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Appropriate returns for Ultra Aire 155XT dehumidifier.

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wxperson

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Discussion starter · #1 ·
I am considering asking my HVAC person to change the Ultra Aire (UA) 155 setup from dumping UA air into the AC return but instead having it "dumped" into the AC's supply... as recommended by Thermastor.

I am a bit concerned about having less air going into the AC's return since that is where the UA supply goes now.

Right now I think the UA gets more than enough return air since we originally utilized 2 14X8" returns to go to the dehumidifier return (originally a different unit). I would like to know if I could use just one 14x8" return to go to the UA unit... and use the other to go to the AC's return.

Is one 14x8" return sufficient for return air to the UA 155?

I have attached the manual for the UA in case that is useful.

Thanks,

George
 

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#2 ·
Ideally we need a return from the open part of the home that is 10" in diameter or equiv. This 100 in.^2. ok 14" X 8".
20 ft. ok.
Route the dry air to a/c supply. This allows the dehumidifier to operate independent of the a/c blower. I would measure the amount of moisture removed by the dehumidifier to confirm operation.
Also suggest that a/c be setup to provide a 30^F split between a/c return temp and the cooling coil or an a/c supply dew point <5^F below the desired dew point in the home.
Keep us posted on the results.
Regards Teddy Bear
 
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Discussion starter · #3 ·
Thanks...

My HVAC person will attach the UA supply to the AC's supply plenum box on Thursday.

Other than not attaching it on the "end" of the plenum box is there anything else he needs to be aware of when choosing a location?

I did order the backflow/gravity damper that is recommended.

Thanks,

George
 
#4 ·
Ok.
Avoid directly opposing the a/c supply or favoring duct going to the master bedroom.
As long you have a tech, nice to know the supply duct pressure with a/c fan on before connecting the dehumidifier. I assume we have a 30^F split on the a/c coil temp verses the return temperature from the home.
Thanks for all of the effort. Keep us posted on the results.
Regards Teddy Bear
 
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Discussion starter · #5 ·
teddy bear said:
Ok.
Avoid directly opposing the a/c supply or favoring duct going to the master bedroom.
As long you have a tech, nice to know the supply duct pressure with a/c fan on before connecting the dehumidifier. I assume we have a 30^F split on the a/c coil temp verses the return temperature from the home.
Thanks for all of the effort. Keep us posted on the results.
Regards Teddy Bear
Click to expand...
Is there a certain supply duct pressure that is cause for concern?
 
#6 ·
+.8" WG for the Ultra-Aire XT155H is max for duct pressure when the a/c blower on. If high, setup the UA to be "off" when the a/c operates. Smaller UAs have a max of .6" WG.
Most a/cs have a design of +.2" WG.
Keep us posted.
REgards Teddy Bear
 
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Discussion starter · #7 ·
teddy bear said:
+.8" WG for the Ultra-Aire XT155H is max for duct pressure when the a/c blower on. If high, setup the UA to be "off" when the a/c operates. Smaller UAs have a max of .6" WG.
Most a/cs have a design of +.2" WG.
Keep us posted.
REgards Teddy Bear
Click to expand...
OK... thanks. Will let you know how it goes.

FYI... did you ever see this article...

http://www.pvhvac.com/blog/installing-whole-house-dehumidifier-right-way/

Seems to ignore the issue of re-evaporation of AC's coil moisture back into the air. Something that I see as a major problem.
 
#8 ·
Not ideal. Blowing warm dry air into the a/c return decrease the moisture removed by the a/c if the a/c operating. When not cooling a/c blower must be operated. Like you said quickly dries the a/c coil if the a/c is short cycling.
We will contact that contractor with this info.
Thanks for the tip.
Regards Teddy Bear
 
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#10 ·
Important that the damper be closed without any air yet be able to blow open into the a/c duct when dehu operates.
Regards Teddy Bear.
 
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Discussion starter · #11 ·
Thanks for the advice... My HVAC guy did the duct work this morning... now I observe :).

One thing I did notice is that the "back pressure" in the crawl space damper is much less now. i.e. at the same opening setting, the noise and air flow from the damper into the crawlspace was much higher before than it is now after re-ducting the UA supply to the AC supply. That seems to indicate to me that sending the air into the AC return was not allowing maximum air flow of dry air.

I have 6 electronic hygrometers that I will monitor and compare to prior readings. Right now outside DP has dropped into the low 60s so it is not a fair comparison. We should have DP back up in low 70s next week.

Thanks for your advice... I will let you know how my comparison works out.
 

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wxperson
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