Heat Loss Calculations

coelcanth

coelcanth said:

wow $570 for the year ?
i thought previously you had said it was double that..

i am in queens and paid about $2000 to heat 2200sq ft last year

ah ok..
using just the six heating months out of last year our bill is closer to $1700.. but that still includes some hot water and cooking gas

we are in ridgewood, in a semidetached 2 family masonry house..
for comparison's sake, our original? attached radiation is less than yours, at around 300sqft edr (72,700btu)
but boiler is oversized at 450sqft of steam (175,000btu input).

the funny thing is, the radiators are rarely more than half full.. except maybe after a real long call for heat on the ice coldest days.

only minor problem is occasional drafts here and there from lack of insulation.. but still i think most rooms are within .5-1 degree F with no control more complicated than an old Honeywell mercury thermostat.
..that and the fact that this new system doesn't seem to be any more efficient than the 50 year old boiler, though i don't have many bills from then to compare against...

ChrisJ

@PMJ how exactly does a larger boiler cold start faster? You've got a larger burner but you also have a larger volume of cold water and iron.

Jamie Hall

ChrisJ said:

@PMJ how exactly does a larger boiler cold start faster? You've got a larger burner but you also have a larger volume of cold water and iron.

Two ways: first, in general the larger boilers have more heat transfer area in relation to the water volume (you might be interested, since I know you are curious about things, to take a look at the flash boilers which the old Stanley Steamer cars had, in a doomed effort to compete with internal combustion -- some had 40 or 50 hp boilers which could go from cold to full power in a matter of seconds). More important, if by "cold start" timing, we are thinking about how long before the steam gets to the end of the main, then once the larger boiler does start to boil, it is generating steam more rapidly.

PMJ

ChrisJ said:

@PMJ how exactly does a larger boiler cold start faster? You've got a larger burner but you also have a larger volume of cold water and iron.

I think burners are sized to a given capacity to get to steam in the header at about the same rate. But after that the larger capacity boiler runs away from the smaller one heating the distribution piping.

ChrisJ

@Jamie Hall how long does it take to get steam to your header from an ice cold start? Meaning the boiler has been off for days.

Jamie Hall

ChrisJ said:

@Jamie Hall how long does it take to get steam to your header from an ice cold start? Meaning the boiler has been off for days.

About two minutes. Then another five to the end of the longest main -- 70 or so feet of 3 inch.

ChrisJ

> @Jamie Hall said:
> @Jamie Hall how long does it take to get steam to your header from an ice cold start? Meaning the boiler has been off for days.
>
> About two minutes. Then another five to the end of the longest main -- 70 or so feet of 3 inch.

Two minutes from an ice cold start? That's astonishing.

PMJ

Jamie Hall said:

ChrisJ said:

@Jamie Hall how long does it take to get steam to your header from an ice cold start? Meaning the boiler has been off for days.

About two minutes. Then another five to the end of the longest main -- 70 or so feet of 3 inch.

Sounds pretty quick.

To rough this in and compare boilers couldn't we calculate how much heat was required to raise the volume of water in each boiler from say 60F to 212F and see how long it would take the burner net on that boiler to do it?

That said, once producing steam, the big boiler obviously wins all other downstream races.

ChrisJ

> @PMJ said:
> @Jamie Hall how long does it take to get steam to your header from an ice cold start? Meaning the boiler has been off for days.
>
> About two minutes. Then another five to the end of the longest main -- 70 or so feet of 3 inch.
>
> Sounds pretty quick.
>
> To rough this in and compare boilers couldn't we calculate how much heat was required to raise the volume of water in each boiler from say 60F to 212F and see how long it would take the burner net on that boiler to do it?
>
> That said, once producing steam, the big boiler obviously wins all other downstream races.

Yes, and an engineer I used to work with came up with something like 18 minutes for mine. Which usually is closer to 20.

I have no idea how any boiler could do it in 2 minutes. Mine will do it in less when it's running often but not when it's room temperature.

