High Humidity

[roswell]

I recently had installed:

Carier 2ton AC unit: 24ACA324A003
Carier 3 ton furnace: 58DLA070-12
Carier Condensor: CNPVP 2414ACA

It replaced a 23 year old system that died. The new unit cools but it removes almost no moisture. Confirmed this with humidity measurements. The old system got the water out of the air but not this new one. I have complained to the installer ... a large company in our area. They could give no suggestions as to why it is worse then the old unit.

I did some studying on my own. At this website and others and I am starting to believe the furnace blower is running too fast for my AC unit.

I learned that my furnace fan's default setting for cool cycle is high. High would be in the neighborhood of 1200 cfm. I was told that for a 2 ton ac unit the air movement should be roughtly 800 cfm. With my furnace currently set on high I am guessing we are pushing roughly 1200 cfm across the coil. Would this not account for the lack of moisture removal we are seeing? And the high humidity we are feeling in the house.

This furnace model has a single speed blower but it capable of asigning one of 4 different speeds to the cool cycle. I found on Carrier's website the install manual for this model. When comparing the CFM for the smaller 2 ton furnace and the model I have it looks like I would need to set my blower motor to run on LOW in order to approach 800 CFM.

I have tried to gett my installer to look into this relationship of blow velocity and poor moisture removal. But they have been now one week studying this problem. They keep saying they are trying to contact their Carier distributor rep. to verify the steps to take.

There are no switches to change out on this furnace. It is just a Black wire for HIGH and a Red wire for LOW. Currently the low is asigned to continuous run. I never turn the fan on continuos run. So I am thinking to switch the black and red wire and get the cool cycle to run closer to 800 cfm.

Does anyone suggest any problem with me switching the wiring myself? The system is the R-410A system so I do not know if the gas needs adjusting if we reduce the blower speed. Does anyone know if I need to sit and wait for someone to check the gas pressures before attempting to cut the blower speed back? What could happen if I do this myself? Would the coil possibly ice up? Or something more nasty?

Any suggestions?

[angy400]

if you attempt something yourself and something goes wrong I am sure your warrany wont cover it..let the a/c guy do the fixing

[roswell]

You are probably right. I mess something up and they are off the hook.
Do you think I am on the right track with the idea of air velocity vs humidity control?

[angy400]

I am just another home owner like yourself having a similar problem you are having and from what i have researched that is a possibility. However our a/c guys are getting us a new valve that goes on the coil. I guess this one is known to be defective and cause some of the problems we are having..so we will see if this works or not.

[jbrannan]

The airflow is to high. Call the company that installed the unit. The airflow should be 350 to 400 cfm per ton. The charge on the unit will have to adjusted when you change the airflow. The high airflow will cause the evaporator to not remove the humidity as well.

[roswell]

I have called them several times suggesting they cut the fan speed. They are suppose to be a Carier dealer.
But they seem to know nothing about the equipment. They did not know my model of furnace has a blower where the speed can be selected.

They give me the line that they are checking with their Carier rep. to be sure they don't mess something else up if they make this change.

I thought this air velocity vs AC tonnage was an HVAC 101 thing. But for these guys it sounds like new info.
They are not a small one man company. They claim to have 19 service trucks on the road.
I have told them I need only one truck to come to my house. But I need one with a driver that know how to fix my install.

I think I am getting the run around. But other than keep calling them I do not know what else to do.

I am starting to believe it does not matter how big the company is. A one man company is just as good as long as that one man knows how to install properly. But how can anyone know he is getting involved with someone who knows or with someone who doesn't have a clue.

I feel I have the 'doesn't have a clue' company now.

[jbrannan]

Call Carrier and explain the problem. The DLA furnace has 4 motor speeds. With a 3 ton drive furnace such as the one you have, the blower speed has to be set lower for the 2 ton ac.

[roswell]

Thank you.

That was one of the first things I did.
But the Carier customer service man could not answer any questions. Their website has more informaton than him. He kept telling me to call the dealer that installed the equipment. Carier customer service is pretty useless. They can give you a phone number for a dealer and that is about it. After I complained to the customer service rep. for his lack of concern for their customer (me) he finally said I could file a complaint against the dealer. And that would lead to the Carier distributor rep. contacting my dealer. I though would never be permitted to speak to the Carier distributor rep.

