HVAC 016 BTU British Thermal Unit a measure of heat

so we talked about a thermometer measures heat intensity not quantity so what does measure quantity that's going to be the btu and b2 stands for british thermal unit you're going to take out your pen and paper and write that down british thermal unit btus we use b to use an hvac exclusively and extensively so in the summer time we're going to do b2 heat load calculations how much heat in b2s is coming into the house and our air conditioner needs to be sized in b2s how much b2 energy it needs to take the heat out

of the house in the summertime in the winter time how much b2 the house is lost a heat loss calculation so b2 is going to be leaving the house going to the air outside and we need to size our furnace or heat pump to see how many beaches of heat we need to replace or put back into the house when we get the refrigeration we're going to talk about btus in different products such as meat we want to cool meat down how many b2s the heat energy is in that meat how much b2 is it

going to take to move that energy out so it's very very popular in hvac it's used on almost every certification test and it has a definition so definition is going to be the amount of heat or the amount of heat energy required to change one pound of water one degree fahrenheit that's the formal definition and that's what you have to learn for hvac you have to know this but it doesn't really have any meaning to you so what we're going to do is apply some meaning to this and then we're going to go into more

detail about b2 it technically has a formula it's the temperature change times the pound of water equals btus but we're going to get a little more into that shortly so by doing this example we have a scale set up i have a i have some pot with me it's legal in the state it's just the pot and i have a little heater set up and we have a thermometer and a scale so we're going to start off by measuring this so what i'm going to do is i'm going to put my stove on top of

the scale i'm going to put this little adapter here so you can see what's happening so here we can measure how many pounds is on our scale right now so on the scale right now we have a degree but i don't want to take into account all of this i want to zero this out so we're going to be talking about scales more when we get into recovery vacuum and recharge so i'm going to press the zero unit out zero it's also called tear on sum now it says everything that's on the scale is now

registered at zero i also have my thermometer taped in here so i'm going to put this second meter on the side and this is going to give us the temperature of what's going to be inside of there so now we're going to add some water to our scale until we get 1 pounds we can actually visualize what one pound is going to be oops went a little over so we got one pound one ounce slightly over and our temperature we're going to put our thermometer inside a little bit better give it a little bit of

time for a thermometer to zero out and we're gonna have a nice starting point so we're gonna round this out to 38 degrees fahrenheit what we're going to now do is add heat energy into this one pound of water so as we add heat energy into it we want to raise this up to so now we're at 39 degrees fahrenheit so we've changed one degree temperature and we have one pound of water that equals one btu so that is one btp energy now let's see what happens if we keep adding heat so i'm just going

to turn this on and let this continue to heat up so if we let this continue to heat up we'll count 38 as our starting point we're still going to have one pound of water on this whole example let's see what happens as we add heat energy so now we're up to 39 so that's we still have one b2 of heat now as you can see we're adding heat energy into the water the temperature of the water is going up so now we have a quantity and an intensity together now we can calculate an actual

b2 number so my thermometer i have here is not quite the ac most accurate but it's going to give us a good idea so let's say that we get it to for simplicity 48 degrees so if we're at 48 degrees now we started at 38 degrees that's a 10 degree temperature change or a 10 degree delta t so if we put 10 degrees here 10 times 1 pound of water that would be an example of 10 b2 the heat energy so don't be afraid of the math it's just simply we're going to take some numbers

to get an answer and what i want you to do morning is visualize that b2 has meaning it actually has something connected to it now we can apply b2s to many things for example we can apply b2 to air as we apply b2s to air air is going to be much lighter than water so it's going to take much less btu to change air it's also going to depend on how much moisture is in the air how dry the air is how much humidity is in the air things like this are also going to play

a part in it we start getting into refrigeration we're going to cool many different products we're going to say cool meat or cool poultry or cool water we're actually going to literally be freezing water which gets into a whole other category beer for example has a b2 rating we take the heat out of that beer we want at a precise temperature there's many many different things we talk about when we're dealing with these btus so right now we're over at um 70 degrees so if we take 70 degrees minus our 38 degree stopping our starting

spot what does that come out to thinking backwards so we got 32 degree temperature change so if we put 32 here 32 degree temperature change times one pound of water that's 32 b2s of heat energy you don't have to be great at math i'm not great at math we have a calculator now that's on our phones which is great cool use your calculators do the math in your head do the math on paper don't be afraid of the math hbac has tons of math involved in it but it's just simple math as we continue to

add heat energy into this water the temperature will change now the catch is if i had twice as much water it's going to change the temperature a whole lot less so we're waiting this water to warm up and change temperature let's look at a few other little different options let's say that i had 10 btus of heat energy and i applied 10 btus to 1 pound of water versus 10 btus to 10 pounds of water if i put 10 btus into one pound of water it would change the temperature of the water 10 degrees it

would be 10 degrees warmer if i put 10 b2s in one pound of water it would change the temperature of that water one degree fahrenheit so the quantity of that water is extremely important the same thing is with air air is going to have its own b2 rating as i add b2 heat energy to air the temperature air will go up but it's going to depend on how much air we're talking about we're going to have our hvac system that's pulling pounds of air through the house across the evaporator coil and we're going to physically

