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clevere1
Premium
join:2002-01-06
Vancouver, WA
kudos:1
Reviews:
·CenturyLink

Central AC system not reducing the humdity in the air?

Ok, I need a little advice here.

I have a Trane 13 seer heat pump, and a trane Forced air gas furnace. The heat pump of course runs most of the year unless the temp is to cold. I have a honeywell thermostat. The thermostat shows the heat temp, AC temp, outside temp, and indoor humidity. I do not have any equipment that reduces humidity in the air except for the AC system.

The AC system generally keeps the humidity in the air to are 41-44%. This is great because in order to help my wife with her allergies, the humidity must stay at the level.

Well so far this summer, the humidity in the house is around 50-52%. I've checked the pump that takes the AC condensation water and pumps it outside, it's working and not over full. I've tried turning on all the fans that vent outside, and I can't seem to drop the humidity. Any recommendations?
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Where's th' DAFFY DUCK EXHIBIT??



zen1

@optonline.net

the longer the AC runs the more humidity it will remove, it must not be running long enough for the amount of humidity in the air.. and opening the house to the outside is a bad idea, it will let the humidity in.. you might need a dehumidifier for the extra humid days that the heat pump can't remove enough humidity(without getting the house really cold).



SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3
Reviews:
·Verizon FiOS

1 edit
reply to clevere1

said by clevere1:

The AC system generally keeps the humidity in the air to are 41-44%. This is great because in order to help my wife with her allergies, the humidity must stay at the level.

Well so far this summer, the humidity in the house is around 50-52%. I've checked the pump that takes the AC condensation water and pumps it outside, it's working and not over full. I've tried turning on all the fans that vent outside, and I can't seem to drop the humidity. Any recommendations?
Before the real A/C guys like SandShark See Profile wake up, I'll throw this out. The colder the exchanger coil the more water it will take out of the air. Have you checked the temperature of the output air. Maybe your not getting cold enough.

Maybe it's more humid outside this year. Turning on the vent fans will only make it worse since the air that it's blowing out has to be replaced by more humid outside air infiltrating through cracks etc.

Edit: just looked at where you are and the normal temp for now 69F with a dew point of 55F That's more dehumidifier weather than A/C

--
--
--
"Facts do not cease to exist because they are ignored." - Aldous Huxley

"I'm tellin' you, man, every third blink is slower" - Fillmore


shezams
My Other Car Is A Zamboni
Premium
join:2001-08-14
Hyattsville, MD

1 edit
reply to clevere1

Do you have a multi speed fan on the air handler? This could make a difference if it were not working correctly or if it is not in automatic. Some high efficiency units vary the speed, and by moving the air more slowly there is more time for the humidity to fall out at the coil. As mentioned the unit also needs to run long enough, so if the unit is not sized correctly for the house it will not dehumidify well. Bigger is not always better - too large a unit will cool but not dehumidify.You could try lowering the temp a bit especially if you have a fairly high setpoint to see if it helps lower the humidity.
--
Simple rules - no offsides, no intent to maim, everything else is all good!



Greg_Z
Premium
join:2001-08-08
Springfield, IL
reply to clevere1

41-44 is way too low. 50-52 is better recommended for indoor humidity.
--
I threw out the map a long time ago. Now I follow my own direction!



Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1
Reviews:
·Callcentric

1 edit
reply to shezams

said by shezams:

could try lowering the temp a bit especially if you have a fairly high setpoint to see if it helps lower the humidity.
I agree with everything you said except for this. If you use a higher setpoint, then the AC will have less humidity to pull out because of the higher temperature. Higher temperature means lower relative humidity... Lower temperature means higher humidity.

The more you cool your house, the more you raise the relative humidity and the more the AC has to work at removing that humidity. If you set the thermostat higher then you have less relative humidity to pull out.

For a brief explanation of relative humidity for those who may not know... Relative humidity is like water in a bucket. If you heat the air up, it's like having a larger bucket. Cool the air down and you shrink the bucket... The amount of water stays the same. That's why it's called relative. If you cool the air down you have the same amount of water occupying a smaller space. This makes for a high relative humidity. If you were to heat the air up, you make the bucket larger and so the relative humidity drops. That's why air in the winter time is so dry but in the summer it's too humid. In the winter we are heating the air, dropping the relative humidity, while in the summer we are cooling it creating the opposite effect.

