Will Limiting On-Off Cycles Save $$$

FXProglJr

This site has helped me solve a problem with uneven heating and I've learned a lot. But now I have another question. One piece of advice I received was to change the pressure setting to 1/2 lb. cut-in and 1-1/2 lb cut out. It seems that's enough pressure and more won't help. Rather, it will hurt the system and cost more. And that's the basis for this question.

I watch my system build up pressure and get to 1-1/2 lbs where it cuts out. By that time, all the radiators are hot. But, in a matter of 3 or 4 minutes, the pressure falls to 1/2 lb and the furnace starts up again even though the cast iron radiators are still hot and adding heat to the rooms. Except for the start of each daytime heat setting, my furnace doesn't make it back to 1-1/2 lbs on the second round before the thermostat says it's got enough heat and turns the system off.

So - here's my question: "Is building/adding a control to the circuit that would prevent the furnace from starting up again for a certain amount of time after it shut down be a money saving idea? I mean, if it takes 15 minutes for the radiators to cool (and I can check that and adjust the time accordingly) wouldn't it help to make sure the system can't start up again for 15 minutes?

I'd appreciate hearing your thoughts.

Jamie Hall

Consider this: while the radiators are cooling, so is the boiler and all the water in it. How much more fuel will it take to get it back up to steam after a longer off cycle? You really want the boiler to be off only just long enough to condense the steam in the system, and no longer -- that is exactly what the pressure control is doing. You may want to experiment with the cycles per hour setting or the anticipator in your thermostat.

Captain Who

Mine mostly only cycles on the pressuretrol when it is recovering from a 8deg overnight setback (53 F nightime setting). It can cycle anywhere from 1 to 6 or more times before the thermostat is satisfied, depending upon how cold it is outside (and thus how cold my walls and windows are). You're actually doing better than me because mine hits the 1.5psi cut-out (actually measures 1.7 to 2.0psi on the gauge) and only takes 2 min to get down to the 0.5psi cut-in which agrees with the gauge and is consistent. Then it only takes 3 min for the boiler to get it back up to the cut-out. Lather Rinse Repeat. Then the thermostat will generally do another little call for heat for good measure 10m or so later and it will possibly hit the cut-out one more time, but usually doesn't make it all the way down to the cut-in before the thermostat says it's all good. This morning I was checking radiator vents under pressure for leakers and heard a few possible late closers where the radiator was pretty hot but I was getting some vent hissing and I checked the pressure gauge and it was having trouble getting past the 1psi mark for quite a while until the vents finally closed all the way and it then it blasted up to the 1.5psi+ cut-out in short order.

Mark N

Captain Who why do you setback to 53 overnight? Are you trying simulate what it is like to live in a cave.

Captain Who

I'll have to read that post because it sounds real interesting, but it strikes me that what you're doing is kind of like making up for the fact that the thermostat doesn't have the degree of anticipator adjustment that you might like, for dialing in the optimal setting. I know my White Rodgers doesn't. It only has two settings: "0.6 deg F" and "1.2 deg F". Pretty inadequate !!

Captain Who

PS: Right now I have mine on 0.6deg F and haven't tried the 1.2deg. I know I WOULD NOT like having my temp change by 1.2 deg, especially since I have it set at only 61 F. If it drifted down to 59.8 before firing I'd be pretty uncomfortable, but I guess I could then set it a bit higher to compensate. This is the kind of thing I want to try experimenting with after I have installed the hourmeter to get some baseline data recorded along with the degree days and avg windspeed for each day.

Captain Who

@MarkS - Some of my happiest days were when I used to live in a cave , but seriously I do it to save money. When I go to bed, it is still relatively comfortable in the house and I get under some heavy comforters on the bed and I'm toasty warm all night. By the time I get up the house is usually back up to temp and I am never any the wiser.

I know what you're going to say....it doesn't save any money lol. Well when I get the hourmeter I'll see if that is the case for my setup and house. If I find it doesn't I'll definitely stop the practice because it is very hard on the burner valve and I believe it causes more loss of water from the system which requires more oxygen laden make up water, etc...

