Multi Dwelling Load Calcs 210.84

[Bignose94015]

I have been browsing this forum for a decent amount of time now and cant seem to find an answer to a questions I have.

I currently have a multi dwelling new construction project. There are over 200 Units in this building.

My main concern is between calculations and demand factors that can be used on this project. With A/C the buildings demand factor per 220.84 is less then if no A/C is used on this project.

2nd is a whispa unit considered electric space heating. The whispa unit itself does not create heat it just blows air over the hydronic piping

So my calcs the way I under stand it.

With No A/C equals 5,297 per the attached doument

With A/C I have 100A less draw @ 5,197



Thanks for all your help

Rick :?

 

[Dennis Alwon]

Welcome to the forum. I hope one of our members can help you. Hang tight.

 

[malachi constant]

The attached calculations do not seem to follow the actual code. Please take a much closer look at the code in question, you seem to be winging it without much understanding.

I assume you are calculating service size, and you want to use 220.84 (your post references 210.84).

Go to 220.84(A). It says you can use the demand factors in Table 220.84 ONLY if you meet the three stated criteria. In your "no AC scenario" I am not sure you meet the third. I am not familiar with a whispa but it does not sound like electric heat to me.

If you put AC in each unit, then you are allowed to use 220.84(C) to calculate dwelling loads only. Per 220.84(B) you still need to calculate house loads like you normally would. House loads do not get the demand factor applied.

Looking at 220.84(C), you need to FIRST add all the following together:
(C)(1) 3VA/SF for general lighting etc
(C)(2) 4500VA/unit for laundry and small appliance
(C)(3) nameplate of all appliances described in (C)(3)a through (C)(3)d.
(C)(4) nameplate of all other motors not described in (C)(3).
(C)(5) the larger of your AC or electric heat load.
Add those up, THEN multiply the sum by your demand factor of 0.23. Now you have your dwelling service load.

Then add your house service load to your dwelling service load. Now you have your total service load.

Seriously, slow down and take an hour to look at the code. This section is pretty straightforward. If you don't want to take the time to look it up and learn it you should not be the one signing off on the design.

 

[Dennis Alwon]

There are also demand factors for household dryers & Ranges-- Tables 220.54 & 220.55

 

[malachi constant]

There are also demand factors for household dryers & Ranges-- Tables 220.54 & 220.55

The way I read it - and I think it is pretty straightforward reading - is 220.54 and 220.55 fall under Part III.

When you get to Part IV you find 220.84, which states you can use Table 220.84 to calculate your load in-lieu-of using Part III.

In other words, if you're using Part IV Optional Calcs, don't even think about looking back in Part III. (Except of course for house loads, as stated in 220.84(B).)

When using Optional Calcs the range gets derated, but only once, and only by the applicable factor in Table 220.84.

 

[david luchini]

In addition to the problems pointed out in your optional method calculation, there are also some problems with your standard (no A/C) calculation.

Your total lighting demand load should be 509,072VA (not 509,372).

This is from the 1st 3000VA @ 100% = 3,000VA
from 3000-120,000VA @ 35% = 40,950VA
Over 120,000VA @ 25% = 465,122VA
Total 509,072VA

And for your range loads you should have 25kW + (750W * 282) (instead of 281)

 

[Bignose94015]

Sorry about rushing through the calcs.

I incorrectly stated 210.84, you are correct in mentioning that it should be 220.84.
This calc only applies to residential loads at this time. house loads will have a completely separate service. If my calculations and interpretations of the service feeder code is correct then adding A/C results in a net loss of VA per 220.84. IF I am missing something which It sounds like I am I would love to hear where and why. I am doing this as a third party to learn for myself and see if my interpretations are correct. I am by no means an engineer.

I attached two PDF's:

One PDF labled "ADD A/C" This calc solely relies on 220.84's demand factor as stated by Malachi.

Malachi stated that I am to include these calcs which I have in my document and applied the 23% demand factor to resulting in a total of 1,870,952 VA or 5,197A.