Gordy

2 minutes to steam from room temp?

https://energy.mo.gov/sites/energy/files/steam-tables_power-plant-service.pdf

PMJ

Gordy said:

2 minutes to steam from room temp?

https://energy.mo.gov/sites/energy/files/steam-tables_power-plant-service.pdf

Thanks for this @Gordy .

Right. It isn't 2 min from room temp.

I looked it up and my boiler has about 33 gallons in it. Using the numbers in this article just heating that to 212 where steam production can start would take my burner about 7 minutes not subtracting for warming cast iron which of course we are. So I'm going to say steam starts to leave my header somewhere in the range of 10-12 minutes starting from room temp which I think is about right from observation. That is starting to leave - not full boil. Obviously this is a gradual process.

I have a temp switch at a remote rad that with the PLC I know exactly how long from start it takes to see steam. The most I see to there after long off periods is 23 minutes +/-. I have safety code in the program that shuts everything down if that number ever gets to a 35 min straight run because that means something is wrong.

ChrisJ

PMJ said:

Gordy said:

2 minutes to steam from room temp?

https://energy.mo.gov/sites/energy/files/steam-tables_power-plant-service.pdf

Thanks for this @Gordy .

Right. It isn't 2 min from room temp.

I looked it up and my boiler has about 33 gallons in it. Using the numbers in this article just heating that to 212 where steam production can start would take my burner about 7 minutes not subtracting for warming cast iron which of course we are. So I'm going to say steam starts to leave my header somewhere in the range of 10-12 minutes starting from room temp which I think is about right from observation. That is starting to leave - not full boil. Obviously this is a gradual process.

I have a temp switch at a remote rad that with the PLC I know exactly how long from start it takes to see steam. The most I see to there after long off periods is 23 minutes +/-. I have safety code in the program that shuts everything down if that number ever gets to a 35 min straight run because that means something is wrong.

23 minutes sounds comparable to mine. Once I get steam to the header it heats the mains fairly fast. After all, it does have the entire boiler's output to do so as has been discussed, I'm not heating radiators with the mains.

Jamie Hall

Cedric is actually more like 5 minutes, not 2 minutes. Sorry. Which makes sense, given the mass of water and the energy input. That's from a cold start, or as cold as he ever gets (around 60 or so). Hasn't been warm enough outside here for him to take a vacation for a while! Normal winter running conditions is about half that, and I guess that's that what I was thinking.

Other timings.. the 5 to 7 minutes to steam at the farthest radiator (75 feet of main plus 12 feet of runout/riser) is about right. There is about a 4 minute difference between steam at the closest radiator (only about 10 feet from the header second header) and the farthest one. If he runs for more than about an hour (which can happen on the coldest days) he starts to cycle on pressure (6 ounce cutout) -- one minute off (can't be shortened -- post purge and pre purge) then about a 10 minute run and so on.

Gordy

I'll ask again.

Why does the boiler have to be sized to the radiation for steam systems?

Gordy

I have the utmost respect for this individual.

https://heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

ChrisJ

> @Gordy said:
> I have the utmost respect for this individual.
>
> https://heatinghelp.com/systems-help-center/taking-another-look-at-steam-boiler-sizing-methods/

Me too.

Jamie Hall

The obvious answer, @ChrisJ , is that it doesn't. As Dave's article points out. Further, while he concentrates on venting and one pipe systems, may I humbly point out that exactly the same kind of thing can be done with two pipe vapour pressure systems, provided you either have managed to keep the graduated metering valves on the radiation or have or can install orifices.

There is, however, a joker in the deck. As usual. Not every owner of a steam system has the patience to do the balancing and tweaking that you do, Chris -- or the funds to hire Dave or another real expert (who are pretty thin on the ground and are, quite justifiably, not inexpensive to hire) to do it for them. It is hard enough to get most people to just clean their boilers and burners, never mind take the time and fully adjust their system. I would suggest, then, that the prudent course for an installer to take with an existing steam system is what is usually done; he or she then knows that the thing really is going to work, though it is very likely oversized for the heat loss, and he or she isn't going to get a call back by an irate consumer.

