One pipe steam and recovery from night setback

Jacob Myron_20

Physics of steam is very important as is the the vapor stat, t stats and all the control settings.

More importantly is the basics of steam heating.

Example a building that requires 100,000 BTUH with a cast iron boiler not equipped with an automatic feeder.

Important item # 1.

Condensate lag: The time it takes for condensate to return from the system to the boiler.

Several things affect condensate lag;

1. Defective vent valves, water trapped in a vent valve.
A vent valve may not spit and sputter, it can vent air but just as important it must allow air to re-enter the system through the radiator and steam main vent valve.

Air re-entry prevents a vacuum from ocurring. Vacuum in a one pipe steam system is not desirable as it will hold water in the radiator and some horizontal piping. This water eventually will return to the boiler but this condensate needs to return as soon as it is formed.

2. Obstructions in the wet return piping.

Scale or mud (iron oxide) that collects at the bottom of the wet piping will cause water to return to slow. Additionally, scale and mud can form in the bottom of the boiler (the lower circulating legs inside the boiler).

3. High efficiency low profile boilers that have insufficient water content or the hight of water to keep a boiler from short cycling.

A cure for this condition is a small condensate pump and a steam trap installed at the end of the steam main or steam mains.

4. Here are some basics:

a. Water expands in volume 1700 times when it changes state, to steam.
b. One pound of water will yield one pound of steam at one psig at 215 degrees F.
c. One edr or sqft. of steam equals 240 BTUs
d. Four edr equal one pound of steam for steam heating.
e. divide 100,000 BTUH by 960 btus and that tells you that the system needs 104 pounds of water per hour to heat the building.
e. divide 104 pounds of water by 68 and that tells you the system needs 1.5 gallons of water per hour.
f. divide 1.5 gallons of water by 60 minutes and that tells you the system needs .025 gallons of water per minute to heat the building.
g. an average condnesate lag for a house is about ten minutes. That means that .25 gallons of water was used to heat the piping and warm the radiators in the building and it would take another 10 minutes for the system to pressurize. In the first 20 minutes a half a gallon of water was used to begin the ull heating cycle. Remember the system without any problems returned .25 gallons of water to the boiler.

At the worst case senario .5 gallons of water left the boiler and add to that the amounbt of water that was pushed out of the boiler into the the vertical drops from the steam main or steam mains connected to the wet return.

Some of the problems that may be present in the system are:
1. back ptched radiators
2. defective vent valves not allowing air to re-enter the steam system
3.sagging steam main and horizontal run outs to the steam risers
4. blockages at the base of steam risers
5. uninsulated steam mains
6. clogged wet return piping
7. partially closed radiator valves
8. leaking packing nuts on radiator valves (causes loss of system water)
9. improperly piped near boiler piping
10. possible cross over between the steam side of the system and the return side of the system.

Night set back in most cases with out special controls and done from a thermostat in degrees, should not be more than 4 degrees F. Graete degree setbacks cause the boiler to run to long to buy back the heat loss. Pardon the pun all the savings that ocuured will go up in smoke.

Jacob Myron

McKern_2

I think I need a quick physics lesson

From what I've read here*, I understand that thermostat setbacks aren't as effective with steam as with forced air and hot water systems, i.e., that there is something inherently inefficient in the way steam systems recover from the setback.

I can see that the recovery period would take longer due to having to reheat the mains and supply pipes before the radiators heat, but that wouldn't be the source of the inefficiency, right (i.e., reheating wouldn't require more BTUs than maintaining the temp)?

So, what am I missing?

Thanks for any help

*after searching the forum on the topic

David Nadle

Inefficient, or less efficient?

A cast iron steam system has more thermal mass than other systems, and if that thermal mass cools off a lot it has to be brought back. But I do not believe that this makes setback inefficient, i.e. wasteful of energy compared to the alternative of no setback.

Nor does it necessarily make setback ineffective. The longer recovery period and the tendency to overshoot the set point are control problems which might be solved with a new thermostat.

It seems to me that if steam setback is inefficient one could write a simple heat equation expressing this; I've never seen it done.