Captain Who

PS: I think whether you save money or not is a function of how much you setback but even more so how long you setback for. In my case it is 8deg and 9hr, 45min.

Captain Who

Data Loggers.........that's a brilliant idea

KC_Jones

When my wife and I both worked I used to have our heat setback to 62 from 10pm until 5 pm the next day. I didn't turn it up in the morning since we both left fairly early. Then I had it set to 68 for when we got home from work. That length of time was definitely saving me money. She is a stay at home mom so now I set back a couple degrees at night and that's about it. I am not worried so much about savings as I am about sleeping comfort. We like it cooler at night.

Fred

In reality, if you make sure you have enough venting on your Mains, you probably will never build enough pressure to cause the boiler to short cycle in the first place, except when you are recovering from a deep thermostat setback (which is not recommended for team systems) and during those few days when it is extremely cold outside (typically 0 or below).
I'd spend the time looking at the main venting before I spent any time designing delays on short cycles.
If you post some info on the length and diameter of your Mains, lots of people can tell you how much venting you need to get optimum performance. Just a rule of thumb is the equalivent of 1 Gorton #2 for every 20 feet of 2 inch Main. If you are no where near that, fix the short cycle issue with more venting.

Typically the pressure should only build to a few ounces of pressure. The Pressuretrol is intended to be more of a "Safety device" that ensures the boiler is shut down before pressures build too high. They really are not intended to be a regular "Pressure Management device.

Fred

Agreed but as he says, his boiler only gets there on the morning start up which to me says he is either using a fairly deep thermostat set back at night or he needs some additional Main venting. In either case building a short cycle set back isn't fixing the problem. Decreasing the thermostat set back and/or increasing the Main venting are likely better options (unless he just likes to play with gadgets. Then go for building a delay )

PMJ

Any system that shuts off having reached maximum pressure has filled it's radiators with enough steam to heat the structure on the coldest day the system was designed for. But the reality is it is never that cold. For the overwhelming percentage of the heating season the radiators need never be close to that full to heat the house. The only way with a system with on/off burner control to only partly fill the rads to an amount appropriate for the average heat loss is to cycle it. There is nothing wrong or inefficient about cycling. A system that has had its burner off only 15 minutes or so will deliver new steam to the farthest radiator in seconds - especially if it fires with the system in a vacuum.

Obviously a lot of people like this original poster notice that always filling to max pressure sends much more steam out than is needed and are looking for ways to - well- not send so much. The answer is not to run so much in the first place. Spread it all out with deliberate cycles.

Fred

While I agree that, on the coldest days, a boiler may cycle on pressure and that is not inefficient. But as you say, "On the coldest days". That should not be the norm every morning, unless he is trying to recover from a deep set back. In that case, the additional run time, even with a delay is probably not saving him much, if anything, in fuel costs. This poster did not say he is always filling to max pressure, just in the morning and adding a 15 minute delay for once a day isn't going to save him any noticable money. Besides that, unless his boiler consistently over runs the thermostat setting, that retained heat given off by those radiators is not lost. It adds to the comfort level of the house until the next call from heat from the Thermostat. Not wasted. If he consistently over runs the thermostat, then it may make more sense to set the thermostat back a degree or two and not add delays that affect how the boiler operates on those really cold days.

PMJ

Fred said:

While I agree that, on the coldest days, a boiler may cycle on pressure and that is not inefficient. But as you say, "On the coldest days". That should not be the norm every morning, unless he is trying to recover from a deep set back. In that case, the additional run time, even with a delay is probably not saving him much, if anything, in fuel costs. This poster did not say he is always filling to max pressure, just in the morning and adding a 15 minute delay for once a day isn't going to save him any noticable money. Besides that, unless his boiler consistently over runs the thermostat setting, that retained heat given off by those radiators is not lost. It adds to the comfort level of the house until the next call from heat from the Thermostat. Not wasted. If he consistently over runs the thermostat, then it may make more sense to set the thermostat back a degree or two and not add delays that affect how the boiler operates on those really cold days.

