2239 Heat Pumps And The Gas Laws
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- Опубликовано: 19 июн 2024
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I've used two split Aircon units to heat my house for the last 5 years. I also run my now 7-year-old electric Zoe (still 100% battery, and brake pads that never seem to die).
Even with these drains, the now outdated solar panels on my flat roof generate more electricity in a year than I use.
Thanks to the laws where I live, I get paid real money for what I generate.
My house was A grade back in '94 when it was built, and admittedly takes little energy to heat or cool it.
I haven't used my gas heating for many years, I save a lot of money.
My solar panels were paid for via savings years ago. For once I backed the right horse 😅
(Long-distance journeys I do by train, not my 22KW Zoe 😂)
I am considering replacing the old gas heating unit with a heat pump. And scrapping the Aircon... hence I'm watching another great video
Another easy to understand lecture, thanks Prof.
It is amazing what the refrigeration cycle can do... And even more impressive is that it can "move" heat around more efficiently than a resistance coil can "make it".
Thanks for the video!
cheers mate
I wish my science teachers at school could have brought things to life as you do.
Could you please comment on the Hendershot electricity generating system?
I'm very impressed with my portable dehumidifier which has a built in heat pump. At 12C or more works really well. Over 100% efficient because you get the "free" latent heat of vaporisation.
Build one please Robert
Nice explanation, thanks!
Dew point (temperature and pressure related), absolute humidity, relative humidity, latent heat, phase change, velocity and pressure (Bernoulli 's principle) are all interesting as well.
Then there's the total energy in the system which can only be increased by adding more. Heat pumps are ok when wet and windy, but how about still air with your house in a frost pocket? Structural damage from frost heave, or how about the flats on the ground floor being frozen from the 3 floors above? No laws against this, currently, to my knowledge.
Thanks as always for your clear and concise explanations!
Thanks mate, well explained.
Thank you for this video! Follow-up question on coefficient of performance:
Why do you get 3-5x more heat moved than the energy you use to compress the fluid? It seems to me the energy you use to compress should equal the energy absorbed from the environment in boiling back to gas.
Wall of text ahead, beware.
Because on heat pumps that use freon and such take advantage of phase change. The compressor does very little work compared to the environment. When the gas is compressed by the compressor freon can easily hit 200c. From there it travels to the outside coils where its exposed to 30c ambient air causing the gas to condense into a liquid. The phase changes of matter take a large amount of energy compared to simply heating up or cooling down. Much like how a pot of boiling water doesn't go above 100c at sea level because all the energy being put into it is being used to turn the water into steam. After the freon is a liquid, it then goes into an expansion valve where the liquid is allowed to rapidly expand and cool down to about 0C. That freezing now gas freon is exposed to 20c air warming it up to nearly the same temperature before it goes back to the compressor where its compressed and also heated up well beyond ambient temperatures. Now why is the freon a liquid when hot and a gas when cold? well because of pressure. any gas under enough pressure at a fix temperature will turn into a liquid because the molecules are forced to be closer to each other and are forced to change phase into something more stable. If the pressure keeps increasing the original gas now liquid can become a solid even if the temperature is well above the original's gas boiling point. The reverses is also technically true, but not everything has a real-world pressure low enough to cause it to either phase change into a liquid or sublimate straight into a gas. Or perhaps no one has taken the time to measure how long glass, steel, and so on, take to vaporize in a perfect vacuum.
Yes.
don't cry for me, don't cry for me, Avogadro...
Man I like your channel.
it's nearly a stirling engine that you turn the wheel
Thank you, Robert....
The good , the bad, and the ugly (temp. Pressure and volume)..😂
The volume of a given gas sample is directly proportional to its absolute temperature at constant pressure (Charles's law)
What is the temperature?
Temperature is actually the measurement of movement.
-----Not necessarily. You can place room temperature water into a room temperature blender and blend it at high speed for a few minutes. Afterwards the temperature of water has not changed, nor was the temperature in water increase while it's moving faster in the blender.
