Cost to generate steam?

RayWohlfarth

I am looking to do a cost comparison of the operating costs of steam versus forced air and hope I can pick your brain. It frustrates me that people think steam is really inefficient when I am not so sure. While the steam boiler is only about 80-82% efficient, I believe the system efficiency is comparable to other types as there is no fan, compressor, or pump required to transport the Btu's through the building or house. I was rereading the revised Lost Art by @DanHolohan (Great job Dan) and he said the old timers designed the system for a 2 ounce pressure drop across the system. If that is the case, that is really small. My working theory is to estimate the area or volume of the steam side of a system?, divide that volume by 1/1700 (The volume when steam condenses), estimate how many gallons that is and from there I can estimate the costs to heat that. I know it takes 1 btu to raise one pound of water one degree and 970.4 btus to change one pound of water at 212 to steam. I could also factor in the air lost through duct leaks which DOE says is 40%. Seems high to me.
All in all, I would be curious what your thoughts are.
Respectfully
Ray

Jamie Hall

Don't overthink it, @RayWohlfarth . Overthinking has gotten me into more trouble than I can remember...!

And yes, @DanHolohan 's note of no more than 2 psi loss is correct, even for very large systems. Most vapour systems operated on more like 2 ounces!

The efficiency of a steam system is determined almost entirely by the efficiency of the boiler. There is a small effect -- very small -- from the pressure drop, since that pressure drop is seen as a slight loss in temperature of the steam between the boiler and the emitters. That can be figured in by accounting for the extra heat needed to create the steam at a pressure of 2 psi gauge vs. the heat released by condensing at about 1 psi gauge (to account for pressure loss in traps and the returns). Not much. Works out to, at most a fraction of a percent.

The other potential loss -- and it can be major -- is heat lost from the pipes on the way to the emitter. This is a hard one to account for. The problem is, of course, that the pipes may be and usually are in the conditioned space, in which case that is not a loss (although it may create other problems!). If the pipes are not in a conditioned space, though, it can be significant.

Bottom line: almost all the heat input at the boiler (99+%, after accounting for the boiler's own efficiency) gets to the emitters. No fans. No pumps.

nicholas bonham-carter

Maybe it should be calculated as:
Energy to heat entire boiler water volume to 211 degrees, plus the additional energy to make the volume of steam needed to fill the pipes.
Or is that what you said?
While you are at it, maybe you can solve the never ending argument about which is more efficient-steam or hot water—NBC

DanHolohan

That 2-ounce pressure drop is per 100 feet, guys. For small systems it’s 1-ounce per 100 feet.

ChrisJ

nicholas bonham-carter said:

Maybe it should be calculated as:
Energy to heat entire boiler water volume to 211 degrees, plus the additional energy to make the volume of steam needed to fill the pipes.
Or is that what you said?
While you are at it, maybe you can solve the never ending argument about which is more efficient-steam or hot water—NBC

The energy used to turn water into steam is 100% recovered when you condense the steam back into water. It's not wasted.

The only reason hot water systems can be more efficient is due to the lower operating temperatures, it has nothing to do with phase change.

For example, if you replaced the water with something that boils at 130-140 degrees at operating pressure, you'd have a condensing steam boiler.

hot_rod

In both cases if the ducting is within the heated space, and the piping is also, is that really a loss?

Piping in un-insulated basement, crawl and attic spaces would be consider more of a loss.

For hydronics, the low, condensing mode operation of the heat could be the factor in operating cost difference.

RayWohlfarth

@Jamie Hall My kids always tell me I overthink everything LOL I think its a gift while they think its a curse

I wrote an excel sheet showing the cost of different boiler types. Its about 40 pages long

@nicholas bonham-carter That is what I was thinking only I will take it to 212 degrees F I am trying to write an excel sheeet to calculate operating costs.

@DanHolohan Guess I need to reread that chapter LOL Ok That is another calculation I guess
@ChrisJ I agree
Thanks for your guidance Gentlemen

RayWohlfarth

@hot rod That leaves another calculation I saw the calc done by RPA on the costcomparison to transport btus using a VRF or a pump and the pump wins!

hot_rod

Other than passive, gravity, or Larry's thermosiphon radiant , I think a small ECM circulator wins for moving energy with the least amount of electrical consumption.

