Thermal comfort inside a tractor cab by evaporative cooling system

A low-cost safety tractor cab with external side shades and wet pad evaporative cooling system was developed to improve the working efficiency and lengthen the effective working time of farmers during the summer who cannot afford to buy an expensive air-conditioned cab. The cab is cooled by passing air through a wet evaporative surface, made up of 40-mm-thick layer of shredded wood packaged between two 15-mm-thick layers of coconut fiber. The evaporative surface is kept continuously wet with recirculation of water by a low-capacity, submersible water pump installed at the bottom of a water tank. The air cooled by evaporation of water from the evaporative surface is sucked into the cab through a duct by an fan located at the center of the cab roof The motor of the pump and fan are energized by a 12-V DC battery of the tractor To protect the glass portion of the cab from direct solar radiation, external side shades of white painted plywood are installed on all sides of the cab. At tractor speed of 5 km/h, relative air velocity at the face of the pad was about 65 m/min. Dry bulb temperature inside the cab was lowered to 300 to 31 degrees C with relative humidity 70 to 72% (giving thermal sensation in comfortable zone) under worst climatic conditions of Bangkok (outside dry bulb temperature of 40.5 degrees C with relative humidity 40%).