anyone ever hear of someone using a heat pump for a steam system?

rhodebump

I know this may come across as a weird question, but just wondering about the future of steam heating in relationship to heat pumps.

From my understanding, I can see lots of hydronic (water) heating system using a heat pump since there is lower temperatures involved with just water.

Since steam requires much higher temperatures, is a heat pump just not feasible?

thank you!
Phillip

Daveinscranton

It would seem to me that if you ran the system at a relative vacuum, you could make your steam at any temperature you wanted.  

My guess is that this may be easier said than done.  

I could see a place for modern materials in such an application.  

I am not going to be the first one to buy such a system.  The science, at first blush, would make sense.  I like the working fluid (water).  Pretty environmentally friendly material, generally.

Jamie Hall

There is no theoretical reason why it couldn't be done. To make it feasible for heating in more northern climates, it would probably have to be two stage, to keep the pressures within a reasonable range on the equipment. But there's no theoretical reason why it wouldn't work.

It's a matter of choosing the right refrigerants so that your high temp condensing temperature pressure and your low temperature evaporating pressures are reasonable.

There would be good deal to be said for using water as the second (high temperature) stage refrigerant -- as you note, it's environmentally friendly and easy to get hold of! Perhaps more to the point, its boiling point/temperature properties are not bad at all in the range of say 50 to 70 F for the evaporator and 210 to 240 for the condenser. One would need a different refrigerant for the low temperature first stage -- ideally something which had a reasonable vapour pressure at perhaps -40 to -50 F and not an outrageous pressure at the 50 to 70 F condensing temperature.

I might point out that almost all present heat pumps for residential or commercial use are single stage and do well with a temperature spread of less than 100 or so, low to high, and function, though not as well, in some cases with as much as a 140 degree spread. That's pushing the pressures pretty far though. The two stage would have less demand on the pressures and therefore should have better performance (i.e. better COP). The two stage scheme I have in mind would have the second stage with a difference of 150, which is a bit extreme -- but the thermodynamic properties of water, which are decidedly strange, appear to make that feasible at good efficiencies. The first stage, using non-polar more conventional refrigerants, would be limited to a maximum differential of 120, to keep the performance up.

I have even toyed with the idea of using the steam heat emitters -- the radiators -- in an existing system as the second state condensers. The problem there is in maintaining the low pressures needed in the evaporator; any system leakage would introduce air, and as my refrigeration/air conditioning/heat pump friends will tell you even a very small amount of non-condensable gas will kill your performance. And most steam heating systems do leak, at least a little!

Would I install such a system as an experiment? Indeed I would. In fact, I'd be delighted to try it. If someone like Mestek would take me up on it, I'd be all for it.

Jamie Hall

Let me add, though... I'd keep Cedric and a tank of oil as a backup!

Daveinscranton

The beauty of water, one of its many beauties, is all the places to put heat in the molecule.  And it loves to condense.  To move 1 gram of water 1 degree Celsius takes one calorie.  The phase change, which is why steam works, takes 540 calories to move 1 gram of water for the phase change to steam.  Perfect.  And it gives up that heat in our radiators.

There are many other working fluids.  But none so beautiful as water.  The alcohols would work but are problematic.  Mercury would work.  Higher temperatures and lower pressures for mercury.  Under the right conditions.  But these are posed as a counterpoint to water.  Safe, non toxic, well behaved, cheap, no environmental concerns, not terribly corrosive.  Water, brought down in boiling point by vacuum, to the other half of the heat pump technology, brought up above, by Jamie, is doable.  Soon too.  Maybe with polymer returns.  Assuming the engineering was done right.  Coefficients of piping materials linear expansion that are problematic notwithstanding, maybe easier to hold a vacuum.  Like with plastic welds.

Could happen in our time.  I would love to see a rebirth of steam.  Maybe at 100-150 degrees Fahrenheit.

Interesting topic.  The thermodynamics should work.

ChrisJ

Daveinscranton said:

The beauty of water, one of its many beauties, is all the places to put heat in the molecule.  And it loves to condense.  To move 1 gram of water 1 degree Celsius takes one calorie.  The phase change, which is why steam works, takes 540 calories to move 1 gram of water for the phase change to steam.  Perfect.  And it gives up that heat in our radiators.

