Is hot water really more efficiant than steam?

Steamhead (in transit)

are sized and located correctly, there should be no loss in comfort.

With convective emitters such as convectors or fin-tube baseboard, the outer shell doesn't get that warm on either steam or water. With cast-iron or steel panel rads there is a difference, but as I said earlier if the steam system is in good shape and running ounces, it doesn't get them oppressively hot. Yes, I've seen some that were, but that can be fixed.

Reinvent

Is hot water really more efficient than steam

I have read here on many occasions that hot water boilers use less energy than steam systems because they do not have to heat the water to it's boiling point. But then I realized that a steam system has a far lower volume of water to bring up to temp. I know every installation is differnt but assuming a standard size system how much difference in energy useage would there really be?

Tony Conner_2

Hot Water Vs Steam

Hot water is more efficient than steam, but there are considerations. Don't just look a boiler efficiency as a stand alone factor.

If you think of a boiler as a heat exchanger (which is all it really is, when you get right down to it), you can have lower flue gas temps for the reason you stated. The lower the temps on the cold side of the HX (the water side in this case), the lower you can get the exit temps going up the stack.

On a new installation, you'll save fuel with a properly designed & installed hot water system. If you have a house with an existing steam system, it usually a MUCH better payback just making it work properly, than spending a relatively large amount of money on converting to hot water. The cash outlay spread is often a few hundred dollars for things like a handfull of air vents on a steam system vs several thousand to do a conversion. You can sometimes get a payback of 2 or 3 years on fixing an existing steam system, vs maybe 15 or 20 years on a full blown swap to hot water.

patrick linhardt

good advice

Thanks Tony,

Your reply is right on the mark.

Best regards, Pat

Steamhead (in transit)

Assuming

the same type of boiler is on each system, and that both systems are properly sized, in good shape and well insulated, there really isn't that much difference in efficiency and there's no difference at all in comfort. A steam system won't freeze up like a hot-water system can, so that makes up for the slightly lower efficiency.

ScottMP

Frank

Heating a room with 212 degree steam as compared to 140° water makes no difference in comfort ??

Please explain.

Scott

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Steamhead (in transit)

You're still

releasing the same number of BTUs into the rooms. Maybe I should have added "and the type of radiation is the same" to my assumptions. I find that in a properly functioning steam system- one in which you're running on ounces as the Dead Men intended, instead of pounds- the radiators' surface temperature is actually below 212 degrees. Maybe this is because the steam pulls a slight vacuum as it condenses, which lowers its temperature.

George Carey

steam vs hot water

or 105*F or 120*F,etc...no difference in comfort level?

Unknown

And...

> releasing the same number of BTUs into the rooms.

> Maybe I should have added "and the type of

> radiation is the same" to my assumptions. I find

> that in a properly functioning steam system- one

> in which you're running on ounces as the Dead Men

> intended, instead of pounds- the radiators'

> surface temperature is actually below 212

> degrees. Maybe this is because the steam pulls a

> slight vacuum as it condenses, which lowers its

> temperature.

Unknown

And...

> releasing the same number of BTUs into the rooms.

> Maybe I should have added "and the type of

> radiation is the same" to my assumptions. I find

> that in a properly functioning steam system- one

> in which you're running on ounces as the Dead Men

> intended, instead of pounds- the radiators'

> surface temperature is actually below 212

> degrees. Maybe this is because the steam pulls a

> slight vacuum as it condenses, which lowers its

> temperature.

Unknown

And....

Because so little steam is released into radiators that are too big, that it only get's as hot as you let it. Because the higher the surface temperature, the more the radiant component heats you and a lowered air temperature would make up the difference in comfort that you need, to feel the same.

Like tipping the Convection/radiant scale of comfort a little toward radiant, and away from air temperature.

Like moving away from the bonfire, even though it is only 40° F air temperature outside. Like moving into the shade on a hot day.

Radiant energy rules.

Noel

Mellow_2

apples vs. oranges

You need to compare the BEST steam system with the BEST hot water system.........I would not use the same boiler, pipes or radiators for steam as I would for forced hot water systems.......if I did the forced water system would burn more energy......steam needs big things radiators, pipes, valves.........forced water works best with the least amount of water and piping (small pipes, valves).....some good forced water boiler can not be used for steam systems only forced water systems.

Unknown

On steam boiler replacements

I used to ask the homeowners how they like the radiator heat , most said words to the effect that they would never dream of trying another heat source . They border on the fanatical . That's proof enough for me about high temp comfort .

