load calculation

[tacomafc]

I have done several residental load calculation before. But I have never had to do one in a real situation. The house is on the large side about 10,000 sq ft. There is a lot of mechanical stuff and appliances. Is there a easy way of choosing what to include in my calculations. I also have 10 air condensor units. Do I also include the 10 air handler units? For me its very different when you don't have every thing spelled out for like a test question. Thank you for your time.

 

[sparkyboys]

Do you no have a set of engineered specs? You would need to know everything that is being put in to the home in order to do the calculation. All the appliances, motors, air, heat, branch circuits, lighting... there are many variables.

 

[growler]

I have done several residental load calculation before. But I have never had to do one in a real situation. The house is on the large side about 10,000 sq ft. There is a lot of mechanical stuff and appliances. Is there a easy way of choosing what to include in my calculations. I also have 10 air condensor units. Do I also include the 10 air handler units? For me its very different when you don't have every thing spelled out for like a test question. Thank you for your time.

You do the load calculations just like you would for a test question. You use which ever is larger the AC or the heat in the calculation. If it's not on the plans then the HVAC contractor should be able to tell you what they are going to install.

If they can't be specific about anything then go on the high side. I can do a load calculation on anything, if they want it to be accurate then give some details otherwise it's going to be on the high side.

Note* ask about future expansion. They may not have hot tubes and Kilns or welders included in the load but ask anyway. Make sure that you don't leave out any major loads such a instantanious water heaters if they are to be used. The square footage doesn't add up very fast but one major load can ruin all your calculations.

 

[Don Gorham]

Look in the NEC part IV of article 220 and start with 220.82. Don

 

[tacomafc]

I completed a small extension on the existing house. I was asked to clean up the messy panels. There are two 200 amp panels for a total of 400 amps. Looking at the panels with all the 100 amp breakers feeding sub panels I thought it did not look right to me. I want to present a very profesional load calculation to the builder and let him know the the service is no longer up to parr. Its a large house and I was not sure in detail how much stuff I need to include and how much is included in the 3 va per sq ft for general lighting. Thank you for your time.

 

[bob]

I completed a small extension on the existing house. I was asked to clean up the messy panels. There are two 200 amp panels for a total of 400 amps. Looking at the panels with all the 100 amp breakers feeding sub panels I thought it did not look right to me. I want to present a very profesional load calculation to the builder and let him know the the service is no longer up to parr. Its a large house and I was not sure in detail how much stuff I need to include and how much is included in the 3 va per sq ft for general lighting. Thank you for your time.

Mike has nice residential load calculator program. Click on Residential Calc.
http://www.mikeholt.com/freestuff.php?id=freegeneral

 

[tacomafc]

I would like to do the calculation myself so i get a better understanding of how to do it. I have 11 geo-thermal units and 11 air handlers. I think I would total all the loads and a 125% of the largest combo unit. And for the appliances I could total all and apply 75% demand.

 

[tacomafc]

Sq ft 13,500 x 3 va= 40,500va
40,500 - 3,000 = 37,500va x 35% = 13,125 va + 3,000 va =16,125va

2 small appliance = 3,000 va
3 laundry = 4,500 va (i have 3 washing machines, gas dryer)

appliances:
Ref #1 = 480 va
ref # 2 = 240 va
ref # 3 = 960 va
ref # 4 = 240 va
ice machine #1 = 480 va
ice machine #2 = 480 va
wine cooler = 480 va
dishwasher #1 = 1,500 va
dishwasher #2 = 1,500 va
microwave = 1,500va
sink disposal #1 = 1000va
sink disposal #2 = 1000 va
hood #1 = 500 va
hood #2 = 500 va

total 10,860 x 75% = 8,145 va



is this correct so far????

 

[K2X]

There is the standard resi load calc and the optional calculation in the nec. Annex D has examples of both but I think there are better worksheets out there. I always come up with about 25 to 50% less using the optional calculation..

 

[iMuse97]

Sq ft 13,500 x 3 va= 40,500va
40,500 - 3,000 = 37,500va x 35% = 13,125 va + 3,000 va =16,125va

2 small appliance = 3,000 va
3 laundry = 4,500 va (i have 3 washing machines, gas dryer)

appliances:
Ref #1 = 480 va
ref # 2 = 240 va
ref # 3 = 960 va
ref # 4 = 240 va
ice machine #1 = 480 va
ice machine #2 = 480 va
wine cooler = 480 va
dishwasher #1 = 1,500 va
dishwasher #2 = 1,500 va
microwave = 1,500va
sink disposal #1 = 1000va
sink disposal #2 = 1000 va
hood #1 = 500 va
hood #2 = 500 va

total 10,860 x 75% = 8,145 va



is this correct so far????

Not sure it's perfect, but definitely on the right track. As you mentioned, you need to do the geothermal units/airhandlers as continuous loads. That will really start to add up, and then find out if they've got some of those other unique loads that growler mentioned; hot tubs, welders, instant water heat, etc.