[kodo]

Hi-

I live in the Philly area in a brick house w/ no central air. We have hot humid summers.

I have an inexpensive ($150) Maytag portable dehumidifier in our basement:
http://www.amazon.com/Maytag-M7DH45B2A-45-Pint-Dehumidifier/dp/B0007P2J48

The basement is about 500sq feet, and we use it as a playroom and home gym.

I have the humidistat set at 50%. The unit is running pretty frequently on high humidity days (>90%).

Under these conditions the unit puts out a lot of heat, heating up the basement, which is too bad as it is otherwise an oasis of cool.

My question is: if I lay out a lot of money for a more efficient unit will it put out noticeably less heat, or, is that heat inherent in the process of dehumidifying?

I suppose another solution would be to set it at 55%. The main goal is to prohibit mold growth. I don't know if %55 is good enough for that.

Thanks,
Kodo

 

[adam_s05]

Energy cannot be created or destroyed

a dehumidifier takes the latent heat from the water vapour in the air and converts it to sensible heat which increases the tempurature of the air which you feel, plus it adds a little heat of it's own while running the compressor and fan motor. so getting a more expensive unit won't help with the heat. It was there to begin with and is still there when it leaves the unit.

I think adding more ventilation is the proper solution to your problem

 

[kodo]

there are a couple of basic things i don't understand.

my goal is to avoid mold growth in the basement. this has been a problem in the past, and is fixed w/ the dehumidifier.

a) i guess the basement is generally more humid then the rest of the house because the foundation is old and because it is cooler down there. but... what i don't understand is that i have read that relative humidity over 60% causes mold growth. if so, then why don't i have mold in the rest of the house when high humidity is common in philly in the summer? is it because the outdoor humidity fluctuates and so dips down below 60% enough of the time that the interior of the house dips also, defeating mold growth? but the basement retains more humidity so dips less often?

b) you recommend more ventilation. but that would defeat the dehumidifier. the basement does have windows. but if i open them i will be letting in humid air from outside.

thanks,
kodo

 

[teddy bear]

Raise the %RH setting. 55%RH is ok for mold control. One correction on the amount of heat a dehu generates, less efficient dehu use much more electricity as the %RH is lowered. It can be as high as 30-40% more heat as the operation continues to lower the %RH. With a small space that you describe, a good residiential dehu should work. Raise the setting cautiously while monitoring the %RH in the space and be aware of musty odors.
After your dehu wares out, investigate the Santa Fe Compact. Many report much less heat and lower %RH. They are expensive though.
Regards TB

 

[genduct]

At this time, ( I'm in Philly too) Sounds like you should just open a window in the basement or use a fan to exhaust at the same open window with the basement door open. The difference is that heat your dehumidifier is creating is costing you $$$$$$. Might as well get it for free.
You have to understand that the quanity of moisture in the basement air is close to the same as the house itself. The higher RH is because the temp is a little lower in the basement ( or you have a water/ dampness problem that is adding to the house RH)
It's physics. The only way to lower the RH is to cool the space

 

[wptski]

How much heat are you refering to? You say that it's set to 50%RH but I assume that you mean on the unit itself, correct?

I have a Santa Fe Advance in my 888 sqft basement and the humidistat is a mile off! I'm well into the dry or 35-45% labeled range and it turns on at around 52-54% and takes it down to 47-48% before turning off. I use a Fluke 971 to check the RH and a GE Protimeter HygroMaster to log/check the RH.

The basement temperature is around 70F. I used a PQ meter to log running time and using 3KWH/day in our latest humid weather with dew points in the high sixties and low seventies.

 

[teddy bear]

At this time, ( I'm in Philly too) Sounds like you should just open a window in the basement or use a fan to exhaust at the same open window with the basement door open. The difference is that heat your dehumidifier is creating is costing you $$$$$$. Might as well get it for free.
You have to understand that the quanity of moisture in the basement air is close to the same as the house itself. The higher RH is because the temp is a little lower in the basement ( or you have a water/ dampness problem that is adding to the house RH)
It's physics. The only way to lower the RH is to cool the space

Do more research! You are in error. Basement surfaces are cool like 60^F. Outside air is 85^F, 60%RH, 68^F dew point. when outside 68^F dew point air comes in contact with 60^F surfaces, condensation occurs. Biological growth follows shortly.
The key is to reduce the dew point of the basement air well below the cool surfaces temperature. Maintain a 50-55^ dew point in the basement space lowers the surface %RH. If the space is 70^F, 50-55%RH is needed to avoid damp surfaces.
Be careful what you say or believe that is on the enternet, inculding my statements.
Regards TB

 

[genduct]

Thanks Ted but let's assume that there is no vapor barrier between the spaces, therefore the grains of water per pound of air is the same, there fore the only thing that changes the RH is the temperature and yes if the basement surfaces are below dew-point , it will sweat. I agree with all that. The person seemed to say that the dehumidifier was running so much that it was heating up the basement.
I thought opening up the window to deal with a basement moisture problem with ventilation vs dehumidification seemed like a return to a simpler time.
Of course having the rain leaders discharge the roof 5 or 6 feet away from the foundation that might begin to deal with the disease vs the symptoms is probably the real solution. Also I think this person is right to be concerned I understand over 80% RH is the bug/slime growing conditions even with out liquid water.
I think you may have misunderstood my intent or I didn't do a good enough job of explaining. Anything that brings clarity is welcome from my point of view Thanks

 

[teddy bear]

Thanks Ted but let's assume that there is no vapor barrier between the spaces, therefore the grains of water per pound of air is the same, there fore the only thing that changes the RH is the temperature and yes if the basement surfaces are below dew-point , it will sweat. I agree with all that. The person seemed to say that the dehumidifier was running so much that it was heating up the basement.
I thought opening up the window to deal with a basement moisture problem with ventilation vs dehumidification seemed like a return to a simpler time.
Of course having the rain leaders discharge the roof 5 or 6 feet away from the foundation that might begin to deal with the disease vs the symptoms is probably the real solution. Also I think this person is right to be concerned I understand over 80% RH is the bug/slime growing conditions even with out liquid water.
I think you may have misunderstood my intent or I didn't do a good enough job of explaining. Anything that brings clarity is welcome from my point of view Thanks

I miss your point about letting outside high dew point air into a cool basement as a method of providing Low %RH to the basement.
Set the home on pers and remove the walls would provide a space below the home that would be hot and dry during a hot day and cool/damp during the night. Plus on rainy wet days the space is going to be wet. How does this help the problem? Ventilation only works when the outside dew points are low.
Outside air as a high dew point that is high %RH when at the basements temperatures. Dehumidifiers reduces the dew point and increase the temperature which eliminates mold. Poor dehus remove some moisture and add a lot of heat. The best remove much moisture and add a little heat.
Regards TB