Effect of blind angles on thermal decay in the UFAD system in summer

Abstract

• Thermal decay depending on blind angle examined two heat transfer effects. • The effect of change in conduction at the bottom surface of the concrete slab on the rate of convective heat transfer. • The effect of change in solar radiation at the top surface of the raised floor on convective heat transfer at its bottom surface. • Optimization of the UFAD system based on analysis of thermal decay and chiller energy consumption, and their dependence on Phi. The objective of this study was to explain and quantify the effect of blinds on the heat transfer paths causing thermal decay and the resulting effects on diffuser discharge temperatures, temperature profiles, supply airflow rate, and energy consumption. To analyze the direct effects of convective heat transfer on thermal decay as blind angle changes, two processes must be examined. The first is the effect of the return temperature on convective heat transfer during operating hours, and the resulting change in conduction rate at the bottom surface of the concrete slab. The second is the effect of change in solar radiation at the top surface of the raised floor on convective heat transfer from its bottom surface, which affects thermal decay. This paper performed an analysis of thermal decay and cooling energy consumption according to the blind angle through a comparison of experimental data and simulation results. Phi means stratification in the room; lower values mean more stratification, which should be considered as a UFAD systems design. The most notable result of this study is the return temperature. It can be seen that during better temperature stratifications, the return temperature was higher due to the plume phenomenon. Although blinds decrease the total indoor cooling load with their shielding effect on the solar radiation load, the rise in return temperature increased the cooling coil load of the air conditioner and the heat storage in the concrete slab. This study will help to understand the relationship between the blind angle, the thermal stratification, and cooling energy usage in the UFAD systems.