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  1. #1

    Properly Sized Equiptment?

    My wife and I just moved into our brand new house in Orlando Florida. It is 3854 sq ft 2 story house. 5 bedroom 4 bath foam filled block 1st floor house. Our upstairs AC unit is working great (Probably because we have most of the vents closed off since it's just her and I) Our downstairs unit it putting out cold air ~ 20 F below return but it doesn't seem to cool down. It ran for 4+ hours last night and cooled 2 degrees. Does this seem right?

    1st Floor
    AHU:FB4CNP024
    ODU: CH14NA024-A

    2nd Floor
    ADH:FB4CNP030
    ODU: CH14N030-A

    Our second floor will cool from 81-75 in about 1.5 hours.

    Thank You
    Dustin

  2. #2
    After running for a little while I just found my unit short cycling. Submitted warranty request through my builder.

  3. #3
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    488
    Closing vents is never a good thing. The system is/was designed to circulate a certain amount of of air 2.5 ton = 1000 cfm. If you reduce that then you will have a system that is not working efficiently or properly. If you were trying to get air to a certain area that would be different not good but different but if you are closing them just because the rooms are not used that is not right or good. It is your house and your equipment so you can do what you want but if you are having several issues with the system down the road remember what I just stated. Worse case scenario is you could damage the compressor by not having proper air flow.

  4. #4
    The thought was that closing the vents in the unused areas would force more air through the vents of the used areas. Is this not correct?

  5. #5
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    1,802
    Quote Originally Posted by tegguy View Post
    The thought was that closing the vents in the unused areas would force more air through the vents of the used areas. Is this not correct?
    That is correct but it may reduce the total volume of air flow below what is needed for proper operation.

  6. #6
    Without a meter there is no way to know the air flow values. So far that unit has been working great it's been the downstairs unit with the issue and no closed vents

  7. #7
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    488
    It does appear that you have a problem with the d/s unit I would have someone qualified to look at it. On the u/s I was just pointing out what you may not have known. I meant no disrespect and did not mean you are having problems with the u/s but that you could in the future from something you are doing today by not fully understanding what was happening.

  8. #8
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    488
    Quote Originally Posted by kdean1 View Post
    That is correct but it may reduce the total volume of air flow below what is needed for proper operation.
    What he is saying is a duct can carry x amount of air at x static pressure. You can force more air through the duct by closing others off but you are increasing the static pressure which in reality decreases the total cfm for the system.

    lets say you have 4 10" ducts which carry 1200 cfm of air at .1 static pressure. you close off 2 of them you are now getting more air out of the other 2 but not 1200 cfm because the static pressure is higher and it is more restricted. Once a blower motor gets to a certain static pressure the total cfm actually decreases.

  9. #9
    Thanks for the information is there any easy way to figure out how many I can close without damage?

    The DS unit had a bad cap and was replaced last night

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287
    Quote Originally Posted by tegguy View Post
    Thanks for the information is there any easy way to figure out how many I can close without damage?
    Close 30% of the diffusers (Vents) and replace the unit every few years. + Best way to SUPPORT YOUR LOCAL MECHANICAL CONTRACTOR.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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