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  1. #1
    Join Date
    Aug 2006
    Posts
    164
    Is it really possible to design a single HVAC system that will cool a single story home equally in all rooms throughout the entire day? Wouldn't 2 systems work infinitely better to adjust to the changing conditions during the day (for example, one east side and one west side)? It seems to me even if the system is designed perfectly (which it never is) to provide worst case air flows to each room that you will either be under or over cooling parts of the house at certain times during the day.

    I have owned 3 homes in Central Florida all 1 story, all 1400-2900 sq.ft., all 1 hvac unit, all had uneven cooling/heating in the rooms. It seems the builders here only go to 2 units for over 3000 sq.ft. or 2 story. I think the reason they go to 2 units over 3000 sq.ft (1 story) is because the requirement exceeds 5 tons, nothing to do with comfort.

  2. #2
    Join Date
    Mar 2005
    Location
    Indianapolis, IN
    Posts
    241
    Zoning system do work when not hacked......

    Cheaper to operate and install as well.


  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,594
    It's pretty rare to find a builder who is willing to put enough money into the HVAC system that it will work beautifully. Zoning or 2 systems are about the only way I know of to do it. On a 2 story house, I've found 2 system and zoned systems may have trouble.

    If you are building a new house, key is telling the builder, and it probably should be a custom home, that you want a priority on comfort even when it costs more. They might have to pay for a dealer with the capability to design a good system, not just slap in some ducts as fast as they can.

  4. #4
    Join Date
    Aug 2006
    Location
    Panama City Beach, FL
    Posts
    17
    That second system is nice when one system goes down and the repair tech has to order a replacement part.

    Especially in Florida. In August.

    Trust me on that.

  5. #5
    Originally posted by eberrong
    I have owned 3 homes in Central Florida all 1 story, all 1400-2900 sq.ft., all 1 hvac unit, all had uneven cooling/heating in the rooms
    You can use single unit for your home. The size of your house is not that big, about 50 by 50 sq ft.

    Zone control can solve your problem.

    I believe the systems you've had ACs sized correctly, but I doubt that the ducts were sized correctly as per loads in each room.

    As for the backup unit when your AC is under maintenance - you can use portable air conditioner/s.

    JMO

  6. #6
    Join Date
    Aug 2006
    Posts
    164
    Originally posted by mjk_na
    Originally posted by eberrong
    I have owned 3 homes in Central Florida all 1 story, all 1400-2900 sq.ft., all 1 hvac unit, all had uneven cooling/heating in the rooms
    You can use single unit for your home. The size of your house is not that big, about 50 by 50 sq ft.

    Zone control can solve your problem.

    I believe the systems you've had ACs sized correctly, but I doubt that the ducts were sized correctly as per loads in each room.

    As for the backup unit when your AC is under maintenance - you can use portable air conditioner/s.

    JMO
    After a lot of reading on this site, I am scared to death of zoning. I love the idea, but the reality of getting it installed properly by a local contractor seems highly unlikely. The last thing I need is to make the problem worse. From what I understand, to do it properly it requires all new ducts (even with the Carrier Infinity system).

    Even if I had all of my ducts sized correctly wouldn't there still be over/under cooling occuring somewhere in the house as the sun moves from east to west. Am I missing something here?

  7. #7
    Join Date
    Aug 2006
    Location
    Carrollton, TX
    Posts
    44
    Originally posted by BaldLoonie
    On a 2 story house, I've found 2 system and zoned systems may have trouble.
    BaldLoonie, could you explain what trouble you have seen with zoned or 2 systems in a 2 story? I am having a custom home built and am curious as to what you meant.

    Thanks!

  8. #8
    Join Date
    May 2006
    Location
    Amory Mississippi
    Posts
    1,002
    entropyknocks, you got that right! I am in PC and I swear August has lasted about 4 months this year.


  9. #9
    Originally posted by eberrong
    Even if I had all of my ducts sized correctly wouldn't there still be over/under cooling occuring somewhere in the house as the sun moves from east to west.[/B]
    No. ACs that are sized as per heat (sensible and latent) gain and losses, coupled with matching air handlers, and correctly sized ducts would give you comfort air just as you need it.

    Of course there will be variations of heat gain throughout the day.

    That is why ACs are sized close to the maximum load requirement. Differences in load requirement can be adjusted by means of damper, variable speed blower, and two stage compressors.

  10. #10
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,594
    Just the natural tendencies of heat to rise and cold to fall.

    Friend had a new, small 2 story. She owns a company and had her own people put the equipment in. Perfectly done, nice Honeywell zoning, foam insulation, tight as can be.

    To keep the upstairs comfy, the 2nd floor zone would be cooling quite a bit. A lot of that cold air fell down the stairs. For most of the summer, she didn't even have to turn the 1st floor stat on and the first floor stayed below where she would have set it for anyway. Solution would have been a door at the top of the stairs but you sure don't see that. And this wasn't an open floor plan.

    Nothing wrong other than she was cooling the main floor colder than desired which increases costs. With zoning, 2nd floor was fine.

    We had to put a 2nd system for the upstairs coolign only, in a zoned house becuase the builder put insufficient ducts to the 2nd floor. And this was an expensive home. Just typical of the way builders treat HVAC.


  11. #11
    Join Date
    Aug 2006
    Posts
    164
    Originally posted by BaldLoonie


    We had to put a 2nd system for the upstairs coolign only, in a zoned house becuase the builder put insufficient ducts to the 2nd floor. And this was an expensive home. Just typical of the way builders treat HVAC.

    I was wondering how you would go about adding a second unit to a house that was designed for one unit. Did you just add to the existing ducting for the second floor and leave the original ducting in place? Wasn't the original unit then oversized? Seems like to do it correctly you would have to redo all of the ductwork and replace the original single unit with 2 newly sized units.

  12. #12
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,968
    eberrong: There are a lot here that will cringe when I say, "Call a professional in." Really though, until someone comes in and does a thorough analysis of your present system will they know what can and can't be done. Adding a second system to your home is not difficult to do, and is certainly not prohibitive.

    Rather than try to walk you through, step-by-step all that needs to be done in order to accomplish this, it would make much more sense to have a reliable, reputable contractor come in and provide you with their expertise. Then, if there is some question that arises, that they cannot or will not answer, then bring that question here. But the person, on site, first-hand, has the best perspective.

    I can't tell you the number of homes I have done that had a single heating-cooling system in place, and we have added a second-story system to the home without any detriment to the first system. In addition it provided the efficiency and comfort the customer was looking for.

    Every home is different AND every customer's expectation is different. All the best, John.
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

  13. #13
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,594
    We've done 2 supplemental systems this summer. The one with zoning and another who just could cool the upstairs and likes it CCCCold.

    Both had huge attics so the air handler was put up there with ducts to each room plus returns. The existing vents were left alone, they do prove the heat which works fine.

    Overall, yes it probably does give the total capacity of the house a bit too much. But I am not worried with a big unit upstairs. Much of what it does ends up on the first floor so that unit doesn't have to run as much so total comfort is there. And both of these HO's liked it cool so probably needed more than typical customer might.

    In our area, 2 system homes are basically those that flat out need more than 1 system can do. So there are many large 2 story homes that should be on 2 systems or a well designed zone system, but have 1 4 or 5 ton single zone and big furnace and aren't comfortable.

    We're pretty close to John Lloyd, sounds like his builders are the same way

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