For an adequate ventilation system it is essential that air comes in in a controlled way. This holds for poultry houses but also for incubators. To achieve this we have to reduce air leakage as much as possible, because any leakage will reduce the amount of air that comes in in a controlled way. As most systems are ventilated by negative pressure (air coming in because air is pulled out of the house/machine creating a negative pressure), an air leakage will very quickly result in significant amounts of uncontrolled air coming in.
In poultry houses, we can test the amount of leakage by checking if we can create a negative pressure. We close all the inlets and doors in the house, and we run one ventilator. If we then measure the pressure difference between the inside of the house and the open air outside, we should see that in the house the pressure is significantly lower than outside. If this is not the case, it means that the air removed by the ventilator is compensated by air coming in through leakages (doors, cracks, openings in walls for water lines or electrical lines, not well closing inlets etc). This means that if we ventilate the correct amount of air in total, only a part of that air comes though the inlets, resulting a lower air velocity in the inlets. If the air velocity in the inlets is low, we have less air speed to reach the center of the house, air will fall down to the floor too quickly without being properly mixed with the air in the ceiling of the house. This will create wet litter and more heating costs, especially in winter times with minimum ventilation. We can compensate the lack of air velocity in the inlets by ventilating more, but that will add to the costs as well.
But also in summer time with tunnel ventilation it will create problems, as all the air that will not come in through the tunnel inlets but comes in in an uncontrolled way will not add to the air velocity in the house, resulting in less cooling effect.
In incubators air leakage also creates unfavorable conditions, because the incoming air will usually be colder compared to the air in the machine. As this air is coming in uncontrolled, this cold air will not be properly mixed in the machine and cold spots will be created.
In incubators we cannot easily check the air leakage by checking the negative pressure as we do in a poultry house. However, we can check the air leakage by checking the air loss if all the dampers are closed. We run a full machine with all the inlets closed, for instance during the first week of incubation when ventilation is not needed. We then bring in a high level of CO2 (or another tracer gas but usually CO2 gas and CO2 sensors are often already available in a hatchery), for instance 10.000 ppm. We let the machine run with the dampers closed and we measure how long it takes to reduce the concentration to half of the initial value. So if we start with 10.000 ppm we check how long it takes until the CO2 concentration is reduced to 5000. When we start with 8000 ppm we check when it reaches the level of 4000. When we really want to be precise we have to correct for the level of CO2 in the incoming air, but checking the so-called half time (reduction of the concentration to half of the initial concentration) without correction for the CO2 in the incoming air is sufficient. This half time is not dependent on the initial level of CO2, so the reduction from 10.000 to 5000 ppm takes approximately the same amount of time (half time) as the reduction from 8000 to 4000 or 6000 to 3000.
In this way we can check how air tight (sealed) machines are, and for instance if there are differences between different machines in the same hatchery. This is important as the level of sealing can have a significant influence on the cold spots in the machine.
The level of sealing is different for different types of machines, so it is not that easy to give an overall target or standard. However, a well-sealed machine should have a half time of minimum 1-2 hours, although good machines can reach levels even up to 4-5 hours or more.