I might add that we steam nuts wonder why people tear out steam and put in forced air -- or why forced air is installed new. Sometimes, granted, its' for air conditioning -- but not always. A very significant part of the answer to that is that, honestly, it's a lot cheaper and quicker to create something which is perceived to work well enough, though it may be very far indeed from an ideal system.

ChrisJ

@Jamie Hall I didn't ask, @Gordy did

Gordy

@Jamie Hall reread the article. My take with venting reconfiguring you can size the boiler to the heat loss.

Something that isn't mentioned is why does one need to completely use the whole radiators capacity in lower load scenarios.

@PMJ method of control needs a much harder look PWM.

I'm not a steam guru. Hot water, and steam have similarities in that there is a boiler, and an emitter. The medium to heat the emitter is different, along with the piping to an extent.

Hot water welcomes oversized emitters as it can get away with lower AWT to meet the load requirements to an extent with a ci boiler. With a mod/con the lower limit of SWT is to meet the load, the boiler has no concerns.

With steam the temperature is fixed so the opposite happens, don't use the whole emitter to meet the load, just use what's required. All this would be based on an old system that was oversized to begin with, or oversized through envelope upgrades.

So what am I missing?

PMJ

I never bought into the open windows theory for why the radiation was oversized. The coal fired boilers had very sensitive pressure monitoring devices that worked in the vapor range. The flow rate of the steam to the rads would change with the demand and the corresponding pressure change did the control. It would take more fire and more steam to maintain the same pressure against bigger demand. Were the rads anywhere near reaching capacity the resulting sudden increase in pressure would close the damper when in fact it needed to be opened. The only logical approach was to have the rads so big that would never be a real possibility even on design day. The notion that people would plan to maintain 70 degrees with the windows open doesn't make much sense.

While I do agree that it is not necessary to size a replacement boiler to be capable of filling this radiation that is never needed at capacity anyway, I do not agree that such a boiler has the negative consequences generally assigned to them. I rather easily run without ever anywhere near filling my radiation and only need 2-1/2 to 3 cph in extra cycles to do that. I am enjoying my lowest heating bill in 25 years this season, and though partially due to a milder winter, it has more to do with the control method(newly tweaked again this year) and the fact that I am sub atmospheric some 80% of the time the burner is firing, and 100% of the time between cycles when it is not. My rads are closer to continuously hot at a lower average temperature.

Thanks @Gordy. I think this method needs a closer look by more folks too.

Jamie Hall

I don't think you're missing anything, @Gordy -- and I agree that with venting reconfiguring you can size the boiler to the heat loss. The problem is not that. It's the difficulty in adjusting the venting (or orifices/metering valves) to get the thing to put the steam where you want it to go. Steam is terminally lazy -- and if there is a radiator nearby with a nice big vent on it, that's where it's going to go -- and happily condense and create it's own pressure differentials, making things worse.

And I completely agree that some of @PMJ 's approaches to coping with a boiler which is oversized relative to the radiation deserve more of a look -- they have real merit, and should work well.

Not that it can't be done, nor even that, ideally, it shouldn't be done -- it's much more a matter of is it practical in the majority of cases to do it?

Perhaps an analogy from the world of cars and trucks -- I can drive a semi from New York to California, loaded, with less horsepower than the average passenger car of today (and a nice Allison or Road Ranger to help out!) -- but can or would the average citizen tolerate the finesse required? And, for that matter, would I really object to having a 500 hp Cat up front, for those odd moments?

ChrisJ

And what about 90% of the steam systems that aren't vapor? The ones that ran at 2psi +-.

The Redflash boiler that was next door had a pressure controller on it from it's coal days and it sure wasn't sensitive and it ran at several pounds.


This is what keeps getting me and PMJ arguing. He bases everything on his 2 pipe vapor system as if all systems are the same. Meanwhile his is a rarity and certainly not normal.

