Steam boiler efficiency

steve_6

steam radiators are generally not big enough to give the proper heat output when you convert to hotwater. Remember steam is 212 degree's, hotwater heats at 180 degree's. also remember your only heating 5-10 gallons of water in a steam boiler to make heat. in a hot water system you could be heating 50- 150 gallons of water to make heat and that means your boiler is running a lot longer before it can put out heat to its capacity. generally when people talk about efficiency their thinking about how much money their going to save on their fuel bill. but the cost of the conversion plus the cost of maintainance on a higher efficiency system certainlly out weigh the savings they might see on their fuel bill. also your going from a system with basicly no moving parts to one with lots of them.

GW

New Steam vs New Hot Water Boiler

Hello Wallies,

I've been asked more than a few times what kind of saving are involved with upgrading from steam. Can anyone refer to past jobs where the cutomer saved x %?

Also, how about a hot water radiator with outdoor reset/constant circulation/TRV? How much could I tell the customer he could save-I don't wan't to stretch the imagination here, just conseravtive numbers would be great.

Gary

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Steamhead

You won't save much

if the much-higher pressure you get with hot-water causes leaks, or if you have to run a new set of return lines because they're too small or nonexistent, or..... go to http://www.heatinghelp.com/newsletter.cfm?Id=22 for more info.

It's true that some hot-water boilers have higher AFUE ratings than steam ones, but that's only part of the story.

And don't forget that a hot-water system can freeze, but a steam system can't since most of the pipes hold no water.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

GW

are you sure?

> if the much-higher pressure you get with

> hot-water causes leaks, or if you have to run a

> new set of return lines because they're too small

> or nonexistent, or..... go to

> http://www.heatinghelp.com/newsletter.cfm?Id=22

> for more info.

>

> It's true that some hot-water

> boilers have higher AFUE ratings than steam ones,

> but that's only part of the story.

>

> And don't

> forget that a hot-water system can freeze, but a

> steam system can't since most of the pipes hold

> no water.

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 157&Step=30"_To Learn More About This Contractor,

> Click Here to Visit Their Ad in "Find A

> Contractor"_/A_





To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

GW

are you sure?

I never said I was going to use the old pipes...

Are you familiar with outdoor reset?

I guess the system would freeze, but so wouldn't the plumbing.

Gary

Steamhead

More info

Many conversions utilize the existing pipes and radiators. However, if you're going to rip out the entire system that further unbalances the cost/benefit situation. It would be much easier and less disruptive to fix the steam system than to tear everything out.

Reset controls do exist for steam. Heat-Timer makes several that you see in larger buildings. There's no reason we couldn't use them in smaller ones.

And if the plumbing freezes but the heat system doesn't, that's one less thing to fix, and the plumbers can work in relative comfort.

You can see I really like steam heat. When properly installed and maintained it works just as well as hot-water, with fewer moving parts. If you're used to steam systems that bang, hiss and heat slowly and unevenly- these systems are telling you something is wrong with them. Usually they can be fixed without too much trouble.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

GW

thanks

We obviously are on two different plains here, I know outdoor reset can't be used with steam.

If it's crazy to spend an extra few thousand $ to convert the entire system, then the people who just spent $600 with us on Kohler shower trim must be just as cooky....

I do jobs all the time that are double what my "competition" will charge.

Gary

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

GW

thanks

> steam radiators are generally not big enough to

> give the proper heat output when you convert to

> hotwater. Remember steam is 212 degree's,

> hotwater heats at 180 degree's. also remember

> your only heating 5-10 gallons of water in a

> steam boiler to make heat. in a hot water system

> you could be heating 50- 150 gallons of water to

> make heat and that means your boiler is running a

> lot longer before it can put out heat to its

> capacity. generally when people talk about

> efficiency their thinking about how much money

> their going to save on their fuel bill. but the

> cost of the conversion plus the cost of

> maintainance on a higher efficiency system

> certainlly out weigh the savings they might see

> on their fuel bill. also your going from a

> system with basicly no moving parts to one with

> lots of them.





