I have been having issues with humidity in my condo. I have not lived here long, so I do not have a long history with it. I am in youngstown oh. I originally started looking into humidity issues when towels that were used started smelling like mildew the next day. RC was around 62% it's highest. I have since purchased a 70 pint dehumidifier (the place is only 1200 sqft). This seems to be doing very little to change the humidity (though sucking up a lot of water).

I have a Nest thermostat that keeps track of my cooling. I currently have its away feature turned off, so it is basically a simple thermostat... but it tells me how much cooling is being done. On average the AC runs about 13 hours a day (on the hotter days, it was running 18.5 hrs a day). I set the temperature to 70 degrees. I should add here that on hot days, it can't keep up. Usually its 10 degrees behind, so if its 87 outside, its 77 in here. The return air temp when measured with a meat thermometer is around 76 degrees, and the vents are putting out 60 degree air. The current temp at the thermostat is 72

When i wake up in the AM, the humidity is down to something like 42... the dehumidifier is usually full, so i empty it. Throughout the day (when the AC is running), the humidity goes back up to 55-58%...very close to where it was without the dehumidifier. It goes up extremely fast. At 9 am it was 42, at 11 am it was 54. The ac started running during that time.

Today, the outside RH is 52%... its more humid inside than outside, at 54% right now.

I feel like there is an issue, as in my parents house (where it is 73% rh outside) they have no dehumidifier and the RH is 41%

I feel like 55-60% rh is too high, and I also feel that a 70 pint dehumidifier should not exhaust itself in a 1200sqft condo. My parents run the same dehumidifier in their 800sqft basement and it keeps Rh below 30. it's as if the AC is pulling in outside air, and I am trying to dehumidify the world.

Any idea of what is going on here?

 

High humidity can be a tough call when a service tech is actually at the residence.

I would see if the outside air duct has a damper and if it is wide open.
(I see 10 inch outside air ducts with no damper at all in high rise condos all too often)

I would verify that the coil is clean and that the secondary pan isn't full of water.

When I think of Condos I think of high rise homes with geothermal or chill water equipment. What type of air conditioning is in use with this application?

If this application has refrigerant running through the indoor coil it should be checked. The airflow should also be checked.

 

This is a condo delevopme t with only two floors. I am on the second floor. There's coils inside with refeigiant running through. It's r22.

Outside air duct? Whee would I find this? There's nothing in the attic to suggest any of the ac is venting outside

 

Air conditioning does not introduce humidity,this is basic physics. You have other issues, like pull outside air into the room/duct, lack of insulation, water in the pan, etc....

 

Humidity control is quite complex because the correct term for the humidity measurements you are using is RELATIVE humidity.
The percentage you are reading is relative to the temperature of the air that you are measuring.
The measurement of humidity level that is a true reading of the amount of moisture in the air is "grains per lb".
This will tell you how much actual moisture there is in a specific amount of air.

The reading you are measuring is the percentage of moisture in the air compared to how much it can hold at a specific temperature.
This is why your reading inside the house appears to have more moisture than what is outside.
You can not compare % RH readings that are taken at different temperatures.

I agree that there is a possibility that your air conditioner could use some serious maintenance.
If the unit is undersized you would expect it to run continuously and not reach set point.
If it is close in capacity to what you need it may not reach set point but you would expect it to lower the humidity.
If you have enough ambition the way to know exactly how much moisture is in your house and outdoors is to use a psychometric chart.

One thing not to difficult to do is shut off the power to the air handler and check the coil for cleanliness.
If you check it immediately after shutting off you could look for the possibly of icing up which could indicate a dirty coil or the need for professional service.
If you do check the coil you need to make sure you look at the upstream side of the coil.

 

I figured someone would correct me on the RH thing... yes, i understand that relative humidity is.. well, relative (to the temperature). My main point was comparing the two systems, my parents are in a more humid area without a dehumidifier, suggesting something is wrong with my system.

There is nothing in the pan and there is no icing. Everything seems as it should be. Now, as far as pulling outside air... the duct work does have some leaks, that taped extensively. I feel like I've got most the big stuff.

Humidity goes up when the ac is turned on, no denying that. I can turn it off and control the humidity quite well. So, the only way this could happen is if some of the return air is coming from outside? If the ac were a closed system (even with leaky doors and windows and whatnot), a 70 pint dehumidifier should be able to make headway in a 1200sqft space, right?

 

That makes no sense.

Yes.... your Rh may rise when first turning the A/C on as there is humid air trapped in the ductwork as well as condensation on the evaporator coil. But the rise should be very brief. Once the coil is cold the humidity should start to drop very slowly. Most of the work done by the A/C is removing the water from the air.

At this point it may be time to have the system and refrigerant charge checked by an HVAC tech.

 

I know it doesn't make sense, thats why it came here. In the am, after the AC has not run all night, at a temp of 70 degrees inside, the humidity will be 41% (running the dehumidifier all night). At about 11-12, after the Ac kicks in around 9, the humidity will be around 55% and it will take until the following morning to get it back to 41% with a 70 pint dehumidifier running nonstop in a <1200sqft place.

That to me is a mystery

If there is humid air or whatnot, would running the fan all day help (i know it would be costly)?

 

I read the beginning when first posted but have not gone back to read all replies, apology but will do if necessary.
A likely cause for the humidity drop at night and then rise after the ac comes on is either a terrible air flow balance from design or leaky or disconnected ducts.
When the pressure is not balances conditioned air is forced out while outside air pushes in, both are bad. Disconnected or leaking ducts that leak to or draw air from the outside do the same.
You stated that you thought this was a possibility do I stopped following as I thought you had it diagnosed.

When the ac runs you are exchanging air with the outside thus the rise in RH. Apology if that has already been stated.

Bud

 

the ductwork was never sealed properly, and I have done my best to tape all the connections off. The air conditioning has not come on yet today, so the RH is still 42. I just doubt its those leaks... they were small in comparison to the volume the system pushes. We will see here in a few hours as the temperature rises.

 

We know it is related to running the ac. I gave you two options, leaks or poorly balanced air flow.

Here are some questions.
1. Do you have a return in every room with a supply register?
2. How much of your duck work is outside of the conditioned space, like an attic or crawlspace?
3. Does your return duct network use "panned ducts" where framing channels are partially covered with sheet metal?
4. Where is your air handler?

For #3 you can remove the register cover and see if it is connected to a metal duct or just an open wood cavity.

If testing is desired, most energy auditors can test the ducts with a pressure fan. I believe code for new homes is requiring this when ducts are located outside the conditioned space.

Sealing ducts in a finished home can be complicated but they are under pressure so even small leaks count. Focus your search towards ducts outside the envelope. Panned returns are the exception because they can appear to be inside but connected through many leaks within the walls to the outside.

Bottom line is, you have found your problem, air exchange with outside air. Now finding the culprit and a solution is your challenge.

Another apology if I have repeated what others have stated. I hate extra reading.

Bud

 

1. there is a return in every room that has a vent, with the exception of the two bathrooms.
2. most of the ductwork is in the attic. Registers are on the floor, so thats behind the walls from top to bottom.
3. the registers are all (i believe) metal duct work, the returns, however, are just channels in the drywall.
4. the air handler is on the same level as the condo (level 2) and right outside the front door in a closet.

I will continue to try to seal up the leaks i have. There are so many poor metal to metal connections, and some are hard to get to. I'm trying to tape them, but I feel like some kind of expanding spray would be easier.

 

If your floor is poured concrete and if any of the ductwork is buried, you can sometimes get water in the ductwork.