Investigation of the optimal heat flux density for the refrigerated warehouses design

Cold warehouses are relatively high energy consuming systems, and their construction are growing. In the design of these buildings, the choice of the insulation thickness is an important factor that affects the owning and operating costs. In practice, it is common to use heat flux density values or R-values given in the technical literatures. These values seem to neglect the possible effects of parameters such as local energy and insulation cost. This work investigates the influence of these parameters on the optimal value to be adopted for the thermal flux density in the design process of warehouses. A mathematical model of the flux is developed. The objective function to be minimized is the present value of the owning and operating costs of the system. Simulations are made using different parameters values: 25 and 45°C for the external air temperature; -20 and 8°C for the products storage temperature; 150000 to 250000 XOF/m³ of insulation and 75 to 200 XOF/kWh of electricity. Contour plots of the optimal thermal flux density are drawn. The results indicate that the optimal heat flux density varies with the site air temperature and the storage room one. Moreover, it is seen that higher values of the thermal flux density can be adopted compared to that given in technical literature (up to 11 W·m^-2 vs 6 or 8 W·m^-2). However, these high values of the thermal heat flux involves the use of high power refrigerating units, increasing the energy consumption.