The Mysterious btu

ccstelmo

I was wondering about btu's. I mean, what happens to them? Where do they go after they've committed hari-kari in the name of keeping things warm?

Back in the day when I was coming up, I had an opportunity to attend a couple of Dan's seminars when he was earning an honest living going hither thither and yon all over the west trying to get us all up to speed and on the same page and all that. I'll never forget his explanation of a phenomena he called "Cold Seventy" (I think). He challenged us to take a thermometer into the grocery store and measure the temperature in the canned food aisle, the breakfast cereal aisle and finally over where they stored the ice cream in the freezer aisle (my favorite place). According to him, the thermometer would read the same in all three aisles even tho our cojones would freeze in the freezer aisle. I tried it. It worked just like he said it did and ever after I've used that principle "Heat goes to Cold" in figuring out a lot of stuff. Those btu's flee from your body toward the freezer, the windowpane, or even a cold beer I suppose.

But where do they go? Heat is a form of energy. Energy can be neither created nor destroyed: it can only change from one form to another. So, when that little btu flees from my body and slams into the windowpane, what actually happens to it? Is there a pile of dead btus on the windowsill? And for that matter, if it changed into another form of energy, what would that be?

Just saying.

GGross

Don't think of a BTU as a physical thing, all you are doing in heating and cooling is transferring heat (energy) from one place to another.

In a heating application, that energy may start from a fuel source, turned into flame, transferred to air in a home, and then slowly transferred to the outdoors (referred to as a building heat loss)

Others here may have a better more scientific way of explaining this.

WMno57

https://en.wikipedia.org/wiki/Urban_heat_island

dko

https://www.physicsclassroom.com/class/thermalP/Lesson-1/Methods-of-Heat-Transfer

EBEBRATT-Ed

The heat in any structure of from people is lost to the outdoors. Don't forget in the summer we get heat gain and run the ac

EdTheHeaterMan

I know where those BTU's go!
It is a magical place over the rainbow
on the other side of the looking glass.
Behind that crystal ball.
and into the Twilight Zone.

And they are no way DEAD! They are alive and well, vacationing in the Bahamas.

But seriously, that energy you are talking about is absorbed by the thing that is colder. that is where the Energy you are emitting in the form of heat is going. It is trying to warm up those frozen pizzas. I know you think that you are Hot Stuff, but those refrigerant compressors are more powerful that the little bit of energy you are emitting and that Popsicle is absorbing. You might be hot stuff, but not that hot!

Think of it like this. Take an 8 ounce glass of water to the closest ocean or lake and pour it in. Did you change the water level? But you saw the water go into the lake or ocean, so why did you not see the water level rise? I think you know why! You're not Commander Data from the Enterprise, so you can not sense the 0.000000000000000000000000000000000000000023618 centimeters that glass of water added to the water level. But it did add to the total volume by exactly 8 ounces.

hot_rod

A BTU is the amount of heat required to raise 1 lb. of water 1°

BTU/hr is the rate at which heat moves in or out of an object. You or a boiler for example.

Temperature difference is what moves the btus from inside a heated building to outside. The temperature difference ∆T, is what causes the heat movement. The greater the ∆ the higher the rate of heat movement or transfer.

If you can find a normal adult these days, it generates about 400 BTU/hr engaged in light activity. The heat release is 62% radiant, 15% evaporation. So cover up if you want to keep the heat from leaving you or the room

HomerJSmith

BTUs is a measurement like inches, pounds, etc. It is a measurement of the effect of heat energy on a physical thing. Energy is immeasurable, you can only measure the effects of energy. The real question is where do all the pounds go when you get off the scale? hmmm Maybe, just maybe Ed Young is right. We live in the Twilight Zone. Ooooh Noooo!

JUGHNE

When you are in the freezer aisle and feeling cold because the heat in your body is going to the ice cream case. Your heat is warming up the ice cream and the freezer is pulling the heat out of the ice cream that you added.

Then thru the refrigeration process your added body heat is discharged outside into the parking lot and possibly helping melt the ice out there. There is another 30% or so of heat delivered outside because of the heat of compression involved in the refrigeration.

So just looking at the ice cream you have been involved in climate change!

Jamie Hall

A BTU is a unit of energy -- and there are many other units. The energy can be realiused as a temperature gain (that an energy input of 1 BTU will raise a pound of water 1 degree F, for instance) or you could take 1,000 of them more or less and convert from one form of latent energy (in a pound of liquid water) to another form of water (a pound of steam at atmospheric pressure). Of you can take that energy and, with a suitable engine, convert it into mechanical energy (converting at the rate of 2500 BTU/hour gives you 1 horsepower) or with other devices into electrical energy (converting them at a rate of 3400 of them per hour will give you a kilowatt of power) or vice versa.

Except in those power conversions, you can come close to 100 percent efficiency (power out equals power in) but you can't get all the way, even with the best devices, and many engines producing mechanical energy from heat energy are much much worse than that.

You can also convert heat energy into chemical energy -- or, commonly, convert stored chemical energy into heat energy (burning fuel in a boiler is an obvious example).

But the energy always turns up somewhere... and, ultimately, as heat.

You can only transfer heat as heat from a warmer source to a cooler one (heat pumps, whether so called or called mechanical refrigerators or air conditioners or whatever) make use of the change in boiling point of a refrigerant with pressure -- evaporating the refrigerant storing heat as latent heat at one pressure and associated temperature, and releasing it back to some other object at a higher pressure, and hence a higher temperature).

delcrossv

Jamie Hall

Oh yeah!

And the three laws of thermodynamics:

Furst Law: you can't win.

Second Law: you can't even break even.

Third Law: your initial stake is zero.

ccstelmo

You guys are so AWESOME! I love hangin' out with you.

CLamb

Jamie Hall said:

Oh yeah!

And the three laws of thermodynamics:

Furst Law: you can't win.

Second Law: you can't even break even.

Third Law: your initial stake is zero.

My chemistry professor expressed the third law as "You have to play the game.".