Going commando!

bob_46

you only need a ruler 6.25 inches long to break an inch into 100 parts. Or you can buy one from Dwyer .

Abracadabra

I was just kidding around guys... ergo the smiley face

There's no way in the world Chris will be able to run his system at that low a pressure

abracadabra waits for ChrisJ to hookup a manometer and post a video of his boiler heating the place at 1/100 of an oz.

ChrisJ

Abracadabra said:

I was just kidding around guys... ergo the smiley face

There's no way in the world Chris will be able to run his system at that low a pressure

abracadabra waits for ChrisJ to hookup a manometer and post a video of his boiler heating the place at 1/100 of an oz.

Well,
If I convert it over to a two pipe minitube system with TRVs on each radiator and run a vacuum pump I bet I could do far better than 1/100 of an ounce.

BobC

It still amazes me that people don't understand how low a pressure it takes to move steam through a system. My boiler is 50% oversized because that is as small as wet based boilers get. I get steam to the input valve of the radiators before the 0-3PSI gauge begins to twitch so it's well below an oz for the steam to move through the system.

I'm waiting to see what Tim comes up with for a staged gas burner that will work on a wet based boiler, hopefully the cost won't be prohibitive. I would like to fire at 105 k till I get to 4 oz or so and then step down to about 65k until the thermostat is satisfied. Now I trip the 12 oz vstat and then cycle 1 minute off and 2 on (starting at about 4 oz) for several cycles.

Bob

ChrisJ

BobC said:

It still amazes me that people don't understand how low a pressure it takes to move steam through a system. My boiler is 50% oversized because that is as small as wet based boilers get. I get steam to the input valve of the radiators before the 0-3PSI gauge begins to twitch so it's well below an oz for the steam to move through the system.

I'm waiting to see what Tim comes up with for a staged gas burner that will work on a wet based boiler, hopefully the cost won't be prohibitive. I would like to fire at 105 k till I get to 4 oz or so and then step down to about 65k until the thermostat is satisfied. Now I trip the 12 oz vstat and then cycle 1 minute off and 2 on (starting at about 4 oz) for several cycles.

Bob

I'm curious why you would want to go all the way to 4 ounces before dropping the burner down Bob? Seems like a waste.

Why not drop the burner down as soon as you hit 1 ounce?

Mark N

Why depend on a Vaporstat. Use a thermal switch at the end of the main. Drop to low fire after the mains have been heated.

ChrisJ

Mark N said:

Why depend on a Vaporstat. Use a thermal switch at the end of the main. Drop to low fire after the mains have been heated.

Why not put a thermal switch on the header so she drops down after it starts boiling. No reason to force steam down the mains any faster than necessary.

Mark N

The piping is part of the pick up, drop back once it is heated.

ChrisJ

Mark N said:

The piping is part of the pick up, drop back once it is heated.

With all due respect I disagree.
I like the low and slow approach my self.

Mark N

The pressure is low, all the vents are still open. Drop it back after the main vents close. You're now firing at a rate the well matches the condensing capacity of the radiators.

BobC

The normal firing rate for my boiler is 105k. I've fired it as low as 76k using a smaller orifice, but the stack temperature starts to get very low (300). How much lower can I go before getting condensation in the stack.

Also The EZ-Gas doesn't like to work at low gas pressure (won't stay lit) so that tells me I would need a pair of valves feeding different orifices that T into the blast tube (maybe a 70k with a 35k that combine for high fire). It would not be as efficient at 70k because it would be getting too much air, it runs about 84.5% normally. It seems the trick would be to find a compromise that would keep the pot simmering without throwing the efficiency in the can.

I know Tim tried using the EZ-Gas in a staged setup and it sounds like the required complexity made it unfeasible. I don't know if he was varying the pressure or pairing orifices to get different flow rates.

Bob

ChrisJ

@Hatterasguy‌,

I have a mixture of Gorton vents on my second floor. Two rooms on small 26sqft radiators have Cs.