To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

GW

thanks

Although I disagree. Are you familiar with outdoor reset? The goal is to keep the water moving. So, your not bringing up all that water from scratch- plus I would not be inclined to keep the old pipes, although it is an option.

As you know, the old steam rads where incredibly oversized. I would never bet my bottom dollar that the old rads will heat the house, but normally it should never be an issue.

Besides, my original question was based on new panel rads, I don't know how the thread shifted towards re using the old steam rads.

Gary

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Unknown

I beg to differ, Gary

Outdoor reste for steam systems have been around longer than my Daddy. It still is in use.

Check it out here.

http://www.mepcollc.com/VV.htm#mepco2

As far as keeping the steam or replacing everything, it comes down to personal preference. It's up to you.

Noel

kf_2

Steam to Hot Water

First off I promise you that a hot water system installed correctly will ALWAYS be more efficient than steam to run for many reasons.

1. The ability for higher combustion efficiencies are possible with water.

2. It takes far less energy to heat hot water to 180 degrees or less. In fact it takes 2,665 BTU's to heat 10 gallons of water that extra 32 degrees.(try running a steam system at less than 212 degrees)

3. Steam systems are essentially pouring water down the drain while heating the building so water and sewer bills are substantialy less with water.

As far as more moving parts to be replaced in water, it seems to me that the only extra moving part might be a circ or a zone valve. Both systems still have burners, and LWCO's, and steam systems in some cases have auto-feeds not to mention the huge buisness in replacing steam traps constantly (or you could let them keep leaking, wasting more water). And by the way I have yet to replace an old rusty return pipe on a properly installed hot water system.

You mention TRV's with steam. While I agree that they will save some money, they are certainly not cheap to buy and I've yet to see any last in a steam system.

I have been involved in many conversions and rarely were the steam radiators not so grossly oversized that you couldn't adequetely heat the building, and at much lower water temps.

Gary,

In answer to your questions;

I have found savings in outdoor reset alone to be anywhere from 4-8 percent in steam conversions. Obviously this could be higher for completely new systems designed at very low water temps. The rule of thumb is for every 3 degrees you lower your water temp, you save 1% of your fuel bill.

As far as boiler to boiler it depends on comb. eff., stand-by losses etc.

I am not trying to bash the contractors that enjoy working with steam. In fact thank Goodness you guys are there because it is a dying art and there is still plenty of it out there. However as much as I would love to own an old 66 Corvette the new ones are much better on gas.


kf

GW

my mistake

I didn't know, I do know hot water a little better than I know steam.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

GW

cool

I was beginning to think I was the only one out there who worked with water boilers. When you say 4-8%, can you expound? My original question was comparing a steam system to a new euro-boiler with outdoor reset, constant circ, new panel rads with trv. Please tell me one could expect more than 8%, I was guessing in the 30% range.

Gary

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

kf_2

Steam to Hot Water

Gary,

It is hard to say. It depends on several things. The combustion efficiency between the new an old ( the formula is New Eff. - Old Eff./New Eff. ie 87%-68% divided by 87%=.218 or 21.8% savings). This doesn't take into consideration standby losses between a new Viessmann perhaps, with 3-1/2" of insulation and an old steam with 0"-3/4". Also keep in mind that ASHRAE says that a boiler that is 25% oversized or greater reduces system efficiency. This means that the addition of an outdoor reset control will insure that the boiler is rarely oversized for the current load conditions. Also the benefit of an outdoor reset control on a boiler that has virtualy no low limit restrictions (ie. Viessmann Vitola, condensing boilers, etc...) can take better advantage of an outdoor reset than a typical cast iron boiler can.

I have seen savings of anywhere between 20% and 60% with these types of conversions depending on what measures are taken. I realize that this is a large spread. There are several software packages designed to do these types of calculations however unless you do a lot of this type of work the software can be quite pricy.


kf

Steamhead

If you compare

a well-operating hot-water system with a poorly-operating steam system, then the hot-water is more efficient.