Great explanation, can you do one for ram pumps
Ductless mini split heat pumps are very affordable and extremely efficient.
Heat pumps a.k.a. Air Conditioner a.k.a. Dehumidifier a.k.a. Refrigerator, essentially the same thing. R = L * atm / (n * °K) a.k.a. PV = nRT.
I would add that geothermal or solar thermal or hot water heaters or any forced hot/cold water loop is fundamentally different in that there is no compression, just heat transference through fins, and typically in one direction only. Although with geothefmal, that one direction tends to always get you closer to the desired home temperature, regardless of season, whereas an electric, gas, oil, coal, or wood boiler can never be used to cool a house in summer, only heat it in winter. Not a bidirectional heat pump, but monodirectional.
I often tell people that pressure and vaccuum are not the opposite due to lack of volume . Its fun to see there mind puzzled. 😂In the context of vacuum, the gas laws still apply, but the relationships may change slightly due to the absence of pressure or the presence of very low pressures. For example:
1. Boyle’s Law: In a vacuum, there is essentially no pressure, so Boyle’s Law doesn’t directly apply. However, as pressure decreases (approaching a vacuum), the volume of a gas expands.
2. Charles’s Law: In a vacuum, temperature can still affect the volume of a gas, but the absence of pressure may lead to different behaviors compared to conditions at normal pressures.
3. Gay-Lussac’s Law: In a true vacuum, there is no pressure to speak of, so Gay-Lussac’s Law doesn’t directly apply. However, if gases are present in a container experiencing extremely low pressures, temperature changes may still affect pressure, although the relationship may not be linear.
4. Avogadro’s Law: This law is about the relationship between volume and number of gas molecules, which can still hold true in a vacuum as long as there are gas molecules present. However, in a complete vacuum, there are no gas molecules to consider.
cheers mate
I live in Alberta, and in winter it can get very cold, -15C can be the norm for daytime highs. My question is, where does the ambient air heat pump get the heat from to warm my house?
-15C is very far away from absolute 0. So there is still heat outside. Although it might not be optimal operating temperature.
At -15C the air should be dry, so you shouldn't be getting energy from water vapour, condensation and ice formation. As far as I can tell the designs are too stupid to get ice to fall off, but rely on a heating cycle.
A water based heat pump would be better. Underground vs surface has an almost constant temperature difference all year. My brother used such a system in Ontario.
Find out the heat capacity of dry air, and see how much you need to shift for a constant 5kW, assuming starting at minus 15, and dropping 35C. They don't publish the lower temperature from what I can see. Fast, very cold, air is dangerous as well. Then see if the minus 15 input air starts getting colder, if you don't have constant replenishment. I made this about 120 litres/second. If the pump sucks and blows in the same place, not sure how the nanoclimate is after 24 hours.
from the heat difference between the expanding tranfer fluid and the ambient temperature - when the gas expands it can drop much lower than minus 15 - as long as there is a eat difference it will work it isn't an absolute temperature difference
Cool 😎
do think you could use a stirling engine to turn another stirling engine to create a cooler? I expect that if you could then the stirling being turned by the first one would have to be significantly smaller. Do you think it's feasible?
Perfectly fine until all the stirling engines reach an equilibrium temperature, at which point they'll stop.
@@simongross3122 granted but that will happen with any Stirling if you don't have active cooling
I think the specific question regarding a "heat pump" is ... why is it "more efficient"?
