Sites: GlobalSpec.com | GlobalSpec Electronics | CR4 | Electronics360
Login | Register
The Engineer's Place for News and Discussion®

Previous in Forum: How to Monitor Current Flow in Rotor Winding in a Slip Ring Induction Motor   Next in Forum: Surge Arrester "Low Current" In Pressure Relief.
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







15 comments
Anonymous Poster #1

Energy

02/26/2013 1:59 PM

We had an energy study done on a commercial HVAC unit. When we got the report back it had several references to "Approximately 0.046 KWHS's per minute on average when HVAC is running". Unfortunately, the engineer who conducted the survey is no longer available.

What does this KWHS's mean, and how do we turn this information into an actual kWh consumption/cost?

Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain - possibly to become "South Scotland" or "Non-Caledonia" from September 2016. Kettle's on.
Posts: 22399
Good Answers: 564
#1

Re: Energy

02/26/2013 2:14 PM

2.76kW x the number of hours run x the tariff value per kWh. Simples.

__________________
The recent explosion of personal telephony across the globe seems to have gone hand-in-hand with a profound reluctance to actually use the damn things for the purpose for which they have been designed.
Reply
Guru

Join Date: Dec 2010
Posts: 1651
Good Answers: 35
#2
In reply to #1

Re: Energy

02/26/2013 2:46 PM

I am having chicken curry now as I read your post.

honest.

weird.

Reply Off Topic (Score 5)
Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: Auckland, New Zealand
Posts: 6002
Good Answers: 245
#4
In reply to #2

Re: Energy

02/26/2013 4:14 PM

As I read THIS post I am thinking about having chicken curry tonight (I already have the chicken defrosting).

What a small world.

__________________
jack of all trades
Reply Off Topic (Score 5)
Anonymous Poster #1
#3

Re: Energy

02/26/2013 3:08 PM

Thank you. We are familiar with the kWh calculation. We did not know if there was anything special about the KWHS's the engineer referred to. At first we assumed this was a typo, but it was repeated in several places. Then we thought KWHS's stood for "kilo-watt hours per second". This would look like:

0.046 X 3600 (Seconds) = 165.600 kWh

165.600 kWh X $0.80 = $13.248 Energy cost per hour.

This appeared to make sense, but wanted to make sure.

If we understood your post:

Using our example, and according to your reply, the calculation would look like this:

0.046 (kWh) X 60 (Minutes) = 2.76 Kwh.

At $0.080 per kWh, this would equal $0.2208 energy cost per hour. This does not appear to be correct.

Did we misunderstand something?

Reply
Guru

Join Date: Jul 2005
Location: Stoke-on-Trent, UK
Posts: 2261
Good Answers: 56
#9
In reply to #3

Re: Energy

02/27/2013 5:12 AM

I agree with #5 it's a ridiculous unit, and if the engineer hadn't already gone, he should be got rid of!

Assuming he meant kWh per minute that's how it should be written (correct abbreviation for kWh, and units don't have plurals). That = 0.046 x 60 2.76 kWh per hour = 2.76 kW.

If you thought KWHS's stood for "kilo-watt hours per second" what does the per minute after it mean?

Does sound 2.76 kW sound right for your installation?

I wish I could by electric at $0.08

__________________
Give masochists a fair crack of the whip
Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Ketchikan, AK, USA
Posts: 15018
Good Answers: 566
#5

Re: Energy

02/26/2013 4:34 PM

What a useless unit! (And incorrectly abbreviated, as well.)

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Reply
Guru
Hobbies - Automotive Performance - New Member Popular Science - Weaponology - New Member

Join Date: Oct 2008
Location: Want to be: 34° 34' 21.60" N, 92° 55' 42.28" W Really am in Arizona
Posts: 26919
Good Answers: 1002
#6

Re: Energy

02/26/2013 5:28 PM

What other priceless jewels did the "no longer available", "engineer" who did this to you leave?

No guarantee?

No recourse for the injured party?

I'd have been suspicious as hell if an "engineer" had submitted this statement, "Approximately 0.046 KWHS's per minute on average when HVAC is running".

That's a SWAG where I hail from.

Turn out the lights on your way out the door.

__________________
In Search Of Intelligent Life, Somewhere; Anywhere.
Reply
Guru

Join Date: Mar 2012
Location: Out of your mind
Posts: 1401
Good Answers: 25
#7

Re: Energy

02/26/2013 8:39 PM

You are in for a good one here!

Basically I am saying you should be going over the raw data and conduct the study yourself. Nothing else will give you peace of mind in this situation.

Or whoever paid for the study has to reap it up again.

Otherwise you have to live without an answer. This unit is meaningless and every calculation around it seems to be too.

My best guess is that it simply means KiloWattHourS 's (in plural) more a texting than a engineering unit! But then this per Minute is as much as saying I went 20 mile per hour in 2 minutes.

