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    30 Sep '19 14:155 edits
    In some previous threads a long time ago (don't remember which) I tried to explain what is called night-sky cooling or radiant cooling and how it can, without breaking the known laws of thermodynamics, cause something on the ground or a roof surface to cool much lower than its surrounding air temperature. This effect does NOT come from the cooling effect of evaporation. And, as I explained in the past, and as explained in this video, it can even be used as a cooling system that requires no electricity at all and even during a sunny day! (although at reduced efficiency). It can even be used to generate electricity (but that part was NOT explained in the video) and thus could be yet another future renewable source of energy! But I remember some people here dismissed this claims thinking that WOULD break the known laws of thermodynamics. But now, by chance, I found this video that explains how I was right;

    YouTube


    Scroll to exactly 4.00 into the video to see examples of "night-sky cooling" I was talking about which is then followed with explinations of how this does NOT break the known laws of thermodynamics.
    Then scroll to 7.30 into the video to see the counterintuitive example of a working device that actually successfully cooled using this effect even during a sunny day and even when its not in the shade but full sun!
  2. R
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    30 Sep '19 19:052 edits
    @humy

    I recall the debate. It was not that I said the effect was impossible, its that in order for it to take place it would require a few things:

    1) Highly engineered materials that limit its emission spectrum to the "space window" the presenter mentions. Apparently, this hurdle can possibly be overcome - but at what cost? A standard 3 kW AC window unit cost about $120 US and if I lived in a hot climate all year round that is about $40 per month to operate. For the sake of argument my air conditioner expense every 5 years ( usage + unit ) would be about $2500. The unit they are describing will also be made of pumps and motors and a special material heat exchanger who's performance will ultimately deteriorate. Assuming similar life spans I'd be willing to pay less that $2500 for the sky cooling unit provided the installation was not too invasive.

    2) The system absolutely will require input energy ( you have made this error again stating it requires no electricity). In our original debate you wrongly said it would not need pumps, motors etc.. Motors and pumps will need to be ran in order to circulate the working fluid throughout the building and through the heat exchanger. In out original debate I admittedly hadn't thought of using a separate sky cooling system and heat engine to generate the power needed to run the pumps. I don't believe any thermodynamic laws would be broken like that, but the economics ( both physical and financial ) of such a system are questionable. So, I will concede that it theoretically could sustain itself without grid energy, if you will concede this is absolutely not equivalent to requiring no input energy to operate.

    Another thing I would like to point out is this will be no free lunch as far as the climate is concerned. Because it will require energy to run, heat will still be generated on Earth proportional to our cooling demands. That is not going to change.
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    30 Sep '19 19:313 edits
    @joe-shmo said
    @humy

    I recall the debate. It was not that I said the effect was impossible, its that in order for it to take place it would require a few things:

    1) Highly engineered materials that limit its emission spectrum to the "space window" the presenter mentions. Apparently, this hurdle can possibly be overcome - but at what cost? A standard 3 kW AC window unit cost about ...[text shortened]... will still be generated on Earth proportional to our cooling demands. That is not going to change.
    1) Highly engineered materials that limit its emission spectrum to the "space window" the presenter mentions. Apparently, this hurdle can possibly be overcome - but at what cost? A standard window 3 kW window unit cost me about $120 US and if I lived in a hot climate all year round that is about $40 per month to operate.
    the cooling system the video proposes to be developed in the future would be NOTHING LIKE any current cooling system, so I don't know why you think any current 'standard' cooling system would be relevant, and should cost almost $0 per month to operate, at least in termed of energy costs (THAT'S the point of it! ). The reason why the current cooling system is costly to run is because it uses a compressor and compressing gas takes a lot of energy. This new cooling system will have NO compressor.
    It is difficult to predict in advance what the cost of manufacture would be but I assume the manufacturing technology would eventually and relentlessly incrementally improve with time until it becomes relatively cheap.
    This is using very DIFFERENT technology from the current so I don't see why you think one can estimate its costs from the current.
    2) The system absolutely will require input energy
    Only the small amount of energy for pumping cooled fluid (or gas) from where it is cold (the actual device that cools) to inside the warm house (or whatever requires cooling) and then circulating that now warmed fluid back to where it is cold. It doesn't work like a current standard refrigerator that requires large energy input for a compressor!
    In theory, it could work without pumps by relying on long solid heat conductors, but that might be very awkward or even impractical to arrange in practice.
    ( you have made this error again stating it requires no electricity).
    Unlike current cooling systems, electricity would at most only be needed for any low-energy pumps, NOT the cooling element itself. THAT'S what I meant.
    Motors and pumps will need to be ran in order to circulate the working fluid throughout the building and through the heat exchanger.
    Not if there is no fluid used because heat is moved around via long solid heat conductors but, as I said, that may be awkward.
    the economics ( both physical and financial ) of such a system are questionable.
    I don't see why.
    it will require energy to run,
    Not necessarily (see above). And, even if fluid is pumped, the required energy would be only that needed to move the fluid around, NOT compress it, and thus should be very little energy used (unless badly designed).
  4. R
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    30 Sep '19 20:178 edits
    @humy said
    1) Highly engineered materials that limit its emission spectrum to the "space window" the presenter mentions. Apparently, this hurdle can possibly be overcome - but at what cost? A standard window 3 kW window unit cost me about $120 US and if I lived in a hot climate all year round that is about $40 per month to operate.
    the cooling system the video proposes to ...[text shortened]... e fluid around, NOT compress it, and thus should be very little energy used (unless badly designed).
    They aren't talking about a radical new way to create an air conditioning system. The presenter says as much when he states "we can improve current air conditioning systems by 10-20%. You're not watching your own video!

