Another Look at Vapor Vacuum

vaporvac

Additional Advantages

Yes, Dave. I, too see that lower boiling point as an advantage beyond a lower fuel consumption. Cooler radiators mean less scalding for those without radiator covers and a softer heat. I would also think this is a way to moderate the temp for those who have upgraded the insulative value of their homes.  I'm glad this thread has come alive again!

I am also curious about your comment on not boiling at the 195deg in a vacuum. Why would that be?  I thought that was the idea of the vacuum which got stronger as the temp decreased. What am I missing?

Dave in QCA

equilibrium

At some point, the system comes to equilibrium.  When the fire first goes off, assuming that the system is filled with steam, the steam is collapsing and pulls a vacuum.  This lowers the boiling point of the water and since the boiler and water is at the point, or warmer, the water boils and produces vapor that circulates and condenses, etc.  As the system cools, eventually the temperature of the water is precisely at or a tiny bit lower than the boiling temperature as determined by the level of vacuum.  All of the vapor has condensed.  The vacuum is stable, the water is not boiling.  Everything is at equilibrium.  If you had a vacuum pump hooked up and turned it on an increased the level of vacuum, the water would again begin to boil and vapor would flow.  Or, conversely, you you didn't affect the level of vacuum, but instead you turned on the fire and started to increase the temperature of the water, it would immediately begin boiling and vapor would flow. 



This equilibrium at 9" vacuum is because not all of the air has been removed.  But, enough has been removed to allow for fast circulation. The deeper the vacuum drawn, the lower the boiling point.  To get to really low temperatures requires a vacuum pump.   And then, that is what is going on with the Dunham Vari-Vac System.  They vary the level of vacuum based on out door temperature, ODR, and can effectively provide the right amount of heat to a large building based on varying the temperature of the vapo......   Just like a commercial Hot Water system does. 

Fizz

Richardson back to vacuum?

Our steam system is old Richardson with 3 add-ons which have taditional traps.  The current piping has the loop replacing swinging check valve.  Original system called for air expeller at end of dry return with swinging check valve to control condensate.  Currently, there is a #2 Gorton replacing original air expeller, and a #1 on add-on return.  I do have vacuum vents that were replaced with current set-up.  I did re-install them, and system went into vacuum, but there is a 32oz low pressure gauge which doesn't show degree of vacuum, though it did reverse to 30oz line.  System worked well, but 2 add-ons stopped heating(only ran through 2 cycles).  What are recommendations?  Current settings on v-stat are 8 & 8.

elfie

does lower system pressure mean greater efficiency?

for those systems where a true vacuum can not be achieved, it still seems that it still is very important to operate the system at the lowest possible PSI level.



does a lower PSI level mean system is more efficienct?  and for larger 'low pressure' steam boilers this is more difficult to achieve because these systems tend to short cycle (even with a modulating burner)

PMJ

Pressure

Any pressure required in the mains to get the steam to go where you want it means there is resistance to the flow. If you can get the job done with little or no pressure anywhere that is the most efficient from an operating standpoint. However, accomplishing this requires a bigger up front cost of bigger pipes. I have read here about some people needing to use venting to slow the steam down coming out of the boiler for it to be dry enough. I would hate to have to slow steam down going to my radiators on purpose as everything I have done with vacuum is trying to speed it up! I am lucky to have an older system (1926) which has larger mains than seems to be spec today. The manifold from the original boiler is still there and the pipes are oversize for the replacement Bryant there now from the 50's. Lucky for sure.



With vacuum the steam is literally sucked down the mains at the start of the cycle. Some of the previous posts have discussed how reducing the time from when the burner fires to when vapor is actually getting in the rads is where most of the increase in efficiency is. Obviously any time to build pressure is just more lost time.



So yes, the lower the pressure the more efficient - provided you can actually get the steam to go where you want it to. I require no pressure at all in mine to fill the most remote radiator.

Ban

Using a solenoid

in place of the Dunham 222 Air Eliminator air check. I was thinking I could replace the air check with a 24V DC, normally closed solenoid that would be wired to the burners or the damper. The idea would be that when the system turns on the solenoid would open and allow for maximum venting out of the AE 222; much more than the original design with only 5 holes. When the thermostat is satisfied and the system shuts down the solenoid would also close to its natural position and it would start to go into a vacuum. What are your thoughts? Any concerns?

