Insane? heating concept -- PMJ? Icarus? Dan?

Jamie Hall

While swapping concepts with @Icarus the other day, and thinking about Things In General in the middle of the night (old folks do that) I came up with an idea which I'd be interested to see followed up. Perhaps @PMJ might be interested. Perhaps @DanHolohan has a contact or two... perhaps one of the folks at Caleffi ( @hot_rod ?) or... who knows.

Anyway.

In brief. We all may be facing a situation where fossil fuel becomes more expensive, if available at all. And there are a lot of steam heating systems out there, as well as a number of uses for steam in process applications. However, while there are electric boilers available, their electricity use is high (no surprise) and, while the local efficiency is great the overall efficiency from generation to point of use is not.

Heat pumps have two problems: they mostly have a limited temperature rise and, worse for heating and process, the output so far at least appears to be limited to hot air or hot water.

The concept I have needs a lot of research, however, in a thmbnail sketch. I am envisioning a two stage heat pump. Stage one, for which I don't have the refrigerant in mind at all, would operate between a cold side source temperature of -30 Fahrenheit and a hot side condensing temperature of perhaps 100 Fahrenheit. But here's the gimmick: stage 2 would operate between a cold side source temperature of perhaps 100 Fahrenheit and a hot side condensing temperature of 212 to 240 Fahrenheit -- and the refrigerant would be water. In a heating system retrofit, the "condensers" would be ... Radiators! suitably refitted with pressure control devices (our familiar orifices or orificed valves might work; traps? probably not); for process steam wouldn't need them.

Thoughts, anyone? Outrageous? Criticisms (such as "you're daft, Brother") welcome...

STEVEusaPA

Flux capacitor would be easier.

Larry Weingarten

Hi @Jamie Hall . The heat pump I mentioned here: https://forum.heatinghelp.com/discussion/181998/heat-pumps-for-hydronics#latest seems to do much of what you describe, but only gets to 180F. Maybe it's a start on a not-so-crazy idea.

Yours, Larry

Jamie Hall

Thank you for that reference, @Larry Weingarten -- it's that first stage that does the heavy lifting.

I really think there may be something to look at here.

ChrisJ

STEVEusaPA said:

Flux capacitor would be easier.

That's a Mr Fusion..............

ratio

That must be where all the electricity is going to come from once they finish outlawing fuel burning appliances.

PMJ

@Jamie Hall , I appreciate the invitation to comment. I am no heat pump or refrigeration expert and so would have little to offer without some study. I celebrate the consideration of new ideas in any form though so please carry on. I will join in technically if I feel I have something to offer.

Solid_Fuel_Man

So say you have a mechanical positive displacement compressor which raises the pressure of this 100 degree water to over the boiling point. 

What kind of pressures are we talking about for the radiation? 

Problem seems the second stage "refrigerant" would need to already be a gas and by raising the pressure forcing it to change states. 

Water isnt a good refrigerant at all as it doesnt readily change from a liquid to a gas unless under a vacuum. 

But I may be missing something.....

STEVEusaPA

ChrisJ said:

STEVEusaPA said:

Flux capacitor would be easier.

That's a Mr Fusion..............

Mr. Fusion coffee maker..

Solid_Fuel_Man

Hey it was the 80s. Black&Decker was king of Mr.Fusion!

Jamie Hall

Actually, @Solid_Fuel_Man , it isn't immediately obvious, but (partly inspired by some of @PMJ 's work, despite his disclaimer!) this is the concept.

The first stage would be designed to work from normal outdoor air temperatures -- between, say, -30 F and 60 F. As any heat pump does, the refrigerant would be chosen to evaporate at some reasonable pressure (which depends on the refrigerant). As usual, it would be compressed and then, through a pressure control device, condensed at that higher pressure -- and at the high stage temperature, which could, conveniently, be around 120 or so. It would transfer that heat to the next stage refrigerant: water. Water, it is true, isn't usually thought of as a refrigerant, but only because in normally useful temperature ranges it is one only at a vacuum. At any rate, the water at that point would be at a pressure of about 1.5 psi absolute, or about 25 inches of vacuum in the old mercury standard. This, I would note, is a quite achievalble vacuum. The vapour would then go through the second stage compressor -- or vacuum pump, if you like, and be compressed to around 15 psi absolute, which is the pressure most steam systems run at. It would pass the system condensers, which may term "radiators", and then complete the cycle to the evaporator.

