T
How much heat is generated
- Thread starter Ponchik
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Joule. SI Unit.
Second. SI unit.
Rate of energy usage is power for which the SI unit is the watt.
It isn't energy or heat.
And no amount of discussion will make it so.
Watts are not a measure of heat. Period.
Whether you or anyone else agrees or not.
Rick Christopherson
Senior Member
You guys do realize that you are arguing solely for the sake of arguing, don't you? You're arguments aren't really fostering this original discussion, so I would recommend that you take these banterings off-line and continue this with PM's. Your technicalities are not assisting the OP or anyone else involved in this thread. It's a sidebar that should be covered in PM's.
I'm explaining basic facts. Shouldn't those in our field know or learn the facts relating to electrical calculations?
Rick Christopherson
Senior Member
No, you are not just explaining basic facts. The two or three of you are engaging in a "Pi???? contest" that really has no bearing on the original discussion. The moderators should have told you to take this off-line a long time ago, but only a couple of the moderators here would have even seen this, and they can't do it because they are involved.
This will be my last comment on the topic because I am already overstepping my bounds, but either take it off-line, or start a new thread. It doesn't belong here.
This will be my last comment on the topic because I am already overstepping my bounds, but either take it off-line, or start a new thread. It doesn't belong here.
mivey
Senior Member
You can assume Jim posted watts when he meant heat energy but I am inclined to think he knows the difference. No amount of discussion will change that (unless Jim just happens to post that did not know the difference).
Oddly enough, I would agree. None of these are really "explaining" anything to those recently involved. We all know the difference in energy and power.
It just seemed odd to nitpick over the difference when Jim obviously knows the difference. Jim was initially questioned because his formula did not addres the wire temperature. It was not meant to address temperature.
Somehow the discussion began to focus on energy vs power instead of heat vs temperature and really just kept going back and forth.
I'll add my last post to say: If someone has a stirring motor in a pond that is never shut off and wants to know how much energy it uses, I see nothing wrong with telling them it uses X kWh per day, per week or whatever rate is prudent.
I often get asked questions like: "how much should we charge someone for energy if they rent our facility and use the lights?". I usually give them a $/hour or $/day rate. Granted, that is not the charge, but they can calculate the charge based on that rate. That is no different that the information Jim provided.
I'd like to believe so. Yet, the following erroneous statements were made:
The formula is P(watts of heat) = I?R
the energy lost as heat is indeed I2R.
There is a direct conversion between Watts, cal/sec, and BTU/HR which are all 'units' of heat.
But the I2R losses are heat losses.
But watt is also joule (per second) and so also a measure of heat
Enough.
kwired
Electron manager
- Location
- NE Nebraska
Seems the most accurate way is to generate electric power on site, make sure generator is full of fuel both before and after they rent the facility then you are certain to not miscalculate.
I guess you could read electric meter both before and after the event also.
Rick Christopherson
Senior Member
Yes you did. I answered it way back in the bgeginning, but you can't get an exact answer without knowing more information about your system.
mivey
Senior Member
I assume you want to know what the temperature will be inside the conduit.
If you can you confirm that 200 feet of the conductor is 0.0388 ohms, how many conductors there are and what the diameter of the conduit is, I can calculate temperature based on those figures if you wish.
mivey
Senior Member
Understandable. I'll accept blame for that.
mivey
Senior Member
Sorry Bes but that is an erroneous statement. The temperature distribution is time dependent.
On a more serious note: Are you guessing individual THHN conductors or what? What boundry conditions are you going to assume? Are you assuming a soil or air installation for the conduit? What about locations/conditions of surrounding cable systems or are you assuming an isolated system? Hand or computer calc?
It isn't a great deal different to the calculations I routinely have to do for temperature rise in electrical enclosures - just a different shape. And I don't get any accolades for getting it right. Just serious pain if I don't.Sorry Bes but that is an erroneous statement. The temperature distribution is time dependent.
I'll take the resistance as of the conductors as that given earlier in the thread unless someone tells me differently.
Air. If it's buried or in water, I'd have to withdraw my offer.
I normally use a spreadsheet that I've generated for the purpose. But, no it isn't a third party computer programme if that's what you're asking.
mivey
Senior Member
Might be similar, but I'm thinking the close bundling of the conductors in such a small space would be have to be handled a little differently than a ventilated enclosure where the space is much larger than the heat source.
That's what I was asking. I've got a spreadsheet for simple configurations but leave the complex stuff to the canned software.
I use my calculations for non-ventilated enclosures. I have another for calculating air flow requirements for force ventilated enclosures. Heat dissipation through the walls still does play a part but usually not very much. I usually ignore that and it gives me a little margin.
I use very little by way of commercial software products. I do my own thing even for fairly complex stuff. I think what first started me down that route is there were no commercial programmes for some of the calculations I had to do. I could do them longhand but that gets a bit time consuming, not to mention tedious if the same fundamental calculation has to be repeated. Writing my own routines seemed to be the way to go. First I used BASIC, but as spreadsheets came along and got more sophisticated with more and better options for data output, I moved in that direction. And haven't stopped since.
I still use BASIC (visual basic) for subroutines but I try to inject a bit of fun and humour into them. These are some of the routines for checking the validity of data entry for a motor performance application I did a while back.
Sub Prat()
Title = "This is not possible !"
Msg = "Selected speed must be slightly lower than synchronous. Enter a new value or accept the calculated default."
Style = vbCritical + vbDefaultButton2
R = MsgBox(Msg, Style, Title, Help, Ctxt)
End Sub
Sub Plonker()
Title = "Not a valid entry !"
Msg = "Number of poles must be an even integer e.g. 2, 4, 6 etc. Try again."
Style = vbCritical + vbDefaultButton2
R = MsgBox(Msg, Style, Title, Help, Ctxt)
End Sub
Sub Cretin()
Title = "Not a valid entry !"
Msg = "Some motor to have such an efficiency or power factor. Try again."
Style = vbCritical + vbDefaultButton2
R = MsgBox(Msg, Style, Title, Help, Ctxt)
End Sub
Sub Imbecile()
Title = "Improbable Value !"
Msg = "The current entered does not tie up with the Voltage and Power for the machine. Check the data. A calculated value is offered as a default. If in doubt use the suggested default value but in any case there is an opportunity now to enter new values."
Style = vbCritical + vbDefaultButton2
R = MsgBox(Msg, Style, Title, Help, Ctxt)
End Sub
Google prat and plonker - I could explain them but it would be even further off topic. Suffice it too say that they are not terms of endearment but a long way short of swearing.
The above is for checking data entry on motor performance that I use to predict efficiencies and power factor at various speeds and loads for VFD applications.
By contrast, the temperature rise calculation is a good deal simpler.
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