My own issue with setback on one pipe steam is that my system doesn't respond well to a long cycle. After a long cycle and a cut out on pressure the system begins to short cycle on pressure until the thermostat is satisfied. This short cycling on and off while most of the boiler's water is already up in the radiators causes hissing in some radiators. I am currently researching a fix using a delay relay to enforce a minimum off time after hitting the pressure limit.

Fred Harwood_2

Setbacks

Thinking about thermostat setbacks, short of formal physics, might start with looking at the three parts of the setback. The first is the cool-down. The second is the resting period at the lower temperature. The third is the reheating.

Because the first and the third parts roughly equal each other, or because the BTUs saved in the first part virtually equal the BTUs spent returning the space to the original temperature, we should think more about the second part.

The resting period at the lower temperature matters most, because the heat loss from the space will be less at the lower temperature than at the original temperature. However, how quickly comfort can be restored at the end of that period without over-sizing the heating plant matters as well, because such a plant would be less efficient when not reheating the space. Especially high-mass radiant heating has such problems. Also, large temperature setbacks and reheats cause structural stress, cavity condensation and rot or mildew or mold, to mention just two common problems.

My experience is that home setbacks of, say, two degrees for sleeping, and of five degrees for periods of one or two days, and of up to 15 degrees for longer periods can save significant BTUs. Of course, living with the heating thermostat at the lowest comfortable setting while wearing that quilted shirt also saves BTUs.

Edward A. (Ed) Carey_3

Use of a delay relay on steam?????

Dave said: "This short cycling on and off while most of the boiler's water is already up in the radiators causes hissing in some radiators. I am currently researching a fix using a delay relay to enforce a minimum off time after hitting the pressure limit".

Dave, I think that you may wish to rethink that idea. It will defeat the very purpose of the differential on the pressuretroll.

By using a TD relay you will allow the water temp to drop below the boiling point, which will cost a lot of additional energy (and $)to bring back to a boil, again and again, on a single heating cycle.

If your radiators are hissing, and the condensate is not returning back to your boiler adequately and quickly, you have other issues there.

Ed Carey

McKern_2

Thanks, Fred, this is getting at the part I'm missing.

First, what is "high-mass radiant heating" in terms of a typical home steam heating system?

Second, re "because the BTUs saved in the first part virtually equal the BTUs spent returning the space to the original temperature": I've always understood that this is true of forced air and hot water systems. But, if I'm reading things correctly, some people contend that after a certain point (~5 degrees) bringing a steam system back to temp requires more BTUs in recovery than will be saved in a 6 hour setback in a typical steam heated home.

As an analogy (i.e., I don't believe the physics apply): it takes more energy to put something in motion than to keep it in motion.

So, is there no basis for this?

Thank you

Fred Harwood_2

Setbacks

No connection between high-mass radiant and home steam systems. However, short setbacks on radiant systems seldom save BTUs because they can't reheat quickly enough for comfort.

Yes, much discussion revolves around steam system recovery losses. Often, the systems discussed have other problems. And, yes, things at rest require more energy to accelerate than to keep moving at a steady velocity. Said another way, raising the kinetic energy of a thing requires additional energy. However, slowing the thing gives that energy back.

In my experience, once tuned up with adequate and proportionate radiator and mains venting and a Vaporstat, a 1950s one-pipe steam boiler matched to its connected load on a T87 thermostat will quickly, evenly, and without overshoot reheat a living space. After all, those radiators were sized to their respective maximum heating loads. And the rapidity of the reheat with steam at 212F means that the boiler will shut down quickly, giving it a small comparative advantage over the cooler medium of air and water. For any given reheat and medium, the sooner the boiler stops, the more energy you save.

Also, when a matched boiler can run without cycling during a reheat, it runs at design efficiency for the duration of the reheat, thus offsetting cycling losses often seen on other systems.

All the above means that steam may be more efficient than other systems when reheating. However, in general, small, short setbacks save little energy when compared to deep longer setbacks for reasons independent of system. Again, if one's home is snug and one's reading chair has a lap blanket, ...

David Nadle

That's the idea

Ed, I don't want to defeat the differential on my vaporstat but for some reason my system does not maintain pressure after it cuts out. The pressure drops to a couple ounces vacuum within a minute. After the first 30+ minute burn the boiler cycles 50% every 80 seconds until the thermostat is satisfied.

