If Social Security and Medicare are so great, why doesn't Congress use those systems for their retirement and medical benefits?
Oh yeah, because they're the opposite of great.
FAA...I grant you. Whatever flaws it might have, it has created a safe and reliable air transport network. Now, they're trying to ruin it by getting general aviation to subsidize business and commercial aviation, so the jury may still be out on that one.
ADA? Well, I've got some issues with their definition of "disability". While it's the furthest thing from Gospel, I think that Penn & Teller's Bullshit episode is pretty on point. As they observe, it's not exactly like people were kicking the crutches out from under disabled people before the ADA.
In principle, I think it's right and good to have reasonable accomodations for people with different physical (and mental) impairments. However, I think the ADA goes a lot farther than that, and turns into a millstone for small businesses.
What the hell is an "average Slashdotter", and who the hell are you to presume what anybody else thinks about anything? You seem to want there to be a hive mind of "average Slashdotters" with you as the voice of reason.
And sometimes the simpler life gives you cholera. You're welcome to be a luddite, but I will use the best tools available to bend the world to my will.
The part where the OP thought that if you have hot gas in a fixed volume, and cooled the gas, the pressure would stay constant. Any system built on that assumption needs further analysis.
As soon as I got to the OP's actual notion (see another branch of this conversation), I found the assumptions that were actually being made, and corrected some misconceptions. For fun, I'm looking at actually designing a cycle based on these principles, just to see if I can do it.
It looks like we're not cooling the house by electricity produced by a turbine, but by expansion of the cool, compressed gas. Is that theoretically possible? Sure. Is it likely to be controllable by any sort of thermostat? That's going to be harder. And, oh yeah, when you're not using that jet of cool air, you also don't get any electricity.
"not trying to pull it out of the same process twice in different ways."
Here's the thing. Your compressor is the only source of that heat. If you want to use energy to heat water, it's more efficient to just do that, rather than using your system. If you want to use energy to cool air, there are reasonably efficient ways to do that.
Each leg of this process (heating water, cooling air in your house, pressurizing air into your tank) have thermodynamic losses associated with them. Evaluating and minimizing these losses are the key to making a system like this work economically.
I'd have to look at my thermo book to perform the analysis. Believe it or not, I'd be glad to do so...but my textbooks are in storage. Maybe when I get home I'll do some hunting and see if I can come up with some back-of-the-envelope calculations.
Is it possible? Anything is possible. Is it likely to work? It sounds pretty Rube Goldberg-y to me.
As a thought experiment, fine and dandy. As a teaching tool, it's probably great. It'd be a great thermo test question. As a machine to save your money? Hmm...might want to just buy some bonds instead.
If you really have a 3:0 price differential (meaning that you get free electricity at night), I think your system will absolutely work. I can think of a lot of other systems that will work a lot better.
Since I really think you don't, I'm still skeptical.
"but to be honest I think I'll just install a heat pump."
Hmm...you mean a simpler mechanism might be more efficient than a complex one? What a stunning revelation.
Here's another simple mechanism for you. Use your cheap nighttime power to run a pump that moves water into a tank on your roof. Have the tank painted black.
Hot water. Power reservoir. No "free" air conditioning, but I didn't really grok how you were going to work that part anyhow. (as an aside, I'd love to see the electrical schematic for your thermostat system.)
I can't analyze your system without evaluating your assumptions. The best way to do that would be for you to share your math with me. If you don't want to do that, that's cool...it's a lot of work. No big deal.
Or maybe you're still laughing at me. If so? Enjoy yourself. Good luck with your perpetual motion machine. If you get it to work, I'll gladly buy one from you.
"For one, did you completely miss the point where the efficiency in question is relative to the fucking dollar?"
Yes. Yes, I did miss that. Which is why I asked for a more thorough explanation, which he graciously "simplified" by making a number of very, very wrong assumptions.
I agree with you 100% that there are ways to game the nighttime/daytime electricity cost differential to spend less money doing the things that we do. I agree that we could use math similar to the math used in thermodynamics to analyze that system. That is an absolutely do-able scenario.
Now, we have to discuss how you do it. The idea proposed is based on incorrect understandings of thermodynamics and is, therefore, suspect. It may be that by analyzing the system correctly, money could be saved. Had the OP given the details I requested instead of trying to simplify things for me, that discussion might have been productive.
Aha! If you want to talk about dollar efficiency, you have to introduce a whole 'nother set of factors. It is theoretically possible to game the price differential and save money. Which is why I asked to see the OP's work. Which never happened. I assume that's because the OP is laughing so hard at my poor grasp of thermodynamics.
