Is there fuel savings with deep setback with steam heat?

PMJ

Captain Who said:

"Frankly I don't believe those who report recoveries of many degrees in an hour or so. The heating system would have to be massively oversized to move the entire structure and all of its contents several degrees/hour. "

What don't you believe exactly? The thermostat only knows the air temperature and to some extent the temp of the wall it is mounted on. What takes a long time to go up also takes a long time to go down. The air is the thing that changes rapidly in temp, but the objects take longer to go down and longer to go up, due to their larger heat capacity and thermal mass, so that even though the air temp has stabilized at the setback temp, that might not and probably isn't the case that all the objects have gone that low, because not enough time may have passed.

My boiler is unfortunately oversized by 32% and it usually takes about 1hr and 40m for my house to recover from the overnight setback of 8 deg, depending upon a lot of factors, mostly outside temp and wind speed. That is going by the second cycle of the tstat, ie. not the first time it thinks it has recovered to the daytime setpoint. Do I have dataloggers monitoring the internal temps of every object in my house? Nope.

PS: I also have ceiling fans in the first floor rooms that are blowing upwards at low speed and that helps to even out the temps of the objects through convection.

It seems there is a real need to believe in this fast recovery stuff. Of course the definition of recovery includes all the contents. In the case of the church, having the air warm and the pews still cold doesn't work! It does in fact take a while to get them warmed up. If we could know the specific heat of the mass of everything we would find it a very large number compared with the 1 hour of boiler output. When you include the structure the actual recovery time is longer - considerably. Perhaps this is the misunderstanding here. A full recovery to me means the whole structure is back at the starting point when I turned off the boiler.

ChrisJ

PMJ said:

Captain Who said:

"Frankly I don't believe those who report recoveries of many degrees in an hour or so. The heating system would have to be massively oversized to move the entire structure and all of its contents several degrees/hour. "

What don't you believe exactly? The thermostat only knows the air temperature and to some extent the temp of the wall it is mounted on. What takes a long time to go up also takes a long time to go down. The air is the thing that changes rapidly in temp, but the objects take longer to go down and longer to go up, due to their larger heat capacity and thermal mass, so that even though the air temp has stabilized at the setback temp, that might not and probably isn't the case that all the objects have gone that low, because not enough time may have passed.

My boiler is unfortunately oversized by 32% and it usually takes about 1hr and 40m for my house to recover from the overnight setback of 8 deg, depending upon a lot of factors, mostly outside temp and wind speed. That is going by the second cycle of the tstat, ie. not the first time it thinks it has recovered to the daytime setpoint. Do I have dataloggers monitoring the internal temps of every object in my house? Nope.

PS: I also have ceiling fans in the first floor rooms that are blowing upwards at low speed and that helps to even out the temps of the objects through convection.

It seems there is a real need to believe in this fast recovery stuff. Of course the definition of recovery includes all the contents. In the case of the church, having the air warm and the pews still cold doesn't work! It does in fact take a while to get them warmed up. If we could know the specific heat of the mass of everything we would find it a very large number compared with the 1 hour of boiler output. When you include the structure the actual recovery time is longer - considerably. Perhaps this is the misunderstanding here. A full recovery to me means the whole structure is back at the starting point when I turned off the boiler.

In this case no one should ever do a setback and recovery using forced hot air because it takes absolutely forever to bring objects back up to temperature using heated air.

Captain Who

"In the case of the church, having the air warm and the pews still cold doesn't work!"

Actually, it might! You have to consider the fact that the ceiling could be super hot compared to what it was when the setback begins. There are some objects that might be overheated after the tstat first thinks it has recovered and those overheated objects will eventually distribute their heat.

That's why I say the only way is to take an average of as many temperature sensors as is reasonable.

PS: Also the radiators themselves are storing more heat at the first or last tstat shutoff points after the "recovery", relative to what they had in them after the last shutoff before the setback period begins. You have to factor that in also.

PMJ

Captain Who said:

"In the case of the church, having the air warm and the pews still cold doesn't work!"

Actually, it might! You have to consider the fact that the ceiling could be super hot compared to what it was when the setback begins. There are some objects that might be overheated after the tstat first thinks it has recovered and those overheated objects will eventually distribute their heat.

That's why I say the only way is to take an average of as many temperature sensors as is reasonable.

PS: Also the radiators themselves are storing more heat at the first or last tstat shutoff points after the "recovery", relative to what they had in them after the last shutoff before the setback period begins. You have to factor that in also.

