Is there fuel savings with deep setback with steam heat?

rrwitherspoon

I try to lower thermostat at night and when everyone not home during the day to 63 degrees and increase during morning rush and evenings. Is the fuel savings worth the deep setback if I can avoid shortcycling off from pressure
limiting vaporstat?

mcvetyty

Here's my experience in trying to answer that question, for what it's worth. This is my third winter in my house that's heated by a steam boiler. The first two, I used a deep setback both at night and during the day while at work. Based on information I'd heard and read here, I've been playing around with it this year and found that these setbacks were costing me significantly more than a steady temperature setting.

Currently I am only using one setback at night of just 2 degrees, and no setback during the day. Compared to last year, my gas usage has been 20% less (although there are of course other things to consider such as the outside temperature and some tweaks I did to my system).

While it may sound arcane, you can do some testing by conducting daily meter reads and playing with it. Obviously you'll want to try and find days that are similar temperature-wise, and do a few of them to get an average, but if your system is like mine you'll save a lot of money by removing the setback.

Also, it might be prudent to note that my system never shuts off via the pressuretrol...Not even close. My thermostat gets satisfied before all of my radiators are even half full of steam, so if your system relies on the pressuretrol than I assume your results may vary from mine as well.

rrwitherspoon

My system only shuts down via vaporstat from deep set backs otherwise turns off via thermostat. Deep meaning 5 degrees
ie from 68 to 63

Captain Who

Here's the way I look at it. If you know the duty cycle (D) of your gas burner (% on time) to maintain that 70 F setpoint and you know the time (T) it takes to recover from the setback temp to the setpoint, then it is worthwhile to do the setback any time

Recovery Time (T) < Duty Cycle (D) x Duration of Setback (S)

Lets say:

Duty cycle to maintain 70 F (D) = 20%
Setback Time (S) = 9-1/3 hours
Recovery Time (T) = 45mins

20% x 9-1/3 hours = 1.87 hours
But Recovery Time is only 45 mins = 0.75 hours

Burner Time saved = 1.87 hours - 0.75 hours = 1.22 hours

Captain Who

Hmmph. I actually just gave you the numbers I have been getting recently on my own system. Of course, it's been a bit on the warm side here in NJ lately (for winter)

Captain Who

Hatterasguy said:

If that's truly the situation, I do believe you're spending a fortune to get steam to the radiators. You save a massive amount of fuel by running one cycle (during recovery) instead of nine cycles.

You lost me there Hatterasguy. I'm not running nine cycles during recovery. It fires the whole time up until the vents start to close around 35m or so, then it cycles on the pressuretroll until the tstat is satisfied. The timing of it varies of course depending upon the outdoor temp and wind conditions. My system is not optimized yet. I'm waiting for my hourmeter and counter to arrive before I make any major changes. Still on backorder (aargh !).

I think we're overcomplicating this thing. The numbers don't lie.

Captain Who

Actually the way my White Rodgers has been operating, there would've been a lot more than 9 cycles in that 9-1/3 hour setback period. But that's really made irrelevant by the way I'm simplifying that with the concept of the duty cycle. At 20% duty cycle (not an actual setting I made, just what has been occurring recently by my observations), it would've been on .20 x 9-1/3 hours. It probably would've cycled more like 30 times, but I don't know exactly.

Captain Who

FYI I have the tstat set at 61 F, with setback to 53 F. Since the tstat anticipates , it is working out to be a setback time of around 9-1/3 hours, even though I have set it for 9-3/4 hours.

Captain Who

I tend to look at it in a more thermodynamics sort of way in which for the most part, the only losses are up the flue and through the walls of the boiler room, which in my case is slight since it is underground in my basement.

PMJ

I don't think there is much point to a large setback on a 24 hour schedule. If you are away on vacation obviously a large one makes sense for the whole time you are gone.