"When the tank has no pressure, there are x moles of gas in it. As you start adding more gas to the tank (you know, storing the compressed air) there's now y moles of gas in it, where y > x. In order to fit more moles of gas into the tank, the gas is cooled, which results in the gas exerting less pressure, and now you can fit more gas into the storage tank without violating the pressure spec on the tank."
100% agreed. Whether you can realize enough savings on the differential cost between AM and PM power usage, is a different issue. Please note that, at night, less energy is required to cool your house.
The OP also mentioned using the "waste" heat to heat water. OK, that's fine. But if that's what you're after, why not use a gas burner, or a (wait for it!) solar water heater?
You certainly can use heat differentials to produce energy. You cannot produce more energy than you used to create the heat differential in the first place. If you can find a "free" heat differential (geothermal, passive solar, etc.) then you can get a net energy gain within your system, because you've externalized the energy required to create the heat differential.
But there's no such thing as a free lunch.
"Taking cheap electrical energy to store energy and suck heat off in order to allow us to store more air, and use that excess heat where we want it"
Clearly, there's nothing in principle wrong with that. The engineering is a challenge. However, there is NOT NOT NOT free energy produced. The claim was an over-unity efficiency, and that's my issue: That is not possible. Period.
"keep it at that pressure, the gas is not going to go to a lower pressure, it can't it has no where to go."
You very seriously need to read a text on thermodynamics. You are completely incorrect. The pressure DOES decrease, because (assuming we're dealing with an ideal gas, which is a pretty good assumption unless you're doing something rather exotic), the pressure in the cylinder is proportional to the product of temperature and volume. PV=nRT. That's the Ideal Gas Law, and it's rather well-regarded in the study of thermodynamics. Since you're assuming constant volume in the cooling process, pressure is directly proportional to temperature.
You're assuming that pressure comes from the physical proximity of gas molecules to one another, and therefore, the pressure will be constant regardless of the energy state of those molecules. That is a fundamental misunderstanding of the physics inside that cylinder.
"I don't see what part of the Ideal Gas Law is being violated."
I didn't say it was being violated. I said that in order to not violate it, you decrease temperature, T, you decrease pressure, P, because the ideal gas law states that pressure and temperature are directly proportional in a fixed volume.
PV=nRT
I might be being a little snippy (I was actually going for 'jocular', but I may well have missed), but I'm pretty confident in the thermodynamics. By all means, illustrate my errors, and I'll be glad to eat crow.
Oh, I read the post. You entered a discussion on solar energy, and then took a left turn into not-solar-energy without specifying such. Yes, I understood your point. No, you were not clear.
So, you're saying that your 24 kwh is going to run a compressor, that will put air into perfectly insulated tanks (I'd really like to see your arithmetic here). OK, fine. Assuming you do so reversibly, you'll get out exactly as much energy as you put in. No, you can't do so reversibly.
But, after you pressurize the tanks, you want to cool them with water. Ideal Gas Law says that if you decrease temperature, you decrease pressure. Now you've got way, WAY less energy in your tanks to reverse-run your compressor (which, you might note, will be less efficient than a compressor optimized to compress).
So, yeah, I still want to see your work, because from where I'm standing, it looks like bullshit.
"(as I said actually reading the original post is such a novel idea)"
Would have been better if you were actually knowing what you were talking about, but OK.
"Why isn't the electric utility installing large solar panels to generate electricity during peak hours?"
Because the electric companies know that PV cells don't give a good ROI, except if and when you can game the electric companies into subsidizing them for you.
"You can save more money if you store energy during the cheap period of the night."
Genius. Why didn't I think of that! Use your solar panels to charge your batteries...at night!
"However factor in the heat you have stored for hot water and you are doing better than 100% "
*eyebrow* I'd like to see your work there, cowboy. Most of the time, thermodynamic processes don't give above-unity efficiency. And by "most", I mean "absolutely all".
Slashdot Mirror
That moist *splat* sound was the point hitting you in the forehead. Nice catch.
If Social Security and Medicare are so great, why doesn't Congress use those systems for their retirement and medical benefits?
Oh yeah, because they're the opposite of great.
FAA...I grant you. Whatever flaws it might have, it has created a safe and reliable air transport network. Now, they're trying to ruin it by getting general aviation to subsidize business and commercial aviation, so the jury may still be out on that one.
ADA? Well, I've got some issues with their definition of "disability". While it's the furthest thing from Gospel, I think that Penn & Teller's Bullshit episode is pretty on point. As they observe, it's not exactly like people were kicking the crutches out from under disabled people before the ADA.
In principle, I think it's right and good to have reasonable accomodations for people with different physical (and mental) impairments. However, I think the ADA goes a lot farther than that, and turns into a millstone for small businesses.