Why does adding underground coils etc help in the efficiency.. this is probably the key component that people would like to know about
once you reach a certain depth the ground temperature is more or less constant, (around 10 deg c in the UK with maybe a variation of a few degrees either way at 1m depth) so on a hot day this is lower than the air temperature and conversely when its freezing outside the ground temperature is warmer than the air- it just makes for a system that doesent get as much fluctuation at the input end so can be designed in a more efficient manner.
it depends what you mean by efficiency - they are just a heat engine so the efficiency of moving heat from area to another is not going to be great - around 37% or so - like any heat engine. If you mean how much it cost you in terms of electricity then you are paying for just the pumps and compressor - so it will be cheaper as you are getting the heat for 'free' - you don't have to pay for heating something up - but then of course the amount of heat you can transfer is going to depend on how hot your heat source actually is
That was really great. I am not very bright but I wonder if you could address specifically how a heat pump uses air from outside that may be cooler and make it warmer in the house (or visa-versa).
I think it is because even though the air outside may be cooler than the air inside your house, it is still warmer than the cold end of a heat pump. The heat pump takes this heat and it helps to warm up the refrigerant gas which is then pumped into hot area of the heat pump. By the time it gets there, the gas is hotter than the air inside your house because of the compression, but also because of the heat taken from outside, and this heat is then added to the heat inside your house. It's mind-bendingly clever since we all believe that heat flows from hot to cold, and it appears that we've got heat flowing from cold to hot. It only appears that way because the thing that's truly being heated and cooled is the gas in the heat pump and then used as a way of transporting the heat to where you want it.
A heat pump pumps heat usually against the external temperature gradient.
@@simongross3122Wow! Thanks for that great explanation. That is really fascinating. I have got to see if I can wrap my head around it. To me the notion that gasses change temperature according to pressure is still absolute magic.
Would this make a Stirling Engine more efficient? Take two heat pumps - use one to heat up the "hot" cylinder of an Alpha Stirilng engine and the other to cool off the "cold" cylinder.
i don't know tbh mate - you could always try it and see
Scrap all heat pumps.
Thank you for the video, easy to understand as always. Is it me or is it an irony that so many external commercial heat pump housings are white? Wouldn't black be better with some added sunshine?
I prefer to explain heat-pumps without the use of formulae. Simply, a volume of gas has two components-the molecules themselves and heat(irrespective of how temperature is defined). Compressing this body of gas, compresses both the molecules and their heat. This results in a denser gas at a hotter temperature-same number of molecules occupies a smaller volume and the same amount of heat now occupies a smaller volume.
Now could you explain why 1 kwh of compression gives 3 kwh of heat instead of electrical resistance heat equivalent. I hope you understand my question
It's because some of the heat is taken from the ambient temperature and is not all due to the compression. Seems like magic, but it's really just arithmetic.
Why do manufacturers claim you get more out of a heat pump than you have in input? How is that possible?
The over 100% efficiency comes from the fact that instead of generating energy from a chemical or electrical source you are moving the heat from one place to another. It doesn't break any laws of the universe to pump a large amount of heat so efficiently that you can claim 300% more heating than the electrical input, especially given the comparable losses for most other forms of heating
Watch the video and pay attention.
@@dermotbalaam5358 I did, but I am genuinely puzzled. It sounds to me to be impossible.
The electricity consumed is not the "input". It just works the pump. The "input" is all the hot air in the great outdoors. Yes, the outdoors is still "hot" even when it's a lot colder than you want your house to be. Anything warmer than minus 273 degC contains some energy in the form of heat, so there is plenty of heat energy available. The wonderful thing about outdoors is that it is big - REALLY BIG! So we can gather the energy from a VERY LARGE volume of the outside air and transfer all that energy into the SMALL volume of air inside your house. Your tiny house gets a lot warmer, while the great outdoors gets ever so slightly cooler. No magic. No scientific laws broken.
Simple as that!
pretty much lol
I thought decrease V then T increases.
Hence hot bike tyre pumps.
That's right. I think he misspoke at one point in the video. But if you heat a gas and it is kept at the same pressure because you can change the size of the container, then the volume will increase. If you compress a gas and don't allow the gas to escape then the pressure and temperature both go up. If you have a gas in a container under pressure and you release some of the pressure by increasing the volume of the container then the temperature will go down. Ideal gas law says PV = nRT where P = Pressure, V = Volume, n = number of moles of gas, R is a constant and T is Temperature. So for a given mass of gas, n is constant. And you can see how P, V and T are related. If you hold any of them constant, then you can see it more clearly.