The total amount of heat a structure loses is a primarily function of the average inside and outside temperatures. So if in fact you change your schedule such that the average inside temperature is lower than previously at all then the total demand is in fact lower. The problems with this all depend on how far you are going to let the temperature drop AND how fast you think you need to recover it. I set back only 3 degrees and only at night to 66. Just a little cooler for sleeping is all. Down to outside 25F or so it will take 4-5 hours for the house to drop that much. But in the morning I start the recovery at 5:30 and I spread it out till noon. 67 by 8am, 68 by 10am and I don't ask for 69 again until noon. Everyone is always greeted by a gently warm radiator in the bathroom in the morning (no exceptions) and we like that. And because the radiators are warm enough to slowly raise the temperature all morning no one notices the 1 or 2 degrees lower we are while it is happening.

My primary reason for doing this is not to save money - I do it for comfort. I like knowing for sure that the rads will be warm in the morning - not random chance and totally up to mother nature. It takes only a small setback to accomplish this. And my recovery is so slow it is hardly noticed. I am convinced that with the slow recovery and the fact that my average inside temperature is a degree or so lower than before I am not losing anything and probably saving a small amount.

Steam systems really don't do a good job of raising the temperature quickly. So large setbacks in a 24 hour schedule are not a good idea. Small ones, however, can be very useful.

Captain Who

I also use two ceiling fans, set to blow upward on the slowest speed setting. Those don't get turned on until I am downstairs to do it myself and not until the tstat is close to shutting down on recovery.

Captain Who

@ Hatterasguy - Why is 1 cycle per hour the magic number? My tstat doesn't allow that to be set. There is only two anticipator settings: 0.6 F and 1.2 F. I currently have it on 0.6 F, but I am going to try the 1.2 F and think that might be best, but we'll see.

BobC

i worked as a technician for the post office for 8 years before my retirement. My shift was 1430 to 2300 so I was away from the house for about 10 hours a day. I used to have the heat come up at 0530 and into a 10 degree setback at 1230, when I came home from work a little after 2330 I did not turn the heat back up because I'd be in bed within an hour or so.

I did this for all 8 winters and found the results mixed at best. The house is almost 100 years old, it's balloon framed and has insulation in the attic but not the walls. I could get the air up to 65 in a little over an hour but the mass of the house took a lot longer to raise. If you stood next to a bookcase you could feel it sucking the heat away from you. On weekends it took a good part of the day to get the house truly comfortable.

I've been retired for over 5 years now and the thermostat sets back at 2130 (I'm usually in bed at 2100 and the temp has fallen by a degree or so) and comes back up by 3 degrees at 0600, at 1500 it goes up another 2 degrees. I burn the about same number of BTU's of fuel as i did back when I was using a 10 degree setback for 17 hours and am more comfortable.

My take is deep setbacks do not save meaningful amounts of fuel with steam systems. Setbacks should be for comfort only, they don't seem to save meaningful amounts of fuel.

Bob

Captain Who

Hatterasguy said:

Every single start of the boiler costs fuel.

I BELIEVE that is probably true. The question is....how much? If I read my gas meter after 5 runs of my burners of exactly 12 mins duration vs the meter reading after 1 hour of a single run, what would the % difference be?

I have noticed that there is a very slight smell of gas for an instant when the burner first fires, but it is extremely slight and fleeting.

Captain Who

OK but on a thermodynamics basis, that heat is not lost to the system, because it is inside the system piping, which is insulated, and the boiler is also insulated and is located in the boiler room which is underneath the heated space. Most boiler rooms are in basements which are below ground, so the losses through the basement walls are not great.

I believe that the heat lost up the flue is the only loss that is really significant, so anything that increases flue losses with respect to heat gained to the heated space is what we should worry about. The question would therefore be.......do shorter cycles vs longer cycles with the same overall duty cycle increase the flue losses? That's assuming that the amount of gas wasted on startup due to a few microseconds of incomplete combustion is insignificant.

PMJ

Hatterasguy said:

PMJ said:

Steam systems really don't do a good job of raising the temperature quickly. So large setbacks in a 24 hour schedule are not a good idea. Small ones, however, can be very useful.

The data that the Captain shows tends to discount the above statement.

