thermostat swing?

Hollis

Is there a good swing setting to use in a programmable thermostat? I'm guessing it may be a bit different in an older high water mass boiler than a more modern low water one (?) I have both boilers . Seem like like the older boiler takes a long time to reheat for steam. I'm wondering if the swing should be set tighter esp in very cold weather (?)
If this is true, would a low water boiler be different?

Captain Who

Tough question. When the boiler is off and not steaming some of the heat from it is lost up the flue, in addition to what is lost to the boiler room air and walls. Some of the heat lost to the boiler room probably makes it up into the heated space, but none of what is lost up the flue does, obviously. It would be very important to have a good closing flue damper. This was made very obvious to me this morning when I discovered that my flue damper was stuck in the open position. I had noticed yesterday that the basement was super cold but a light bulb didn't go off until this morning when I was checking out the new CycleGard during recovery from setback and it was so cold down there that I was almost shivering.

EDIT: By swing I thought you meant overnight setback. Now I see that you were referring to the CPH setting for Honeywells and the like and the Slow or Fast setting for White Rodgers.

Fred

What is the water capacity of the older boiler? What brannd/model programable Thermostat are you using? Are the boilers oil or gas and have the burners been properly sized/fired? Typically, I would expect the firing to compensate for size/mass but hard to say what you have in the old boiler (especially if it is old enough to be conversion from coal to gas or oil).
Is there suffecient gas supply/pressure into the house for the burners to operate at capacity?

PMJ

My experience is a little different.

The amount of preheat required is directly related to how long it has been since the last burn. So fewer burn cycles in a day requires that the part of each burn devoted to preheat is longer. I wouldn't be able to take advantage of any natural vacuum with long cycles as it would all disappear between each one. I have found in my system that the preheat time required from dead cold is about 20 min. From an off time of about 90 min the preheat is about 8 min. At 3 cycles per hour each one with a 10 min burn with natural vacuum between each one the preheat time is less than one minute. I don't believe there is a big difference in total % of burn time devoted to preheat based on number of cycles. In fact I would probably argue it actually goes down with more and the efficiency better.

48 cycles per day would be about 10,000 cycles in a heating season. At that rate it would take 100 seasons to get a million cycles. I think gas valves a rated at many more than that so it hasn't been much of a concern for me.

PMJ

Hatterasguy said:

Now you've got my curiosity piqued. I don't have the benefit of any vacuum but I can certainly reduce the cycle time from 90 minutes to 60 minutes and see how much of a benefit I get in preheat reduction.

My guess is, without vacuum, I won't see anywhere near the reduction that you observed. I still must drive the air from the mains at a fraction of an ounce (all that is available on start).

If my preheat time reduces from the current six minutes down to four minutes, as an example, the net result is the same in terms of total preheat time. I would highly doubt I can get lower than 4 minutes, even if the cycle time was reduced to 30 minutes.

I have the additional problem with 30 minute cycle times regarding the run time. At 35°F, the run time is exactly 33% of the cycle, not including preheat. That's 10 minutes. Now increase that to 50°F and the boiler will be doing run times of only 5 minutes. When the run time gets this low, accumulated differentials in the delivery system get to be a problem.

So, effectively, 60 minutes would be the absolute lower limit for me and I'm not inclined to do it without a significant reduction in preheat (at least 50%).

With the equivalent of open pipe venting the time it takes to preheat is just about how much the mains have cooled down - which is how long since last fire. As the cycle time gets shorter they have cooled down less and therefore it takes less time to preheat - dramatically so. Steam should travel extremely fast down an already hot main if the venting is adequate(as in you can't hear any air coming out).

This is the subject that took me a while to understand - that all preheats are not equal, not close. I gradually changed my strategy to extending call times and shortening cycles. It turned out that this way the preheat % of the total burn time was the lowest.

PMJ

Hatterasguy said:

PMJ said:

I gradually changed my strategy to extending call times and shortening cycles. It turned out that this way the preheat % of the total burn time was the lowest.

Can you explain "extending call times"?

