Calculating ventilation

Calculating ventilation system requirements to create sufficient air exchange and meet quality aims is relatively simple.
The most important piece of information to establish is the maximum stocking density (or peak total flock weight) that will occur during each crop of birds.
That means working out what the maximum weight of each bird will be, multiplied by the number of birds in the flock. It is crucial to establish the total, both before and after thinning and base the peak ventilation requirement on whichever is the larger figure.
For example, at thinning on day 32-34 a flock of 40,000 birds weighing 1.8kg each would amount to a total stocking density of 72,000kg.
If 5,000 birds are then thinned out the 35,000 remaining would go on to reach a maximum average liveweight of 2.2kg/head and a total flock weight of 77,000kg. This figure should, therefore, be used to work out how much air movement is needed.
With the total weight confirmed it is then possible to work out the capacity of the ventilation system using an established conversion figure as a multiplier.
Hydor uses a conversion figure of 4.75 m3/hour/kg liveweight to arrive initially at a quantity of air removed per hour.
This conversion figure varies between equipment suppliers but 4.75 will ensure that the system will cope in extreme conditions.
For example, using a maximum flock weight of 50,000kg the air movement required per hour would be 237,500m3/hr.
To arrive at an airflow per second this is then divided by 3,600 (the number of seconds in each hour).
The final air movement required would therefore be 66 m3/s.
From that it is possible to calculate how many roof fans are needed. With Hydor’s HXRU vertical agri-jet 800mm diameter fan that would require a total of 14 extraction units sited in the apex.
For each fan, a total of eight inlets in the sides of the building are needed to draw in the total amount of air. In the case of the above example, that would require 112 inlets to be able to draw in the 66m3/s peak required.
Two winch motors are needed – one for each side of the shed – to raise and lower the inlet flaps and a 0.67kw motor for each of the fans.

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Post time: Sep-06-2021