2 pipe Steam converted to weather responsive hydronic.

DavidL

Ok, so I haven't been on the wall in a really long time, maybe many years. But the kids always come home.......

So here is the issue.
I have a customer who has an apartment building 18,500 sq ft., 2 pipe steam. The old boiler had a few leaking sections last fall. So we did what I usually do, convert it to condensing hot water/weather responsive control. Done this many times, works well & saves energy. Everyone is happy......

The other day I looked at the building behind this one, for a different owner, same size building, built at the same time
early 1920s, this building has been owned by the same family for 60 years, much better shape and well cared for.
However, someone at some point took out the steam traps and put air vents at each radiator(2 pipe steam). This building is heated by 800,000 btu Weil Mclain boiler with tankless coil. The supply mains are well insulated, the returns
are not. The boiler is controlled by a weather responsive control.

My assumption is I'm gonna save this owner a bunch of money by converting his system to hot water.
I request a copy of his utility gas bills for the last 4 months to compare them with the gas bills of the building behind
that has been converted to hot water. To my shock and dismay........ the steam system with a tankless coil and no steam
traps consumed 14% less fuel than the same size building, same size condensing boilers, with converted cast Iron rads,
on a 1.6 reset curve with separate atmospheric gas water heaters.

Please remember I am looking at the actual bills, both buildings have replacement windows.

Ok everyone, why is the steam building costing less to operate?

Looking for a good answer.

Thank you in advance for anyone willing to take the time and step up to the plate.

Dave

Jamie Hall

Interesting. I hate to say this, Dave, but I think that you may have just discovered that a good steam system is the equal of a good hydronic system, all else -- such as the type of boiler (condensing vs. non-condensing) in terms of efficiency.

There are, of course, many variables in a heating system which affect the fuel burn. It has been the contention of a number of us over the years that the choice of heat transfer -- steam or hot water -- is not one of them. The "much better shape and well cared for" most assuredly is.

Were it my call, I would ensure that the existing steam system is brought up to speed -- possibly reinstalling the various traps and changing the venting back to what it was in the first place -- which will improve the efficiency still more.

And then stop right there...

If you have to replace the boiler, stay with the steam and make sure it is piped really well.

DavidL

Jamie,

I have done dozens of conversions, we always document consumption. Generally save 30 to 50%. A system with steam in the returns should use 15 to 20% more fuel than a system with properly operating traps.

Dave

DavidL

I agree with you, hot water should be more efficient.
I have not done a heat loss, but the buildings were probably build by the same guy a 100 years ago, both building have replacement windows. And both buildings are the same size.
both buildings, the supplies are insulated not the returns.
The steam boiler uses a tankless coil in the winter and an oil fired hot water heater in the summer months, The hot water building uses Atmospheric gas hot water heaters. I am only comparing usage for the last 5 months. Every month the Steam
building uses about 14% less gas? go figure!

Dave

JUGHNE

How about the pumping energy for the HW system? Makes the steam look better still?

Steamhead

DavidL said:

I agree with you, hot water should be more efficient.
I have not done a heat loss, but the buildings were probably build by the same guy a 100 years ago, both building have replacement windows. And both buildings are the same size.
both buildings, the supplies are insulated not the returns.
The steam boiler uses a tankless coil in the winter and an oil fired hot water heater in the summer months, The hot water building uses Atmospheric gas hot water heaters. I am only comparing usage for the last 5 months. Every month the Steam
building uses about 14% less gas? go figure!

Dave

What you- and a whole bunch of other people who come on here and insist on converting steam systems to hot water- always overlook is that, invariably, you are comparing a steam system that's in bad shape with a brand-new hot-water setup. This is NOT a fair comparison, never was and never will be.

I cannot believe that you've NEVER had a problem on such a conversion. Pretty much every conversion I see is messed up somehow- parts of the building over- or under-heated, leakage, you name it. Liability lawyers love this stuff. We don't get involved.