In other words, when I cut out at 12 ounces, I'm at negative ounces in seconds, the vaporstat cuts in, and I'm back at 12 ounces in 40 seconds. The pressure that the vaporstat sees after cut out is not the pressure at the radiators.

Now, about 90% of the time the thermostat is satisfied long before the system cuts out on pressure, so there's no hissing. Only on very cold days--or if I used setback--would the boiler enter it's short cycling mode.

So my reasoning is: there is some time T that the boiler must remain off to allow enough condensate to return to the boiler so that the system will not push water into the vents the next time it comes on. I know T is > 40 seconds and < 30 minutes. I need to experiment to find T. Who knows, maybe it's just 1 or 2 minutes.

Do you still think the relay is a bad idea?

RonWHC

The (at one time)

largest selling commercial steam heat control has had a set back feature since the early 1960's. Possibly earlier. Their newer controls, & the one we now use has a built-in set back timer, provision for earlier set back, & variable pick up. Neither manufacturer would have gone to that trouble if setback offered no benefit.

Since almost every installed steam system is oversized, & since the boiler should match the installed load, a properly sized boiler should easily pick up a reasonable setback 90% of the time. The very conservative 10% is for design, or below design days. May never be an issue w/ most systems.

Not being a residential type; I can't say if any of the new crop of smart stats can do steam as intelligently as they do water & air. I do know they had problems w/ steam in the past. Most geeks can't think steam. It's a generational thing.

Set back on steam systems can save $$. The devil is in the details.

Fred Harwood_2

Relay

David, I agree with others here that you may have an undiagnosed problem in you steam system. For example, above you say: "This short cycling on and off while most of the boiler's water is already up in the radiators causes hissing in some radiators."
Most of the boiler's water should not be up in the radiators at any time. Perhaps a half inch of your sight glass may be elsewhere in the pipes, but something truly is wrong if most of the boiler's water is anywhere but in the boiler.
The rapid cycling of the Vaporstat also suggests something wrong. Vaporstats have various configuations. What specific model do you have? Also, does the Vaporstat mercury bulb bounce at any time?

Fred Harwood_2

Devilish Details

Thanks, Ron. I agree with you that setbacks save energy, and that the Devil is often in the details. And I'm old enough to remember when government mandated that controls have setbacks, especially for public and commercial buildings. I've even made some with clock relays and multiple thermostats.

That said, I'm often the guy a homeowner has turned to when the new electronic thermostat fails to produce big bucks in energy savings as advertised. That's the reason that I suggest to thrifty homeowners that they simply reduce the setting and dress accordingly. That way they have more hours at lower settings, and tangible savings.

The setback discussion has been around for a long time, and probably next year will receive renewed government attention. No doubt, manufacturers will soon follow with improved adaptive controls. At bottom, however, is the simple fact that no control or pattern of minor setbacks or government edict can make up for an inefficient or compromised system. Which makes The Wall invaluable.

David Nadle

I agree

Fred, I know I have an undiagnosed problem. I'm stumped. I would love to figure it out and avoid the use of a relay. It's inelegant. But I have tried many other things first. I truly appreciate your interest and I'll do my best to answer all your questions.

I might be inaccurate to say that "most" of the boilers water is in the radiators. But if I were to start with a water level less than halfway up the glass there's a chance I'll cut out on low water after a long burn. It's a small boiler, and it takes more than 30 minutes to reach that point. I don't think this is abnormal or uncommon for a small boiler. Am I wrong?

Maybe I have a condensate return problem. It does get back though. I have tried pitching radiators. I have dry returns, and the wet is all less than 2 years old. I don't know how to get the condensate back any faster.

The vaporstat is a newer non mercury model 0-16 oz. I think it's working properly, verified by a low pressure gauge on the same pigtail. It's not the most accurate device I've ever used. (It's set for 10 out / 2 in but the gauge reads over 11 when it cuts out.) It is seeing vacuum and zero pressure soon after cut out, so it rightly cuts in.

Any suggestions?

McKern_2

Well, now I have to go back and try to figure out where I got the idea that there are some issues regarding energy savings with night-time setbacks!

Jacob Myron_20

Recovery from night set back

Physics of steam is very important as is the the vapor stat, t stats and all the control settings.

More importantly is the basics of steam heating.

Example a building with that requires 100,000 BTUH with a cast iron boiler not equipped with an automatic feeder.