But a well-operating steam system approaches the efficiency of a well-operating hot-water system, assuming the boilers are similar.

There is much less water to be heated in a steam system than in a hot-water system. And with a modern boiler and good venting and pipe insulation, you start making steam in a few minutes and it gets to each radiator shortly thereafter.

The key is how efficient the distribution system is. Once the boiler adds heat to the water, its job is done. From that point, the system must move the heat to the rooms. This is where many steam systems lose efficiency, but the problem is easily fixed.

Both steam and hot-water are much, much more comfortable than scorched-air!

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Tony Conner

Why...

...is combustion eff higher with a hot water boiler? You can certainly have lower stack temps with hot water, but that's the measure of the eff of the boiler itself, which is essentially just a heat exchanger. Combustion eff and boiler eff are not the same thing.

It does take more energy to heat water to effect the change of state when it becomes steam. However, this additional (latent) heat is given back in the rads.

Why are steam systems essentially "pouring water down the drain"? That sounds like a pretty crappy steam system. Why not just fix the leaks?

The biggest problem with getting components like TRVs to last in steam systems is misapplication and/or a botched installation. It's the same with steam traps.

Hot water systems are somewhat more eff than steam. To me, a big factor in the decision on what to do with any given system should be "What's the payback?" If it costs a couple of thousand dollars to have a marginally functioning steam system put right, and ten thousand to re-do it as hot water? What if it's a fairly modest house with heating bills that are maybe $1,500 a year? Even if you can cut this guy's annual heating costs in half with a new hot water system, that's a savings of $750 a year. You're way over a decade on the payback. No business would even consider such a project.

If you're going to compare the very worst a steam system can be, with the very best a hot water system can be - what kind of comparison is that? Unfair, at best. I've seen these kinds of comparisons before. Take a neglected old steam system with 9 out of 10 40 year old steam traps failed, and every joint leaking that can possibly leak. Replace it with a hot water system, along with all the rotten old single-glazed windows, etc and claim a huge eff increase for the new heating system. Hardly apples to apples.

And I don't know anybody who buys a Corvette of any vintage basing their decision on "gas mileage".

steve_6

both hot water and steam

are superior heating systems. It sounds like you should listen to kf, he's telling you what you want to hear.

Tony Conner

If...

...you live in an area of relatively obscene energy costs (like most of Europe), then that's the clincher. There's a payback to almost always rip out old steam systems, and drop in hot water. To say the same thing applies in the same way to North America, is incorrect.

kf_2

Whoops!

I replied in the wrong spot.


kf

kf_2

Steam to Hot Water Cont.

Steamhead & Tony,

You will never catch me advocating "schorched air" I agree that given a choice between steam and air steam makes the most sense. But in some cases the payback for installing hot water over warm air is so long that it normally wouldn't make sense residentialy either. People chose against warm air for other reasons such as, comfort, longevity, healthier etc... And by the way, Gary never asked about payback, just savings. Likewise I never talked about payback.

As far as combustion efficiency it is defined as: The measured CO2 content of the exhaust gas is compared to the theoretical maximimum CO2 content that would result if the complete combustion of the fuel occurred. The resulting combustion efficiency is then read from a standard combustion chart for the fuel being burned. The higher the CO2 content and THE LOWER THE EXHAUST TEMPERATURE the higher the combustion efficiency. So lower stack temps is a property of combustion efficiency. By the way the less air introduced to combustion the higher the CO2. In an atmospheric boiler lets say, air will be pulled faster through a hotter heat exchanger. I have never heard of "boiler efficiency" do you mean system efficiency? This would be based on everything from pipe & boiler insulation to size of heat emmitters.

Also you stated that a steam boiler has less water to heat than a water boiler allowing for faster heating. However, it takes most boilers 4-6 minutes of run time to reach steady state efficiency. A boiler in a perfect world should never be off. Also, a lot of what you are heating in a steam system is air. Air has a much less specific heat value than water, needing more energy to heat the same space. The water/air in the steam pipes are much hotter than water in a water system speeding up the stand-by losses to the surroundings even with the same pipe insulation. This goes the same for the boiler.