There are many other working fluids.  But none so beautiful as water.  The alcohols would work but are problematic.  Mercury would work.  Higher temperatures and lower pressures for mercury.  Under the right conditions.  But these are posed as a counterpoint to water.  Safe, non toxic, well behaved, cheap, no environmental concerns, not terribly corrosive.  Water, brought down in boiling point by vacuum, to the other half of the heat pump technology, brought up above, by Jamie, is doable.  Soon too.  Maybe with polymer returns.  Assuming the engineering was done right.  Coefficients of piping materials linear expansion that are problematic notwithstanding, maybe easier to hold a vacuum.  Like with plastic welds.

Could happen in our time.  I would love to see a rebirth of steam.  Maybe at 100-150 degrees Fahrenheit.

Interesting topic.  The thermodynamics should work.

You need to be careful with the wording.

Many on this forum are under the impression the energy water absorbs to change to steam is lost forever and is why it's "inefficient" when in reality 100% of that energy comes back when it condenses.

Daveinscranton

100% comes back in the reverse phase change, steam to water (liquid).  The phase change is exploited to convey heat.  It is perfect.

Jamie Hall

Glad to see @dabrakeman likes my choice of working fluid for the second stage! As I noted -- and so did he -- water is really strange stuff, with very helpful thermodynamic properties right in the pressure and temperature ranges we need. Handy.

And yes, @ChrisJ is quite right -- there are a lot of people on the Wall, never mind out on the street, who have absolutely no idea at all why heat transfer through phase change works -- i.e. steam heat. Even though I suspect there are very few of them who don't have a mechanical refrigerator... or air conditioner... or heat pump...

But then, I had an aunt once who was convinced that you had to put a cap over a wall plug or the electricity would leak out onto the floor...

SteamingatMohawk

Your choices of the term "comes back" is confusing.

ChrisJ

SteamingatMohawk said:

Your choices of the term "comes back" is confusing.

You get the energy you put into creating steam back. It comes back, doesn't go into space never to be seen again.

Nothing was lost.

Though, I am having trouble understanding entropy when it comes to phase change. It's a bit above my head and I cannot tell if there are minute losses, or if they are returned as well.

If anyone who actually knows wants to comment that would be great.

ChrisJ

@rhodebump I've literally wanted to build a hermetically sealed steam system for years now.

I'd think building one that's a heat pump where the radiators are the condensers could work just fine as well.

Of course, I'm not talking about using 100 year old cast iron radiators and leaky valves. It would need to be a completely new creation.

It would be a beautiful thing........
And I'd bet, if you built it correctly it would last a very long long time without any problems or attention.

Jamie Hall

ChrisJ said:

@rhodebump I've literally wanted to build a hermetically sealed steam system for years now.

I'd think building one that's a heat pump where the radiators are the condensers could work just fine as well.

Of course, I'm not talking about using 100 year old cast iron radiators and leaky valves. It would need to be a completely new creation.

It would be a beautiful thing........
And I'd bet, if you built it correctly it would last a very long long time without any problems or attention.

Not so sure about your last sentence there, @ChrisJ -- we seem as a society to be perfectly happy with mini-splits (which is what it would be, in a sense!) which last ten years or so. But yes, it would be a beautiful thing.

ChrisJ

Jamie Hall said:

ChrisJ said:

@rhodebump I've literally wanted to build a hermetically sealed steam system for years now.

I'd think building one that's a heat pump where the radiators are the condensers could work just fine as well.

Of course, I'm not talking about using 100 year old cast iron radiators and leaky valves. It would need to be a completely new creation.

It would be a beautiful thing........
And I'd bet, if you built it correctly it would last a very long long time without any problems or attention.

Not so sure about your last sentence there, @ChrisJ -- we seem as a society to be perfectly happy with mini-splits (which is what it would be, in a sense!) which last ten years or so. But yes, it would be a beautiful thing.

Are you suggesting it's impossible to build such a thing that would go decades without attention?

I'm not saying companies would do it now, or people would pay for it. I'm saying it's possible.

Matt_67

It could be done if the joints were all brazed and only sealed valves were on the system. It would have basically no leak tolerance though, as even a small leak would soon bring non-condensables into the system.

Jamie Hall

ChrisJ said:

Jamie Hall said:

ChrisJ said:

@rhodebump I've literally wanted to build a hermetically sealed steam system for years now.

I'd think building one that's a heat pump where the radiators are the condensers could work just fine as well.

