reidential load calc issue

[Daja7]

I did a load calc for a project using a load calc program. (the one on Mike holt stuff) and it comes up with 19,220 VA. The inspector turned it down because his calcs come up with over 20,000 va

2300sq ft 2 small appliance, one laundry.....11,400

2- 2 ton a/c one with 10KW suplemental strip and on refrigerator.
The program says 19,220.
using Residential optional calculation

I have not done a manual calc in ages so i may be missing something. or is the load calc program wrong?
Thoughts

I have used the mike holt program for two years and this is first ime i have been questioned. It is a great easy program to use.

 

[Smart $]

I did a load calc for a project using a load calc program. (the one on Mike holt stuff) and it comes up with 19,220 VA. The inspector turned it down because his calcs come up with over 20,000 va

2300sq ft 2 small appliance, one laundry.....11,400

2- 2 ton a/c one with 10KW suplemental strip and on refrigerator.
The program says 19,220.
using Residential optional calculation

I have not done a manual calc in ages so i may be missing something. or is the load calc program wrong?
Thoughts

I have used the mike holt program for two years and this is first ime i have been questioned. It is a great easy program to use.

I've not used the MH Load calc program so cannot comment on it... but FWIW, you cannot do a proper NEC load calc using ton rating of AC units. The proscribed NEC load calc method says you must use nameplate values.

Also, I find it hard to believe a residential service has only general lighting, 2-SABC, and laundry while having two AC units and 10kW heat strip.

 

[suemarkp]

Are the AC units really heat pumps? If so, you most likely need to add them all together instead of taking the higher of heating/cooling load. There aer factors applied to heat pumps, so you need to see how the calculator is doing it.

No electric range or dryer or water heater?
No dishwasher or disposal or built-in microwave?
Refrigerators are usually covered by the kitchen small appliance circuits, unless that fridge is an additional one.

What size is this Service? As long as the inspector didn't get over 24KVA you're still good on a 100A Service (but I don't think I'd do a house now days, especially one with electric heat, that cuts things that close).

 

[Daja7]

sorry, i should have clarified. this is for a generator load calc. cannot go over 20Kw. these items are the only loads on the gen panel.

 

[JoeStillman]

I think the inspector is saying he wants you to size the generator output according to the max output of the generator.

Residential load calcs are mostly based on class 3 falsities. You remember the 3 classes of falsities? 1) Lies. 2) D%&#3ed Lies. 3) Statistics.

 

[Smart $]

sorry, i should have clarified. this is for a generator load calc. cannot go over 20Kw. these items are the only loads on the gen panel.

So the system has an automatic transfer switch. An MTS wouldn't have the limitation. Any load shedding built in to the ATS?

Another factor that can come into play is the generator is rated in kW with an assumed power factor (usually .8 I believe). If your load actually has a higher power factor, the rated kW can be exceeded by the difference, because loads are calculated in kVA. A 20kW generator rated at the assumed .8 power factor should actually be able to handle a 25kVA at a 1.0 power factor. However, with the 2 AC units, I doubt the combined loads have a 1.0 power factor. Likely somewhere in between.

 

[suemarkp]

Depending on how you read 220.82(A), one could argue that the feeder must be 100A or larger to use the Optional calculation (or you just round up to that is it comes in less). So for a 20KVA generator, you may need to use the standard calculation.

 

[Daja7]

[we just load sheded the A/C and done. easy fix , i was just wondering how the load calc program came up with this calc and the inspector interprets differently.