Split System, High Humidity - HVAC - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 07-24-2011, 12:50 AM   #1
Newbie
 
Join Date: Jul 2011
Posts: 18
Rewards Points: 10
Default

split system, high humidity


Hi All:

Found myself a problem, that I need some advice on.

I have American Standard X59 4 ton compressor and and a variable speed air handler TW-E set at 4 tons 450 CFM/Ton.

The problem I'm seeing is that the humidity seems to be high even with the system running, 60% humidity. This is a system hat dehumidify for 4 minute s and then ramps up to full speed to cool. Researching the problem, I found that the fool that installed the system sold me an over sized system by .5 ton maybe more. I found a great sizing calculator online and with guesstimates found that I should have a 2.5 ton system. Tomorrow I will do a more detailed calculation, but the site I was on generalized that a 2110 SQFT home in the NE should have a 3.5 ton unit installed.

The air handler is very configurable and I wanted to get some experienced opinions before I made any changes to the system.

First, I am able to change the CFM's/ton from 450 to 400, would this help my humidity problem?

Second, I just began reading about mismatching units. If I configure the air handler as a 3.5 unit, do I stand a chance of freezing the unit with a 4 ton compressor?

Thanks a lot for anything you think of.

-pauli

Advertisement

pauli is offline   Reply With Quote
Old 07-24-2011, 06:02 AM   #2
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,457
Rewards Points: 4,560
Default

split system, high humidity


450 a ton is too much if you want lower humidity. Set it for 350 a ton. Should make a big difference in you RH.

Advertisement

beenthere is online now   Reply With Quote
Old 07-24-2011, 10:12 AM   #3
Newbie
 
Join Date: Jul 2011
Posts: 18
Rewards Points: 10
Default

split system, high humidity


Quote:
Originally Posted by beenthere View Post
450 a ton is too much if you want lower humidity. Set it for 350 a ton. Should make a big difference in you RH.
Thank for the confirmation, I was up late last night doing some reading, it was suggested that lowering the CFM's would work for humidity problems, but would it create another issue as well?

By lowering the CFM's, your actually changing the force at which the unit can throw air. I originally had a static pressure issue, were the duct guys built a square supply box which cause some bad negative pressure. I had someone come in and replace that with a reducing supply pipe. The negative pressure problem went a way, and a result is that there was this incredible amount of throw from the grills. The humidity never changed, it never got worse or better.

So now if I change to 350CFM, which I can do by changing the correct dip switch for my size compressor, what will that do to the throw from the grills, will it be the same, only less noticeable? I guess I'm worried about the house not cooling as well as when it set to 450 CFM's. Maybe that's a good thing?

thanks

-pauli
pauli is offline   Reply With Quote
Old 07-24-2011, 10:18 AM   #4
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,457
Rewards Points: 4,560
Default

split system, high humidity


Throw will be decreased, since both static and velocity pressure will also be decreased. The system will run longer, and remove more moisture. Which will give the system more time to mix the room air and conditioned air.
beenthere is online now   Reply With Quote
Old 07-24-2011, 10:26 AM   #5
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 10,084
Rewards Points: 806
Default

split system, high humidity


Use a proper heat load calculator. Some of those free cheap ones just round off figures and are not very accurate. You get what you pay for.

Load Calculator
__________________
"Cut it twice and it is still too short".
yuri is online now   Reply With Quote
Old 07-24-2011, 11:37 AM   #6
Member
 
Join Date: Aug 2008
Posts: 131
Rewards Points: 75
Default

split system, high humidity


Quote:
Originally Posted by beenthere View Post
450 a ton is too much if you want lower humidity. Set it for 350 a ton. Should make a big difference in you RH.
I would try 400 CFM/ton first to see if that corrects the humidity problem. If not, then try 350.
kb3ca is offline   Reply With Quote
Old 07-24-2011, 11:44 AM   #7
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,457
Rewards Points: 4,560
Default

split system, high humidity


Quote:
Originally Posted by kb3ca View Post
I would try 400 CFM/ton first to see if that corrects the humidity problem. If not, then try 350.

At 350, he may be able to set his stat higher, and feel more comfortable. But he can experiment as much as he wants, till he finds the right setting for him and his house.
beenthere is online now   Reply With Quote
Old 07-24-2011, 12:34 PM   #8
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,976
Rewards Points: 2,048
Default

split system, high humidity


I would think that a lower coil temperature will result in better dehumidification.

If the mechanics don't have any adjustments then lowering the fan speed should result in a lower coil temperature.

If the minimum coil temperature is not that low then the system will never do a good job of dehumidifying.

The same batch of air will be at a higher humidity if its temperature is lowered. Dehumidification happens when the air is cooled so much that its humidity would want to go over 100% in which case some of the water vapor condenses out.

If the coil freezes up then you need to increase the air flow so the incoming air keeps the coil from getting that cold and the condensed moisture runs off before it can freeze.

