>there is a difference of pressure, i dont care what you call it. Use some of that energy to help drive the compressor. Is a crazy idea?
the difference in pressure is caused by the compressor, you want the compressor to ... push itself?
call it what you want, put a Di Pietro compressed gas motor or whatever. A device that recovers some of the energy from the high pressure gas expanding to help the compressor consume less energy
theoretically you could put a turbine there
gasses expand and cool on a turbine, same as in an expansion valve
but liquid + vapor is murder on the turbine blades
there ARE refrigeration cycles with two turbines
but they are slightly different and less efficient for other reasons
OP here, i finally have found it. The idea is correct and it has been researched, but the cost does not justify the improvement.
https://www.sciencedirect.com/science/article/pii/S1876610215027897
i knew it, didnt even read OPs post but its always the same
what are you going to have the turbine do? push against the high pressure side at the right speed so it just barely lets the right amount of material through to the low pressure end at the right speed? just use an expansion valve lol
Turboexpander.
It is more efficient but i guess it is not used because efficienct gain isnt as worth if for another point of failure(leak, lube), design(material for cold, gas liquid slurry phase change interacting the blades, range of working condition) and maintnence for home use. Also a turbine is very peaky in output and efficiency range vs their rpm, and start up slow. They are going to be tiny for home use.
Came here to say the same thing. The purpose of the refrigeration expanding and contracting is to pick up and then bleed off heat, it’s optimized for that process.
I always tell guys I’m training to think of the refrigerant as sponges being moved around a circle that absorb water and then get it squeezed out.
OP, imagine that process, why would it make sense to frick with the absorption and expelling of the water to get back a little potential energy? You don’t want to limit your limiting factor to get a small bonus elsewhere
OP here, i finally have found it. The idea is correct and it has been researched, but the cost does not justify the improvement.
https://www.sciencedirect.com/science/article/pii/S1876610215027897
this is common knowledge actually, in industrial applications it is indeed done, but for simple home applications it's not worth it as it's not that much loss in efficiency
you're not moronic OP, for once
his observation is absolutely correct
fricking garbage thread, people on mount stupid everywhere. dare to bet no one ITT has ever seen a T-s diagram or knows what it is
i guess i'm going to spell it out for anons. in this T-s diagram, the dotted line from 3-4' is an isentropic expansion, while 3-4 with a valve entropy is generated (aka it is not reversible, obviously)
you can clearly see that the heat into the system Q_L would be greater from 4' to 1 than from 4 to 1.
that, and you could generate work from a turbine between 3 to 4'.
the reason they don't in smaller applications is because usually the work done by a compressor is far smaller than the heat that is transferred from the cold reservoir, so that small bit of work you could get back from a turbine is often not considered
>you can clearly see that the heat into the system Q_L would be greater from 4' to 1 than from 4 to 1.
scrap that, it doesn't really matter. you're generating heat in the expansion valve instead of transferring it from the cold reservoir but Q_H remains the same
been a while since i've bothered with this stuff
Long answer, because a lot of answers you've already gotten clearly don't understand exactly why this isn't done.
A huge factor in the efficiency of a phase-change heat pump is the pressure ratio between the hot and cold sides. This makes sense intuitively, because a compressor that has to force the working gas to be ten times as dense on one side will have to work much harder than one that needs to only make the working gas twice as dense. The thing is, you don't want a compressed gas. You want a liquid. All of the cooling power of this kind of heat pump is in the latent heat of vaporization of the refrigerant.
This is important, because it means that, once the liquid has evaporated, it has no more cooling power, and you want to get it back to the compressor with as little resistance as possible. Remember, restriction to flow means less pressure at the compressor inlet, which means a higher pressure ratio, which means less efficiency.
You can't really run a turbine on a mixture of gas and liquid. In the best case scenario, the efficiency of the turbine gets tanked, because the liquid isn't actually doing anything but getting in the way. In the worst case, the liquid slowly erodes the turbine (this is a concern in steam turbines). This means that a turbine won't function as an expansion device, because, by necessity, the turbine will either need to work entirely with the liquid refrigerant (which makes it just a restriction in the liquid line) or entirely with gaseous refrigerant (which makes it just a restriction in the vapor line).