"Looking at 220.84(C), you need to FIRST add all the following together:
(C)(1) 3VA/SF for general lighting etc
(C)(2) 4500VA/unit for laundry and small appliance
(C)(3) nameplate of all appliances described in (C)(3)a through (C)(3)d.
(C)(4) nameplate of all other motors not described in (C)(3).
(C)(5) the larger of your AC or electric heat load.
Add those up, THEN multiply the sum by your demand factor of 0.23. Now you have your dwelling service load."
Spreadsheet #2 "NO A/C" I used NEC 220.42 to calculate lighting small appliances and laundry circuit.
NEC States that
first 3,000 at 100%, 3,001-120,000 at 35% and the balance at 25%.

NEC 220.53 was used for fastened in place equipment and allows a demand factor of 75%

Last but not least 220.54 was used for the dryer load and 220.55 was used for the range load.

Calculating per these requirements results in a higher VA compared to adding AC and using 220.84. The result of no AC is 1,906,821 or 5,297A.

In conclusion adding A/C per 220.84 results in 100A difference.

The numbers look correct to me but feel free to correct my inexperience.

Thanks

Eric

 

[Bignose94015]

In addition to the problems pointed out in your optional method calculation, there are also some problems with your standard (no A/C) calculation.

Your total lighting demand load should be 509,072VA (not 509,372).

This is from the 1st 3000VA @ 100% = 3,000VA
from 3000-120,000VA @ 35% = 40,950VA
Over 120,000VA @ 25% = 465,122VA
Total 509,072VA

And for your range loads you should have 25kW + (750W * 282) (instead of 281)

I appreciate the two corrections :thumbsup:. This has been a very tedious learning process for me. And my spreadsheet is still in its infant stages. Correction made.

 

[david luchini]

Sorry about rushing through the calcs.

I incorrectly stated 210.84, you are correct in mentioning that it should be 220.84.
This calc only applies to residential loads at this time. house loads will have a completely separate service. If my calculations and interpretations of the service feeder code is correct then adding A/C results in a net loss of VA per 220.84. IF I am missing something which It sounds like I am I would love to hear where and why. I am doing this as a third party to learn for myself and see if my interpretations are correct. I am by no means an engineer.

You are thinking about this all wrong. Adding the A/C doesn't result in a net less of VA. Using the permitted optional calculation results in a lower VA because it has different demand factors.

What you should do is add your A/C load to your first calculation, the "non-AC" one and see what the demand load will be, using the standard calculation.

Then compare the Standard with A/C to the standard w/o A/C. This will be an apples to apples comparison.

 

[Dennis Alwon]

The optional is always lower, I believe. Art. 220.84 only applies if the conditions in (A) are met

 

[Bignose94015]

You are thinking about this all wrong. Adding the A/C doesn't result in a net less of VA. Using the permitted optional calculation results in a lower VA because it has different demand factors.

What you should do is add your A/C load to your first calculation, the "non-AC" one and see what the demand load will be, using the standard calculation.

Then compare the Standard with A/C to the standard w/o A/C. This will be an apples to apples comparison.

Using my NO A/C calc using 220.53

1997 X 282 = 563,154 VA @ 75% demand factor for a total of 422,365 or an additional 1,173A which makes my calc even more lopsided.

The only reason I am allowed to use the optional method is do to Electric Space heating or air conditioning oper 220.84 A.3.

When all three requrimetns are met of 220.84 the resulting load would be less then an installation that does not have A/C. I cannot understand why this is the case.

I must be missing something.

 

[david luchini]

Calculating per these requirements results in a higher VA compared to adding AC and using 220.84. The result of no AC is 1,906,821 or 5,297A.

In conclusion adding A/C per 220.84 results in 100A difference.

The numbers look correct to me but feel free to correct my inexperience.

I think you are still not calculating 220.84 correctly.

With the numbers you provided: 1,980486VA lighting, 1,642,086VA appliances (including A/C), 3,426,300VA Range and Dryer, you get a connected load of 7,048,872VA.

23% of that is 1,621,241VA which is 4500A at 208/120 3Ph. That's 797 Amps less than the standard, non-a/c calculation.

 

[Bignose94015]

The optional is always lower, I believe. Art. 220.84 only applies if the conditions in (A) are met

It is just shocking to me that adding an A/C load results in a lower VA demand for the ubilding when in reality there will be a higher service demand.

