explain xkcd - User contributions [en]

2790: Heat Pump

2023-06-16T23:39:17Z

172.71.142.158: /* Explanation */

{{comic
| number = 2790
| date = June 16, 2023
| title = Heat Pump
| image = heat_pump_2x.png
| imagesize = 740x400px
| noexpand = true
| titletext = If I'm not going to upgrade to a powered one, I should at LEAST stop leaving the door open so often.
}}

==Explanation==
{{incomplete|Created by a BIG CHUNGUS HEAT PUMPER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
A {{w|heat pump}} is a system which applies the {{w|ideal gas law}} to transfer heat from a relatively cold area to a relatively hot area, i.e. to heat an insufficiently warm room/building or to cool an insufficiently chilled room/building, even if the outside air is at the opposite heat-gradient for the purpose. The extra energy used to achieve this prevents the {{w|second law of thermodynamics}} from being violated, and is usually assumed to be added to the warmer side of the system. This is why the back of a refrigerator will feel hot, as it maintains the cooler internal temperature (and why leaving its door open does not cool the room that it is in down, just heats it up as it fruitlessly attempts to both heat and cool the same air-mass).

In this comic, [[Cueball]] has a ''manual'' heat pump, and he is manually heating an area by walking from the warm area (colored in ''red'') to a colder area (colored in ''blue''), and "drawing" residual heat into the "bellows" (accordion-shaped device) by expanding them to cool them below the outside air temperature (more intense blue). He then returns back to the warm area and compresses the bellows to concentrate heat above the sustained room-temperature (more intense red), then letting it radiate away and increasing room temperature before going back outside to repeat the process of drawing heat out of the cooler air. As expected, this is a laborious process, as captioned in the text below the panel. Manual heat pumps of this kind do not exist in real life[citation needed], but are partly emulated by devices such as {{w|fire piston}}s. The {{w|air source heat pump}} effectively does the same thing as this comic, but by using components installed across a wall (letting fluids/vapors flow between the two sides) rather than moving physical components through doors.

The title text refers to the problem of having to open the door to carry the device in and out. This would let the warmed air flow out, and cool air flow in, to undo some of the effort used to attempt to increase the difference. In lieu of some device that does not require the door to be opened at all, he should at least promptly close it between each passage through it.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Cueball indoors (light red background) holding a light red accordion-shaped device in his hands and walking towards an open door.]

:[Cueball outdoors (light blue background) with the door closed, the device is still light red.]

:[Cueball extends the device and it turns blue.]
:''Release''

:[Cueball looks behind while the device has turned light blue.]

:[Cueball walking back inside through an open door, the device is still light blue.]

:[Cueball indoors with the door closed. He squeezes the device and it turns red.]
:''Squeeze''

:[Cueball looks at the door while the device is glowing in bright red.]
:''Radiate''

:[Cueball is leaving the indoors area (now a slightly darker red background) through an open door.]

:[Caption below the panel:]
:Manual heat pumps are such a pain.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics with color]]
[[Category:Physics]]

2790: Heat Pump

2023-06-16T23:37:49Z

172.71.142.158: /* Explanation */ clarify that the "bellows" are the accordion shaped device

{{comic
| number = 2790
| date = June 16, 2023
| title = Heat Pump
| image = heat_pump_2x.png
| imagesize = 740x400px
| noexpand = true
| titletext = If I'm not going to upgrade to a powered one, I should at LEAST stop leaving the door open so often.
}}

==Explanation==
{{incomplete|Created by a BIG CHUNGUS HEAT PUMPER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
A {{w|heat pump}} is a system which applies the {{w|ideal gas law}} to transfer heat from a relatively cold area to a relatively hot area, i.e. to heat an insufficiently warm room/building or to cool an insufficiently chilled room/building, even if the outside air is at the opposite heat-gradient for the purpose. The extra energy used to achieve this prevents the {{w|second law of thermodynamics}} from being violated, and is usually assumed to be added to the warmer side of the system. This is why the back of a refrigerator will feel hot, as it maintains the cooler internal temperature (and why leaving its door open does not cool the room that it is in down, just heats it up as it fruitlessly attempts to both heat and cool the same air-mass).