Of course, I'm not talking about using 100 year old cast iron radiators and leaky valves. It would need to be a completely new creation.

It would be a beautiful thing........
And I'd bet, if you built it correctly it would last a very long long time without any problems or attention.

Not so sure about your last sentence there, @ChrisJ -- we seem as a society to be perfectly happy with mini-splits (which is what it would be, in a sense!) which last ten years or so. But yes, it would be a beautiful thing.

Are you suggesting it's impossible to build such a thing that would go decades without attention?

I'm not saying companies would do it now, or people would pay for it. I'm saying it's possible.

Certainly it's possible. Look at old refrigerators... question is, would people pay for it? and, related, is it the best overal=ll way to go? Lots to think about!

fentonc

@ChrisJ - This is how many heat sinks used on high-power computer chips work. It's something like a small sealed copper chamber (at low pressure, I think, to lower the boiling point) that contacts the chip on one side and a lot of fins with air blowing over them on the other side. The water continuously boils and recondenses, moving heat from one side to the other.

jumper

Industries thermocompressed steam to boost temperature. That is heat pumping.
Usually used a steam jet which is not energy efficient but can still conserve energy for some applications.
When energy became precious screw compressors were tried.
There's a lot of energy in flash steam and it can be utilised by compressing it to higher pressure/temperature.

Consider district steam supplied at medium pressure. If you can usefully wring 50° from condensate then you can reduce consumption by about 5%. Is it worth it? What's several $thousand$ per annum? At today's 1% interest owner may think $hundreds of thousands$. Or ten year payback. Or she may beg me not to call her anymore.

ayetchvacker

Jamie Hall said:

There is no theoretical reason why it couldn't be done. To make it feasible for heating in more northern climates, it would probably have to be two stage, to keep the pressures within a reasonable range on the equipment. But there's no theoretical reason why it wouldn't work. It's a matter of choosing the right refrigerants so that your high temp condensing temperature pressure and your low temperature evaporating pressures are reasonable. There would be good deal to be said for using water as the second (high temperature) stage refrigerant -- as you note, it's environmentally friendly and easy to get hold of! Perhaps more to the point, its boiling point/temperature properties are not bad at all in the range of say 50 to 70 F for the evaporator and 210 to 240 for the condenser. One would need a different refrigerant for the low temperature first stage -- ideally something which had a reasonable vapour pressure at perhaps -40 to -50 F and not an outrageous pressure at the 50 to 70 F condensing temperature. I might point out that almost all present heat pumps for residential or commercial use are single stage and do well with a temperature spread of less than 100 or so, low to high, and function, though not as well, in some cases with as much as a 140 degree spread. That's pushing the pressures pretty far though. The two stage would have less demand on the pressures and therefore should have better performance (i.e. better COP). The two stage scheme I have in mind would have the second stage with a difference of 150, which is a bit extreme -- but the thermodynamic properties of water, which are decidedly strange, appear to make that feasible at good efficiencies. The first stage, using non-polar more conventional refrigerants, would be limited to a maximum differential of 120, to keep the performance up. I have even toyed with the idea of using the steam heat emitters -- the radiators -- in an existing system as the second state condensers. The problem there is in maintaining the low pressures needed in the evaporator; any system leakage would introduce air, and as my refrigeration/air conditioning/heat pump friends will tell you even a very small amount of non-condensable gas will kill your performance. And most steam heating systems do leak, at least a little! Would I install such a system as an experiment? Indeed I would. In fact, I'd be delighted to try it. If someone like Mestek would take me up on it, I'd be all for it.

I’d love to buy you lunch someday! I daydream about stuff like that all the time. 

ChrisJ

fentonc said:

@ChrisJ - This is how many heat sinks used on high-power computer chips work. It's something like a small sealed copper chamber (at low pressure, I think, to lower the boiling point) that contacts the chip on one side and a lot of fins with air blowing over them on the other side. The water continuously boils and recondenses, moving heat from one side to the other.

Those are heat pipes and yeah very much so. You can use different liquids to change the performance etc.

I believe most have a wick in them to return the water as well if they're upside down or not perfectly downhill.

rhodebump

Thank you for all your thoughts. I am going to give everything a read a couple of times to try to absorb everything. I think we all on the same page that the properties of steam heating is something we love and hope that future technology can make use of.