Pressure Optimization

cubicacres

We recently added a 0-3 psi gauge to our single-pipe steam boiler per the picture (gauge pic & my avatar pic is the boiler). I noticed after running a while it was just above 2.5psi as shown in the photo. We thought our pressuretrolls were set at the minimum amount of pressure (about 1 cut in & 1 or 1.5 differential?), but can verify this.

Are vaportstats just more fine-tunable pressuretrolls, and does getting as low as possible under 1 psi save a certain % of gas costs per month? Ex, 50% less psi,1 down from 2psi =25% gas savings? We're concerned if we dial it down it might cut off and interrupt a heating cycle, reducing efficiency in the long-run.

BobC

Pressuretrols are often pretty far off. If your sure the pigtail is clear and the little hole at the base of the brass pressuretrol is clear you might want to try calibrating it. This procedure was posted by one of our members -


Pressuretrol Calibration:

If you see the pressure on the low pressure gauge go much over 1.5 to 2 lbs follow this procedure to re-calibrate the Pressuretrol:
Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a tiny fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with) . You may need to play with it to get it exactly where you want cut out to be.

This picture shows what screw he's talking about, note it's been locked down with blue glop.
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Bob

Jamie Hall

Well, vapourstats could be regarded as more fine tunable pressuretrols, although it might be more accurate to say they are more sensitive. They come in two ranges -- 0 to 16 ounces and 0 to 4 psi. One would use one of the other, depending on one's application.

Now that you have a nice 0 to 3 psi gauge, though, the first thing (before you change anything!) to do is to watch it as you go through a heating cycle. What you should see (I hope) is that the gauge will register very little pressure -- say less than half a pound (lower is better! for quite some time after the boiler fires up. Indeed, if you have a collaborator, you could have them keep an eye on the slowest radiator, and let you know when that radiator starts to heat up. Ideally, when that radiator starts to heat up you should still be at the low pressure reading -- it shouldn't have changed much. What you should see then is the pressure should start to rise. That is the pressure -- for your system -- at which you want the pressuretrol or vapourstat to shut the burner off, to let the system catch up to the boiler.

If it's less than about 1.6 or 1.7 psi -- which is about as low as a pressuretrol can reliably operate -- you should have a vapourstat. But before you rush out and get one (yeah, I know, it's Christmas and a shiny new vapourstat under the tree would be nice!) there is at least one thing to think about.

Specifically, what was the more or less stable pressure which the system ran at, before it started to rise? If it was more than half a pound or so, how is your main venting? That more or less stable pressure is a direct reflection of your main venting and piping, since that is the pressure it takes to get the air out of the mains. It really shouldn't be over that half a pound or so; in fact, ideally it should be around 0.2 psi for a more or less typical residential system -- even a fairly big one.

Would the reduced fuel burn from not raising the pressure beyond what is needed to get that last radiator going save enough to pay for the vapourstat? Hard to say. It certainly isn't even close to proportional to the pressure setting, but it will save some fuel.

You mention a concern about interrupting the heating cycle. It will interrupt the burner running, if the heating cycle is long enough (on the main system I care for, it sometimes interrupts on very long recoveries). But this doesn't hurt the heating cycle -- those radiators will keep on delivering heat quite happily while the burner is off, working on the excess steam which was produced before the burner shut down. Most important, though, this causes at most a minor reduction of efficiency. Consider. While the burner is off, waiting for the system to catch up, it isn't burning any fuel. When the system catches up, it will fire up again. True, there is a small loss in there -- if there is a post purge and a pre purge, the gasses left in the fire chamber will have cooled off -- but the boiler itself will not have cooled significantly (which you can verify by noting that steam is produced almost immediately when the boiler fires up again)(I have, parenthetically, a disagreement with my delayed restart using a timer friends on this one -- you want as short an off period as is reasonable, so the boiler doesn't cool off).

Some would say that the additional wear on the burner from stopping and starting is a consideration. However, with any kind of luck at all (unless you got the system at midnight plumbing supply, off the back of an unmarked box truck) all the components should have a service life of many tens to hundreds of thousands of starts. Even if you ran 24 heating calls every day all winter, and each call involved the burner cycling on pressure four times (in which case your boiler is wildly ovesized, and you have other problems) that's only about ten thousand starts per winter. If the boiler is reasonably matched to the system, so that you have only perhaps three or four pressure cycles per start, and only on recovering from a setback on a cold morning, the difference is even less. So yes, it is a consideration, but in my view a minor one.