I was told I needed to keep working with the guy who installed my equipment. Give him some more time, I was told. Customer Service did give me a phone number for another Carier dealer that I could call and ask about my system. I did call that dealer. He happened to be factory certified dealer. He quickly suggested lowering the fan speed. But he coud not do it because he did not install it.
And my house sits just outside of his territory so he would not come even if I paid him.
It seems my house sits just outside of every factory authorized dealer. So I get the regular dealer. Who as it turns out may or may not know what he is selling. And as for installing it ... well it is flip the coin thing.

I will keep the pressure on my current dealer.

[smngmu]

Yes,your motor speed is too high.Yes,the charge will have to be adjusted.Yes,you could do it yourself-BUT DON'T.It will void ALL warranties or worse.Yes,call the manufacturer directly and tell them of this.There's a good chance that the tech that came is not fimiliar with this system and instead of blowing something up is looking for answers elsewhere.Your problem started with a two ton A/c hooked to a three ton furnace.

[roswell]

Everyone,

I finally got the installer to step the fan down.
It was set on high (maybe 1200 cfm) and now it is on low(maybe 945 cfm). Since I have a 2 ton condenser and a 2 ton coil it would have been nice to get the speed down to 800 cfm or less if possible. But my fan will not go any lower.

The result: humidity has stabilized at 60%.
When the outdoor humidity is 68 or 69% the system now puts out 60% air. I tested it with a humidity tester. But the odd thing, when the outside is 58% it still puts out 60% air. So when the AC kicks in and the room is already at 60% then nothing happens to the humidity. It remains at 60%. Conclusion my second floor is 60% and I can not see how it will ever go lower.

This is still progress because before lowering the speed the ac was causing the humidity to actually rise when it ran. At least now the humidity is stable. It just seems that 60% is bit high to be the stable point.

I don't understand this since my old 23 year old unit running to cool the first floor and basement area consistantly keeps the humidity at around 50% in those areas.

I can't help but wonder if there is something else going on.
My AC guys are no help. They just want run away from this problem.

Any other suggestions?

[4l530]

Originally posted by roswell
Everyone,

I finally got the installer to step the fan down.
It was set on high (maybe 1200 cfm) and now it is on low(maybe 945 cfm). Red wire is now on 'COOL' or 'HIGH' terminal? (Just asking to be sure, and because you noted the position of these wires earlier).

The result: humidity has stabilized at 60%.
When the outdoor humidity is 68 or 69% the system now puts out 60% air. I tested it with a humidity tester.
Now, is the hygrometer in a stationary position in the room, or is this with holding the hygrometer in the airstream leaving the register?


I can't help but wonder if there is something else going on.

A few questions--Condition of the duct system (guessing it runs through the attic)? Did they recheck the charge after reducing the fan speed? Assuming your other thread is regarding a different system, is this one the same size (tonnage) as the one it replaced? If the drain terminates where you can see the flow, is it flowing mucho water or not so mucho?
Sorry for all the questions, just trying to get a handle on it.

[roswell]

You do not ask too many questions. Please ask many more.
I want to understand better.

The first question: The Cool relay now has the RED wire plugged in (I checked it myself). The manual says that should be low. The guy did go backout outside and sit a little while with his gauges. This is an R-410A. He said he bled some gas off.

He came back inside and shined a light type temperature gauge at the vents. I think he said he saw a 13 or 14 degree drop at the vents. He did not want to bother testing the drop at the coil. But after he left I tested this myself. I happen to have the same temp. probe as one of the earlier techs. used to test this temp. drop across the coil. I tested it in the same locations he had used. These are my readings: 75 going in and 57.8 just after the coil. So about 17 degree drop.

Second question: Humidity ... I tested it in both locations.
If the hygrometer is placed on the wall not in direct contact of the air flow it was reading around 61% and after the ac ran and the air moved a little the percentage fell to 60%. If I hold the thing in the exit vent's air stream it holds steady at 60%. If I take the thing to outdoors it climbs but when I hold it back on the air stream it falls quickly to 60% and never moves below that.
I know these devices can be unreliable. I work in a laboratory where we use these things every day. I have checked the calibration of my hygrometer and it is pretty accurate.