One key is the least expensive way to transfer energy from the chemical form, gas, oil, wood, to useable heat.
A nice wood stove is always an option

RayWohlfarth

@hot rod I agree with the ecm circulator

jumper

Where does the electricity for a pump or blower come from? When you burn fuel you degrade its essergy less when raising steam than when scorching air.

RayWohlfarth

@jumper That is what I was thinking. For example a furnace is 90% efficient to generate heat. The furnace uses a certain amount of energy to transport that heat around the home or building.

Jamie Hall

RayWohlfarth said:

@jumper That is what I was thinking. For example a furnace is 90% efficient to generate heat. The furnace uses a certain amount of energy to transport that heat around the home or building.

A very important point. While a steam boiler uses very little electricity to power its burner, its maximum efficiency is limited by the sensible heat of combustion to around 85%. More or less. But it uses a truly insignificant amount of energy to transport that heat (neither did gravity hot water...) A condensing hot water boiler can recover the latent heat as well, boosting its efficiency to perhaps 95% -- but only when it is actually condensing (return water less than about 140, give or take) so unless it is very very carefully designed and installed and controlled, one can't get that all the time (and you might have forced draught or induced draught blowers). Then on top of that it needs to have the circulation pumps, which do draw energy. Are there such things as condensing forced air furnaces? If so, the same thought applies -- but on top of that they have the blowers, which take a fair amount of power.

I'll be very interested to see what sort of numbers you come up with when you finish crunching!

hot_rod

A few different efficiencies come into the picture. Boiler efficiency, the amount of fuel consumed output divided by input (fuel)

As Jamie noted, some boiler require electricity to operate. With mod cons power is used to ignite and operate, even post purge. Most mod cons need circulation when fired. I've never seen an electrical consumption figure for just running the boiler.

Not much power required to run a standing pilot boiler, none if it has a thermo-pile

The distribution efficiency, how much energy used to "move" the heat, pump or fan power.

And building efficiency, I'd assume the buildings would be identical
that you would model?, just swap systems.

RayWohlfarth

@Jamie Hall So true. Flue gases with 5% O2 has a dewpoint temperature of 130 degrees F water temperature . It does not reach over 90% efficiency until the water temperature drops below 100 degrees F. I will be working on this calc and let you know. Thanks for the feedback

RayWohlfarth

@hot rod That is what I am thinking. Using a standard building and comparing the different types of efficiency

Solid_Fuel_Man

I'm going to take a stab and say a residential sized radiant with a mod/con draws 200 watts, less than 50watts for boiler and a generous (non-ECM) 75 watts each for two circulators. If I were home right now I'd even fire up my system and get a real reading. I'm actually surprised I haven't done a real world power consumption measurement yet.

RayWohlfarth

@Solid_Fuel_Man Thats a great idea. I can do the same I still need to figure out a formula Thanks

The Steam Whisperer

I've been including some of these efficiency comparisons in by steam seminars for several years now. The DOE did a lot of tests in the early 90's looking at efficiencies of forced air versus other types of heat, so doing a little research at the DOE website will probably come up with a lot of info. While this doesn't directly answer your initial question, if addresses overall real life efficiencies.
From the DOE:

Duct losses from a typical home system were about 23% before the heat or cooling reached the rooms.

Increase of air leakage rate of structure with ductwork present but not in use 10%

Increase in air leakage during operation of furnace fan: 50%

Residential boiler power draw ( my own calcs):

Steam ( max) 20 watts

Cast iron hot water: 110 Watts

"High Efficiency" hot water: 450 watts

Forced air: 925 watts

Savings due to radiant heat delivery of steam or hot water radiator type systems:

Lower thermostat setpoint by about 2 to 3 degrees = about 6% to 9% savings. Radiant heat provides the same wetbulb, black body but at lower air temps. Increased humidity due to lower air leakage also improves comfort.

Reduced air leakage due to less hot air at ceilings due to radiant heat.


Also, condensing steam heating plants are available and in use. The Art Institute in Chicago has two steam boilers that run in the low 90's thermal efficiency.

With two pipe steam return water temps on many of our updated systems run near 70 F nearly all year and around 100F in the coldest weather.

Other potential savings for hot water and steam over forced air:

Room by room temp control



The thermal output of forced air and hot water boilers is inflated by the heat output of the motors required to move the heat, so the thermal efficiencies numbers are incorrect when compared to steam, which uses almost no electricity.

Just a few things to ponder!

