00:01
So we're told that one method of passive solar heating is to stack gallons of liquid water inside the buildings and inside of buildings and expose them to the sun.
00:14
The solar energy stored in the water during the day is least at night to the room air providing some heat.
00:20
And so we want to consider a house that is maintained at 22 degrees c and whose water heating, let's see, his water heating is a system.
00:31
By 350 liters of water storage system.
00:36
The water is heated to 45 degrees c during the day.
00:41
I want to determine the amount of heating this water will provide to the house at night.
00:46
And a surrounding temperature is 5 degrees c.
00:50
And we want to determine the exorgy destruction.
00:54
Okay, so again, this is basically just kind of using energy storage, you know, water as an energy storage device.
01:02
So water is a good energy storage device because the heat capacity is pretty high.
01:08
Where i used to have a house where we had a, had a what's called a russian furnace.
01:14
And it would have a big, it had like a big mass of bricks.
01:21
Sometimes these are called masonry heaters.
01:23
And you have a firebox here.
01:25
And then you'd have the exhaust gases which curl around here and then go out the chimney.
01:31
So you have this whole mass of bricks.
01:33
So you burn a really hot fire in here, so the wood burns very efficiently, and there's hardly any, you know, ash or, you know, junk going out.
01:43
It's very clean.
01:45
And what happens is, is that, you know, you can always burn wood very hot, but the problem is is that that means that you basically, you're going to get something, well, number one, a surface that's really hot in your house.
01:57
And also, basically, it's going to just, you know, you're going to have, it's not going to even out the heat.
02:02
So what happens here is then the bricks, because of this exhaust gas, actually blank, the time it's going out here, it's pretty much cooled down to probably about room temperature.
02:14
And so all the heat gets absorbed by these bricks.
02:19
So we have all of these bricks getting absorbed by the heat.
02:23
And they get pretty, you can actually, i did a little project with my daughter one time.
02:27
We took a thermal camera.
02:28
And you can see obviously where, you know, the bricks get hottest right here, right, at the back of the firebox.
02:34
But there's quite a few bricks between, you know, the wall and the firebox.
02:38
So they never get hot enough to burn anybody.
02:40
But you can't hold your hand on there for too long or you start to it might start to burn, but not like instantaneously burn anybody.
02:49
So then you can see that basically that the bricks get, you know, basically right in this area down here, they're very hot.
02:57
Up in here, they're very, i mean, they're pretty very warm.
03:00
Here they're very warm.
03:01
Here they're, you know, just slightly a of room temperature.
03:04
But the thing is, is that the thermal capacity of the bricks, because it's a huge mass of bricks, is quite high.
03:12
So you basically storing, you basically burn really hot fire, get the bricks warmed up, and then they basically then radiate the heat into the room for the rest of, you know, until they cool down.
03:24
So the problem with that, i always joke of my family, is that the time constants.
03:30
So that, but from the time, you burn a big, burn a really hot fire until these bricks get warm, you know, can be roughly about six hours.
03:41
So you're always trying to time things right because you can't just, you know, there's no thermostat to just turn it, turn it to something, turn it up or turn it down.
03:52
Anyway, that's an aside.
03:54
But in this case, we are trying to store energy from the sun that's warming this water up...