DIY Home Improvement Forum banner
1 - 20 of 35 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter · #1 ·
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
 

·
Administrator
Joined
·
41,875 Posts
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.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #3 ·
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
 

·
Administrator
Joined
·
41,875 Posts
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.
 

·
Hvac Pro
Joined
·
23,688 Posts
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
 

·
Administrator
Joined
·
41,875 Posts
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.
 

·
Registered
Joined
·
9,626 Posts
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.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #9 ·
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
 

·
Administrator
Joined
·
41,875 Posts
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.
 

·
Registered
Joined
·
615 Posts
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.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #12 ·
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
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #13 ·
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
 

·
Administrator
Joined
·
41,875 Posts
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.
 

·
Registered
Joined
·
7 Posts
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.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #16 ·
Hi DryDog, thanks for the comments:

I live in Connecticut, its humid where I am only during the July August time frames, well I'm sure you know.

Interesting you should mention the thermostat.

We have problems with the A/C after a few weeks it was installed. The installer washed his hands of it.

When I brought in someone else, he noticed the supply (chamber) was wrong. He basically said that they made it big enough to fit the takeoffs. This was the cause a lot of back pressure and harmonics inside the return plenum. He retro'ed a nice supply pipe that resembles something like an anti matter chamber (sorry), which when finished, pushed more air then we every felt at the same air handler configurations.

Well when he was finished, he traded out my ritetemp 8022C with a Honeywell visionPRO 8000. Thats when I noticed the air handler cycling every 15 minutes. But I was thinking that the air was now passing the thermostat faster and was cooling down quicker, so I let it go.

Do you think the honeywell might be partial cause of the issue? The ritetemp has a swing control that I set for 2 degrees, the Honeywell uses a different function Cool Temperature control, it set to 1. Choose if room does not reach cool setting after recovery.

Any opinions of the choice of thermostats?

I always check the ducts there was no leaks. My windows do leak and it is something I'm looking into. Well more than that, My house was built in the late 80's and still have the original double pane glass in them. I'm trying to remember the make of them so that I can replace the weather striping. They were a big company I think the name started with a W and was targeted by Home Depot, back then when HD wanted to put every window maker out of business. I wish I could remember the name so that I can get those pieces between the windows.

In the next coming days I plan to hold the temp at 72 degrees and watch for ice to build. Maybe it will do something to the humidity as well, I was told, you need to get the moisture out of everything. I'm not sure a day of cycles will do that.

Anyway it sucks doing this on my own, thank everyone for the help. Does it make sense to drop back and punt with a 3.5 compressor and reconfigure the air handler?


-pauli
 

·
Administrator
Joined
·
41,875 Posts
Check to see what the CPH is set for on your thermostat. Set it to 2.

The cool setting your talking about, is only a setting that effects it when coming out of temp set back.
 

·
Registered
Joined
·
7 Posts
Sorry to hear that your (original) installer treated you poorly. I believe that your situation can be improved with some work, and quite possibly some $$$ outlay.

Poor duct work appears to be an epidemic in most areas. Quite sad when I see a homeowner pay for the latest greatest high end system and it is connected to the original (poor) duct work. Duct work does not have a direct effect on humidity, but it will affect the efficiency of your air handler and the comfort of your home in a large way. I've only visited a couple of houses that I felt had good duct work originally installed; every other house had problems. I've corrected duct work issues in every house I've owned - since just moving in is not enough work....

The Honeywell VisionPro 8000 is a good thermostat (in my opinion). beenthere is correct that your Honeywell will cycle the system based on the CPH (cycle per hour) setting. With a CPH of 2 your system will have two run cycles each hour. The only knock on your thermostat is that it is a very capable thermostat with many settings that can be confusing to the average homeowner. Typically these thermostats are set up and commissioned by the HVAC contractor because of the complexity. Read through your manual and/or check out the Honeywell web site to learn about your thermostat. You may want to get your contractor back to help if needed.

