What is the right cylce time for 1 pipe steam system?

jalubarsky

Previously I posted two discussions about my 1940's single steam system and both were very helpful to getting my house far more balanced, comfortable and efficient. My gas bills compared to last year are about 20% less with similar degree days. I added 5 Gorton #2's in total to my three mains and 6 of my radiator vents were replaced. I also added a 0 - 3 psi gauge so I could tune my Pressuretrol settings. I also insulated a lot of my mains including most elbows that were never wrapped.
Two issues remain for me.
First is my pressuretrol. I have tried to lower it further so it cuts out under 2 psi however the lowest I can get it is 2.7 cut out. (It used to be between 4 - 5 psi.) If I lower the setting any further the mercury switch gets stuck open and hence no heat. Previous suggestions were to make sure it is perfectly level which I checked and adjusted to the best of my ability.
Second issue is now that the temp in NJ has been quite cold my system is cycling on and off in less than 5 minutes when the system is cranking. Every radiator in my house is toasty and very balanced. I also noticed that when the 2.7 psi it reached my pressure gauge now takes far longer to drift down toward zero versus originally it used to drop to zero very quickly. I conclude that this means my vents and overall system are tighter and running better.
One suspicion I have is my boiler may be oversized for my system. It is a Burnham IN6PVNI-M2. My system has 17 relatively small radiators. House is 1 1/2 levels around 2,300 sq. ft.
Any comments on my logic or situation?
Final point is I am very pleased because my house is far more comfortable with quicker time to heat up BUT still trying to understand how I can lower my pressure and optimize.

Jamie Hall

Oh dear. Well, yes -- one can get very sophisticated indeed with the controls. However... a good thermostat should be able to hold the temperature at the thermostat within a degree or so. Maybe tighter. The Visionpro in the place I care for holds within half a degree; it's set for steam -- one cycle per hour.

That said, a vapourstat may be the way to go. But before you do that, get a 0 to 3 psi gauge and put it on the same pigtail as the pressuretrol and find out what pressures the pressuretrol really is tripping at. As I said in a previous post on, I think, this system, the mercury types, while exceedingly reliable, are also very sensitive to levelling particularly at the low end of their ranges. What you need to do now is to compare the pressure gauge reading with the setting of the pressuretrol and the action of the mercury switch. Pay no attention to levelling the box, nor to the little pendulum arrow. Adjust the pressuretrol so that (just for example here) if the pressuretrol is set to cutout at 1.5 psi, the mercury switch tips at 1.5 psi as shown on the pressure gauge. It should then tip back all by itself at something very close to the cutin pressure...

I honestly have yet to figure out how running a boiler for a fixed time, based solely on exterior air temperature, can be made to work -- at least not on the place I care for, since both the solar gain and the infiltration loads are at least as large a factor as the temperature differential!

Fred

First, calculate the total EDR of all your radiators. You say they are relatively small but you have 17 of them. The Burnham should have a plate on the side panel that tells you its Sq. Ft. of steam output. Determine how close the radiator EDR and the Boiler Sq. Ft of steam is.
As far as your Mercury switch pressuretrol is concerned, you can switch that out for a Vaporstat and run at lower pressure (Ounces instead of pounds) or you can slightly tilt the Pressuretrol slightly so that the mercury switch trips a little earlier. Watch the 0-3PSI gauge when you tilt the pressuretrol (only in slight increments) until you get it where it trips at 1 to 1.5PSI.
I'm not convinced yet that your boiler is actually oversized. Even if your radiators are just 25 EDR each, that totals 425 Sq. Ft. of EDR. I think the Burnham IN6 net Output is 450 Sq. ft. That should work fine but again knowing the EDR of the radiators is critical to determining how well the boiler is sized.

Jamie Hall

MarkS said:

Jamie, (going a bit off-topic)...

I'm curious about the building you care for.

Jamie Hall said:

a good thermostat should be able to hold the temperature at the thermostat within a degree or so. Maybe tighter. The Visionpro in the place I care for holds within half a degree; it's set for steam -- one cycle per hour.

I assume you have an independent temperature measurement to check this since the VP only displays in whole degrees. What I don't understand is how your overshoot can be so low; when the stat shuts off the rads still put out heat. Do you have that much infiltration? And if so, how does it not get too cold running 1 CPH in a New England winter?

Jamie Hall said:

I honestly have yet to figure out how running a boiler for a fixed time, based solely on exterior air temperature, can be made to work -- at least not on the place I care for, since both the solar gain and the infiltration loads are at least as large a factor as the temperature differential!

In the case of EcoSteam, the time calculation for a given cycle is based on current outdoor temp, the building heat loss, and the heat capacity of the boiler. Can't do much about the solar gain issues though; are there not curtains in your building? How is it that the sensitive artifacts stored there aren't affected adversely by solar gain?

