Another Look at Vapor Vacuum

Dave in QCA

cracking pressure is low

In my case, the cracking pressure is less than an ounce. If the swing check was mounted vertically, it would take more to open it. Mounted horizontally, it requires next to nothing to crack the swing plate open far enough to allow venting to take place.

PMJ

Swing Check Cracking Pressure

Not trying to be argumentative Dave but I spent some time looking for check valves and couldn't find any as low as you say. Looking at a catalogue now for bronze check valves the lowest cracking pressure I see is 8 ounces. Did you put your gauge right before the check to see what it took to open it? Anyway the catalogue number is probably worst case so you are probably lower than that with your mounting as you say.

Since we are already at single digit ounces it seemed to me that every ounce of back pressure at the vent point I got rid of was significant. That is how I ended up with just opening the pipe with a solenoid valve. I never put a gauge there because I really don't hear anything coming out. Maybe I will just to see what it is.

Ban

I need more, I want more,

Vacuum! I can't seem to get more than 5 inhg. I am on a desperate quest for more and it has really made me look at the system precisely. I found leaks everywhere, just think if you were going to convert the 2-pipe steam to forced hot water, what a hot mess that would be. My strangest leak is in the casting of a radiator, a Burnham base board to be exact, which has not been repaired yet. Any suggestions on this in general? Any suggestions on the repair of the cast iron radiator leak?

nicholas bonham-carter

Missing check valve?

Shouldn't there be a check valve under the "ham", in a Dunham system?--NBC

nicholas bonham-carter

Much ado about nothing!

I noticed what seems to be a missing check-valve under your ham, as a result of studying all the Dunham literature, in preparation for re steaming my cemetery chapel Dunham system. In that system, the check valve was turned upside down, so I wonder-on purpose, or by accident. Also I wonder what purpose it serves.

I can see why they introduced the vacuum pump, as all the dry return piping will still have some air in there, unless some way could be found to briefly use steam to push out the air, and then cut off. An alternative could be a very large header on the boiler which could serve as an accumulator as the burner cuts off, and the system drops into vacuum.

Could a cheap air compressor serve as a vacuum pump?

This is now the most fascinating subject on the wall!!--NBC

nicholas bonham-carter

Deep vacuum

If the vacuum were deep enough, could the water in the wet returns boil?

I think we need a separate subsection for vacuum steam here-Dan?--NBC

ChrisJ

Yep

I'd love a section for vacuum systems.

If someone proves a single pipe system can work with vacuum I'd convert mine for sure.



I don't think our pets would be happy though. When the two cats and chihuahua hear the Gorton's chirping they all run for a radiator.

Dave in QCA

Interesting...

Nicholas, you bring up an interesting point that I had not considered before. However, in thinking about it, the wet return lines most likely would be at or about the level of the bottom of the boiler. The water at the bottom of the boiler as well as the wet returns would have a higher pressure then the water at the top of the boiler, which would be subjected only to the pressure of the pressure of the air/vacuum above the water. This would create a differential of about 1.8" Hg with the water on the bottom of the boiler and in the return lines being exposed to less vacuum or higher pressure. This is because of the weight of the water above. In this case, I don't think the water in the return line would boil with the exception of the top few inches in the point where the line drops below the NWL of the boiler.



Different vacuum systems are set up with different control scenarios. From what I understand, many of the current operating systems are simply set up so that the pumps start when the call for heat occurs and will continue to run until the vacuum drops to around 8"Hg. However, the systems that run on a differential, the pump will continue to operate until a differential of 1" Hg is established, this is equal to 8 oz of pressure differential between the steam and return lines. At either of this conditions, I don't think it is likely that the water in a wet return would boil. However, if you ran a pump that was capable of producing a vacuum that was well below that which was necessary to cause the boiler to begin to boil, I think that the entire boiler and return lines would be boiling very rapidly.... of course until the vapor filled the system and then the vacuum pump would have to continue removing vapor to prevent the system from coming to equilibrium.

ChrisJ

Dumb question

I have what may be a dumb question but I need to ask because I want to know.



What was the original purpose of the hartford loop? Is it to keep the pressure at the input and output of the boiler about equal so water doesn't get pushed out via the return from pressure?



Is it even necessary with a vacuum system?

ttekushan_3

vapor filling the system

Dave in QCA, you said, ".... of course until the vapor filled the system " and I think that's the key. My hunch is that if return temps are high enough for reboil, vapor will already have filled the system. And regardless, the highest temperature water in the system, as you also said, being at the top of the boiler would preferentially supply the vapor. It would boil off first and maintain the vapor flow in the preferred direction.