If your air handler and ducts are located in your attic (which I assume is not conditioned), a leak in the attic can cause large amounts of outdoor (or attic) air to enter your home. This can swing the humidity levels in your house when the system operates. Leaks may be easy or difficult to to find depending on the accessibility and configuration of your A/C system and attic.

Windows. Most houses I've visited have other leakage problems that should be addressed before the windows. Older double pane windows work well if the glass packs are intact and the sash/frame seals are good. Add storm/screen windows on the outside and you have a pretty good window system for your area. I often see quite a bit of open leakage area under sill plates, and around rim/band joists (sometimes see light) that will reduce infiltration more than replacing serviceable windows. Ceiling penetrations into the attic are other common leak paths.

I am an advocate of improving the building enclosure; unfortunately most HVAC contractors are not able to offer this service. You might consider hiring an energy rater in your area to come and review your house. A good rater will give you a report (and show you during a walk-thru) the problems found with your house. They should also suggest possible corrective actions and usually can help you understand the probable payback of the investment to fix the problems. Often there are some improvements that you can DIY without hiring a contractor. Improving the enclosure is very efficient as it reduces the energy required to condition your house and improves the comfort within your house. A word of warning; you need to get a reasonable amount of fresh air into your house while it is occupied - if you tighten it up to the point where natural ventilation can not supply enough fresh air, you will need to add mechanical ventilation.

Your house is a sponge - it is constructed of many hygroscopic materials that will adsorb and desorb water. Many of these materials will take days to reach an equilibrium if you change the temperature and humidity inside your house. A day of low temperature setting may lower the dew point of the air within your house, but it will not dry out the house materials. You should have an air change in your house at least every 5 to 6 hours, so your humidity will be back a few hours after you set your thermostat back up if nothing else is changed.

Replacing equipment - This depends on the age/efficiency/cost of your equipment. If you can make a payback/comfort argument for replacement, then go ahead. If the equipment is relatively new with plenty of life left, I doubt you will get you payback from a replacement. If your equipment is new, but (you believe) over sized, I suggest you consider making your investment in improving the building enclosure and adding a whole house dehumidifier that ventilates with conditioned air, rather than changing the A/C system - you will have a comfortable and efficient house (even with the over sized A/C). With a dehumidifier controlling humidity independently, you may be comfortable at a higher temperature setting on your thermostat with a reduction in A/C run time. If/when you have the A/C replaced, ask the HVAC contractor for a manual J and manual D, possibly a manual S report- a good energy rater can help to determine if the HVAC contractor has properly specified the system/duct work for your house. Many contractors simply use rules of thumb (ton/XXXsf, replace with same size unit) when replacing systems. Doing this properly will likely cost some $$ versus going with the low bid.

Unfortunately the investment to make your house more comfortable and efficient does not (superficially) enhance it's value as much as aesthetic upgrades. Comfort and efficiency are not visually apparent to a buyer, and many buyers are blissfully unaware of the comfort/efficiency of a house when they close. Only after they move in, do they become aware of the truth. Too bad that comfort and efficiency quickly become much more important than those gorgeous granite counter tops.

http://yourhome.honeywell.com/home/products/thermostats/7-day-programmable/visionpro+8000.htm
http://www.resnet.us/directory/raters
http://www.ultra-aire.com/

Good luck with your upgrades.
 

·
Registered
Joined
·
18 Posts
Discussion Starter · #19 ·
Check to see what the CPH is set for on your thermostat. Set it to 2.

The cool setting your talking about, is only a setting that effects it when coming out of temp set back.

Hey Beenthere:

Thanks for all your help, I'm thinking that the thermostat setting is 220 1st stage compressor cycle rate, was already set at 2.

Should I go for 1 or 4?

Thanks again for the advice.

-pauli
 

·
Administrator
Joined
·
41,875 Posts
Usually factory setting is 3. 4 would give you more cycles, and remove less humidity. 1 will tend to over shoot temp, and may allow humidity to build up. See what it is actually set for.
 
1 - 20 of 35 Posts
Top