Buderus Hot Water vs. steam

Peggy Gillespie

I have a house that is half heated with a 40 year old oil burner/boiler with steam heat and radiators and the burner/boiler is wearing out (the other half of the house has propane hot water baseboards). I have two contractors telling me two different things, one guy does a lot of European style heating systems, and the
other is my regular oil company. The Euro guy is saying the Buderus with outdoor reset and panel radiators with TRV heads and constant circulation willbe about 30 to 40% more efficient than the equivalent installation which
is simply a steam boiler swap out (for a new Smith or Peerless). The oil company says there's only one
or two % savings if any and that they will both provide the same comfort and efficiency. The oil man himself has a Buderus system in his house and his company installs them. He said I just don't need to spend that money. The Euro private guy seems very knowledgeable and said it would save a lot on the oil (30% or more) and that the oil burner people want to sell the cheaper system as they will earn more because of the more oil I will burn. I don't know who is right; can anyone shed some light
on this subject for me?

Ron Schroeder

Are both boilers in the same room? If they are, one possability would be to use the steam radiators as hot water radiators and combine both systems on the new boiler as a single multi zone all hot water system. You could even keep the propane boiler as a backup with the proper piping. Since steam is sized for the radiant but hot water is sized for the load, you could see even more fuel savings if the steam boiler was oversized and the replacement boiler was correctly sized. It's hard to go wrong with a Buderus or other triple pass boiler.

Bob Morrison_3

30 or 40 percent more efficient? (BM)

Comparing a new how water boiler with panel radiators/TRVs to conventional steam with radiators: thirty or forty percent more efficient is simply incorrect. The new hot water boiler itself will be 85% to 95% efficient, depending on how it operates - with high temperature emitters (panel radiators) it will operate in its lower range. The steam boiler itself will operate at 80%-82%. Of the two distribution systems, the steam piping heat loss will exceed the hot water piping, but do the heat losses contribute to heating the basement and thereby to the house? I'd estimate a small (2%-4%) difference, assuming that some of the distribution losses do not contribute. Overall, it would be reasonable to argue for a 5 - 10 percent improvement of hot water to steam. But, not 30 to 40 percent.

Bob Morrison

thp_8

Hallelujah

:-)

Ron Schroeder

Bob,

I would suspect much more than 10% between steam and hot water. It is more possable to mitagate losses from over sizing with hot water that you can't do with steam. Also you can do outdoor reset with hot water but you can't with steam. I have seen in excess of 50% savings in a few cases when steam systems were changed to hot water keeping the same radiators.

Radiators can usually be operated at lower temperatures than 180 degrees, especially if there has been any additional insulation or other conservation measures since the radiators were origionally sized.

GW

combustion efficiency?

Bob, I'm not sure you understood the whole picture here, she is being told the "system" as a whole would be at least 30% more efficient. It's not the simple comparison between combustion efficiency of the two boilers.

http://www.buderus.net/Default.aspx?tabid=34&cid=12&ctitle=multi-purpose

If you look at Buderus' marketing peice on the outdoor reset control, you'll see that they're claiming "up to" 30%. Well, because we're talking old clunky steam to new modern Buderus with panel rads, TRV, constant circ, now we're talking about a Corvette versus a Buick. Not even a close comparison.

Just my thoughts,

Gary

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Bob Morrison_3

efficiency guessing (BM)

By efficiency, I'm referring to the overall system, i.e., to the ratio of heat in the space to fuel input. And, my estimates are guesses, based on industry standard numbers for the equipment performance and experience as an energy engineer. As I understand it, the thread's question is comparing a new, replacement steam boiler to a new hydronic heating system, including distribution and high temperature emitters, such as finned tube or panel radiators. And, as I understand it the underlying question is "will a new hydronic system pay back itself by cost savings due to higher efficiency operation?"

Let's get more specific: where are the losses from the steam system compared to the hydronic? Boiler efficiency losses, standby losses from the equipment and distribution losses due to higher temperature steam and condensate piping. The combustion efficiency differences at the boilers will range from 5 to 10 percent, the standby loss difference is neglible and the piping losses will range from zero (all piping within heated spaces) to 5 percent, which is a guess - I've never calculated it for a residence. Where's all the other supposed efficiency gains? Remember, all else is equal in this comparison: the setpoints are the same, operating hours the same, etc. Oversizing of a boiler will result in shorter cycles, but there's no pre- or post-purge losses (as in commercial boilers), so a forced draft, somewhat oversized residential boiler's relative operating efficiency losses will be neglible.

The hot water radiators can be operated at a lower temperature (I selected mine to satify the design load when operating at 160 F), which will save on distribution losses, but by how much? If the piping is in a heated basement, there's no savings.