Dave in QCA

PMJ is doing that

But, don't wire it up the way you have described because it will open when there is still vacuum in the system and you don't want that.  Read the post from  PMJ February 17, 2012 @ 6:45 PM.



Also, have you tried to get an accurate measurement of the opening diameter of the cap on your present 222 air check?  I have found a person who is making the discs for the Trane vents with similar air checks.  Maybe they are even exactly the same....   But, I suspect that he might be willing to make the discs for a much lower figure than it would cost at a machine shop.

Ban

PLC

What is the PLC that you used?

elfie

pressure and latent heat

another reason for lower steam pressure is related to latent heat



there is a benefit to latent heat transfer (ie. release of energy from steam that causes the radiators to get hot) where latent energy transfer is more effective when pressure and steam temp are lower



the existence of higher pressure, i guess restricts movement of free flowing steam from the boiler header pipes into the mains and radiators



it seems counter intuitive (ie. you would think the higher pressure would cause the steam to move faster thru the system but I guess there is resistance to steam flow if the mains and rads are under higher pressure in front of approaching steam).



the existence of a vacuum is interesting because it tends to suck the steam from the boiler (so in most systems, getting pressure as low as possible while still being able to cause rads to get hot is the best that most systems can do).



i hope i am getting all this right

PMJ

Using solenoid

Dave is right - you don't want to kill the vacuum at the start of the cycle. I got a pressure switch that I have set to switch at about a quarter of an oz. I have it plumbed on the dry return right next to the solenoid valve. It opens the solenoid at the exact moment that the vacuum is gone and the return just starts to show pressure. Mine goes thru my PLC so I can see it on the computer but that is not necessary - you can just wire it direct.

One other caution - I also have a mechanical check valve in parallel with the solenoid just in case it fails. If it did the system would be completely closed - wouldn't want that. The reason I don't just go with the mechanical one is that I can't find one with a cracking pressure less than 2-3 ounces. Why even that much pressure in the dry return.

Ban

Repairing the Dunham 222 Air Eliminator

Check valve is what I have decided to do. I nixed the solenoid for venting on the AE due to cost, complexity and the reasons Dave pointed out. If I used the solenoid I would immediately lose vacuum on firing unless a PLC was added (is that an outdoor reset?). I am still concerned about the CFM of the original check valve. I have 22 Radiators in the house and relying on 6 holes to exhaust the entire system seems iffy. Because of this I have decided to make a manifold on the top of the AE out of 3/8" black with plugs in it. This way if it is not adequate venting I can figure out a solution later (hoffman 76, solenoid, or homemade Dunham air check look alike). Attached below are the 3 materials I experimented with (brass, copper, copper with neoprene and neoprene) to repair the air-check. The solid neoprene seems to work the best with the cracking pressure very minimal. The copper and neoprene comes in second.

Ban

Schematic above

My system looks almost identical to this one pictured in the schematic with two noticeable differences. First, I don't see a return equalizer with stop cock and check valve on mine, and second, the top of my air eliminator check-valve is defiantly lower than the middle of the return condensate (as pictured). My plan for that was to just raise the check valve up when I make the manifold for the AE. Also, my water level is significantly lower than what is pictured in the schematic. I am fairly certain I had a boiler similar to this one pictured.

Dave in QCA

Plenty Big Enough

The Dunham 222 Air Check was furnished on the 220 Air Eliminator.  As a unit, it was rated for up to 2,000 EDR. 

Remember, a direct comparision to the venting capacities of modern main vents may not be accurate because of the different conditions in which they operate.  The modern main air vents will vent all of the air in the mains every time the steam cycles.



On the first steam cycle, the Dunham air check will vent the air in the mains and some of the air in the radiators, the amount of air is dependent on how long of a cycle it is and how much of each radiator is filled with steam.  During this first cycle, you will probably hear a fair amount of hissing air being relieved from the air check, but not as much as you might imagine.  On subsequent cycles, since the air has been prevented from reentering the system, you may hear no air being exhausted at all.  It all depends on how long the cycle is and if any air has leaked back into the system.  I am told by a person that was with Dunham for many years, that on subsequent cycles, you may occaisionally hear a little burp, but most often nothing at all.