I do agree, there is always a limit and the total length of pipe between each boiler and radiator is what matters. Meaning, the length of the main plus the run out to the radiator is one thing from the radiator's point of view. The longer the run, the more pressure you need to get steam to it.

What that pressure is, I have no idea but what I do know is it's not 2 pounds in most cases.

ChrisJ

Hatterasguy said:

ChrisJ said:

What that pressure is, I have no idea but what I do know is it's not 2 pounds in most cases.

Absolutely.

There is no discussion regarding anything over one lb. That's going to be more than sufficient for any of our typical residential units.

However, recommending that everyone get down to ounces is just not practical unless the boiler is perfectly matched to the radiation, the main venting is plentiful, and/or there is modulation available.

We tend to encourage much lower pressure settings for everyone without realizing that they might get into a situation where the boiler starts hundreds of times per day because of our recommendations. When the boiler is oversized by more than 50%, a 2 lb. setting on a pressuretrol is not unreasonable.

Yes and no,
My recommendation is keep it as low as possible, and half an ounce is very possible. At the same time if the system cycles even once during a normal heating cycle I feel it's a problem. If the system cycles I'd raise the pressure until it stops up to about 8 ounces or so.

It's an art in my opinion. You need to get the system to run as low as possible but avoid constant cycling at the same time. If you need to go up to a pound to make the specific system work, then you do but no one should ever think they need a pound to get heat.

David Nadle

I think we all need to be more careful about telling people to turn down their pressure limit devices using language that implies it will have any effect on operating pressure. Operating pressure and pressure limit settings really shouldn't even be discussed in the same sentence. I think many people on this forum have been unintentionally misled by this over the years.

ChrisJ

David Nadle said:

I think we all need to be more careful about telling people to turn down their pressure limit devices using language that implies it will have any effect on operating pressure. Operating pressure and pressure limit settings really shouldn't even be discussed in the same sentence. I think many people on this forum have been unintentionally misled by this over the years.

I think you are correct. But how do we fix it?

The boiler being matched to the load and venting control the operating pressure, nothing else. Limiting devices such as a Pressuretrol in my eyes should rarely have to shut the burner down on a properly operating system.

Honestly, I view my Pressuretrol as nothing more than a safety device and mine is set to trip @ 1.5 PSI per my Wika 3 PSI gauge. While going above 1.5 PSI is not a safety issue I feel it's hard on vents and causes unnecessary noise and stress.

Charlie from wmass

A boiler that is over sized benefits most by limited pressure as it is not burning fuel beyond the needed pressure to heat the system. A properly sized boiler gains less by the low cut off pressure as it does not reach pressure so easy. A boiler that is not burning fuel is not wasting fuel.

Charlie from wmass

A boiler that is over sized that short cycles wastes leas fuel then one allowed to climb to 5 or 10 psi.

jumper

I agree with David Nadle. If you really want accuracy you need a gauge that is made to be directly connected to hot steam.And that instrument has to be periodically calibrated against a manometer.In another thread I asked about using some sort of thermometer instead of pressure?

ChrisJ

jumper said:

I agree with David Nadle. If you really want accuracy you need a gauge that is made to be directly connected to hot steam.And that instrument has to be periodically calibrated against a manometer.In another thread I asked about using some sort of thermometer instead of pressure?

Why would you need a gauge to be connected directly to hot steam? Does anyone even make such a gauge?