I'm the one who said max pressure because when there is only one cutout pressure and you hit it you are at max pressure for the system. I agree with you that any heat that is inside the house is not wasted. But I am also saying that a system that is cycling at all on pressure is overshooting the target some amount on a regular basis because of the delay of the heat getting from the radiator to the room. The poster is observing the condition when he knows the radiator is already hot enough to satisfy the tstat and the boiler doesn't really doesn't need to come on again but does anyway because it is pressure based control. It is not that coming on again is so wasteful, but it is less even heat by quite a bit.

When I realized that to really even out the heat I couldn't let my burner run continuously until the tstat was satisfied a lot of things changed for me. I just find it an interesting subject. For instance, when you think about it, for heat to be really even (actual temp in the room changes very slowly inside a very small range) you realize that call times need to be extended and burner run times shortened, the picture looks considerably different. And reading a lot about pressure related problems on this site I will observe that never running the burner very long is a big help in keeping the pressure down. I never have enough pressure in my 1000 EDR system for it to be possible to use it for control anyway.

Jamie Hall

A minority comment... from one who is adverse to gadgetry, needs economy overall -- and cares for a house museum.

It's that last one. I doubt that many of us have the problems in that regard that I do -- but there are both things in the house (pianos, books, paintings, furniture) and the house fabric itself (plaster, wide board floors) which do not play well with daily temperature swings of more than two or three degrees. Long gradual seasonal changes are usually not too bad -- but the damage from wide daily swings such as comes from wide daily setbacks can, over time, add up to hundreds of thousands of dollars.

PMJ

I don't see a need for wide setbacks either Jamie. Mine is 3 degrees. I let it drift down to a minimum of 66 from 69 starting at midnight. On an average night that will take 5 hours. Just a touch cooler for sleeping without any hot radiators. No dramatic recovery required either - especially when you spread that out too. I use a standard thermostat for that - wake is 67 at 6am, leave is 68 at 9am, return is 69 at 12pm. Nothing fancy.

FXProglJr

Hi and thanks for all the input but I think I have not expressed my initial question well enough.

Yes, my system cycles on pressure several times each morning to recover from the night time setback, but that’s expected and not where I’m concerned.

Several times during each day, the thermostat calls for heat and the system fires to make steam. By the time the pressure reaches the cut-out pressure (1-1/2 lbs), all of the radiators are hot and still adding heat to the room. But, before the radiators can cool, the system pressure drops enough to restart the furnace. The system does not make it back to 1-1/2 lbs pressure before the thermostat gets satisfied and turns the boiler off.

My feeling is that the rooms would have made it to the set temperature without the 2nd furnace start in each cycle. I understand that the heat generated by the 2nd start is not lost, but it does result in a wider temperature swing for each thermostat cycle and an unnecessary furnace start.

I’m still a novice at steam heating (but a tinkerer at heart) and was wondering if delaying a restart after a pressure cut-out would save enough money to make the project worthwhile.

For those who are interested, here are some basics for this system:
1. Boiler – Peerless ECT-04…….151,000 BTU/hr……..471 sq. ft. steam – net.
The riser from the boiler to the header is 2"
The header over the boiler is 4".
The mains are 1-1/2" each
The returns are all 1"
The pipe that goes from the header back to the bottom of the boiler is 1-1/4"
All of the taps going from the mains to each individual radiator are 1"

NOTE: the boiler is in the center of the 45 ft long house. There is a main from the boiler to the front of the house and another to the rear of the house for the first floor. There is a similar setup for the 2nd floor. Each end of each main has a tee fitting with a Gorton No1 vent on top and a return pipe on the bottom. The mains and the returns are sloped properly.
2. Burner – Riello 40F5 w/1.25 gal/hr nozzle
3. LUX TX-500E thermostat set at 72*day/67*night and 1* differential
4. Honeywell Pressuretrol 1604A 1165 set to cut out at 1.6 lbs and cut back in at 0.5
5. 0-3 lb gauge
6. There are 11 connected radiators - 6 on the 2nd floor and 5 on the 1st – for a total EDR of 316

Jamie Hall

As Hatterasguy noted, your boiler is significantly oversized. Like half again bigger than it should be. You will get cycling on pressure that way, no way around it. And yes, it is costing you significant money. As he suggested, see if it can be downfired, at least to 1gph (0.9 would be even better) -- but that is a job for a really good burner tech. and boiler man.