Have you measured the diameter of the opening inside the cap.  What is the largest disc that will fit inside?

SWEI

subsequent cycles

is what makes me want to experiment with a fully modulating burner.

Ban

Air-check

seems to be 3/8" I am really excited about getting this system to work in a vacuum again! I want to thank everybody for their help and knowledge.

Dave in QCA

Combine with Vari-Vac

The combination of a fully modulating boiler with a Vari-Vac system is intreaguing and in fact, make my head spin.

The Vari-Vac system used a modulating vacuum level assisted by a vacuum pump and a modulating steam valve supplying heat into the building mains from a fixed pressure boiler.  It stands to reason that if the boiler could modulate, that you could control that and eliminate the modulating steam valve.   WOW!

Ban

I have a Vacuum!

I finally have put my system back together. Boiler fires fine, Dunham Air Eliminator is checking the air perfectly, and my crossover traps are finally stopping the steam! I still have vacuum leaks for sure, but with 22 radiators and 90 year old pipes I am pretty happy with these preliminary results. I want to thank everybody for getting me obsessed with returning my system to its proper vacuumized status! Radiators are defiantly staying warmer longer.

Kevin_in_Denver_2

Full Modulation is Possible

Just food for thought:



A Modulating Condensing boiler can be coupled to a steam generator with a heat exchanger. It would require the modcon to operate at 200F or higher, so you wouldn't get the benefit of flue gas condensation, but the burner would modulate.



The steam generator is just a tank with a coil in the bottom and a gap at the top.

It may be hard to find one that has very low mass and can handle vacuum.

SWEI

full modulation is available

http://www.midcointernational.com/products/low_nox/ is basically a mod/con burner head setup for a conventional boiler.

ChrisJ

Vacuum!

Congrats! Glad to see you are making progress.

Dave in QCA

Somewhat Dissapointing Results

My new boiler and venting system as been in operation for close to 2 months now.  Here are my observations.



The system will pull a vacuum of 4-5" Hg on a 20 minutes steaming cycle and 5-6" Hg on a 30 minute steaming cycle. 

Steaming seems to begin faster, steam travels down the main faster, and while there is a little bit of air venting each time, it is a VERY SMALL amount compared to a start when the system is completely filled with air.

I do not appear to be able to produce subatmospheric vapor in these conditions.  I am guessing that I would need to put a vacuum pump on the return system and draw it down to a deeper vacuum... Experiments will follow!



While I thought that my system was very tight, I discovered a pinhole leak in one of the 2" end of mains that loops back to the boiler room.  Repair will be soon.  All of the radiator valves have been tightened up and do not appear to be leaking.   I do have one radiator that has a crack in it.  It is about 4" from the top and I'm sure it's leaking a bit.  There may be leaks in other pipes, but hopefully not.  All of the system risers are inside the calls.  Given that they are inside the walls, they are also insulated, which helps the overall system.



Even If I get no additional benefit from vacuum, the fact that they system venting is through a check valve that does not allow the reentry of air when the burner shuts down does appear to reduce the burn time that is required to get the air out of the system.   Since the flow of air in and out of the system is reduced, on could assume that oxygen corrosion and the formation of carbonic acid would also be reduced. 

PMJ

This sounds very much like my results

except you are getting more vacuum than I am. My 90 year old system has a lot of leaks and I have not replaced all the original Mouat valves which except for holding vacuum work just fine.



I spent a lot of time dreaming about a vacuum pump but I ended up thinking that it probably was not worth the noise/electricity. The main contribution of the vacuum is as you have found - steaming is faster, the steam travels out through the system faster, and why horse all that corrosive air in and out of the system each cycle if you don't have to. I have come to really like the lack of moving parts and the natural vacuum didn't require any new ones.



Thanks for the update and I'll be looking for more info from any additional experiments.

Peter

 

Ban

I kind of felt the same way,

even though I was excited to have a relatively good amount of vacuum after all of these months I ended up in some ways a bit more confused. I am trying not to get more obsessed with the system this year (my immediate thought was to pipe in a vacuum pump right away). In many ways PMJ is right, it is kinda nice hearing the subtle sounds of the Dunham Air Eliminator with no advanced electronics or complexities. My original goal was 10" of mercury with a boiling point of 192.19 degrees F.