You may want to have someone come in to see whether the system has the proper amount of Freon and is operating at its best.
__________________
Forget super sized fries. The Washington Redskins could promote healthy eating with First Lady Obama by choosing a (red skinned) turnip for a mascot.

Last edited by AllanJ; 07-24-2011 at 12:40 PM.
AllanJ is offline   Reply With Quote
Old 07-24-2011, 09:57 PM   #9
Newbie
 
Join Date: Jul 2011
Posts: 18
Rewards Points: 10
Default

split system, high humidity


Thanks everyone for the input:

We like to keep the temp around 74, its high, but we don't want to bleed the grid.

This is what I did so far:

1) Set the air handler to 350 CFM/ton.

2) Opened all the dampers, I had to adjust them to control the air flow.

3) I did not change the rating of the Air handler, it is still configured as a 4 ton handler.

Results:

Previously, the air handler would cycle every 15 minutes. !5 minutes on and 15 minutes off. This is including the enhanced mode dehumidifying cycle which is 7.5 minutes long when the system was running.

Now, the system is on for at least 30 minutes. The humidity is still on the high side about 50%, but the unit has only cycled twice at 74 degrees.

This is still better than the 60% I saw in the past, but I'd like to get it down to 45%. I'll watch this for a week or so and see what happens, maybe over time the RH will drop to 45% or lower. I tell you, its tough to get use to not hearing the vents. That will be an adjustment.

Thanks

-pauli
pauli is offline   Reply With Quote
Old 07-24-2011, 10:01 PM   #10
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,457
Rewards Points: 4,560
Default

split system, high humidity


Get an IAQ(YTH9421)thermostat. It can slow the blower down for the whole run cycle if the humidity is above set point. Or leave it go to full speed, if the humidity is below set point.
beenthere is online now   Reply With Quote
Old 07-24-2011, 10:51 PM   #11
REP
Member
 
Join Date: Jul 2011
Posts: 615
Rewards Points: 500
Default

split system, high humidity


Quote:
Originally Posted by pauli View Post
Thanks everyone for the input:

We like to keep the temp around 74, its high, but we don't want to bleed the grid.

This is what I did so far:

1) Set the air handler to 350 CFM/ton.

2) Opened all the dampers, I had to adjust them to control the air flow.

3) I did not change the rating of the Air handler, it is still configured as a 4 ton handler.

Results:

Previously, the air handler would cycle every 15 minutes. !5 minutes on and 15 minutes off. This is including the enhanced mode dehumidifying cycle which is 7.5 minutes long when the system was running.

Now, the system is on for at least 30 minutes. The humidity is still on the high side about 50%, but the unit has only cycled twice at 74 degrees.

This is still better than the 60% I saw in the past, but I'd like to get it down to 45%. I'll watch this for a week or so and see what happens, maybe over time the RH will drop to 45% or lower. I tell you, its tough to get use to not hearing the vents. That will be an adjustment.

Thanks

-pauli
You are on the right course.If you are indeed oversized you need to get the unit slowed down so its on longer.Just as Beenthere is telling you.
What you might not be thinking about.Everything in your house holds humidity..Rugs ,drapes ,wood furniture,the dry wall walls and cieling,almost everything except glass and rock.Everytime you make tea or coffee,anytime you boil water or even roast a roast releases moisture.
It might take a week or so to get at some of the humidity locked into your house.
A NOTE however is to keep an eye on the indoor coil for signs of frost.This is how a frozen a coil starts and if you see signs then you want to bump up the cfm .If you had had a proper load calc done then you would not be having this problem.This is info that you should share with all your friends and relatives LOL assuming those two groups are not mutual HAHA.
REP is offline   Reply With Quote
Old 07-25-2011, 12:11 AM   #12
Newbie
 
Join Date: Jul 2011
Posts: 18
Rewards Points: 10
Default

split system, high humidity


Quote:
Originally Posted by beenthere View Post
Get an IAQ(YTH9421)thermostat. It can slow the blower down for the whole run cycle if the humidity is above set point. Or leave it go to full speed, if the humidity is below set point.
Beenthere:

I will look into this, as I'm not so sure the lower CFM are working. The unit has slipped into the 76 degree setting for over night, the humidity levels have returned.

According to my installers guide, I can get an optional humidistat. Not sure were it goes but there is wiring instructions for R and BK. Not sure if this is in the unit or at the thermostat as you suggest.

Anyway, do you or anyone think that I should just dump the 4 ton compressor and get a 3.5?

Also if someone could be so kind as to tell me what I've done?

I mean whats the difference between a 3.5 air handler configured for 400 CFM/ton and a 4 ton unit configured for 350 CFM/ton?

Thank again for everyone's help.

