View Full Version : Need help sizing a PTAC unit
07-03-2009, 07:03 PM
I am building a room within a commercial building so that I can heat and cool my work space without having to heat and cool the whole 3000 sq ft space. The building itself is insulated already, and the room that I am building will also have insulated walls and ceiling. R13 in the walls and insulation in the ceiling. There will be no windows in the room, just two 6'doors. The ceiling will be 9' and the space is going to be 1000 sq. ft. How many BTU's would I need to cool and heat a room like this since the building itself is already insulated and the sun will not be a factor? There will only be one or two people and fluorescent light fixtures and concrete floors. I was looking at purchasing a PTAC unit with a heat pump. I am in Georgia . Since I am essentially building an insulated room inside of an insulated building, I don’t think any of the BTU calculators would be useful in my situation. Any help on this would be appreciated. Thank you,
07-03-2009, 07:13 PM
Use HVAC Calc.
You don't have solar gain. but, since your not heating or cooling the building. You still have the same temps surrounding the room your building, as though it were a stand alone structure.
When its 95 outside, your building will be hotter then 95 if its not air conditioned.
07-03-2009, 08:14 PM
I downloaded the HVAC calc the other day, but since I am not in the HVAC business, there are a lot of terms that I am not familiar with. Going online and "Googling" btu calculators, I put in the info requested. I did this this with several different ones and came up with a different answer everytime! I got answers from 11,000 to 30,000 btus, so these were not very much help.
07-03-2009, 08:45 PM
Online calculators aren't worth the bandwidth they take up.
07-03-2009, 09:24 PM
I agree 100% with that! I was just looking throught the HVAC-Calc. I downloaded the trial version and when I plug in the info, and hit results, I get no info. I guess I'll have to purchase the program to get any answers.
07-03-2009, 09:52 PM
One suggestion if you have a block wall to go through ,use a mini split/ductless unit rather than the ptac-depending on the room configuration.
A small hole for lines and power is much better than a big hole for a ptac.
07-05-2009, 11:25 PM
You will need approx. 10 kw. good luck:cool:
07-06-2009, 12:20 AM
I am building a room within a commercial building so that I can heat and cool my work space without having to heat and cool the whole 3000 sq ft space.
What are the coldest and hottest temperatures that are likely to occur in the un-conditioned portion of the building?
What's the floor of your interior room made of and what's underneath it? (e.g. soil, an un-conditioned basement, a conditioned basement, etc).
If the rest of your building is completely unconditioned, a ductless heat pump will be more economical than a PTAC. A ductless heat pump will be able to reject heat into the (relatively) cooler outside air rather than into the very hot air inside the unconditioned building. This will lower operating costs.
01-20-2011, 03:45 PM
Pianoman, this will probably help you out with sizing your PTAC. The good news is that there are only 4 sizes to choose from:
<a href=”http://www.ultimateptac.com/”>PTAC Unit Sizer – PTAC Selection Wizard</a>
Best of luck.
05-04-2011, 10:12 AM
A high SEER inverter technology mini-split can be over-sized without the same penalty as with a PTAC.
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