a/c

Paul S_3

HEY GUYS , HOW IS THE PROPER WAY TO SIZE A A/C UNIT. I NEVER DID ONE FROM SCRATCH, I MOSTLY JUST DID DIRECT REPLACEMENTS. I JUST WON A BID TO REPLACE A EXISTING 20 TON PACKAGED UNIT AND I WANT TO SEE IF THATS THE CORRECT UNIT, AND ALSO WANT TO KNOW FOR FURTHER WORK.

 THANKS PAUL

meplumber

I use a program called HVAC Calc.

The proper (and legal) way is to do a full Manual J heat gain/loss.  I use the HVAC Calc program.  It isn't free, but the reports that you are able to generate are great.  For my money, it is one of the easiest, most comprehensive heat loss programs available.  There are more comprehensive and there are easier to use, but this is the best combination of the two in my opinion.



Good Luck.

Techman

Hang on

a sec,You won the bid,calling for a 20t unit.I think you HAVE to honor the contract.Even if the bldg requirers only one ton ,you are obligated to deliver the contract .Unless ,legalily,you can convince the proper people to allow you to change what is "wrong".Be careful!!! Is this a roof top unit? Does the existing roof curb fit the new unit? A 15t unit will not match up to the old 20t curb.

Eugene_Silberstein

No Manual J

If the system is 20 tons, you should not be doing a Manual J. Manual J is for residential applications. You should be doing a Manual N, which is the load calculation for commercial applications.