Temperature measurements... there are good thermometers in several of the rooms of the building (not, oddly, where the thermostat is!) which I keep an eye on...

The temperature control is significantly worse in warmer weather (relatively speaking). In cold weather -- say teens and below -- the radiators are big enough so that they stay reasonably warm, if not steam hot, between cycles. This helps a lot. On a warmer -- say 30s and up -- sunny and windless day, that doesn't happen and some spaces get cooler. On a day when it is in single digits and little wind, the building is amazingly even.

Infiltration is a real bear in this place. It sits on top of a hill with a completely open west to northwest exposure. On a still day, the infiltration is minimal -- it is remarkably tight, actually, considering age and construction. On a windy day... all bets are off. Judging mostly by boiler cycle times, the heat loss can and does double. I might add that this raises havoc with the relative humidity... and the pianos, particularly, have humidifiers near them for exactly that reason. I have been known to carry a lot of water!

Sensitive artifacts don't like sun. You are absolutely right! However, there are curtains and venetian blinds in place which are used when and as needed. The interesting thing about them is that they don't really reduce the solar gain -- they get warm in the sun, and re-radiate that warmth into the room. Or so casual observation suggests...

Best thing to do is to come and visit us!

Jamie Hall

How come my system works with one poor old thermostat in a 7,000 square foot building?

PMJ

The outside temp doesn't tell much about what the sun is doing or the wind, both of which change the load considerably. However, it is a lot more information than nothing and I think the more sophisticated controls make good use of it for those who wish to go that route.

One thing I notice in the controls discussion though is that it seems like people are trying to identify an exact amount of heat required to satisfy the stat and then get that heat back in without overshooting. But if you adjust your thinking away from satisfying the stat , things look quite different. I take a very different approach. If my house happened to fall from tstat cutout to cutin in one hour let's say, it lost a certain amount of heat. I have no interest in putting that same amount of heat back in in one hour or even two. I would have it take as long as possible to replace that lost heat and try to add additional heat at a rate just so the inside temperature is rising and not falling. I attempt to make it rise at the slowest rate possible and spread the call out as long as possible. It turns out that finding on/off cycle times that will accomplish a slow long climb under different outside conditions for your structure is not that difficult without any sensors.

The question of this thread is what is the right cycle time for a given system. I propose that those considering that question also consider a related one - what is a good average call satisfaction time. Since the definition of perfectly even heating is an endless call that is never satisfied, spreading out the "recovery" from tstat cutin to cutout is a reasonable thing to consider too.

Fred

Every system and I guess every body has their own set of nuances. I'm pretty much in Jamie's court on this one but I understand the approach you guys are taking as well. As for my system, heating 5000 sq.ft, with a boiler that is about 15% to 20% oversized, using only a thermostat, the temp variance is never more than 1 degree (under set point) and never over shoots the set temp. The thermostat kicks the boiler on at about 1/2 of a degree and the room temp may drop another 1/2 degree before the temp begins to build to set point. At outside temps anywhere from 15 degrees up to mid forties the Boiler runs for 15 to 20 minutes, one cycle per hour, never short cycling and pressure never gets above 2 Ounces (except when outside temps are sub-zero). From an outsiide temp of 15 degrees down to 0, the boiler will run for 20 to 25 minutes, again, once per hour. Below 0, and we have maybe 3 to 5 days where, with wind chills we've gotten to -30 degrees, the boiler may run 30 to 40 minutes each hour and may short cycle 2 or 3 times before the thermostat is satisfied. Having a short cycle happen 3 to 5 days out of the season is acceptable to me (here is where the personal nuance comes into play).
It just seems to me that if you run a boiler on a timer or with other controls, in conjunction with a thermostat that you are either always under your desired temp (albeit minimal) meaning that you set things up to strive for a goal that is 1/2 to 1 degree above what you really want (knowing that the other controls will keep it from getting there) or, in the case of a timer, maybe intentionally overshooting a bit knowing that it will be some specific amount of time before the timer restarts the boiler cycle.
In the end, a good thermostat works for most of us and most home owners don't necessarily want to add any more controls (and complexities) than is necessary to keep us comfortable as cost effectively as possible, given that requirement.
Again, I understand those who want to try different approaches "just because". That's how new options evolve.
That's my story and I'm sticking to it.

Jamie Hall

Let me say that I quite agree -- in principle -- with both Hatterasguy and PMJ here. The ideal heating system would supply (or remove, to be general) -- at all times in all spaces -- exactly the amount of heat required to maintain the space and contents temperature at the desired setpoint. No argument.

A second aspect of this is to do this as efficiently as possible, of course.

This sounds simple. In practice, it isn't, and where the apparent differences of opinion come in is in defining, for a particular situation, what is "good enough", having realised that the optimum strategy -- adjusting the instantaneous heat gain or removal by the conditioning system to the match the instantaneous heat loss or gain, as the case may be, of the space in question may not be practical.

