Calculate demand load for dryers in apt building

[97catintenn]

My exam question (based on 2005) was:

Calculate the demand load (in VA) of the dryers for and apartment building that has 12 units and 1 public unit (13 meters). The 12 units all have 5kw dryers and the public unit has 2 2kw dryers.

Answer: Table 220.54 Demand Factors for Household Electric Clothes Dryers

I have a total of 14 dryers so my demand factor is 47-(14-11) which equals 44%

(12 dryers X 5000w X 44%)+(2 dryers X 2000w X 44%) = 28160w

What do I do next to convert it to volt amps? 28160 wasn't one of the answers

 

[jumper]

You sure they do not want amps. Watts to VA is a power factor question not usually found on a test in this format and cannot be answered given this info.

 

[97catintenn]

Maybe? I can't remember for sure. I do remember the answers being in the neighborhood of

A. 24700
B. 47600
C. 65000

Not exact answers, but that was the basic spread. The question also gave information about all the appliances and such, but I thought it useless info and all I needed was the dryers for the calculation.

 

[jumper]

was the service 3 phase by chance?

 

[jumper]

was 32000 one of the answers?

 

[97catintenn]

If it is single phase, then is my answer correct?

 

[97catintenn]

was 32000 one of the answers?

Yeah, probably, how did you come up with that?

 

[jumper]

If it is single phase, then is my answer correct?

I think so.

 

[jumper]

Yeah, probably, how did you come up with that?

gimme a few. busted arm. only one hand to type.

 

[jumper]

14 dryers

5 5 4

twice the no. between any 2 phases=10

12x5kw+2x4kw=64kw

demand factor t220.54 for 10 dryers, 50%

32000w

220.54 Electric Clothes Dryers ? Dwelling Unit(s). The
load for household electric clothes dryers in a dwelling
unit(s) shall be either 5000 watts (volt-amperes) or the
nameplate rating, whichever is larger, for each dryer
served. The use of the demand factors in Table 220.54 shall
be permitted. Where two or more single-phase dryers are
supplied by a 3-phase, 4-wire feeder or service, the total
load shall be calculated on the basis of twice the maximum
number connected between any two phases. Kilovoltamperes
(kVA) shall be considered equivalent to kilowatts
(kW) for loads calculated in this section.

 

[97catintenn]

That must be it. To further confirm, the last sentence in the code you provided said that KVA shall be the same is KW in this example. And I do remember the answer being in VA.

Tough question. Thanks for the help :thumbsup:

 

[resistance]

I think you guys need to re-evaluate your answers.
-If I understand it correctly: 1. You have 12 household electric dryers located inside each unit?
2. Then you have two (2) common area dryers?
If I’m correct, then look at your answers again.

 

[resistance]

I would like to know how you came up with your answers???

 

[97catintenn]

Each unit, which is an apartment, has one dryer rated at 5kw. And the public area has 2 dryers rated at 2kw each.

Sorry for not clarifying, I read your post and thought you just moved on

 

[resistance]

No, I’m here. I guess my question is for jumper.
I have a question for you. You had a multiple chose question with only three answers to choose from? Are you sure of those answers, because it would seem all three are wrong, including the 32Kw or Va.

 

[jumper]

No, I?m here. I guess my question is for jumper.
I have a question for you. You had a multiple chose question with only three answers to choose from? Are you sure of those answers, because it would seem all three are wrong, including the 32Kw or Va.

I am listening. I did not pick the answers, I merely tried to answer, your show.....

 

[97catintenn]

Alright, I'm all in. How is 32kVA wrong?

my test had four answers, I can remember the exact numbers other than my answer wasn't one of them.

 

[resistance]

-The dryer demand factor= 46% [12 dryers-11=1] So: 47-1=46% DF allowed
-12 dryers (5Kw min)= 60KW
-60kw(.46)=27.6KW

Then onsite Laundromat:
-2 dryers (5Kw @ 100)=10Kw Note: No demand allowed
Ans=37.6kw or 37.6va


Heck, I could be wrong—seeing that I’m rusty

 

[97catintenn]

Why are you calculating your demand factor on 12 dryers when there are 14 total?

also there are 12@5kw and 2@2kw

 

[jumper]

-The dryer demand factor= 46% [12 dryers-11=1] So: 47-1=46% DF allowed
-12 dryers (5Kw min)= 60KW
-60kw(.46)=27.6KW

Then onsite Laundromat:
-2 dryers (5Kw @ 100)=10Kw Note: No demand allowed
Ans=37.6kw or 37.6va


Heck, I could be wrong?seeing that I?m rusty

OP said:
The 12 units all have 5kw dryers and the public unit has 2 2kw dryers.