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In order to choose the right dehumidifier you have to find out your need for dehumidification.
This could be done by following the check list below.
1. Determine what climate is needed
How is moisture causing a problem? Is it the relative or absolute humidity that is your problem? It is also necessary to know the temperature in order to calculate the size of the dehumidifier.
2. Moisture load from ventilation
Ventilation should be minimized when dehumidifying a room. Normally there is some ventilation in a room, when doors are opened or necessary ventilation for people in the room.
A tight room can have as low as 0,1 air changes per hour, a not so tight room with for example doors often open can have as much as 0,3 air changes per hour. Normally the ventilation air is outdoor air, which design moisture content has to be determined, see appendix for normal design conditions.
mV = 1,2 • V • (x1-x2) / 1000
where mV = moisture load from ventilation [kg/h]
V = total ventilation [m3/h]
x1 = water content for ventilation air, in most cases outdoor air [g/kg]
x2 = water content for the room air [g/kg]
3. Moisture load from people
People give out moisture to the room when they breathe and also through perspiration.
People at rest give out around 0,05 kg/h, whilst a person working will give out around 0,3 kg/h.
4. Moisture load from water surface
The warmer the water the more moisture given out to the air. Also dry air and turbulent airflow across the water surface gives a high evaporation rate.
mw = s • A • (x1-x2) / 1000
where mw = moisture load from water surface [kg/h]
s = coefficient for vaporization, normally 25 [kg/(m2 h)]
A = open water area [m2]
x1 = water content for saturated air with the water temperature, see table page 21 [g/kg]
x2 = water content for the room air [g/kg]
5. Moisture load evaporated from product
It is very difficult to calculate the moisture load from products as there are so many variables involved. A rough estimation has to be done case by case and then triaged.
6. Moisture load by diffusion
There is some moisture load by diffusion through building fabrics. Compared to other moisture loads this is normally negligible. In order to make things clear, we have a calculation example, where you can follow a moisture load calculation. You can also use the on-line calculation for immediate answers.
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The dewpoint |
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-solutions for humidity-related problems. Seibu
Giken DST AB |
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The dewpoint pdf |
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Humidityproblems
ARBS 2008, APRIL 21-23, MELBOURNE