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Optimum Ventilation.

Traditional ventilation systems aim to minimise heat loss while preventing the build-up of excessive CO2 and humidity, which require the birds to consume more feed to achieve the same weight. This compromise has to be adjusted as the birds get older and ought to be, but is not always, adjusted to account for seasonal changes in ambient temperature and humidity.

There are many purposes for ventilation:

  • Supply oxygen-laden fresh air
  • Cooling: removal of heat released during respiration and activity, and also the solar gain through the structure, particularly in the summer.
  • Drying: remove moisture from the air (released during respiration or evaporating moisture in the droppings). If the litter is allowed to get wet then the production of ammonia will increase.
  • Remove harmful gases (carbon dioxide released during breathing or ammonia created by microbes operating on water in the litter).
  • Remove dust particles suspended in the air from the skin of the birds.
  • Dilute disease-causing organisms in the air.

As can be seen, greater ventilation has many benefits but requires the grower to burn more propane.

As margins are tight, profitability may depend on how well individual farm managers respond daily to bird appearance, weather and house conditions while containing their propane costs.

Using a cheap source of fuel for heating houses offers growers to change over from operating minimum ventilation rates to optimum ventilation rates.

Traditional Ventilation

Farmers use propane burners to directly heat the air in a house. Every tonne of LPG used introduces 1.6 tonnes of water and 3 tonnes of carbon dioxide directly into the house. This process also uses up oxygen and should this get too low carbon monoxide can also be created. The unwanted gases must be removed through ventilation. The replacement fresh air from outside needs to be warmed. This results in even greater use of propane. As propane is expensive, growers try to use as little as possible. Low ventilation rates raise humidity, create wet litter and ammonia and compromise bird health.

Optimum Ventilation

A choice of hydronic heating systems is used to deliver clean, dry heat, without adding water or unwanted gases to the house. The litter provides sufficient energy to more than replace propane. Ventilation is configured to optimise conditions. Keeping house humidity below 60% results in drier litter. Dry litter contains less available water for bacteria to use in a process that creates ammonia. Controlling ammonia significantly helps environmental conditions, improving bird welfare, performance and the wider environment. Hydronic heat is delivered at significantly lower temperatures than LPG, greatly reducing heat stratification within the building. The heat can be delivered through wall mounted radiators, or an air recirculation system. Energy modelling of the heat required to optimise ventilation suggests many sites can more than double the quantity of heat they traditionally use in order to improve conditions for birds.

The drying effect of ventilation

Optimum ventilation provides more heat and draws a greater volume of air through the house, in order to manage house humidity. This, coupled with not introducing the gases associated with LPG combustion, results in better growing conditions.

Because chickens drink a lot of water and enjoy a warm environment, the Relative Humidity in the house can be high. If the air outside is colder, its ability to carry vapour is reduced. The Relative Humidity of the air may be higher than inside but due to the temperatures it may still be desirable to increase ventilation. When the cold air is brought into the house and heated up its water carrying potential is increased and its relative humidity is decreased. Brining in this air and removing existing air then has a ‘drying effect’.

This below tool calculates the ‘drying effect’ of bringing in new air. If you change the inside and outside temperatures and relativity, see how the water content of the air changes. If the water content of the air outside is lower than inside then bringing more air into the house will have a drying effect.

Change the inside and outside temperatures and relativity using the sliders and controls and see how the water content of the air changes. If the water content of the air outside is lower than inside then bringing more air into the house will have a drying effect.
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The 21-28 day period when LPG is normally turned off is the critical period for maintaining dry litter. Improved liveability for the whole period of growth has been shown to be positively correlated with humidity and temperature during weeks 3-5. The bhsl program of optimum ventilation provides heat for improving house conditions right through the flock, subject to the being a drying effect as a result of the outside temperatures and relative humidity.
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