If you want to reduce your relative humidity, you should set your thermostat higher, add a vapor barrier to your attic insulation and buy a de-humidifier.
--
"The penalty good men pay for indifference to public affairs is to be ruled by evil men."
- Plato -


mityfowl
Premium
join:2000-11-06
Dallas, TX
reply to clevere1

Actually your in the screwed zone!

You need less tonnage of AC so that it runs longer. The longer it runs the more humidity it removes. More tonnage cools faster but doest remove as much moisture/humidity.

So you either need to switch to a smaller ac condenser or you need a dehumidifier.

Lots cheaper to incorporate a dehumidifier.

The system has to run to remove the humidity.



clevere1
Premium
join:2002-01-06
Vancouver, WA
kudos:1
Reviews:
·CenturyLink
reply to Greg_Z

said by Greg_Z:

41-44 is way too low. 50-52 is better recommended for indoor humidity.
not when you have a dust mite allergy.
--
Where's th' DAFFY DUCK EXHIBIT??


mityfowl
Premium
join:2000-11-06
Dallas, TX

1 edit

why not just put some bleach in the ducts?

I abosuloutly guarentee that the mites won't like bleach.



mityfowl
Premium
join:2000-11-06
Dallas, TX
reply to clevere1

Now it sounds like excuses.


shezams
My Other Car Is A Zamboni
Premium
join:2001-08-14
Hyattsville, MD
reply to Sly

The idea with lowering the setpoint slightly is to get the unit to run longer and condense out more moisture - I do get humidity - I do building automation. On a commercial scale we slam open chilled water valves to the cooling coils and reheat as needed to control humidity, but even a standard AC unit will drop out more humidity the longer it runs - if it is oversized you will be too cold before it has a chance to do the job - the too large coil will make the air cold too quickly and the unit will cut off before it has time to drop out the moisture. A slower fan speed would help some because it gives the air more time at the evaporator coil and will let the unit run longer and so drop the moisture out. A dehumidifier may be the cheapest solution if the AC is doing what it can and has no maintenance issues.
--
Simple rules - no offsides, no intent to maim, everything else is all good!



SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3
Reviews:
·Verizon FiOS

1 edit
reply to Sly

As I said in a previous post, if you look at the weather where clevere1 See Profile is a dehumidifier is the obvious choice.

Sly See Profile I understand you're concern about relative humidity but you seem to miss that the A/C is removing moisture as it cools the air. If the home is sealed well, there will be less additional outside moisture entering. Most of the heating will be conductive or radiative. Every time the A/C runs the more moisture it removes, gradually lowering it.

Dust mites
»www.achooallergy.com/about-dust-mites.asp
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--
"Facts do not cease to exist because they are ignored." - Aldous Huxley

"I'm tellin' you, man, every third blink is slower" - Fillmore



Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1
Reviews:
·Callcentric

1 edit
reply to clevere1

Agreed with others in that you are sort of in the "screwed zone". Yes running the AC will pull out moisture but it will also "shrink" the size of the room. In this case, running the AC might actually raise the relative humidity because it is cooling down the house too fast. Another option may be to raise some blinds to let a little heat in. If the OP has rooms closed off, then open them. This will give a little more time for the AC to remove moisture since it will have to run longer.

Another option is a heat-pipe retrofit. I'm not really sure where you can get them from as I've looked for one myself... but basically it's a passive device which mounts in the air handler and super cools the air to draw moisture out. After the moisture condenses, the heat pipe then warms the air back up to where it was before it was super cooled. The net effect is that your house still gets cool... but you now have a section of your heat exchanger which is much cooler and this draws moisture out more efficiently.

»www.heatpipe.com/

[edit] added pics...
--
"The penalty good men pay for indifference to public affairs is to be ruled by evil men."
- Plato -


iiiiinovation

@sbcglobal.net

quote:
In this case, running the AC might actually raise the relative humidity because it is cooling down the house too fast.
quote:
Relative humidity is like water in a bucket. If you heat the air up, it's like having a larger bucket. Cool the air down and you shrink the bucket...
how can the AC "raise" humidity? the AC has to put out water vapor and saturate the air to raise humidity, doesn't it? also, i'm no expert but how does the humidity "shrink"? doesn't cool air hold less water molecules then hot air in a cubic feet? now lets say a room with 48 cubic feet is 85 degrees F - those 48 cubic feet of air will hold more water molecules therefore humidity is higher. what if the room gets cooled to 70 degrees F - now the 48 cubic feet are holding less water molecules which means less humid. now getting the AC involve in the picture, at a lower set point the evaporator coil will gather more air water molecules because it has to run longer to cool the house down which in turn lower the humidity. at any rate, it will lower the humidity but the house will be cooler making it uncomfortable.