Important item # 1.

Condensate lag: The time it takes for condensate to return from the system to the boiler.

Several things affect condensate lag;

1. Defective vent valves water trapped in a vent valve.
A vent valve may not spit and sputter, it can vent air but just as important it must allow air to re-enter the system through the radiator and steam main vent valve.

Air re-entry prevents a vacuum from ocurring. Vacuum in a one pipe steam system is not desirable as it will hold water in the radiator and some horizontal piping. This water eventually will return to the boiler but this condensate needs to return as soon as it is formed.

2. Obstructions in the wet return piping.

Scale or mud (iron oxide) that collects at the bottom of the wet piping will cause water to return to slow. Additionally, scale and mud can form in the bottom of the boiler (the lower circulating legs inside the boiler).

3. High efficiency low profile boilers that have insufficient water content or the hight of water to keep a boiler from short cycling.

A cure for condition is a small condensate pump and a steamtrap installed at the end of the steam main or steam mains.

4. Here are some basics:

a. Water expands in volume 1700 times when it changes state, to steam.
b. One pound of water will yield one pound of steam at one psig at 215 degrees F.
c. One edr or sqft. of steam equals 240 BTUs
d. Four edr equal one pound of steam for steam heating.
e. divide 100,000 BTUH by 960 btus and that tells you that the system needs 104 pounds of water per hour to heat the building.
e. divide 104 pounds of water by 68 and that tells you the system needs 1.5 gallons of water per hour.
f. divide 1.5 gallons of water by 60 minutes and that tells you the system needs .025 gallons of water per minute to heat the building.
g. an average condnesate lag for a house is about ten minutes. That means that .25 gallons of water was used to heat the piping and warm the radiators in the building and it would take another 10 minutes for the system to pressurize. In the first 20 minutes a half a gallon of water was used the begin the heating full heating cycle. Remember the system with any problems returned .25 gallons of water to the boiler.

At the worst case senario .5 gallons of water left the boiler and add to that the amounbt of water that was pushed out of te boiler into the the vertical drops from the steam main or steam mains connected to the wet return.

Some of the problems that may be present in the system are:
1. back oitched radiators
2. defective vent valves not allowing air to re-enter the steam system
3.sagging steam main and horizontal run outs to the steam risers
4. blockages at the base of steam risers
5. uninsulated steam mains
6. clogged wet return piping
7. partially closed radiator valves
8. leaking packing nuts on radiator valves (causes loss of system water)
9. improperly piped near boiler piping
10. possible cross over between the steam side of the system and the return side of the system.

Night set back in most cases with out special controls done from a thermostat in degrees should not be more than 4 degrees F. Anything longer than that will cause the boiler to run to long enough to buy back the heat loss and all the savings that ocuured will be lost in the warm up period.

Jacob myron

Jacob Myron_20

Recovery from night set back

Physics of steam is very important as is the the vapor stat, t stats and all the control settings.

More importantly is the basics of steam heating.

Example: a building that requires 100,000 BTUH with a cast iron boiler not equipped with an automatic feeder.

Important item # 1.

Condensate lag: The time it takes for condensate to return from the system to the boiler.

Several things affect condensate lag;

1. Defective vent valves, water trapped in a vent valve.
A vent valve may not spit and sputter, it can vent air but just as important it must allow air to re-enter the system through the radiator and steam main vent valve.

Air re-entry prevents a vacuum from ocurring. Vacuum in a one pipe steam system is not desirable as it will hold water in the radiator and some horizontal piping. This water eventually will return to the boiler but this condensate needs to return as soon as it is formed.

2. Obstructions in the wet return piping.

Scale or mud (iron oxide) that collects at the bottom of the wet piping will cause water to return to slow. Additionally, scale and mud can form in the bottom of the boiler (the lower circulating legs inside the boiler).

3. High efficiency low profile boilers that have insufficient water content or the hight of water to keep a boiler from short cycling.

A cure for this condition is a small condensate pump and a steam trap installed at the end of the steam main or steam mains.