Canucker

That's awesome @The Steam Whisperer Those numbers are perfect for explaining to people why I haven't "upgraded" my home to forced air just to have A/C. Thank you for taking the time to do that.

jumper

Heating system has to make occupants FEEL warm. Radiant heating makes us comfortable at lower air temperature. There's a chart in ASHRAE handbook illustrating comfort zone for air temperature at differing radiant environment. Since steam heat can deliver 200° radiant it doesn't necessarily require as much HHV or LHV.

When electric is mandatory I find ceiling height panels use quite a bit less energy than baseboards. Almost all the heat is radiant so occupants leave the thermostat relatively low. But with baseboards they crank it up to feel warm,then they crank thermostat down because too warm,and then they complain.

Steamhead

The Steam Whisperer said:

Also, condensing steam heating plants are available and in use. The Art Institute in Chicago has two steam boilers that run in the low 90's thermal efficiency.

Tell us more!

leonz

If you really want to see how efficient steam heat is you should look at the fuel comparison charts on the coal pail forum and then look at coal boilers that are used to make steam as they take little power to run-110 volts and the traveling bed coal stokers(110 volt) that burn pea sized anthracite and the underfed pot stokers(110 volt that burn rice coal make lots of steam with low fuel consumption.

The thing is that these boilers have a hold fire timer that lets the stoker run a few minutes per hour to maintain the fire to make steam or hot water when there is no call for heat and a coal stoker used for steam will generate a huge amount of dry steam with very low fuel use.

I run hot water baseboard with my coal stoker and I hate it.
I wish I had steam heat but for 12 dollars a day to heat the poorly insulated place with 225 feet of 3/4" fin tube baseboard I no longer need to think about burning oil ever again.

JohnNY

I'm often asked to provide cost comparisons for steam heating via municipal (Con Ed) steam here in NYC vs having a boiler.
Surprisingly, the boiler always wins. Just saying.

Solid_Fuel_Man

I'm still curious as to the 70 degree condensate, knowing that almost impossible even with radiant slab and water.

I'll be home tomorrow (working on the road) and I'll get a real wattage consumption number for a real world mod/con system with two pumps total. I think some of this electrical consumption numbers are way over estimated for water systems.

Other than residential sized systems, all the steam systems I work on have at least one condensate return pump.

Steamhead

Solid_Fuel_Man said:

I'm still curious as to the 70 degree condensate, knowing that almost impossible even with radiant slab and water.

In a 2-pipe system with properly functioning traps/water seals/orifices, you're not going to get much heat in the dry returns. What little there is has usually dissipated by the time it reaches the boiler.

Solid_Fuel_Man said:

Other than residential sized systems, all the steam systems I work on have at least one condensate return pump.

Which probably isn't needed. We're in the process of removing one from a Dunham system right now.

RayWohlfarth

@The Steam Whisperer (Formerly Boilerpro) Thank you so much. That is exactly what I am looking for. I heard the DOE suggests a 40% loss on ducted systems.
Thanks @Canucker , @jumper , @Steamhead , @leonz , @JohnNY , @Solid_Fuel_Man

RayWohlfarth

Now here is something else to consider. It is a running joke that you can tell which rooftop is not working by the one with the snow on top. How much is lost to the air? If you are doing a snow melt, you would need 350-450 Btu's per square foot. Would that not be that same loss for the rooftops?

The other question is would radiant heat be less expensive because it is not heating the air and only the objects? Seems the like volume would be much lower.
Thanks

GBart

This thread made me remember an old mansion in Madison Ct on the water. Think it was built @1800's??, anyway this is a Dead Men Story.

My guess is the system was re engineered or installed in the 30's, could have been a summer home before that. It had this rather large steam boiler, there were two large air handlers in the basement with huge steam coils in them, each did one floor. There was however steam piping running through the home.

Each bathroom had a steam radiator, a large one so that whenever either zone called all the bathrooms got heat, my guess is they were always toasty warm.

hot_rod

RayWohlfarth said:

Now here is something else to consider. It is a running joke that you can tell which rooftop is not working by the one with the snow on top. How much is lost to the air? If you are doing a snow melt, you would need 350-450 Btu's per square foot. Would that not be that same loss for the rooftops?

The other question is would radiant heat be less expensive because it is not heating the air and only the objects? Seems the like volume would be much lower.
Thanks

The type of system... boiler, pump, control, etc cannot change the building load. It takes X amount of energy to overcome the delta, inside to out.

