AN EVALUATION OF HEATING AND VENTILATION CONTROL STRATEGIES FOR LIVESTOCK BUILDINGS

Thermal responses and supplemental heat consumption of a livestock building airspace were investigated using a simulation program and Typical Meterological Year weather data for a cold (-23 to -32 degrees C) and a warm day (-4 to 7 degrees C) in the Canadian Prairie Region. Three different control strategies using different sizes of heating/ventilating equipment and different controller time constants were evaluated. In an either-or-temperature (EOT) control, stage 1 ventilation was provided continuously by fan 1; stage 2 ventilation and the heater were controlled by the same temperature actuated switch such that either the heater was on or stage 2 ventilation fan 2 was on, but not both. In an either-or-neither temperature (EONT) control, stage 1 ventilation was provided continuously and the heater and stage 2 ventilation were controlled by separate actuated switches with a fixed interstage differential. In a temperature-humidity control (THC), all stages of ventilation were controlled thermostatically and the heater was controlled by a humidistat. THC control strategy provided the best thermal response and used the least supplemental heat. EOT control could achieve a variable ventilation rate for moisture control when fans and heater were correctly designed. EONT control provided good temperature control but failed to control humidity. Oversizing of heating/ventilating equipment resulted in poorer thermal response and higher energy consumption for EOT and EONT systems but had little effect on the THC system. Controllers with large time constants economized the use of supplemental heat but introduced poor thermal responses for all three control strategies.