How do you shorten the cycle to, say, 30 minutes but extend the call time?

What's the control method?

Call time is extended because I don't run the burner long enough to satisfy the tstat quickly - on purpose. I deliberately move very slowly from cut in on the tstat to cutout - takes hours when it is cold out. This is the most even heating. If you could hold the temp perfectly in the middle of the dead band the call would never be satisfied.

PMJ

Hatterasguy said:

Interesting.

Still begs the question:

How are you controlling it? Clearly, the 'stat isn't cycling the boiler? A timing device of some sort?

Yes a timing device, a PLC. I spread the burn time out in evenly spaced pieces which achieves the same result as modulation.

PMJ

Hatterasguy said:

PMJ said:

Hatterasguy said:

Interesting.

Still begs the question:

How are you controlling it? Clearly, the 'stat isn't cycling the boiler? A timing device of some sort?

Yes a timing device, a PLC. I spread the burn time out in evenly spaced pieces which achieves the same result as modulation.

Nice.

I do the same with the Tekmar 279 without a thermostat and without any indoor sensors. But, my strategy has been exactly opposite to yours.

What is your burn time and your total cycle time at an ambient of 35°F?

What do you think it would be at 50°F?

Here is some approximate data for 24 hours periods at 3 different average temperatures - enough to get the idea anyway:

At 45deg: 12 calls for heat 580min total call time
ave call length 48 min
29 burner starts
159min total burner run time
ave burner run time 5.48 minutes

At 25deg: 8 calls for heat 1107min total call time
ave call length 138 min
55 burner starts
361 min total burner run time
ave burner run time 6.56 min

at 5deg: 5 calls for heat 1353min total call time
ave call length 270min
60 burner starts
488 min total burner run
ave burner run time 8.13 min

So as you can see as it gets colder the length of the calls goes up dramatically and the boiler cycles more. I think it is very efficient because of the vacuum and the heat is obviously very even. Every time the burner goes off boiling continues for several minutes as the vacuum drops the boiling point. On each restart boiling resumes immediately because it is still under vacuum and the new steam flies out the mains chasing the vacuum away. And because I never let the air back in I don't have to chase it back out on every cycle. When it is cold out I am saying there really is no preheat on each cycle or if you insist call it less than a minute each.

PMJ

2 pipe system. 1000EDR. Less than $100 PLC. Software free. Logic entirely up to the user so development ongoing. In sum, for the steam buff this = fun.

Think of it this way - in any given 24 hour period a set amount of total burner run time is needed to compensate the heat loss of the structure. All I do is spread that time out in shorter burns - it is the same total amount. My main goal at first was just to even out the heat - that is to avoid any overshooting and the longer off periods which allowed the mains to cool down. Then I realized that the more even the heat, the slower the climb from tstat cutin to cutout had to be. But I only had one boiler burner speed to work with which is "high". So I tried shorter pulses. I found that once my well insulated mains were heated they really didn't cool down at all in 15 minutes of off time so when it is cold and I pulse the boiler all day long I have minimal preheat time. I also found that the boiler never needed to run more than 50% of the total time to heat down to 10 below. So my program always has 20 minute cycles but 3 different burner on/off "speeds" - 5/15,8/12,10/10.

Then I went to work on the natural vacuum. The piping is 90 years old and it leaks. I removed all the vents from everything. I put one 3/4 inch solenoid valve on the dry return which gives me open pipe vent quality and complete close on the burner off part of the cycle. On continuous 10/10 operation about 40 inches water vacuum is still there on each restart.


Hope this helps.

Captain Who

I'm envious of your system. It's beautiful. I guess it would be cost prohibitive to try to convert a one pipe steam to a vacuum system such as yours, since every single radiator would also have to have a solenoid valve that was controlled by the central computer. I also wonder about the electrical cost of operating all of those solenoids.

I do want to implement an electrical solenoid mains venting system on mine eventually with a temperature switch on the end of the main and a solenoid valve at the end of the dry returns.

Have you ever considered making a living converting people's systems to one that operates like yours?

