Amps v Amp hours v Amps/Hr

[valhalla360]

Originally Posted by StuM

Clearly you don't.

"how many BTUH do I need per hour" means " how many BTU per hour do I need per hour".

See, you've still got one too many "per hour"s in there. The correct question is just "how many BTU do I need per hour" or "how many BTUH do I need".

My bad. It's been a while since I've worked with BTU but as you say that translates to BTU/(hour^2) which would imply some sort of BTU acceleration.

[transmitterdan]

Originally Posted by StuM

Just a minor correction to TD and V360:

BTUH is in fact a standard engineering abbreviation for BTU per hour. Not BTU hours.

I know it goes against the rules, but that's what happens at times with historical imperial units. Same with the MBH used earlier in the thread - 1 MBH = 1000 BTU/hr.

Hey isn't there a thread about imperial/metric that has just been revived? Yippee

You are right. It's unfortunate that this acronym has been adopted because it leads directly to the type of misunderstanding we have here. If the acronym were BTU/H or BTUPH then it would be less likely to confuse.

[StuM]

Originally Posted by transmitterdan

If the acronym were BTU/H or BTUPH then it would be less likely to confuse.

If the US would join the rest of the world, throw away those archaic units and use SI then it would ...

[HappyMdRSailor]

Originally Posted by valhalla360

My bad. It's been a while since I've worked with BTU but as you say that translates to BTU/(hour^2) which would imply some sort of BTU acceleration.

My favorite so far... AWESOME!

[HappyMdRSailor]

Re BTU acceleration...

Every female which I have been acquainted with seems confirm this as a true fact.... That the larger the differential in setpoint of any thermostat = higher rate of heat transfer...

[skipmac]

Originally Posted by StuM

If the US would join the rest of the world, throw away those archaic units and use SI then it would ...

Oh if only we would. The benefits are countless.

A big one, US made machinery, cars, etc would be more acceptable by the rest of the world so help our exports.

I took a degree in electrical engineering in the US. Almost all the math and calculations were in metric, it was so much easier and the different units and functions related to each other so easily and logically. Occasionally we would get a problem in Imperial units just to make sure we could relate. Almost universally the students would convert the problem to metric, solve then convert the final answer back to imperial.

[skipmac]

Originally Posted by HappyMdRSailor

Re BTU acceleration...

Every female which I have been acquainted with seems confirm this as a true fact.... That the larger the differential in setpoint of any thermostat = higher rate of heat transfer...

I see you have met my wife.

She is also convinced that getting into a cold car if you turn the fan on max, blowing freezing cold air up your legs, will also make the heater get warm faster.

[svlamorocha]

Originally Posted by Stu Jackson

I couldn't disagree with you more.

The "fudge factors" you mention are actually conversion factors that are completely in line with the dimensional analysis that, I completely agree, are absolutely necessary.

They were included in a couple of the examples sailorchic included earlier.

Stu
I believe that we agree. I am not saying that unit conversion factors (such as 12 inches/foot) are bad or unnecessary. I am saying that it is bad to *unknowingly* mix them with universal constants such as pi, or magnitudes that are "almost constant" such as gravity or the density of water. PE prep materials and many US-based codes have plenty of evidence of this sort of unconscious mix.

Taking this to a boat example, I cry every time I see trained electricians who cannot work out DC voltage drop starting with the resistivity of copper. They will tell you there is a magical table that saves them from knowing that one number but they do not know that the table does not work when the cable gauge varies somewhere in between the two ends.

[HappyMdRSailor]

Originally Posted by skipmac

I see you have met my wife.

She is also convinced that getting into a cold car if you turn the fan on max, blowing freezing cold air up your legs, will also make the heater get warm faster.

And no amount of description of the system operation will convince them otherwise!!!

[StuM]

Originally Posted by HappyMdRSailor

Re BTU acceleration...

Every female which I have been acquainted with seems confirm this as a true fact.... That the larger the differential in setpoint of any thermostat = higher rate of heat transfer...

