Control systems in pig buildings

Most control systems work to adjust the heating and ventilation to achieve correct building temperatures. Control of ventilation rate using humidity and gas concentration is posisble, but this is rare. 

Controlling the temperature in buildings will have a positive impact on pig performance and reduce energy waste, find out more about using sensors below.

Table 1.  The reduction in growth and the additional feed needed if the temperature is 1°C below lower critical temperature

Extreme temperatures

Extreme external temperatures can cause internal building conditions to get out of control. At high extreme temperatures, the external temperature approaches the required internal temperature. In this case, increasing ventilation has little or no effect on the internal temperature as there is no difference between the internal and external temperatures to drive cooling. Air conditioning or adiabatic cooling may help, but more often than not it is uneconomical.

At low extreme external temperatures, the installed heating capacity (if such a system is installed) can reach a point where it is no longer able to compensate for the heat loss of the building. The solution is to add more heat. However, like additional cooling, this may also be uneconomical.

Between these limits, the building can be controlled to give acceptable inside temperatures and good air quality.

Temperature sensors rely on a change in the property of a material with temperature. Modern sensors have moved away from using physical property changes, such as the thermal expansion of metals (bimetallic strips) or gases (capillary tubes), to changes in the resistivity of electrical components (resistance thermometers and thermistors).

The latter method is more stable, accurate and sensitive to change and most of the technology used to control ventilation and heating is based on this type of equipment.

Some less common temperature sensing techniques take into account the effect of radiation (infrared), either with an electronic sensor or a ‘black body’ sensor that absorbs infrared heat.

Lying behaviour and sensor placement

Temperature sensor alarms

It’s possible to integrate sensors for humidity and trace gas concentration (CO₂, ammonia, etc.), but it is more expensive and requires more maintenance. Usually, these sensors control minimum ventilation rates in response to changing air quality conditions.

For the more complex control systems, inputs can now include sensors for position (for actuator feedback), flow and energy. Cameras and sound are even being used to estimate weight and monitor aggression and the incidence of disease.

Most control systems are based on a programmable electronic device that can handle multiple sensor inputs and control outputs. Essentially, they are mini-computers that can be adapted to handle an infinite number of control requirements.

The largest of these might have multiple digital or analogue inputs/outputs and have interactive control interfaces. They are often networked to other devices to provide complex communication, recording and analysis functionality.

Some of the most widely used and useful features of livestock systems are:

Multiple sensing 

Control based on information from many sensors (temperature, humidity, etc.).

Multiple outlets

The ability to coordinate several devices, such as fans, heaters and duct dampers, to provide good conditions.

Profiling

Can be programmed to automatically vary the temperature or ventilation curve over several days to take account of the changing requirement of the stock as animals grow.

Reporting

The facility to record and output information from sensors and the status of components (heaters, fans, actuators), so the user can access a historical record of what has occurred.

Remote access

The ability to be interrogated and set by remote computer equipment, or mobile devices such as smart phones, which may be located many miles away from the site being controlled. This is very important now as we are moving into an age where all feedback and system settings will be made on remote devices – tablets, phones or computers.

Complex interactive analysis

To use information from lots of sensors to inform management decisions, which might go beyond simply adjusting the environment. For example, using data on water consumption, energy use, feed input and animal weight to inform the most appropriate management decisions.

Precision farming

The possibilities for control are no longer technology bound, limited only by the imagination of the designer and the farmer's incentive to use the technology. We now engage in precision livestock farming, where the understanding of the environment, feed and water consumption leads to continual objective assessment and determines the actions to be taken.

This includes changing building temperature, feed intake and medication, animal behaviour, animal sounds and location. The scope is increasing as technology develops.

More information on sensors and control systems can be found in the controlled environment for livestock guide.

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