Load Calculations --heat pumps 100%

[Jammer310]

Mike,
Inspectors in our county area requires us to include 100% demand load on both compresors and air handler for Service load calculations as referanced in (2002 NEC 220.30) I know still.

Now on the 2005 NEC this article shows its been revised.
Article 220.82(C)4

Question: Can I calcutate 100% demand load for the compresor and 65% on the Air Handler?

thanks
jammer310

 

[Bob NH]

Mike,
Inspectors in our county area requires us to include 100% demand load on both compresors and air handler for Service load calculations as referanced in (2002 NEC 220.30) I know still.

Now on the 2005 NEC this article shows its been revised.
Article 220.82(C)4

Question: Can I calcutate 100% demand load for the compresor and 65% on the Air Handler?

thanks
jammer310

From the 2005 NEC:

220.82(C) requires the largest of the six selections.

220.82(C)(2) identifies 100 percent of the nameplate rating of the heating when a heat pump is used without any supplemental heating. That would include the air handler.

The air handler has to be working for the compressor to be working, except maybe for a brief period at startup. I don't see any realistic justification for eliminating the air handler load. That would be like trying to eliminate the load of the fan in the evaporator/condenser unit because it isn't the compressor.

 

[suemarkp]

The fan and controls in the air handler are almost trivial (1KW or so) compared to strip heat, and variable speed air handlers rarely draw nameplate amps. But I agree it needs to be included at 100% ONLY IF there is not supplemental strip heat (which is typically 7KW to 20 KW). The strip heat is a killer, and I see no reason why it shouldn't be treated any differently than a pure electric furnace. Doing 20 KW of strip heat at 100% makes no sense to me, as it rarely runs at full tilt, especially if the compressor is still running.

So if you have a heat pump with strip heat, it seems reasonable to me to use the compressor MCA plus the air handler MCA. Note that modern HVAC components use a 125% nameplate value and typically use the term MCA on both the airhandler and the compressor. I'm glad this was fixed in 2005, as it creates quite a bit more capacity on my service (30 amps).