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  1. #1
    Join Date
    Nov 2005
    Location
    Northern VA
    Posts
    512
    I have a new Infinity system installed, and it's running great. There is an issue with the Infinity Control that requires AC Airflow set to Maximum as a workaround; until that's fixed the system won't be doing the Comfort reduced airflows in cooling. Also, the system has not been balanced yet, but there's not much balancing that can be done other than adjusting how far room dampers are open.

    Furnace - 58MVB080-20
    Condenser - 25HNA648A300
    Evap coil - CNPVP6024ATAAAAA

    This is a heavy masonry and plaster house, not tight construction, high thermal mass. No direct sun on the thermostat.

    Manual J heat loss for the house is approx. 26k sensible, 4k latent at 95 OAT/72 IAT. I keep the system set on 73 degrees, 46% humidity. The published design temp for my location is 92 according to the county; there are more than a few days a year that exceed that temperature.

    The Infinity condenser is a 4-ton unit. Even after derating the unit for 73 degree indoor return air - which is being overly pessimistic, since the return air should be a few degrees warmer than that - it's still slightly "oversized". But it's acting "right sized", struggling to keep up when outdoor temperatures go over design.

    The weird thing to me is what temperature I feel comfortable at, and how it changes during the day.

    Morning - AC does not run. Comfortable at 73.

    Afternoon - AC turns on High and stays there, even if it's only in the 80s outside. Might need to bump the thermostat down to 72 to be comfortable, otherwise it seems to take too long to start running the AC after the house starts to heat up. Indoor humidity 40% or less, even when it's muggy outdoors.

    Evening - AC continues to run, usually on High, eventually staging down to Low, up to High, down to Low, as would be expected at less than full load. 73 starts to feel too chilly.

    Night - AC runs late into the night, usually shuts off about midnight to 2 am and stays off for the rest of the night unless it comes on to dehumidify. 74 feels about right.

    Is this normal? Should I just set the schedule to move the setpoint around and be done with it, or is this an indication of some other problem? It does seem weird, though I know that the Infinity Control doesn't behave like a traditional thermostat when it comes to system operation and runtimes.

  2. #2
    Join Date
    Aug 2006
    Location
    High Point, NC
    Posts
    155
    When you are moving around, going in and out of house, cooking, etc.. one temperature feels more comfortable. When you sit to watch TV and rest, this temperature will start to feel cold.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,821
    Until the control issue is taken care of, you can't tell if the ysystem is working right or not.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    One thing that happens in a masonary construction is that during the day the bricks absorb a lot of heat and because of ther large mass it dumps heat into the house after the sun goes down.

    Suggestion: Program a setpoint change of 1 to 2 degrees about dinner time for an hour or so. That's what I did.

    [Edited by keepitsimplestupid on 08-28-2006 at 08:28 PM]

  5. #5
    Join Date
    Nov 2005
    Location
    Northern VA
    Posts
    512
    First off, I do realize that a final determination can't be made while anything is abnormal about the system. However, the workaround is just putting the airflows back to where they would be with a Thermidistat - I didn't think that would affect much. Maybe I'm wrong on that point.

    This isn't an activity levels issue; I'm almost nocturnal and am just as active when 73 starts to feel cold as I am when 72 is needed. Once the airflows are corrected I suspect the anticipator setting may need tweaking; the odd thing there is that it underconditions during part of the day and overconditions during other parts.

    I do wonder if it could be a solar gain issue to some degree. I knew that thermal mass shifted the peak load back a few hours; I hadn't realized that the effect was this dramatic.

    Also - is keeping the inside of the house at 73 degrees really going to take 3/4 ton off a 4-ton system? Both I and my installing contractor thought the system was going to be slightly "oversized" when it went in.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,821
    Originally posted by perel

    Also - is keeping the inside of the house at 73 degrees really going to take 3/4 ton off a 4-ton system? Both I and my installing contractor thought the system was going to be slightly "oversized" when it went in.
    Just over 3/4 ton.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Balancing is still balancing and still can occur with zoning. Rooms have smaller or larger heat loads. Air flow directed on you will make you feel cooler because of evaporation. A drape being open in a sunny room will make you feel warmer.

    look here and pay attention fo figure 1.12, the Comfort Chart:
    http://media.wiley.com/product_data/...0fahrenheit%22

    and here for zoning's impact on comfort (43 pages).

    http://www.carrieraircon.com.au/Resi...0fahrenheit%22



    [Edited by keepitsimplestupid on 08-28-2006 at 11:46 PM]

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