Control of temperature, relative humidity and carbon dioxide for reduced ventilation in commercial otato storages

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Irvine, Douglas A.
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A microcomputer based monitoring and control system was designed, assembled, and field tested as a reduced ventilation controller in a commercial multi-bin potato storage in southern Manitoba to reduce energy consumption during winter months. The system was integrated with an automatic temperature controller to control the fresh air inlet, and used CO$\sb2$ and temperature as parameters for control of the fan operation in one of two 650 t bins monitored. The CO$\sb2$, temperature, and relative humidity as well as the fan status, and fan energy consumption were monitored in two adjacent 650 t potato storage bins. Potato storage facilities could reduce the demand for electrical power by turning ventilation off while emptying bins and grading potatoes for shipment during the months of December, January, and February. Monitored CO$\sb2$ concentrations increased quickly enough during any 8 to 10 h period, when all fans in the facility were simultaneously off, to warrant CO$\sb2$ set-point control to turn a fan on. Most times, the rapid removal of CO$\sb2$ from the test bin by the fan and continuous dilution from infiltration and exhaust with operation of fans in adjacent bins prevented the controlled fan from providing adequate ventilation when CO$\sb2$ was used as the only criterion for ventilation. The differential temperature between the upper and lower elevations of the potato piles were seen as a necessary criterion for ventilation when a bin ventilation fan remained off for an extended period and other fans were operating. A pre-set minimum differential temperature would also be the best criterion to turn fans off, rather than a lower CO$\sb2$ set point.