-pauli
pauli is offline   Reply With Quote
Old 07-25-2011, 12:17 AM   #13
Newbie
 
Join Date: Jul 2011
Posts: 18
Rewards Points: 10
Default

split system, high humidity


Quote:
Originally Posted by REP View Post
You are on the right course.If you are indeed oversized you need to get the unit slowed down so its on longer.Just as Beenthere is telling you.
What you might not be thinking about.Everything in your house holds humidity..Rugs ,drapes ,wood furniture,the dry wall walls and cieling,almost everything except glass and rock.Everytime you make tea or coffee,anytime you boil water or even roast a roast releases moisture.
It might take a week or so to get at some of the humidity locked into your house.
A NOTE however is to keep an eye on the indoor coil for signs of frost.This is how a frozen a coil starts and if you see signs then you want to bump up the cfm .If you had had a proper load calc done then you would not be having this problem.This is info that you should share with all your friends and relatives LOL assuming those two groups are not mutual HAHA.

Thanks, I am worried about Icing, the unit is in an attic ventilated by two Gable vents with no fan. I do hope to get one installed, some day.

The unit is now in program 4 for overnight, sitting silent at 76 Degrees. I'm thinking about bringing that temp down for a few days, as the humidity level have rebounded to their previous state of 60%.

I am thinking about just trowing in the towel and getting a 3.5 ton compressor, but I will wait and see.

Thanks
pauli is offline   Reply With Quote
Old 07-25-2011, 05:14 AM   #14
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,457
Rewards Points: 4,560
Default

split system, high humidity


A 3.5 ton at 400 CFM per ton will have a warmer coil then a 4 ton at 350 CFM per ton. The colder the coil the more moisture removed from the air.

The R and BK terminals are in the air handler. The IAQ stat has terminals that will connect to those terminals.

The amount of humidity in your house is also effected by your homes air leakage. The more it leaks, the higher your humidity will be. Sealing your home better, will also help lower your indoor hmidity. Sealing around windows, wall switches and receps is a good place to start.
beenthere is online now   Reply With Quote
Old 07-25-2011, 01:35 PM   #15
Newbie
 
Join Date: Jul 2011
Posts: 7
Rewards Points: 10
Default

split system, high humidity


Good advice so far on this thread. I will add a few other things to check....

If humidity control is high on your list, do not run your air handler fan continuously - it will evaporate all of the water on your evaporator (cold) coil back into your house within minutes of your condensing unit shutting off. This can make a very noticeable difference in many homes.

I do not know where you are located, but with your air handler and ducts located in the attic, duct leaks can be a major humidity issue. I suggest you make sure that you do have any leaks in your supply or return ducts corrected. You can ignore this advice if your air handler and ducts are within the conditioned space (in your basement for instance).

beenthere is correct that air leakage will have a greater effect on the humidity than the temperature within your house. If you have a leaky house and the dew point is high outdoors, you will have a hard time controlling your humidity. Be aware that some amount of fresh air is necessary to maintain a healthy atmosphere within your house - if you have a ventilation system, I do not suggest you disable it without consulting a local professional.

Slowing down your CFM in your air handler will increase the amount of dehumidification your A/C performs. The dew point of the return air will define your evaporator temperature. You may have freezing problems during season(s) with low dew points if you slow the air down too much. Water is not removed from your house until it falls from the evaporator coil into the drain pan and is directed down a drain. Most evaporators hold one to three gallons of water while operating - this water stays on the evaporator once the A/C turns off and re-evaporates back into the air until the A/C starts again. when the A/C restarts, it must "fill" the evaporator coil before any water goes down the drain. Understanding this, you can see that long run times help to remove water (all the way down the drain) while short run cycles do not. Use a thermostat that makes your A/C run for 30 minutes or more - most cheap "builder" thermostats do not.

Humidity control - Unless your system is equipped with reheat, these thermostats (with humidity control) just over cool your house below your temperature set point. This does remove water from the air, but it lowers the temperature as well. These two effects counteract each other when you measure relative humidity. Unfortunately A/C does a great job of lowering relative humidity in your house only when it is hot enough to require the A/C operation.

Whole house dehumidifier - these are great additions if you live in an area where high dew points are pervasive outdoors. The Ultra-Aire units provide dehumidification, air filtration, and fresh air ventilation allowing your A/C to focus on cooling (only). If there are times of the year where you experience high humidity, but your A/C rarely runs, a dehumidifier is a great solution. This is the best option for a comfortable and healthy home. Look at the Ultra-Aire units as they are Energy Star listed and very efficient at removing water.

Advertisement

DryDog is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
High humidity in house in winter reddog General DIY Discussions 7 06-28-2011 06:38 PM
high humidity in my house mfinley HVAC 1 06-23-2010 06:55 PM
high humidity inside my house mfinley Building & Construction 1 06-22-2010 05:03 PM
beware humidity system? Emaderton3 HVAC 5 02-11-2010 12:52 AM
High humidity (RH) spm25 HVAC 3 11-06-2009 08:50 AM




Top of Page | View New Posts