I saw the numbers. I don't believe any steam system that has been off 9 hours will raise the whole structure it was designed for 8 degrees in one 45 minute burn.

rrwitherspoon

Good topic I see I thank everyone for their opinions I will move the thermostat more conservatively from now on

Captain Who

That is my recent numbers PMJ. It depends greatly upon the outside weather conditions. Even though the setback is 8 degrees, that doesn't mean that it always makes it that low. My setback temp is 53 F, but this morning when I came down to do some work on one of the radiators before the system started up, the tstat was still showing 58 F. Everything DEPENDS.

Captain Who

Another factor which I didn't mention is that the average temp during the on program period was around 41 F, but the average temp during the setback period was higher at around 45 F. That is definitely not typical and is due to a warm rainy weather pattern that moved in overnight. So, the boiler would not have had to run a 20% duty cycle if I had no setback period. Maybe it would've been more like a 41/45 x 20 = 18%. Still saved a significant amount of fuel however.

Captain Who

Right now I believe the cycle it just ran was more than one hour. Still don't get the significance of that or why it needs to be exactly one hour all the time. I like to not have my room temperature vary noticeably when I am up and about, so I appreciate the tstat doing its job in that respect. After I retire for the night, couldn't give a ....... lol. I didn't time it exactly but the boiler was off for quite a while. Current temp 46 F outside.

I'm not convinced that my system is wasting much fuel at all during the program period. Doesn't mean that a setback won't save though, if it is for a long enough time. I was just trying to give an example with that simple equation I gave. Other people can check their own systems and report back to this thread.

Captain Who

PS: This screwy tstat tends to do 3 tentative short cycles of around 3 or 4 mins before the tstat is satisfied. Then it will be off for however much time it deems necessary before starting the next series of short cycles (could easily be an hour or more). I realize that may not be exactly ideal. It is obsessed with not overshooting I guess. 1.2 F anticipator setting should be much better for steam than the 0.6F setting I currently have it on.

Captain Who

To determine if my boiler system is wasting fuel you'd have to know what the heat loss of the building is, the btu input to the boiler, the surface area of the building, the cu ft. of interior space, etc. etc.. Now we are over simplifying things lol.

Captain Who

Who said anything about "reduced heat loss from the building"? It's really simple. If the burner is off long enough vs maintaining the setpoint temperature, the fuel expenditure to recover the setpoint temperature is MORE THAN MADE UP FOR by the savings in not maintaining the setpoint temperature. There IS a breakeven point, as far as the setback duration. That's what my simple equation proved. You even said yourself that you think there is a savings in increasing the cycle time to 2 hours and you described it as a 2 hour setback. Well take that out to a much longer time period and the savings is even greater. I really don't get what the confusion is.

Captain Who

PS: Happy Holidays. I'm out.

rrwitherspoon

I wonder what Dan Holohan thinks?

SWEI

Slightly off-topic, but with temperature-modulated hot water heat it is even tougher. We implement optimal start algorithms in DDC to manage both the pre-start time and also the supply water temp based on depth of setback, outdoor air temp, and even the time required for the past several recoveries. It's a hairy multivariable set of equations that always boils down to trial and error. In high mass, radiant-heated buildings, we find that even a 5 degree setback is not really worth doing unless the unoccupied period is at least 24-48 hours.

nicholas bonham-carter

Most interesting! If you are going to use setbacks, then make sure your system is as well vented as possible.
I would like to see some comparisons of fuel usage between steam, and forced air.
I do believe that you can feel more comfortable at a lower constant temperature, than one which fluctuates lower and higher.--NBC

Mark N

I've lived with steam heat for 25 years. I was advised by father to leave the thermostat at 1 setting and leave it alone. It is set to 70 all heating season. I converted to natural gas 6 years ago and have been tracking my gas usage for heating ever since. I track by the month(they read my meter in the middle of the calendar month) and by the year.

2009- 531.443 therms, $1.498/therm, $796.10
2010- 625.933 therms, $1.327/therm, $830.61
2011- 712.797 therms, $1.185/therm, $844.66
2012- 587.118 therms, $1.095/therm, $642.89
2013- 711.444 therms, $1.004/therm, $715.29
2014- 785.356 therms, $0.853/therm, $699.90

My boiler is a Burnham IN-4 connected to 260 sq ft EDR. Also, this house is located in Central New Jersey.

