Back to vacuum.

thfurnitureguy_4

So with timer installed and steam season underway, the thoughts turn to moving steam faster down the pipes.
My situation is a one pipe steam system with 2 - 250' runs of 3" main pipe.
Boiler at the very back and radiators on first and second floor the whole length.
I have about 10 big Gortons at the end of the mains and my run time to vent the mains is still about 30 min.
Venting time is the same through a 1.5" open fitting as it is through the Gortons. So I believe I am well vented but just have a long way to travel.
I saw the post about the vacuum systems being installed at the radiators but with about 30 radiators in the system and the length of the runs back to a central vacuum pump it would be expensive to pipe.
If my goal was to improve and not perfect, would installing non (vacuum) venting radiator vents to all the radiators first and then installing a vacuum pump to the mains help?
I am thinking of plumbing a manifold into a pair of Big Mouth vents on both mains. Vacuum switch to shut off the pump once a vacuum is reached.
Because the radiators vents have check valves and no longer vent vacuum, the radiators are pulled into vacuum with the whole system when the pump runs. I assume low temp steam is what is filling the system once the air is pumped out. I see a couple of scenarios.
1- The mains fill with low temp "vacuum steam" and the radiators and connecting pipe stay empty until the pressure goes from vacuum to pressure.
2- Vapor travels through the system in vacuum including the radiators, temperature increases as pressure increases out of vacuum.
What you think?

jumper

I've suggested before that I'd plug ALL vents,evacuate air with vacuum pump,and then see what happens. Nobody has tried it as far as I know. What is there to lose but the time to plug vents and then replace vents if it doesn't work?

A big issue may be to locate leaks. Most suspect valve stems. We've already had a thread about vacuum grease.

Kahooli

If you're going to try it, I'd say do this instead:
1) plug everything and test what level of vacuum you can maintain in the system cold.

if it's pretty high,
1) Get rid of the thermostatic air vents entirely.
2) replace them with the pump and two solenoid valves.
3) make the pump bring the system to some vacuum threshold (say -150 inches water or whatever your system will hold reliably) before each cycle, then close the solenoids,
4) fire the system. Your boiler will create positive relative pressure steam that will travel to the lowest pressure, toward the radiators.
5) ideally it will act like a vapor chamber cooling system, with the heat source steaming the phase change medium into a vacuum chamber to the coolest points and condensing.

That's an interesting idea. I might try it this spring

EBEBRATT-Ed

Check the firing rate of the boiler against the boiler nameplate. Your taking too long to make steam and vacuum won't fix that. More venting won't fix it either if an 1 1/2" open pipe won't do it

How is the water line? Stable? Any surging etc.? Cutting out on low water or another limit mid cycle?

PMJ

@thfurnitureguy ,

What are we heating again? Two 250 foot runs of 3" sounds like a lot. 30 minutes to steam at the end of the main is after the boiler has been off how long? How big is the boiler? What is the EDR of the system again?

MilanD

Yes, something is definitely off. 250' x 2 mains of 3" should not take 30 minutes to vent. 15 max. Are your mains insulated? Is the boiler (gasp!) - undersized?

thfurnitureguy_4

I did EDR calculations years ago and the boiler was sizes about twice what was needed, there have been additional radiators removed since and the system always has cycled on pressure. When the system was oil fired we used the max 4 GPM Nozzle with the same time results. Time results were with a warm boiler. Is there a calculator for steam velocity through 3” pipe?

PMJ

thfurnitureguy said:

I did EDR calculations years ago and the boiler was sizes about twice what was needed, there have been additional radiators removed since and the system always has cycled on pressure. When the system was oil fired we used the max 4 GPM Nozzle with the same time results. Time results were with a warm boiler. Is there a calculator for steam velocity through 3” pipe?

I don't think 30 min is that high if the pipes are cold at the start. What kind of building is this? The steam is just for heating?

SeymourCates

Ed Ebebratt is correct.

You have accomplished all you can do with venting. Vacuum won't affect the time one bit if the problem is condensing in the mains.

Focus on the insulation of the mains and the cycle time. This system would greatly benefit from operating based upon variable cycle time (Tekmar 279) rather than a thermostat. Those 300' mains have to be kept warm if you are to have any success with heating that building in a reasonable time.

The final issue is the quality of the steam. Post a photo of the near boiler piping. Wet steam doesn't want to go anywhere in a hurry.

PMJ

SeymourCates said:

Ed Ebebratt is correct.

You have accomplished all you can do with venting. Vacuum won't affect the time one bit if the problem is condensing in the mains.