You do make two good points: first, the second stage refrigerant would be a gas -- water vapour -- when it passed to the compressor (vacuum pump), as it would be evaporated by the heat produced by the condensing of the first stage refrigerant (and, as a result, the first stage heat pump could be regarded as doing the heavy lifting). And, of course, you are quite correct that water doesn't readily vapourize at normal temperatures -- unless under a vacuum. But why shouldn't it be under a vacuum? It can, and should be.

The output of the heat pump would be water vapour at somewhere around 212 F. Steam, in other words. And the system, as envisioned, would drop quite conveniently into any perfectly ordinary two pipe steam system (particularly vapour systems), needing only alterations to the input metering at the radiators.

And stopping up vacuum leaks... !

I might add that there are extensions possible: by operating the system at lower pressures (again, with a nod to @PMJ ) one could modulate the system to better match the building load, for instance.

Solid_Fuel_Man

Seems quite feasible. I was also picturing pretty much the entire system in a vacuum, or less than atmospheric conditions. 

Problem I see practically is that nature abhors a vacuum, and maintaining one with all the pipework etc would be a challenge. And if air (non condensibles as we call them) then it seems we would need a system or air removal in the subatmospheric system. 

PMJ

Nature doesn't mind my vacuum so much I guess. Nearly 100 year old piping I've done very little to. Attached is what pressure looks like in my system - and this is on a really mild day. I spend very little time at a max of atmospheric. The rest all negative and effortless - no pumps. Even showing a setback here which took 3-1/2 hours to dissipate.

I think the vacuum part is actually quite possible.

ChrisJ

All copper and brazed like I've been saying for 5+ years.......

Jamie Hall

Both compressor/vacuum pumps would actually be quite large -- you're handling a fair amount of refrigerant.

To @Solid_Fuel_Man 's point just up there, once the initial air were removed from the system and you have the leaks fixed, air is not a problem (as @PMJ notes).

It's really not that unconventional -- the only really off the wall part is the idea of integrating an existing steam heating system into it as the condenser section of a heat pump -- and using water at subatmospheric pressure as the "rerigerant".

ChrisJ

You don't need vacuum pumps once the system is charged...

hot_rod

there are HPs claiming 160F with Co2 refrigerants, getting closer.

Would money be better spend upgrading the structure so the rads could work at lower temperatures? Instead of trying to drive the heat pumps to those "steam" temperatures?
Probably 80% of the years the radiators would not need steam temperatures to cover the loads..

Jamie Hall

ChrisJ said:

You don't need vacuum pumps once the system is charged...

Actually, at least in this concept, you do. Remember that heat pumps and allied whizbangs -- refrigerators, air conditioners, and the like -- rely on the difference in boiling point of the refrigerant at various pressures to transfer heat. In all of these gadgets, heat is put into the system at a low pressure in the evaporator, vapourizing the refrigerant. That vapour is then compressed, and passed to a condenser where, since the pressure is higher, the refrigerant will condense and release that heat and return as a liquid to the evaporator. Rinse and repeat. But the compressor has to be there to create and maintain that pressure difference.

In a conventional steam system, the energy required to vapourize the working fluid is from combustion, and a small amount of additional energy is required to create a pressure difference to move the fluid. The temperature difference between the evaporator and the condenser is very small, so there is no need to establish a pressure difference by other means.

Jamie Hall

hot_rod said:

there are HPs claiming 160F with Co2 refrigerants, getting closer.

Would money be better spend upgrading the structure so the rads could work at lower temperatures? Instead of trying to drive the heat pumps to those "steam" temperatures?
Probably 80% of the years the radiators would not need steam temperatures to cover the loads..