Captain,

I was on the board of Trustees. The complaints didn't stop until we started 12 hours out. It is a huge stone structure. Keeping a structure at steady temp and raising the whole thing up are two very different animals - really.

Captain Who

I don't doubt that, just what I was getting at in my previous comments about heat capacity and thermal mass. That is an extreme example, since I doubt many of us here live in stone castles. You probably also had a very long setback period as well.

Jamie Hall

"But before we panic too much about 2-4 degree temperature changes destroying our homes consider a couple things. Most churches, for instance, can't really afford to heat vast sanctuaries 24/7 to the 72 the parishioners desire for 6 hours on Sunday. Many around me, vast steam heated structures from the building boom of the 1920's with priceless pipe organs and plaster and woodwork inside really do use setbacks. One I am quite familiar with allowed the temperature to fall 10 degrees during the week and has done so for decades. It also still has no air conditioning."

And both the setback and recovery are long enough so the damage is much less than the more rapid setbacks which seem to be the subject here. Nonetheless, many pipe organs which I have played -- and I have played a lot -- are astonishingly out of tune. I wonder why...

However. I have absolutely no doubt that for many applications, setbacks do save both fuel and money, and if it works for you, go for it. My sole points are that there are some applications where setbacks can and do cause problems, and these problems should be considered when determining how often, and how much, to set back temperatures.

Don_197

I read every single post in this thread........and ya know what I took away from it?? We need something OTHER than a thermostat to control our RADIANT HEAT. thermostats measure AIR TEMPERATURE! RADIANT HEATS THE OBJECTS WITHOUT HEATING THE AIR....(well ok.....then the objects heat the air....whatever! LOL) if someone would invent a way to control a radiant system that doesn't invlove a thermostat.....the savings would be astronomical! If we were home all day and could actually run our systems by "comfort level" instead of air temperature......we would save tons of fuel! I have proven this with a 14 year old boy being in control of the system! (he's 20 now and we now live with scorched air.....uggghhh!) I wish I were Tesla........if I was I could figure it out and make a mint! 8-)

Gordy

If you were Tesla you would have designed free energy........No one would care about setback.

SWEI

PMJ said:

I was on the board of Trustees. The complaints didn't stop until we started 12 hours out. It is a huge stone structure. Keeping a structure at steady temp and raising the whole thing up are two very different animals - really.

Amen to that I'm in the process of tuning the setback algorithm for a 1949 Church right now, and it's not easy. We needed ~8 hours to recover 5°F when boosting supply water temp 10°F over the ODR setpoint. This week, we changed that to 18°F and will see how that goes. As we near design conditions, ODR setpoint plus 18°F becomes more than the boiler high limit. More math.

archibald tuttle

Gordy said:

If you were Tesla you would have designed free energy........No one would care about setback.

I quoted this response just cause it was shorter than its inspiration. Of course that is the irony of invoking Tesla. Is it possible to have revelation short of free energy.

I absolutely agree that theoretical science says that setbacks save money and i'm really impressed with the devotion of many on this thread to proving that emperically.

But the tension between ODR control and setback operation seems to be central to how heating goes in this country. It is possible to have both, but one wonders if the ODRs for America really need to have two curves. One for normal operation and one for recovery . . . I don't know the programming of all the ODR controls but even those that monitor the indoor space as a a variable i think are looking for rate of change rather than the distance between present temp and therostat setpoint which would be more appropriate inquery for recovery water (or steam temps for those looking to setback steam into vacuum).

But, aside from condensing, and maybe some modest extension of service life of peripherals is there a point to ODR? Essentially, once you're over 140 you might as well be at 180. I keep thinking that stack losses ought to be more with higher stack temps but my combustion meter keeps telling me that free air is way more important.

So setbacks don't make much sense for floor radiant installations where temps are always below 140 and response is to outdoor temps not indoor temps, although imagine you could chisel away a tiny bit with a timed algorithm that modifies floor curves through overnight periods and maybe even gets weather forecasts anticipating wind and sun. That's rearranging angels on the head of a pin but it ought to be able to be done with a minor bit of computer programming if some nerd would stop reading heating help and get to work.

jch1

I just posted this in another thread, but thought it may be of use to those reading this one. With my thermostat (ecobee), I can extract data down to every five minutes detailing when the thermostat is calling for heat, outdoor temps, humidity, etc. It even goes one step further and tells me how many seconds the thermostat was calling for heat in five second intervals. Here's the data from the past week:

