A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1991

A low cost safety tractor cab with external s ide shades and wet pad evaporative cooling system was designed and developed to improve the working efficiency and lengthen the effective working time of farmers who can not afford to buy an expensive air conditioned cab. The cab is cooled by passing air through a wet evaporative surf ace, made up of 40 mm thick layer of wood shred packed between two layers of coconut fibre (15 mm thick each layer). The evaporative surface is kept continuously wet with recirculation of water by a low capacity submersible water pump installed at 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 a fan located at center of cab roof. The motors of pump and fan are energized by 12-volt D.C. battery. To protect glass portion of the cab from direct solar radiation, external side shades of white painted plywood are installed on all s ides of the cab. Dry bulb temperature inside the cab was lowered to 30-31°C under worst climatic condition (outside dry bulb temperature of 40.5°C). Though relative humidity inside the cab was increased to 70-75 %, its humid effect was counteracted by low temperature and high air velocity (3 m/sec) produced by the fan. The thermal sensation inside the cab remained within comfortable zone at worst climatic conditions in Bangkok. Noise level at the operator's ear was reduced to 84-86 decibels which is less than permissible limit (90 decibels).