21st century vacuum/vapor system?

SWEI

I've been toying with the concept of a 'modern retro' vacuum/vapor system based on

currently available (or easily fabricated) components.  It should be able

to be retrofitted onto an existing two-pipe pressure system, and

may also be useful in rehabilitating vintage vacuum/vapor systems which

have suffered from knuckleheading.



Is anyone doing this now?  How feasible is it?





thanks, all~

jumper

depend how tight system is

It would not be that expensive to try the following. Replace the radiator trap cartridges with some sort of labyrinth or orifice device. Then mechanically evacuate air from system. Vapor moves from boiler to terminal, condenses, and hopefully condensate finds its way back to boiler. You can't use vented components like those combination vacuum condensate pumps. Best to avoid pumps and go for generous B dimension.



Nobody will promote such a system because there's nothing to sell. Steam trap salesman will hate you and accuse you of being energy inefficient. Perhaps somebody working for GEM could give a professional opinion.

ChrisJ

Not me

I'm just learning how to make TRVs work, I'll leave vacuum and vapor to the more experienced guys for now. 

Eastman

new vacuum systems

I feel like a modern vacuum system should leverage higher distribution pressure deltas.  The supply and return lines need to shrink to the point where flex copper or composite plastic can be utilized.



I would think such a system should be capable of holding a much harder vacuum.  Then perhaps a mod/con can be utilized via some kind of improvised indirect steam generator.

SWEI

cutting edge

clean sheet designs are interesting for sure.



I'm really looking for a way to improve existing two-pipe systems -- something along the lines of what Hoffman describes in 'How to Lock Out Air, the Heat Thief.'   In that era, systems were built with the expectation that over time, progress and upgrades would happen to them.  I'd like to see some of that progress.



Surely there is some currently configurable arrangement of pipes, valves, and traps which will deliver a working vapor/vacuum system?

Rod

Shop Vac Vapor

Hi- The only way a modern vacuum steam system would be practical is if it was built from scratch along the lines of Gerry Gill's mini tube system. This has very small system internal volume so you wouldn't need a large vacuum pump setup. As tracing down and finding vacuum leaks is a"bear" I question whether it is worth the trouble in these old systems. The best line of thought I've come across in a while was in a post in the middle of Jan 2012. Read down to where Terry talks about using shop vac as a vacuum source.

http://www.heatinghelp.com/forum-thread/139813/Another-Look-at-Vapor-Vacuum

A shop vac will remove a lot of air quickly and will produce about 4 to 6 inches of vacuum.

This is equivalent to a negative 2 to 3 PSI of vacuum which gives you a nice pressure differential for steam distribution. It would seem to me that this would offer a low cost way to increase the efficiency of a 2 pipe system

- Rod

Steamhead

The only objection to a shop-vac

is the noise level. But there has to be a quieter pump we can use. The pump would need some setup to catch any water that got to it and return it to the boiler. Dunham even marketed such a pump for residential use, as part of its DH differential-vacuum system. You can find it in their #414 Handbook.



Don't forget, a lot of Vapor systems had only one central air vent. This meant only one interface between the system and the atmosphere, which made it pretty easy to form a vacuum.



Also don't forget that pumps use electricity, which increases the system's total energy consumption. Whether or not this offsets any fuel savings has yet to be determined. We have to keep reminding the mod-con people of this, so we shouldn't make the same mistake.

SWEI

vacuum pump

would be great to avoid if possible.  Look what Dunham, Hoffman, and Trane did without them.



Phase two probably involves weather-responsive control of vacuum, which may require a pump.  I'd like to see the basic system work using minimal electrical power and computer/complexity.

ChrisJ

How tight?

Heres something I don't understand.

Ok so an intermittent system like we use today may have trouble forming a vacuum on the first time.  So what?  Fire it up a few times and deal with the issues until she builds a good vacuum, shouldn't take long.



