Single pipe to vacuum?

Fizz

What's the current thinking on swapping a single pipe into vacuum? I did it on my Richardson System by just swapping-out Gorton main vents with Mepco quick vacuum vent and changing t-stat to hot water. The results have been very satisfying: heat is even and steady. Our daughter is in process of buying house with single pipe. Of course if system works well now it may be mute. Thanks.

Fizz

ChrisJ

Rumor on the streets is balancing issues and perhaps condensate return issues.

Personally, I'd like to see someone try in their own home though to see if these issues can be overcome.

Fizz

What are the perils? Is risk greater than reward?

MilanD

Wouldn't you also need vacuum vents on each rad?

Fizz

Probably, Who makes them?

Kahooli

You could probably put a 1/8 inch check valve on any vent to make it vacuum capable. As long as the opening pressure on the check is small, a few ounces max

Fizz

That's a possibility. Will look into it.

Kahooli

Something like this eh?
http://www.usplastic.com/catalog/item.aspx?itemid=85435

1/3psi cracking pressure, so you have to overcome that in system pressure before any rads will vent at all on cold start.


I also found some that have cracking measured at a few inches water (way better) but they're $50 each!
Some scouring of the net will probably reveal an appropriate one that doesn't cost so much.

Mark N

Vacuum vents for 1-pipe steam haven't been manufactured for a very long time.

Fizz

Thanks guys!

PMJ

The minimum cracking pressure of most check valves is higher that the max pressure I ever see in my system. That is how I ended up using a solenoid valve - one I could be sure was actually open when I wanted it to be and one which required no pressure in the system at all to open. But then I have the large advantage of only needing one.

Another subject to keep in mind. Everyone is very used to thinking about vents as needing to close against steam. But in the case of radiators, if a vent (or a trap in 2 pipe) is closing against steam then that rad by definition has more steam in it than is required for the conditions 90+ percent of the time. Hence overshooting and longer off periods. When you limit the run time so as to prevent your rads from ever filling that much, steam never gets to a vent or a trap. So going down this route allows considering using simple check valves if all they are ever seeing is air. I removed some traps altogether in my system where I wanted the least resistance possible to air leaving the rad. And the way I fire the boiler it is basically impossible for the rads to ever fill enough to get steam to a trap. Some very small rads in bathrooms I let fill completely(the family seems to like that) and they have traps but mostly they are removed or in a few I increased the size of the orifice in the Mouat elbow.

ChrisJ

PMJ said:

The minimum cracking pressure of most check valves is higher that the max pressure I ever see in my system. That is how I ended up using a solenoid valve - one I could be sure was actually open when I wanted it to be and one which required no pressure in the system at all to open. But then I have the large advantage of only needing one.

Another subject to keep in mind. Everyone is very used to thinking about vents as needing to close against steam. But in the case of radiators, if a vent (or a trap in 2 pipe) is closing against steam then that rad by definition has more steam in it than is required for the conditions 90+ percent of the time. Hence overshooting and longer off periods. When you limit the run time so as to prevent your rads from ever filling that much, steam never gets to a vent or a trap. So going down this route allows considering using simple check valves if all they are ever seeing is air. I removed some traps altogether in my system where I wanted the least resistance possible to air leaving the rad. And the way I fire the boiler it is basically impossible for the rads to ever fill enough to get steam to a trap. Some very small rads in bathrooms I let fill completely(the family seems to like that) and they have traps but mostly they are removed or in a few I increased the size of the orifice in the Mouat elbow.

Solenoid on each radiator along with a pressure switch that trips at around 0.25" WC and a thermister all tied into a controller that monitors each room's temperature and the outdoor temp.

When the pressure switch sees 1/4 of an inch of water, it opens the solenoid, when the pressure drops near 0 it closes the solenoid.

The thermister is to protect against steam ever escaping.

PMJ

ChrisJ said:

PMJ said:

The minimum cracking pressure of most check valves is higher that the max pressure I ever see in my system. That is how I ended up using a solenoid valve - one I could be sure was actually open when I wanted it to be and one which required no pressure in the system at all to open. But then I have the large advantage of only needing one.

Another subject to keep in mind. Everyone is very used to thinking about vents as needing to close against steam. But in the case of radiators, if a vent (or a trap in 2 pipe) is closing against steam then that rad by definition has more steam in it than is required for the conditions 90+ percent of the time. Hence overshooting and longer off periods. When you limit the run time so as to prevent your rads from ever filling that much, steam never gets to a vent or a trap. So going down this route allows considering using simple check valves if all they are ever seeing is air. I removed some traps altogether in my system where I wanted the least resistance possible to air leaving the rad. And the way I fire the boiler it is basically impossible for the rads to ever fill enough to get steam to a trap. Some very small rads in bathrooms I let fill completely(the family seems to like that) and they have traps but mostly they are removed or in a few I increased the size of the orifice in the Mouat elbow.

Solenoid on each radiator along with a pressure switch that trips at around 0.25" WC and a thermister all tied into a controller that monitors each room's temperature and the outdoor temp.

When the pressure switch sees 1/4 of an inch of water, it opens the solenoid, when the pressure drops near 0 it closes the solenoid.

The thermister is to protect against steam ever escaping.

I like it Chris. A bit of equipment for each room but I like the concept.