Of course, the practicality of any control strategy also involves possible limitations of the heat delivery system. For example, reasonably rapid or step changes in heat loss simply can't be matched by a system which has any significant thermal mass -- such as might be a cast iron radiator. Indeed, a system which has significant thermal mass either has to have a system for anticipating load changes, or tolerate deviations from the setpoint when the load changes; from that standpoint, it is evident that forced air systems (preferably heat pump powered, for efficiency) can react much more quickly than either hydronic or steam or vapour/vacuum systems, and are thus significantly easier to control.

Modern hydronic systems with outdoor reset, modulating boilers, and sensitive distributed interior space temperature measurement and zoning can also do very well indeed, although without very sophisticated predictive control algorithmns and multiple sensors for windspeed, exposure, etc. they can't achieve the no deviation form setpoint criterion (they can come very close, depending on the sophistication of the control strategy). Straight steam systems, much as I love them, must resort to on/off control of the steam, as steam condenses (in a straight steam system) at one and only one temperature; thus, to maintain the emitters at the correct temperature to compensate for the heat loss of the space, they must turn on and off. If the heating system is at all distributed, ideally this will take the form of relatively short cycles, so that the emitter temperatures are as constant as possible. This is the direction which Hatterasguy is advocating, if I understand him properly. Vapour/vacuum systems, if equipped with a vacuum pump, can achieve the same results as a modulating hydronic system, provided only that the boiler heat input can be modulated in some way (either turn down of the flame, or pulse length modulation of the flame).

Having said all that -- and there is more which could be said! -- I at least am inclined to say... hold on here. What ever happened to KISS?

ChrisJ

I never saw my VisionPro 8000 maintain temp within 0.5 degree alone.

Best it ever did was maybe +- 1 degree on more mild days but when it gets into the single digits outside, watch out. 3-4 degree swings. Sometimes it overshot so much even the VP decided to show a higher room temperature, and we all know about the VP's dirty little secret.

Jamie, how come your huge system works so well? I have no idea, but my system didn't. Maybe your radiation is much better matched to the heatloss of the building.


To the OP, in my opinion the correct CPH setting for steam is either 1 or 2 CPH. Many systems can pull off 2 cycles per hour and you won't know until you try. Be warned, if using a Honeywell thermostat it may take time to re-learn things if set to 2 CPH. You may find it turns the burner on and shuts it off before you even get heat. It'll do that a few times, and slowly increase the run time each cycle until it settles in.

Let it run for a day or two before deciding to go back to 1 CPH.

Mark N

I have a Honeywell FocusPro 5000 set to 1 CPH and here is what I've observed. I placed a digital thermometer that reads in 10ths of a degree increments. They FocusPro is set to maintain 70 and I never use set back. I did this a few years back on a cold night. when the the thermometer read 70.1 the heat turned on. Ran an approx 20 to 22 minute cycle. The thermometer still read 70.1 dregrees. Over the next 30 minutes the temp rose to 71.1 on the thermometer. Then started to descend back to 70.1 and the heat came on again. I watched it for 3 cycles and it operated the same way all 3 times.

Jamie Hall

ChrisJ -- this place is astonishingly well set up in terms of the match between the boiler and the radiation, and between the radiation and the various heat losses. Not my doing. The dead men who set up the original system did an excellent job, and Charles Garrity and I conspired to match the boiler to the radiation very closely (it does cycle on pressure -- at about 6 to 8 ounces -- a couple of times towards the end of very long runs --no big deal).

This morning was 7 below zero Fahrenheit, with a 20 mph wind. Place is quite pleasant, and Cedric isn't running all the time! So in theory it could be colder or windier. I have no desire to test the theory...

ChrisJ

Mark N said:

I have a Honeywell FocusPro 5000 set to 1 CPH and here is what I've observed. I placed a digital thermometer that reads in 10ths of a degree increments. They FocusPro is set to maintain 70 and I never use set back. I did this a few years back on a cold night. when the the thermometer read 70.1 the heat turned on. Ran an approx 20 to 22 minute cycle. The thermometer still read 70.1 dregrees. Over the next 30 minutes the temp rose to 71.1 on the thermometer. Then started to descend back to 70.1 and the heat came on again. I watched it for 3 cycles and it operated the same way all 3 times.

I should note,
If the outside temperature stays fairly constant, my VisionPro will maintain a decent temperature but as soon as it changes, it throws the thermostat off.

If it's 40F during the day and 15F at night it has to relearn everything and it gets all discombobulated. By the time it relearns and gets things working nice the outdoor temperature changes again.

It's a shame the outside temperature never stays the same otherwise the thermostat would work very well.

Tomorrow we're showing a high of 29F and a low of 7F.