be taking b2 heat energy away from that air so b2 is a very important part now if we can see we're adding b2 heat energy the temperature water continues to climb we're at 142 btus so we started out at 38 and we're now at 145. so we just do some quick math i'll take 145 minus 38 and that gives me a temperature change of 107 degrees fahrenheit we still have one pound of water that's a hundred and seventy 107 b2s right there i wouldn't understand it it does have some kind of connection so btus or

waiting for this water to heat up we're going to continue to talk a little bit more about v2s so the question is if it's btu is the amount of heat required to change one pound of water one degree fahrenheit does british and the rest of the world use pounds in fahrenheit and the answer is no the rest of the world actually uses celsius and the rest of the world uses the metric symbol of the metric system for calculating weight so america is pretty much the only country i know that's still using btus the british thermal

unit britain has actually changed it they have now using what we call the calorie and most the rest of the world are using calories you see calories if you're talking about going in a diet but calories is a heat energy or an energy rating so calorie the deficiency of calorie is the amount of heat required to waste one gram of water one degree celsius it's a very similar thing but the idea is that the the metric system is easier to think about if we wanted to talk about a tape measure you have 1 16 and

then you have an eighth and then you have 3 16 and then you have all your different numbers at the look of the tape measure it's difficult to count but if i wanted to count the metric system it's one one point five two two point five three three point five four now for me to transfer over to the metric system would be difficult because i spent my whole life learning imperial system however the rest of the world has made that change and their kids are learning the uh the metric system right now and it's much

much easier don't hate the metric system it's actually very simple simple system to work with it's just that we get used to our waste i personally since we're the only country still using uh pounds and fahrenheit we should call it the atu for the american thermal units but americans don't like change so we're going to keep it the btu uh the british storm unit anyway that's just a little fun fun worthless fact of where it comes from although calorie knowing calorie is how they rates the metric system for btus that is fairly important to know

so the next thing is we see that this water right here is actually starting to boil and my thermometer is not accurate it is uh showing much off so water boils at 212 degrees fahrenheit water is boiling at 212 degrees fahrenheit so we know that water boils at 212 so our thermometer is a little bit off but let's say that we started out at 32 degrees fahrenheit and our water is now at 212 degrees fahrenheit how many btus does it take to change water from 32 degrees liquid to 212 degrees liquid so it's going to

do a little quick math and we're going to put in 212 minus 32 equals 180 so it takes 180 btus of heat energy to change water from 3dos 32 all the way up to 212 degrees fahrenheit degrees fahrenheit now the next thing we're going to do is we're going to continue to add heat energy to this water as we continue to add heat energy into this water we're adding heat energy we're adding heat energy we're adding heat energy we're going to see the temperature of this water is not going to change at all everything we've

talked about so far the changing temperature of water from 32 liquid to 30 to 212 still in liquid is 180 b2 this is called sensible heat and we raised that temperature pretty fast within a few minutes we went from 32 all the way to 212. 212 is going to be our key number here this will be what we call a saturation temperature so all the way up now up until now we had sensible heat water is boiling changing state for liquid vapor you can physically see it boiling but our temperature is still going to be

at 212 degrees fahrenheit this is where we change so the last video we talked about sensible heat we can measure sensible heat now we're going to talk a little bit about a different type of heat we got our water to 212 although our thermometer is not measuring very accurately i have some very old probes look to this new meter so i should have got some better probes hooked up here but the difference is we still have that one pound of water we're at 212 degrees fahrenheit and we're adding heat energy into this water now we

see it's boiling it's changing state from a liquid to vapor but it's boiling it's still at the exact same temperature we're putting btus of heat energy into this water but the water is staying at the exact same temperature so we got to think let's move our probes over here to catch it on fire so we have to think what if we put more b2s the heat energy in so let's take our torch over here we're gonna let our torch up and add more heat to it so as we add more heat energy let's see if

our temperature starts to change and even though our temperature is a little bit off we're boiling faster where the heat's at but it's still at 212 degrees fahrenheit maybe we just simply need more heat so let's grab another torch over here and that's light up the other side of this let's get this hot let's get this really heated up right let's add some heat energy into this water right so we're adding tons of heat energy to it this heat this uh container is made of aluminum aluminum is really good at transferring heat so it's transferring

heat from the container and the fire on the outside to the water on the inside we have the electric skillet on the bottom adding heat energy to it we're boiling very very fast but notice that we're still at our same temperature going to be at 212 degrees fahrenheit we are still not heating up notice here when i put my flame inside how the flame changes dramatically that's because there's steam coming off because the steam and moisture is coming off we end up with actually less heat energy so i'm having more heat transfer by putting it

on the metal itself so no matter how much heat energy i add to this water it's still at 212 degrees fahrenheit but we know that we have b to use the heat energy right here in this propane canisters we know that we're taking electrical energy and converting heat energy we know for a fact that we're still adding b to use the heat energy to this water and it's not changing in temperature but we are for sure 100 adding heat energy to this but it's not changing temperature but we know that we're putting b2 so where

is the heat going where does the heat go