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Hello,
i am modelling a greenhouse and the relative humidity results fluctuate a lot and sometimes remain constant at 100% (since i have an absolute humidity gain that comes from the plants).
My question is how can i set the humidity capacitance ratio of the zone to consider the effect of the plants inside the greenhouse ? and does the range have to be between 1-10 ?
Thank you
Mohamed.
Mohamed,
I think you have to be a little careful here; the humidity capacitance multiplier is a way of telling the building model that there are other things apart from the air in the zone that are able to absorb and desorb moisture. If your evapotranspiration model is already accounting for the moisture exchange between the plants and the air then you would not also want to account for the same again with the capacitance multiplier. Of course there are other things in the zone that might also be able to contain moisture (not the least of which is the soil). I would recommend that you run the simulation a few times, one with a humidity capacitance multiplier on the low side of what you consider to be reasonable (2-3?) and one on the high side (10?) and see if your simulation points to a different conclusion when you make those different assumptions.
As a side note, I think RH is a difficult metric to use, especially in greenhouses and have come to rely much more heavily on monitoring and controlling the absolute humidity ratio instead. The trouble with RH is that greenhouses don't have a lot of thermal capacitance. So with no change in moisture content at all, if the sun comes out suddenly and the drybulb temperature in the greenhouse goes up rapidly then your RH will fall. Likewise when the sun goes down, the RH goes up very fast not because there was a change in moisture content but because the temperature changed.
kind regards,
David
