Humidistat


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Old 06-12-10, 05:21 AM
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Humidistat

I find that the humidity is rising in my house while the temperature is not going up to turn on the AC.

Is this what a humidistat does. Turns on the AC because the humidity is high, but not the temperature??
JIm
 
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Old 06-12-10, 06:05 AM
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Not a pro on ac systems, up north most just fit in a window for a few days. Now, there may be a humidistat that controls the ac system, but you would just switch from one problem to another. A properly sized system would work either way. A system that is too big, will fail to remove enough humidity during its short runs. If you run it longer to lower the humidity, the temperature will/may become uncomfortable, and expensive.

Where you may want to look, is the source of the moisture. Outside air leaks into the house carry lots of moisture that has to be removed. Basements can be another source. Kitchens and bathrooms need to be vented to the outside when they are producing large quantities of moisture. Plants, aquariums, boiling water, or water leaks needing repair can all contribute ti the excess moisture.

The ac pros will be along to comment on the performance of your system to be sure it is removing the moisture it should. If you can post some details, like size/age of the house and size/age of the system it will be a start.

Bud
 
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Old 06-12-10, 09:33 AM
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As bud said lots of sources for moisture. But yes that is what a humidistat does. Unless you have a very good stat your system most likely does not have one. And even the good stat use a very cheap humidistat.
 
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Old 06-12-10, 10:04 AM
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Thanks airman, so the good controls actually attempt to monitor the RH. Do they also vary the cooling capacity to increase or decrease the air processing and thus the humidity removal? Or some other method that allows then to control both moisture and temperature?

Bud
 
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Old 06-12-10, 09:24 PM
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Bud yes they will over cool a degree or two to lower the rh. On the industral side they will bring on heat to remove the rh.
 
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Old 06-13-10, 12:02 AM
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In forty years of living in South Texas I've never seen humidity levels like we're seeing, day and night. Under normal conditions the humidity level is kept at bay by the normal cycling of the A/C. But this 90% RH is a challenge. Opening exterior doors with a strong breeze blowing lets moisture in. Indoor water use. IMO houses aren't as tight as they make out to be. I'm sure the breeze pushes air through any leak spot. I have a humidistat, all mine does is slows the blower speed when the indoor humidity exceeds my RH setting. The slower air speed removes moisture better and it prolongs the A/C cycle, also removing humidity. That's working good because before the A/C cycle is over, the blower shifts up to high speed, so that tells me the system is fighting high humidity levels but wins the battle (temporarily). My humidistat does NOT trigger the A/C to go on. The A/C goes on based on temperature.
 
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Old 06-13-10, 12:05 AM
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Also, we're having to manually work with the stat....daytime 76 and nightime 74. I could program it but their saying humidity levels will drop later this week.
 
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Old 06-13-10, 03:25 AM
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srercrcr, you mention: "IMO houses aren't as tight as they make out to be." When we measure/calculate the actual leakage of a home, a complete exchange of air within the home will occur every one (leaky house) to three (tight house) hours. That will give you an idea as to the battle you are fighting with those very high outside RH levels. Plus, 90 air at 90% RH goes over 100% when the temperature is lowered to your 76 inside temp. I'd have to check the charts to see exactly where the dew point is, but I'm sure it turns to rain before 76.

Bud
 
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Old 06-13-10, 04:55 AM
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Thanks for the responses!! What would be a good way to add some humidity control?
What I would really like is a thermostat that senses outside temp and keeps the house a few degrees cooler. I find myself constantly tweaking the thermostat.
JIm
 
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Old 06-13-10, 07:07 AM
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What I would really like is a thermostat that senses outside temp and keeps the house a few degrees cooler.
You must live very far north or have a high tolerance for heat. Around here a few degrees cooler would be 90. Maybe you need a dehumidifier not an AC.
 
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Old 06-13-10, 08:03 AM
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Florida Gulf Coast in Ft Myers area!! About straight across from San Benito TX. I find if I keep it too cool in the house I do not want to go outside. I guess on those 90 plus days it would be more than a few degrees.
JIm
 
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Old 06-13-10, 08:33 AM
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Originally Posted by jjrbus View Post
Florida Gulf Coast in Ft Myers area!! About straight across from San Benito TX. I find if I keep it too cool in the house I do not want to go outside. I guess on those 90 plus days it would be more than a few degrees.
Well I keep it cool in the house because I don't want to go outside. LOL
 
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Old 06-14-10, 01:22 AM
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Another thought regarding the battle against high humidity is the indoor coil could have some crud accumulated on it. That warm air going across the cold coil is where the moisture is removed, so crud cuts that ability drastically. Right now at 4 am its 75 degrees outside with 80% humidity, stat set at 74 with ceiling fans inreasing comfort level. It cycles infrequently, maybe every 15 minutes....just no heat load. If I put the stat at 73 it will be blanket time. Just can't win!
 
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Old 06-14-10, 04:44 AM
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Assuming your ac is working properly, it just may be too big and unfortunately, any improvements you make to reduce the energy costs and heat gain, will just make that ac look even bigger. A smaller ac unit has to run more often to bring the temperature down. That increased run time results in more moisture removal. So if a new system ever pops up as being needed, consider a smaller unit.

Now, to solve today's problem, Ray's comment about needing a dehumidifier would actually work. A dehumidifier is basically the inside and outside halves of your central ac all in one box. And they are much more efficient, as the hot and cold air is reused in the heat exchange process, which allows the unit to run continuously and thus remove the moisture. Except, they monitor humidity, not temperature. Operated in conjunction with your central ac, it would reduce the run time for the main system and allow you to use a slightly higher temp setting to achieve an even greater comfort level.

Some of the pros here have some dehumidifier models they like, and you could be comfortable tomorrow. And from what I saw on the HEAT (weather) channel, you may need that.

Bud
 
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Old 06-14-10, 04:50 AM
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Also I would make sure your fan is running at 400 cfm a ton in cooling. this will remove more RH.
 
 

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