    Please go to around 9:23 s in the video.
    Listen carefully.
    Then pause at 9:52 s. You will see an operational schematic proposed by the presenter.

    Everything about the air conditioner is still an air conditioner (including the compressor). It will still draw power from the grid. The effect is simply not large enough with current engineering capabilities to economically take advantage of as a stand alone unit ( that MABEY, SOMEDAY could change...words of the presenter, not my own), otherwise that is what they would be proposing. You are suffering from selective hearing to suit a personal narrative, and then arguing Thermodynamics with a Mechanical Engineer. If that is what you truly wish to do (again...), fine. Otherwise, its a clever use of recourses and I thank you for bringing it to my attention. However, the question remains, will it be economically viable.
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    30 Sep '19 21:482 edits
    @joe-shmo said


    Then pause at 9:52 s. You will see an operational schematic proposed by the presenter.

    Everything about the air conditioner is still an air conditioner (including the compressor).
    Arr, I missed that tiny bit.

    However, note how the cooling effect on the cooling element (not to be confused with the rest of the cooling system including pumps) does not require any energy input thus it must be still possible to make an effective cooling system based on that cooling element without any compressor and without breaking any laws of physics. After all, such a cooling effect without the compressor exists in nature!
    See
    https://en.wikipedia.org/wiki/Radiative_cooling
    So it MUST be possible to, without the compressor, arrange it artificially for cooling purposes!
  6. R
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    30 Sep '19 22:01
    @humy

    There is a requirement of a pump on the cooling element. Look at the diagram again.
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    30 Sep '19 22:067 edits
    @joe-shmo said
    @humy

    There is a requirement of a pump on the cooling element. Look at the diagram again.
    I don't deny the whole cooling system they show includes the pump but why would a cooling element consisting of just a layer of metamaterial good at radiating heat to outer space require a pump for passively radiating heat to outer space? That happens whether pump pumping or not. (although a pump may be needed somewhere in the whole of the cooling system just to make it much more practical else heat may too slowly and inefficiently move from the thing that we want cooled to the cooling element if rely only on heat conduction with no forced convection)
    See
    https://en.wikipedia.org/wiki/Radiative_cooling
    To see how the physics of the cooling effect can work WITHOUT either pump and/or compressor.
  8. R
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    30 Sep '19 22:5210 edits
    @humy

    It is just fundamentally an exchanger, nothing more than a very efficient exchanger. You have to get the heat to the exchanger for it to be exchanged! You are more than welcome to sit there all day in your very warm house as energy is being carried through a pumpless system via free convection, you are going to have a very warm house, because energy from the outside environment will have ample time to replenish it as it trickles out! Heat transfer is a time weighted phenomena. It is not just the bulk transfer of energy, but energy per unit time (ie Power) which is crucial.

    look, If you are honestly having trouble grasping this ( and don't trust my opinon) don't take my word for it, take the example of countless engineers in the design of AC units: If AC units didn't need pumps and fans to operate effectively I can assure you they wouldn't have them! This unit, if ever actually realized will do nothing to change that. They are not fundamentally changing the air conditioner process, they are simply increasing the efficiency of a single one of the components. End of Story.

    Just to be clear, I repeat. I understand the phenomenon can transfer heat without a pump, but it has almost no practical value with respect to the problem at hand in that mode.