Basically want you want to know is what is the most efficient way to turn fuel to heat, to over come that load.

To my way of thinking the condensing equipment, when used in condensing mode, squeezes the most energy from the fuel.

I'd also think the lowest possible SWT to cover the load would be most efficient? IF you could heat the space at DD with 120F, lower on above DD seems like the most efficient? If the distribution is via radiant surfaces, MRT can factor in and further reduce air temperature control logic as the comfort decider

I don't see how driving water thru a phase change to steam, requiring additional BTU at 85% or so efficiency with typical available residential steam boilers. How could that be more efficient than a 90 plus condensing boiler and low temperature distribution and heat emitters? Assuming of course both are properly designed, sized and installed.

Nothing against steam, the feel, look and nostalgia, but why 212° to heat a space to 70F? Why not 80- 100°?

Be interesting to see what you come up with.

RayWohlfarth

@GBart Sounds like someplace fun to explore
@hot rod Guess this kinda got away from me. If the hydronic system is sized properly using condensing and ecm pumps, I dont think there is a system which can beat that. I am curious as to comparing operating costs between the different types. I will let you know what I uncover

jumper

Another example of radiant effect is a home with both CI rads & baseboard convectors. The rooms with CI radiators feel warmer. That's because the surface of the wall and ceiling are warmer.

Canucker

I think the point is @hot rod that you need to factor in the energy to deliver the 80-100 degree water. The steam is moving just through the phase change, no pump, no electricity. The water boiler needs the pump and other controls to move the heat. I think the difference between 85% steam and 90+% water gets a lot closer in operating costs, if all the energy used is measured. I could have an electric furnace with no duct work in the basement running at 100% efficiency but it's a pretty expensive way to heat the rest of my house, unless designed for. I believe that's what you're looking for @RayWohlfarth ?

hot_rod

Canucker said:

I think the point is @hot rod that you need to factor in the energy to deliver the 80-100 degree water. The steam is moving just through the phase change, no pump, no electricity. The water boiler needs the pump and other controls to move the heat. I think the difference between 85% steam and 90+% water gets a lot closer in operating costs, if all the energy used is measured. I could have an electric furnace with no duct work in the basement running at 100% efficiency but it's a pretty expensive way to heat the rest of my house, unless designed for. I believe that's what you're looking for @RayWohlfarth ?

Good point.
I think Taco crunched some numbers for circulator operating cost per year. The difference between ECM and PCS.

The Steam Whisperer

The type of system DOES effect how much heat it takes to heat a building. The DOE studies have already proved that. It's not just delta tee through the envelope that tells you how much capacity you need to heat a building. Radiant systems deliver higher comfort at lower air temps than heated air systems, so thermostat settings are lower, reducing fuel usage. Radiant systems reduce air temperatures near ceilings.... this has been shown in all sorts of radiant floor tests, which in turn reduces the delta tee through the envelope. In addition, lower air temps at ceilings reduce exfiltration pressure due to less stack effect pressure developed ( the hotter the air the stronger the stack effect). Advanced studies have been done to see if slightly pressurizing attics can reduce these losses. It's even been shown that dark roofs can reduce the air temp inside attics below the outdoor temp in the winter due to the transfer of radiant energy to a dark, clear night sky (another reason to ventilate attics). Colder attics increase heat loss.

Its already clear that almost any system is more efficient than forced air, but weather steam or hot water is more efficient is really difficult to tell. Hot water can have higher thermal efficiencies.... usually about 1 to 1.5% from the data I have seen on typical cast iron atmospheric equipment. However, hot water systems use a whole lot more electricity..... that's why ECM motor pumps make alot of sense as does high delta tee systems ( less pumping needs and smaller piping for smaller distribution losses). ECM pumps however cost a whole lot more money. However, comparing a condensing steam boiler with a two pipe steam system that runs very low return temps year round ( with almost no electrical use) versus a condensing hot water boiler with considerably rising return temps year round ( with much higher electrical use) is a very good question. We are probably getting to the point of splitting hairs.

