Typical ventilation controllers turn devices (heaters or fans) on and off in response to temperature changes as detected by one or more temperature probes suspended in the animal facility. Current ventilation control strategies as implemented by almost all ventilation controllers installed in production facilities contribute to temperature variation.
For example, the typical staging of fans in a grow-finish facility would be stage 1 operates from 50% minimum speed at controller set point to 100% minimum at 2F above set point (bandwidth). At 2.5F above set point stage 2 comes on at 50% and ramps to 100% at 4F above set point. Stage 3 comes on at 5F above set point, etc. Which fan stage operates is a function of heat production by the pig (pig weight dependent), heat loss/gain from the facility structure (insulation levels and air leaks) and ambient temperature (amount of heat that can be added to each unit of incoming ventilation air). This means temperatures vary within the pig facility over a 24 hour period, sometimes by quite a bit.
There is a new generation of ventilation controllers coming on the market from several suppliers that change how fans are staged in response to the call for heat removal from a facility. Rather than turning fans on/off in response to incremental rises in temperature, the new controllers turn fans on/off in an attempt to maintain a constant temperature in the facility using sophisticated computer logic.
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