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Old 06-10-2010, 11:21 PM   #1
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Heating & Cooling Analysis


Is this a manual J, if not would it be accurate enough for SW Florida?????
JIm
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Old 06-11-2010, 05:16 AM   #2
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Heating & Cooling Analysis


Looks like a generic simplified form someone or organization made up for their area.

It uses a fixed multiplier for what ever area it was originally created for.

Look at the infiltration line. It uses a 3.5 multiplier on the sq ft. So its not allowing for humid areas like much of Florida, or arid climates. And has no allowance for homes with cathedral ceilings.

No section for shy lights, etc.

So accuracy, depends on where the house is. And if its construction is outside the parameters of that form or not.

Also. It has no break down for sensible and latent load in cooling. Just gives a total load. So no way to know if the size A/C picked by its numbers. Will met sensible capacity.


Use it, and compare its results to the size A/C you have now.

I wouldn't use or trust it though.

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Old 06-11-2010, 08:00 AM   #3
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Heating & Cooling Analysis


It seemed far too simple. But thought I would ask. It was interesting and I was able to see some differences by changing windows, insulation etc. JIm
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Old 06-11-2010, 08:13 AM   #4
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Heating & Cooling Analysis


A house in Arizona and an identical house in Florida, will have different loads because of infiltration air alone(even if the outdoor design temp were the same).
The amount of moisture in the air in Florida will be at least three times as much as Arizona
The solar gain during the day wouldn't be the same either. So a wall in Arizona will have a higher heat transfer multiplier then one in Florida.

A good load calc will tell you your sensible and latent load requirements separately. So you can select the proper equipment match up.

You can use HAVC Calc. It cost 49 bucks. And will tell you your sensible and latent loads.Allow you to do what ifs. Such as changing windows, adding more insulation. Sealing your house for better infiltrations rates(lower). Etc.
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Old 06-11-2010, 08:44 AM   #5
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Heating & Cooling Analysis


I was able to borrow a 1985 edition of a Manual J from the local library.
With a spreadsheet and several hours of tedious work you could probably do a reasonable job of a heat calc.
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Old 06-11-2010, 09:56 AM   #6
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Heating & Cooling Analysis


I actually bought a Manual J when I was planning my AC replacement. It was a bit pricey ($40 IIRC) but that's pretty small considering the investment and potential headaches if you get in incorrect unit.
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Old 06-12-2010, 07:52 AM   #7
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Heating & Cooling Analysis


Looks like I have to do it the right way. I will check the library, if they don't have it I will probably go with the online one. I am glad my AC did not go out and I had to get a new one immediately. I could have ended up with a real mess.
Thanks again JIm

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