Theory time.

AMservices

Canucker said:

There is a practical limit to how much vacuum you want in a heating system. Too much vacuum will lower the boiling point to a level that won't heat the room. The rads will be warmer than the steam in the system, possibly causing them to sweat. At that point you've got AC using R-718 refrigerant

Radiant Cooling. The Germans are already doing it. Do you think the radiators would condense much past a relative humidity of 50%? Might as well redesign a radiator while we're at redesigning the whole steam system.

ChrisJ

The radiators aren't going to sweat because there's nothing to keep them cold. The water will turn into a gas and stay that way.

In order for them to sweat, you would need a way to pull a lower pressure on them, not happening in a steam system. Once the water evaporated, it's staying that way, forever. Pressure will never drop lower than the house's temperature allows.

Canucker

@ChrisJ I'm trying to picture the systems I work with. I believe @Charlie from wmass wanted to use a vac pump to lower it? If you're only using the pump to lower the pressure once, then sealing it off, you're correct, it won't condense, there's no where for the evaporate to go. Now, if you have to keep opening a valve to top up the vac level, then the gas has somewhere to go and it will start to lower the temperature of the system, I've watched it happen.

ChrisJ

Canucker said:

@ChrisJ I'm trying to picture the systems I work with. I believe @Charlie from wmass wanted to use a vac pump to lower it? If you're only using the pump to lower the pressure once, then sealing it off, you're correct, it won't condense, there's no where for the evaporate to go. Now, if you have to keep opening a valve to top up the vac level, then the gas has somewhere to go and it will start to lower the temperature of the system, I've watched it happen.

Agreed, under those conditions.
Personally, I'd want a 100% sealed system, no pump after initial pull down.

Charlie from wmass

I was assuming that the vacuum pump would need to be occasionally reuse in order to purge air that enters the system through leaks. Obviously the system would be maintained in order to minimize such leaks.

Canucker

So there is a limit to how much vacuum you'd want. I don't see how boiling the water @ 32F would be much use to you. Would adjusting the boiling point with vacuum based on the OAT you need to heat the building be useful? (I'm glad this is theoretical because we're adding a lot of moving parts to this simple steam system. lol) It's a fascinating mental exercise, to be sure. I'm glad you posted it @Charlie from wmass

jumper

I can assure you from experience that you won't buckle even a soft copper tube with vacuum. Toronto had ventless steam heating systems. A vacuum generator periodically evacuated air. You could call them one pipe although terminals usually had two connections (overhead distribution). At least one building used only one terminal connection. There were issues in that one for reasons now not known.

The terminals had louvers/dampers for control. I suppose that today the one with two connections could be modulated with a two pipe type TRV.

If I wanted to try this in a house with radiators,I'd start with a HW home. Old HW homes get flooded when pipes rust through,so the homeowner is motivated to replace pipes. I'd run new supply with TRVs to top of rads. Maybe use the old air vents? Probably I'd manifold in boiler room like modern radiant and use small flexible like Igor does. At worst the homeowner doesn't have to worry about flooding anymore.

Charlie from wmass

You're now entering iron fireman territory.

SWEI

ChrisJ said:

pull deep vacuum, fill with water and then top off with argon, nitrogen, helium etc to raise the pressure to what I want to boil at.

If it's truly sealed, the oxygen will passivate into the metal in a few weeks and you'll end up with mostly nitrogen anyway.

ChrisJ

SWEI said:

ChrisJ said:

pull deep vacuum, fill with water and then top off with argon, nitrogen, helium etc to raise the pressure to what I want to boil at.

If it's truly sealed, the oxygen will passivate into the metal in a few weeks and you'll end up with mostly nitrogen anyway.

Eh?
Oxygen will passivate into the metal and become nitrogen?

Huh?

DanHolohan

AMservices said:

The condensate can drain back through the steam, but air won't.

Gravity applies to air as well as to water. Steam will always rise higher than air. And if the steam goes up, the air must go down.

AMservices

I asked Igor if the he really needed vacuum lines and why pulling a deep vacuum wasn't enough. That's when he explained to me that the air not removed from the vacuum pump would be pushed further into the radiators and without having a vacuum line pulling from the top and the pump coming back on mid cycle to remove the air only part of the radiator would Heat. He told me he had seen this with his own eyes in the lab test.
Having the vacuum lines was also why Paul's system work so well.
I just didn't see air slipping past steam. I thought one people raise the pressure they were just compressing it deeper into the system.

Charlie from wmass

If the gravity did not apply to the air then the air vent would need to be at the bottom of the radiator not two-thirds of the way down. Where do you think the rest of the air goes after the air vents close?

AMservices

If the system runs long enough like on a design day and the radiator Heats all the way across, then I would think that the steam has compressed the air towards the lowest point of pressure.
Is there always a cold spot in the bottom corner opposite the supply valve?

