adding laundry to multifamily units - how to calculate

[malachi constant]

I have a client that wants to add a "30A/2P 208V" stacked washer/dryer to each of 60 dwelling units. There are 360 units in the building, so 300 will not get the laundry. I'm assuming a load of 5000VA for the washer/dryer.
I assume they will also have to add the 20A/1P laundry receptacle.
I have collected all information about existing appliance nameplate data, unit panel/breaker information, and service size. I also have the "house load" utility info from last twelve months.
Each unit is roughly 1100 SF and includes an existing garbage disposal (672VA), dishwasher (1152 VA), range (8000VA), microwave (1800VA). That's about it.

FYI, two important things to note that I am not used to seeing:
1. There is not any AC or electric heat in a given unit - it is a centralized HVAC system with each unit containing a 1/20HP 1A booster/circulating fan.
2. The unit panels are each protected by 80A breakers.

There are two relevant calculations that need to be made: unit panel loads, and overall building service loads.

Unit loads is easy - follow 220.83 Existing Dwelling Unit, (A)-no additional HVAC installed. For a given unit add up your 3VA/SF general lighting, small appliance branch circuit, laundry branch circuit, and nameplate data. Without showing my math for an 1150 SF unit I'm getting 66A on an 80A panel. No problems here.

Service loads is where I think I am doing it right, but shocked at the number. As there is no heating/cooling and these are 80A panels I cannot use optional calcs, so I am going through standard calcs:
* 220.42 - 3VA/SF, demand factors per table 220.42, between about 1050SF/unit x 360 units works out to about 300kVA after demand factors.
* 220.52 - 3000VA per unit x 360 units for small appliance, 1500VA per unit x 60 units for laundry is 1,170kVA.
* 220.53 - 75% demand factor applied to dishwasher, disposal and circ fan - 360 of each - 525kVA.
* 220.54 - dryers - only 60 of them x 5000, demand factor of 25% = 75kVA. I believe I can apply another 70% demand factor per 220.61(B) = 53kVA
* 220.55 - 360 x 8000 x 0.16 for ranges = 461kVA, 360 x 1800 x 0.30 for microwaves = 195kVA, so 655kVA total for this. I believe I can apply another 70% demand factor per 220.61(B) = 459kVA.

When I add those up I get 2495kVA, or 6928 amps at 208V/3P. This does not count house loads, which are approximately another 800A (x 125% per 220.87(2)). I am told there is one service to the building for both house and dwelling loads combined, and it is rated for 4000A. Even when I delete the washer/dryer and laundry branch circuit I get 6500A (again, not including house). Am I doing something wrong here? Can someone do a quick walk through the numbers and see if there is something off? Is there a better way to calculate, more ways to derate, etc?

Thanks!!

(edited - found a calc error - was counting 1500VA laundry branch circuits in 360 units instead of just the 60 units)

 

[malachi constant]

No comments on this, eh? How about if I rephrase...

Has anyone ever done a multifamily dwelling (the larger the better) without any air conditioning or electric heat? If you did a large complex, do you recall about what the service size was? For instance, including house loads I'm coming up with almost 8000A (at 208V) for 360 units, which works out to about 22A/unit. This is about what I would expect (maybe a little higher) then when I use the optional calcs for units with AC. I understand the standard calcs are less forgiving than the optional, so maybe this is right on, I don't know.

I just hate to tell the client they can't do something they want to do, and find out I was not following the code correctly.

Thanks!

 

[kwired]

I have not checked your calculations but am not sure if you are taking demand factors for the laundry and small appliance branch circuits. 220.52 has similar wording for both "These loads shall be permitted to be included with the general lighting load and subjected to the demand factors provided in Table 220.42."

I also question whether or not your microwaves should be added in or included with general lighting load, or be assumed they are on the SABC's - some more details about them may make a difference I don't think micrwaves are intended to be covered in 220.55, but would fall under 220.53 if not included in general lighting load or SABC load.

 

[david luchini]

I agree with kwired. Put the SABCs and Laundry together with the general lighting and apply the demand factors.

Also, I come up with 307.5kW for the ranges, using Column C, and using the "twice the maximum between any two phases" from 250.55.

For dryers, I come up with 79.5kW.

You can't add another 70% reduction to the range and dryers like you are. That reduction is for the Neutral.