Actually it does, a lot. I agree with you only on the first cold start cycle. After that open vented mains cool down much faster when room temperature air is allowed back in to fill the huge void created by collapsing steam. So on all new cycles more time is spent rewarming pipes(same as "condensing in the mains"). With vacuum, on all cycles after the first one much less rewarming is necessary. Consider adding up all this lost time from every cycle. Big number. It seems that this is the part that is easy to miss. When you cycle evenly there are no long off periods except in very mild weather and no times without significant natural vacuum. Running this way your entire system stays significantly warmer and therefore is faster to deliver steam always.

I also agree that these mains need to be properly insulated or none of this is going to work very well.

SeymourCates

The thought that eliminating the air to prevent prematurely cooling the mains is interesting. Let's look at the data. A 300' main (3") has a mass of 2274 lb. If we let the air return to the 300' main, we allow 1.232 lb. of air to enter. The specific heat of the air is .24 BTU/lb./degree. We need to raise the temperature of the air by 150 degrees when it enters. This will require 44 BTU.

The specific heat of the iron is .122 BTU/lb/degree, Since we need to cool 2274 lb. of iron, the temperature drop caused by the loss of 44 BTU (required to heat the air) is therefore .16 degrees.

I suggest to you that the introduction of air into the mains is effectively meaningless from the standpoint of cooling the mains between cycles. If you have sufficient venting, the air is not causing the issue with extended time in any way.

jumper

Maybe the issue is not btu but consuming steam to move air?
Steam locomotives were equipped with feed pumps (as opposed to injectors) to save steam.Not energy.

SeymourCates said:

The thought that eliminating the air to prevent prematurely cooling the mains is interesting. Let's look at the data. A 300' main (3") has a mass of 2274 lb. If we let the air return to the 300' main, we allow 1.232 lb. of air to enter. The specific heat of the air is .24 BTU/lb./degree. We need to raise the temperature of the air by 150 degrees when it enters. This will require 44 BTU.

The specific heat of the iron is .122 BTU/lb/degree, Since we need to cool 2274 lb. of iron, the temperature drop caused by the loss of 44 BTU (required to heat the air) is therefore .16 degrees.

I suggest to you that the introduction of air into the mains is effectively meaningless from the standpoint of cooling the mains between cycles. If you have sufficient venting, the air is not causing the issue with extended time in any way.

PMJ

@SeymourCates,

What is interesting to me is how today numbers are used to explain away and render as meaningless techniques the dead men used very effectively to enhance the performance of these systems. They did so past the coal days and on into gas and oil fired systems. By your numbers they were just wasting their time were they not?

The cooling effect I speak of occurs primarily at the rads as when the boiler shuts off most of the air returning quickly to the system goes through them. They end up being cooled by many times more than their volume of air. And that air quickly gets back to the mains and opens those vents too. But of course having the rads go back and forth from 200 to room temp doesn't mean anything by the numbers right? Just the same I know a whole lot of folks out there wish their rads didn't have to do that.

Regardless, you will grant me at least that there is no advantage gained by running the system backwards at the end of every cycle with this air. You will grant me that removing the air again and reheating even a small amount every time doesn't beat not having to do it. I do hope we can agree it is an improvement even if we can't agree on a number for it.

I run a system that has a boiler making steam a very significant amount of time with the burner off and steam moving towards the rads a much higher percentage of the time than when it was vented. The result is a much more steady process and much more even heat. I think some dead men are smiling. I am quite sure the OP here will be much happier if he gets some natural vacuum going.

AMservices

The cheapest way I see making a one pipe steam system operate as a natural vacuum Is to use check valves In conjunction with all your vents and stage fire the boiler.
The system needs to be able to Operate as the old coal fired systems did. Basically never shut off during a call for heat.
You see, there's a reason 1 pipe vacuum systems are not around and its thanks to the thermostat and fuel burners replacing the coal burniing fire box. people would have to start a fire in the morning and let damper controls throttle the air the fire gets.
Think about how the water boils in those 2 types of systems.
When the thermostat calls, the boiler is burning X to boil the water. Steam shoots out of the boiler into the mains and heads straight for the largest open hole in the system, your main air vent. Now steam can evenly fill the run out to the radiators. Steam enters the radiators, goes across the top and down towards the air vent closing it, leaving the rad half full of air.
If there's no check valve, as the steam is condensing it's starting to make a vacuum and moves to the colder spots in the radiator, the vent opens and more steam can enter when more air leaves.
If a check valve is there, after the steam hits it the first time, it closes and can't let more air out because the check valve is keeping it closed. Now with a vacuum starts to form with both steam and air expanding inside, Pressure goes up tripping the pressure troll, Burner cuts out and the vacuum starts to form even quicker. Air can potentially expanded back down into the run outs and mains before the burner comes back on.
In a coal system the fire never cuts out completely, so steam can steadily fill the piping and radiators.
If you can stage or modulator the burner so that there is always a flame, Everything should work beautifully.
Burner will come on quickly, start to fill the system, as the pressure slightly increases the burner will down fire and continue filling the system until the thermostat satisfies. Burner shuts off, No air is let back in, Natural vacuum takes place and Starts balancing.