ChrisJ

Jamie Hall said:

ChrisJ -- this place is astonishingly well set up in terms of the match between the boiler and the radiation, and between the radiation and the various heat losses. Not my doing. The dead men who set up the original system did an excellent job, and Charles Garrity and I conspired to match the boiler to the radiation very closely (it does cycle on pressure -- at about 6 to 8 ounces -- a couple of times towards the end of very long runs --no big deal).

This morning was 7 below zero Fahrenheit, with a 20 mph wind. Place is quite pleasant, and Cedric isn't running all the time! So in theory it could be colder or windier. I have no desire to test the theory...

That's the best assumption I've got. My radiation is 50% too big for the house so even a minute of run time too long makes a pretty big difference. This is why I switched from an EG-45 to an EG-40, to try and slow the thing down some. It's like a coarse adjustment vs a vernier adjustment on a piece of equipment. I'm in coarse mode, you're in vernier mode.

Mark N

All of us are oversized on radiation to heat loss, but what amount I do not know. Even on the coldest night my rads heat 1/2 to 2/3rds. The vents might start to feel warm. I don't think I've ever observed the vents close.

ChrisJ

Mark N said:

All of us are oversized on radiation to heat loss, but what amount I do not know. Even on the coldest night my rads heat 1/2 to 2/3rds. The vents might start to feel warm. I don't think I've ever observed the vents close.

Hi Mark,
No, not all steam systems are oversized and even the ones that are vary quite a bit.

Jamie just said his radiation is pretty well matched to the building.

KC_Jones

I would tend to agree not all are over sized. My radiation comes in at 63600 (one rad removed so originally 69600) and my calculated heat loss is right around 60k. So while I am over sized on radiation it is just barely. This morning I woke up to 9 degree outside temp, my design day is 7 and every rad in the house was fully hot and cranking. I like days like this because the house is honestly at maximum comfort level.

Mark N

Were they cranking becuase you were coming out of a recovery or were you just maintaining temp? When I woke up at 5 the heat was off and rads just warm to the touch. The outside temp was 8 degrees. I don't think we should be using modern design day temps with our systems. In my area the design day temp is 10 degrees. At that temp my boiler is hardly working to maintain temp. Runs a 20 to 25 minute cycle and will sit off 60 to 75 minutes. Its been quite a few years since we seen below zero temps. Would be interesting to observe how things work at -5 or -10 degrees.

jalubarsky

I must admit that as a home owner much of these comments are well beyond what I would consider engaging in. My thermostat does keep my house within a degree or two of my normal set point which is 68 degrees. BTW I added a 0 - 3 gauge on my pigtail a while ago and that is what I am reporting as the current pressures. I will try to re-level my pressuretrol to get it to kick off at a lower pressure although as someone stating this might get me to cycle even quicker which is not wanted at this point. Considering all of my radiators are very toasty I do conclude that my boiler is just producing more steam that my system can digest (so to speak). Again my house is running far better than when I started this process so at this point I may leave well enough along. Unless of course someone has other suggestions that I cannot resist. Thanks again for all these wonderful inputs.

PMJ

jalubarsky said:

I must admit that as a home owner much of these comments are well beyond what I would consider engaging in. My thermostat does keep my house within a degree or two of my normal set point which is 68 degrees.

You are among the vast majority of steam owners who feel this way and surely there is nothing wrong with that. I'm glad you are doing well with your system. What you are reading here are the comments of some folks who just really like tweaking their systems and kicking around ideas on how to improve. We find it fun.

I live in a city where most of the homes were built in the 1920's and still have steam. The most common complaint I hear around here is the one Mark S. describes on his site about lag and overshooting which he has done a great job addressing with his control system. I do wish that the systems around me ran better for then I bet fewer would be torn out each year. So that is why I am attracted to the discussion here - just kicking around ideas on how to make it all better.

I was disappointed to say the least when I first realized that the original coal fired system in my own house had a nicer control system than what I started with here 22 years ago. There was no thermostat at all with coal - no on and off - just a fully modulated analog controlled fire supervised by single digit ounces of pressure. Sure, I understand handling the coal was itself a pain, but the control itself was better than today's standard gas setup when it was cold and you actually needed heat. I assume the warmer days required some opening of windows now and then. So they got rid of the coal problem but then left us with significantly less control over things. And I am afraid that this lack of control has resulted in less efficient systems and has hastened the demise of residential steam generally. I think the conversion could have been handled better.

Jamie Hall

Those old coal systems did work astonishingly well -- for heating. But I hate to think what the efficiency was when the dampers closed down... and coal is dirty and darned hard work, even with a mechanical stoker. We had one when I was young, and I still remember the rejoicing in the family when we finally got an oil burner installed!

BobC

Nothing is heavier than a barrel of coal ash, especially if it was more than half full.

Bob