    P.S.
    In the future if you are going to call me out about previous discussions had between us, please make sure the discussion can be referenced so we can confirm what was actually said. Its very childish to go "someone said blah blah blah, ( for which you clearly misunderstood the blah blah blah ), and I said blah blah blah, and this video says my blah blah blah was right" ...Even though you again were confused about your own provided content. Apology accepted.
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    01 Oct '19 08:567 edits
    @joe-shmo said

    Just to be clear, I repeat. I understand the phenomenon can transfer heat without a pump, but it has almost no practical value with respect to the problem at hand in that mode.
    I already repeatedly said it might not be practical without the pump. Time will tell.
    But it should be possible to AT LEAST design a cooling system with night sky radiant cooling WITH a pump BUT still WITHOUT a compressor (or "condenser", which is actually the correct technical term for it. But I keep saying "compressor" to emphasize it compresses) and thus save most of the energy that would otherwise be required to run it because the pump would merely be for moving the fluid/gas around, not compressing it, and, most of the required power of the pump in a cooling system WITH a compressor is normally for just the compression as that requires a lot of energy.
  10. R
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    @humy said
    I already repeatedly said it might not be practical without the pump. Time will tell.
    But it should be possible to AT LEAST design a cooling system with night sky radiant cooling WITH a pump BUT still WITHOUT a compressor (or "condenser", which is actually the correct technical term for it. But I keep saying "compressor" to emphasize it compresses) and thus save most of the ene ...[text shortened]... ling system WITH a compressor is normally for just the compression as that requires a lot of energy.
    A "compressor" is NOT a "condenser"! I don't know where you are getting this idea from? The condenser is the external heat exchanger ( that effectively is the entire system which they are creating...). The system they are designing will simply be in series/parallel with the standard unit.

    And you are once again making assumptions about not needing a compressor to be more effective. What calculations have you done to compare thermodynamic efficiencies of the refrigeration cycle?!? My guess is NONE! In your theoretical proposal of a self sustaining system in order to gather heat from the room some type of refrigerant must be cycled, the same as it is done now. The reason they use refrigerant is because it is very cold and compressible, and that compressibility greatly increases the thermal efficiency of the heat transfer mechanism. If they can make a material that emits to the "space window", they are going to want to do that at the highest temperature difference possible such that the emission to space holds, not at -50 C (the temp of the refrigerant). That is not going to change, its part of a fundamental law of physics. The thermal efficiency of a cycle is proportional to that temperature difference of the thermal reservoirs. They want to effectively squeeze the heat out over the largest possible temperature difference to increase the overall thermal efficiency of the process. In short, they may very well choose to use a compressor! As I said earlier, they are not changing the process; they are changing a component of the process that allows it to be more efficient. The designers will still want it to be as thermally efficient as it possibly can be! You are once again overstepping your knowledge of heat transfer trying to prove me wrong...why are you doing this?
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    01 Oct '19 14:338 edits
    @joe-shmo said
    A "compressor" is NOT a "condenser"!
    Thanks for correcting me. I forgot the compressor and condenser are SEPARATE parts of the same cooling system (+ I also forgot for a moment that the pump normally doubles as the compressor; so that's my double error; Me bad). But that doesn't change my argument; The pumps have to use up most of their energy because of the compressor (and have to BE the compressor); thus take the compressor out of the picture and you take out the main usage of energy needed to run the cooling system because now the pumps merely have to move fluid or gas around, not pump much harder to also (significantly) compress it.
    And you are once again making assumptions about not needing a compressor to be more effective.
    That depends on what you mean by "more effective". If what you mean is be able to cool MORE, then, no, because I make the exact opposite assumption. But if you mean more energy efficient for a given amount of cooling effect (even if total cooling effect is too small to be considered adequate, because that's a different issue), then that's just a matter of logic; No compressor means less energy used.
    ...trying to prove me wrong...why are you doing this?
    Actually, I am not. I agree with you on at least most if not all things.
  12. R
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    01 Oct '19 15:092 edits
    @humy

    It comes down to the details of the process. Power demands must be realized for it to be a functional air conditioner. Refrigeration process uses the latent heat of vaporization to absorb heat at constant temperature and pressure. That means refrigerant stays cold ( -40 C to -50 C ) during the heat absorption process. Again demands MUST be met. We wont have a massive internal/external heat exchanger for window size AC units (there is only so much living space) . It simply wont be feasible. The system will need to be compact. As such we will need to extract heat at a high rate at maximal efficiency. In a compact system there is going to be a compressor that increases the working fluids temp to (100C ), meeting power demand at maximal thermal efficiency. Again thermal efficiency is proportional to the temp difference if possible ( 100 C - (-270C) ) is much better than ( -40C - ( -270C). Systems for cooling cannot take up the entire livable space of the home just to be effective.
  13. R
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    02 Oct '19 18:54
    @joe-shmo

    I don't like to beat a dead horse, but I've done some back of the envelope calculations to better explain my take on the engineering challenges associated with a system that utilizes only a pump, refrigerant, and the special material.

    Its a closed loop that consist of a cooling coil ( in contact with the air of your home) and a condensing coil ( the special material radiating heat to space), and a pump to ensure uniform temperature of the system while the system is removing heat.