On the other hand, a hydronic system is quicker in response, quieter and arguably can provide a more comfortable environment - no doubt about it, but these notions aren't part of the economic comparison.

Bob Morrison

Ron Schroeder

Hi Bob,

You can't go by just combustion efficiency or AFUE unless you are at full load. Part load efficiency, like most of the heating season, can be substantually lower than combustion efficiency or AFUE, especially for steam.

Standby losses for steam are also higher due to the higher boiler temperature.

Steamhead (in transit)

\"Can't do outdoor reset with steam\"?

That's funny, I'm installing a tekmar 269, which is an outdoor reset controller, on a large steam system tomorrow. On steam, the controller resets the steaming time rather than the water temperature, but it is still "outdoor reset".

For reset to work well on steam, the system must vent air from the mains quickly so all radiators have equal access to the steam.

You'll read about this tekmar installation when I update my company's Find a Professional ad.

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Steamhead (in transit)

Overall system efficiency

probably isn't that much different- assuming both the hot-water and the steam system are in excellent condition. If the steam system is uninsulated, badly vented or has other problems, of course a hot-water system will be more efficient. But you can get back that lost efficiency in the steam system quite easily, and for far less money than a complete tear-out which is what the one contractor wants to sell you.

One of my customers who has one-pipe steam saved 36% on her oil consumption over last season, simply by having me fix the basics on her system. Go here for more:

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

Peggy, I wish you were in the Baltimore area!

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Mellow_2

referances

A list of people that have changed systems like yours can be helpful...... IF the oil co. has changed systems like yours before, to a "euro system" than the would have a lot of happy people ready to tell you how much they saved. They would also have the oil bills to prove it. The euro guy sounds like he knows how good the product is but can prove it because he is not selling the oil and keeping track of the usage. The oil co sounds like they might install the euro boilers but run them like they run the old boilers. I mean, they do not use the best controls to get the most out of the product or they conect them to an old systems without making very important changes to improve the system eff. I would ask for referances and talk to the people that have changed systems. they will tell you they saved alot.

mellow

Bob Morrison_3

Estimates and educated guesses (BM)

Ron,

I agree with you - full load efficiency values do not equal seasonal values. And, the steam boiler standby losses will be higher than the hydronic's, if all other aspects (surface area, insulating value etc) are equal. But, this thread's off-the-cuff comparison addresses only the question if the hydronic system is a 30 - 40 percent improvement over replacing the steam boiler? Assuming two good functioning systems, it is much more likely a 5 - 10% improvement on energy savings. Moreover, the payback from energy savings for the hydronic system change from the steam boiler replacement will mostly likely be in the 15 to 20 year range.

Bob Morrison

Long Beach Ed

Like Steamhead...

... I'll chime in with the recommendation to repair the steam system so that it operates correctly.

Even a 20% decrease in operating costs would take decades to recoup the cost of an entirely new heating system. Add to this the cost of maintaining the new systen vs. the old and usually the transformation is not cost effective.

Ron Schroeder

Hi Bob,

Comparing a NEW steam boiler on the existing radiators to a NEW hydronic boiler with a conventional triple aquastat on the same radiators, I could see possably only a 10% savings with hydronic over steam. But by using proper controls and piping like outdoor reset and a buffer tank if needed (which you CAN'T do with steam), I would be very surprised if the savings was less than 30%.

Add in the possability of moving the propane baseboard system over to the new oil boiler and you will have even more potential savings due to oil being less $/btu.

Another thing that might be done would be to stage the propane boiler to come on only when it is very cold and size the oil boiler for only 50-70% of the load which would supply enough heat for 90% of the season by it's self.

Of course, this is assuming that the steam system is not a one pipe system. If it is one pipe, the added labour of installing the returns would probably make a hydronic conversion unreasonable in cost.

Ron Schroeder

Hi Steamhead,

Since you can't make steam at less than the boiling point of water (except at lower pressure) will reset on steam save energy or just improve comfort?

