Load Calculation for Single Family Dwelling Unit

[duck_huntr85]

Hey all,
Im doing some example calculations for single family dwellings. But in the example it says the dwelling unit has baseboard heaters that draw 18kVA and a heat pump that draws 6kVA. When doing the calc. for the heating/AC system I know you are supposed to omit the smaller of the two but i dont know if that applies here. What am i supposed to do with the heat pump? Thanks in advance for your response.

 

[Dennis Alwon]

IMO, Unless the heat pump is not being used in the heating cycle you must use both as the heat pump may also come on with the baseboard heaters.

 

[duck_huntr85]

Getting confusing now

Getting confusing now

My boss says the same as you. But i called my instructor who said that the baseboard heat is the primary source of heat and it is assumed that they will NOT be on at the same time. Im going with his answer because he is the one who will grade this but his explanation was kind of weak and it is possible for them to be on at the same time.

 

[jumper]

IMO, Unless the heat pump is not being used in the heating cycle you must use both as the heat pump may also come on with the baseboard heaters.

I agree, not really different than supplemental heat strips in an AHU.

 

[Dennis Alwon]

My boss says the same as you. But i called my instructor who said that the baseboard heat is the primary source of heat and it is assumed that they will NOT be on at the same time. Im going with his answer because he is the one who will grade this but his explanation was kind of weak and it is possible for them to be on at the same time.

You know what happens when we ASSUME. I don't agree with the instructor.

 

[jumper]

My boss says the same as you. But i called my instructor who said that the baseboard heat is the primary source of heat and it is assumed that they will NOT be on at the same time. Im going with his answer because he is the one who will grade this but his explanation was kind of weak and it is possible for them to be on at the same time.

Bad assumption, as Dennis stated, unless there is is a complete changeover between the two systems: both can run simultaneously.

 

[duck_huntr85]

Got into a heated debate with the instructor

Got into a heated debate with the instructor

So i called my instructor back just to make sure that (in their eyes) i need to omit the heat pump from the calculation. I told how I didnt agree with his answer since it does not specify that the heat pump was for the AC and that they are not necessarily non-coincidental loads. He said "add it if you want and we'll make it wrong, i dont know waht you want me to say. It is clearly stated in the NEC that the heat pump would be omitted from the calculation." I told him i am a Journeyman electrician and i do have an understanding of the NEC and said tell me what article it says that in because all i can find remotely close to what he was suggesting is 220.60. But that article doesnt answer my question. He said "I dont have time to do your homework for you. if you dont believe me, add them together and we'll mark it wrong for you" So i guess thats that. But i still agree with you guys. It doesnt specify that they won't be on simultaneously so i think they both need to be included in the calculation.

 

[jumper]

Your instructor is a !@#$%&$#. Code reference should be cited.

Good luck on your exam.

 

[G._S._Ohm]

". . .i dont know waht you want me to say. . ."

I think he does know what you are wondering about.
For starters he could explain his reasoning and his interpretation of whatever code citations he feels are relevant.

There are at least three factors:
what the code says,
what is a reasonable interpretation of that code [the premise] and
is the reasoning from premise to conclusion logical?

This "homework" remark sounds like
http://en.wikipedia.org/wiki/Straw_man

You could check if your instructor shows symptoms of
http://en.wikipedia.org/wiki/Obsessive–compulsive_personality_disorder
so at least you know what you're dealing with.

 

[duck_huntr85]

I think you're right on the money G S

I think you're right on the money G S

This isn't the first arguement I've had with this guy either. When i was learning ladder logic my book showed the stop button, on all schematics, as a NO contact. Which is obviously wrong and it took me a half an hour to get him to admit it. They say it takes all kinds, but man i can do with out the know-it-alls. An electrical instructor showed realize that the NEC is open to interpretation at times. Im almost tempted to get this guy in trouble with his boss. But maybe thats a bit excessive. I like the bit about the "straw-man", thats something i see more of than i care to admit.

 

[K2X]

I can see in my 1st year textbook "Electrical Wiring "16th edition Mullin, Page 596, and page 660 call for the largest value to be entered . Electric Furnace, AC,or Heat pump. I'd have to go through my homework and tests but I think i got that one wrong once or twice also.

 

[duck_huntr85]

But is it in the NEC K2X?

But is it in the NEC K2X?

How old of a text book is it? If you could site an article in the NEC that says such a thing, I'd greatly appreciate it.

 

[Little Bill]

have your instructor read 220.82(C) and exampleD2(c) in Annex D. It has to be shown/stated that supplemental heat will not be on at the same time as the heat pump to be able to omit the heat pump kva. Whether it is the baseboard heat or heat pump that is the supplemental heat, IMO, it would have to state that they won't be on at the same time. Ask the instructor if he would be willing to calculate it his way and have an inspector look at it.

 

[tryinghard]

..."I dont have time to do your homework for you. if you dont believe me, add them together and we'll mark it wrong for you"...

They'll mark you wrong for being conservative for higher load results??

Do they mark wrong for Future __kva, I don't think future is addressed in 220.

 

[K2X]

Re. textbook date and code art

Re. textbook date and code art

2009.. I was thinking the texbook was wrong and the instructor teaches the textbook and uses the answer keys. It's hard to argue with textbooks and sometimes instructors can be equally as difficult. Good luck.

 

[gotmud]

instructor is wrong!!!!! they both have the potential to come on at same time so they both have to be calculated as heat load....

 

[tryinghard]

I'm with gotmud. Notice also Annex D2(C) "*If supplementary heat is not on at same time as heat pump, heat pump KVA need not be added to total." Converse meaning applies here, if it can then they both need to be included, and the example includes both!

 

[tryinghard]

...add them together and we'll mark it wrong for you"...

Add the additional labled as additional future