And, given that a lot of these steam systems are in such bad shape, how efficient do you think your shiny new mod-cons will be after five or so years of typical landlord neglect? How long do you think they'll last when treated like that?

I'd have to see the system in question to know for sure, but there's probably a lot more to this story. They may have orificed all the inlet valves, for example, to keep steam out of the returns.

If you push a conversion on these folks, it will probably come back to bite you. And since these people talk to each other, if the owner of the building you converted finds out about this, I'd bet he'd conclude you took his money.

Jamie Hall

I stand by my original comment: all else being equal, the medium of heat transfer does not affect the efficiency of the system. That italicized bit is extremely important.

There are many things, however, which can and do affect the overall efficiency of a heating system. Some are intrinsic to the system: for instance, to modulate a steam system takes a different control strategy from modulating a hydronic system. It can be done for both, however (vacuum assisted steam, if one wants to mess with the vacuum pumps, can modulate way down!). Some technologies are much better suited to one medium or the other; condensing boilers, for instance, are much easier to implement for hot water than they are for steam, although, again, they are possible for both.

Some things are very similar for both -- maintenance of the boiler itself, for example.

The list could go on an on -- without even getting into such complexities as cost/benefit ratios!

It simply won't do to take a categorical position -- on either side of the which is better question, never mind the rather vexed question of retrofitting. Each case will be different, and must be evaluated on its own merits and circumstances.

ChrisJ

DavidL said:

Ok everyone, why is the steam building costing less to operate?

Looking for a good answer.

Thank you in advance for anyone willing to take the time and step up to the plate.

Dave

Because that steam system unlike all of the others isn't broke.

Hat may be right, that typical steam systems won't be as efficient as a hot water system with a condensing boiler.

But it's doubtful the difference would ever be big enough to warrant a conversion of a system.

Not to mention HW systems do have drawbacks.

New England SteamWorks

Steamhead said:

What you- and a whole bunch of other people who come on here and insist on converting steam systems to hot water- always overlook is that, invariably, you are comparing a steam system that's in bad shape with a brand-new hot-water setup. This is NOT a fair comparison, never was and never will be.

And patently obvious. No one would even consider converting if the steam system was running properly. To willing incur that type of (conversion) expense, a steam system would have to be stupendously bad.

I have intimate knowledge with an 19th century duplex. Both sides identical, each side around 4000sqft.

One side steam, the other FHW. Since the beginning of recorded time, the hot water side was far more efficient.

Then "The Holohan Method" was applied to the steam side.

Surprise. The steam side is now just as efficient as the FHW side.

jumper

Don't know why,but TRVs seem to work better with two pipe steam than HHW. From a heat transfer point of view steam condensation in the radiator works better than hot water when you consider scale and air layer in radiator. On the outside of the radiator higher temperature from steam enhances radiation and convection.

If I really cared about boiler efficiency I'd probably use the money saved from NOT buying a super efficient boiler and then figure out how to recover (and use) energy from stack.

Jamie Hall

jumper said:

Don't know why,but TRVs seem to work better with two pipe steam than HHW. From a heat transfer point of view steam condensation in the radiator works better than hot water when you consider scale and air layer in radiator. On the outside of the radiator higher temperature from steam enhances radiation and convection.

If I really cared about boiler efficiency I'd probably use the money saved from NOT buying a super efficient boiler and then figure out how to recover (and use) energy from stack.

If I were a perfectionist, that's exactly what I'd do -- a condensate heat recovery heat exchanger in the stack. However, the added expense and added complexity, never mind maintenance, sort of discourage me. Cost/benefit, and that sort of nuisance...

AMservices

My name is Ed.
I'm an HVAC contractor that installs and services anything to do with heating and cooling people in there homes.
I work with all these systems and there owners directly, and get to hear the good and the bad of all the different ways we go about dumping BTU'S into there living space.
Also living in new England most of my life, I have lived with most of these systems and have experience the pros and cons for myself.
What I've learned in comparing condensing boilers over any other non-condensing boiler is the 15-20% you will be lucky to save is lost when that first part fails or you schedule your first tune up.
The the cost of all the upgrades won't be recouped over the life of the system.