If you just try to do it anyway, what you get is the liquid refrigerant expanding in the turbine, cooling _the turbine_ down, and then doing nothing as it passes through the cold side heat exchanger in gaseous form.
In a real-world system, what this would most likely get you is a mixture of liquid and vapor refrigerant exiting a very cold turbine, with the turbine having done nothing but use up some of the cooling power of the liquid refrigerant. Again, if you design it to work with just liquid refrigerant, it will just increase the pressure on the outlet of the compressor, thus increasing the pressure ratio. If you put it after the evaporator, it will just decrease the pressure on the inlet of the compressor, again increasing the pressure ratio. It doesn't matter that it's actually a turbine, either. A piston expander or any other kind of work-extracting engine you use will have the same detrimental effect on the overall system.
The thing is, calling an orifice, capillary, TXV/EXV, etc. an "expansion device" isn't exactly correct. Or, rather, it's a bit of a misnomer. It doesn't "expand" the refrigerant at all. The actual phase change/expansion of the refrigerant takes place in the evaporator, . The expansion device is only there to provide the restriction to flow necessary to produce the pressure difference the refrigerant needs to be in a liquid and gaseous state on the high/low sides of the system.
The HVAC industry has been experimenting with ways to increase efficiency for decades. If your idea was even remotely viable they would be doing it already.
The whole line is always high pressure goober.
there is a difference of pressure, i dont care what you call it. Use some of that energy to help drive the compressor. Is a crazy idea?
>there is a difference of pressure, i dont care what you call it. Use some of that energy to help drive the compressor. Is a crazy idea?
the difference in pressure is caused by the compressor, you want the compressor to ... push itself?
The cost of a valve vs the cost of a secondary turbine is huge. To save 0.07 mpg in the car the price tag goes up 1500$.
For a storefront like Costco or large grocer it may start to make sense to have a multiphase coolant loop.
>turbine or something
saying you have no idea how a heat pump works without saying it.
call it what you want, put a Di Pietro compressed gas motor or whatever. A device that recovers some of the energy from the high pressure gas expanding to help the compressor consume less energy
you don't want that in a heat pump.
also it won't work. compressor compresses gas using energy turbine steels energy making compressor work harder.
theoretically you could put a turbine there
gasses expand and cool on a turbine, same as in an expansion valve
but liquid + vapor is murder on the turbine blades
there ARE refrigeration cycles with two turbines
but they are slightly different and less efficient for other reasons
i didnt see the picture but its impractical and expensive
i knew it, didnt even read OPs post but its always the same
what are you going to have the turbine do? push against the high pressure side at the right speed so it just barely lets the right amount of material through to the low pressure end at the right speed? just use an expansion valve lol
Turboexpander.
It is more efficient but i guess it is not used because efficienct gain isnt as worth if for another point of failure(leak, lube), design(material for cold, gas liquid slurry phase change interacting the blades, range of working condition) and maintnence for home use. Also a turbine is very peaky in output and efficiency range vs their rpm, and start up slow. They are going to be tiny for home use.
>Why no heat pump has this?
Expanding the refrigerant to drive a turbine is going to reduce its capacity to accept heat.
Came here to say the same thing. The purpose of the refrigeration expanding and contracting is to pick up and then bleed off heat, it’s optimized for that process.
I always tell guys I’m training to think of the refrigerant as sponges being moved around a circle that absorb water and then get it squeezed out.
OP, imagine that process, why would it make sense to frick with the absorption and expelling of the water to get back a little potential energy? You don’t want to limit your limiting factor to get a small bonus elsewhere
it doesn't and you don't know what you're talking about
OP here, i finally have found it. The idea is correct and it has been researched, but the cost does not justify the improvement.
https://www.sciencedirect.com/science/article/pii/S1876610215027897
this is common knowledge actually, in industrial applications it is indeed done, but for simple home applications it's not worth it as it's not that much loss in efficiency
you're not moronic OP, for once
>Idea to improve efficiency of heat pumps
You don't understand what a turbine is, nor what an expansion valve is.