The failed TRV's most commonly fail due to either rust deposits (which can't be avoided with air, iron, and water) or not being able to withstand the high temperatures of steam.

I've yet to meet someone who has asked for a vintage steam system in thier new house based on how much money it will save them.

I do agree that most residential homes would not switch to water based on paback alone but most of my experience in this type of work has been done in large commercial buildings where the paybacks have been significant.


kf

Tony Conner

Boiler Effeciency...

...is heat out, in BTU/hr divided by heat in, in BTU/hr. When considering boilers (steam or hot water), you have to discount the heat from everything heading into the boiler - the air, fuel, and especially the water (even from an ecomomizer attached to the boiler). To get a proper eff, you need to do a "heat balance". This is almost never possible, as very few boilers, except for huge central station steam generators are instrumented to do this. The "normal" way is to use the heat of the steam out, minus the heat of the feedwater (this is far and away the biggest "running start" the steam boiler gets and dwarfs all others combined) divided by the heat input of the fuel. Hot water boilers, if they were instrumented to do so, could be evaluated the same way. While inlet and outlet water temps are routinely available, you'd need an accurate flow meter though. I don't know that I've ever seen a hot water boiler with such a metering device on it. "Combustion eff" has largely come to be taken as "boiler eff", and this is incorrect. While there are some savings to be had in fuel with lower water temps, they are pretty marginal. Having said that, if you combine the heat savings in lower stack temps, lower heat losses through piping due to lower fluid temps, etc, it can add up to some measurable savings. Not astronomical savings, however. If you assume similar comfort from steam & hot water, however, it all comes down to "payback" in my mind. How fast can I recover my investment?

Could I justify (in a business sense) installing a steam heating system in a new house? No. Could I justify repairs & modifications to an existing system? Very possibly. Even very likely, if it hasn't been butchered.

As far as fuel supplier's data goes, I'm afraid I'll have to pile it with the rest of the studies and polls I get subjected to on a regular and ongoing basis, along with most consultant's reports. The first thing I ask myself anymore is "Who commission this poll? Who generated these numbers, and how do they stand to profit by them? Who financed this university professor's research?" I just don't believe most of them anymore. If it's a topic I can understand (and I admit, that rules a lot out...), I find some books, and read for myself. I prefer older books, since I find them not quite as tainted by modern spins.

Quite honestly, the local gas and oil guys, along with the vast majority of consulting engineers, and yes - even most current "steamfitters" wouldn't know what a pound of steam was if they had in their pants pocket. And I think a lot of perfectly salvagable steam systems are getting junked for no reason other than lack of understanding about how they should operate. And that's a shame, technically, and financially.

Bob Bona_4

I'm

jumping in, for a second. Pay back is not in the equation for most folks in my area. Not too many people have the time or inclination/dedication to maintain a steam system. It becomes such a pain in the rear, it doesn't take much to have a slick air salesman convert them to ductwork.

For us, as contractors/tech's, steam heat is neat, historic, vintage, and all that, but to the average homeowner, it's not. Let's not lose sight of that.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Tony Conner

Payback...

...is in pretty much everybody's equation. Lack of education/understanding leads to people fumbling the calculation. And it's understandable - most people are just too busy. But that doesn't necessarily make what they're doing the right thing. I think what they're doing represents much more a "default decision" than anything. They've likely spent a bundle on people who held themselves out as knowledgable with steam, and are still living with problems.

I see it all the time in industrial applications. Plants tearing out steam equipment they often could have made work (very nicely) for a few thousand dollars, and replacing it with with equipment that costs many times that. And the new stuff often doesn't work as well as the steam system COULD have.