In this comic, [[Cueball]] has a ''manual'' heat pump, and he is manually heating an area by walking from the warm area (colored in ''red'') to a colder area (colored in ''blue''), and "drawing" residual heat into the "bellows" (accordion-shaped device) by expanding them to cool them below the outside air temperature (more intense blue). He then returns back to the warm area and compresses the bellows to concentrate heat above the sustained room-temperature (more intense red), then letting it radiate away and increasing room temperature before going back outside to repeat the process of drawing heat out of the cooler air. As expected, this is a laborious process, as captioned in the text below the panel. Manual heat pumps of this kind do not exist in real life, but are partly emulated by devices such as {{w|fire piston}}s. The {{w|air source heat pump}} effectively does the same thing as this comic, but by using components installed across a wall (letting fluids/vapors flow between the two sides) rather than moving physical components through doors.

The title text refers to the problem of having to open the door to carry the device in and out. This would let the warmed air flow out, and cool air flow in, to undo some of the effort used to attempt to increase the difference. In lieu of some device that does not require the door to be opened at all, he should at least promptly close it between each passage through it.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Cueball indoors (light red background) holding a light red accordion-shaped device in his hands and walking towards an open door.]

:[Cueball outdoors (light blue background) with the door closed, the device is still light red.]

:[Cueball extends the device and it turns blue.]
:''Release''

:[Cueball looks behind while the device has turned light blue.]

:[Cueball walking back inside through an open door, the device is still light blue.]

:[Cueball indoors with the door closed. He squeezes the device and it turns red.]
:''Squeeze''

:[Cueball looks at the door while the device is glowing in bright red.]
:''Radiate''

:[Cueball is leaving the indoors area (now a slightly darker red background) through an open door.]

:[Caption below the panel:]
:Manual heat pumps are such a pain.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics with color]]
[[Category:Physics]]

Talk:2790: Heat Pump

2023-06-16T23:36:34Z

172.71.142.158:

woah! an xkcd with color what was the last one with color? (im kinda new to xkcd) [[Special:Contributions/172.71.122.48|172.71.122.48]] 21:17, 16 June 2023 (UTC)Erfaniom

I suppose color was needed to show the air temperature. Odd, though, that in summer (in the northern hemisphere), the character is trying to increase the indoor temperature. [[User:Davidhbrown|Davidhbrown]] ([[User talk:Davidhbrown|talk]]) 21:27, 16 June 2023 (UTC)
:He's not. He's moving the hot air from inside to the cooler outside. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 22:18, 16 June 2023 (UTC)
::I actully think he's warming the inside, already warmer than outside, by effectively (and literally!) squeezing the heat out of the cooler outdoors air.
::By compressing the cool outdoor air, he increases its temperature (p1v1/t1=p2v2/t2) to warmer than the warm indoor air, creating a squeezebox->room flow of heat energy, then returns to the outside before decompressing and lowering the temperature in his squeezebox below the cool-air temperature in order to create an outdoors->squeezebox flow of energy and repeat. (The comic has the cycle start at roughly half-way through that, and wraps round, but the heat-to-room seemed the most obvious starting place here.)
::Right now, I'd not wish to heat my indoors up (even at 11:30pm, like now), so I agree that it's a funny time of year show heat-adding (rather than heat removing), but it definitely is that. [[Special:Contributions/172.70.86.154|172.70.86.154]] 22:31, 16 June 2023 (UTC)

Wasnt there a "My hobby is to open my refrigerator and when people tell me that doesnt help, I sneak into their house and use their AC?" Comic? I cant find it, but we should link it in the "how leaving a fridge open doesnt help" section [[Special:Contributions/172.71.142.158|172.71.142.158]] 23:36, 16 June 2023 (UTC)