Third question: This is in the attic. The duct work is pretty good I think. It is sealed pretty well I think. I did not check the temp. at the vents with my gauge after we turned the speed down but earlier I had tested it and I had found a 1 - 2 degree rise in temp. at one of the vents compared to the temp coming off the coil. This was not at the farthest distant vent but still the air did have to trave quite a bit to get to where I tested it. That leads me to think the ducts are as good as I can hope for. The ducts were not changed from when the old system was in there. And the old system worked pretty good ... really good for humidity control I now know.

This system is the same Condenser unit tonnage as the oil unit, 2 tons. The coil is a 2 ton coil. The furnace though is a 3 ton unit. The old unit was 23 years old. Carrier could not tell me how big the fan was on that one. But it was a 75,000 BTU furnace. The humidity did not even come close to this new one.

Oh ... please do not confuse this thread with my other one.
The other thread is related to my first floor's replacement.
I am suffer installer shock here with this install and I was just trying to understand if I was making the right choices with that install. My mind cannot handle two mistakes.

The last question: The water flow ... I can not see it.
It might be flowing but it goes down a PVC pipe where it joins with a PVC pipe for the first floor units drain.

Thank you.

[lugam]

get a dehumidifier from sears or ebay and you will notice a big difference in the humidity levels,and you wont have to use your a/c system that much to bring it down,i have one in my house and it works great,and i live in houston,my a/c works great but at night it wont cycle as often so humidity rises without turning the a/c on,and the dehumidifier pulls 3 amps compared to 16 to 20 depending on the size of your unit,install the unit in a central location of the house, close to the return air,check the internet and you'll find the test results on a small dehumidifier compared to a central cooloing system or central dehumidifier.

[teddy bear]

In the end, you will need a good eff. dehumidifier for humidity control during the shoulder season and during no cooling load weather(Santa Fe, 5 pints/kw not sears 2pints/kw,please).
Right now though you need to make sure your a/c is doing as much as it can. Your a/c should be able to maintain 50%RH during high cooling loads(+12 hours/day). During high outdoor dew pointsWith only a few hours of operation a day, the a/c will not be able to maintain 50%RH with hi. Your coil and cold air temperature is a little high.
A high quality air filter may do the job of slowing air flow enough get the colder coil temperature you are after. A comment on your interpeting outdoor humidity. Get away from %RH and use dew points of the air inside and outdoors to evaluate moisture levels. This will clearup the confusion of a/c raising %RH. A/c raises %RH while lowering dew points.
http://science.howstuffworks.com/framed.htm?parent=question650.htm&url=http://www.esb.act.gov.au/firebreak/humidity.html The dehu TB

[dash]

Roswell,

They need to test the ESP(External Static Pressure)of the duct system,at the inlet and outlet of the furnace.

Then look at the Fan Data Chart for the furnace,to determine actual cfms of air flow.

If cfms are too high on low speed ,it's easy to reduce them ,just by adding "resistance"(could be a damper or a piece of meatl at an angle in the main trunk) to the duct system.

This way you could get down to 350 cfms per ton,and improve the dehumidification ability of the system.

[Xavier]

Does your system have a TXV?

[dash]

Originally posted by Xavier
Does your system have a TXV?

The OP may not know,but all Carrier's new line ,which his/her model numbers are,require a TXV .

[Xavier]

Dash can you please explain the function of the TXV, and how it affects Flow, Delta T, and Humidity in the home

[roswell]

The manual for this coil states that it comes with a TXV valve already installed.

[4l530]

Just a thought here--it seems to me that they don't exactly do the best job of insulating that TXV sensor bulb from the factory...maybe I'm just nuts, I just like to see those super insulated and positioned exactly right. Might be worth looking into, don't know how much it will help.
I like dash's idea about the restrictor plate. ^^

[Xavier]

Roswell, couple of questions, did anyone do a heat gain calculation? Regarding the TXV I was waiting for someone to explain/confirm the function of the TXV. My understanding is that the old way (rule of thumb) of setting flow is not the best way when you have a TXV. I too have a new two ton system for my 2,500 sq ft two story home in Michigan and set the flow at the highest speed using discharge temp & humidity as the variables.