Thanks,

Peggy Gillespie

From the owner--more clarification

Thank you all for the opinions--of course I still feel confused. Here is the situation. The steam heat(40 yr. old boiler) heats 6 radiators in one half of the house where my teenagers lived, but they are now off and only home at holidays and college vacations. I only use that half of the house when I exercise or to do laundry...and sometimes on weekends when my daughter comes home (besides vacations)...otherwise I keep it pretty low. The heating contractor would put wall radiators and remove the steam radiators (rather than retrofit them). The new steam boiler or the Buderus with outside reset would be just for this section. Cost difference is around $5000 for just a boiler swap out (and burner) vs. $11,000 (I'd get new radiators, piping, etc). The other half of the house, where I primarily live is heated by propane. There is a new Amtrol hot water heater there, and baseboard heat in two big rooms (bedroom and kitchen/living room, and bathroom. They are zoned so bedroom is separate. The water heater (propane fueled) heats water for the entire house which means the laundry and bathroom in the side of the house where the steam oil heat is. There is only a crawl space (very small) under the kitchen (gas heat) and part of the living room (steam heat area), so to attach the two systems keeping the baseboard in my half of the house would add another $2500. This would use the current water heater. So I've been trying to figure out whether I should just do the cheap fix and it won't matter that much in the long run (savings) as I don't use that half of the house that much (oil heat), or if it's worth spending the money and getting Buderus for that half of the house as I would save so much on oil, it would be worthwhile in some years; or whether I should spend the $13,000 to do the entire house with one system. I have to take a loan (home equity) to do any of this, so it is both a financial question and an efficiency question. If in about 4-10 years, it would cancel out this cost in savings and I wind up with a great system, then I'd probably be willing to do it. If its fairly marginal given my situation and that it is just one person (I also use a lot of wood heat to keep the kitchen and my bedroom warm, and we get a lot of sun here which helps) most of the time...maybe that will help clarify my question. If my heating contractor is right and I save 30-40% on oil every year (currently use about l000 gallons, maybe less this year), it could be worthwhile...but if it's just 5-10%, maybe not.

Ron Schroeder

Hi Steamhead,

I wish there were more qualified HVAC technicians like you around the country.

Maintanance and proper adjustments can really make a differance.

About two years ago, two people down the street from me both had work done to their identical oil heating systems.

One of them had a "free" boiler installed by the gas company (boiler was free, installation was several thousand dollars)and he saved 30% on his heating bill.

The other one changed service companies and had his old burner/boiler properly cleaned and adjusted. He saved over 50% on his heating bill and the cleaning was only about $100. ;-)

Ron Schroeder

Hi Peggy,

Since you are not using the steam heated part of the house much, maybe a "tune up" by a qualified professional would be the most bang for the buck. (make sure the professional is qualified for STEAM, most are not)

If the new system is ~ $10,000, and you cut your oil usage in half ($1000/yr at $2.00/gallon)it would take 10 years the savings to pay for the equipment if fuel prices don't go up, less if they do.

It's hard to tell without seeing if changing out your radiators is needed. Radiators don't "wear out" or lose efficiency. Some people spend a lot of money installing old radiators because they like the look. If they are two pipe and large enough to heat the space, I would lean toward keeping them whether you change to hydronic heat or stay with steam.

Another thing to think about is will you be able to get someone qualified in steam for repair and tune-ups in the future in your area. Also you may want to think of resale value depending on how long you will be staying in your house.

Are your boilers in the crawl space?

Steamhead (in transit)

Short answer-

both.

For this to work well, the boiler must produce steam quickly when it starts up, and the system must distribute steam quickly and evenly. Then the reset controller can accurately regulate how much steam the boiler produces, and that quantity of steam will heat the building to the desired level.

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ttekushan_2

Distribution loss rant

Are the pipes to your radiators going outside the house for a tour of the winter scenery before they return to the radiators to do their job of heating?

If not, why is everyone concerned about distribution losses?
Reticulation losses, ie those involved with heat distribution rather than heat generation are in fact particularly low with steam. Downtown buildings in cold climates are routinely heated with city forced air. Oh. I mean city hot water. Now I remember. City Steam. Loss along those miles of lines (at high pressure, of course) is so remarkably low. Home heating systems are low pressure throughout but it is illustrative of how steam flows so readily. The heating process itself (condensation of steam in the radiators) actually draws more steam from the piping into them. Miraculous how steam systems don't need fans and pumps. Do you think there's value in that? I do.

If you are comparing the performance of a brand new high efficiency hot water boiler to a worn out encrusted steam boiler you have waaaay too many variables involved to make a meaningful comparison on future savings of a changeover in the heating medium. Yup, I've seen a new hot water conversion save large $$$. Ditto forced air (bear with me on this). But I have PERSONALLY descaled, flushed out, rebalanced, revented/retrapped, and tuned up neglected steam heating systems and seen 50% savings (per degree day--ask any other steam guys-they'll confirm it) without even changing the boiler.

If you conveniently remove the effect of failed and encrusted components from your equation by converting to hot water, your results are inherently fallacious because you have "corrected" those problems buy removing the components in the conversion. Guaranteed that a high efficiency hot water system with failed controls and mixing valves, etc etc won't look so good on the cost of operation side! It probably wouldn't even work. Bad mixing valve destroying a high cost boiler is your financial problem. I sometimes wish steam systems would just stop working as soon as something is a little off spec. That way we wouldn't be having discussions about the inefficiency problems with steam. Nevertheless, they keep right on working in some fashion or another when just about every trap and vent and the boiler are technically in failure mode.

Can you electronically control a steam heat system? Why not? I love the Tekmar 269 single stage steam control with outdoor reset (I am in no way associated with Tekmar).