BTW, i do get your example about the pipes. the pipes warm up the air, since warm air hold more water molecules, and when they pass over the evaporator coil it gathers/collects more water off of the warm air going over it. stilll, the AC alone is removing humidity by condensation.

i'm open for any corrections.


iiiiinovation

@sbcglobal.net
reply to clevere1

EDIT:

BTW, i do get your example about the pipes. the pipes warm up the air, since warm air hold more water molecules, and when they pass over the evaporator coil it gathers/collects more water off of the warm air going over it. stilll, the AC alone is removing humidity by condensation.

NM, those "heat pipes" cool the evaporator air intake a bit, DOH! (must be the hangover i had this morning). this quote explains it all.

"Old energy-inefficient air-conditioners had very cold cooling coils, which removed sufficient moisture from the air. Today's high efficiency machines have much warmer coils as the coil is generally larger, and less energy is used to cool it, but they save energy at the expense of not removing as much moisture. The problem, up until now, has been how to run a cooling coil cold enough to remove plenty of moisture, while not having to use extra energy to do so."

»www.tropickool.com/heatpipes.htm



Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1
Reviews:
·Callcentric

1 edit
reply to iiiiinovation

You're getting relative humidity and absolute humidity mixed up... Yes, it's true that running the AC will reduce the amount of water in the room... but it also cools down the air which reduces the total amount of water the air can hold.

If you have 85 degree air and it is at 100% relative humidity, this means that that air can not possibly hold any more moisture. If you were to cool that same air down, you reduce the amount of water that the air can hold because as the air molecules cool down, they move closer together, leaving less room for the water. When you cool the 85 degree air down that was at 100% relative humidity, some of that water will have to precipitate out (condense) while the air is cooling. Just because the water precipitates out does not mean that the RELATIVE humidity is reduced.

If you have air at 65 degrees with 100% relative humidity and you have 85 degree air at 100% relative humidity, the 85 degree air will have more actual moisture in it even though they are both at 100% saturation. It is the relative humidity that we are trying to reduce in our homes, not the absolute humidity. As relative humidity increases and the air becomes more saturated, that moisture is likely to condense in the walls and insulation and form mold and mildew... 85 degree air at 50% relative humidity is better than 65 degree air at 80% relative humidity. That 65 degree air is closer to the saturation point and so it is more likely to condense even though the 85 degree air might actually have more moisture in it. The 85 degree air can hold more moisture and so relatively speaking, the humidity feels lower.

When you run the AC, you are cooling the room. This reduces the amount of moisture it can hold. So while you are cooling the room down, the AC is pulling some moisture out but it is also reducing the amount of total moisture the air can hold at the same time. If the room cools down faster than the water can condense, then the relative humidity will rise. The absolute humidity may drop but it is the relative humidity that determines when the water absorbed in it will condense.

Going back to the OP, if the AC is cooling down the house too quickly, then open up some window shades and give the house some heat to force the AC to run longer. This will give more time for the AC to pull moisture out of the air and lower the relative humidity. Having a proper moisture barrier is important though. Never open a window or turn on an exhaust fan. By doing so, you are pulling humidity into your home and as it hits your cool air, it will condense and feed mold.
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"The penalty good men pay for indifference to public affairs is to be ruled by evil men."
- Plato -



iiiiinovation

@sbcglobal.net

OK, so i see what you mean. by lowering the temperature the air will have less room to "hold" the water vapor therefore will raise the relative humidity to 100% humidity faster because relative humidity means, and i quote, "Relative humidity is the amount of moisture in the air compared to what the air can "hold" at that temperature. When the air can't "hold" all the moisture, then it condenses as dew." so...past 100% relative humidity is where water vapor will condensate. AC condensate means it's throwing water out from the air inside but it's not leaving the house at a comfortable relative humidity level. in other words if the relative humidity outside the house is 80% at 89 degrees F, lowering the temperature inside the house in an attempt to reduce the relative humidity inside will fail because you will "overflow" the amount of water vapor the cooler air inside the house can "hold" (i.e. raise relative humidity).