Probably, where it can be done. One would need -- as @ChrisJ implied above -- to evacuate the existing system first, so you could operate the cycle at the lower temperature -- @PMJ has worked on this -- but once that is done if one can get the pressure right, it would certainly be simpler with a single step! Perhaps more significantly, with the addition of small vacuum exhaust connections -- perhaps in the manner of a Paul system -- one might be able to persuade one pipe steam systems to work, too.

Without getting into the politics of this -- that was never my job as an engineer, never mind now! -- it seems to me that some real creative thinking needs to go into this. Not for new construction, although creative thinking is badly needed there, too, but for handling the built environment and for process steam in a more efficient manner.

Jamie Hall

I might add, by the way, that I bring it up here on the Wall, as I know of nowhere where there is a bigger or better collection of really bright and creative people!

ChrisJ

@Jamie Hall.  I've been suggesting this for years in different forms.  But my idea had always had an all copper / brass system that's brazed and evacuated.   Very similar to a refrigeration system.

hot_rod

The power of vacuum at work here. A 30°ambient day water in a copper cup on an evac tube solar collector.

With old iron pipe radiator systems you would want to keep rust and crud out of the HP somehow, may need a HX between the systems.

Jamie Hall

hot_rod said:

The power of vacuum at work here. A 30°ambient day water in a copper cup on an evac tube solar collector.

With old iron pipe radiator systems you would want to keep rust and crud out of the HP somehow, may need a HX between the systems.

Good point, though I'm not sure but what that is less of a problem than might appear. If the condensate receiver at the low pressure end has a filter and enough volume...

That would be part of the practical application side of the work.

The problem @ChrisJ is looking at -- keeping "noncondensables" (air!) out of the system also needs some thought, but again I'm not sure that it would be necessary to go to the copper and brazing extreme. When one thinks about it, we keep saying that a gallon a month is pretty bad for makeup water -- and that implies that we expect even our old clunkers to be pretty darn tight!

ChrisJ

Jamie Hall said:

The power of vacuum at work here. A 30°ambient day water in a copper cup on an evac tube solar collector. With old iron pipe radiator systems you would want to keep rust and crud out of the HP somehow, may need a HX between the systems.

Good point, though I'm not sure but what that is less of a problem than might appear. If the condensate receiver at the low pressure end has a filter and enough volume... That would be part of the practical application side of the work. The problem @ChrisJ is looking at -- keeping "noncondensables" (air!) out of the system also needs some thought, but again I'm not sure that it would be necessary to go to the copper and brazing extreme. When one thinks about it, we keep saying that a gallon a month is pretty bad for makeup water -- and that implies that we expect even our old clunkers to be pretty darn tight!

Either do it right, or don't bother. 

Solid_Fuel_Man

Essentially what your guys are doing with vacuum steamers, is operating at "water" temperatures. 

Honestly, I dont see the huge advantage of steam then. The phase change is where you can fit more energy through a given pipe size. This negates the whole water vs steam arguement. 

Back to Jamie's idea. It would be interesting to see how much energy this would take. You could build a trial system by just using a low grade heat source to get your 100 degree water vapour. Then perfect and record the energy it takes to raise that to what you need for heating purposes. 

I always go down the path that many structures can be heated directly with 100 degree water! 

ChrisJ

Solid_Fuel_Man said:

Essentially what your guys are doing with vacuum steamers, is operating at "water" temperatures. 

Honestly, I dont see the huge advantage of steam then. The phase change is where you can fit more energy through a given pipe size. This negates the whole water vs steam arguement. 

Back to Jamie's idea. It would be interesting to see how much energy this would take. You could build a trial system by just using a low grade heat source to get your 100 degree water vapour. Then perfect and record the energy it takes to raise that to what you need for heating purposes. 

I always go down the path that many structures can be heated directly with 100 degree water! 

I do not believe lowering the temperature changes the latent heat of vaporization.  