Finally, in another post, a hot water heating system was claimed to be running at 103% efficiency. Energy out must be greater than energy in. Doubtful. Someone responded that there must be a refrigeration cycle involved to get ratings that start looking like the Coefficient of Performance (COP) of a refrigeration cycle. Funny they should bring that up. The distinguishing characteristic of a refrigeration cycle is the use of latent heat in evaporation and condensation. Steam heating systems apply the latent heat principle for distribution and heating. Since the heating medium is above ambient temperatures mechanical compression is not used as forced evaporation gets the cycle going, and going inherently to full completion ('cuz your heated environment is always cooler than the heating medium and the steam wants to be water, shedding all that heat energy).

The latent heat principle is what boosts the efficiency of a condensing boiler. It is not the primary heating form. Let those water temps get a little out of control and the efficiency boost is lost. And you still have to shove all that water around continuouly. And you better tell it where to go with sophisticated valving and zoning controls because it can't inherently seek out the colder areas of a heated space. With steam, 90% of the heating process is with the latent heat of water, with some coming from the "sensible" heat of the condensate.

This is why a well tuned steam heating system with an apparently lower efficiency boiler (around 82% AFUE whatever that really means in practice) can still operate very economically.

And my final thought on this one, why on earth doesn't a single residential steam boiler manufacturer reconfigure their boilers for the use of an economizer? Economizers are used on large industrial boilers all the time to recover flue gas heat. I was looking at one that recovers so much heat that you have to line the chimney or run the vent directly outdoors as the exit temps are around room temperature. Sound familiar? This type of set-up for residential use would bring fuel consumption of steam systems well below anything else, hands down.

Thats it.

-Terry

Ron Schroeder

Hi Terry,

While it is true that the losses on the pipes for city steam is remarkably low, it is only low as a percentage of the delivered BTUs. The same size pipe with hot water would have less losses but would be delivering far less BTUs.

I have seen the efficiencies of over 100% for some european boilers. The reason for that figure is the way they calculate efficiency. The main thing is that they use an artificially low figure for the BTU content of the fuel.

By the way, there are a few experimental fuel fired heating systems that DO use the refrigeration cycle to truly get efficiency greater than 100%. While both steam and refrigeration cycles both use latent heat, they are compleatly different and you can't get over 100% with steam.

While steam can be quite efficient, it is a simple law of Physics that prevents steam from ever achieving quite as high of efficiency as hot water. The limiting factor is the absolute temperature of the heat transfer medium and the temperature of the boiler in standby. The cooler the transfer medium, the higher the combustion efficiency can be. The only way to get steam at temperatures as low as hot water is to operate the steam system under vacuum.

Steams biggest advantage is transferring tremendous amounts of energy with relativly small pipes.

In the real world, systems never operate quite up to their theoretical efficiency. Many far less than they are capable of. Many (most) hot water boilers are controled improperly, piped improperly and sized improperly. And some steam systems were poorly designed(I think the old steam guys did a better job mostly).

As you said, descaling and other tuning and maintanance can often return large amounts of lost efficiency.

ttekushan_2

Well, I said it was a rant!

I really do understand what you are saying. It was just one of those days. I had just gotten done with a frustrating day of trying to argue the benefits of tuning up the existing steam plant of a 120,000 square foot facility. You see, they are being sold on the idea of rooftop units because the heating unit is virtually included FREE with the A/C units. Nevermind that the construction of the structure (solid masonry, reinforced concrete, 20' high ceilings) make it impossible to heat some of the peripheral areas, and the floor area adequately. "Just install electric baseboard in those areas." Great. And I was sitting there listening to a slick salesman saying how inherently inefficient steam systems are and that it is a relic of no modern value.

And another one lost to rooftop units is a really nice '60's era zoned hydronic system with good 1 1/4" steel fin tube. Update that boiler, and they would have had something really special. Too late on that one.

Steam can and should be very economical over the long haul is my point.

Sooo. Any thoughts on the residential boiler economizer idea? To me, this is the missing link to the modernization of steam systems. Every other heating type has been maximized with every available technology. Steam has not. This puts it at an artificial disadvantage.

If boilers were updated in this way I could almost see steam return to use in larger residences and commercial buildings!

-Terry

Ron Schroeder

Hi Terry,

I hate to see a good zoned system replaced with rooftop or unit heaters too. And while electric baseboards are efficient, thier "fuel" is usually more expensive than any other option.

I am sure that an economizer would improve a steam system but it wouldn't improve steam as much as condensation helps hot water.

Steam can be a real advantage in commercial situations where the heat needs to be transported long distances, especially thru partially conditioned spaces like warehouses before it gets to the load.

I am not so sure about large residences, they may not be big enough to utilize the advantage.