Next, why can't we keep a vacuum?   Build a mini tube system using all copper tubing and solder it at every joint.  I doubt you will have any leaks if done properly and this means once you get the vacuum, you've got it.  This means also soldering directly to the radiators, no threaded adapters anywhere.  Any threaded connection risks a leak sooner or later while soldering or brazing (even better) will not.  Put a quality ball valve in between the system and the vacuum vent so you can be assured the cheap little metal check valve won't loose your vacuum.

Of course this means building a NEW steam system, but you did say a 21st century system.

SWEI

NEW steam systems

are just not going to happen in our part of the world, other than for industrial applications, and even those are taking a big hit from thermal oil.

 

Eastman

What type of retro features are you looking for?

Because there have been a number of threads over the years dealing with two-pipe vapor systems, and it sounds like a more or less solved problem.



For example, in the thread Rod linked to, PMJ seems to have really licked the issue.  It sounds like he has implemented a modern solution, similar to a superior hybrid of two vacuum control techniques discussed in "Six Kinds of Steam Heat."  (Yes that article is for one-pipe but I think the ideas carry over.)

JStar

Vacuum pump

I'm on the road right now, and really wanted to try this in our shop first...maybe I'll have some spare time today to experiment.



Build a gas power burner with an air pump where an oil pump would normally be on the gun. Use the air pump to pull a vacuum every time the boiler runs. The only nuance is relieving excess vacuum while a call for heat still exists. Maybe a solenoid and bypass to a relief valve? The pump could even run without the burner sparking or energizing the gas valve.

Ban

For oil,

This idea sounds interesting. I have natural gas though. I am planning on putting my system into a natural vacuum by this Sunday--hopefully. Toying around with the idea of pumps though, How do you control the vacuum amount? How did they control the vacuum amount in the past? How should we do it in the future?

ChrisJ

Dumb question

But is it theoretically possible to collapse the system if the vacuum is too high?  I assume it is so my other question is, is it realistically possible? I would assume cast iron radiators and steel pipe can handle an insane amount of vacuum.

SWEI

quite possible

but a simple vacuum breaker set at 20 inches or so would take care of it.

ChrisJ

20 inches

Wouldn't the system need a way to control vacuum relative to outside temperature?  More vacuum on warmer days, less on colder?

SWEI

vacuum control

Yes, that would be ideal (see phase two.)  The mechanical vacuum breaker is a safety device (like the manual reset pressuretrol) just in case the controls run amok.

Mark N

Under pressure

The vacuum doesn't crush the pipe, it is the pressure on the outside that crushes the pipe. At sea level the pressure is 14.7psi. Adding a few inches vacuum in a steam pipe won't matter. Other places become the weak points. The valve packing, the gauge glass, the fittings. I doubt you could draw enough vacuum for the pressure to crush cast iron. The air would leak in at the weak spots first.

jumper

vapor goes to cold

If there is no air the steam naturally rushes to terminals. You don't need any differential pressure between supply and return. Condensate returns by gravity. That's why I suggest replacing radiator traps. As to what pressure to evacuate to: use a steam table. When pressure equals saturated steam pressure the air has been evacuated.



My suggestion is not original. Steam coils are sometimes piped along this line of thinking.



I also like the idea of using soft copper. If you don't trust brazing, look into flare fittings.

Eastman

Yeah

Theoretically, the hardest vacuum you could create would still only amount to sea level pressure.  I can't imagine anything of consequence being damaged.

SWEI

right

wouldn't collapse healthy pipes -- it's the old, rusty ones I worry about.

Eastman

if there is no delta p...

Then there is no transport.

Eastman

If the pipes can't handle 14 psi...

Then shouldn't they really be removed?

jumper

colder is lower pressure

Steam cools in radiator. Cooler steam has lower pressure. A lot lower if it condenses. That's the delta P you need, Eastman. Otherwise how does one pipe steam work ?