Fred

I think the average homeowner needs to understand that steam moves faster at lower pressures (counter intuitive to the average layperson) and:
1. That we suggest venting on the Mains sufficient to keep the preheat cycle to as close to 0 pressure as possible.
2. Once the Main is hot and the Main vents are closed, a certain amount of pressure (typically a few ounces, depending on the distance to the furthest radiator) is required to get the steam to those radiators.
3. That the boiler must be sized as closely as possible to the Radiator EDR and that a boiler that is significantly larger will increase pressures and cause short cycling (an attempt to use boiler controls to minimize fuel waste and not make steam that the system can't use effectiently) or to increase pressures well beyond what is required to get steam to the furthest point on the system. (There is a formula in one of Dan's books for calculating that pressure.) On my system it calculated out to 5 oz. even though my boiler runs a normal cycle at 1 oz, I have to believe the operating pressure in the mains and radiator runs is higher than it appears at the boiler gauge or steam would not get to that radiator. I'm sure that pressure is masked by the open radiator vents that the steam is racing towards.
4. That on very cold days and when trying to recover from deep set backs (when we reach a point, in the heating cycle) where the system is, for all practical purposes, really closed (all main and radiator vents) pressure will build to a point where the boiler controls will (may) cause short cycling because we know that somewhere beyond 1.5 to 2PSI, we are not effectively using the steam the boiler is making and the radiators no longer have the capacity to condense and release that.
5. That if the boiler is properly installed and sized, the main vents are adequate, and the system properly balanced, the boiler will run at a pressure necessary to satisfy the thermostat and anything up to that pound to 1.5 PSI is probably ok. Beyond that, something is not running as it was designed.
IMHO

Fred

"Maybe the book is incorrect on the minimum pressure required................"
That was my first suspicion

ChrisJ

I've yet to see more than 1/2 an ounce at my boiler during a normal heating cycle and all of my radiators heat the amount I want.

Either the book is wrong, or we are misinterpreting it. I thought there was something that stated most steam pipes are sized for a 1 ounce per 100 foot drop?

PMJ

I'm not sure I understand what the definition of a short cycle is in this discussion. Maybe someone could offer one at this point.

What I see in this discussion is that people are noticing that if a properly vented system is running to a pressure stop, it is putting more steam into their system than they need. So, they are looking for ways to operate accurately at lower pressures. However, they then see that as you get closer and closer to zero pressure there is no room to operate and then the fear of too many cycles takes over - however many that is.

But the reality is that because of the delay in steam systems something has to stop the boiler during the call or you will overshoot. The standard system has no other choice than pressure and that really isn't so bad. If you run up to 16 ounces now on a small system I doubt there is much to be gained spending a lot to try to get to 8 or 10 unless there are other problems to be cured. I am talking about a well running system here.

A much easier way to manage pressure and keep it down is just to use time and cycle on purpose to spread things out. I would suggest an addition to Dan's "crank it down" of "spread it out".

So I would ask at this point - how many cycles per day is too many and why?

ChrisJ

Hmmm.

Somehow my "nix the pigtail due to issues" thread turned into "how low is low and why are we pushing for it" thread.

That's ok, I've sidetracked enough threads in my time for this to continue for 235 pages. Please continue.

Fred

I think most of us consider a short cycle to be when, during a heating cycle, the burner is shut down on pressure before the thermostat has been satisfied and, after the initial burner run time, the burner continues to cycle on and off at 1, 2 or 3 minute intervals because the thermostat is still calling for heat and after the longer initial cycle, the pressure quickly drops to cut-in and back up to Cut-out pressures repeatedly.

PMJ

MarkS said:

@PMJ, I think for purposes of this discussion a "short cycle" is one that is prematurely interrupted due to an operating limit being reached, as opposed to a deliberately timed cycle like you and I are running.

So is there a timed cycle duration that is too short? I think we can all agree that any timed cycle that preheats the mains but delivers no heat to the radiators is too short. After that, it's more opinion and personal preference than hard fact. @Hatterasguy dislikes any cycle where the preheat time is longer than the time sending steam to the radiators. I won't run a cycle shorter than 10% of the overall cycle time (3 out of 30 minutes), and I think if you can achieve a preheat:heating ratio of 1:2 or 1:3 you're doing OK.

Thanks Mark, That makes sense and helps a lot.