4. Here are some basics:

a. Water expands in volume 1700 times when it changes state, to steam.
b. One pound of water will yield one pound of steam at one psig at 215 degrees F.
c. One edr or sqft. of steam equals 240 BTUs
d. Four edr equal one pound of steam for steam heating.
e. divide 100,000 BTUH by 960 btus and that tells you that the system needs 104 pounds of water per hour to heat the building.
e. divide 104 pounds of water by 68 and that tells you the system needs 1.5 gallons of water per hour.
f. divide 1.5 gallons of water by 60 minutes and that tells you the system needs .025 gallons of water per minute to heat the building.
g. an average condnesate lag for a house is about ten minutes. That means that .25 gallons of water was used to heat the piping and warm the radiators in the building and it would take another 10 minutes for the system to pressurize. In the first 20 minutes a half a gallon of water was used to begin the ull heating cycle. Remember the system without any problems returned .25 gallons of water to the boiler.

At the worst case senario .5 gallons of water left the boiler and add to that the amounbt of water that was pushed out of the boiler into the the vertical drops from the steam main or steam mains connected to the wet return.

Some of the problems that may be present in the system are:
1. back ptched radiators
2. defective vent valves not allowing air to re-enter the steam system
3.sagging steam main and horizontal run outs to the steam risers
4. blockages at the base of steam risers
5. uninsulated steam mains
6. clogged wet return piping
7. partially closed radiator valves
8. leaking packing nuts on radiator valves (causes loss of system water)
9. improperly piped near boiler piping
10. possible cross over between the steam side of the system and the return side of the system.

Night set back in most cases with out special controls and done from a thermostat in degrees, should not be more than 4 degrees F. Graete degree setbacks cause the boiler to run to long to buy back the heat loss. Pardon the pun all the savings that ocuured will go up in smoke.

Jacob Myron

Fred Harwood_2

One-Pipe Steam

David, in many cases small boilers do not like high water lines, which cause the steam to take excess water droplets with it up into the mains. A boiler that needs skimming acts similarly. Coupled with a condensate return problem, excess carryover can empty a boiler.

What's the make, model, and EDR rating of your boiler. What's the EDR radiator load, and what size and length are your mains. What's the model # on that Vaporstat (I've a reason for asking). How high above your waterline is the end of the dry return. Have you removed and proved that the pig tail and boiler taping are clear? Any pictures?

In short, a steam system constantly produces steam, which constantly returns as condensate. Run time should have nothing to do with the ability of the boiler to produce steady steam or to accept the return of the condensate (at low pressures). Only the small amount of water initially needed to fill the system with steam and its returning trickles of condensate should be out of the boiler or stacked a bit in the wet returns. Independent of thermostatic control or runtime, the boiler should be unable to get to low-water cutoff. Time to go back to the basics, even if that means internal inspection of the dry and wet returns.

RonWHC

In my residential

days, I'd field calls from some customers unhappy w/ the Chronatherm Stats we sold w/ boiler/furnace upgrades. Seems they figured if 5* of set back could save UP TO 15% - 10* would save 30%. Never saw it work that way.

"Reasonable" means different things to different folks. Lawyers have made a mint, or 2, w/ laws that use that word. A reasonable setback for me, is probably too much, or too little, for you. In commercial buildings, we set back drastically when the building is closed. 6 PM Friday til 7 AM Monday is a long time. Unless O/D Temps approach design, 20+* setback saves a big bunch.

On multi-family, we shoot for 3-5*. To hit those numbers, we not only have to know the system, but the structure, the make up of residents, & their preferred sleep hours. It really is a matter of different strokes for different folks. Condos & Coops do some really wierd stuff. But, it's their $$.


As to setback screwing w/ systems: So what? If the system isn't up to snuff, you're wasting $$, setback, or not. We service 12 to 100 unit 1 pipe steam buildings. Most w/ modern cast iron boilers. No cond. receivers. No boiler feed tanks (except the one DF sent our way). No water level problems. All w/ nite setback controls. As w/ setback, proper steam operation also has a devil in the details. Most often more than one.

David Nadle

Math check

1 gallon of water weighs 8.3 lbs. If you need 104 lb water per hour per 100k BTUs. Dividing 104 by 8.3 yields 12.5 gallons per hour. With your ten minute lag I get 2.1 gallons used per ten minutes.