 

[eutaw42]

MUTI-fAMILY

MUTI-fAMILY

Try the calculator for apt loads and loads for total building -- provided by Flashworks.com -- I have used it for years -- hand checked and accurate -- they give you a few free tries -- easy to use.

 

[malachi constant]

Kwired & David - you are absolutely right about the SABCs being added into the general lighting load. I didn't read those close enough. That is a huge factor to have missed, thanks.

Some new questions on microwaves and refrigerators:
Microwaves - the verbiage in 220.55 says, among other things, "counter-mounted cooking units and other household cooking appliances in excess of 1 3/4 kW shall be permitted to be calculated in accordance with Table 220.55". As this microwave is (barely) in excess of 1 3/4 kW I assumed you had to apply it here, although a strict reading doesn't say you HAVE to apply it here, only that you are PERMITTED to apply it here.

So what is the rule of thumb for MW and fridges? If they are on their own dedicated breaker, you count them (1800VA microwave counted under 220.55, or 220.53, with the fridge under 220.53)? And if they are on the SABC you can ignore them as they are implicitly included in 220.52? Could you, if it was more favorable, count a microwave on a dedicated breaker as basically a third SABC?

Some other questions for David:
* On ranges: I am not following how you got 307.5kW. I see the verbiage about "twice the maximum number connected between any two phases" but I don't follow it at all. If you were somehow able to use column C for the ranges it looks like a simple calculation: 25kW + 3/4kW*360 = 295kW. Not sure how you got to Column C, and once there I am not sure how you got to 307.5kW.

* On dryers: I don't see how you got 79.5kW. Looks like a straightforward calc: 5000VA * 60 * 25% = 75kVA. What are you doing different?

* On neutrals: You are probably correct about the additional 70% applying only to neutrals. I assume your interpretation of 220.61 is the correct one.

Learning more every day. Thanks gentlemen.

 

[malachi constant]

Sorry to post again--looks like my last reply made it into the thread, but when you are in the main page it doesn't reflect that there was a new reply added.

Nothing is easy.

 

[Smart $]

...

Some new questions on microwaves and refrigerators:
Microwaves - the verbiage in 220.55 says, among other things, "counter-mounted cooking units and other household cooking appliances in excess of 1 3/4 kW shall be permitted to be calculated in accordance with Table 220.55". As this microwave is (barely) in excess of 1 3/4 kW I assumed you had to apply it here, although a strict reading doesn't say you HAVE to apply it here, only that you are PERMITTED to apply it here.

So what is the rule of thumb for MW and fridges? If they are on their own dedicated breaker, you count them (1800VA microwave counted under 220.55, or 220.53, with the fridge under 220.53)? And if they are on the SABC you can ignore them as they are implicitly included in 220.52? Could you, if it was more favorable, count a microwave on a dedicated breaker as basically a third SABC?

...

I have to wonder why you are calculating all the microwaves at 1800VA. Even a dedicated SABC is calculated at 1500VA. Granted some high-wattage microwaves exceed 1500VA (e.g. 1200W output, ~1650VA input), but 1500VA is probably a good average. Yes there are microwaves with higher input/output, but these are considered commercial microwaves, and many require a dedicated 20A circuit/receptacle.

 

[davidaengelhart]

I believe I know what everyone missed. As you used 220.83 for the unit calculation which is restricted to a single phase 3 wire service to the units, and you calculated the building with 3-phase 208, nobody took into consideration of the real load being connected to the transformers for the single phase 3 wire services to the units. How many units are really getting connected to each "A", "B", and "C" transformers? That would be the answer to the building load calculation.

 

[david luchini]

* On ranges: I am not following how you got 307.5kW. I see the verbiage about "twice the maximum number connected between any two phases" but I don't follow it at all. If you were somehow able to use column C for the ranges it looks like a simple calculation: 25kW + 3/4kW*360 = 295kW. Not sure how you got to Column C, and once there I am not sure how you got to 307.5kW.

* On dryers: I don't see how you got 79.5kW. Looks like a straightforward calc: 5000VA * 60 * 25% = 75kVA. What are you doing different?

* On neutrals: You are probably correct about the additional 70% applying only to neutrals. I assume your interpretation of 220.61 is the correct one.

I assumed your range is actually rated more than 8.75kW and not more than 12kW (I've never seen a range rated 8kW.) That is why I used Column C.