Date.....Avg. temp..... System on time (converted to hrs)
1/29 ........36.3 ........ 4.3
1/30 ........27.8 ........ 5.41
31st ........32.1 ........ 4.98
1st ........29.1 ........ 6.08
2nd ........15.4 ........ 6.75
3rd ........19.8 ........ 6.29
4th ........22.6 ........ 6.25


When the temp is in the teens-twenties, my boiler is on for around six hours the entire day. That's with a 3-4 degree setback when I'm sleep and out of the house (we're either sleep or not in the house for a total of 17 hours), so it's set at 72 deg. for 7 hours, and 68 deg for 17. Obviously, this doesn't account for other factors such as wind speed, sunlight, etc., but useful information to know nonetheless.

Captain Who

@jch1 - That's nice to have that feature on your thermostat. What model is it? Of course, in my case it would over-report the burner on time because my system cycles on the pressuretrol in a spectacular fashion in the last half of the recovery period, and during the 1st cycle after recovery. The rest of the day it usually only runs maybe 1 to 2 ozs of pressure towards the end of the cycles.

Gordy

Curious of the run time being longer on the 1st with 29.1 avg. temp verses the 30th with a lower outdoor temp.

jch1

It's the ecobee SmartSi thermostat. It has the same interface as their newer ecobee3, but without the touch screen and extra room sensors. Same app and data is recorded (with the exception of what the additional temperature sensors provide).

As to the discrepancy, that could probably be explained by two things. We have a weekend schedule where temperatures are set at 71 from 6am to 11pm (17 hours), then it goes back down to the sleep schedule. So I'm sure the higher temperature has an effect on run times.
Second, Chicagoland got hit with a pretty bad storm/blizzard on Sunday the 1st. I didn't realize that the data provided includes wind speeds, so here are the averages in km/h:

1/29... 22.33
1/30... 11.9
1/31... 10.64
2/1... 28.72
2/2... 19.83
2/3... 8.45
2/4... 14.29

So comparing the 1st and 30th, there's a pretty big difference in on-times as well as wind speed. I guess this goes to show that there are tons of variables involved here.

It'll be interesting to see what kind of data I get today, as the current temp is 4 degrees.

Gordy

What about solar influence. I assume wind speed is weather station data via internet?

jch1

If anyone is interested, here's the data for yesterday, the coldest day in the past few weeks
2/5
avg temp... on time (hrs)... wind speed avg
10.8......7.47.....11.95

Don_197

I used to work for a DDC company and we installed a Knight Boiler in a convent that had a very generous bb radiation system. this was my parish.....so I was very interested in saving them money, and they happened to have a DDC system that I just happened to be monitoring remotely. As part of the boiler install I included a controller and a few sensors (return, supply, and zone temp) and I could modulate the boiler using either setpoint or direct control of the modulation rate. I wrote an algorithm for them that monitored setpoint deviation (how far away from setpoint am I?) and I also used the OD sensor that was already installed. I basically said "as I get from 0 to 1 degrees below setpoint, shift the ODR setpoint UP by 0 to 50 degrees (and of course limited the max setpoint to 180) and as I get from 0 to 1 degree above setpoint shif the ODR setpoint from 0 to 50 degrees DOWN from ODR SP. then all I did was tweak the ODR setpoints a coupld times over the winter looking for "happy enough" and wallah.....the system has run continuously for years now and save a TON of money AND I am able to program a 5 degree night setback in and the system compensates for it with the above algorithm by immediately turning the water setpoint up 50 degrees when coming out of setback. Sometimes you CAN have the best of both worlds.....but not often 8-)

SWEI

We're doing similar things right now with a DDC system in a church. 100 degrees of proportional band for a 2 degree space temp difference is far more than I would have guessed.

I'm curious how this works as the OAT approaches design conditions and the ODR target temp approaches the boiler high limit setting. This is when setback recovery is hardest. e.g. calculated ODR setpoint of 184°F at 14°F OAT, yet the boiler absolute max limit is 192°F. OAT is falling at midnight, but we don't really know where it will be at 6:00 AM. There's an 8:30 AM service where we need to hit setpoint. It's an interesting challenge.

handbanana

Guys - i didn't read every post here, but read enough to think of this (forgive me if this analogy has been used):

It's kind of like driving down the highway and going full acceleration, then letting full off the gas until your speed decreases 'too much (setback)' and then nailing the gas again to max speed (recover) and then doing again.

Damn good way to:
Waste gas
overuse your equipment.

Nothing more economical than a steady foot, right?