Jamie Hall

ChrisJ said:

Solid_Fuel_Man said:

Essentially what your guys are doing with vacuum steamers, is operating at "water" temperatures. 

Honestly, I dont see the huge advantage of steam then. The phase change is where you can fit more energy through a given pipe size. This negates the whole water vs steam arguement. 

Back to Jamie's idea. It would be interesting to see how much energy this would take. You could build a trial system by just using a low grade heat source to get your 100 degree water vapour. Then perfect and record the energy it takes to raise that to what you need for heating purposes. 

I always go down the path that many structures can be heated directly with 100 degree water! 

I do not believe lowering the temperature changes the latent heat of vaporization.  

It doesn't. The latent heat of vapourization is the same.

What I am interested in here is some way which accomplishes two end objectives: first, assuming that one has to use electricity as the energy source, what is the most efficient way to go about doing that? Second, is there an approach which can be found which minimizes the cost of converting the existing built stock?

If it were possible to create steam -- that is, water vapour at 212 Fahrenheit -- in an energy efficient manner, then it could be essentially a drop in process (with appropriate sizing, of course) in every steam heated application -- whether space heating or beer kettles or whatever. Electric boilers accomplish the latter, and are available -- but they aren't drop in, as the electric power requirements are formidable (which is, of course, the problem with electric resistance heating in general).

Further, although some installations can be heated using low temperature water, most, I believe, cannot. And the practicality of converting what had been a steam system to hot water is poor, as has been discussed on the Wall many times.

I admit to some self-interest here; Cedric's home could not be converted to hot water, unless that water were very hot indeed (around 190 to 200), even if the piping and radiators could withstand the pressure -- which is unlikely -- and the flow velocities in the mains and returns would be unacceptably high. Placing new piping and enlarged radiation would be ferociously expensive -- we don't talk price, but think Lamborghini level budgets.

But Cedric is not unique. It's all very well to talk about new construction -- but there is a staggering amount of housing out there which is older, and where the tenants and landlords have no money in the budget to fix what's there, never mind switch to something else. There is another whole batch of housing where, for various reasons (in Cedric's case, historic preservation) where even if the money were there for, say, conversion to hot water, the cost of the conversion is impossible to justify.

Hence the reason for the quest: is there a way to take a steam heated structure or process and convert the steam source to run on electricity at an acceptable level of efficiency?

jumper

KISS. If they cut off your gas go electric radiant with thermostats in each room. Most of the time rooms are comfy at 55° because they're empty. Remember that purpose of heating is to make folks feel warm. As opposed to being warm. Which is why I favor steam heat in theory.

Jamie Hall

Just to take my own example... that's fine, @jumper . Cuts my power needs when they do outlaw oil from 500 amps 3 phase 408 to around 400 amps... neither of which is available.

ChrisJ

Jamie Hall said:

Just to take my own example... that's fine, @jumper . Cuts my power needs when they do outlaw oil from 500 amps 3 phase 408 to around 400 amps... neither of which is available.

You need 700,000 btuh continuous there?

Jamie Hall

When all the loads are added in... there are electrical loads, too -- this is a farm. Current service is 200 amp single phase 240 -- and is just barely adequate at times.

Matt_67

One of the challenges is the amount of power required for that first stage. It looks like Cedrick is somewhere around 300k into the radiators. We usually estimate about 3000 BTU / HP for low temp refrigeration so roughly 100 HP needed for that first stage when it’s really cold out. Maybe a bit less when heat of compression and perhaps more efficient equipment is taken into account. It’s going to take a pretty large electrical service to start that.

Jamie Hall

Matt_67 said:

One of the challenges is the amount of power required for that first stage. It looks like Cedrick is somewhere around 300k into the radiators. We usually estimate about 3000 BTU / HP for low temp refrigeration so roughly 100 HP needed for that first stage when it’s really cold out. Maybe a bit less when heat of compression and perhaps more efficient equipment is taken into account. It’s going to take a pretty large electrical service to start that.

Ah! Thank you, @Matt_67 ! Not being a refrigeration guy, that's the sort of information I really need!