Since you have a 3phase, 4 wire service, you have to use the "twice the maximum number connected between any two phases" rule. You have 360 ranges (360 apts.) so you have 120 ranges connected between any two phases (in other words there are 120 A-B apt feeders, 120 B-C feeders and 120 C-A feeders.) Twice 120 is 240. So you base your calculation on 240 ranges. So 25kW + 3/4kW(240) = 205kW. 205kW/2 phases = 102.5kW per phase. 102.5kW times 3 phases = 307.5kW equivalent 3 phase load.

It's a bit confusing, but D5(a) in the Annex give a pretty good example.

I did the same for the dryers. 60 dryers/3 = 20 between any 2 phases. Twice 20 = 40, so base the calc on 40. 5kW * 40 dryers = 200kW. The demand factor from 220.54 is 35-(0.5*(40-23)) = 26.5%. Applying the demand factor: 200kW * 26.5% = 53kW = 26.5kW per phase, times 3 phases = 79.5kW equivalent 3 phase load.

 

[malachi constant]

EDIT - double post, apologies

 

[malachi constant]

Smart $: The electrical contractor surveyed the existing equipment and informed me the nameplate rating on the microwaves is 1800W each. For the purposes of these calculations I have been assuming VA = W. Generally speaking do people ignore countertop microwaves in the calculations? What if they are on a third SACB? (Does that ever even happen?) In new construction, on the projects I work on, I'm used to them being MW/hood combos, on their own circuit, so getting added in. But of course I'm usually in Optional Calcs 220.84 so my experience isn't very helpful on a number of fronts. Regardless, I've got a 1800W countertop microwave, it is not known whether it is on one of the two required SABC or if it is on another dedicated 20A circuit that could be construed as third SABC. Thoughts on how to proceed?

davidaengelhart: Not completely sure I follow you, but if you are thinking there has been some translation error between single phase and three phase I believe you are incorrect. 220.83 is being used for the single phase unit panels. When I start adding the overall building service up I am tossing out the 220.83 calcs and using a completely unrelated set of codes that allow for the three phase considerations.

david luchini: The electrical contractor surveyed the existing equipment and informed me the nameplate rating on the ranges is 8kW each, so I think column B applies. (This is consistent with most ranges I've ever seen cuts for, maybe my region has a different living standard when it comes to what a range should be.) Thanks for the "twice maximum" explanation, that makes sense. I am not sure why you are using 40.5kW per stacked washer dryer - the only info we have is a 30A two-pole breaker, I am assuming 30A*208V*sqrt(1)*80% = ~5kW.

So I've cut it down to 5400A. Here's the revised math:
* 220.42 - 3VA/SF, demand factors per table 220.42, between about 1050SF/unit x 360 units, plus the two SABC and one laundry circuit from 220.52, works out to about 2,273kVA before demand factors and 582kVA after.
* 220.53 - 75% demand factor applied to dishwasher, disposal and circ fan - 360 of each - 525kVA.
* 220.54 - dryers - 60 of them, but use the "twice the max number connected between phases" rule and multiply 40 x 5000, demand factor for 40 works out to 26.5%, so...53kVA.
* 220.55 - Not 360 but 240 x 8000 x 0.16 for ranges = 307kVA; 240 x 1800 x 0.30 for microwaves = 130kVA, so 437kVA total for this.

When I add those up I get 1597kVA, or 4433 amps at 208V/3P. This does not count house loads, which are approximately another 800A (x 125% per 220.87(2)), adding those puts me at 5425 amps. That's 2500A less than I started, and maybe can reduce it further if I can figure out the microwave. However even I eliminated the microwave, and took the laundry & wash off the loads (as they are not installed yet) I am still at ~5000A, which is 1000A over what the service is supposedly rated at. Hmmmph.

 

[Smart $]

Smart $: The electrical contractor surveyed the existing equipment and informed me the nameplate rating on the microwaves is 1800W each. For the purposes of these calculations I have been assuming VA = W. Generally speaking do people ignore countertop microwaves in the calculations? What if they are on a third SACB? (Does that ever even happen?) In new construction, on the projects I work on, I'm used to them being MW/hood combos, on their own circuit, so getting added in. But of course I'm usually in Optional Calcs 220.84 so my experience isn't very helpful on a number of fronts. Regardless, I've got a 1800W countertop microwave, it is not known whether it is on one of the two required SABC or if it is on another dedicated 20A circuit that could be construed as third SABC. Thoughts on how to proceed?

...