PMJ

Captain Who said:

I'm envious of your system. It's beautiful. I guess it would be cost prohibitive to try to convert a one pipe steam to a vacuum system such as yours, since every single radiator would also have to have a solenoid valve that was controlled by the central computer. I also wonder about the electrical cost of operating all of those solenoids.

I do want to implement an electrical solenoid mains venting system on mine eventually with a temperature switch on the end of the main and a solenoid valve at the end of the dry returns.

Have you ever considered making a living converting people's systems to one that operates like yours?

i

Thanks but I think this is an owner/operator kind of thing. I can't see the average homeowner paying a contractor for the time required to tweak things.

I'm thinking about the one-pipe thing. Definitely more difficult with more moving parts. The spread it out thing will work without doing anything else though. You might just give that a try for starters. Could be done with a simple pulsed output from a single input(the tstat) for very little money.

Mark N

The best way to accomplish what you are looking to do with a one-pipe system is to convert it to an air-line system using a Paul Vent. Hofffman still sells Paul vents. The are Hoffman #3 vents.
Using an air line system speeds the distribution of steam in a one-pipe system

Captain Who

Very interesting. So it has already been invented, that figures (See "Vacuum Air Line System"):

http://www.mepcollc.com/pdf/literature/iom/Steam Systems.pdf

Mark N

Off course it has, they also used to manufacture vacuum vents for one-pipe steam. It only worked well with a coal fired boiler. After the switch to intermittent firing they were discontinued. There is a great article in the heating museum "How to Lock Out Air, The Heat Thief"

PMJ

Mark N said:

Off course it has, they also used to manufacture vacuum vents for one-pipe steam. It only worked well with a coal fired boiler. After the switch to intermittent firing they were discontinued. There is a great article in the heating museum "How to Lock Out Air, The Heat Thief"

Very good article and well worth everyone's read. I'm not sure about the 30% claim but I do know with vacuum it is some % more efficient and way better on comfort. I do know that the steam travels much faster not having to push the air out each time. I can still hear some boiling in the boiler at least 5 minutes after the burner goes off so the vacuum does pull more steam up into the mains than would happen without it.

I guess I'm just not understanding why the vacuum thing seems to have been abandoned in residential with the switch to gas and oil and intermittent fire.

Captain Who

"I guess I'm just not understanding why the vacuum thing seems to have been abandoned in residential with the switch to gas and oil and intermittent fire."

Me too. Very disappointing. I'm wondering if it became too difficult to have a vacuum tight system with all the 70+ year old systems out there. The thought of the 30% savings had me chomping at the bit and they also mentioned a 2 year payback and a 5 year warranty on those vacuum vents (no longer made).

I guess someone has to come along and come up with a cost effective solution which may be the combination of a regular vent and a solenoid valve controlled by a pressure switch for each radiator. The solenoid valve would be always closed except in the case where air got into the system and you need to let the vent do its job to let it out before vacuum operation can be restored.

I guess the first step before anyone considered attempting this is to vacuum test your entire system by heating all radiators fully and shutting down all vents with a ball valve or something and watch the vacuum gauge to see how low it will go and how long it will maintain that setting.

ChrisJ

Something to keep in mind is your mains are losing heat the entire time the boiler is running.

The hotter the piping is, the greater the heat loss. As the piping cools, heat loss is reduced but is at it's peak while you are producing steam.

I run 2 cycles per hour for comfort, not to keep my piping or boiler hot. Same rules as piping apply to the boiler, the hotter it is, the faster it's losing heat.

In my opinion, preheat time is moot because you need to heat the piping anyway, and just because it seems longer doesn't mean you lost more energy from it. Also, in most places the heat is lost somewhere under the home being heated and therefore a majority of it likely ends up in the home.

If your system comes up to a boil fast and gets steam out to the radiators fast I see no problem with running 2 CPH. Sometimes, you may find the thermostat calls for heat but shuts down before the radiators even get hot. Personally, I'd ignore that because it doesn't waste much energy and it will just make the system heat the home faster on the next cycle.

If you have an older boiler, something in the 30-40 gallon range and uninsulated piping I would go for 1 CPH.