Charlie from wmass

I was thinking that replacing the radiator valve with a full size radiator elbow may allow for better flow of air and steam

Charlie from wmass

I have not found there to be a cold spot except for on two pipe systems where supply and return we're on the same end of the radiator. I found that in these cases if I raise the far end of the radiator it heated more thoroughly

AMservices

So you think then the air will drain like condensate back to the boiler and your pump?

ChrisJ

https://en.wikipedia.org/wiki/Heat_pipe

Charlie from wmass

It may require a baffle in the elbow and the radiator Spud. Like vent Rite uses in their air vent

Charlie from wmass

This may also require a different style of pump to produce the vacuum than what is used for refrigeration work. More like the pumps that @pumpguy produces

Charlie from wmass

The hard part would be having controls that would have an algorithm based on system pressure vs. Outdoor air temperature. For the sake of this discussion negative pressure i.e vacuum is still pressure.

Charlie from wmass

So pretty much what Chris listed only on a grander scale

AMservices

An oil free vacuum pump. So the oil doesn't become saturated.
If you're going to use a mechanical pump why not just run vacuum lines? I think you'll have an easier time getting the results you're looking for

Charlie from wmass

But they already make water and Venturi based vacuum pump. They just don't make them small enough for most residential systems.

Charlie from wmass

I was also thinking that receivers for vacuum pump systems are made out of cast iron so that they do not collapse unlike the standard condensate receiver tanks which are made out of steel.

Jamie Hall

Optimists... I honestly think that you will have real problems maintaining a sealed system at any kind of real vacuum in the real world! But most of the theory is reasonable... and there were, of course, vacuum systems of various flavours, back in the day.

On the oxygen passivation -- what will happen (assuming your system really is sealed!) is that the oxygen will combine with the iron, leaving the nitrogen -- which is about 80% of the air -- behind.

ChrisJ

Jamie Hall said:

Optimists... I honestly think that you will have real problems maintaining a sealed system at any kind of real vacuum in the real world! But most of the theory is reasonable... and there were, of course, vacuum systems of various flavours, back in the day.

On the oxygen passivation -- what will happen (assuming your system really is sealed!) is that the oxygen will combine with the iron, leaving the nitrogen -- which is about 80% of the air -- behind.

Copper it is.

izhadano

Hello everyone,
not long ago I've started a thread which may resolve some of your concerns:
boiler/tube/radiators collapse under vacuum
getting perfect vacuum, etc.
Perfectly sealed system, newly installed, would run with very seldom vacuum pump help, but it's doubtful that piping/radiators in retrofitted old steam system can make this.
Also, pulling air from each radiator would help to heat system evenly. If you pull the air from main only, vapor will push the residual air into radiators and block it there when boiler starts.
Hope this help.
Igor

SWEI

ChrisJ said:

SWEI said:

ChrisJ said:

pull deep vacuum, fill with water and then top off with argon, nitrogen, helium etc to raise the pressure to what I want to boil at.

If it's truly sealed, the oxygen will passivate into the metal in a few weeks and you'll end up with mostly nitrogen anyway.

Oxygen will passivate into the metal and become nitrogen?

Huh?

In a sealed system, the ~21% of air that is oxygen will combine with various materials in the system, leaving mostly nitrogen along with a percent or so of argon. As long as the system remains sealed there is just not enough in there to worry about.

ChrisJ

SWEI said:

ChrisJ said:

SWEI said:

ChrisJ said:

pull deep vacuum, fill with water and then top off with argon, nitrogen, helium etc to raise the pressure to what I want to boil at.

If it's truly sealed, the oxygen will passivate into the metal in a few weeks and you'll end up with mostly nitrogen anyway.

Oxygen will passivate into the metal and become nitrogen?

Huh?

In a sealed system, the ~21% of air that is oxygen will combine with various materials in the system, leaving mostly nitrogen along with a percent or so of argon. As long as the system remains sealed there is just not enough in there to worry about.

Yeah,
But in my design there is no air in it.
You pull a deep vacuum, lower than 500 microns and then fill with water and some inert gas.

Same procedure as doing refrigeration, only, with steam.

BobC

If this were done their could be no valves or vents of any type in the steam system. Any valve that would be truly leak proof would cost more than the boiler. That brings up another question is any boiler that tight, I'll bet no manufacturer will certify it to be so.

In any case for balance I think it's going to have to be a 2 pipe system, maybe with orifices for balancing. If you go through all of this will it be enough better than a minitube system to warrant the increased cost?

Bob

ChrisJ

BobC said:

If this were done their could be no valves or vents of any type in the steam system. Any valve that would be truly leak proof would cost more than the boiler. That brings up another question is any boiler that tight, I'll bet no manufacturer will certify it to be so.

In any case for balance I think it's going to have to be a 2 pipe system, maybe with orifices for balancing. If you go through all of this will it be enough better than a minitube system to warrant the increased cost?

Bob

Modcons with no pumps, no bladder tanks.

hvacfreak2

BobC said:

If this were done their could be no valves or vents of any type in the steam system. Any valve that would be truly leak proof would cost more than the boiler. That brings up another question is any boiler that tight, I'll bet no manufacturer will certify it to be so.