What seems to work best with both systems is modulating input and outdoor reset, which has been shown to be very effective in every hot water system study I have ever seen. I think this is the sensible place to be for nearly all hot water and steam systems. Hot water does have an advantage for ease of conversion to outdoor reset, however outdoor reset for hot water systems often means continuous operation of all pumps... which in turn eats up efficiency gains on the fire side. Two pipe steam can be converted to outdoor reset/ modulating input using TRV's or supply orifices and / or variable vacuum. One pipe steam can be converted using variable vacuum. However, using a vacuum pump involves more electricity usage, so the fire side efficiency gains are offset by increased electrical consumption. However, tight steam systems only need vacuum operation occasionally, so this usage can be very low. Naturally induced vacuum systems can be used but the typical operating levels of vacuum are usually about 8 to 12 inches mercury vacuum, bringing steam temps only down to about 195F.

For condensing steam boilers take a look here: http://www.heatsponge.com/

ChrisJ

Either way, I'm betting a very well sealed and insulated building with the least efficient system will always use less energy than a leaky badly insulated building with the most efficient system.

The Steam Whisperer

I agree. The worse the leakage and insulation of the building, the more beneficial it is to have an efficient radiant heat system...either steam or hot water. If you can get some passive solar with an efficient envelope its incredible how low your fuel usage is. I was spending less than $1000.00 per year for gas in our previous 1905ish 3200 sq ft home for heat, hot water, cooking and dryer in northern Ill. I renovated using R-19 in the walls and the airtight drywall method. Lots of south and east facing windows. Windows were nearly all original and fairly tight with oooolllddd aluminum storms. It wasn't worth upgrading the storms .....almost never is.

hot_rod

I suppose the same logic would apply for a cast iron radiator against and outside wall? What is the surface temperature of a steam radiator. Seems like the dealt T would be quite high, higher than a stratified FA ceiling?

Would a tube type radiator also present hotter ceiling temperatures compared to low temp radiant floors for example, with convection currents in the mix?

I remember all the radiant operating cost studies that were done. I also remember caution against putting the fuel savings number down in writing.

It would be interesting to take an IR camera around buildings with various heat emitters and get a look at where the heat and hot spots are.

For a study to be a fair apples to apples the room temperature would need to be maintained at the same number, even if radiant is as comfortable at lower room air temperatures.

ChrisJ

hot rod said:

I suppose the same logic would apply for a cast iron radiator against and outside wall? What is the surface temperature of a steam radiator. Seems like the dealt T would be quite high, higher than a stratified FA ceiling?

Would a tube type radiator also present hotter ceiling temperatures compared to low temp radiant floors for example, with convection currents in the mix?

I remember all the radiant operating cost studies that were done. I also remember caution against putting the fuel savings number down in writing.

It would be interesting to take an IR camera around buildings with various heat emitters and get a look at where the heat and hot spots are.

For a study to be a fair apples to apples the room temperature would need to be maintained at the same number, even if radiant is as comfortable at lower room air temperatures.

Absolutely.
I brought this up and was shot down repeatedly by Hat a long time ago....

I said something along the lines of "A cold wall sucks the heat right out of a steam radiator" and he argued it....

RayWohlfarth

Wow You guys are really making me think way too hard. I will be teaching a couple of classes on steam boilers and wanted to show the attendees a comparison showing the operating costs. I guess there are so many variables. I remenber going to
John Siegenthaler's class and he was talking about how it was so much more efficient to use zone valves rather than circulators due to the energy consumption. It just frustrates me that so many assume that steam is ineffecient and old technology. Hope to have an answer within a week
@Canucker That is exactly what I was thinking. I am going to compare the operation over an hour but that will not tell the whole story as a steam boiler with cast iron rads will stay hot longer than a furnace and require less cycles. My brian is going to explode
Thanks

ChrisJ

RayWohlfarth said:

Wow You guys are really making me think way too hard. I will be teaching a couple of classes on steam boilers and wanted to show the attendees a comparison showing the operating costs. I guess there are so many variables. I remenber going to
John Siegenthaler's class and he was talking about how it was so much more efficient to use zone valves rather than circulators due to the energy consumption. It just frustrates me that so many assume that steam is ineffecient and old technology. Hope to have an answer within a week
@Canucker That is exactly what I was thinking. I am going to compare the operation over an hour but that will not tell the whole story as a steam boiler with cast iron rads will stay hot longer than a furnace and require less cycles. My brian is going to explode
Thanks

Technically...……..steam heat and a heat pump transfer heat using the same method. Phase change.

The heat pump uses vapor compression, but they both boil a liquid and then condense it again to transfer the actual heat.