PMJ

Mark N said:

I've lived with steam heat for 25 years. I was advised by father to leave the thermostat at 1 setting and leave it alone. It is set to 70 all heating season. I converted to natural gas 6 years ago and have been tracking my gas usage for heating ever since. I track by the month(they read my meter in the middle of the calendar month) and by the year.

2009- 531.443 therms, $1.498/therm, $796.10
2010- 625.933 therms, $1.327/therm, $830.61
2011- 712.797 therms, $1.185/therm, $844.66
2012- 587.118 therms, $1.095/therm, $642.89
2013- 711.444 therms, $1.004/therm, $715.29
2014- 785.356 therms, $0.853/therm, $699.90

My boiler is a Burnham IN-4 connected to 260 sq ft EDR. Also, this house is located in Central New Jersey.

I have close to 4 times your EDR and round numbers I use 3-4 times the gas. I am in my 22nd year in my house.

The unfortunate thing about proving anything one way or the other about setbacks is that you would have to run each way exclusively for long periods(probably whole seasons) to show anything conclusively. The sun and wind variables that greatly affect demand don't show in degree day figures. Month to month comparisons won't mean much because you can't really say what the actual demand was accurately enough to tell anything.

Setbacks or not, a well running system is the important thing. Everyone seems to agree that lower pressure is better. So if you can get to operating with vapor below a pressure that can even be used for control and go to natural vacuum between cycles it would seem that it would be hard to get much lower average pressure than that.

I think that once a system runs well, practical setbacks say up to 5 degrees won't change overall efficiency by much more than single digit percentage points either way. Say in theory if Mark N. could save even 10% with a setback (and I'm not saying he could) would it be worth $75 in a whole season to sacrifice comfort if he likes it at constant temperature? I doubt it. As I said, I do believe a small setback saves something - but it is nowhere near a big enough issue to sacrifice any comfort if you like constant temperature.

archibald tuttle

Hatterasguy said:

We are most definitely not "overcomplicating" this thing. It's a very interesting subject and it points toward the very high losses that occur in a steam system during startup.

would like to focus a little more on the difference between "startup" and cycling on pressure.

one technology for steam that lags (disastrously in my instinct but jumping to conclusions isn't always the right way to leap i await the crowdsourced intelligence here) is moderated fire. I believe there is someone coming with a moderating fire conversion burner (for oil it might be harder without and alternative to traditional nozzle atomization -- similar to waste oil burners in some ways so maybe not inaccessible given the growing simplicity of and access to process combustion controls).

The point being that recovery is likely to involve many more pressure trips if steam must be maintained for an extended period and the firing rate is such as to produce steam quickly for modest duty cycles at average temps. so maybe 10 to 15 minutes vs. 45 of 90 or various cited recovery cycles in the thread here.

Assuming that there is no great variable fire techology in the offing for steam (if i can make it to AHR this year i keep looking, we'll see how the wallet and weather hold up for a january visit to Chicago -- they are really optimists at AHR) the question remains, what really are the costs of pressure cycling and is there a frequency of starts that actually augers parts failure (although there are lot of solid state relays available cheaply now). I don't really imagine that motor starts are out of hand for oil or forced air combustion gas. of course atmospheric the only wear is the gas valve. i get the sense if you are getting 6 to 10 cycles an hour during recovery you aren't really making headaches and every minute you aren't running is a minute you aren't burning fuel.

now maybe there are slight alterations to draft and perfect efficiency when reheating the chimney a bit each cycle although if the cycles come relatively quickly, unless you have no mass in the chimney or it is really frigid out and the chimney is on the exerior of the building and you've managed to slow down the air flow through boiler enough to reduce stack temp., then i don't get the feeling this would cause that much issue.

But some point to cycling as bad. Maybe the question here is, what really is a "short cycle" where that term is meant to imply something undesirable.

And on that note, my continued seeking for a real alternative to the mercury vaportrols that seemed to have the ability to actually regulate those cycles with a degree of precision.

