R410 Vs R22 humidity removal

tswatekAugust 30, 2012

In June 2012, I replaced my 10 yr old compressor and handler and always seem to be sweating in my house since the change. I've had the new AC contractor come out 3 times since the install and I just don't understand why I "feel" so hot when all the temp settings are the same as with the old unit. The first two visits, they said the R410 needed to be topped off a little and the 3rd time, they said all refrigerant levels and pressures were right to specs. This is driving me crazy 'cuz I live in FL and even when wearing shorts and a tank top in my house, I'm wiping sweat from my forehead regularly. I keep my 3 zones in the 75-77 range, as I did with my last system. My thermostat reads that the temps are right on, but it just feels like it's not pulling anywhere near the humidity out of the air as the old system did. Here are some specifics:

Old unit: Carrier 5 Ton, 10 SEER, R22, 3-zone, variable speed handler

New unit: Amana 5 Ton, 15 SEER, R410, 3-zone, variable speed handler

Other possibly pertinent info: The unit I replaced is for my downstairs area, which is about 80% of my total living area. I also have a 2 1/2 Ton Carrier system for my upstairs and the downstairs and upstairs handlers sit side by side. The new AC contractor looked at all my duct work for downstairs and said that my downstairs handler wasn't getting enough air supply and he recommended increasing the air flow. He did this by cutting a hole between the supply cavities between the two handlers.

What I'm wondering, though, is if the new 5 Ton unit is now pulling too much air from the supply ducts that used to be just supplying the 2 1/2 Ton upstairs unit, I've definitely noticed that it's a lot more comfortable upstairs since the change, but way less comfortable downstairs. I'm no AC expert, but I'm a pretty intuitive DIY guy and I think this may be the root cause of my humidity issue.

The new AC contractor told me these two things: 1) While the industry officially says they're the same, contractors know that R410 systems pull less humidity out of the air than R22 systems; and 2) Just crank the air down an extra 4-5 degrees occasionally to pull out the humidity, then put it back to my normal comfort area. Any thoughts on how to improve my humidity situation?

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I am not a PRO, but would like to throw out a comment or two.

The ability of an a/c system to reduce humidity is dependent on the temperature of the evaporator (inside) coil. With the emphasis on 'higher SEER' (larger coils) these days, a higher SEER coil of the same capacity will have a higher (hotter) temperature, and thus will condense less water.

Airflow is also a factor. Most units are run with an airflow of 400 CFM per ton. This will produce an expected degree of performance with respect to sensible (temperature you can feel) and latent (humidity) capacities (removal).

Your home's heat gain profile may require more latent capacity than is being delivered. If so, the airflow can be adjusted (approx 350 CFM/T) to increase latent capacity.

By the same token, some contractors may adjust the airflow higher (> 400 CFM/T) to achieve a higher SEER. In such a case, humidity removal will suffer.

Five ton units have special needs with respect to return air. I will refrain from commenting on your situation.


    Bookmark   August 30, 2012 at 3:30PM
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HVAC is not my trade. It seems to me that it is not the trade of your new contractor either. But he might be a politician. Moisture in the air does not "recognize" which refrigerant is in the system.

    Bookmark   August 30, 2012 at 5:23PM
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You house has 7.5 tons of cooling. How large is the downstairs and upstairs in floor area?

Have you measured the humidity in the house? If so what are the readings? What is the typical times of the downstairs air handler? How minutes is it on and how many minutes off?

The comment about R410 pulls less humidity than R22 systems is nonsense. I have a R410 AC and I can get the humidity down to 38% without too much difficulty.

    Bookmark   August 30, 2012 at 5:41PM
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It sounds like high RH inside to me.

I have 410 also.
while RH is 80% outside @ 79 degrees
inside it is 73 degrees and 50% RH.
yesterday and today is rainy due to
Isaac. I'm in La.
I also have vs ahu and it removes
humidity quite well.

can you close off hole between r/a that
contractor cut? just to see what difference
it makes in 24 hour period.

air leaks in return contribute to high humidity.

Mike-home I wondered same thing.
florida & la. have an abundance of 500 sq ft
per ton hvac guys. at that "sizing" shortcycling
is pretty much a given, as is lack of dehumidification.
this is what the homeowner is complaining
about..'sweating' ...classic symptoms of high RH.

how big is your house?
what are your run times? (amount of time a/c runs)
where are returns?

best of luck OP.

    Bookmark   August 30, 2012 at 7:43PM
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Another factor: If the new unit is a lot more efficient than the old one, it will not run for a long, hence will not have as much time to remove humidity from the air.
ie: My A/C guy said its better to get a slightly smaller unit so it will run more and be able to keep the humidity down. If you get too big a unit (too efficient) that cools quickly, it will not be able to cycle as much air over the cooling coils to dehumidify the air.

    Bookmark   July 16, 2013 at 3:44PM
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