Fred Harwood_2

Setback fun

Commercial buildings in my time as a plant manager kept me busy second-guessing the occupants. Back then, government required setbacks, so setback they were. Then, management decided that employee flextime would improve morale, reduce road congestion, idling cars, wasted gas, etc., and started allowing just about anyone to come to work, whenever. Well, that meant that at unpredictable times someone would be punching the override and heating up the whole place just for one or two night owls. To make matters worse, the last one out did not know they were the last one out, and so left it in override all night (Saturday, Sunday, whenever). Made pocketing setbacks difficult, at best.

David Nadle

Answers

I did much skimming over the last heating season. In my opinion the water is very clean. No droplets above sightglass. No priming or surging. Somtimes a tiny dribble down the sightglass when operating. I don't know for sure there's not a lot of water in the steam but I get no symptoms of that unless I have a very long cycle. I do not keep the waterline high.

Boiler is a Utica PEG112C, 281 ft^2, connected to 280 ft^2 of radiators. Vaporstat is Honeywell L408J1009. Dry returns are about 4 feet above the water line. Pigtail is brand new brass, installed last month. 0-30 oz. gauge mounted to it is responding well.

It seems the boiler can send water up slightly faster than it can return. Given enough time I would expect the LWCO to eventually cut out. With an appropriate water level (half the glass) I do not get a low water condition.

Fred Harwood_2

For fun

This from a 11/2008 paper on setbacks:

4.3 Moisture in building envelope component
Although the thermostat setback improves the energy efficiency of the house as demonstrated here,
the effect of high indoor relative humidity fluctuation, as the consequence of thermostat setback, on
the durability of building envelope components also need consideration. This is because the low
indoor temperature coupled with unchanged moisture supply results in more condensation on windows
surfaces and building envelope components. As the whole building hygrothermal simulations results
suggest the amount of condensate on the window surfaces increases by 2.10 and 1.82% for the single-
step and multi-steps-up cases, respectively, compared to the reference case. Moreover, the simulation
results show that the relative humdity at the back of the interior gypsum board increases by about 3%
from the reference case during the night time when the thermostat setback period is on. These cyclic
moisture loadings with short amplitude and frequency may have an effect on the moisture performance
of of the component.

RonWHC

Not to prolong

this, Fred. But, the commercial bldgs I'm familiar with write operating hours into the Lease. You can come in, & get heat or A/C. But, you pay extra for it.

Many work-a-holics have a 1500 Watt Oil Filled Radiator in the office. Great compromise.

Fred Harwood_2

Answers

Mains size and length? Mains insulation? Photos?

Water level, resting boiler, half way up should be OK.

The nut is how can it send water as steam faster out than the water as condensate can return? Also, where is that water?

The Vaporstat sounds OK.

McKern_2

RE "setbacks should not be more than 4 degrees F. Greater degree setbacks cause the boiler to run too long to buy back the heat loss."

That was my understanding when I posted the question, although I didn't understand the physics behind this.

However, it seems that all the responses maintain that there is nothing inherently inefficient in the recovery period.

I haven't had a chance to search the forum for past discussions, but I was under the impression that there was some debate about the subject.

McKern_2

BTW--I'm in a 6 unit, self-managed, condo building with a history of neglecting the system while simultaneously pursuing wrong-headed cost-control strategies.

I've learned a lot through the forum and my copy of The Lost Art of Steam Heating came off the bookshelf in October and hasn't been re-shelved since. I've been sharing info with other unit owners, but I must say, old ideas about how things should/shouldn't work die hard.

David Nadle

More answers

Mains are in a big dry loop like two counterflow headers joined at the ends (see attached diagram), about 64 ft. x 2 in. Mains, near boiler, and takeoffs all insulated with 1 in. fiberglass. Mains vented at high point (opposite corner to boiler) with one Gorton #2 and one Gorton #1.

Instead of asking how the boiler can send water up faster than it can return, maybe we can look at it another way. The boiler puts a certain net amount of water in play each minute it steams. That amount is not necessarily constant. It might be positive initially and eventually cross zero and become negative.