The one thing I will mention here then is that it took me a while to really register is how different the requirements are from say 45 degrees out when hardly any heat is needed at all to say 20 degrees. In 45 conditions the preheat time is an issue because so little total boiler run time is needed that there are necessarily long off times. But when heat is actually needed, I found preheat times almost a non-issue. The standard system with only a pressure control has no choice but to treat them the same as you know already.

PMJ

Fred said:

I think most of us consider a short cycle to be when, during a heating cycle, the burner is shut down on pressure before the thermostat has been satisfied and, after the initial burner run time, the burner continues to cycle on and off at 1, 2 or 3 minute intervals because the thermostat is still calling for heat and after the longer initial cycle, the pressure quickly drops to cut-in and back up to Cut-out pressures repeatedly.

That is the trouble with using pressure as the control input variable - especially as it gets lower and lower and there is no deadband anymore. The old steam systems could do it because it was never on/off - they just adjusted the damper on the fire.

ChrisJ

MarkS said:

ChrisJ said:

Hmmm. Somehow my "nix the pigtail due to issues" thread turned into "how low is low and why are we pushing for it" thread.

So how's it working?

I've had no problems at all without a pigtail or trap of any kind.
The pipe doesn't even get warm after the valve 18" down.

Like the tech from Dwyer said, it works even better than a pigtail.

@MarkS‌
I'm curious what your digital unit would show if plumbed this way? I suspect you would no longer have to calibrate before each cycle.

ChrisJ

Hatterasguy said:

Fred said:

I think most of us consider a short cycle to be when, during a heating cycle, the burner is shut down on pressure before the thermostat has been satisfied and, after the initial burner run time, the burner continues to cycle on and off at 1, 2 or 3 minute intervals because the thermostat is still calling for heat and after the longer initial cycle, the pressure quickly drops to cut-in and back up to Cut-out pressures repeatedly.

With that definition, there are quite a few boilers that short cycle.

If we advise to get the pressure down into the range of ounces, the same boiler will have more short cycles. It will probably be more efficient despite all those short cycles because it starts and stops itself many times within a short period to maintain a narrow range of pressure.

The only question that begs is how many (short) cycles per day is a reasonable number?

I would like to see data comparing the same system cycling constantly between 1 ounce and 5 ounces vs one never cycling but climbing up to 1.5 PSI.

Fred

HATTERSGUY SAID: "With that definition, there are quite a few boilers that short cycle.If we advise to get the pressure down into the range of ounces, the same boiler will have more short cycles. It will probably be more efficient despite all those short cycles because it starts and stops itself many times within a short period to maintain a narrow range of pressure.The only question that begs is how many (short) cycles per day is a reasonable number?"

There probably are a lot of boilers out there that short cycle but I'm not sure getting the pressure down into the range of ounces is an issue. It's setting the controls down to unreasonable lows. As I said earlier in this post, my boiler runs on 1 oz of pressure but the vaporstat is set for a Cut-out of 12 oz. and a Cut-in of 4 oz. so running in the ounces doesn't generate more cycles. The boiler is controlled by the thermostat rather than the Vaporstat or Pressuretrol. Having too much boiler for the radiation, too little Main Venting, undersized Main or Radiator runs, Deep set-backs and very, very cold days (extended boiler run times) are what contribute to short cycling, in my mind..

Sorry Chris, I think we did Hijack your thread!

Charlie from wmass

I can say that when boilers run at lower pressures they burn less fuel. That is simple physics, it takes more fuel to reach 5X p.s.i. then to stop at X p.s.i. When the burner is off even during a short cycle it is not burning fuel. These are self evident cases. If a boiler runs for 15 minutes to climb to 2 p.s.i. it burners 1/4 of the b.t.u.'s it is rated for that hour. If the same boiler runs in 4 bursts of 2 minutes to maintain the lower pressure it has saved 7 minutes of burn time.