Boilerpro_3

Think back to Mike's radiation studies....

and others now completed on radiant effect in heating. Also look at tekmars heating curves for outdoor reset. Running radiators at lower temps produces a higher percentage of radiant heat than running those same radiators at higher temperatures. At higher temperatures, hot air convection currents set in, so a steam system starts to pick up one of the less desirable characteristics of forced air, hot air stacking at the ceiling. Low temp cast iron radiators(like on a typical gravity conversion) will trump the efficiency of steam as it interacts with the structure, especially one pipe steam where the radiators heat fully vertically, section by section, creating funnels of superheated air. Two pipe systems, or one pipe systems with two pipe rads, tend to heat horizontally across the radiator, so that air convecting up through the radiator will not get as hot, so there will be less stacking. This is the big reason why I don't like steam convectors and convert them to water.

Boilerpro

Christian Egli

Preaching to the choir

I will attempt to show how steam is indeed more efficient, watch as I jump off the cliff.

Where do inefficiencies go in our heating systems? Two places only, up the chimney for one, and secondly, out the front door or more exactly through the envelope of the building.

Ultimately all the energy we burn in our boiler ends up outside. It does. No matter how well we insulate a home. The tea in your thermos bottle will reach ambient temperature, given time.

Time is of the essence. The quick loss of efficiency is through the flue. The slower path is through the walls. How do we gain on efficiencies? Like the Jeff Gordon‘s, by racing the clock.

How would you design a boiler to reduce flue loss? You could lower the heating fluid temperature in an attempt to reduce flue temperature. No doubt, hot water at 120F is colder than 212F for steam. Although this difference looks like a 50% margin it is actually much less significant when compared with the several thousand degrees the flame is at. What, maybe a few percents?

What else can we do? Maybe build boilers out of fantastically heat carrying metals like silver, or make the heat exchanging part infinitely large. On these two issues, steam and hot water boilers are built the same way, so, no difference.

We could find a heating fluid with infinite heat carrying capacity, that would boost efficiencies, wouldn’t it? Well, we know water is the best carrier of heat, it can pack more heat within its molecules than almost all other fluids. That’s impressive, it amounts to about 1 BTU per pound and per degree. So, all you’ve got to do is hope you can pump enough of the stuff through your boiler to match the firing rate. If you can’t keep up, your efficiencies drop like a rock.

And what does steam do? It packs roughly 1000 BTU per pound. Wow! You won’t need much to rival the biggest flame your burner can throw. Plus, there is an added bonus. Once turned into steam, water actually becomes a gas which moves out of the way a heck of a lot faster than a solid or even a liquid can.

So as far as loosing heat to the chimney, steam has the advantage that it removes heat real fast, faster than it can go up the flue.

I know, condensing boilers have an edge. And if we were to give the same edge to steam boilers (which we do in power plants and large set-ups) steam would outdo forced air and hot water, hands down.

On the issue of envelope loss, the same race against time takes place. The idea is to heat the home when we’re occupying them and not a minute longer once we leave. Meanwhile, heat leakage to the outdoors will occur at a given and steady rate, therefore, it makes no sense to heat a home while it is not occupied.

Any heat applied during an unoccupied period is purely wasted on the birds.

I agree, most systems are meant to keep a steady temperature, but this is mainly out of fear the pick up time would be too extraordinarily long.

And it is extraordinarily long for hot water, you’ve got lots of idle water to heat up and lots of inertia all around. Steam, on the other hand, is stupendously quick. The minute the boiler is steaming, all the radiators turn into broilers. That’s efficient.

What would you think of the driver at the Nascar race who would take 12 minutes to release his clutch at the start line while the other racers left him behind in a huge cloud of steam?

So, bet on steam… or choose whatever system you might prefer based on comfort issues. I like roasting in front of a steam radiator, it’s just too cozy.

In commercial applications radiant gas heater work wonders.

thp_7

Jeff #24

I like the JG part of the post. The chase race I believe will have more rule changes soon without having the 8 & 24 in the mix. Bud & Du Pont lost out on a lot of advertising. I am sure they are not happy.

Ron Schroeder_3

The mechanical engineering world has discovered

that for every three degree F reduction in the supply temperature, one percent less energy is used. Since energy is not measured in degrees but in after tax dollars, the reduction in supply temperature should also result in a reduction in operating cost to the heating system owner, no?

I just though I would throw that in the mix.

pitman9

Sounds like you're making a good argument for

electric baseboard.

Heats quickly.
Turn it down when you're gone cause you can blast the temp right back up there.

