickness and solar absorptivity on time lag and decrement factor using this approach. They found that increasing wall thickness improve the thermal inertia effects as decrement factor and time lag.…”

Comparative Study of the Impact of Bio-Sourced and Recycled Insulation Materials on Energy Efficiency in Office Buildings in Burkina Faso

“…Further research has shown that compressed earth blocks are more durable than adobe materials [51,52] and provide the same or greater thermal response than concrete in warm locations [51,[53][54][55]. Toure et al [56] studied the effect of envelope thickness and solar absorption on time lag and decrement factor. They discovered that a thicker wall improves thermal inertia effects such as decrement factor and time lag.…”

Multivariate analysis for assessing the thermal performance of vertical opaque envelopes in extended regions

“…By contrast, the difference between T sa and T e could be too small for walls of very light colours. The choice of the α-value deserves a separate study (see for instance Toure et al, 2020) and will not be addressed here.…”