Excess Relative Humidity-New Rheem Prestige - http://www.hvacmechanic.com/ Forums
Original message
| Steve S
 |  "Excess Relative Humidity-New Rheem Prestige"
, posted Tue 12 Aug 02:13  
We recently had a new 16 SEER / 2-Stage Variable Speed Rheem Prestige System installed in our home.
We live in New Mexico with relative humidity hovering around 20% outside. Our inside RH with the A/C running is constant at around 50-55%. We have an electric range/oven but is only used about once a week. No teens (extended showers)in the home. Washer and (electric) clothes dryer is in seperate room with exhaust fan vented to the outside. No house plants. Based on water collected at drain pipe, only about 16 ounces of water is removed from our 1600sf home daily.
Techs have checked ducts in the attic and all are secure. Drain pipe was checked and is open and clean - just not much moisture being removed from the home.
House feels 'damp' all the time.
We have tried running the fan intermittedly and constantly with no difference in RH noted. Any ideas on how to lower the RH inside the home?
Thanks,
Steve in New Mexico
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Replies:
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| jean55
| "Re(1):Excess Relative Humidity-New Rheem Pre" , posted Wed 3 Sep 10:04
Well we have the same problem here in NoVA. We recently replaced our 14 yo attic A/C with a Trane XL15i. (High humidity was a problem before the replcmt, as well.) I can't figure out where the humidity is coming from either. It gets up to 62%. We do keep our thermostat set around 78-80, cuz with the high humidity it feels too cold if it's set lower.
Now we're considering replacing our downstairs unit and I read that the 2-stage do a better job of controlling humidity, but not based on your experience right?
When the attic unit was replaced I asked them about replacing the ductwork at the same time. They didn't think it was needed. I doubt that they checked if for leaks. How do you find someone to do that--walked around on the joists, digging under the insulation, etc? I'm just getting really fed up trying to find any HVAC guy who says this is not normal. Why when I walk into an A/C mall is it dry? Why can't we get the humidity below 55% when the outdoor humidity is 33%, unless we open the windows?
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| ampulman
| "Re(1):Excess Relative Humidity-New Rheem Pre" , posted Tue 12 Aug 17:21:
I am a homeowner, but consider myself fairly well versed in HVAC technology, especially, Rheem equipment.
Coincidentally, I just had a Rheem Prestige furnace and a/c installed. Somehow, someone is confused as the Prestige furnace is the Mod at 94+% efficiency (or Prestige air handler). Also, Prestige a/c's (2 stage) are not available in 1/2 ton sizes.
Something is drastically wrong; 3-1/2? tons for 1700 SF, you say that cooling is adequate, plus it runs long cycles, so there should be enough latent capacity to reduce your indoor humidity. Do you have a 2 stage thermostat?
Was a heat calc (manual J) done? What are you using to determine your indoor humidity? Is your fan set up at higher than 400 CFM/ton?
My a/c (RARL)really wrings the humidity out of my air. I have a humid basement and OD humidity can run high, but typically run mid 40's (have gone as low as 39%)indoors.
My first inclination is infiltration, but from where? Do you have a basement?
Would you post the full model numbers of your furnace/coil/condenser/thermostat? It would be helpful.
AM
P.S., I know you have high temps there. I think that setting your indoor temp and leaving it there will avoid the super long recoveries from setback. Also, any humidity gained during the off-period will exact a penalty as the unit will be working harder in an attempt to reduce humidity, thus prolonging the recovery period.
[this message was edited by ampulman on Tue 12 Aug 17:29] |
| bigglenn357
| "Re(1):Excess Relative Humidity-New Rheem Pre" , posted Tue 12 Aug 06:45
How many tons is your unit? An oversized system will run a shorter time but without it running long enough you end up with a cold damp house.
Big Glenn
"Imagination is more important than knowledge" (Albert Einstien)
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| | Steve S
| "Re(2):Excess Relative Humidity-New Rheem Pre" , posted Tue 12 Aug 10:11
Thanks bigglenn357 -
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(Specs from our receipt)
Our new unit is the Rheem Prestige Series, A/C Furnace Split.
100,000 BTU, Variable speed, 80%+ efficiency 21" , up-flow furnace with ECM motor technology,
Rheem 3.5 Ton R-410A with TXV on the furnace
Rheem 3.5 Ton R-410-A, 2 stage, 16+ SEER efficiency condenser installed outdoors.
*************************
Also verified, our home is 1,760SF
We are not experiencing short running times. In fact, it can take 3-4 hours of continuous running to drop the temperature from 74° to 71° when the outside temp. is around 90° and outside RH is around 18%.
Can't understand if it is that dry outside, how it gets up to 50% RH inside our home.
There is usually a 15 - 20° difference in temperature between the coils (actually at the first duct leaving the unit) and the return-air duct.
Basically I'm happy with the cooling operation, except for the extended run times to lower the temp. just 3-4 degrees in the afternoon.
I'm unhappy with what I consider to be excess humidity in my home that I don't feel our 'lifestyle'(only 2 people living in the home,cooking,washing,showers) is contributing to.
The inside RH doesn't vary but by 2-3 degrees throughout the day and night. If it was due to our 'lifestyle', I would assume it would drop during the approx. 12 hours overnight when we are not cooking, washing, eating, exercising. It doesn't drop.
Thanks so much for taking the time to address this with your experience and expertise.
Best,
Steve in New Mexico
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| | yuri
| "Re(3):Excess Relative Humidity-New Rheem Pre" , posted Tue 12 Aug 17:05
What type of device/gauge are you using to read the humidity? If it is a cheap thermometer/table type unit then they are usually inaccurate. If the tech is using an electronic stick type or sling psychrometer then you will get a true reading. Sounds like your unit is running properly but you may want to get the tech to check the thermostat differential setting. Most 2 stage furnaces will switch stages if the temp drops more than 1 deg F. Not sure about the differential for cooling. Did your previous unit keep the humidity lower?
Yuri
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| | tinner73
| "Re(4):Excess Relative Humidity-New Rheem Pre" , posted Tue 12 Aug 22:12
sounds like your furnace is too big as well.
union trained in Chicago
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