You might think that, and you're certainly entitled to your opinion. I'm certainly not convinced that batteries are a good way forward.
Right, because most government initiatives achieve their goals and don't have unintended consequences.
Seriously...what is your benchmark for a successful government program that would justify MORE government involvement in, well, anything ever?
Consistency is the something of some kind of...other...thing...
: )
As long as you assume that every retailer has a perfectly optimized pricing model, you're right.
I bet you a shiny nickel that they don't.
"yet the average Slashdotter thinks"
What the hell is an "average Slashdotter", and who the hell are you to presume what anybody else thinks about anything? You seem to want there to be a hive mind of "average Slashdotters" with you as the voice of reason.
Guess what, Sparky. You ain't.
"Somethings the simpler life is actually better."
And sometimes the simpler life gives you cholera. You're welcome to be a luddite, but I will use the best tools available to bend the world to my will.
There were no good old days.
Then the pressure changes, linearly with n.
The part where the OP thought that if you have hot gas in a fixed volume, and cooled the gas, the pressure would stay constant. Any system built on that assumption needs further analysis.
As soon as I got to the OP's actual notion (see another branch of this conversation), I found the assumptions that were actually being made, and corrected some misconceptions. For fun, I'm looking at actually designing a cycle based on these principles, just to see if I can do it.
It looks like we're not cooling the house by electricity produced by a turbine, but by expansion of the cool, compressed gas. Is that theoretically possible? Sure. Is it likely to be controllable by any sort of thermostat? That's going to be harder. And, oh yeah, when you're not using that jet of cool air, you also don't get any electricity.
"not trying to pull it out of the same process twice in different ways."
Here's the thing. Your compressor is the only source of that heat. If you want to use energy to heat water, it's more efficient to just do that, rather than using your system. If you want to use energy to cool air, there are reasonably efficient ways to do that.
Each leg of this process (heating water, cooling air in your house, pressurizing air into your tank) have thermodynamic losses associated with them. Evaluating and minimizing these losses are the key to making a system like this work economically.
I'd have to look at my thermo book to perform the analysis. Believe it or not, I'd be glad to do so...but my textbooks are in storage. Maybe when I get home I'll do some hunting and see if I can come up with some back-of-the-envelope calculations.
Is it possible? Anything is possible. Is it likely to work? It sounds pretty Rube Goldberg-y to me.
As a thought experiment, fine and dandy. As a teaching tool, it's probably great. It'd be a great thermo test question. As a machine to save your money? Hmm...might want to just buy some bonds instead.
If you really have a 3:0 price differential (meaning that you get free electricity at night), I think your system will absolutely work. I can think of a lot of other systems that will work a lot better.
Since I really think you don't, I'm still skeptical.
"but to be honest I think I'll just install a heat pump."
Hmm...you mean a simpler mechanism might be more efficient than a complex one? What a stunning revelation.
Here's another simple mechanism for you. Use your cheap nighttime power to run a pump that moves water into a tank on your roof. Have the tank painted black.
Hot water. Power reservoir. No "free" air conditioning, but I didn't really grok how you were going to work that part anyhow. (as an aside, I'd love to see the electrical schematic for your thermostat system.)
You're welcome? I think?
I can't analyze your system without evaluating your assumptions. The best way to do that would be for you to share your math with me. If you don't want to do that, that's cool...it's a lot of work. No big deal.
Or maybe you're still laughing at me. If so? Enjoy yourself. Good luck with your perpetual motion machine. If you get it to work, I'll gladly buy one from you.
"It was too much to hope that they would think for 5 minutes to understand what you are saying."
If somebody claims over-unity efficiency, they definitely have some 'splainin' to do.
"For one, did you completely miss the point where the efficiency in question is relative to the fucking dollar?"
Yes. Yes, I did miss that. Which is why I asked for a more thorough explanation, which he graciously "simplified" by making a number of very, very wrong assumptions.
I agree with you 100% that there are ways to game the nighttime/daytime electricity cost differential to spend less money doing the things that we do. I agree that we could use math similar to the math used in thermodynamics to analyze that system. That is an absolutely do-able scenario.
Now, we have to discuss how you do it. The idea proposed is based on incorrect understandings of thermodynamics and is, therefore, suspect. It may be that by analyzing the system correctly, money could be saved. Had the OP given the details I requested instead of trying to simplify things for me, that discussion might have been productive.
He didn't, so it wasn't. GIGO.
Aha! If you want to talk about dollar efficiency, you have to introduce a whole 'nother set of factors. It is theoretically possible to game the price differential and save money. Which is why I asked to see the OP's work. Which never happened. I assume that's because the OP is laughing so hard at my poor grasp of thermodynamics.
