NEC 2020 A/C condenser load calculations

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joecalvin

joecalvin

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Location
Austin Tx
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Purchasing / Estimator
Guys, we have been discussing the proper formula to use when calculating the load of an A/C condenser. This would be based on having gas furnaces and using the A/C tonnage as the primary load for the calculation. I have my calculation sheet set up to multiply the tonnage by 1540 to get the VA for the unit. Is this accurate? I have not updated that formula in 10 years so I wanted to make sure that I am passing on the right information.

Let me know.

Thanks
Joe
 
joecalvin said:
Guys, we have been discussing the proper formula to use when calculating the load of an A/C condenser. This would be based on having gas furnaces and using the A/C tonnage as the primary load for the calculation. I have my calculation sheet set up to multiply the tonnage by 1540 to get the VA for the unit. Is this accurate? I have not updated that formula in 10 years so I wanted to make sure that I am passing on the right information.

Let me know.

Thanks
Joe
Click to expand...
Imagine your equipment as a BTU pump with an energy efficiency ratio (EER) of xx watts/ BTU! That 1,540 conversion figure holds true if the EER of your heat pump is 7.79 (~8) W/BTU.
In order to determine the BTU capacity of your heat pump, you multiply the tons of refrigeration (TOR) by 12,000 BTU per TOR. Then you divide by the EER rating of your heat pump to get the watts input needed by your heat pump.
Since the value of EER changes with different units/ brands, your 1,540 multiplier will sometimes hit and sometimes not! Say your new unit has an EER of 10 watts/BTU, your multiplier becomes 12,000/10 = 1,200!
Hope this helps.
 
topgone said:
Imagine your equipment as a BTU pump with an energy efficiency ratio (EER) of xx watts/ BTU! That 1,540 conversion figure holds true if the EER of your heat pump is 7.79 (~8) W/BTU.
In order to determine the BTU capacity of your heat pump, you multiply the tons of refrigeration (TOR) by 12,000 BTU per TOR. Then you divide by the EER rating of your heat pump to get the watts input needed by your heat pump.
Since the value of EER changes with different units/ brands, your 1,540 multiplier will sometimes hit and sometimes not! Say your new unit has an EER of 10 watts/BTU, your multiplier becomes 12,000/10 = 1,200!
Hope this helps.
Click to expand...
Thanks Topgone, that is very helpful.
 
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