An Investigation of the Thermal Performance of a Tropical Greenhouse Constructed with an Earth Air Heat Exchanger

Abstract

The thermal performance of earth air tunnel heat exchanger (EATHE) integrated single span saw-tooth greenhouse was assessed in peak summer for tropical climate. With side and roof vent opened, natural ventilation due to wind and stack effect controlled the air movement and temperature inside the GH. In this configuration average temperature inside GH remained higher than the ambient temperature by 1.5 °C for the entire period of the experiment. For EATHE (installed at a depth of 3.2 m) assisted GH with polyethylene (PE) cover, the air from EATHE outlet entered inside GH at 33 °C and the average temperature within the GH was maintained at 4 °C lower than the ambient temperature. When the shading net was installed over the PE cover with EATHE, the transmitted radiations into the GH were reduced from the roof and the inside temperature was maintained 7 °C below the average ambient temperature (i.e. 45 °C). The measured temperatures along the length of EATHE were compared with the indigenously developed code-named PEAT (Performance analysis of Earth Air Tunnel) and found to be in good agreement within ± 4.5 % deviation. The temperature distribution inside the GH was predicted using a CFD model in Ansys-FLUENT with ± 5 % deviation from experimental results. With parametric analysis from the PEAT code and CFD model, desired depth of EATHE and mass flow rate of air required to bring down the GH indoor temperatures to the optimum plant growth range was determined.