Thanks for that.....I got confused as well
(For me) Charles's law was not intuitive at all - at first. I needed to be hammered it in before continuing on the video. First accept "the gas" in this law has 4 properties:number of molecules, volume, temperature and pressure. Difference between quantity(amount, numof molecules) and volume must be strongly noted. "Quantity" means number of molecules i.e amount. Situation happens under constant pressure. That might mean the container i.e. volume has perfectly loose walls so gas can freely expand. The law states the quantity of gas(number of molecules) stay the same. After that first feeling is that growing temperature of given number of gas molecules generates more volume. At the same time pressure keeps the same as confined volume has perfectly loose walls. Then scrap the container concept alltogether and think just abstract volume.
After all this it is perfectly intuitive to think that volume of gas can expand with temperature and pressure does not change.
It did take quite a while just to figure out the 4 laws of gases.
Back in the days of dinosaurs. My faux father converted a single cylinder 500cc Velocette motor into a compressor. The exhaust valve passed the compressed air from the cylinder to the storage tank and the inlet valve allowed air into the cylinder. When starting, the inlet valve was held down until the electric motor run up to speed. It would keep 4 high pressure spray guns running simultaneously at 100 psi none stop.
Boil's law😊
Avogadro’s Number, 6.02 x10 to the 23rd
I have a habit of stating the obvious.
The reason I do so is because of the number of people I have encountered, that have never been taught the obvious.
A thermostat is an automated on and off switch that is controlled by the ambient temperature in the room.
It matters not how low you put the thermostat.
If the thermostat is set at 78 degrees, external air is 80 degrees and the air inside the room is 90 degrees; setting the thermostat to 60 degrees is not going to cool the room off. It's going to waste money.
I was waiting for mid video haircut?
What I don't get is if you put all of the gas laws aside and take the first law of thermodynamics, it basically says everything balances you don't get something for nothing.
So if its 2 degrees C outside and I want it 20 inside, plus my hot water at 60 how does the maths for that stack up? I can only see it working by a lot of energy being put it from another source than the air, namely electricity.
I suspect that a lot of electricity is used both for running the compressor, and probably for running an immersion heater in the cylinder used for transfer from the closed loop heat pump system to the heating/hot water system.
Sadly I haven't found anyone trust worthy and independent, like Robert, who has explained/calculated this yet
There's also called a law of conservation of energy that clearly sounds made up by crude oil companies. I'm sure Robert knows where you're coming from. We ordinary folk have no control over the greedy reptilian laws nor allowance of patents. Yet.
2°C outside has a massive volume you are only taking a tiny fraction of that energy out of the mass and concentrating it in a small space like indoors
Heat pumps just move heat from one place to another. They don't create heat like burning fuel does.
If you are burning fuel to create heat, then energy conservation means that even with perfect efficiency, you will only get 100% heat energy out of the fuel energy you put in.
However, if you use that fuel to move heat, rather than create it, that actually uses a lot less energy. Running a compressor and all the other losses in a heat pump system, are still a lot less than what you would need to create heat. The same amount of fuel energy can move up to 5x more heat than if that fuel was burnt to create heat.
Even at 2 deg C, there's still heat that can be extracted. That's how your freezer can get down to -22 deg C.
Air-source heat-pumps a.k.a noise-pumps don't work.
Why ?
The energy density of air is extremely low.
That's why they have such a big fan, to cool thousands of cubic meters of air each hour.
------
To tackle that problem, you first need to isolate your whole house, in such a way that it is hardly using any energy at all, so your heat-pump won't get overworked. But in a well insulated house, instead of purchasing an overpriced heat-pump you could also do with a cheap, small, low-noise natural-gas-boiler.
There are also fanless heat exchangers.