ChrisJ

Jamie Hall said:

Consider this: while the radiators are cooling, so is the boiler and all the water in it. How much more fuel will it take to get it back up to steam after a longer off cycle? You really want the boiler to be off only just long enough to condense the steam in the system, and no longer -- that is exactly what the pressure control is doing. You may want to experiment with the cycles per hour setting or the anticipator in your thermostat.

Jamie,
The way it look at it is the boiler's heat loss is continuous and the hotter it is, the more heat it is loosing into the surrounding area.

Just because the burner is firing doesn't mean it stops losing heat. Same goes for piping, those pipes loose the most heat when steam is going through them and as soon as they start to cool the heat loss drops. 120F pipes loose far less heat than 212F pipes. I also feel the heat my pipes and boiler loose, probably more than half ends up in my house anyway so is it really lost?


My personal setup is currently set to go into hold mode for 10 minutes if I see 4 ounces. This allows the radiators to cool down making them ready for more steam if need be. Feeding saturated radiators steam they cannot condense doesn't help anyone. If I still need heat after 10 minutes she fires back up. This only happens during a recovery.

PMJ

FXProglJr

I think you are on the right track with this actually. I would rather a boiler too big than too small. The boiler itself and insulated basement mains really don't cool down that fast. As I said before, a system that fills with steam to a single fixed pressure stop is filling rads with enough that would cover the maximum heat loss the system can handle - the amount required on the coldest days. I don't see the point in doing this on average days. And any properly sized boiler is capable of filling to some pressure well before the tstat is satisfied if it is allowed to.

There is a percentage on vs off for all systems that will handle the coldest days. For my system that is 50% on/off continuous cycles and I can heat to -20F. In other words, my boiler never needs to run more than 50% of the time to heat the place. All I do is make that happen exactly evenly - time based, not pressure based. When it is really cold I do that in 3 cycles per hour, 10 min on and 10 min off. I'm going to suggest that you find out what that percentage is for your system over time.

Now because I have a PLC I am doing more different things, but you might consider just getting a simple on/off timer module that gives an adjustable time on/time off output whenever your thermostat is calling for heat. Actually, I started out this way before the PLC to address exactly the problem you describe. It doesn't cost much and would even your heat out quite a bit. You just put it in between your tstat and your boiler and then you have total control of run/wait times during the call for heat.

Captain Who

The only heat loss from the boiler when it isn't firing that doesn't help to heat the building would be heat lost up the flue. The flue damper mitigates most of this though. I still don't like what I'm seeing with my White Rodgers thermostat the past few days, where it is doing a series of 4 short cycles so as not to overshoot the setpoint, I guess. I checked the first radiator on the main yesterday and it wasn't even starting to receive steam yet when the thermostat decided to shut off after the 1st short cycle. It had only been firing the burner for maybe 3 mins.!!!

I believe this would be lessened if I changed the anticipator setting from the current setting of 0.6 F to 1.2 F, but I haven't tried it yet. Maybe today, especially since it is warm out again today.

Jamie Hall

Do try the higher anticipator setting. It may help a lot.