Jamie Hall

Folks -- there really are too many variables, most of which can't be measured, never mind controlled. Some folks like to think they save, some (ytself included, based on 10 years of records, feel otherwise (but the spread in the data is too great to be statistcally significant)),

There is another factor, however: the effect of the setback on the structure of the house and its contents. As you note from my signature, I superintend a house museum. What we have found, with no argument, is that the damage and required maintenance to the structure (particularly plaster, but also old wood floors) and the contents (particularly the three Steinway grand pianos, but also the library and some types of furniture) costs far more than any savings we could hope to make on fuel. This will not apply, of course, to many houses -- but it should be kept in mind.

archibald tuttle

I'm totally onboard with this type of approach but could the setup you describe be 'right' if you don't make 6 oz. on full fire. i guess if all the rads get hot and you use a heat anticipator of some sort (i.e. build lead times into your setback) I would imagine it is slow to first steam. . .

but the problem for regulating short cycling and fire is the same as the problem for regulating steam period -- nobody has made a decent vaporstat in a decade . . .

. . . eer, what about this.

http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gage-Switches-Digital/SeriesDH3/ModelChart

i'm ready to jump and try it out although they don't rate it for steam temps/conditions, i'm thinking maybe two siphons. (belts and suspenders). It could be $300 mistake, but that is what you have to pay for a real mercury vaportrol is you can still find one. so would i be willing to risk this once to try? go ahead, keep egging me on, i'll try it, i'm warning you . . .

archibald tuttle

Jamie Hall said:

Folks -- there really are too many variables, most of which can't be measured, never mind controlled. . . . What we have found, with no argument, is that the damage and required maintenance to the structure (particularly plaster, but also old wood floors) and the contents (particularly the three Steinway grand pianos, but also the library and some types of furniture) costs far more than any savings we could hope to make on fuel.

Assume you say this from some emperical experience in keeping up appearances (and auditory qualities) and not just on the assumption that regular 10 or 15 degree temperature swings cause might cause the kind of damage you report. It is a point well taken for those curating the type of experience you point out. But I haven't had so much trouble with plaster on a relative basis in houses where we use setbacks at the low end of that range.

As to all the other variables, it seems to me what is still lacking are relatively simple and affordable loggers. As it is, digital and relational temperature control is still in the 19th century from what i can see. i got my last several digital controls self built by nerds on the net. (I hope that that is understood as an endearing reference by the way. I have undieing respect for htose who can't find what they want at a price they are willing to pay and so make it themselves.) e.g. http://www.ebay.com/itm/SBE-Solar-Tech-Digital-Differential-Thermostat-w-Pwr-Supply-Solid-State-Relay-/291142804500?pt=LH_DefaultDomain_0&hash=item43c976a414

So I keep waiting for somebody to make a decent accessible logger where i don't have to buy someone's softward and nonsense and where the culture of the company is not cult like. i just was something simple that has a enough channels so i could record sun, wind, wind direction, outdoor temp, firing hours (and setting where modified fire is available), pressure, boiler water temp. although the predominately important variable would just be an hour meter for single fire boiler.

when you have a lot of information you need an inexpensive practical way to get a handle on it.

brian

Fred

It's rated to 140 degrees F. That is the upper limit of the gauges we use and, I believe the Pressuretrols/vaporstats. The pigtail is what keeps the temp down below that range. It does say "Wetted materials" "Consult Factory". Not sure if that impies there are some additional measures required to use it on a steam/water based system.
I'm beginning to think there is an obsession with getting pressures down to as near 0 as possible (I guess I'm guilty of this too) I am sure there is a margin of error between 0 oz. of pressure and say 3or 4oz. where there is little to no impact on a steam system. It does take some pressure to get steam to the furthest radiator (little though it may be) but that will vary from system to system, both in Main, radiator run lengths, pipe size/resistance, boiler size/variance from radiator EDR, etc. Why the obsession for a 0 oz. goal? We all know that most open systems run well up to a pound of pressure and, except on rare occassions the cut-out of these devices is never reached and the Cut-in is always 0 at the start of a heating cycle. What am I missing in these discussions?

