Chapter 7 - Review: Electronic Ventilation Controller Terminology

The following are terms that may be encountered when dealing with ventilation controllers.

Bandwidth – Associated with variable speed fans, refers to the temperature difference to cause a variable speed fan to change from operating at a minimum rate to a maximum rate. Bandwidth is usually an input for variable speed fans.

Cycle timer – Used to cycle fans on and off in timed intervals, for instance, two minutes on and then eight minutes off. This is a method of reducing the ventilation rate to a rate lower than the smallest fan can provide running continuously. This method is generally not the best one for livestock buildings.

Differential – Refers to the temperature difference between ventilation stages. This is generally an input on most controllers. The advantage is that all the temperature settings are relative to set point. It the set point is changed, all other stage settings remain the same, relative to the set point. Heater differentials are degrees below the set point.

Humidistat – Measure relative humidity and control ventilation rate based on the humidity set points. These generally are secondary to thermostats due to general reliability.

Minimum speed – The lowest speed that a variable speed fan runs at. This is expressed by a percentage that is input by the user. Some controllers use motor curves that approximate percent air movement while others are only a percent of voltage.

Minimum speed curve – This is programmed change in minimum ventilation. Multiple minimum speed settings are entered along with the coinciding day to allow for changing needs of ventilation related to poultry growth. This is used to gradually increase the minimum ventilation as the birds grow.

Motor curves – Some controllers are capable of using pre-programmed information about fans and motors to adjust variable speed fans. Because fan output is not proportional to voltage, this makes for more accurate control at low speeds.

Multiple temperature probes – Some controllers are capable of using more than one temperature probe. The readings are then either averaged or used for zone control with some very sophisticated controllers.

Offset – A temperature differential in which nothing happens. For instance, there is generally an offset for heating which is the difference between the set point temperature and the point at which the heater is turned off. In ventilation it is generally the number of degrees between when one variable speed fan is full speed and the next one starts.

On/off control – simple control by either having fans on full or off.

Ramping – Similar to the concept of a minimum speed curve except it is a changing temperature program based on the anticipated temperature needs of the growing animals.

Relative temperature – Used in controllers to allow the user to create a ventilation program that can be easily changed without resetting all the temperatures in the program. For instance, if the set point of a controller was 78°F and the other stages were to come on at 82°F and 86°F, they would be entered as a relative temperature of 4°F (82-78) and 8°F (86-78).

Set point – The desired target temperature for a room. Ventilation and heating temperatures are averaged and used as the basis for control.

Temperature averaging – When multiple temperatures probes are used the measured temperatures are averaged and used as the basis for control.

Temperature curve – Multiple temperatures are entered along with the coinciding day. This is used to gradually decrease the temperature as animals grow and their required temperature decreases.

Thermostat – A controller that measures temperature and turns equipment on and off based on the measured temperature.

Variable speed controller – A controller that proportionally changes the speed of a fan in order to regulate air flow.