That's my opinion anyway.

Captain Who

"It only worked well with a coal fired boiler."

Well the article WAS written in 1927 when most people were probably still using coal for fuel but it doesn't really imply that it only will work well with coal. But here's what it says:

Any good heating and plumbing shop in a few hours (without tearing out your present steam plant or putting in any new piping) can, by making one simple change vacuumize your present one pipe steam system - enabling you to get up steam in 15 minutes (not an hour); and keep radiators piping hot 3 hours (not 30 minutes) after fires are banked and steam pressure drops. What is more, this one change can save you one-third of any fuel you now use - WHETHER IT BE COAL, OIL OR GAS.

SWEI

Captain Who said:

the article WAS written in 1927 when most people were probably still using coal for fuel but it doesn't really imply that it only will work well with coal. But here's what it says:

Any good heating and plumbing shop in a few hours (without tearing out your present steam plant or putting in any new piping) can, by making one simple change vacuumize your present one pipe steam system - enabling you to get up steam in 15 minutes (not an hour); and keep radiators piping hot 3 hours (not 30 minutes) after fires are banked and steam pressure drops. What is more, this one change can save you one-third of any fuel you now use - WHETHER IT BE COAL, OIL OR GAS.

These are the very words that inspired me to ask (and I continue to do so): How do we do this today?

Mark N

If you read the Lost Art of Steam Heat, Dan doesn't recommend any naturally induced vacuum, only mechanically induced with a pump. Some have had good luck with getting it to work. Most over the years had nothing but problems and I would assume the vacuum vents didn't sell and were discontinued many years ago.

Captain Who

Dan, do you know anything about why and when the vacuum vents were discontinued? Did they take a beating on their 5 year warranty offer? Are aging steam systems just too leaky compared to when they were built to make it work in a trouble free fashion?

Mark N

Do you own a Copy of the "Lost Art of Steam Heat"? It is explained in the section on "Naturally Induced, Vapor/Vacuum Systems" starting on page 242. It didn't function properly with intermittent firing and was abandoned.

PMJ

I read that in the Lost Art too. I'd like more detail as to exactly what about a particular system would make what is described so well in the "Heat Thief" article above by Hoffman impossible. For what it describes is exactly what I have done for years now.

Captain Who

PMJ - exactly. I don't think this is like the 200 mpg carburetor we're talking about here. Those testimonial letters were very convincing. I find it hard to believe that this cannot work with intermittent firing, especially with 2 stage burners and modern digital thermostats with lots of temp swing and/or CPH adjustment points.

Keeping the air out would make boilers and steam pipes last so much longer. Perhaps that's the problem in this planned obsolescence non utopian society where the almighty dollar rules over quality of life.

ChrisJ

Keeping the air out is the only thing attractive to me to be honest.

That air is rotting everything including the boilers. That's why my dream steam system is all copper and brass with silver soldered connections. Pull a strong vacuum on it, fill it with dry nitrogen until you're at the boiling point you want and you're done.

PMJ

ChrisJ said:

Keeping the air out is the only thing attractive to me to be honest.

Any space with the some or all of the air removed is a vacuum. If you remove air you don't have any choice but to enjoy the other positive benefits of vacuum.

ChrisJ

PMJ said:

ChrisJ said:

Keeping the air out is the only thing attractive to me to be honest.

Any space with the some or all of the air removed is a vacuum. If you remove air you don't have any choice but to enjoy the other positive benefits of vacuum.

I don't understand?
Was something I said inaccurate?

Fred

Hoffman still makes and markets the #76 Vacuum vent for Mains (looks just like the #75) and I would think a TRV without a vacuum Breaker would be usable on as a vacuum vent on a radiator. Of course I could be missing something here, but for a few hundred dollars someone could test the theory of a natural 1 pipe vacuum system.

Mark N

The Dead men couldn't make this work with intermittent firing on one-pipe steam. What has changed? The Paul system is the way to go for one-pipe steam.

