humid weather in basement

[crb7]

hi guys

i have a problem with my design and i will appreciate if anyone can help me.
i have a room in basement, that has high humid weather. its a residential room. is it possible to use exhaust fan for reducing humidity? if yes, how many ACH should i take?

 

[IRstuff]

But, is the humidity from the room, its surroundings, or the general environment?

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[crb7]

its not from the weather. i guess both surroundings and room.

 

[Compositepro]

If the outside air is dry, ventilation is your immediate answer. If not, you need a dehumidifier. Ultimately, you may need to look at diverting rain water away from the house, or install a pump in a sump to lower the water table around the basement.

 

[crb7]

tnx Compositepro

can u help me to choose the right ACH for the room?

 

[LittleInch]

Well if you do a simple search you fond that ACH typically range from 5 to 15 for residential properties.

Given your basement sounds like its rather humid, then 10 to 15 sounds like the right sort of number.

10-15 ACH will need a decent sized fan though and if you want to use it for residential purposes might need to be quite big to keep the velocity and noise down.

How big is this basement and what do you want to use it for?

Can you use dehumidifiers?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[saplanti]

In residential environment the source of humidity is very important. If you ask me you need to eliminate the source which may be water leak from plumbing of the upper floors, or from the walls (if you see some cotton like accumulation or mold), or sometimes from the ground under the floor.
In case the area is unheated and the humidity source is non of them above or similar, so heating or ventilating might be solution for short term.

 

[crb7]

tnx LittleInch and saplanti.

The basement is 21 m2 with 3m height so its volume is 63 m3.

 

[IRstuff]

Seems to me that you need to determine the source of the moisture and try to eliminated it at that source. Otherwise, you'd be looking at running an air handler 24/7, which sounds neither efficient nor reliable.

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[BronYrAur]

In what part of the world is this room located? With such a large air change rate, you will no doubt need to heat and/or cool the incoming air. Expensive for a residential basement. I would find the source as others have said. A portable dehumidifier would be an easy first step. You can get one with a built in pump to eliminate the need to empty the bucket.

 

[EnergyProfessional]

Study a psychrometric chart. note that the warm air that shows you 50% RELATIVE humidity, may be 70% RELATIVE humidity once cooled to basement temperature. So bringing in any new humid air won't help.

Unless the basement has a water source (i.e. ground water penetrating, hanging up wet clothes), all the moisture comes from air that enters the basement. Does the air come from an air conditioned home, or from the more humid outside?

If you don't have moisture sources (obviously you would want to remove those) and don't have infiltration from outside, just have some large opening to the rest of the house.

if you have a moisture source, or infiltration from outside, a dehumdifier may help. but careful, many people think they need one and show the water it collects as evidence. but if air comes in all the time, you are just dehumidifying the world. if your basement is just cold (look at psychrometric chart again), a dehumidifier won't work well,. they are rated to work at 80°F or some other ridiculous value.

No humidity problem will ever get resolved without looking at psychroemtrics. what, are you in Florida, or Arizona, or Alaska? Is the house cooled, and by what to what conditions? You won't get a good answer without that information.

 

[AdrienneGC]

There are two air change rates which will determine the indoor air quality: 1) the volume flow rate of total air into the space, and 2) the volume of fresh air you are introducing into the space.

For #1, a load calculation determines the total volume of air required to condition the space.

For #2, the EPA's website recommends 0.35 ACH but not less than 15 CFM per person or outdoor air, ASHRAE says 7.5 cfm/person + 0.01 cfm/ft^2. Ventilation air purges stale air and any toxins that accumulate, and creates a positive pressure in the space. Duct leaks, exhaust fans, stack effect, etc., can cause a negative pressure meaning that unconditioned hot/humid air will be pulled into the house through cracks and voids which is bad for building materials and bad for indoor air quality. If you put the building into slightly positive pressure by introducing outdoor air in a controlled fashion into the return of the air handler (and possibly pre-treating it), dry/conditioned air will be pushed out of the house through cracks and voids continually drying building materials while improving indoor air quality.


Here is an air change rate calculator to convert from flow rate to air change rate - it is in both English and metric units.


Adrienne Gould-Choquette, P.E.

http://www.adicotengineering.com