Dwelling calculation

[Kessler4130]

Hey guys I have to present a load calculation to an inspector tommorow for an addition.

The total square foot, is 2935
The appliances/equipement are listed below all in KW.

Range - 10.92
Hot water - 4.5
Dish - 1.44
Micro - 1.56
Washer - 1.2
Dryer - 6.72

Furnace1:
ckt1 - 7.68
ckt2 - 11.52

Furnace2:
ckt1 - 15.36

I used the optional calculation with heat, since the outside units are not heat pumps and came up with 184.675 amps.

If anyone has any time to spare I would apperciate it if you could double check this for me, it has been a long time since I have had to do a calculation and certainly do not want to show an inspector one that is wrong.


Thanks

 

[nyerinfl]

2935 sf x 3va = 8805 va
S.A. + Laundry = 4500 va
Appliances = 38.1 kW
*Washing machine not included, part of the Laundry Circuit.

38,100 + 8805 + 4405 = 51,405

51405
-10000 = 10000
41405 * 40% = 16562 + 10000 = 26562 va. /240 = 110.68A. You still need to add the greater of your heat or A/C to this. Done with optional method. I would've added the heat but I wasn't sure about your description of the load.

 

[Kessler4130]

I am sorry, there are 2 furnaces, one has 2 circuits the second only one, I used the heat in my calculation, since the ac units are much smaller and are not heat pumps. I believe it was 34.56 kw of total heating load before any correction factors for the calculation.

Also I appologize I had mistyped the dishwasher load as 14.4 it is actually 1.44

I was kind of unsure about using the washer in my calculation since I had included a laundry circuit, which brings my new load to 182.675


If I missed anything please feel free to call me stupid .

 

[tallguy]

S.A. + Laundry = 4500 va

I know this is correct... but could someone explain why a 20A SABC is calculated at 1500va, only 62.5% of continuous capacity?

 

[charlie b]

I know this is correct... but could someone explain why a 20A SABC is calculated at 1500va, only 62.5% of continuous capacity?

For the simple reason that calculating load is not the same process of designing a circuit. Or did we already deal with that issue?

(WARNING - even if a bit late - that was "engineering humor." It's OK for normal people to not get the joke.)

 

[tallguy]

For the simple reason that calculating load is not the same process of designing a circuit. Or did we already deal with that issue?

Let me put a finer point on my question then... I would have expected it to be 80%, since that is what is allowed for a continuous load. So, for a 15A circuit 1500va makes perfect (OK, almost -- 1440va would be perfect) sense to me. But why count 15A and 20A exactly the same @ 1500?

I guess I'd have to look into the history of 220.52 to satisfy my curiosity... I'll just have to hope that Charlie Brown can come up with something since he seems to be the guru of obscure documentation.

 

[suemarkp]

2935 sf x 3va = 8805 va
S.A. + Laundry = 4500 va
Appliances = 38.1 kW
*Washing machine not included, part of the Laundry Circuit.

38,100 + 8805 + 4405 = 51,405

51405
-10000 = 10000
41405 * 40% = 16562 + 10000 = 26562 va. /240 = 110.68A. You still need to add the greater of your heat or A/C to this. Done with optional method. I would've added the heat but I wasn't sure about your description of the load.

Your appliance total doesn't add up. I get 25.14 KW for the appliances (minus the clothes washer). Adding the square feet and SA circuits, this comes to 38.45 KW. Somehow you've adding something twice. 38.45 - 10 = 28.45 KW. 28.45 * 40% = 11.38 KW.

So now you get 11380 + 10000 = 21.38 KVA plus the heat. Heating is tricky -- how many separately controlled heating elements are there (may need to ask the HVAC guy because those larger ones must have subdivided heat, we just don't know if they are separately controlled)? You use a 65% multiplier for 3 or less separately controlled heating elements and 40% if four or more. Assuming you only have three, this is .65 * 34.56 = 22.46 KW

So total service demand load is 21.38 + 22.46 KVA = 43.84 KVA. At 240V, this is 182.7 amps.

 

[Kessler4130]

Your appliance total doesn't add up. I get 25.14 KW for the appliances (minus the clothes washer). Adding the square feet and SA circuits, this comes to 38.45 KW. Somehow you've adding something twice. 38.45 - 10 = 28.45 KW. 28.45 * 40% = 11.38 KW.

So now you get 11380 + 10000 = 21.38 KVA plus the heat. Heating is tricky -- how many separately controlled heating elements are there (may need to ask the HVAC guy because those larger ones must have subdivided heat, we just don't know if they are separately controlled)? You use a 65% multiplier for 3 or less separately controlled heating elements and 40% if four or more. Assuming you only have three, this is .65 * 34.56 = 22.46 KW

So total service demand load is 21.38 + 22.46 KVA = 43.84 KVA. At 240V, this is 182.7 amps.

The error in Nyerinfl's calculation is my fault, I had the dishwasher as 14.4 and it was supposed to be 1.44. The heating is controlled from 2 locations, 1 from each furnace. Thank you for double checking me, my largest concern was I was doing the heat correctly and I was. I feel confident that the calculation I give the inspector this morning is correct.

Thank you