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Old 07-16-2011, 10:24 AM   #16
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I will post results of the load calculation when it is complete. I appreaciate all the good info. I am fairly certain the unit is undersized, the chore now is to get the builder/installer to admit it and help rectify the situation

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Old 07-16-2011, 11:08 AM   #17
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Technically/ legally I wonder what they are liable for in way of performance. If the minimum building standard is to provide a 20 difference between outside and in then they may have fulfilled their obligations. May not be comfortable but they did the minimum. We may have a few lawyer types here who may know?
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Old 07-16-2011, 12:10 PM   #18
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@Yuri, if the industry standard is the Manual J load calculation and if the load calulation says the unit is too small, would they then not be liable to make it right?
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Old 07-16-2011, 12:11 PM   #19
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In Florida, a load calc should be on file with the building department.
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Old 07-16-2011, 01:28 PM   #20
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I don't know the legal aspects of that. Need a lawyer to comment. I know there are MINIMUM standards for maintaining heat in rentals and lots of buildings and houses and ductwork size is built to minimum standards. Does not make for a comfortable house but they don't care. Not sure if Manual J is a minimum standard w/o regards for "comfort". We size our ACs here to run continuos on the hotter days (over 90 is HOT here) but that usually only lasts a week at a time 3-4 X a year. Rest of the time they cycle on off and can keep a house at 72 easily.
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Old 07-16-2011, 04:13 PM   #21
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I dug around i the department of public records for th ecounty I live in and found all the permits and paperwork for the house. They DID do som eform of calculation for the ac size but I am not sure what all this means. came out with a total gain of 34750 Btuh and then there is a page that is titled Residential System Sizing Calculation where it has the 34750 listed and the is says Sensible (SHR=0.75) 105.0 30375, below that says Latent 174.1 10125, below that Total (Electric Heat Pump) 116.5 40500. Now the column with Sensible, Latent and total is titled Submitted cooling capacity, next column is % of calc then the last is Btuh. Sound slike a bunch of bable to me, can anyone decipher it?
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Old 07-16-2011, 04:43 PM   #22
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Total cooling load calculation 34750Btuh
--------------------------------------------------
Submitted cooling capacity ---------% of calc. ---------------Btuh

Sensible (SHR = 0.75) ----------------105.0----------------- 30375

Latent -------------------------------174.1 -----------------10125

Total (Electric Heat Pump) ------------116.5 -----------------40500



Does this make more sense?? Tride to scan and attach but the file was too big

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Old 07-16-2011, 04:57 PM   #23
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A A/C is rated its nominal size at an outdoor condition of 95F, and an in door condition of 80F drybulb and 67F wet bulb. As it gets hotter outside, and or you set the indoor temp lower, it loses capacity.

SHR stands for sensible heat ratio. Meaning that of the 34,750 BTUs of load, 75% is sensible, and 25% latent. Sensible is the ability to lower temp, and latent is the ability to remove moisture from the air. There are multipliers used to determine the capacity(you see them in the system sizing you posted) the A/C needs to have at the design conditions/temps. Did it list design temps? If so, what are they.

Check the load calcs for other houses in your area by the same builder and HVAC company. And see if they are the same. If they are the same, then you kn ow the one you have(and those others) are all from the same house, and a separate one for your house was never done.
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Old 07-16-2011, 05:24 PM   #24
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I am following you so far. what are the numebrs listed under the % of calc ?? On this calculation, it says it is design temp of 94 setpoint of 75 outdoor WB of 77 with interior RH at 50%. I do not see anything that lists any numbers for the actual ac unit however

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Old 07-16-2011, 05:30 PM   #25
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Only thing I see for the ac unit is where it says the efficiency is SEER 10 (which I think it is a 13) and capacity is 40.5kBtu/hr

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Old 07-16-2011, 09:19 PM   #26
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The percents are the amount of capacity over the load calc the unit is sized to.

However, I think the on file calc and sizing has been fudged. And is probably the same one they used for other houses.

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