Heat transfer through building opaque envelope is responsible for approximately half of the total heat loss and gain to and from the surroundings. Therefore, insulation materials are commonly used in the building envelope to reduce the heat transfer. Recently, lightweight wall materials with lower thermal conductivity are used in construction along with the commonly used materials such as heavy concrete and earthen materials. In this perspective, there is a need to understand the optimum insulation thickness for different types of building construction materials to minimize unnecessary usage of insulation materials. This study investigated the optimum insulation thickness for different construction materials following a life-cycle approach, where an analytical optimization methodology based on the degree-days method and life-cycle cost analysis was used. In total, 4 insulation materials and 15 building construction materials were considered in the optimization study. The objective function was to minimize life-cycle cost corresponding to the decision variables including insulation thickness and the thermal conductivity of insulation and wall materials. The results showed that the use of insulation in lightweight wall materials is not economically feasible because of their negligible cost-saving potential (below US$2.5/m2-year). However, the walls with heavy concrete and earthen materials that have high thermal mass must be insulated due to their highest cost-saving potential (US$14–26.39/m2-year).
The compression of insulation causes around a heating, ventilation, and air-conditioning duct usually resulted in dew formation around the outer surfaces because of low temperature, which causes significant energy and financial losses. The parameters such as supply airflow rate, supply air temperature, ambient airspeed, and the convective heat transfer coefficient (ho) plays significant role in dew formation. In this paper, the parametric study is performed to investigate the effects of these parameters on the external surface temperature of the duct to avoid condensation. A mathematical model is developed to quantify these effects using preliminary data obtained from the heating, ventilation, and air-conditioning system of a pharmaceutical company.The results reveal that external surface temperature increases with an increase in insulation thickness and supply air temperature, whereas it decreases with higher supply air flow rate. It is estimated that the minimum insulation thickness at joint and bend should be maintained between 15-55 and 15-35 mm, respectively, with a variation in ho between 6 and 22W/m 2 K to avoid condensation. Additionally, it is estimated that air flow rate should be greater than 1.4m 3 /s at 10W/m 2 K and 2.2m 3 / s at 22W/m 2 K. Similarly, the ambient air speed should be greater than 2.8 m/s at 6W/m 2 K, respectively.Practical application: Building services engineers have a paucity of information on the effects of the compression of heating, ventilation, and air-conditioning duct thermal insulation. It can cause condensation that will adversely affect the insulation material, thereby increasing the maintenance cost as well increasing the heat loss from the duct so affecting the conditions of supply air. Proper insulation thickness and operating parameters are important for building owners and operators to control ongoing expenses of buildings. This paper seeks to quantify the effect of insulation compression to improve understanding so that this important area may be properly considered by the building services engineer.
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