Packless radiator valve would also be a good investment with that set up.

The vacuum pump will not be a good investment unless you're able to remove the air from all of the radiators.
If you try evacuating from just the mains, after the steam has reached the point of the run out no more air will be able to be evacuated from that radiator and the remaining air will just be compressed into the radiator.

jumper

You can talk yourself into any scenario. For example,when there's air in the radiator then steam will condense at lower temperature so it'll take longer to warm the room? Then steam heat will be more even? Maybe? From that point of view smaller pipes will work better too? Maybe?

I believe that there's no such thing as too little air in any hydronic system.

SeymourCates

@PMJ

Let me tell you about an airplane that was highly regarded as the premier machine of its time. It transcended all previous technology and offered more space and more speed than anything that came before it. It was designed by dead men.

The airplane is the Boeing 747.

This month, United Airlines retired the last Boeing 747 from their fleet. Think about that before hanging your hat on the technology of dead men. Life evolved and the technology of the past should not be embodied as an example of how to build a system today.

The cooling effect you speak of at the rads results in the exact same calculations and the exact same result. Say a CI read with an EDR of 30 holds 10 gallons of water. The internal volume is
.16 cubic feet. When the vent opens, the most air that can possibly enter the radiator (when all the steam has condensed) is .16 cubic feet. The weight of this air is .128 lb. It takes 4.36 BTU to raise the temperature of the air by 142F. I am sure you will agree that this energy loss is insignificant.

Of course you are correct that it makes no sense to run the system "backwards" at the end of every cycle. However, the efficiency improvement strictly due to the elimination of the air cycling is negligible.

The only advantage to the vacuum system is the capability of boil water at reduced temperature. Now you have a more efficient system as the lower temperatures result in lower standby losses to the unconditioned space. Furthermore, you have the capability to operate the boiler for a longer period of time, thereby minimizing the off cycle and minimizing the temperature degradation in the piping.

There is a reason that vacuum systems have gone the way of the B-747, The juice is not worth the squeeze.

The only caveat is the fact that you personally are able to utilize vacuum for no financial investment on the two pipe system. The moment one needs to invest in $40. check valves or vacuum pumps or dedicated vacuum lines from the rads to the pumps in a one pipe system the gains are completely mitigated.

The OP might be "happier" if he utilizes vacuum but it absolutely will not result in any improvement in the time to get the steam to the end of the main. Only cycling the boiler on a schedule (as you currently do) will accomplish that.

PMJ

@SeymourCates ,

I must respectfully submit that there are problems with your 747 retirement story as it pertains to our discussion here. The 747 is one model of airplane - a piece of hardware. Vacuum is a natural phenomenon determined by laws of physics and shall we say cannot be retired. If vacuum is not worth the squeeze today, as you put it, then it never was worth it as the math on that has never changed. Your position on this requires that all the dead men were also simply wasting their time with vacuum.

But I am glad that we have at least reached agreement that horsing the air in and out every cycle is a negative and not a plus. We then can surely agree to part company with my belief that the condition is clearly worth doing something about with natural vacuum, and you taking the position that it clearly is not worth any $$ effort at all as any losses in performance are minimal.

If I have learned anything about steam heating it is that this is a game of fractions of ounces of pressure difference and minutes. And very small differences in these things working for you rather than against you over 24 hours a day can produce dramatically more comfortable and even heat. I have learned that in steam comfort is about much more than efficiency numbers. The comfort improvement I have experienced with vacuum I would gladly pay more for. Thankfully I get both - the comfort and a lower fuel bill. Your statement that "The only advantage to the vacuum system is the capability of boil water at reduced temperature" pretty much clarifies our difference on this. I assure you that the net affect of vacuum on my system is about way more than that.

I thank you for the discussion. I think readers here have plenty on this now to draw their own conclusions.