How to control cycling on a boiler which is producing more steam than the system can condense is amazingly complex, really. Back in the bad old days of coal, when no one really worried about efficiency, there were some marvelous mechanical contraptions whic regulated the draught on the fire inversely with the steam pressure -- at very low pressures. The more pressure, the less draught, and vice versa. They usually tried to balance out at two or thee ounces. Combustion efficiency when almost closed was, as you might imagine, pretty horrible! But they worked splendidly. Nowadays not so much. Multi stage gas burners help a lot. Really big power boilers will have staged oil burners. Most of us are stuck with modulating the firing rate by controlling the ratio of on time to off time, and in my view there isn't that much difference between rather short cycles, usually with a vaporstat, and longer ones -- though my preference is to minimize the time taken to come back to a boil using as short an off time as the burners will allow. If radiators heated very quickly, it would be a lot simpler!

Captain Who

@Hatterasguy - It's good to know there are "cheap" dataloggers. What are you going to get?

I'm personally very conscious of being more comfortable, even though the air temperature may be the same, when there is a slightly warm radiator near me all the time. It's too bad that would be impossible to achieve in my system without a multi stage burner. I don't suppose the dataloggers will measure that comfort level.

Probably some energy from the boiler is also lost to the basement and just goes towards heating the concrete walls, etc. and is not ever felt upstairs.

Gryfon19

More of a general question, but since it came up earlier in terms of calculating the recommended number of vents: exactly which portion of the pipe is considered the steam main? Is it essentially the length of pipe until if reaches the first riser?

Or, in my case, the "main" pipe goes two directions essentially sending steam to the front of the house and the far end/back of the house. Is all of what I see going horizontal technically the main?

KC_Jones

It is a "main" until it gets to the last radiator take off, after that it is a condensate return pipe. Remember though on larger applications "mains" can be vertical as well.

Gryfon19

OK, so is it possible to have 2 "mains"? As I mentioned, the steam pipe heads in opposite directions. Maybe it meets up somewhere behind the wall though? Or could there be two separate loops served by the same near-boiler piping? Just trying to get a proper idea which pipe lengths to measure for venting. Bottom line, I'm confident I need more (there's currently only one).

KC_Jones

Start a new thread so you don't hijack this one and you will get better responses as well. Oh and pics of what you are talking about help too. Also here is a link to a recent venting discussion.
http://forum.heatinghelp.com/discussion/comment/1356085#Comment_1356085

Jamie Hall

It really is a fascinating topic -- the original one, I mean. And coming up with a definitive answer is, I suspect, nearly impossible. It would depend so much on what happens to the "lost" heat -- which isn't part of the boiler at all.

Maybe someday someone will come up with a smoothly variable burner system and boiler combination with a turndown ratio of say 6 to 1 or better which will maintain high efficiency across the range, and we can control it to hold a low but constant system pressure... maybe combined with some way to hold a system at vacuum, so we can modulate the heat output of the radiators...

Don_197

Search "Chop Cloc" on this website.......it has the cycles per hour delay that you are after.......and is fully adjustable. Even if you do everything above......the Chop Cloc can save you money in the warmer times. I have one......and they work great on ANY heating system. Easy to install, and a snap to set up.

Eastman

@Hatterasguy regarding 90 minute cycles with Tekmar 279

"It takes approximately 13 minutes to build sufficient steam and return some condenstate to the boiler room and get the condensate sensor up to 140F which triggers the cycle to start the timing."

Would the system require a 13 minute warmup if you ran it at, say, a 30 minute cycle?

Eastman

Yeah, I would think cycle rate should be dependent on other variables, not fixed.

vaporvac

Jamie Hall said:

If radiators heated very quickly, it would be a lot simpler!

So is this an argument for steel rather than CI rads? I always favoured the latter due to their increased thermal mass.

Jamie Hall said:

Back in the bad old days of coal, when no one really worried about efficiency, there were some marvelous mechanical contraptions whic regulated the draught on the fire inversely with the steam pressure -- at very low pressures.

When I re-read the old trade and technical mags, I'm always struck with how concerned about efficiency they were. I think maybe it was a case of technology not being able to deliver the efficiency. I also think folks were concerned with coal consumption as well, because while cheap in today's dollars it was a larger relative % of one's income. I have all the old papers on my house from the original owner (who was quite wealthy), and he was always trying to find a way to decrease his bills.