Eastman

I agree

I agree.  But there is a system delta.  And vacuum systems don't necessarily have lower deltas then non-vacuum systems.  Gerry's mini-tube system demonstrates the advantages that high pressure differentials can bring.

PMJ

Never too much vacuum

Mark is right - especially on old systems there are leaks and the vacuum is lost as air leaks in. You don't get as much vacuum as you wish you could. When the burner shuts off the amount of vacuum formed naturally is directly related to how full the system was with steam at the time - obviously the colder the day the more full it is. The most I see is about 40-50" of water which isn't really all that much. But on cold days I fire 3 cycles and hour - 10 min on/10 min off each until the call is satisfied. The 40" holds easily for the10 minutes and when the burner comes back on it takes about 2-3 minutes before all the vacuum is gone from the new expanding steam. The really nice thing is that you don't have all that air rushing in and out of the system each cycle.

I have thought about adding a pump but I doubt it would be worth the energy required to operate it. The free vacuum is hard to argue with though. And I wouldn't worry about uneven vacuum and pockets of air or anything. Since traps are rarely closed( and Mouats can't) the whole system is really just one big pipe and everything equals out. I have put vacuum gauges in many locations and they all read exactly the same. I didn't have any new balancing issues at all when I went to vacuum.

Eastman

PMJ

Are you still using a single vent on your system?

PMJ

Just one vent

Yes, just one on the dry return.

Eastman

Smart vent

Your "smart vent" (if you don't mind me calling it that) seems to be by far the best solution I've read about on heatinghelp for naturally induced two-pipe vapor systems.  Do you ever have firing cycles that remain sub-atmospheric?  Or does the system always crack open?

PMJ

Always cracks open on each cycle

I experimented with modulating the fire just with the main gas valve and could find a place where the rads were slightly warm and the system was just barely in vacuum (solenoid would open and close during the same firing). But with any significant demand the system will not be staying in vacuum. The more sophisticated stuff like modulation is interesting to be sure but I also really like the simple maintenance free stuff. I have one solenoid valve vent, one pressure sensor, and no rad vents. The vaporstat is set at about 1psi as sort of as a safety but I am never anywhere near that so it isn't used at all in normal operation. Very few items in this system to keep track of and maintain. I just spread out the firings with the PLC during the calls to ease the temperature up to the tstat cutout over a long period of time. It really evens things out.

Eastman

Here's what I'm curious about...

What I'd like to know...  Is why the system doesn't achieve a harder vacuum.  You mentioned that you feel there is no need for a mains vent.  But I can't help but wondering if that is promoting the mixing of steam with air, and reducing the potential for a deeper vacuum.  I'm not thinking about system balance, just the potential for keeping steam and air separated.  I would think allowing the mains to fully vent, and then triggering your return vent, would maximize the removal of air.

PMJ

more vacuum

I really think it is just the leaks. Didn't Dan write in one of the books that steam and air won't mix? Anyway, I am pretty convinced that it is just the leaks in a 90 year old system. All 40 plus inches will be completely gone in about 1-1/2 hours if there is no call for that long.

PMJ

more vacuum

I really think it is just the leaks. Didn't Dan write in one of the books that steam and air won't mix? Anyway, I am pretty convinced that it is just the leaks in a 90 year old system. All 40 plus inches will be completely gone in about 1-1/2 hours if there is no call for that long.

Eastman

I haven't read any of Dan's books

But that rings hyperbolic.  All gases diffuse.  The lower the density the more diffusion is relevant.  However, if your loosing total vacuum in an hour and half, sure sounds to me like you're right.

jumper

gasses diffuse

I agree with Eastman, even though Holohan's expertise is awesome. Pushing air with steam must be very inefficient. Especially when the motive gas is half the molecular weight of air and the motive pressure is only slightly higher.



It seams to me that less piping is better in respect to air leaking in. So my 21st century system would be one pipe. For balance and control I'd use enclosures with adjustable dampers or some such. Greening Steam deals with enclosures somewhat.