PMJ

> @ChrisJ said:
> And what about 90% of the steam systems that aren't vapor? The ones that ran at 2psi +-.
>
> The Redflash boiler that was next door had a pressure controller on it from it's coal days and it sure wasn't sensitive and it ran at several pounds.
>
>
> This is what keeps getting me and PMJ arguing. He bases everything on his 2 pipe vapor system as if all systems are the same. Meanwhile his is a rarity and certainly not normal.
>

@ChrisJ , I thought we already established that your boiler was sized closely to your radiation plus a smaller pickup factor. We also established that your boiler needs to run about 1/2 the time on design day. So running on a continuous basis (coal fired) your radiation couldn't have been full ( more like 1/2) to heat on design day. How could it possibly have been run at 2 psi?

ChrisJ

> @PMJ said:
> > @ChrisJ said:
> > And what about 90% of the steam systems that aren't vapor? The ones that ran at 2psi +-.
> >
> > The Redflash boiler that was next door had a pressure controller on it from it's coal days and it sure wasn't sensitive and it ran at several pounds.
> >
> >
> > This is what keeps getting me and PMJ arguing. He bases everything on his 2 pipe vapor system as if all systems are the same. Meanwhile his is a rarity and certainly not normal.
> >
>
> @ChrisJ , I thought we already established that your boiler was sized closely to your radiation plus a smaller pickup factor. We also established that your boiler needs to run about 1/2 the time on design day. So runinng on a continuous basis (coal fired) you radiation couldn't have been full ( more like 1/2) to heat on design day. How could it possibly have been run at 2 psi?

That's a good question.

I don't know?

Does anyone have the instructions on the pressure / damper setups that were commonly used back then?

PMJ

So I think we have brought into focus the most important element of this sizing issue. The radiation in the original design condensed steam continuously. Condensing continuously, a much smaller amount of active radiator is needed. A partially filled radiator is actually slightly sub atmospheric so the pressure at the boiler header required to move the steam there is very low - single digit ounces. Many here have observed this to be true.

The original systems had some pretty clever devices to modulate the fire based on these low header pressures. The radiators themselves had to be oversized significantly as filling them would cause a rapid change in the system pressure and upset the control device sending it in the wrong direction. I think we all can see there is a lot of "excess" radiation out there. It was not excess to the original design.

This was one of the first things I realized at the start of my work - that the installed radiation was well in excess of what was actually required from a BTU standpoint - but made good sense from a control standpoint. And as I learn more about this I find that more and more my focus turns to the real time information a partially filled radiator provides about the conditions. The inputs to my control are shifting there. I am finding that even at the same approximate fill level the condensation rate changes a lot with the demand. Maybe more on that another time or thread.

What I have not been able to make sense of was how the switch to intermittent fire has ultimately resulted in the current standard control scheme, this roller coaster of fill all the way up or nearly so and wait, wait, wait. It may be very reliable, but it is surely not anywhere near as even heat as the original continuous operation. Looking through my 1956 Bryant literature I see a "pressure tender" - looks like a device to modulate the gas flame based on header pressure. I am not seeing a pressure range spec for it. But I get the impression that back then there was an effort to modulate the flame similar to what would have been on the coal fired boiler my current one replaced. The pressure range would have had to have been really low or it would have been useless as anything more than a few ounces would have roasted everyone running continuously.

PWM does offer a way off the roller coaster. It does not require that many more cycles. I am quite confident that those cycles do not result in a loss of efficiency of any significance if there is a loss at all. I am sure though that in a 2 pipe system with vacuum in between the result is significantly more efficient.

Gordy

A loss of efficiency through cycling more can’t be much if any, so long as the boiler gets a decent fire time in its cycle.

The most efficient boiler is one that is off. The next step is controlling jacket, and flue losses, after that which is really not about efficiency, but about wear, and tear cycling components in the boiler often.

Comfort is a main goal. I’ve never had the opportunity to coexist with a steam heated environment in a home.