[thorton]

QUOTE: Your problem started with a two ton A/c hooked to a three ton furnace.

This is absolutely correct. Way too much fan speed. You should have had a variable speed fan installed. Just my opinions, I'm not a tech, I'm a homeowner.

Thorton
________________
Common sense isn't that common

[hivacer]

Is your coil in the return or supply side of your system in the attic? If it in the return side the drain should be trapped, supply it shouldnt. Is the coil level, or sloped toward the drain? If it is holding water it could be adding humidity.

Also the installers need to get the cfm to 700-800 and bring your temp drop across the coil to around 20. You paid for a new 2 ton system and it should be done right. If not I would raise a stink with carrier until they get one of there people out.

You should not have to buy a dehumidifier until your air conditioner is working right.

[lynn comstock]

Roswell,

You are doing an extremely good job of observing and analyzing your problem. High airflow is uncommon as a problem, but you figured it out by yourself. Kudus.

If you have the fan set on continuous, change it to auto. (This allows the water in the coil at the end of the cooling cycle to drain out. On continuous fan, the airstream holds the water in the coil and allows it to re-evaporate back into the air.)

Dehumidification only occurs while the compressor is running. If the compressor is cycling 4 times per hour less humidity is removed. The first five minutes of operation mostly get the system back to efficient operating conditions.

We also need to know what temperature are you keeping your home at. A colder setting will give the unit longer run cycles and more run time. What is your run time per hour? Set it colder and see what happens...at least as a test.

What is your climate (city, state)? In humid climates infiltration of humid air can overwhelm an air conditioner's capacity for dehumidification. The homes and ductwork must be well sealed in humid climates. In the cheap-energy days electric strip heat was used in some areas (like Florida) to "reheat" the air so the air conditioner would run longer cycles and achieve suitable humidity control.

You could also experiment with restricting the airflow by blocking part of the airflow. A simple way is to by the pleated filter. This will double the resistance of the filter to the airflow. Use the temperature split across the indoor coil (Supply air temp. minus the return air temp) and aim for 20 to 22 deg. F. See what that does for you.

None of these suggestions will impact your warranty.

[wormy]

Just to add a little more fuel to the fire...

Your humidity reading at a supply grille should be close to fully saturated.... or almost 100% RH

The hygrometer should be placed into the air stream prior to exiting the supply grille. Otherwise you can get a 'mixed air' reading from the air being induced into the air stream leaving the vent.

Tests you can run...
On a HOT/MUGGY day (we are running out of them)
Set two thermometers (digital preferably) and two hygrometers on a table away from any air streams and heat sources such as sunlight
Turn the system OFF
Turn the Fan ON
Let it run for about an hour or so to dry up all the water in the drain pan and on the coil
CHeck the thermometers and hygrometers to make sure they read the same.
Place one thermometer and hygrometer at the return air grille and another thermometer and hygrometer in a supply grille closest to the unit (remember to put the probe into the air stream leaving the grille. Preferably in the middle) (if the supply grille is 'in the line of sight' of the furnace, then move to another grille.)
After 10 minutes of run time (FAN ONLY) check your readings.
Check your readings.
Temperature IN should be pretty much the same as Temperature OUT.
Same as the humidity readings.

This test was to check for air leaks in your duct system.

Next Test.
NOTE: THIS TEST IS NOT ACCURATE
But its the best you can do as a homeowner and using the tools you have. It should give you are pretty good idea what the airflow is though.
Call your gas company.
Ask them 'How many btu's are in each cubic foot of gas that they supply'
If they have no idea what your talking about.
Figure 1025 btu's per cubic foot
Leave your thermometers in the vents
Take your hygrometers out (unless they can stand hot air)
Turn your gas heat on for the unit you are testing
ALL other gas appliances need to be OFF
Go to your gas meter
Use a stopwatch and time how long it takes to use one cubic foot of gas (dial on left should either read 1/2 cubic foot per revolution or one cubic foot per revolution)
SCroll down to the table on this web page...
http://www.bacharach-training.com/referpage/clocking_gas_meter.htm
Plug in the time you just got into the first column.
Go to the next column that coincides with what meter you were using (use the 1/2 cu ft column if your meter had that particular dial)
Take that number and multiply it by the btu value you got from your gas company.... or if that info is not available.... multiply it by 1025
Now you have the BTUH of gas being consumed.
After 10 minutes of run time (longer is better)
Check your return temp and supply temp
CFM = [(BTUH * 0.8)] / [1.08 * (Supply Temp - Return Temp)]

Note for other homeowners reading this....
alot of furnaces are set up for the heat to blow one fan speed and the cool another fan speed... so the resulting CFM is only going to tell you what you have on your Heating speed.