To go with your racing analogy (and my daughter & I are hard core racers - see her in the attached file) just how comfortable would most people be riding with JG? I think most would prefer the nice comfortable luxury of radiant rather than the speedy steam.

bigugh_4

Not a bad concept,

Now insulate, insulate, insulate, and you can lower the supply temp even more! Oh and try a Blower door inspection and stop the infiltration for a really low heat bill!

Steamhead (in transit)

But

aren't you running those convectors close to steam temp due to their sizing, especially on colder days and coming out of setback?

Boilerpro_3

The classic answer.......\"It depends\" ....

Since most steam convector systems I've worked with (and there are not that many)are relatively new they tend to be closer in size to the heat load. Most of these run about 180F or so on recovery. This I'm not too concerned about, since it is for rather short periods of time.

The inefficiency in typical day operation is as the steam cycles on and off in the convectors. Since they don't have the mass of iron, they heat up very quickly, causing the air to be superheated, sending it to the ceiling. Then they cool quickly and start the process over again. I bet that you could reduce the fuel usage considerably in a steam convector system just by converting to cast iron rads. The mass of the rads act like a thermal flywheel to the very quick supply of heat from steam, keeping the air temperature down, and providing more radiant heat.
To expand on the water temperature question on design days or during recovery, I've found that most steam radiator systems tend to need about 180F average water temperature at most. My first conversion that I did (one pipe steam to hot water) only needed 140F water temperature on the design day.
Some interesting math on boiler sizing>>>> Assume 400 EDR steam x 240btu/hr/EDR = 96,000 btu/hr x 1.33 (pick up factor) = 128,000 btu/hr boiler size. Now if that system is converted to water and the load calcs tell you you only need 140F water,.... boiler sizing math>>>>>> 400 EDR available x 100 btu/hr/EDR (at 140F water temp) = 40,000 btu/hr. For hot water I don't use a pick up factor since I use return temp protection on any boiler installed in a high water content system. If you left the system steam, the boiler would be 3.2 times the size necessary for the design day and probably hard to control. You can imagine how low the boiler efficiency would be running on steam instead of using the right sized boiler after conversion to water.

I am in no hurry to convert a steam system to water, however, when the boiler and one pipe system are so grossly oversized, it should be considered. Oh course with two pipe, just install a bunch of orifice plates and downsize the boiler to match the new radiation load based on the current heat load.

Boilerpro

Steamhead (in transit)

Or use TRVs

to "reduce" the rad size. Or change to smaller rads, maybe those new wall-hung ones. BTW did you see the thread I posted, actually an update of an earlier thread, describing my TRV project?

Boilerpro_3

Yep,

I am installing my first all TRV hot water system this week. No thermostats, just full outdoor reset on a cast iron boiler, TRV's on every convector, central hallways on Watts EPDM radiant tubing running directly off reset(no TRV's) and one kitchen Watts EPDM Radiant with a TRV for control.
Me Thinks the owners will realllly like it!
(Oh and a Triangle Tube indirect on the side)

Why would you want to change rads.... the orifice plates will downsize the rads?....only in two pipe, oh course.



Boilerpro

Steamhead (in transit)

I was referring

to a one-pipe system, where orifices won't work.

Boilerpro_3

How has that worked

Using TRV's on One pipe and downsizing the boiler? I suspect as long as there are no setbacks, it would work great. Still haven't been able to experiment much more with undersized boilers and adjustable rad vents. Not much steam nearby that I can play with....not much heating systems in general out here in the boondocks!

Boilerpro

Steamhead (in transit)

This project

hasn't gotten to that stage yet. We're documenting fuel savings using one-pipe TRVs in a typical small house. We got all the other variables out of the way last season and posted substantial savings- 36% from start to finish.

Bill Burton from Danfoss got the idea to do this, and he provided the TRVs. We won't be changing the boiler's firing rate this season since it would be an unwanted variable at this stage.

Here's the link:

http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=22035&mc=22

Boilerpro_3

Anxious to hear, but got to wait till spring...

> hasn't gotten to that stage yet. We're

> documenting fuel savings using one-pipe TRVs in a

> typical small house. We got all the other

> variables out of the way last season and posted

> substantial savings- 36% from start to finish.

> Bill Burton from Danfoss got the idea to do this,

> and he provided the TRVs. We won't be changing

> the boiler's firing rate this season since it

> would be an unwanted variable at this stage.

> Here's the

> link:

>

> http://forums.invision.net/Thread.cfm?CFA

> pp=2&Thread_ID=22035&mc=22

Boilerpro_3

Anxious to hear, but got to wait till spring...

for the full report.

Boilerpro