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  1. #14
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by toireht View Post
    dash,
    don't understand what you mean. can you explain please?

    thanks
    james
    First this applies if your load calc is correct.

    Your calc came up with sensible and latent btus,you need equipment that is rated to cover each of those numbers


    ARI and manufacturers ratings are for what the equipment will produce at specific indoor and outdoor temp.

    Charts usually show various OD temps and the capacity for each.

    Indoor is at 80 F,footnotes on the chart may tell you this.

    For every degree indoors below 80 the sensible capacity is to be derated ,835 sensible btus for each degree below 80 ,per 1000 cfms of air flow.

    So, 835 btus X 12 degrees X 1.2(for 1200cfms)= 12,024 deuct in sensible ,and 12,024 increase in latent.

    With the new latent number,half the excess latent capacity(over the latent load calc) can be added back to the reduced sensible.

    Seems you calc is off since you have a 3 ton(I think) or you weren't running it at 68 F,in the past.

  2. #15
    Join Date
    Jul 2008
    Posts
    12
    Quote Originally Posted by dash View Post
    First this applies if your load calc is correct.

    Your calc came up with sensible and latent btus,you need equipment that is rated to cover each of those numbers


    ARI and manufacturers ratings are for what the equipment will produce at specific indoor and outdoor temp.

    Charts usually show various OD temps and the capacity for each.

    Indoor is at 80 F,footnotes on the chart may tell you this.

    For every degree indoors below 80 the sensible capacity is to be derated ,835 sensible btus for each degree below 80 ,per 1000 cfms of air flow.

    So, 835 btus X 12 degrees X 1.2(for 1200cfms)= 12,024 deuct in sensible ,and 12,024 increase in latent.

    With the new latent number,half the excess latent capacity(over the latent load calc) can be added back to the reduced sensible.

    Seems you calc is off since you have a 3 ton(I think) or you weren't running it at 68 F,in the past.
    thanks for the info, I guess what I am needing to do is change the 68 degrees in the software i am using. can you tell me what I should use. I am trying to determine what tonnage to size a new system. I can't get any techs in my area to do a manual j cal. I have double checked my measurements, insulation and variable that I put in the software. the software list tonnage but not sure how to read it or if it listing for ac or heat.

    thanks
    james

  3. #16
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,741
    Use 72 for winter, and 74 for summer.
    When it list gain, that is for cooling. loss is for heating.
    Contractor locator map

    How-to-apply-for-Professional

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

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