There is a consideration in the opposite direction, too, however: neither vents nor traps are really happy at higher pressures. Yes, they are rated for it (typically up to 3 psi working pressure), but they will last longer at lower pressures. Again, to cite the system in the main building I care for, all the traps are original to the system -- 80 years old -- as is one of the two main vents (I added one a few years back; don't really need it) -- since the system has never subjected them to a pressure differential greater than 12 ounces per square inch; I have heard others quoting a ten year life for traps.

I'm rambling -- but I hope my thoughts help!

Fred

It sounds like the Pressuretrol is reasonably calibrated. If the Cut-In is set at "1" and the Differential is set at "1.5", the pressure will be allowed to go up to 2.5 PSI. Set the Cut-in to .5 and the Differential to "1". That will keep the pressure capped at about 1.5 PSI.

EBEBRATT-Ed

The real trick is to get the system to heat(if possible) by not building pressure.

Optimize venting
Check EDR of radiators versus boiler capacity
Down fire the boiler firing rate (if possible) and if your calculations show the boiler oversized.

A vaporstat will cost$$ and won't do much for your operation. It may or may not be easier to set as many have complained the vaporstats are not accurately calibrated as well

cubicacres

Thanks-we'll monitor it and see what we find.

cubicacres

We watched the 0-3psi gauge today (31F outside vs. 0F last week, so maybe not the best comparison), and it had 0psi pressure for the first 5-10 minutes after the burners fired-up (we didn't use a timer today, so guessing on my times), then went to 0.4psi and stayed there or a bit higher up to .45psi for what seemed about 10-20 minutes before it shut off. We suspect shut off on low water, since the LWC/Feeder light was on just after the burners stopped, but we also saw the tekmar 279 showed 68F (the target heat) in the indoor sensor's room, so that could have done it as well. When it was colder last week, I thought it went up to 3psi before shutting off on pressure, low-water, or tekmar target heat reached from the indoor sensor. Our tekmar indoor sensor has always been within 2 degrees F of the 68 indoor target, so it seems we're at least keeping it consistent for the tenants.

We used a lower-cost IR camera attached to a phone we picked up recently (SEEK Thermal for android) and saw heat was building on the last radiator on the longest main line, but the vent was still 68F and didn't close yet before the burner shut off. The camera showed the first half of the radiator heated up before shut off. I suspect another few minutes would have closed the vent, but not sure.

Do we need it to start rising from a plateau level to verify if that's our baseline system pressure? The last radiators on each main line have larger gorton radiator vents (others on the line ahead of them have hoffman vari-vents), so hopefully that last about 15 feet past the last bedroom on the longest line with the smallest main diameter pipe in the common area hallway is the best to use for testing to ensure everyone's getting enough heat.

Would you recommend testing on a colder day to see that pressure rise again past the .45psi range, or trying to get the water/tekmar shut-off pushed back?

nicholas bonham-carter

Making these tests with the Tekmar is problematic. Cross the control wires for each test: time from hot header to first hot radiator, and to last hot radiator. Hopefully, the rads are getting steam at the same time. It sounds as though you have selected vents from the Gorton website, which is too simplistic to be right. They make good vents, but don’t follow their instructions Willy-Nilly.
First, your main vents should allow the air to escape at a back-pressure of less than 2 ounces. The rad vents should not be chosen for speed, until you know what is needed to accelerate a rad here and there-usually at the top floor. Hoffman 40’s are good slower tad vents.
What you should be aiming to do is to balance the low resistance to the escaping air from the main vents with the higher resistance of the radiator vents, so that the steam fills the basement pipes completely, before it begins to travel up to the rads. A string of rads is like a soaker hose in your garden. All the holes should be the same size, or too much water will come out the bigger holes too soon, and dry the lettuce in the areas with the smaller holes.
The aim should be to get the air out quickly, while still enabling all of the rads to get steam at the same time. Ideally, pats of butter on the rads should all melt at the same time, (a good loaf of country sour dough rye, and a toaster will be useful for this test).—NBC