My results have been interesting, on average, over the past couple of days, when the burners turn off the vacuum tends to stay in the 1" - 3" of HG depending on the length of the cycle. The way it needs to be viewed is this effort proved wonderful things so far (as anticipated):



1. The System runs much better overall and is balanced better.

2. There is tremendously less effort to get steam to the radiators and start heating the space.

3. Less corrosive air entering the system

4. When the system fires back on it is in a vacuum for at least the first 25% of the cycle. This means that I am still steaming at less than 212 degrees! I can hear it start to boil almost immediately after the burners start!



I am happy with my results for this year. My goal for the rest of the heating season is to find all of my leaks. I have found four so far due to the action I have taken on the system. One of the leaks I found destroyed part of the sub-flooring over the years. I would have never known if I hadn't done this. Out of curiosity I used a shop vac to pull the system into more of a vacuum on the return side. The most I could get with it was 6.4"hg.

ChrisJ

Wonder

If I could ever experiment with vacuum.  If I vent too fast I end up with cold radiators due to lack of steam.  Does this mean with vacuum I'd constantly have radiators starved of steam?

Eastman

Dave

Dave, there is no vent on the return?

Dave in QCA

No Vent Device

There is a vent through a 1/2 pipe and a swing check valve, but no typical vent device such as a Hoffman 75 or Gorton 2.



The original Dunham system would have used and air eliminator and an air check or a swing check on their larger systems.  The air eliminator had a float guarded against rising water in the returns due to pressure in the boiler.  There was not protection against steam because unless a trap in the system fail, there is no steam in the return.  If a trap fails, the system should not mask the condition, you want to see the steam. 

This installation is guarded against rising water in the returns with a Vapor Stat to limit the boiler pressure.

Ban

Vent on the return

Looks like this: http://www.heatinghelp.com/forum-thread/144863/Restoration-of-my-Dunham-Air-Eliminator



(Dunham system)

Dave in QCA

My Vent

Looks like this.

Eastman

?

How does the Duhnham function on a one pipe system?

Dave in QCA

2-pipe Only

The Dunham Air Eliminiator, The Dunham Air Check, and any other device that does not have the capability to close on steam are all only for return pipe venting on a 2-Pipe system.

PMJ

Cracking Pressure

What is the cracking pressure of that swing check valve? In that size I would think at least 6 oz or even more. That is why I ended up running a solenoid valve - the entire system pressure is raised whatever the cracking pressure is. I wanted zero resistance at the vent.

Dave in QCA

to small to measure

On the ounces gauge on the boiler, the needle is still resting on the peg when the check opens and vents. If I run it on high fire, it will come up to two ounces while venting and the check is open and blowing pretty hard.

Eastman

That's what I thought, but...

I thought Ban has a one piper.  Ban?

PMJ

Pressure at the boiler

For some reason which I never understood I don't show anything at the boiler either but I show maybe 1/2 an oz at the place where I removed the vent from the steam main at the farthest point of the loop away from the boiler. In theory there has to be more pressure right at the boiler and a drop to that point but I never can see it on a gauge. ?????

I can barely hear or feel anything coming out of the vent valve on the dry return on full fire well after the vacuum is gone. My thinking is if it makes noise coming out then there is unwanted pressure in there and the vent hole isn't big enough.

Eastman

At what point in the cycle does this happen?

At what point in the cycle does this happen?

Ban

Yes but,

my home is a 2-pipe Dunham. I have apartment buildings which have one-pipe systems. We are always trying to make things more efficient so knowing as much about vacuum has been very important to me. The check valve that I made for the Maid-O-Mist air vent is partially based on the Dunham Air-eliminator assembly, by the way.

PMJ

It takes about 2-3 minutes

after the burner comes on at the start of the cycle for all the vacuum to be gone and the vent opens. Is that what you were asking about?

Eastman

pressure conundrum

The boiler gauge reads zero, and yet there is 1/2 psi at the end of the steam main.

PMJ

It is 1/2 an ounce at the end of the main

(or at least not sitting on the pin). Dave said his boiler ounce gage is resting on the pin too when it takes some pressure at the far end to open his check valve. I don't get it either.

Eastman

stack effect?

stack effect?