When the outside temperature climbs, the fresh air demand increases in order to create sufficient evaporation and cooling (in extremely hot and humid situations obviously work with a minimum of ventilation). High ventilation volumes go hand in hand with a higher air speed through the filter which leads to a quadratic increase in filter resistance. In this kind of situation soiled and undersized filters in particular means too little fresh air is coming through. The cooling installation will be unnecessarily pressured (extra energy costs) and problems with evaporation can arise.

The coarse filter in the outlet should have at least a minimum of ¨÷ m©÷ filter surface per 100 m©÷ growing surface. This will prevent over pressure in the growing room becoming too high. It’s better to replace the filters each growing cycle The (relatively costly) fine filter in the inlet can be replaced at a later stage. Replacing it too soon is an unnecessary expense, but leaving replacement too long also means air resistance becomes too high – with all the inherent consequences The only safe option is to measure filter resistance with a pressure meter at full ventilation levels If maximum filter resistance has been reached (depending on the type of filter around 250 Pascal) its time to replace the fine filter.

Jan Gielen, Specialist climate & energy, C point

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