I highly suggest getting a qualified tech to check your system for you.
Checking the refrigerant pressures and line temperatures should reveal expansion valve troubles and other problems if you have any (including varifying correct charge)
They have other means (more accurate than above) to check your air flow also.
If you haven't been there already, check Carrier's web site and look in the upper right corner for 'find a dealer'

If you can't find a Carrier dealer good enough...
then you can try...
http://payments.acca.org/ContractorLocator/

[roswell]

The story has come to a good ending.

Thank you everyone for the all the great information and advise. I decided since I am planning to live in my house for many more years to come that I did not want to try to live with this situation of an mismatched furnace & AC. I live in a rather high humidity place, a suburb of Atlanta, Georgia. After a lot of complaining, the company agreed to take back their furnace (of course at a considerable loss to me). I had a different company install a variable speed furnace.
The Carrier 80% Infinity 58CVA070-12, of course along with the Infinity thermostat.

The results are unbelievably nice. To any homeowner reading this story I can say if you are not planning to sell your house in a few years please consider spending the extra bucks and going to the variable speed system. You will not regret it. The comfort level is definetely worth the extra money.

This post has been all about humdity troubles but the story took so long to complete that we are now just starting to get a few cool nights. And I have had the chance to use heat too. The variable with two stage heating is so much quieter and comfortable than the old single stage furnace.

End of story...

[coolguysfl]

Pls do'nt measure the RH coming off the coil (vents). As the air has just gone over a coil below the dew point - by design it will be near 100% RH -- thats OK. As soon as it mixes w/ the indoor air it will stabilize & decrease.

Also you're not running the FAN in the ON position are you? If so, return it to AUTO - you are rehydrating the air.

[lentz]

Have been able to help with a high Humidity problem by changing the fan speed and then rechecking the freon charge.

[udarrell]

I have called them several times suggesting they cut the fan speed. They are suppose to be a Carrier dealer.
But they seem to know nothing about the equipment. They did not know my model of furnace has a blower where the speed can be selected.

They give me the line that they are checking with their Carrier rep. to be sure they don't mess something else up if they make this change.

I thought this air velocity vs AC tonnage was an HVAC 101 thing. But for these guys it sounds like new info.
They are not a small one man company. They claim to have 19 service trucks on the road.
I have told them I need only one truck to come to my house. But I need one with a driver that know how to fix my install.

I think I am getting the run around. But other than keep calling them I do not know what else to do.

I am starting to believe it does not matter how big the company is. A one man company is just as good as long as that one man knows how to install properly. But how can anyone know he is getting involved with someone who knows or with someone who doesn't have a clue.

I feel I have the 'doesn't have a clue' company now.
This is very strange as there are simple install instructions that usually explain setting the blower speeds for a specific A/C tonnage; these guys are unbelievable. WOW!

On a 3-ton blower to get to around 800-CFM or down to 700-CFM you'd probably have to go to the medium-low third speed tap for 'around' 790-CFM I'm 'guessing' it's probably @ around 0.6" of static pressure to 'perhaps' get around that CFM. Depends on the duct system's efficiency...

If you have humidity problems you might be able to get it down close to 700-CFM for a 2-Ton A/C.

Only testing airflow CFM will tell you what you need to know when selecting speed taps, because duct system ESP varies greatly; TEST & Verify actual CFM. Is it a TXV/TEV Coil System?

A lot of small-one-man owner-operations are knowledgeable & follow "best practices," for installs & service work & in this new Energy Era some do Home Energy Efficiency Audits along with duct system & air flow analysis.

Your situation is unbelievable!

[motoguy128]

Any particular reason you felt like digging up a 6 year old thread? :)

You can also fire the furnace and measure temps rise and get a descent approximation of airflow.