Need Sizing Info

[thailen]

I have some old - as old as 20 years - compressors for four shotgun houses and need to replace three of them. Since they were installed originally, the houses have been insulated(9" attic fiberglas blown-in), reroofed(with 5/8"CDX underlayment, roofing paper and three-tab shingles) and tightened up. A separate A/C system was installed for each apartment in a two apartment house. The ceilings are 12 feet high, with original pine floors and the total footage for each apartment is 750 square feet. Each room has one 68" x 30" window and I believe the vents are in the ceiling.
What tonnage is needed for the soon-to-be replaced compressors?

[seatonheating]

I have some old - as old as 20 years - compressors for four shotgun houses and need to replace three of them. Since they were installed originally, the houses have been insulated(9" attic fiberglas blown-in), reroofed(with 5/8"CDX underlayment, roofing paper and three-tab shingles) and tightened up. A separate A/C system was installed for each apartment in a two apartment house. The ceilings are 12 feet high, with original pine floors and the total footage for each apartment is 750 square feet. Each room has one 68" x 30" window and I believe the vents are in the ceiling.
What tonnage is needed for the soon-to-be replaced compressors?


www.hvac-calc.com

[garya505]

You need to have a load calc done or do one yourself.

Or, alternately you could size by rule-of-thumb, seat-of-the-pants, whats-in-the-truck or some other equally questionable method and then sit back and wait for the occupant's complaints. :limb:

[thailen]

I'm NOT an air-conditioning technician, engineer or architect. I CAN follow formulas, if I have the correct info - either using the info in my original post - or other info that you can tell me to plug in.
Please send me helpful information, as opposed to general comments which I am unable to understand or to follow.

[garya505]

I'm NOT an air-conditioning technician, engineer or architect. I CAN follow formulas, if I have the correct info - either using the info in my original post - or other info that you can tell me to plug in.
Please send me helpful information, as opposed to general comments which I am unable to understand or to follow.

You can use this to calculate the heat gain and loss:
http://www.hvac-calc.com
From that you can size your equipment.

[seatonheating]

I'm NOT an air-conditioning technician, engineer or architect. I CAN follow formulas, if I have the correct info - either using the info in my original post - or other info that you can tell me to plug in.
Please send me helpful information, as opposed to general comments which I am unable to understand or to follow.



But you can't click and follow the instructions for the link I gave you..hmmm.

[garya505]

But you can't click and follow the instructions for the link I gave you..hmmm.

That was my thought as well, but I'm having a good day and just trying to be more polite than usual. :LOL:

[seatonheating]

That was my thought as well, but I'm having a good day and just trying to be more polite than usual. :LOL:


Hey Gary, you got that list for me yet :). ?

[garya505]

Hey Gary, you got that list for me yet :). ?

I'm doing landscaping this afternoon, but I plan to work on that later today. I currently have the crappiest-looking front yard on the block.

[farhanmahmood]

how to find
CARRIER TECHNICAL DEVELOPMENT PROGRAM copies in pdf ?

[thailen]

but got nothing. What's the secret?



You can use this to calculate the heat gain and loss:
http://www.hvac-calc.com
From that you can size your equipment.

[seatonheating]

but got nothing. What's the secret?


Here's a direct link to the homeowner's version:

http://www.hvaccomputer.com/hvac/form/GetTrialForm.asp?site=hvaccomputer

[thailen]

You guys have tried to give me web sites for making calculations designed to determine the right size Compressor for my A/C system. I clicked on both, but got nothing. What's the secret?
P.S. I have no trouble getting any other web site on the internet, just not yours...




Here's a direct link to the homeowner's version:

http://www.hvaccomputer.com/hvac/form/GetTrialForm.asp?site=hvaccomputer

[garya505]

You guys have tried to give me web sites for making calculations designed to determine the right size Compressor for my A/C system. I clicked on both, but got nothing. What's the secret?
P.S. I have no trouble getting any other web site on the internet, just not yours...

The link is fine. There is something wrong with your computer or internet connection.

[thailen]

I did get a redirect page to a page saying I could get the program for residential computing sizing for $49...
Isn't there a cheaper program? Another list of Googled A/C sizing sites seem to all be tilted toward engineers and A/C technicians...





but got nothing. What's the secret?

[beenthere]

I did get a redirect page to a page saying I could get the program for residential computing sizing for $49...
Isn't there a cheaper program? Another list of Googled A/C sizing sites seem to all be tilted toward engineers and A/C technicians...

CHEAPER?

You might want to look at the price of other ones. There are ones that start at 500 plus bucks.

49 bucks to do it right is dirt cheap.

49 bucks is the limited time home owner version. Your not going to find a more accurate one for less.

[thailen]

Why should I pay $49 for something that should be real simple for a guy like me, who built his own house, back in '88. I thought I could use the formula from the city HVAC permits office. I brought them a diagram of the house layout and they showed me how to compute the numbers(ducts, returns, etc.) based on R and U values. I spent four hours sketching out the sizes, R and U values and the size of the compressor and blower. In short, I (and a friend) did everything except pressure test the system and feed freon. It must have worked, because the inspector passed it the first time.
I'm not trying to get a HVAC license; all I want is a rough idea of the compressor size I need given the upgrading of the numbers in my initial thread.
Is that too complicated?

[beenthere]

Why should I pay $49 for something that should be real simple for a guy like me, who built his own house, back in '88. I thought I could use the formula from the city HVAC permits office. I brought them a diagram of the house layout and they showed me how to compute the numbers(ducts, returns, etc.) based on R and U values. I spent four hours sketching out the sizes, R and U values and the size of the compressor and blower. In short, I (and a friend) did everything except pressure test the system and feed freon. It must have worked, because the inspector passed it the first time.
I'm not trying to get a HVAC license; all I want is a rough idea of the compressor size I need given the upgrading of the numbers in my initial thread.
Is that too complicated?

You can spend 49 bucks to do it right. Or just keep on guessing.

If 49 bucks is too much. Buy window units and small space heaters. And save yourself all that other money.

[thailen]

the house has a compressor sitting in back, connecting to nothing. The fact is, the apartments are complete with ducts and vents and a blower. All I want to do is replace the 15 year old compressors, sized for a house that at the time of installation, had no insulation, leaky windows and doors, and other gobblers of energy. Those compressors were sized at 1.5 tons. Given the upgrade in all phases of energy conservation, is 1.5 tons really needed? Or can I size down a half ton?



You can spend 49 bucks to do it right. Or just keep on guessing.

If 49 bucks is too much. Buy window units and small space heaters. And save yourself all that other money.

[beenthere]

the house has a compressor sitting in back, connecting to nothing. The fact is, the apartments are complete with ducts and vents and a blower. All I want to do is replace the 15 year old compressors, sized for a house that at the time of installation, had no insulation, leaky windows and doors, and other gobblers of energy. Those compressors were sized at 1.5 tons. Given the upgrade in all phases of energy conservation, is 1.5 tons really needed? Or can I size down a half ton?


No, I'm not under that impression.

And if they already have 1.5 ton condensers. You ain't gonna find smaller condensers for A/C. You would need to use refrigeration condensers, to get smaller.