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Heat transfer question...

Doug_7
Doug_7 Member Posts: 233
Infiltration has to do with how tight the exterior shell is. Closing off a room on the inside of the house will have no effect on the infiltration rate of the house.

With a room closed off, there is less total heat load, the air-conditioning equipment will run shorter on-cycles, longer-off cycles and less total cycles per day. With less total run-hours per day, equipment life will be extended. So you save money up-front on power use and you save money long-term on equipment life.

Closing off a room and shutting off the heating/cooling zone for that room will save you money, because this reduces the amount of heat transferred through the exterior wall of that room from the outside.

Think of the entire building shell - the wall of the closed-off room has less delta T and less heat gain than before the room was closed off. This means slightly less total heat gain for the house - and slightly less air-conditioning requirement. Just like the day was not quite so hot outside.

Doug

Comments

  • You have a large house...

    with lots of rooms and you are cooling it. In an attempt to limit your expenses you shut off a portion of the rooms (they are zoned so you can do this) and close the doors to them. Will this actually save you some money or will it just force the other operating zones to pick up the slack and save you very little, if anything. My thoughts are that because these isolated rooms are still within the envelope of the insulated exterior walls there is still heat gain in those rooms that must be addressed by the rest of the system. There is no insulation within the interior walls so, for example, if one room is 80* and the adjacent room is 72* there will be some transfer of energy from the warm room through the uninsulated wall to the cool room which the system must then remove. Any opinions on this?

    Anyone have any figures on what it takes money wise to cool the average structure per square foot. I'm coming up with about 11.5 cents per sq ft per month for my average build 2000 sq ft house here in CT. Does that seem right?
  • Doug_7
    Doug_7 Member Posts: 233
    Heat Transer is proportional to delta T

    The driving force for heat transfer by conduction is delta T - the temperature difference. If you reduce the delta T, you reduce the QUANTITY of heat being transferred.

    The quantity of heat transferred is proportional to the delta T. Double the delta T and you double the amount of heat transfered.

    So, if a room is closed off and is 80* rather than 72* there is less heat being transferred from the outside into that room. If the outside wall was at 88* then the quantity of heat being transferred from the outside into that room is half what it would be if the room was at 72*.

    So you are saving money.

    Doug
  • EJ hoffman
    EJ hoffman Member Posts: 126
    What about r values and infiltration

    intierior walls and doors are different than exterior walls won't infiltration be quicker depending on design.
    Lessing the load will also cycle the equipment more so do you save up front yet lose in the long run due to premature equipment failure?
  • zeke
    zeke Member Posts: 223


    Good explanation!
  • Yea,,,

    Thanks!
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