Kind of like...

Don_197

Ah yes.....I like the analogy...................all we are doing with the analogy is "slowing down through the lower speed limit areas.......smoothly) Our goal with the above is to never produce more btuhs than what the building is losing.......and we do that with absolute positivity that the lower the firing rate we can accomplish (as well as the lower the return water temps) the more efficient it is running. this is where modcons shine. One thing I have learned is that if you don't control a modcon differently than you control a high mass boiler......it won't be much if any more efficient......and at twice the cost....THATS A WASTE!!!

ChrisJ

handbanana said:

Guys - i didn't read every post here, but read enough to think of this (forgive me if this analogy has been used):

It's kind of like driving down the highway and going full acceleration, then letting full off the gas until your speed decreases 'too much (setback)' and then nailing the gas again to max speed (recover) and then doing again.

Damn good way to:
Waste gas
overuse your equipment.

Nothing more economical than a steady foot, right?

Kind of like...

Actually,
This is a very common way to increase gas mileage. Gasoline engines are very inefficient at light load.

This method is known as Pulse and Glide.
http://en.wikipedia.org/wiki/Energy-efficient_driving

Pulse and Glide[edit]
Pulse and Glide (PnG) is also known as Burn and coast and periodic driving. This method consists of rapid acceleration to a given speed (the "burn" or "pulse"), followed by a period of coasting down to a lower speed, at which point the burn-coast sequence is repeated.[25][26] Coasting is most efficient when the engine is not running, although some gains can be realized with the engine on (to maintain power to brakes, steering and ancillaries) and the vehicle in neutral, or even with the vehicle remaining in gear.[26] Most modern petrol vehicles cut off the fuel supply completely when coasting (over-running) in gear, although the moving engine adds considerable frictional drag and speed is lost more quickly than with the engine declutched from the drivetrain.

Some hybrid vehicles are well-suited to performing the burn and coast. In a series-parallel hybrid (see Hybrid vehicle drivetrain), the internal combustion engine and charging system can be shut off for the glide by simply manipulating the accelerator. However based on simulation, more gains in economy are obtained in non-hybrid vehicles.[25][26]



Of course, this is also a bad analogy for other reasons as well. For example a boiler is most efficient when run for extended periods.

handbanana

pulse and glide.. seems better on paper than in the real world.
Try it sometime...for a month.

Continued 'rapid acceleration' dramatically decreases fuel economy, and is taxing on parts. I meant it in that way.

"For example a boiler is most efficient when run for extended periods."
I was thinking of this as analogous to a "steady foot on the pedal".
Maybe I'm not looking at this right..

Good insight though, thank you. Now I'll be reading about P&G for the next 2 days..

ChrisJ

handbanana said:

pulse and glide.. seems better on paper than in the real world.
Try it sometime...for a month.

Continued 'rapid acceleration' dramatically decreases fuel economy, and is taxing on parts. I meant it in that way.

"For example a boiler is most efficient when run for extended periods."
I was thinking of this as analogous to a "steady foot on the pedal".
Maybe I'm not looking at this right..

Good insight though, thank you. Now I'll be reading about P&G for the next 2 days..

I do, do it in real life.
It's also how people pull 60+MPG out of a Chevy Cruze.

I also don't know if "continued rapid acceleration dramatically decreases fuel economy". I'd say wind resistance is the primary cause. For example, put a 40HP engine in your car and run it wide open on the road and I think you'll be impressed at your mileage assuming the car is decent aerodynamically to begin with.


Oh, and you're name is just WRONG.

PMJ

There really is no comparison at all with what is being discussed now to a fixed speed boiler. There is nothing about boiler operation to compare with physically accelerating a moving mass like a car. There is no gas pedal to step on to make the standard boiler work harder or less hard. The load on the boiler itself is not dynamic and constantly changing like the load directly and physically connected to a car engine. If the steam system operates at very low pressure the boiler is just putting steam into a big open pipe at a fixed rate and at a fixed efficiency. This is completely different than the load a car engine sees.

As was stated earlier in the thread, the total heat loss of the structure is simply a function of the difference in the inside and outside temperatures( with the assumption that all other factors just average out over time). The total heat loss is what must be replaced by the boiler. Setbacks reduce this temperature difference and therefore the total loss. In most cases the setback is small and so are the savings.

handbanana

The point was to not heat cold pipes via deep setback defeating savings of setback. Just keep cruising steady.

I know when I'm licked.
Tapping out.

ChrisJ - Tonight.....you..