The density of water vapor is 0.804g/litre, which is significantly less than that of dry air at 1.27g/litre at STP (i.e. 0 deg C & 14.504 psi).
If you are not convinced, check it out at: http://en.wikipedia.org/wiki/Water_vapor
What is the implication?
"More humid" air is lighter than "less humid" air. This is what happens in our weather system every day. Warm moist air rises several Km high up in the atmosphere to form clouds.
Somebody labeled this as "stupid logic"..
If you recall the lessons of high school chemistry (elementary science):
Water molecule is H2O - 2 Hydrogen atoms & 1 Oxygen atom -> molecular mass of 2+16 =18 units (neglecting the electrons mass).
Likewise, air is about 21% Oxygen & 79% Nitrogen
Molecular mass of O2 is 16x2 -> 32 units
Molecular mass of Nitrogen N2 is 14x2 -> 28 units
I'll leave the rest to common sense.
What this means to our bird house micro environment?
For simplicity of putting the idea across, let's assume the bird house has the same temperature & pressure between floors. If we create "more humid" air on lower floors, the "more humid" air will drift upwards to upper floors gradually.
How do I made use of this principle?
At a 4-storey shop unit bird house, the 2nd storey has the most birds - i.e. many nestlings are around during the day too. I wouldn't set up the humidifier at that level. What I did was to place the humidifier (with hygrostat control) near the staircase on the ground floor & let the humid air drift upwards slowly.
I did achieve 75% to 80% R.H. most of the time.
Lately, I am testing another approach. I have a dripping tap just enough to keep the ground floor wet but not flooded. The idea is using the floor surface to provide a wide evaporation surface. If this works out well, then the humidifier on the ground floor is not required.
4 comments:
assuming all levels to be equal and your source of w vapour is from the bottom, then by deduction the top floor will always play catch up ( slowest to reach 100 rh)
Come December if yr hse is well ventilated will the top floor be too dry ...the driest
i would prefer to achieve dew point tempreture on the top floor and let condensate slide to the bottom.
I do have additional humidifiers on the upper floors. My intention is to avoid one at the second storey where birds are most populous at the moment.
In real life, conditions are not static always e.g. varying wind pressure that affect airflow in/out of entrance hole etc.
I monitor & data log each floor and take corrective action accordingly.
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