(Yes, that was with an eye roll.)
"When the tank has no pressure, there are x moles of gas in it. As you start adding more gas to the tank (you know, storing the compressed air) there's now y moles of gas in it, where y > x. In order to fit more moles of gas into the tank, the gas is cooled, which results in the gas exerting less pressure, and now you can fit more gas into the storage tank without violating the pressure spec on the tank."
100% agreed. Whether you can realize enough savings on the differential cost between AM and PM power usage, is a different issue. Please note that, at night, less energy is required to cool your house.
The OP also mentioned using the "waste" heat to heat water. OK, that's fine. But if that's what you're after, why not use a gas burner, or a (wait for it!) solar water heater?
You certainly can use heat differentials to produce energy. You cannot produce more energy than you used to create the heat differential in the first place. If you can find a "free" heat differential (geothermal, passive solar, etc.) then you can get a net energy gain within your system, because you've externalized the energy required to create the heat differential.
But there's no such thing as a free lunch.
"Taking cheap electrical energy to store energy and suck heat off in order to allow us to store more air, and use that excess heat where we want it"
Clearly, there's nothing in principle wrong with that. The engineering is a challenge. However, there is NOT NOT NOT free energy produced. The claim was an over-unity efficiency, and that's my issue: That is not possible. Period.
Hold on. We're talking about air in pressure vessel. n is constant.
Yes, clearly, if you hold P constant, and T goes down, you must add more gas.
"keep it at that pressure, the gas is not going to go to a lower pressure, it can't it has no where to go."
You very seriously need to read a text on thermodynamics. You are completely incorrect. The pressure DOES decrease, because (assuming we're dealing with an ideal gas, which is a pretty good assumption unless you're doing something rather exotic), the pressure in the cylinder is proportional to the product of temperature and volume. PV=nRT. That's the Ideal Gas Law, and it's rather well-regarded in the study of thermodynamics. Since you're assuming constant volume in the cooling process, pressure is directly proportional to temperature.
You're assuming that pressure comes from the physical proximity of gas molecules to one another, and therefore, the pressure will be constant regardless of the energy state of those molecules. That is a fundamental misunderstanding of the physics inside that cylinder.
"I don't see what part of the Ideal Gas Law is being violated."
I didn't say it was being violated. I said that in order to not violate it, you decrease temperature, T, you decrease pressure, P, because the ideal gas law states that pressure and temperature are directly proportional in a fixed volume.
PV=nRT
I might be being a little snippy (I was actually going for 'jocular', but I may well have missed), but I'm pretty confident in the thermodynamics. By all means, illustrate my errors, and I'll be glad to eat crow.
"its still at high pressure at this point, cooling it doesn't lower the pressure."
Horse puckey. What you describe is an intercooler, and is common in turbocharged engines. It is NOT, repeat, NOT, a source of free energy.
"A lot of this is counter intuitive I will admit"
If by "counter intuitive" you mean "violates the laws of thermodynamics", then yes, I'd say it's counter intuitive.
Oh, I read the post. You entered a discussion on solar energy, and then took a left turn into not-solar-energy without specifying such. Yes, I understood your point. No, you were not clear.
So, you're saying that your 24 kwh is going to run a compressor, that will put air into perfectly insulated tanks (I'd really like to see your arithmetic here). OK, fine. Assuming you do so reversibly, you'll get out exactly as much energy as you put in. No, you can't do so reversibly.
But, after you pressurize the tanks, you want to cool them with water. Ideal Gas Law says that if you decrease temperature, you decrease pressure. Now you've got way, WAY less energy in your tanks to reverse-run your compressor (which, you might note, will be less efficient than a compressor optimized to compress).
So, yeah, I still want to see your work, because from where I'm standing, it looks like bullshit.
"(as I said actually reading the original post is such a novel idea)"
Would have been better if you were actually knowing what you were talking about, but OK.
"Why isn't the electric utility installing large solar panels to generate electricity during peak hours?"
Because the electric companies know that PV cells don't give a good ROI, except if and when you can game the electric companies into subsidizing them for you.
"You can save more money if you store energy during the cheap period of the night."
Genius. Why didn't I think of that! Use your solar panels to charge your batteries...at night!
"However factor in the heat you have stored for hot water and you are doing better than 100% "
*eyebrow* I'd like to see your work there, cowboy. Most of the time, thermodynamic processes don't give above-unity efficiency. And by "most", I mean "absolutely all".
"(which AFAIK were originally intended to be state matters in the US, too)"
Aha! Ze point! She comes to you like a thief in ze night!