During incubation we need to ventilate to supply oxygen and remove carbon dioxide, moisture and heat. A point of discussion is always the amount of ventilation needed for the supply of oxygen and especially the removal of carbon dioxide, as this last one is the limiting factor for the metabolic rate of the embryo. This question is relevant, as it is very costly to install too much ventilation capacity in a hatchery, but it is even more costly to not install enough capacity and have a reduction in hatchability.
A lot of different values are used in the field, based on many years of experience with different machines. However, we can also calculate the theoretical value that we need for removal of the produced carbon dioxide, to at least have a starting point how much ventilation needs to be installed.
We know from research that embryos produce a specific amount of carbon dioxide and use a specific amount of oxygen per unit of heat that they produce. As we know the heat production rather precise, we can calculate the amount of carbon dioxide produced per (fertile) egg and per machine. With this production of carbon dioxide, we can calculate how much ventilation we need in m3 per hour if we know the concentration of carbon dioxide in the incoming air and the concentration we want to have in the machine.
In the downloadable excel program we can calculate the theoretically required ventilation rate if we:
know the size of the machine and percentage of fertility
know the heat production of the embryo
know the carbon dioxide in the incoming air
and know the carbon dioxide in the outgoing air.
In the ventilation is an RQ value (the level of carbon dioxide production compared with the level of oxygen consumption) given, which indicates if the embryos are using fat, carbohydrates or protein. For practical purposes this RQ value can be kept at 0,67.
A table is given with heat production values coming from literature, but they can also be altered. On the left side of the calculation individual values of heat production can be used for specific calculations.
Also the average heat production and the average ventilation is calculated, as a multi stage machine has more ages in the machine, but especially because when a ventilation rate for a hatchery needs to be determined, we have to realise that in a single stage hatchery there are many machines in all different stages of incubation, which all require a different level of ventilation.
For the hatchery phase we have to calculate for both eggs and chicks. Chicks require more ventilation as their heat production and with that their carbon dioxide producton is higher. In the calculation sheet an estimate of the distribution between eggs and chicks for each day is made. The hatchers are assumed to have the same size as the setters, although in practical situations they will most often have a smaller size.
The calculations are based on carbon dioxide. In practice we also have to consider ventilation for heat and ventilation for removal of moisture. This is not included in this calculation.