Imagine I burn for 30 minutes--a long time--and fill all the radiators with plenty of steam. The vaporstat cuts out. There is some non-zero amount condensate up in radiators and mains and the remaining steam is still condensing. The presssure at the boiler falls fast, drawing everything back towards the boiler. But before a lot of it can get back, maybe even before some vents can open, I'm steaming again within 40 seconds. Only now, the rads and mains have water in them. So I push some to the vents and I get some hissing. Is this a plausible explanation?

nicholas bonham-carter

short-cycling

have you clocked your gas meter [or checked your burner]. it is remotely possible that you are over-fired.

you could also check your pressure at the radiator to be sure that you are in line there [i have the old 0-5 psi gauge on a tee before the vent on a rad i can see from the kitchen.

as far as the condensate lag, see "my reservoir tank" below--nbc

Fred Harwood_2

Answers

I don't think I understand your mains, especially near the boiler. I've not seen the arrangement and slopes you show in your diagram. Some pictures of the near-boiler piping would help.

Counter-flow mains need strong slopes and very low steam velocities and pressures, or the steam will hold back the condensate and puddle it in the mains.

The slope shown in your diagram suggest that the main once was parallel-flow (counter clockwise) with the end at the lowest point back by the boiler and then dripping into a wet return. The parallel flow of steam and condensate would speed the return of the condensate. Again, some pics might help.

David Nadle

Mains

As far as I know the mains are as they always were, except the vents and insulation added by me. This house is circa 1930. I did some reading that suggested old coal fired systems were sometimes set up this way. Ignore the diagram near the boiler. It actually depicts the boiler I replaced. All the installers I interviewed were scratching their head at my mains.

I attached a shot of the new boiler from just after it was installed.

Bulley

setbacks

This is an issue I've been thinking about for a long time. I'm just now starting to "investigate". I think you are missing a few variables mainly related to the building envelope and the system piping. You are correct that you could define this with an equation but the biggest poing is that each house is different. If you meter your energy the best way to figure this out is by experimenting and taking energy readings. That way you don't miss something with the equation. BTW, its much worse with scorched air systems. At least with radiant you are heating the person and not all the air in the whole house. Then you're talking even more energy and even less reason to set back unless the home has a tight envelope and a good HRV.

Boston_2

I run into very similar \"problems\"

with my single pipe system that David runs into with his system; however, mine is not a counter flow. Once we updated our boiler to a new Burnham IN6 and fixed the problems from the installer, the system comes up to pressure quickly. When the system system is trying to recover from a temperature setback, the system will heat the radiators all the way across, but it will take time for that heat, to warm the air in the room enough to satisfy the thermostat. The system will now cycle on and off, from pressure. I think what Dave is trying to accoumplish, is giving the system a chance, to depart the heat from the radiators to the air, before cycling back on, thus reducing the number of times the system has to cycle.

I have also noticed, when my radiators are really hot, that my new radiator valves leak a little ( I have several different types); they will all make a small gurgling and hissing sound. The only radiator valves that I have found that don't leak, are the cheep ones that I got at Home Depot. Unfortunalty they make a racket when they open and close… pssss... PING, pssss... PING.

David Nadle

psssssss...

[EDIT: my math was off... some numbers changed below]

I think the failure of even good quality vents to hold is related to this short-cycling condition with radiators already full of steam and condensate. I can't tell you how many Gortons I've tossed for "psssss". I was killing the messenger.

I also think its possible that adding delay could end up saving fuel. Radiators are obviously still effective heaters at temperatures below 212. A radiator at 155 is still emitting 50% of the power it was at 215. During the delay period, while the radiators are giving up heat, the thermostat may be satisfied. For example, if it takes 6 minutes for my radiators to cool from ~215 to ~155, and in that time the thermostat is satisfied, I have saved 3 minutes of fuel. If the thermostat is still calling, worst case I have to reheat the water from 155 to 212, which is a small compared to the heat required to make more steam. My boiler burns 5600 BTUs in 3 minutes. That could reheat 12 gallons. My boiler only holds 5 gallons.

Fred Harwood_2

Photo

I'm sorry, Dave, but I can't figure out your boiler piping. How about another photo from the side, or from each side?

David Nadle

Pics for Fred Harwood

Fred, here ya go. My near boiler piping has already been vetted by this forum a year ago. I wish I knew what you were looking for.

Fred Harwood_2

Photos

Thanks, David. (Sorry for earlier calling you Dave.) What I'm looking for is the condensate that should be in the boiler rather than in the rads and mains. Reviewing the piping often provides clues.