I am not saying they can't be rated 1800W, just very unlikely all of them are... and at an 1800W input rating you are very near the borderline for commercial-rated microwaves. AFAIK, the highest-output, consumer-targeted, countertop microwaves are 1200/1250W-rated. I looked up a few ratings:

• [*=1]GE 13.9A 1650W input[*=1]Sharp 13.8A (input wattage not provided)[*=1]Panasonic 12.7A 1460W input

Now what do you think the odds are that every appartment has an 1800VA (i.e. 15A input) countertop microwave?

I can't attest to how "people" calculate microwaves. IMO, they are typically plugged in to an SABC, so they are included with the SABC's... and yes, more than two SABC's isn't much of a stretch.

 

[david luchini]

david luchini: The electrical contractor surveyed the existing equipment and informed me the nameplate rating on the ranges is 8kW each, so I think column B applies. (This is consistent with most ranges I've ever seen cuts for, maybe my region has a different living standard when it comes to what a range should be.) Thanks for the "twice maximum" explanation, that makes sense. I am not sure why you are using 40.5kW per stacked washer dryer - the only info we have is a 30A two-pole breaker, I am assuming 30A*208V*sqrt(1)*80% = ~5kW.

Interesting, I've looked at small (24") ranges and still have never seen anything smaller than 9kW. I didn't use 40.5kW per washer/dryer, I used forty (40) 5kW dryers (200kW total)

So I've cut it down to 5400A. Here's the revised math:
* 220.42 - 3VA/SF, demand factors per table 220.42, between about 1050SF/unit x 360 units, plus the two SABC and one laundry circuit from 220.52, works out to about 2,273kVA before demand factors and 582kVA after.
* 220.53 - 75% demand factor applied to dishwasher, disposal and circ fan - 360 of each - 525kVA.
* 220.54 - dryers - 60 of them, but use the "twice the max number connected between phases" rule and multiply 40 x 5000, demand factor for 40 works out to 26.5%, so...53kVA.
* 220.55 - Not 360 but 240 x 8000 x 0.16 for ranges = 307kVA; 240 x 1800 x 0.30 for microwaves = 130kVA, so 437kVA total for this.

I'm not sure I would include the circ fan as an "appliance." Seems more like a "motor" to me, wouldn't change things too much though.

For the dryers, you didn't follow the "twice the max" all the way through. The equivalent three phase load would be 79.5kVA.

For the ranges, you didn't follow all the way through either. The equivalent three phase load would be 460.8kVA. I wouldn't include the countertop microwaves if they plugged into SABCs. The load for the two SABCs already has that covered. (If they were hardwired, I would include them separately.)

When I add those up I get 1597kVA, or 4433 amps at 208V/3P. This does not count house loads, which are approximately another 800A (x 125% per 220.87(2)), adding those puts me at 5425 amps. That's 2500A less than I started, and maybe can reduce it further if I can figure out the microwave. However even I eliminated the microwave, and took the laundry & wash off the loads (as they are not installed yet) I am still at ~5000A, which is 1000A over what the service is supposedly rated at. Hmmmph.

Yeah, I don't see how the got a 4000A service, even before you start adding laundry. Did a job a few years back with approx 240 units (might have been a little larger sf each) with central heating/cooling loads, and ended up with (3) 2000A 208/120V services for the apartments, and (1) 2000A 480/277V for the house loads.

 

[davidaengelhart]

The units are single phase which are only connected to 2 of the 3 phases of the service so not all units are connected to all 3 phases of the service, so you can not use the additive loads for the 3 phase service calculation because they are not all connected to all 3 phases of the service.

 

[davidaengelhart]

So from any 3 units, only 2 are connected to any one phase. That is probably how they derived the 4KA service.

 

[david luchini]

The units are single phase which are only connected to 2 of the 3 phases of the service so not all units are connected to all 3 phases of the service, so you can not use the additive loads for the 3 phase service calculation because they are not all connected to all 3 phases of the service.

I'm not sure I understand, but if you are suggesting that he can't use Section 220.83 for "additional loads to an existing dwelling unit" for the total 3 phase service calculation, it is a moot point because he didn't use 220.83 for the total 3 phase service, just the individual dwelling units.

So from any 3 units, only 2 are connected to any one phase. That is probably how they derived the 4KA service.

How would this get the service to be smaller than 4000A? If the total load for the 3 phase service is larger than 4000A as calculated per 220.40, the fact that the individual apartment feeders are single phase won't change it.