AMservices

@thfurnitureguy
Got a little off track here. You want to improve the time it takes to fill your mains? What is the boiler firing now, how many risers are coming off the boiler (1 or 2) and what diameter is the pipe?
That's what we need to know to calculate steam velocity.
If the velocity is to high, water will be thrown into the main killing you steam production.
You say there 30 radiators, so I'm guessing the EDR is around 1200?
How well is everything Insulated?
Pictures always help

mikeg2015

MilanD said:

Yes, something is definitely off. 250' x 2 mains of 3" should not take 30 minutes to vent. 15 max. Are your mains insulated? Is the boiler (gasp!) - undersized?

You sure? I have 90' of 3" and it's taking me 10+ minutes to vent. I think I calculated the mass of the iron, and it was around 8' of firing to heat it up.

Here's my solution(s):
1) vent the radiators slower. This takes a leap of faith, and it's a arduous process. But ultimately, you need to "squeeze" the steam down the main a little. I've tried pinching back on the radiators the heat up too fast with the Hoffman 1A, but at some point, steam will stop going there altogether, as other vents radiators look more inviting. second, once things warm up, the vent is now too slow for the size of that radiator.

2) Add vents along the way. This goes against what some others have preached, but I think after 90' of pipe and 7 elbows, that's enough pressure drop that the first couple radiators have less resistance. So I've added one vent about 2/3rds of the way along the system and am going to add another at the 1/3 mark. Just going to use a vari-vent. Worst case I just plug it. I drill and tap the fittings, not straight pipe.

3) If a particular radiator is still stubborn, could be the runout has some crud in it, it's unusually long, if it's been shut off for a while and/or radiator isn't pitched very well.

mikeg2015

... could someone explain where the energy goes if you are making wet steam. If the steam velocity drops, then the pressure must increase? Or are you just ending up with superheated steam? But less steam volume?

AMservices

> @mikeg2015 said:
> ... could someone explain where the energy goes if you are making wet steam. If the steam velocity drops, then the pressure must increase? Or are you just ending up with superheated steam? But less steam volume?

I believe it's absorbed back into the water then the water falls back to the boiler where it has to start again.

Why is the pressure increased if the the velocity drops?
Steam moves faster at lower pressure, but the size of the opening In the boiler block and the firing rate will change its exit velocity.

thfurnitureguy_4

Guys, sorry for the delay but holidays and work are hindering the discussion. Some questions about the system have come up.
- Insulation of the mains; a mix of 2” fiberglass and 1” glass but everything is covered. Each year I replace more of the 1” with 2”.
- One post listed 10 min to vent 90 feet of 3”pipe, I have almost 3 times that much pipe and it takes 30 min, so I think I am in the ball park, I agree better insulation will help.
- Boiler is a Burnham V905-A. Modified to burn gas using a Beckett burner , high fire only. It has two 3” steam risers into a 6” insulated header. The header splits into two mains that run the length of the building

On a good note the system using the timer holds the call temp on a cold day. Vapor stat set at 8 oz and the timer set to pause restart after pressure, for 30 min. Old setting built pressure to 1.5 psi and cycled on pressure 2-3 times before satisfying the stat. New setup cycles once. Stat is satisfied before the pause is over on a 20 degree day.
Installed 6 more of the modified Maid o mist check valve vents so now 2 floors are “suck-less”, about 10 to go before full vac can be tested. Darn global warming is holding up my tests..
Anybody make a low pressure vac\ pressure gauge?

Kahooli

iD LOVE SOME PICTURES!

FriendlyFred

Hey @thfurnitureguy - I was intrigued by your home brew checkvalve as mentioned in this post: https://forum.heatinghelp.com/discussion/163151/pressure-in-1-pipe-steam/p1

I took a swing at thinking how you could build something similar. The attached diagram outlines how you could use an O-ring around the orifice to friction-fit an appropriately sized tube over the vent outlet, but also act as a sealing surface for a small Delrin checkvalve. Amazon sells small segments of Delrin rod of varied diameters. Building the actual thing would require some guess and check to get the diameters and clearances correct, but honed it, it might be a mechanism that can be rapidly replicated and installed.

thfurnitureguy_4

On the right track. Some things I did that worked.
Keep the m-o-m vent orifice but drag the face of it over a file to remove the burr caused by the letter stamped into it. It will help the puck seal.
Re-sized or new 45 acp casing is a good pressfit over the removable orifice so no need for the o-ring.
Drill out the primer hole to be bigger than the largest vent you need.
I used thin copper sheet to make the puck. Hammered flat between 2pieces of steel and filed to flat but Delrin could work if smooth.

MilanD

@thfurnitureguy - how did you do with that vacuum retrofit? Is it done and how is it performing? How about the rads on which you installed it?