so...it is safe to say that during high relative humidity out side the house- lowering the temperature inside the house will increase relative humidity. in such case, to keep relative humidity at a comfortable level (below 50% for OP), it will require the aid of a dehumidifier or cheap ways to control relative humidity inside, like trying to get the inside air warmer (e.g. opening curtains on windows), so the AC will run for longer periods of time having more time to condensate more water vapor while keeping relative humidity at a comfortable level with out having to lower temperature.

nice...i need to look into this further because i don't quite grasp the concept but thanks for the input.

the OP should gather good info from this . if not i don't know any easier way to explain this whole deal.



clevere1
Premium
join:2002-01-06
Vancouver, WA
kudos:1
reply to clevere1

Thanks all for the input. I'm going to purchase a dehumidifier.
--
Where's th' DAFFY DUCK EXHIBIT??



SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3
Reviews:
·Verizon FiOS

said by clevere1:

Thanks all for the input. I'm going to purchase a dehumidifier.
Thanks for alerting me to dust mites. It would explain some of the problems I have.

K Patterson
Premium,MVM
join:2006-03-12
Columbus, OH
kudos:1
reply to clevere1

Having been a design engineer for humidistats, I would suggest that you not trust the humidity reading on your thermostat. Beg, borrow, or steal a sling psychrometer. It has two thermometers, one of which has its bull covered with a wet wick. You whirl it around for a few seconds, read the thermometers, and look the humidity up in a table.



Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1
Reviews:
·Callcentric
reply to iiiiinovation

said by iiiiinovation :

the OP should gather good info from this . if not i don't know any easier way to explain this whole deal.
NP. I know it's not real easy to explain... That's why I like the bucket analogy. A warm room is like a large bucket while a cool room is like a small bucket. Relative humidity is the measure of water concentration in the air at a given temperature. If you "shrink" the room by cooling it off, the same amount of water is now squeezed into a smaller space and so the relative humidity increases.
--
"The penalty good men pay for indifference to public affairs is to be ruled by evil men."
- Plato -


SparkChaser
Premium
join:2000-06-06
Downingtown, PA
kudos:3

An A/C sanity check. Outside 83F RH=66, inside 73F RH=46



Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:1

So?



iiiiinovation

@sbcglobal.net
reply to Sly

sorry to bring this up again but lowering the temperature will lower RELATIVE HUMIDITY because lowering HUMIDITY it self will, in fact, lower RELATIVE HUMIDITY. therefore, by lowering the temperature in the AC, the evaporator will gather more water from the air in effect lower, after a while, the HUMIDITY and lower RELATIVE HUMIDITY. the longer the AC runs...the more HUMIDITY it removes...the more RELATIVE HUMIDITY "shrinks" (up to a point). what we failed to include in the equation is the outside RELATIVE HUMIDITY and temperature play a BIG role in how much HUMIDITY/RELATIVE-HUMIDITY you can remove from your house with out having to have the inside AC temperature setting at an uncomfortable level.

in other words if the inside house is 79 degrees F and RELATIVE HUMIDITY is 55%, the longer the AC runs the lower the RELATIVE HUMIDY will be (up to a point depending on the outside numbers because the outside temp and relative humidity play a big roll, before inside temps move out the comfortable zone).

just like in the hot summer days - the hotter it is the more the AC has to run to keep the inside house at a comfortable temperature. same can be said about low temperatures - the lower the temperature is outside the harder the heater will have to work to keep a comfortable temp inside the house. therefore, the higher RELATIVE HUMIDITY outside the house is the harder the evaporator AC will have to run to remove humidity (condensate) therefore lowering the temperature below comfortable levels. the lower RELATIVE HUMIDITY outside is the higher AC house temps will have to be to keep RELATIVE HUMIDITY within 50%.

in other words the AC is not enough to maintain it about 50% inside the house RELATIVE HUMIDITY if the outside is very high/low.

so in conclusion, both, lowering the temperature (lower set point) and raising the temperature (high set point) will both help control RELATIVE HUMIDITY but will sacrifice comfortable temperature levels .

so...we are both right

i'm open to any corrections.