multifamily calculations

[mjf]

I apologize in advance to those of you who had "formal" training/schooling and have no time for someone trying to continue to learn and improve thier ability to earn a living in this business.

Trying to teach myself how to do calculations for an existing (1960's) 6 family condo. One unit wants to add thier own washer and dryer. They will require an upgrade. Working on calc to see if main service will also need to be upgraded.

Existing units have gas cooking equipment (ranges).
heat, hot water and laundry facilities are common to all units and provided from a seperate service.
each unit has a 20amp 240volt A/C receptacle.
each unit is 1200 sq. ft.

using the example in annex D (2008)

gen lighting--1200 sq ft @ 3VA/fsq ft =3600VA
2 S/A branch circuits =3000VA

first 3000 @100%---------------------3000VA
3600 @ 35% -------------------------1260VA

I understand how to calculate these out according to the example.

Not sure what to use for the A/C circuit and if I'm supposed to include anything else(for any other existing branch circuits).

Again, I apologize for asking about what is probably extremely simple to most all of you.

 

[malachi constant]

Hi Mike,

Last week I had the exact same question (albeit on a larger scale). I posted a similar question and learned a lot in this thread: http://forums.mikeholt.com/showthread.php?t=147549

Note that my understanding changed as responses came in - some things I thought were right by the end of thread had to be corrected. I tried my best to correct everything at the end there. See if you can use that thread as a template for walking through the code sections - I think 220.42, 51, 52, 53 and 54 all apply to you.

 

[mjf]

Hi Mike,

Last week I had the exact same question (albeit on a larger scale). I posted a similar question and learned a lot in this thread: http://forums.mikeholt.com/showthread.php?t=147549

Note that my understanding changed as responses came in - some things I thought were right by the end of thread had to be corrected. I tried my best to correct everything at the end there. See if you can use that thread as a template for walking through the code sections - I think 220.42, 51, 52, 53 and 54 all apply to you.

Thanks.......read through the thread (quickly) and it confused the heck out of me. I'll go through it and the specified code sections again when I have more time to dig into it.


I have to admit that when I read a code section that sends me to another section that sends me to an exemption and to another code section........I get lost. :dunce:

 

[bobbymari]

you should definetly get familiar with load calculations but if you plan on doing alot of multifamily there is a great load calc software by canaday enterprises. just google canaday enterprises load calculation software. you simply input loads and it does the time consuming math work for you. great tool to have

 

[malachi constant]

Thanks.......read through the thread (quickly) and it confused the heck out of me. I'll go through it and the specified code sections again when I have more time to dig into it.

I have to admit that when I read a code section that sends me to another section that sends me to an exemption and to another code section........I get lost. :dunce:

Here's a primer:
STEP 1 - Add the dwelling unit loads together as follows (note this is ALL dwelling units combined, so include 7200SF instead of 1200SF, 12 SABC instead of 2 SABC, etc):
* 220.42 - General Lighting - you use 3VA/SF to get general lighting VA. Then skip ahead to 220.52 and add in your small appliance and your one new laundry circuit here. Add all these up and use the demand factors in Table 220.42 for dwelling units (100%/35%/25%).
* 220.50 - Motors - calculate air conditioning, exhaust fans, etc as you normally would (i.e. per article 430).
* 220.53 - Appliances - add up all appliances such as dishwashers, garbage disposals, etc. Multiply by demand factor of 75%.
* 220.54 - Dryers - add your one new washer/dryer. Since there is only one you use a demand factor of 100% per Table 220.54.
* 220.55 - Ranges - they are gas, so nothing to add here.
Add all those up, that is your total service for the six dwelling units.

STEP 2 - Add up all your house loads like you would for a "normal" job - common area lights, HVAC, elevator, laundry, receptacles, etc.

STEP 3 - Add steps 1 and 2 together. That's your service load.

Think I got that right, though as the previous thread proves I don't know this method inside and out. I highly recommend you follow along in the code and try to figure out where I'm coming from on each step.