But I welcome you to build and test your device.
his observation is absolutely correct
fricking garbage thread, people on mount stupid everywhere. dare to bet no one ITT has ever seen a T-s diagram or knows what it is
i guess i'm going to spell it out for anons. in this T-s diagram, the dotted line from 3-4' is an isentropic expansion, while 3-4 with a valve entropy is generated (aka it is not reversible, obviously)
you can clearly see that the heat into the system Q_L would be greater from 4' to 1 than from 4 to 1.
that, and you could generate work from a turbine between 3 to 4'.
the reason they don't in smaller applications is because usually the work done by a compressor is far smaller than the heat that is transferred from the cold reservoir, so that small bit of work you could get back from a turbine is often not considered
tl;dr yes it's possible but usually not worth it
>you can clearly see that the heat into the system Q_L would be greater from 4' to 1 than from 4 to 1.
scrap that, it doesn't really matter. you're generating heat in the expansion valve instead of transferring it from the cold reservoir but Q_H remains the same
been a while since i've bothered with this stuff
Long answer, because a lot of answers you've already gotten clearly don't understand exactly why this isn't done.
A huge factor in the efficiency of a phase-change heat pump is the pressure ratio between the hot and cold sides. This makes sense intuitively, because a compressor that has to force the working gas to be ten times as dense on one side will have to work much harder than one that needs to only make the working gas twice as dense. The thing is, you don't want a compressed gas. You want a liquid. All of the cooling power of this kind of heat pump is in the latent heat of vaporization of the refrigerant.
This is important, because it means that, once the liquid has evaporated, it has no more cooling power, and you want to get it back to the compressor with as little resistance as possible. Remember, restriction to flow means less pressure at the compressor inlet, which means a higher pressure ratio, which means less efficiency.
You can't really run a turbine on a mixture of gas and liquid. In the best case scenario, the efficiency of the turbine gets tanked, because the liquid isn't actually doing anything but getting in the way. In the worst case, the liquid slowly erodes the turbine (this is a concern in steam turbines). This means that a turbine won't function as an expansion device, because, by necessity, the turbine will either need to work entirely with the liquid refrigerant (which makes it just a restriction in the liquid line) or entirely with gaseous refrigerant (which makes it just a restriction in the vapor line).
If you just try to do it anyway, what you get is the liquid refrigerant expanding in the turbine, cooling _the turbine_ down, and then doing nothing as it passes through the cold side heat exchanger in gaseous form.
(cont'd.)
In a real-world system, what this would most likely get you is a mixture of liquid and vapor refrigerant exiting a very cold turbine, with the turbine having done nothing but use up some of the cooling power of the liquid refrigerant. Again, if you design it to work with just liquid refrigerant, it will just increase the pressure on the outlet of the compressor, thus increasing the pressure ratio. If you put it after the evaporator, it will just decrease the pressure on the inlet of the compressor, again increasing the pressure ratio. It doesn't matter that it's actually a turbine, either. A piston expander or any other kind of work-extracting engine you use will have the same detrimental effect on the overall system.
The thing is, calling an orifice, capillary, TXV/EXV, etc. an "expansion device" isn't exactly correct. Or, rather, it's a bit of a misnomer. It doesn't "expand" the refrigerant at all. The actual phase change/expansion of the refrigerant takes place in the evaporator, . The expansion device is only there to provide the restriction to flow necessary to produce the pressure difference the refrigerant needs to be in a liquid and gaseous state on the high/low sides of the system.
The HVAC industry has been experimenting with ways to increase efficiency for decades. If your idea was even remotely viable they would be doing it already.
I like the new chatbot, it surely knows how to mass reply.
>This entire thread is cancer
You sure didn't contribute one bit to the quality.