Jamie Hall

I agree with almost all of what @PMJ said above -- except for one thing: the installed radiation was not always oversized for the heat loss. Probably was, true, much of the time -- and in buildings which have had substantial upgrades to the envelope, almost certainly is true. But... it's not true all the time, and its those outliers which can be real gotchas. If in doubt, calculate. Doesn't take that long. I wouldn't be aware of this except that it happens that Cedric's home is one of those outliers: if it is both cold and windy at the same time, he runs almost continuously and the whole thing just barely keeps up.

ChrisJ

> @Jamie Hall said:
> I agree with almost all of what @PMJ said above -- except for one thing: the installed radiation was not always oversized for the heat loss. Probably was, true, much of the time -- and in buildings which have had substantial upgrades to the envelope, almost certainly is true. But... it's not true all the time, and its those outliers which can be real gotchas. If in doubt, calculate. Doesn't take that long. I wouldn't be aware of this except that it happens that Cedric's home is one of those outliers: if it is both cold and windy at the same time, he runs almost continuously and the whole thing just barely keeps up.

Does it build pressure? Keep in mind a properly designed modern system would NOT keep up. It's my understanding a slight drop during extremes is expected.

You're saying your system almost runs continuously, but doesn't and yet still maintains temp.

PMJ

The question in @Jamie Hall s case is when he says almost continuously in extreme conditions is it stopping on pressure or on the tstat. If pressure and barely keeping up then radiation is not oversized. If stopping by tstat then radiation still has room to fill. How much is sort of a guess.

Jamie Hall

Does it build pressure? It's a tossup. Sometimes it will get up to 6 ounces (normal running is 4) and shut off briefly -- long enough for the post-purge and pre-purge -- and then fire right up again. Which I take to mean having finally reached (takes about an hour to get there) all the radiation condensing at maximum rate. In more seemly conditions the thermostat gets there first.

But I'll be the first to admit that the combination of the structure, the radiation, and Cedric is a real outlier in steam heat.

PMJ

> @Jamie Hall said:
> Does it build pressure? It's a tossup. Sometimes it will get up to 6 ounces (normal running is 4) and shut off briefly -- long enough for the post-purge and pre-purge -- and then fire right up again. Which I take to mean having finally reached (takes about an hour to get there) all the radiation condensing at maximum rate. In more seemly conditions the thermostat gets there first.
>
> But I'll be the first to admit that the combination of the structure, the radiation, and Cedric is a real outlier in steam heat.

Sounds like a close match on both. Glad I have extra on both. I agree your case is an outlier.

mikeg2015

IF I ever get my new (used) boiler installed this summer, I should have a good test bed for the undersizing theory. It will have hi stage output equal to EDR with no pickup and low stage should match EDR with upstairs TRV’s closed (typical in colder weather with lots of stack effect). I’ll use the vaporstat to control that. However i need ot re calibrate it. Set to 2oz, it reaches 7-8oz before it cycles off. I’ll use the pressuretrol as the safety limit.

Low stage output will be very close to heat loss. Should reduce standby losses significantly, especially in moderate weather.

Couple considerations:

Wit ha smaller boiler, header losses become more significant, as the header stays warm more of the time. So insulation is very important.

Water volume could be an issue with a long header and a boiler with only 2 gallons from normal to low level.

At low vapor pressures, an equalizer is less critical as steam relies more on velocity than pressure differential to and the system runs are partial vacuum much of the time. But I wonder if a Gifford loop is a good idea. Wondering if I can save a little and use 1-1/4” copper for the equalizer and 1” for the condensate return pipe. Would be cheaper to fully insulate too. Worst case, wont be that hard to replace. I’d still have a full 2-1/2” on the vertical dry return drop and use a T as a dirt leg to catch most of the crud. Could save a lot on pipe and fittings.