PMJ

ChrisJ said:

PMJ said:

ChrisJ said:

Keeping the air out is the only thing attractive to me to be honest.

Any space with the some or all of the air removed is a vacuum. If you remove air you don't have any choice but to enjoy the other positive benefits of vacuum.

I don't understand?
Was something I said inaccurate?

Didn't mean to offend Chris. Sorry if I did.

The way you put it I read (looks like mistakenly) that you attempted to separate the reducing corrosion benefit of removing air from the other possible benefits being discussed - which currently were under discussion in the string as to their existence at all.

Could I rewrite your line this way - "Creating a vacuum in the system is the only thing attractive to me to be honest" and be accurate as to how you feel about it? If so, then I merely read into what you wrote something that was not there and I apologize.

Captain Who

I'm thinking take a Maid O Mist vent with the removable orifice and attach a custom designed swing check valve with a hardened steel ball on a viton o ring seat with a counterweight on an adjustable pivot arm to play around with different cracking pressures. You'd want to see how low you can go with the cracking pressure.

The check valve sub assembly would be u shaped facing downwards with replaceable orifices of different sizes at the vent side to keep the Maid O mist adjustability feature and the pivot arm/check valve seat would be at the bottom of the U.

Mark N

Do a search on the Wall for "Vacuum air vents on one-pipe systems". It is from a few years ago. Never heard back from Richard Ban on how it worked out.

ChrisJ

PMJ said:

ChrisJ said:

PMJ said:

ChrisJ said:

Keeping the air out is the only thing attractive to me to be honest.

Any space with the some or all of the air removed is a vacuum. If you remove air you don't have any choice but to enjoy the other positive benefits of vacuum.

I don't understand?
Was something I said inaccurate?

Didn't mean to offend Chris. Sorry if I did.

The way you put it I read (looks like mistakenly) that you attempted to separate the reducing corrosion benefit of removing air from the other possible benefits being discussed - which currently were under discussion in the string as to their existence at all.

Could I rewrite your line this way - "Creating a vacuum in the system is the only thing attractive to me to be honest" and be accurate as to how you feel about it? If so, then I merely read into what you wrote something that was not there and I apologize.

You didn't offend, just confused me.
I'm not sure about the other benefits but I do know a system without air in it is a system without corrosion. When I said pull a vacuum on the sealed system I'm talking in the neighborhood of 100-500 microns with several nitrogen purges. Same practice you would do on a refrigeration system if you're being extra careful.

I don't have anything helpful to add in regards to the other aspects.

PMJ

ChrisJ said:

Ok. You do want a system in vacuum and you want it to be totally sealed from the atmosphere too. It would be nice to know if that could work in theory even. I don't know.

KC_Jones

PMJ said:

I was wondering the same thing. What would happen if you just closed up the whole system, removed all the vents and pulled a vacuum on it. I would think it is a matter of being able to pull enough vacuum to always be ahead of max steam production minus the condensation. Also the system being tight enough to maintain that vacuum....probably the bigger problem. Anything like this would probably only be worthwhile on an already properly running system. The logic in me says there is no way it's that simple....of course has anyone ever tried it?

ChrisJ

Well, if the system is hermetically sealed my vacuum pump can do down to around 20 microns if you wait long enough. 1000 microns is probably enough for such a thing.

I believe water boils at around -60F at 20 microns.
That's why I said to refill using dry nitrogen until you get to the boiling point you want e.g. 120F. This would keep the system corrosion free.

It would basically be a huge heat pipe system using water.
http://en.wikipedia.org/wiki/Heat_pipe

I think we're way off topic now. The op was asking what swing to use on their thermostat.

SWEI

ChrisJ said:

I'm not sure about the other benefits but I do know a system without air in it is a system without corrosion. When I said pull a vacuum on the sealed system I'm talking in the neighborhood of 100-500 microns with several nitrogen purges.

No need to do that, actually. Over the first few weeks of operation, the oxygen in a sealed system will slowly combine with pipping and other components, leaving you in effect a nitrogen bubble inside. Pressurized drainback solar systems work this way, and run many years using cast iron circulators.