    The pump is necessary to move heated fluid to the special material heat exchanger. If it was not there the system would need to develop a large temperature gradient across the exchangers for heat to flow by free convection. Meaning, the coil that is supposed to be actively cooling your house, would heat up to a temperature close to that of room temperature before very much heat exchanging occurred with space. Once it does that the rate of heat it can draw from the room will be very small. So it would very slowly cool your room, so do you wish your room to be cool within 15 minutes or sometime next week?

    Perhaps there is some argument that can be made for climates that are hot 24/7 365 days a year that this unit just cools the home endlessly once installed. But I don't really know of such a climate, and I believe most users would want to turn the thing on or off with changing temperatures.

    All of that above does not really turn out to be the big issue as far as I can tell. The problem with system ( pump or no pump ) is the steady state temperature of the working fluid. The mode of heat transfer of the cooling coil ( inside the home ) is predominantly free/forced convection ( free or forced depending on if you wish to add an intake fan to the design )

    Q_in = h*A_in*(T_in - T_f)

    "h" is the convection coefficient and from personal experience free air passing over a coil "h" at best will be 100 W/(m^2*K)

    "A_in" is the surface area of the cooling coil (interior to the home)
    "T_in" is the temperature of the space we wish to maintain ( I chose 20 C for the analysis )
    "T_f" is the working fluid temperature.

    The special materials mode of heat transfer is radiation to space, hence

    Q_out = ε*σ*A_out*(T_f)^4

    "ε" is the emissivity of the radiating body. For a Black Body ( perfect emitter over all wavelengths ε = 1) A physicist might correct me on this, but I would think this material specifically designed to emit at certain wavelengths to take advantage of the "space window" will have an emissivity much lower than 1. for the analysis I chose ε = 0.5

    "σ" is Boltzmann's constant
    "A_out" is the radiating materials surface area
    "T_f" is again the temperature of the working fluid.

    From there it is setting up an energy rate balance for the mass of working fluid Assuming all the heat is "sensible", meaning it goes into changing the temperature of the fluid and not its phase. The steady state solution for the working fluid temperate is:

    ε*σ*A_out*(T_f)^4 - h*A_in*(T_in - T_f) = 0

    Next, I had to decide what a pretty unreasonable amount of special material would be to install up on roof in an apartment building ( seeing as how this roof must be shared by all tenants with there own material for there own systems). Also, the cost of this amount of material I expect to be very high. I concluded that it would be A_out = 15 m^2 of material. Then I chose a cooing coil surface area, and plotted a solution for "T_f". Once I had a solution I recalculated the power being drawn from the home from

    Q_in = h*A_in*(T_in - T_f)

    Then I manually ( by iteration of the solution) just maximized that power with respect to the area of the cooling coil. With my values the power output of the system maximized around 3.1 kW, when the cooing coil surface area was 10 m^2. You may think, look its producing 3 kW, we did it!

    Then I went over to my "window unit" - the whole system fitting entirely within the frame of my window ( which is also 3 kW ) and estimated the surface area of its cooling coil to be 0.27 m^2.

    And that is the kicker. The system would need around 40 of my standard window units coils strewn about the house , and a half of a single family home roof space to produce the same cooling effect as my single window AC unit that cost me $100, and $40 a month to operate.

    Please feel free to argue any points, correct the analysis, etc...
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    02 Oct '19 19:42
    @joe-shmo said
    @joe-shmo

    I don't like to beat a dead horse, but I've done some back of the envelope calculations to better explain my take on the engineering challenges associated with a system that utilizes only a pump, refrigerant, and the special material.

    Its a closed loop that consist of a cooling coil ( in contact with the air of your home) and a condensing coil ( the special m ...[text shortened]... 0, and $40 a month to operate.

    Please feel free to argue any points, correct the analysis, etc...
    Naive question: Is this something that could be integrated more cost effectively into new construction vs. retrofitted? I know this is the case for geothermal, for example.
  15. R
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    02 Oct '19 21:512 edits
    @wildgrass

    Yeah, If it is a new build they might be able to integrate one of these systems. The question is at what cost? For some kind of passive system like humy is talking about ( if my calcs are in the ball park) it appears like it is going to take a large amount of "space window" material, plumbing, and regular heat exchangers integrated throughout a home. So it seems like it will be a very large initial expense. I know I personally wont be ripping down all my walls to integrate one of those types (and I can probably afford it), so how are all the poor from the developing nations he is concerned about ( mainly concerned about offsetting their newly developing carbon emissions, not their personal comfort ) going to afford to do so? I think for a long time, if it makes it though all the hoops it will just be what the presenter says, an efficiency boost to current units.
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