2020 Exam Prep Calculation Question - Unit 10 Challenge Q's #27

[paullmullen]

Here is Challenge Question 27 from Chapter 10 of the 2020 Exam Prep book.





My solution is 196A. Kinda close to (b) and kinda close to (a)

When I compare my solution to the one in the answer key, I get this:

	My Solution​	Answer Key​	Match?​
General Lighting Load	8040 VA​	8040 VA​	YES​
Appliances	7380 VA​	7380 VA​	YES​
Dryer	10,000 VA​	10,000 VA​	YES​
Cooking Equipment	11,000 VA​	11,000 VA​	YES​
AC vs Heat	10,710 VA​	10,000 VA​	NO​

From that point on, the math is just broken because of the difference.

I think the problem is that the provided solution in the answer key ignores the fact that there are two air conditioners per unit. The only way I can get to the provided solution is to drop the number of air conditioners per unit to 1.







Here's my math:




What am I doing incorrectly?


Thanks,


Paul

 

[ggunn]

Here is Challenge Question 27 from Chapter 10 of the 2020 Exam Prep book.


[...]


What am I doing incorrectly?

I dunno; assuming that whoever wrote the question and the answer knew what they were doing?

 

[rojay]

Maybe you should check online for errata?It looks like they left out the AC load for the second unit.

 

[Tulsa Electrician]

Would not omit the smaller of the two. The two ac units are 120 volt
Electrician heat is the larger of the two. Then the largest motor would be?

 

[suemarkp]

The question is not clear is 21A one airconditioner or both of them? If it is both, then the heat is the larger HVAC load. And in that case, what is the largest motor load to get hit with the extra 25% factor?

 

[Tulsa Electrician]

I would say 2 ac units, @ 21 amps 120v each.
Based on Step five in Pic

 

[Tulsa Electrician]

Man I missed a word above.
I would omit the smaller of the two.
Omit AC units. Use ele heat.

 

[Tulsa Electrician]

The question says nothing about them running at same time. You pic shows you deleted can run at same time.

 

[rojay]

I would say 2 ac units, @ 21 amps 120v each.
Based on Step five in Pic

I missed that! I was thinking each unit was 21 amp. Tossing out the smaller AC load makes sense then

 

[paullmullen]

Would not omit the smaller of the two. The two ac units are 120 volt
Electrician heat is the larger of the two. Then the largest motor would be?

Well, in fact the code does call for the smaller of the two (AC or Heat) to be omitted if they are not coincident: 220.60

 

[paullmullen]

Man I missed a word above.
I would omit the smaller of the two.
Omit AC units. Use ele heat.

Ah... sure... omitting the smaller makes sense, but I think with 2 A/Cs per unit, the A/C load is the larger, right?

 

[paullmullen]

The question is not clear is 21A one airconditioner or both of them? If it is both, then the heat is the larger HVAC load. And in that case, what is the largest motor load to get hit with the extra 25% factor?

Well... the math in the solution seems to think that it is 21A for one unit, but you're right that the language of the question could be read two different ways. Hmmm...

 

[ggunn]

Well, in fact the code does call for the smaller of the two (AC or Heat) to be omitted if they are not coincident: 220.60

View attachment 2567643

Why would you assume that the A/C units would not be running at the same time?

 

[paullmullen]

Why would you assume that the A/C units would not be running at the same time?

I assume the A/Cs run at the same time, but the A/C and Heat do not.

 

[Tulsa Electrician]

Well, in fact the code does call for the smaller of the two (AC or Heat) to be omitted if they are not coincident: 220.60

View attachment 2567643

I did a typo and corrected later, sorry.

Man I missed a word above.
I would omit the smaller of the two.
Omit AC units. Use ele heat.

Ah... sure... omitting the smaller makes sense, but I think with 2 A/Cs per unit, the A/C load is the larger, right?

I would say no.
I read it as dwelling one ac load 21 amps@120v and heat @ 5kw
Total for both
Ac
21*1.25+21*120=5670
Heat
5000*2= 10,000
Omit the AC units.


What is key for me it does not say heat pumps. They may be window AC for all we know

What if each unit has 2500 kw of heat. I took it as totals.
Look at the key pic closely its doing total AC and heat load.
It's using 21*120 *1.25 then adding the 21.
It's lso using 5000*2

 

[paullmullen]

I did a typo and corrected later, sorry.


I would say no.
I read it as dwelling one ac load 21 amps@120v and heat @ 5kw
Total for both
Ac
21*1.25+21*120=5670
Heat
5000*2= 10,000
Omit the AC units.


What is key for me it does not say heat pumps. They may be window AC for all we know

What if each unit has 2500 kw of heat. I took it as totals.
Look at the key pic closely its doing total AC and heat load.
It's using 21*120 *1.25 then adding the 21.
It's lso using 5000*2
View attachment 2567653

Sorry about the fake-out about "heat pumps". It's in my notes just in case, but it wasn't in the math here.

For sure, you've described the solution as done for the answer key, but when I read the question, it's not what I read.


Thanks for engaging.