Jamie Hall

Gifford Loop is fine -- just a little different from the Hartford loop. But... I'd not use copper for the equalizer. 1 1/4" iron would be fine -- but the equalizer does see steam, and shouldn't be copper. The condensate return could be 1 inch, and could be copper -- it never sees steam. But if you do use 1 inch, make sure you have cleanout provisions at both ends -- and use them. Slow returns would really not be helpful.

ChrisJ

> @Jamie Hall said:
> Gifford Loop is fine -- just a little different from the Hartford loop. But... I'd not use copper for the equalizer. 1 1/4" iron would be fine -- but the equalizer does see steam, and shouldn't be copper. The condensate return could be 1 inch, and could be copper -- it never sees steam. But if you do use 1 inch, make sure you have cleanout provisions at both ends -- and use them. Slow returns would really not be helpful.

I used a 2" copper equalizer. Copper has no issues with steam,as long as it's straight runs that can cope with expansion. I also have two short vertical runs to radiators that are copper. I didn't do them but I don't mind them.

Now the downside, I paid way too much for that length of 2" type L copper. It hurt, a lot.

BobC

@Jamie Hall My 100 year old house was built with only 196 sq ft of radiation for a 1-1/2 story 1,200 sq ft NE Cape a block from the North Atlantic. These are not tight houses and are impossible to tighten up significantly unless they are stripped to the studs and foamed.

The house stays ok down to -10 but not all of it. especially when the wind barrels out of the northeast.

Bob

mikeg2015

Probably do 1-1/2” equalizer, but stay black pipe down to a brass Tee for the Gifford loop. Probably bush it at the T, use a 1-1/2x1-1/2x1” Tee with a street 45 to make it a “Y”.

I plan to use a dirt leg at transition from 2-1/2” to 1” copper that will also be a condensate system lop point drain. Then also have a Tee at the bottom of the equalizer also as a low point drain.

Good stuff.

Biggest challenge is removing a 2” plug so I can add a hot water loop for a small indirect tank. Probably need a hammer and torch to loosen it up.

kenjohnson

I'm curious if your boiler is oil-fired? If it is, then you might be able to do what I did with my oil-fired water boiler - restrict the burn-rate by having the plumber install a different nozzle (I might have the term wrong...).

Basically, my oil boiler is oversized for my house by 3x (it is the smallest available boiler, basically). At 1 gpm firing rate, the radiators couldn't get rid of the heat fast enough and the boiler would short-cycle. So I had the plumber put in the smallest nozzle allowable (0.5 gpm) and that kept the firing rate of the boiler more constant.

Henry

Steam heating systems work on-off. One needs sufficient capacity for the installed radiation mainly because when there is a demand, the boiler must be able to provide sufficient pounds of steam. Upon start, the steam hitting the cooler rads will immediately condense and form a vacuum. If the boiler is not of sufficient capacity, it will shutoff on low water. Been there, seen that done by other boiler installers. Most commercial installations will have two or more boilers. While one boiler would be sufficient, the others are there for the start cycle to met the radiation demand.

foresthillsjd

@kenjohnson it’s natural gas.

So, I make a lot of recipes with my pressure cooker. And I think of it like a combination boiler/radiator system. You add flame, liquid inside heats, comes up to pressure, and you reduce the flame so to keep the pressure high enough to keep the indicator up, but low enough that it is not constantly venting. And the flame required to reach that equilibrium point depends on how full the pot is.

So I still don’t understand why on a gas-fired steam boiler, it’s on or off. If you were able to modulate the flame and adjust the water level in the boiler, shouldn’t any boiler be able to dialed back? (I know the answer is no, just trying to understand why.)

Jamie Hall

Actually, @foresthillsjd , the answer isn't no, it's yes. Any boiler can be dialed back. Question is, what happens when you do? Unless the boiler and burner system is designed for it, the answer is that the efficiency drops dramatically. It's related to the design and geometry of the burner and the fire box and the various passages for the heated gases, and it's a fine art to get it so the efficiency can stay decent over a wide range.

Not to mention that you need some mechanism to keep the fuel to air ratio correct, to avoid problems along those lines as well.