I have a fantastic older WM pdf of studies (both real world and theoretical) dealing with decreasing fuel consumption: Twinning, multi-stage gas valves, additional jacket insulation and power-burners were the most effective. My little SF TR50 has wonderful insulation compared to my old Dunkirk and really decreases the time to re-boil. Someone years ago posted about super insulating their old atmospheric and it seemed to work well. (Now, if only I could get my Tstat working properly) Colleen
P.S. Jamie, I don't mean to take away from your point.

PMJ

Eastman said:

Yeah, I would think cycle rate should be dependent on other variables, not fixed.

This is exactly the idea I have been trying to promote.

Time to get steam to rads is related to how long the boiler has been off and changes dramatically with that - but it is a pretty fixed relationship for each system. Percent on vs off time and cycle rate needed after first heat up depends on how cold it is. The PLC approach allows you to measure time since last burn, call or whatever and respond differently each time as you see fit. You aren't stuck with someone else's idea of what you need after your $300 bucks or so is gone. You keep learning and developing as you go. And you keep getting new ideas from this site to incorporate into your control. For the steam buff it is just plain fun.

PMJ

Hatterasguy said:

PMJ said:

after your $300 bucks or so is gone.

...................$920.................

Yikes!

KC_Jones

With numbers like that the ROI on the new boiler will be very very short.

PMJ

Hatterasguy said:

PMJ said:

Yikes!

Do consider the fact that I needed a hands off unit that would do the task reasonably well. The cost of the unit is only about 7% of the cost of the entire conversion to gas.

Also consider the fact that the building burned $15K of oil last winter and I'm quite sure it won't hit $4.5K in gas this winter.

Taken in the grand scheme of things, it's still a bargain for this building.

Understood. Your needs are different than those of a homeowner. I'm sure your unit beats no control by a lot.

PMJ

MarkS said:

This is why you don't see a lot of outdoor reset on single-family residential steam. The ROI on a $1K control is a lot shorter on a commercial/multi-family building, but it's a hard sell for a homeowner.

This is why I enjoy seeing what I can do with no moving parts and no sensors to maintain. It turns out that if you are planning on long call times and are focused on moving room temps very slowly from Tstat cut in to cut out(which one could argue is the definition of even heat) and you can measure both of those times in your control; then you can "discover" how cold it is outside by how long the call goes on. As it takes longer and longer you can gently up the % on time of the cycles. This really is the basis of my control - how long the boiler has been off determines the length of the first burn after a new call. And how long the call has been going on determines the % on and off of the burner during the 20 minute cycles. Not perfect for sure but very little out of pocket up front cost and there is basically unlimited potential for further development. And sensors can be added as inputs if I so choose.

PMJ

Hatterasguy said:

It would appear that such a control is always looking backwards............a change in outdoor temperature wouldn't be recognized for awhile...........resulting in over or under heating.

Can't you easily adapt an outdoor sensor to it? You'd then have everything you needed...............

All I can tell you is that it is amazing how little it takes to just keep the temp from dropping. It appears to me that most people are trying to get the tstat satisfied as fast as possible and get the boiler turned off. No, this scheme doesn't work well for that. But if you make your goal to satisfy the call as slowly as possible(which does minimize overshoot) things look entirely different. I really don't want a fast response. I just need to keep the temp from falling further once there is a call for heat. This approach really works a lot better than it would appear at first glance. Sure, there is a real temptation to add sensors -and I may. I've just been surprised by how far I could get without any - and I still haven't hit a wall yet.

These units can be configured to take almost any type of input signal - digital or analog. I think Mark S. has already done these things and knows the most about them.

Captain Who

There's also solar energy uptake by the building. That varies from day to day, along with wind and temperature.

KC_Jones

Hatterasguy said:

The venue for selling it is probably the most critical aspect for its success. It's not an item you can pop onto e-bay and hope for good results.

Dan has a store on this site...seems to get a lot of steam traffic.