Page 2 of 4 FirstFirst 1234 LastLast
Results 14 to 26 of 43
  1. #14
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    Genco

    Look at the product literature, the evap coil/outdoor unit combination will be listed with a s/t# ( sensible to total heat ratio ), this number shows how much sensible heat removal the coil has. The rest is latent heat. Find the one with the lowest sensible heat ratio and you will have the one with the best latent heat removal. Check performance data with outdoor unit combination.

    Hope this helps,
    Richard

  2. #15
    Join Date
    Apr 2002
    Posts
    11,808
    Originally posted by cem-bsee
    Carnak: how does one dry the outside ambient air to be able to draw in dry air to reduce the humidity in the house?
    The post was from someone on the Gulf Coast = hi humidity ambient, just as here in Huntsville AL where low outdoor ambient humidity equates to something 85% or less ( per the Channel 31 weatherman 2 mo ago).
    In my post I mentioned a 'fresh air intake' to the return air duct, and I also mentioned operating the air handler in 'Auto' mode, meaning the air handler blower runs only when the compressor runs.

    When this happens, the fresh air is cooled and dehumidifiied by the cooling coil and the home is pressurized the home with dry air.

    Dry air then tries to leave the home when the system is running. This reduces the amount of humid air trying to infiltrate into the home from the outside. This keeps humidity from the home in the first place.

    The mixed air entering the cooling coil has a slightly elevated dry bulb and wet bulb temperature compared to straight return air. The cooling coil will be able to grab more sensible and a lot more latent heat from this mixed air than it could from pure return air. It is much easier to remove the humidity of the outside air this way, than it is for the cooling coil to try and remove extra humidity from dry return air at 75F and 50% RH, to compensate for the humidity added by the uncontrolled infiltration of humid air.

    I am dealing with high humidity as well, ambient dewpoints of 80-81F right now, I do not think it is any higher in the gulf.

    You do not have the thermostat fan swith in the "ON" position, as the fan will run steady, constantly re-drying the coil/drain pan when the compressor cylces off. As well running the fan steady will pump humid air into the home when the compressor is not running.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  3. #16
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I am a homeowner. From all that I have been told, the installer who said he "didn't like" TXVs has probably identified himself as a hack who couldn't control your house humidity if he wanted. That may be a harsh exaggeration, but you should know that he does not understand your concerns.

    If the installer has to choose between 3.0 and 4.0T coils, he should be fully aware that the 3.0T choice will run colder and remove more humidity. But you should not have to manage this decision if you get the right installer. You need to inform him you are interested in humidity control and not just eye popping SEER numbers on paper (which I doubt will pay off for you in the real world). I suggest you ask him how he feels about doing a Manual J and Manual D calcs on your house. If he wants to charge you a sum for it, consider him further. If he indicates he does not do business that way, you are on less firm ground with him. Would the pros agree with this notion?

    Some of the things suggested *have* been generalities, but truly there are craftsmanship issues which make a whole lot of difference. My way of knowing this, is finding just how big a goof was made by a prior installer, several times.

    There was a question how a fresh air intake, can provide dry air in a humid climate. The answer I see is, that air goes thru the AC before getting into your house and that's how it is conditioned (i.e. dehumidified). The argument is that this fresh air intake tends to eliminate the outside air leaks already present in your house. Any air leaking into your house from other sources, has no opportunity to be conditioned. Measuring this phenomenon would be a great subject for a research paper, but I have not found one on this topic so far.

    Hope this helps -- P.Student

  4. #17
    Join Date
    Apr 2002
    Posts
    11,808
    Less than a design day in the Caribbean, early in the morning.


    Partly Cloudy 88F
    Feels Like
    101F
    Updated Sep 9 08:00 a.m. Local Time
    UV Index: 1 Low
    Wind: CALM
    Humidity: 75%
    Pressure: 29.91 in.
    Dew Point: 79F
    Visibility: 6.2 miles

    Sweet Home Alabama

    Right Now for
    Mobile, AL
    Save this Location On The Spot Weather


    Partly Cloudy 77F
    Feels Like
    77F
    Updated Sep 9 08:25 a.m. CT
    UV Index: 1 Low
    Wind: From N at 7 mph
    Humidity: 77%
    Pressure: 30.08 in.
    Dew Point: 69F
    Visibility: 10.0 miles

    Looks like well below design conditions in Mobile but it is still early in the morning right now.

    I see dewpoints of as high as 81 here, however it pretty much hovers around 80 for a good six months of the year, day and night.












    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #18
    Join Date
    Jul 2005
    Location
    Orange County, NY
    Posts
    936
    Here's your SIMPLE answer

    Go get a load calculation done
    Go with the 3.5 ton Condenser (if it matches the load)
    Go with the larger Evap. coil (4 ton) WITH TXV
    Go with a FanHandler drive (http://<a href="http://www.fanhandle...andler.com</a>
    Go with a static pressure control for fanHandler
    Go with 300 CFM or lowest permissible CFM

    Then
    Watch as your skin cracks

    If you don't like that then install a whole house de-Humidifyer on the Return duct It will act as a PRE-DRYER for your system.

