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  1. #1

    New Appartment, oversized HVAC...

    I'm a Navy trained HVAC tech, so I know nothing about residential HVAC, but I understand the refrigeration cycle.......

    I just moved into a new apartment, brand new building.

    The A/C short cycles horribly. From talking with the super (a construction manager in his day job) the units are over-sized almost double (no numbers but I can get them if needed). Based on the other issues with this brand new building, I'm not surprised...ie, when switched to "fan" the compressor runs continuously, even with A/C switched off. (I think I can re-wire that.)

    I've been doing allot of reading about oversized units and the overwhelming consensus is "rip it out and get the right size". I agree but unfortunately not going to happen in my case. What can I do to minimize short cycling? Decrease wild temp fluctuations? (gets COLD quick, then gets stuffy/hot, then COLD). would a dehumidifier help? what to minimize power bills? (I pay electric...). I've already closed down on all the vents to minimize the tornado effect, this seems to have helped a little bit.

    I doubt asking the owner to fix it properly will get me anywere, unless maybe I suggest he pays for the electricity until it's fixed. 3 weeks into a 1 year lease, so moving isn't a near term solution.

    Thanks in advance.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,902
    How big is the apartment? How many exposed walls? Floors? Ceiling? How cold do you keep it?

  3. #3
    Join Date
    Nov 2004
    Location
    Austin, TX
    Posts
    870
    I don't have any neat clean tricks for reducing the capacity of the system.

    Bouncing a few ideas around.

    Install a dehumidifier to reduce humidity.

    Install window units and ignore the installed AC system. It's too large, and will keep your home cold and clammy unless you live in a very dry climate.
    The individual window units will give you zoning and redundancy of equipment.

    Reducing the fan speed will give you a colder coil and greater humidity removal, it will also reduce the capacity somewhat, you may not be able to slow the fan enough to matter.
    Reduce it enough and the evap coil will freeze up necessitating a freeze stat to shut off the condenser so the coil will thaw automatically.

    Install a barometric bypass damper to bleed part of the supply airflow into the return air, exactly what we do with a zoned system when some of the zones are shut off. You may still need a freeze stat.

    Install an EPR in the condenser to bleed high pressure hot gas into the low pressure hot gas line to maintain a minimum pressure on the low pressure side of the circuit. I've never tried it but it may work.

    Install a smaller compressor in the condenser to match requirement of home. Slow fan speed down to 350cfm per ton of compressor. Match metering device to the capacity of the compressor.

    Lots of ideas, no pretty cut solution.
    I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.
    ― Benjamin Franklin

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,262
    Fan should be in "auto". Get a good dehumidifier like the Santa Fe Compact or best you can afford. Locate in a place with access to drain and not sensitive to noise. You can set up the dehu to run on timer to control noise when in the area. Set the dehumidistat for 50%RH. Slow air flow to 20-25^F split between return supply. Most fan have several speeds or better air filter to slow flow to get split. Set the t-stat up when unoccupied. Get a good long run when you return. Crack window for fresh air when you are in the space or small window fan with 50 cfm of fresh air to purge indoor pollutants. All a/cs are oversized when the cooling loads are low or none. 50%RH with desired temp will work good well.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Quote Originally Posted by BaldLoonie View Post
    How big is the apartment? How many exposed walls? Floors? Ceiling? How cold do you keep it?
    1000sqft, 2nd floor so only front/back walls are exposed.

    typically 74 during the day, unless it starts getting clammy, then 72/3. 71 at night

    thanks for the suggestions guys, I asked the super if I could make some minor mods, "hell no" was the short answer.... looks like a dehum is my main option..

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