archibald tuttle

Actually i was thinking of the 25". I'm not retentive over keeping it as close to zero as possible although in order to cut short cycling what i find useful is accurate control cut out in the 10 to 12 oz range and cut in at 1 or 2 oz. For boilers without modified fire, i've been running a regimen like this although even on the mercury controls the pick-up, i.e. the subtractive differential is touchy. If i'm not careful i can get a circumstance where the control never picks up. With the physical threshold switches that replaced the mercury this is even worse. i'm kind of hoping these controls I linked to could handle the temps with a couple of siphons to protect my investment.

in addition to giving switching they also have the typical output for logging devices as well.

brian

jumper

Best answer is it depends.If radiation is sized to warm up your space in thirty minutes,you may want to setback all the way to off.Quebec ski lodges were operated like that.Very early in the morning and in the late afternoon the one pipe radiators whistled and it got toasty fast.The rest of the time skiers skied,slept,were in the dining room,or sucked up being chilly inside.Or they wore their ski clothes inside.

ChrisJ

I like a setback and in my experience even before the EcoSteam it saved me money doing a 3 degree setback at night.

If your system builds pressure easily and cycles multiple times during a recovery I'd avoid it.

archibald tuttle

MarkS said:

Brian, I have something you might want to try since you're willing to experiment. It's off-topic for this thread so I'll start a new one.

that never stopped me before. Should just change my moniker to jack so everyone can say hi jack after every one of my posts.

speaking of which, i just got one of those 'personal' notes from Dan Holohan telling me that someone had accepted my answer (which i of course find highly suspect). Anyway, it cited a comment on this thread by number. But i don't see where to find the numbers and the link just takes me to a page without highlighting a post. does anyone know where you find the comment number?

archibald tuttle

PS - MarkS points those of us interested in vaportrol substitutes to this new thread:

http://forum.heatinghelp.com/discussion/152838/idea-for-a-vaporstat-alternative

archibald tuttle

actually this link took me to the second page of the thread but i can see from the link itself that it targets a specific comment.

e.g. http://forum.heatinghelp.com/discussion/comment/1357564#Comment_1357564



i just have no idea where to right click on a comment to find its number so i have no idea which 'answer' rwitherspoon was 'accepting'. that is actually a useful function that is easy to find on some forums so you can direct folks to a specific comment in a long thread -- whether or not it is accepted as an answer.

and i did scare quote 'personal' on purpose. i know those notes are computer generated. just tweaking Dan and co. have to tweak since i don't twit.

brian

Captain Who

I still haven't installed my hourmeter and counter yet. I hope to do that this week when I get some flag style spade connectors. Anyway, I have been doing some "data logging" for the past 2 weeks (1/19 to date) using the gas meter and I am certain that in my system I have around a 20%+ savings during the setback+recovery period over the alternative of not having any setback. I have a 8deg setback which is programmed to begin at 10pm and end at 7:45am. I have been using weatherunderground.com downloaded data from a weather station 2.3mi away from me and have been calculating the avg wind chill temps and avg degree hours from this data. It also has solar radiation data but I haven't yet determined how to incorporate this data but it clearly has the effect of making the data skewed conservatively towards even more savings, if I knew how much to mathematically weigh it into the calculation. I excluded days where I did my washing (both clothes and myself!) since I have gas water heater and dryer. When I cooked I compensated for the minimal effect of the gas used by the range and oven. I also counted the followup thermostat cycle after the recovery one completed as part of the recovery period because it takes a little while for the walls and furniture to come back up to temperature, even though the ceiling is at above normal temps after the first time thermostat gets satisfied.

Setback+Recovery Period: 0.527 cu ft per hr per degree hr
Regular Operation Period: 0.655 cu ft per hr per degree hr
Setback+Recovery Period = 45.7% of full day on avg.

Savings during Setback+Recovery Period = 19.5% w/o factoring solar radiation benefits to regular operation periods

Savings during full day (not factoring solar rad benefits) = 8.9%

I've been making too many sacrifices doing this 2 weeks of testing so I'll suspend testing until I get the hourmeter + counter installed so I don't have to restrict my hot water + oven/range + dryer usages.

EDIT: wunderground.com (not weatherunderground.com)