Good luck!

__________________
Common Sense Dictates
Reply
Associate
Technical Fields - Technical Writing - New Member Engineering Fields - Environmental Engineering - New Member

Join Date: May 2009
Location: The 'Hub of the South Pacific'; 18.15°S, 178.45°E
Posts: 29
#8

Re: Energy

02/26/2013 11:51 PM

You most probably know this already but anyway; a Watt-hour (Wh) is a unit of energy → power (e.g. 1000 W) × time (e.g. 1 h) = 1000 Wh = 1 kWh. In the pure sciences the Joule (J) is perhaps more commonly used as a unit of energy → power (1000 W) × time (3600 seconds) = 3600 Ws = 3600 kJ (= 1 kWh).

The 'no longer available' engineer probably meant that the HVAC unit was consuming 46 Wh (165.6 kJ) of electrical energy every minute.

What this means in actual cost? Well, in this little corner of the world that would depend on our electrical utility's latest tariff (right now ~34 cents/unit, where 1 unit represents 1 kWh). If you are billed monthly like we are here it might have been more helpful if the 'engineer' had done the energy audit over a month. That way you can simply multiply the tariff by the monthly consumption to get the monthly cost.

__________________
VT
Reply
Guru

Join Date: Dec 2010
Posts: 790
Good Answers: 56
#10

Re: Energy

02/27/2013 8:59 AM

2.76 kW consumption, as estimated by other posts, does not seem unreasonable for HVAC.

Does the HVAC (or its motor) not have a rating plate which gives its consumption and heating/cooling capacity to put you into the right scale?

Reply
Anonymous Poster #1
#11

Re: Energy

02/27/2013 9:44 AM

Thank you for all of this great information!

FYI, this is a Trane 7-ton gas pack HVAC unit with a single compressor. The plate data says 10.0 RLA and an actual consumption of ~ 8 Amps at 470 VAC.

The original testing was done by Duke Energy and we just thought that they were a lot smarter (KWHS's) than we were. That is why we originally wanted to know what the KWHS's acronym actually meant…

Reply
Guru

Join Date: Dec 2010
Posts: 790
Good Answers: 56
#15
In reply to #11

Re: Energy

02/27/2013 10:27 AM

8 amps 3 phase, 470 V with 0.9 power factor and 0.9 efficiency gives 470√3 x 8 x 0.9 x 0.9 = 5200 watts rated input. About 2.76 kW average input or about 50% duty over a period of time looks realistic. One would expect a figure per day (for a given ambient and output temperature) rather than minutes

I would have expected Duke Energy to know that the standard forms for units and multipliers are k = kilo; W = Watt; h = hour; s = second and write so - kWh. Especially since K = Kelvin (temperature degree), S = Siemen (conductance). However, I have a suspicion the writer did not know how to make a plural or use " ' " - so s and 's were added in the hope one was correct - in any case, one may write "kilowatt-hours", but there is no need to add plural s onto unit symbols.

Reply
Guru
Hobbies - DIY Welding - New Member

Join Date: Sep 2007
Posts: 1399
Good Answers: 52
#12

Re: Energy

02/27/2013 9:47 AM

The missing information is the outside temperature. You can have the system running continuously, but the compressor (the part that uses most of the energy) will not run until the thermostat calls for cooling, So, you probably need to know the energy consumed only while the compressor is running. Another method is to do the calculation based on the difference between the inside and outside temperature and to average the energy consumption. The units will then have a per deg. in the denominator.

Reply
Anonymous Poster #1
#13

Re: Energy

02/27/2013 9:58 AM

We do know that the testing was done at the (Power) disconnect, so all of the "Draws" (Compressor, blower, etc.) were accounted for. This unit is also a cycling system, therefore, we know that the compressor was running during these readings. This unit is at a remote location so we will have to look and see if we have any pictures of the plate data. The Trane model is YSC060A4EMA2T, with a Copeland SSR061A4BPA compressor if that is any help.

Reply
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 3663
Good Answers: 526
#14

Re: Energy

02/27/2013 10:06 AM

"The original testing was done by Duke Energy and we just thought that they were a lot smarter (KWHS's) than we were. ..".

I can see why Duke Energy is struggling to survive and lost a lot of their holdings; they were scam artists who were manipulating the energy market, now it appears that extended right down to the Engineering level...

__________________
** All I every really wanted to be, was... A LUMBERJACK!.**
Reply
Reply to Forum Thread 15 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

67model (2); Anonymous Poster (3); Codemaster (1); cuba_pete (1); IdeaSmith (1); jack of all trades (1); JRaef (1); lyn (1); PWSlack (1); Tornado (1); VT (1); welderman (1)

Previous in Forum: How to Monitor Current Flow in Rotor Winding in a Slip Ring Induction Motor   Next in Forum: Surge Arrester "Low Current" In Pressure Relief.