Evolution of design criteria for earth air-pipe cooling system of greenhouse

Abstract

A mathematical model has been developed to evolve criteria for optimally designing an earth air–pipe cooling system employed in greenhouses. Relations have also been developed to compute the size of earth air pipe cooling system required for the space to be cooled. This cooling system is characterized by two parameters i.e. pipe length and cross-section and volumetric air flow rate (m3s-1m-2 floor area). These two parameters have been optimized to remove the maximum heat flux from the greenhouse enclosure. For a given environmental parameter ϕ (ϕ = (Tr-Ts)/(Ta-Ts)), the optimum air flow rate (m3s-1m-2 floor area) cab be computed. A polynomial relation between environmental factor (ϕ) and climatic factor (CF) was given. For creating a desirable temperature inside greenhouse the value of ϕ is decided and then CF is calculated. The ratio A/At has been related to ϕ and CF. For a given value of flow velocity (vt), we can determine the cross-sectional area of pipe in m2. This model has proved to be very useful in designing the optimal cross sectional area of pipe and optimal volumetric air flow rate for removing the maximum heat load from the greenhouse.