    Core


  6. #19
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,361
    Originally posted by gencon
    How do I spec my new ac requirements to get a system that will have high latent heat removal?
    Do oversized or undersized evaporators have a higher latent heat capability
    gn
    Are you looking for humidity control with low/no cooling load? A simple high SEER a/c sized for design conditions with or without an txv valve, with air tight ducts,and low air flow will provide 75^F,<50%RH during peak cooling load,+10 hours per day. During the night hours, moisture or latent load continues, sensible load declines, and indoor %RH rises slowly. Most a/c remove approx. 3,000 btus of latent,(3 lbs)per hour of moisture(75%Sensible heat ratio) with 75^F, 50% RH return air.
    3 lbs. X 10 hrs. X 3 ton = 90,000 btus lat.(90 lb)(10 gals.)/day of moisture removal.
    This will keep most homes dry with 75^F outdoor dew point. Higher or lower outside dew points require more or less a/c hours operation.
    As the outdoor temperature declines, hours of a/c operation decreases. The complicated, expensive, two speed a/c with perfect controls should switch to low speed when the cooling load is reduced 50%. Now we have + 10 hours of low speed or 1.5 ton of a/c, while outdoor dew point(latent load) may be the same. Low speed (1.5) a/c operating 10 hours removes half as much moisture (45,000 btus or 45 lb/day). This is slightly better than cycling a single speed 3 ton for 5 hours. Removing less moisture raises indoor humidity, typically to 60%-65% RH. With a/c, overcooling is required to remove moisture. We need to operate on low speed 20 hours to remove the 90,000 btus of latent (90 lbs). During extended rain at 65^F-75^F, humidity control is impossible. Providing make-up fresh air ventilation makes humidity control more difficult yet.
    High indoor humidity in addition to being uncomfortable, also grows mold. Consequently, several manufactures are selling whole house dehumidifiers that are combined with central a/c. When the a/c does not remove enough latent, the dehus automaticly operate until the desired humidity is reached. A 100 lb. per day dehu is capable of maintianing 50%RH without operating the a/c in 2,500 sqft.home. Some dehus have elaborate ventilation strategies to provide fresh air when occupied. These dehu systems are simple and cost less when combined with simple high SEER a/c than multi-speed a/c. The dehus can also be added to the mutli-speed a/c. TB "web dehu peddler"

  7. #20
    Join Date
    Apr 2004
    Location
    Bartlett, IL
    Posts
    6,619
    I don't get it, there are plenty of 3.5 ton coils at the supply houses I deal with.
    I think genco is a general contractor (hense the genco) that wants to DIY.

  8. #21
    Join Date
    Jul 2004
    Location
    NW Arkansas
    Posts
    1,288
    Originally posted by gencon
    And you wonder why the public throws AC guys and lawyers into the same pool.

    gn
    I guess I am screwed. I am a commercial HVAC tech and my wife is a lawyer.

  9. #22
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    At a party

    >>I guess I am screwed. I am a commercial HVAC tech and my wife is a lawyer.

    When you go to a party, don't tell them where you really work, tell them you are from the IRS instead. They will like you better!

    Best wishes -- P.Student

  10. #23
    Join Date
    Apr 2005
    Posts
    28

    Talking

    Finally getting some action and info!!!

    Carnak; completely understand you fresh air concept; Up north I did the same thing to help stop cold infilteration in 70 vintage leaky houses. How big a air inlet for a 3.5t do you recommend, I like the idea.

    2hot 2 cool; not even close. I have looked at detail tech data on 2 manufactures now; no 3.5 t coils; they all recommend going with 4t. I thought all the pro keep preaching "matched units" and your going with a generic 3.5t coil? The 4t coils gains in latent is over 1000btu's on most combos vs the 3t coil. Even more interesting is that the seer 14 vs 13 is a hoax. The 13's have more tot btu and more sensible that the 14's. Seems like they are trading total btu and comfort in order to make 14. Also they are derating the 14 by on average about 2000 btu's to reduct power consumtion of the compressor to get the rating. Your right about one thing, I have been a general and an engineer but I don't want to do a DYI. Trust me you don't do bricks, sheetrock or brain surgery yourself! I just want to find someone who understands more than me to put in a "weel engineered system" which I'm more than willing to pay for.
    wgrr: My sincere consolences!

    On the Rheem site under condenser unit, you can down load some pdf files that are really eye opening.
    gn



  11. #24
    Join Date
    Apr 2002
    Posts
    11,808
    Pressurization gets used up north but it runs the risk of driving the humidity into the walls in the winter time.

    As a starting point, I would try to estimate the infiltration rate of the home and work backwards from there. It should hopefully work out to a CFM flow of less than 10% of what the air handler moves. Perhaps sensible gain of infiltration divided by 1.08, divided by indoor/outdoor temperature differential.

    I would size a short intake for about 10% outside air, in your case I would try an 8 inch round intake with a manual damper. With the system running close off damper until you just feel a slight cool breeze leaving from a cracked door or window. Check all sides of the house.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  12. #25
    Join Date
    Apr 2002
    Posts
    11,808
    Results using heat pipe technolgy air handlers in a commercial application



    Everyone laughs at the cheapo thermo-hygrometer, but you let it sit for a while and its pretty good.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  13. #26
    Join Date
    Apr 2005
    Posts
    28
    It took twice before I got "remove the damper"
    I was thinking that 6 or 8 in intake seems hugh; but with a damper you could tune it for max performance.
    gn

Page 2 of 4 FirstFirst 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event