In any case for balance I think it's going to have to be a 2 pipe system, maybe with orifices for balancing. If you go through all of this will it be enough better than a minitube system to warrant the increased cost?

Bob

This.

For the topic of older systems it is probably best to forget the micron scale altogether ( or at least the 500 standard ) . I say to pull what you can , from wherever you can and let some vacuum vents do the rest ( radiator and main ). There may be a check device that would allow for use of traps ( or a Big Mouth ) as a main vent ( a modern anti-syphon valve for a vacuum pump maybe ). Anything to get close to a modern version of the old vapor systems would be interesting to see.

Regarding 1 pipe systems , I had a thought of dripping each riser into a steel tank to act as a seperator. The vacuum line from the top would end up at a manifold at the pump location , drain at the bottom to wet return. Thats still more work than running tube to each radiator though , lol. Another benifit of pumping from the radiators is that it is furthest from that vacuum - killing water level in the boiler ( water line in general ). But heck with it , pipe something up even if it's wrong to see something run in vacuum !!!

PMJ

I agree that planning on much tightness in an old system is a mistake. Having run a leaky old 2 pipe in light natural vacuum for many years I can say that even a little vacuum does a lot.

I have found with my system that when I close it up with the burner off and let it sink into vacuum the pressure is the same everywhere - there are no pockets of anything anywhere. I have measured the pressure in the dry return to be slightly lower than the header due to the fact that the boiler is still producing some steam as the pressure falls, and steam is still condensing in the rads - so the steam keeps moving into the rads even if slowly. And leaky system and all, there is shockingly little air to vent on next fire when you just don't let it back in. The only vent opening I have in the whole 1000 EDR system is one 1/2 inch solenoid valve in a remote part of the dry return out of which there is never enough air coming to hear anything.

I have discovered that venting has only to do with getting out air that you let back in. It really isn't a cold start issue at all. On cold start it takes way longer to heat pipes up than to vent the air so a really small vent will do for that. Once hot though, all that air you let in each time is in the way and has to get out quickly - every cycle because the steam can move fast in already hot mains if all that air wasn't in the way.

If I had a one pipe system I would be trying closing up everything and replacing rad vents with check valves. I don't see why it wouldn't work basically like my 2 pipe. The only difference I see really is that I get to do it all with one check valve and the 1 pipers have to check every rad. Unfortunately a lot of checks to buy and maintain- and one bad one would spoil the whole party.

ChrisJ

Wouldn't work on my system, it'd likely cause severe balancing issues, especially on my two 50% oversized bedroom radiators that are mostly off most of the time. Actually, my bedroom is usually ice cold, and when it does heat, just a few sections out of 20.

The Steam Whisperer

Way up near the top of this topic was a comment saying there are no controls for a variable vacuum heating systems. There have been and I understand still are prepackaged systems and controls for this type of operation. The Webster Modulation system was one I have seen alot here in Chicago....was very popular with the Roman Catholic Diocese I believe. The old versions of these systems ( about 100 years ago) were all mechanical. I think there are at least 2 or 3 manufacturers of these variable vacuum control systems today.

Charlie from wmass

I have seen the Webster controls with outdoor reset, but they were original to the systems and no longer functional, just steam punk wall art.

ChrisJ

The Steam Whisperer said:

Way up near the top of this topic was a comment saying there are no controls for a variable vacuum heating systems. There have been and I understand still are prepackaged systems and controls for this type of operation. The Webster Modulation system was one I have seen alot here in Chicago....was very popular with the Roman Catholic Diocese I believe. The old versions of these systems ( about 100 years ago) were all mechanical. I think there are at least 2 or 3 manufacturers of these variable vacuum control systems today.

I really wish you'd get more involved in the pickup factor wars on the forum.

Then again, maybe you're just smarter than I am and have realized it's a waste of time. Hmmmm.

Sailah

The Steam Whisperer said:

Way up near the top of this topic was a comment saying there are no controls for a variable vacuum heating systems. There have been and I understand still are prepackaged systems and controls for this type of operation. The Webster Modulation system was one I have seen alot here in Chicago....was very popular with the Roman Catholic Diocese I believe. The old versions of these systems ( about 100 years ago) were all mechanical. I think there are at least 2 or 3 manufacturers of these variable vacuum control systems today.

I am working on one now. Would only make sense in a large building due to the controls needed. The prepackaged units operate on a proprietary system that is very outdated.

Our new version of this is in specific response to large public housing projects in NYC. It eliminates the proprietary controls and allows interface with standard BMS protocols.

Integrating all the sensors required is a daunting task but we are leveraging the very newest Internet of Things (IOT) radios to enable fairly simple retrofits without running a lot of wires.

Hatterasguy said:

Are they available with outdoor reset capability to vary the vacuum based upon the heatloss of the building? That's really what is required off the shelf.

Yes that's what we are addressing in our new Vari Vac system. I'll post more details when I am able

Steamhead

Dave, I think you mean the Webster "Moderator" control system. The "Modulation" system was basically a standard Vapor system that did not have a Return Trap.