AIR CONDITIONING OF LIVESTOCK BUILDINGS
The set of elements that compose the air conditioning installation have the function of achieving an optimal environment inside the building, with an appropriate atmosphere for the good development of the animals and favorable for their health.
The design of the installation, which allows the creation of an appropriate microclimate inside the building, is conditioned by the regional climate, the characteristics of the building itself and the animals that occupy it.
The goal is to facilitate the exchange of the atmosphere inside the building with the outside, taking into account that the animals give off heat and water vapour, as well as other gases such as ammonia, hydrogen sulphide and methane, which are produced by the animal droppings. Emissions depend on the species of animal, its concentration, weight, type of feed, etc.
Basic data on air conditioning
Things to consider:
- Physical factors, such as temperature, relative air humidity, luminosity and air speed over animals (especially in summer).
- Factors linked to the animal, considering its heat production, population density and harmful gas content.
- Environmental factors, such as climate and building insulation.
The air-conditioning of livestock buildings is essentially carried out by ventilation, which can be natural or artificial.
- Natural or static ventilation is based on natural laws (temperature difference, convection currents, wind speed and direction, using air inlets and outlets in the walls and on the roof). When based on natural conditions it is irregular and depends on the weather conditions. When the temperature difference between the indoor and outdoor air is low (2 to 3°C) a reduced air circulation is created; when the temperature difference is high (10 to 15°C) the air movement is intense and has to be controlled with dampers. The natural ventilation system is not used in facilities for intensive handling because of its random behaviour; it is suitable for facilities with large volumes of air per head. It is essential to locate the chimneys and windows to take advantage of the orientation of the building and the dominant winds and in accordance with the microclimate of the region.
- Artificial or dynamic ventilation allows the interior conditions to be adjusted independently of the climatic conditions. It is done by using low pressure fans of the helicoidal type and support heating in winter. It allows for fully automatic regulation, but requires greater investment, which must be paid for by improvements in livestock production. For summer, artificial ventilation must maintain an indoor temperature and relative humidity in the recommended range; water evaporation and condensation can be used to change the temperature of the renewed air. By using the heat pump the temperature can be optimised, but this implies operating costs that are often not compensated for.
They allow the air flow to be modified by varying its rotation speed, modifying the speed of the motor that drives it. Each type of fan has its own characteristic curves depending on the speed of rotation, which can be modified with variators of the voltage that feeds the motor that drives it. They can act according to two principles: the underpressure (extractors) or the overpressure of air, with or without air recycling. Either system gives good results, provided the installation is well calculated and constructed; the farmer must adjust them according to the environmental conditions.
Passive building heating and cooling systems:
- Design buildings to reject solar radiation in summer and to use it in winter.
- Use the walls of the building as masses for heat storage.
- To take advantage of the temperature changes between day and night, using the night radiation effect as a cooling source in summer.
Source: Spanish Ministry of Agriculture, Fisheries and Food