I suspect that return water boiling wouldn't be a significant issue, since that hot kettle of water can supply vapor faster than the returns could.



Of course, introduce a motorized zone valve with separate vacuum returns and all bets are off!

Dave in QCA

Hartford Loop

The Hartford loop is defined as the turning up of the wet return and its connection to the equalizer about an inch below the normal boiler water line. The purpose of this was to prevent accidental draining of the boiler. For example, if a return line suddenly broke, the boiler with a Hartford loop will drain down only to the point of the Hartford connection. If the wet return connected directly to the bottom of the boiler, the entire boiler would suddenly drain. And.... then you've got a huge problem!



The equalizer is intended to make the pressure at the boiler outlet and inlet be subject to the same pressure, and yes, so pressure in the boiler does not push water up into a return where the pressure might be less.

ttekushan_3

two cats and a chihuahua

That's so cute!



But it's the same instinct that's always drawn me to steam radiators too!



I think a primal need is satisfied when our heat sources are actually hot. ;-)

Dave in QCA

Very Good Point

tte, you make a very good point and I agree with you completely. I was thinking in terms of an absolute condition with a cold boiler and very deep vacuum.

ChrisJ

Hartford

Dave,



So with a boiler that has a fuel burner and a LWCO doesn't that make the hartford loop pretty much obsolete and unnecessary?



I realize that even a LWCO can fail, but in that case the boiler will still slowly drain via condensate loss as return water comes back and leaks out.

Dave in QCA

An added measure of safety

Given modern firing that can be immediately shut off operating with a primary and a secondary LWCO, it is a pretty safe bet that the LWCO would shut of the flame. But, we all know that LWCO devices fail because we still have dry fired boilers from time to time. But, lets assume that a wet return pipe broke and quickly dumped out the contents of the boiler, and at that time the LWCO shut the boiler down, The heat the might remain in the firing surfaces of the cast iron, refractory walls of combustion chambers, etc., might be enough to damage the boiler. The bottom line is that if you have a broken wet return you don't want the boiler to dump its contents on the boiler room floor. The Hartford loop is a simple piping scenario. Of all the stupid things that can happen to controls, intentionally or be neglect, there is not much that can be done to the Hartford loop once it has been built in the piping.

ttekushan_3

I'm going to go out on a limb

and say "yes. it is obsolete."



Larger systems with separate boiler feed pumps do not utilize a hartford loop, only a check valve.



Electric controls have obviated that, and as you point out, the hartford connection doesn't prevent a "dry fire" condition should the controls fail.



---

I'll add that the hartford connection also tends to hold condensate back when the water level drops and exposes the return connection to equalizer steam pressure. So it works the other way too. The water can't return until the fire stops or is reduced. This is why a hartford connection that's above the normal water line can cause boiler flooding with float operated auto fills and can also exhibit hammering at the end of the cycle a minute after the fire stops.



After all that, I think they should still be properly installed. A little tradition never hurt anybody. And as D in QCA just pointed out before I could post this one, it's so simple and reliable it makes no sense to leave it out of the picture.

ChrisJ

ok

I agree, just wanted to make sure I complete understand its function. Besides the fact its a backup safety think code in most if not all areas.





Back onto topic, what problems would the wet return boiling possibly cause?

PMJ

Energy Savings and Vacuum

I'm not seeing the great benefit from and energy standpoint of paying for mechanical means to achieve a lot of vacuum. The main energy consumption here is the heat required to change the state of the water from liquid to vapor - and this is 1000btu/lb regardless of the boiling point. As we know it is this heat that is delivered to the room when the steam condenses back into water at the radiator. And, though we can lower the initial temperature that boiling starts at with a vacuum the boiling point very quickly rises to 212 as the steam quickly kills the vacuum and we are again stuck with the 1btu/lb/degreeF we need to raise the returning condensate all the way back to 212 anyway during the firing cycle.

When I initially converted my system back to natural vacuum between cycles I had ideas about possible great savings with a mechanically induced vacuum. Now I don't think so. I think the real benefit is just in starting the boiling quickly and in speeding the steam to the farthest places and this is achieved quite satisfactorily with the free natural vacuum. I also believe that while the initial boiling point is lowered by lower pressure, the heat of vaporization is actually raised as vacuum is increased and works against you.

ttekushan_3

Heat of vaporization

Latent heat does increase. And it is delivered to the radiators, not lost. The steam also has less density at lower pressure thereby reducing the amount of total heat in the radiator, lower radiator temperature and reduced resistance to circulation. Mechanically induced vacuum return allows the reduction of boiler size due to the easing of "pick-up" factor requirements.