Also consider this - if you tried a check valve setup on just one rad in a whole house of vented rads I think you would see that one heat more than it did before. Consider that when the boiler shuts off all the mains are full of steam. Since that one rad's vent/check closes right away the vacuum created by the collapsing steam in it will pull more steam from the full main feeding it and condense even more. Meanwhile, all the other rads are sucking air from their rooms and obviously not pulling steam from the mains. At 3 cycles an hour of this that rad will condense a bigger share of the total than it did before. Now think about all of them doing this and a bit more steam being produced than before for the same amount of fire if the entire system sinks into vacuum 3 times an hour. Believe me this small amount of extra steam and extra forward motion does add up.

PMJ

For those interested consider one more thing.

When you are filling any system with steam where it goes is about resistance to the flow of air which has to be displaced - venting. But with the burner off and the system all closed up where the steam available in the mains goes is now more about where in the system steam is condensing the fastest. I have found that it flows more in the vacuum phase to rads in the cooler rooms which are condensing at a slightly faster rate than those in warmer rooms. The net result of spending so much time each hour in the vacuum condition(more than 75% of the total time during a call for heat) is a surprising evening out effect. When steam only flows into rads in a pressure condition - no matter how slight - it is pushing against air leaving and it is about venting. But in the burner off and system closed condition steam is then being drawn into rads from the mains by vacuum. Very different. As we all know very slight differences in pressure create very different results about where steam goes. My system spends so much time in a significant vacuum condition with steam being drawn into radiators instead of pushed that it took me a while to fully appreciate how significantly this changed where in total the available steam went and which rads got what share of the total. I was honestly surprised (and pleased) how much this evened things out.

MilanD

Per @ChrisJ earlier post on condensate returning, here's this thread talking about trv possibly creating vacuum and keeping condensate in the rad.

http://forum.heatinghelp.com/discussion/159769/boiler-pressure-venting#latest

I'm unsure how would a pitched radiator on the 1-pipe not drain whereas 2 pipe would, aside from steam pressure pushing the condensate out of the rad and through 2nd pipe.

There was a post here with a 1 pipe system rad having 2 pipes, 2nd one coming out as in 2 pipe system but tying back on the supply riser with a tee below the rad valve, and with a throttling valve before the tee. Perhaps this setup would allow better condensate draining on a differential pressure of steam coming into rad through a bigger opening and condensate coming out on a smaller one opposite of the valve side, then by gravity down the riser.

PMJ

MilanD said:

Per @ChrisJ earlier post on condensate returning, here's this thread talking about trv possibly creating vacuum and keeping condensate in the rad.



http://forum.heatinghelp.com/discussion/159769/boiler-pressure-venting#latest



I'm unsure how would a pitched radiator on the 1-pipe not drain whereas 2 pipe would, aside from steam pressure pushing the condensate out of the rad and through 2nd pipe.



There was a post here with a 1 pipe system rad having 2 pipes, 2nd one coming out as in 2 pipe system but tying back on the supply riser with a tee below the rad valve, and with a throttling valve before the tee. Perhaps this setup would allow better condensate draining on a differential pressure of steam coming into rad through a bigger opening and condensate coming out on a smaller one opposite of the valve side, then by gravity down the riser.

I really don't think there is any possibility of vacuum in a rad preventing condensate from flowing out in either system one or 2 pipe.

The right way to think about vacuum is that the entire system is essentially at the same pressure - just less than atmospheric. So gravity still brings the water down same as before. There are very slight differences in the absolute pressure at various places but the differences are small. I have several vacuum gauges at various places and they all read the same thing within a couple inches of water.

This is one thing I do have a lot of first hand experience with now. I have seen not one shred of evidence that vacuum interferes one bit with the flow of condensate.

MilanD

@PMJ

I have no doubts in what you are saying about your system. It must also be quite economical not to have to vent the mains, plust to draw steam via vacuum much quicker. Great!

JUGHNE

I agree and can understand that if the entire system is at the same pressure or vacuum amount then gravity will function as normal as it sees no pressure difference.

This becomes obvious for an AC coil that is under negative pressure from the air blower being downstream. Without a trap the water will not drain, rather be drawn back into the drain pan, eventually the level in the pan will cover the drain opening and will flow out until that seal is broken by the air being sucked back in thru the drain hole. The cycle repeats usually overflowing the drain pan. A deep enough trap will allow the condensate (under a vacuum) to drain out into the trap and exit under atmospheric pressure.

But the finger over the end of the straw pulled out of the glass of water holds that water in the straw until perhaps an air bubble creeps up the straw.

That was my post concerning the TRV w/o vac bkr.
I have heard this first hand at least twice from 3 stories up coming down to the boiler room with the "flush" sound.
Also on the same floor is a large CI rad with the supply valve off as tight as possible. There is no vent on this rad, I put a small valve on the vent opening. Steam sneaks past this 100? year old valve and fills this rad with cond. I have opened the small valve on the vent opening and had the water drain down as air was sucked into the vent hole.

jumper

Just theory here. Steam drives air and it's the air that prevents condensate from draining. But if air is evacuated then there'll be excellent heat transfer between steam and condensate so any vacuum lock won't last long.

The Toronto apartment systems I talk about usually had two connections to convectors,regardless of whether there were dedicated return pipes or single stacks. But in at least one building only one connection was used. It worked well when superintendent evacuated periodically.

So simplest way to try vacuum on one pipe is to remove vents and plug holes. Attach a venturi ejector to the system with some tight valves in between. Evacuate the air and see how it works.

If balance is an issue I'd try covering part of radiators in rooms that are too warm.

Fizz

Very intriguing Jumper.

AMservices

http://forum.heatinghelp.com/discussion/161394/vacuum-boost-retrofit-for-1pipe-and-2-pipe-steam-systems#latest