You say that the mains vents are at the high junction across from your boiler. Do the radiators on one counter-flow main differ in any functional way from the radiators on the other CF main? (More or less heat, water, hissing, etc.)

I don't have my LASH book with me at the moment, but I'm pretty sure that the pitch is insufficient for your counter-flow mains.

How closely does you radiation EDR match your boiler EDR?

The above, and the boiler's side risers, are beginning to make me think about possible problems with steam velocity in a counter-flow system.

By the way, the reason that I earlier brought up the T87 and its amazing and simple anticipation was because it works just like the timing relay you propose. Also in the LASH, I think it was, Dan shows an upward sloping sawtooth showing how reheating should work. In other words, the boiler runs until the anticipator shuts it down, then it refires, etc., cycling until reaching set point and without overshoot. Your system may be particularly vulnerable to the absence of anticipation and the resulting resting periods that allow for condensate to return.

David Nadle

To clarify, it's really just one main. Both counterflow legs are joined at the high point. In a way, it's like a giant version of the big no-no of a takeoff between two risers. The location of the takeoffs don't seem to make a difference though. One side of the rectangle is sloped a little less than ideal but the other three are ok. My boiler is almost an exact match to the total radiator EDR.

I must say I find your promotion of reverting to an anticipator thermostat and your aversion to using a delay timer to be at odds with each other. You are basically saying get a T87 and set the anticipator so the cycle always ends before the pressure limit. This totally undercuts the arguments you made against a delay relay. Besides, I like the P+I algorithm of the digital Honeywells. I think it's beter for comfort.

Oh, and all my friends call me Dave.

Fred Harwood_2

Good Luck

I've made all the suggestions I can think of from the relative isolation of my computer. Good luck with your problems, and if you find a solution, I'm sure that Wallies will want to know what it was.

nicholas bonham-carter

p + i

dave, can you elaborate a bit on the p + i algorithm of the visionpro [i have one on my 1-pipe ] and why you like it? thanks--nbc

David Nadle

PID

PID is a principle of control systems: proportional, integral, derivative. Three different ways of looking at the same input signal, used in some combination to determine an output. In this case the input signal is the error (difference between room temp and thermostat set point).

A thermostat using P+I combines the present value of the error and the cumulative history of the error over time. In practice this allows much tighter control around the set point. Less swing, no droop. An anticipator thermostat can only add an offsetting error which is neither P nor I.

To be clear, I don't prefer the Honeywell thermostat becuase it's P+I. Thermostats could get much smarter than that and someday they probably will. But I do like it because it works well in my house.

Fred Harwood_2

Boiler water

David, I just noticed that you say your boiler holds only 5 gallons. For comparison, my Burnham 74 steams with 12.5 gallons. With 8 pounds of steam and condensate held up in your counterflow mains and the rads, you are down to 4 gallons in the boiler, a 20% reduction in boiler water.

Especially with your slow condensate return, that seems to pose a critical boiler water issue. Perhaps Steamhead or others could comment?

Phil_17

short cycling and firing rate

Hi David,

For the longest time I have been pondering a question which is mostly the opposite from yours... My boiler can run for a long (like an hour) time without ever registering more than an ounce of pressure on the low pressure gauge installed next to my vaporstat. My conclusion was that my firing rate was either too low, or "just right".

A few weeks ago we had an ice storm here in central mass, and the interior temperature dropped to about 50 before I managed to lay hands on a generator and get the boiler firing again. Coming out of this deep "recovery" the boiler ran for about 90 minutes before all my radiators were heated fully across and the vents closed. At this time I actually saw the pressure on my boiler climb above the 0-1 oz. range that I've become accustomed to. In fact it actually got to my 10 oz. set point on the vaporstat and I finally have confirmation that that too works as expected.

Long story - short: My system cycled off for about 30-45 seconds as the pressure dropped back to 2 oz. and then ran for about 7 minutes until it reached the 10 oz. point again. This continued until the house returned to 65 degrees.

I think my boiler could be fired ever so slightly higher, but by having it closely matched to the connected load the vaporstat cycles are nice and long. In your case, I wouldn't focus so much on the time it takes for pressure to drop, as on how quickly pressure builds. I think your system could be down-fired a bit (by a pro of course) and that would likely end your problems with the short cycling.

-Phil