Your point is well taken, however, since there are many ways of eliminating the pick up factor in steam heating. Off the top of my head, there's: Orifice vapor systems, Minitube with tiny piping, conversion to fin-tube (including cast iron fin) radiators, naturally induced vacuum on very tight systems, mechanically induced vacuum, and of course, any and all combinations of above.



I really like the vacuum operation where it's an existing installation with the requisite big pipes and radiators and with an undersized boiler that can't muster equal steam distribution since it lacks adequate headroom. We can then turn an energy pig of a system into a highly efficient one. That possibility alone makes the discussion worthwhile to me.

jumper

lots of ways

There are a lot of ways to make steam heating work at less than 0 psig. Including one pipe.

And even with single rate burners. There are payoffs in large industrial buildings. On a house the real question is is it worth it? I'm somewhat familiar with one pipe vacuum. Here are some numbers. A cold radiator under vacuum has an absolute pressure of about one third psia. Boiler water cooled to even 100° has a pressure of about one psia. That difference will hold 18 inches of condensate. And it may be a bad idea to let your boiler get that cold.

PMJ

Pick up factor etc

I have one of those big pipe vapor systems but with a big boiler too. And I see pick up factor as only a small issue when it is warm outside and not much heat is needed anyway.  When I actually need heat the boiler is still warm and is never more than single digit minutes from steam anyway. When I really need heat steaming begins immediately at fire in the natural vacuum. Last I checked that big boiler that I paid to heat up is still inside my house with all its heat and warming the floor above it.

Do we agree that vacuum does something at startup but a minute or two into any firing would be completely gone? It seems to me that the overwhelming majority of the heating process is going to go on at atmospheric conditions anyway.

jumper

depends as usual

PMJ asks pertinent questions. Big single stage goes to cut out quickly. Is that good or bad? Well it depends as usual. For example finned tube terminals also heat up quickly. But big fat radiators don't. One of vapor heating's goal is that terminals provide less heat for longer periods during mild weather.

ttekushan_3

I don't think we actually disagree.

. . . unless you really want to. :-)



" It seems to me that the overwhelming majority of the heating process is going

to go on at atmospheric conditions anyway."



Very true. I think the gray area is that the ancients of steam heating used at least three different meanings of vacuum steam heating, one of which overlaps with vapor heating. The one that overlaps vapor heating is naturally induced vacuum. The others are vacuum return assistance and the third is true subatmospheric operation. The last two require pumps. And in particular, subatmospheric operation requires a fairly high HP liquid ring vacuum pump that can maintain below atmospheric pressure on supply and return under all conditions. You're not going to find subatmospheric in a home (nor just about anywhere else these days) so, nope, when the heating gets going, it'll be pretty much atmospheric.



I think mechanically assisted return can result in shorter run times during milder weather, where the heating industry seems to focus its attention. But my experiments have shown that a jet pump operating with a 1/25th HP motor can have great benefit for very little electrical use.



I'll defer to Nash Jennings' and Oak Services' case studies on vacuum return improving seasonal fuel consumption by 30%. If a 3 HP motor can reduce fuel consumption that much on a 5 million BTU heating plant, it seems worthwhile.

My own jet pump vacuum assist pumping station (using a cheap generic hydronic pump, 1/25th HP) has been working very well for 2 years, but the application is a 400 EDR area within a much MUCH larger heating system and all I was trying to achieve was even heating without a flooding subheader and violent water hammer in a problematic part of the system. Which it does. But any impact on fuel consumption is impossible to assess.

Currently, another such pumping station of similar design is about to be implemented in a 600 EDR two pipe system with undersized boiler and slow return problems. Nothing else will change and a 1/12th HP pump will be used to drive it. We have a much better chance of measuring fuel consumption differences this way. The design is such that the system will function with or without the pump and without affecting performance with the pump disabled. I really want to find out how this affects seasonal fuel usage.



"Last I checked that big boiler that I paid to heat up is still inside my house

with all its heat and warming the floor above it."



Yes. And the pipe too. That it's in the home is why that heat loss (if you can keep most of it from going up the chimney) is not really a loss. Steam is erroneously knocked for the issue of warm pipes and boiler. But still, if we can limit run times, then we're saving.