 

[david luchini]

Using my NO A/C calc using 220.53

1997 X 282 = 563,154 VA @ 75% demand factor for a total of 422,365 or an additional 1,173A which makes my calc even more lopsided.

The only reason I am allowed to use the optional method is do to Electric Space heating or air conditioning oper 220.84 A.3.

When all three requrimetns are met of 220.84 the resulting load would be less then an installation that does not have A/C. I cannot understand why this is the case.

I must be missing something.

That doesn't make you calc even more lopsided.

It makes it 6469 Amps with A/C and 5297 Amps without A/C. Isn't that what you would expect?

Now the optional method would make it 4500 Amps with the A/C, as compared to 6469 Amps from the standard method. Give up on the idea of comparing the optional method with A/C to the standard method without A/C. Its apples and oranges.

 

[david luchini]

It is just shocking to me that adding an A/C load results in a lower VA demand for the ubilding when in reality there will be a higher service demand.

This is where I'm trying to impress upon you that your logic is wrong.

You did the standard calc for no A/C and got 5297 Amps.

You did the standard calc with A/C and got 6469 Amps.

Adding A/C results in a higher VA demand!

You did the optional calculation allowed for dwellings with A/C and it reduced the demand to 4500 Amps.

Adding the A/C did NOT reduce the demand. Changing the calculation method did.

 

[Dennis Alwon]

I agree with David however I do understand where the OP is coming from. One wouldn't expect such a difference between the methods.

 

[Bignose94015]

I think you are still not calculating 220.84 correctly.

With the numbers you provided: 1,980486VA lighting, 1,642,086VA appliances (including A/C), 3,426,300VA Range and Dryer, you get a connected load of 7,048,872VA.

23% of that is 1,621,241VA which is 4500A at 208/120 3Ph. That's 797 Amps less than the standard, non-a/c calculation.

I think our range and dryer load is different.

I come up with
Range : 11,000VA X 282= 3,102,000
Dryer : 5,000VA X 282= 1,410,000
For a total load of 4,512,000 for a total load of 8,134,572.

 

[Bignose94015]

This is where I'm trying to impress upon you that your logic is wrong.

You did the standard calc for no A/C and got 5297 Amps.

You did the standard calc with A/C and got 6469 Amps.

Adding A/C results in a higher VA demand!

You did the optional calculation allowed for dwellings with A/C and it reduced the demand to 4500 Amps.

Adding the A/C did NOT reduce the demand. Changing the calculation method did.

I agree with you 100%. The optional calculation that is allowed to be used when there will be an acutal higher load on the building results in a smaller service.

The main reason this is so puzzling to me and hard to explain to an owner is as follows.

Mr Owner wants to save some money so deletes all A/C units within the building.
Mr Contractor comes back and tells the Owner yeah you are going to save on the mechanical side of things but do to this revised equation even though you are shedding load we will actually have to upsize A: the PG&E service requiring the dry vault to expand an additional 20' resulting in you the Owner losing the rent on at least 1 unit. B: Additional PG&E fees. C: 4th Switchboard D: Upsizing Wire ect ect.

The above is my dilemma.


Thanks

Eric

 

[Smart $]

In addition to the problems pointed out in your optional method calculation, there are also some problems with your standard (no A/C) calculation.

Your total lighting demand load should be 509,072VA (not 509,372).

This is from the 1st 3000VA @ 100% = 3,000VA
from 3000-120,000VA @ 35% = 40,950VA
Over 120,000VA @ 25% = 465,122VA
Total 509,072VA

And for your range loads you should have 25kW + (750W * 282) (instead of 281)

I appreciate the two corrections :thumbsup:. This has been a very tedious learning process for me. And my spreadsheet is still in its infant stages. Correction made.

Hold on here. You cannot use 220.42 and its Table for determining demand on General Illumination, i.e. when using Part IV Optional method.

Under the Optional Method, demand for general loads is determined under 220.82 (B).

 

[david luchini]

Hold on here. You cannot use 220.42 and its Table for determining demand on General Illumination, i.e. when using Part IV Optional method.

Under the Optional Method, demand for general loads is determined under 220.82 (B).

That was using 220.42 when using the standard method, not the optional method.

The OP's non-A/C calc used the standard method and the with-A/C calc used the optional method.