That's so true! I keep telling the better half that turning the thermostat down to 20C doesn't cool the saloon any faster, it just means that it doesn't stop using power when it gets to the preferred 26-27C. She still does it all the time though

[skipmac]

Originally Posted by HappyMdRSailor

And no amount of description of the system operation will convince them otherwise!!!

I must be a slow learner since I keep trying to explain the operation, to no avail.

[transmitterdan]

Guys, I spent some words trying to convince others that we are not a bunch of misogynistic old men. And then the thread takes this turn....

Meessa give up...

[exMaggieDrum]

Originally Posted by svlamorocha

Stu
I believe that we agree. I am not saying that unit conversion factors (such as 12 inches/foot) are bad or unnecessary. I am saying that it is bad to *unknowingly* mix them with universal constants such as pi, or magnitudes that are "almost constant" such as gravity or the density of water. PE prep materials and many US-based codes have plenty of evidence of this sort of unconscious mix.

Taking this to a boat example, I cry every time I see trained electricians who cannot work out DC voltage drop starting with the resistivity of copper. They will tell you there is a magical table that saves them from knowing that one number but they do not know that the table does not work when the cable gauge varies somewhere in between the two ends.

I'm a "trained" technician, and I went to electrical schools, and I got ABYC certs for 10 yrs, etc. etc. What I can tell you is that everyone I knew, and everyone I worked with understood that you can only work out resistance when dealing with each leg of the same gauge. Then you would have to add the others, but in general I don't remember any times where I had to work out that since you always go with the most conservative (lower gauge wire) for a circuit. I guess you could go through the math and do it but I just don't ever remember a circuit like that coming up.

I can't imagine why you would have a circuit with a big gauge wire going to a small gauge and then going back to a large gauge. Going from small to large (solar panel input to battery cables e.g.) or large to small (battery cables to panel feed e.g.) is normal, but you have to analyze the loads on each leg separately as you always have different amps in each leg. You have been exposed to some "untrained" techs if you have seen otherwise.

[Stu Jackson]

Originally Posted by TeddyDiver

Doesn't matter what you call them, either the factors are "fudged" or the basic quantities are "fudged" but that's the reason behind this "fudged" thread

This was in response to my post:

The "fudge factors" you mention are actually conversion factors that are completely in line with the dimensional analysis that, I completely agree, are absolutely necessary.

I'm sorry, you are simply wrong. When I get some time later today I'll find a few examples for you.

A conversion factor is simply a way of translating units to assure the proper dimensional analysis.

[svlamorocha]

Originally Posted by exMaggieDrum

I'm a "trained" technician, and I went to electrical schools, and I got ABYC certs for 10 yrs, etc. etc. What I can tell you is that everyone I knew, and everyone I worked with understood that you can only work out resistance when dealing with each leg of the same gauge. Then you would have to add the others, but in general I don't remember any times where I had to work out that since you always go with the most conservative (lower gauge wire) for a circuit.

I am also certified by ABYC and have in front of me E-11 2015 and the Study Guide v4.2014.

The process you and I describe requires yo to calculate the drop in each segment given a certain length, current and gauge/cross section. I challenge you find such "problem" in the ABYC materials. While you are at that try to find if a "trained electrician" needs to know how to calculate the resistance in ohms of a certain length of wire of a certain material and cross section. The section about Ohm´s Law reads like a kindergarten story.

I bet you will only find the table that lets you pick a gauge that will keep drop below 3% or 10% for a given length and current. Therefore you can be "certified" as "trained" without knowing how to quantify in volts or % the overall drop from battery to load given cable gauge, length and current, which is what matters to the load. While we are at that, the curriculum does not even require you to be able to calculate drop for a single length of wire, only to find the smallest gauge of wire that will not exceed 3% or 10% drop.

I am all for training in general and ABYC is part of that. I vote with my time (to get certified) and money (for membership). I am just making the point that the bar is lower than what paying punters think because the basic understanding of the underlying physics has been taken out of of the curriculum.

This reminds me of the "expectations gap" in the world of large-corporation financial accounting, which is the gap between how meaningful accountants think their financial statements are (not a lot) and what the users of those statements think (much higher).