Fred

Charlie from wmass said:

I can say that when boilers run at lower pressures they burn less fuel. That is simple physics, it takes more fuel to reach 5X p.s.i. then to stop at X p.s.i. When the burner is off even during a short cycle it is not burning fuel. These are self evident cases. If a boiler runs for 15 minutes to climb to 2 p.s.i. it burners 1/4 of the b.t.u.'s it is rated for that hour. If the same boiler runs in 4 bursts of 2 minutes to maintain the lower pressure it has saved 7 minutes of burn time.

The problem is that many boilers run for 12 minutes to get to 2PSI and then runs 4 short 2 minute bursts on top of that to satisfy the thermostat. That is a total of 20 minutes of burn time.

Charlie from wmass

If they ran to 4 psi which is above the pressure for most air vents they would run for 25 minutes then turn off. Try it next time you have time to waste on a system. Let it cool down and crank the pressuretrol to 3.5 and time it.

Fred

Charlie from wmass said:

If they ran to 4 psi which is above the pressure for most air vents they would run for 25 minutes then turn off. Try it next time you have time to waste on a system. Let it cool down and crank the pressuretrol to 3.5 and time it.

I believe it.

Charlie from wmass

I would widen the pressure range to get it to 3 or 4 cycles. Keep cut in as low as possible to have reliable reset. That means make sure you do not set cut in so low that a vacuum is required to trip the control, be it pressuretrol or vaporstat, to on. I prefer to size the fire rate to seldom reach cut out pressure for the system and only shut off on temperature, but sometimes we just need to make the best of the hand we are dealt.

David Nadle

Food for thought: Is the steam faster because the pressure is lower or is the pressure lower because the steam is faster?

New year's resolution: When writing "run at" pressure, make sure I don't mean "stop at" pressure.

Some perhaps controversial thoughts: The relationship between operating pressure and burn time is probably not linear. The economic difference between operating at 4 oz/in^2 and operating at 1 oz/in^2 may be insignificant. The benefit to lower limit pressure should be multiplied by the fraction of cycles per season where the pressure actually builds. Concerns about "short-cycling" boilers after a pressure limit are overblown.

KC_Jones

Actually in my mind it isn't steam pressure it's system pressure we are seeing on the gauge. The "pressure" is actually the inability of the air to escape fast enough so really it's more about the air pressure than the steam pressure. Steam will only make pressure if you confine it. In the steam heating system the pipes AND the air confine the steam. If they air can't get out of the way fast enough the system starts making pressure. The steam will move as fast as you allow it to move and the only way to move it faster is to let the air out faster. The way I think of it is this. If you had a length of pipe and I had my hand over one end and you blew into the other end you would make pressure because I wasn't allowing the air out. Now suppose I made a tiny opening with my hand you would still have pressure, but slightly less because I was allowing the air out. Now suppose I removed my hand. You would make one quick puff get all the air out of your lungs and no pressure would be created. You didn't make the pressure on your end I was controlling the pressure by allowing your breath out at a certain rate. Now if you are able to blow at a rate faster than that pipe will allow out when wide open that is the same as an oversized boiler it makes steam faster than the system can handle it. Again as is stated so many times the sizing of the boiler is critical for system operation.

ChrisJ

Personally, I hate it if a boiler eve cycles once during a heating cycle. It bothers me.

Should it bother me? I don't know, but it does. To me it's like a reminder, the boiler saying "IT'S NOT RIGHT!!!!!!!!!!!!" every time it does it.

I'm a perfectionist, I know that and people who know me know that.

ChrisJ

Here's a video showing what my 3.0 Wika on the siphon is now showing compared to the siphonless Dwyer gauge.

Of course the Wika is a much higher pressure gauge but it shouldn't be reading a slight vacuum when there's actually pressure. If I remove the gauge it will rezero but over time it will end up in the negative again.

Sorry for the low quality of this cinematography. I'm not very good at it.


http://youtu.be/XEJ4JD6ojjg

ChrisJ

Hatterasguy said:

ChrisJ said:

I'm a perfectionist, I know that and people who know me know that.

Read my lips:

Two stage gas valve.

Ok, Lips,

For what?