There's been quite a discussion here among heating professionals regarding "boiler eff", "combustion eff" and "system eff". They are NOT the same thing. If a lot of the people here don't understand the difference, how will the customers? I take published boiler eff numbers as essentially the same thing as government fuel economy ratings on cars. They're done under standardized, lab conditions. Conditions that you'll NEVER see in the real world. Like the small print says - "... for comparision purposes only, actual mileage may vary." At least with cars, you get an odometer to know how far you've gone, in addition to a reading off the pump as to how much gas you've just put in the tank. Most small boilers (and most industrial boiler, as well) HAVE NO ODOMETER. Or if they do have one, it's a cheap, inaccurate piece of junk. Pretty much everyone ASSUMES the published boiler eff numbers are valid. Bad news - I've worked in powerplants where the boiler steam output numbers were accurately measured, and it's a real eye-opener. If you've got an industrial boiler that can maintain anything much over 80%, you've got a tight operation. I've worked in others where the numbers were total, utter fiction. "Ooooh, look. We're getting 115% boiler eff!" Um - unless the laws of physics have been suspended, probably not.

kf_2

Payback

Again I agree that the payback in switching from steam to water for an average home would rarely entice the homeowner. The original question however, was is there a savings. As I said my experience with this type of conversion has been predominately large commercial and multi-family buildings. Lets take an old large factory heated (not process) by steam that uses 80,000 therms of nat. gas a year. (approx $.80/therm in my area)If we could save even 25% thats a pretty quick payback as far as a commercial building is concerned. About efficiency, the bottom line is money out divided by money in. This is system efficiency, the only one that counts!

I agree with the comment that reducing water temps. has marginal savings to a point. In recent years however, the advent of condensing boiler technology has changed that. We can now scavange latent heat from flue gasses and transfer it back into the boiler and of course the lower the water temps are below the dewpoint of the fuel (approx 136* nat. gas & 117* #2 oil) the more heat we can recover. I have found that in most cases that radiators or heat emmiters in commercial buildings were either grossly oversized or the building's envelope has been updated since the original install which makes them perfect candidates for lower and modulating water temps.

One of my previous occupations was as a commercial energy auditer for an engineering firm that worked with local gas utilities to propose measures for saving energy in commercial buildings. In my area the Gas Utilities have been mandated by the government to reduce fuel usage, so financed by small conservation charges on fuel bills they offer incentives for implementing energy saving measures such as; new heating systems and building envelope improvements providing the payback made sense. Our firm was payed based on the proposed therm savings of the project. While we were contracted to run this program we had a 105% accuracy rate on our proposed savings to the customer. This means that we sometimes estimated less than was actually saved. I have seen the reduced fuel bills and not just read about them in reports or studies.


kf

Steamhead

But

in your large old factory, if you could get a similar energy-use reduction by fixing the steam system, the initial cost would be less so the payback would be faster.

How many bad, missing or improperly sized vents, bad traps, uninsulated pipes etc. do we see when looking over steam systems? I see a lot of all of the above, and it doesn't cost that much to fix them. Once they're fixed, the fuel consumption drops right off.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Tony Conner

In A Great many...

...old factories I've seen (and I've seen quite a number), you could effect a 25% savings by simply fixing a couple of condensate pumps. By the time you get the scale off the boiler tubes and do the steam traps, I'll bet I can hit something approaching 50% in a great many cases. And for a fraction of the cost of a "complete make-over".

You said above that you didn't know what "boiler eff" was. What if the problem was simply the boiler being scaled-up? The impact on boiler eff is HUGE. And therefore, by default, the impact on overall system eff is HUGE. I've seen high pressure steam boiler stack temps drop from 700*F to under 500*F by simply cleaning the crud off the heat exchange surfaces of the boiler.

I have no doubt that you achieved the savings you say. I also have no doubt that, in many, if not most cases, I could also achieve comparable savings - at a fraction of the cost.

Steamhead

Movin' on up.....

to the top of the Wall, for the benefit of those who posted in the "Steam to hot water conversion in LARGE building" thread, so they can read this one before it drops off the Wall.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"