"When I really need heat steaming begins immediately at fire in the natural vacuum."



Actually, I find this true of atmospheric operation too. The larger systems I've dealt with actually will puff air out of the vented condensate receivers within moments of when the power burners light on low flame. I don't know where steam's detractors get away with implying that a boiler has to heat for 10 minutes ever single cycle.



The question becomes, whether mechanically assisted venting and return creates a net savings of energy between electricity and fuel and whether that combination exceeds the total efficiency of other heating media. We already know that steam's advantage is its latent heat, and the more the better per pound of steam generated.

Unless there are intractable problems, the simplest is what you are doing. And probably the best under many circumstances. There is value in a finely tuned yet simple system.



My last sentence on this thread

http://www.heatinghelp.com/forum-thread/140419/Why-hot-water-and-not-steam#p1322681

sums up where I stand on the fundamental issue.

PMJ

We don't disagree

Everything you say here looks right to me. I would like to learn more about this. I've read the claims about the 30% savings on a system that took 8psi to push steam where it needed to go and then took only 2psi with a small vacuum pump. To me, big systems mean big total leaks which were actually sort of vents in the first place? I admit l am probably missing something and would love to learn what it is. It doesn't ever take 2oz to fill my 1000 edr system so I can only assume that the pipes are too small in a heating system that needs 8. I also run a 6 million btu process steam boiler at 12 psi but that is needed to push condensate up out of tanks it heats a whole floor above it.

SteamCoffee

Any updates on the various project concerning vapor?

jumper

Jinx! I've been wondering the same. Especially after the recent Zhadanovsky article Dan posted.

Dave in QCA

@SteamCoffee Thanks for bringing this thread back up. Since I started this thread back in January of 2012, I have been able to make a lot of observations of my Dunham system. In addition, I have gotten my hands onto more of the Dunham publications. Dunham was perhaps leader in vacuum, starting with the short-lived Vacuo-Vapor system and after several other systems along the way, creating the VariVac. Why I find interesting is the concerns, benefits, and rationale for vacuum changed over time. I have intended to more completely analyze this development and write paper on the subject. However, it is a task that I have not gotten started on as of yet, other than a whole lot of thinking!

My observations on my system, operating as a Dunham Home Vapor system with self-induced vacuum are disappointing compared to what my hopes were. The boiler does begin to produce steam and it does begin to circulate and enter the radiators before the vacuum is eliminated through the production of steam and heating of the mains, but it is rather insignificant in its effect. The advantage that I do see is that the steam distribution is improved and the issue of venting is reduced because there is so little air in the system to be pushed out. There is venting at each cycle, but the amount of air being expelled is much less than if the system was allowed to draw air back in and relieve the vacuum during the off cycle. This, it appears, assists in improving the even distribution of steam. That is the same factor for which we see huge menorahs of main vents being installed.

I think Igor's work is very exciting! He has reached out to me, but I have been to occupied with other things to answer him. I intend to do that soon. I am also considering pursuing possible vacuum pump operation to see a true modulating temperature system can be achieved.

nicholas bonham-carter

In an ancient thread here, someone had spoken of experiments with a shop-vac connected to the system and wired in with the controls to increase the naturally induced vacuum. I can't remember the level of success.
What about having some sort of accumulator tank for holding a vacuum, (even a very large and long drop header)?
The air in the returns is not expelled beyond the radiator traps, and crossover traps, and this would lessen the vacuum at startup. A pump would help remove this lingering air, and start the boiling earlier, but maybe there is some other more passive way to reduce the amount of air in the system-maybe moving the radiator traps as far downstream as possible.--NBC

Dave in QCA

Nicholas, what you are describing as an accumulator sounds a lot like the Dunham Vacuo-Vapor system. I looked for the link to it in the Museum, but I can't find it there! I thought I scanned my copy and sent it to Dan. Ugh. I am getting to the place where I think I have done the things that I have intended to do, but never got around to.

jumper

My understanding about commercial buildings is that rationale for vacuum operation was to reduce heating system's capacity during mild weather and weekends. Of course pump manufacturers sold more pumps.Another rationale.

In this century the logical approach for homes is to seal vents and mechanically evacuate air.Use an air powered jet evacuator.You'll have other uses for the compressor.

nicholas bonham-carter

http://forum.heatinghelp.com/discussion/comment/1380379#Comment_1380379