What I've learned about steam is it can be the most reliable, evenly balanced, and now the most efficient heating system.

Having a steam system start up with the piping holding a vacuum makes steam at much lower temperatures, fills the piping faster with more balance, increases the volume of steam so there's less water needed even to fill the larger pipe. Steam also brings Latent heat with it so there's more Btu output at the radiator and not 1 pump is used to deliver this heat.
When a steam system is running right, it can be the best system to live with and when the industry realizes that vacuum steam systems installed in new homes with all the right insulation, you can have smaller radiators and smaller piping and complete control over the heating of every radiator, without needing a lot of pumps, mixing valve and potential problems.
Steam hit the wall when people could no longer afford to install it. Not because forced hot water did a better job. Hot water use to be cheaper.
But now we need to have more base board around the outside walls and more piping laced under the floors to offset the drop in btu we're have lowering the temperature of the water. And the cost of a condensing boiler is in the same ball park as a 5-6 section steam boiler.
If someone has a working steam system or just has the piping, they should really look at what it would cost to make that system run as a vacuum steam system because that's going to be a sure way to get a payback and have a system that has proven to last 100 years.
All the technology is available. You just have to know how to incorporate it into your project and not do what everyone else is doing because they say it's better.

I could go on all night but I won't. So let me end this by say STEAM RULES,

gennady

We did oil to gas conversions in 2 identical brownstones in Brooklyn one within few blocks from another. One had steam system, another hot water system.
We installed steam Slant Fin boiler with trvs and viessmann vitodens in these houses. Then we analyzed bills. They were actually very close, within 3-4%, even without accounting for electrical consumption.
Since then I always advise clients not to convert to hydronic system. Few listen. In case of gut renovation we do conversions to hot water if client insists. Otherwise the cost is prohibitive.
Properly done steam system is on par with hydronic in all aspects. Just my 2 cents.

ChrisJ

@Hatterasguy

How does electric usage and the mass of the water in a hot water system effect the efficiency in a CI system?

Everyone keeps telling me more mass means less efficient some how and yet no one has explained where this "wasted energy" disappears to.

Dave in QCA

To David L., thanks for posting this very interesting thread. It illustrates what the steam folks have been arguing for a long time. A good, well-maintained, and well-controlled steam system is going to operate quite efficiently and the operating cost difference between it and a hydronic conversion seldom produces a reasonable payback.

You have indicated that the buildings are nearly identical and have done a good job of describing the heating systems, but there are many more questions that I have, for things that could account for the difference. You indicate that the hydronic building is being controlled by an outdoor setback. Is there any other control? Has any body rechecked the indoor temperature at various conditions? Is the building overheating? If so, obviously, no matter what the combustion efficiency is, overheating a building will waste all the savings.

On the steam building, is the building being effectively controlled? What is the method of control? If the building is evenly heated, but not overheated, that in itself, produces great economy. Given that the traps have been removed, I am guessing that the system is operating either as a two-pipe vented, or inlet orifices were installed, and the radiator vents that were added are serving no purpose. Inlet orifices accomplish a great deal in terms of evening out the heat in a building. Henry Gifford has an extensive track record of producing great fuel savings in buildings by adding inlet orifices.

I think it comes down to even distribution of heat throughout the building and good control, to provide steady even heat with absolutely no excess heat or overheating. Combine that with a properly installed steam boiler and you're going to have good economy.

jumper

My experience is that maintenance is eventually neglected. HHW suffers faster than steam. At least with steel pipes from the fifties. Building owners did not want to pay for side stream demineralizers. But then city did not want flush out stuff in drains. Today environment guys might not want stuff on parking lots either.

gennady

Hatterasguy said:

gennady said:

We installed steam Slant Fin boiler with trvs and viessmann vitodens in these houses. Then we analyzed bills. They were actually very close, within 3-4%, even without accounting for electrical consumption.
.

You do realize, if the above is true and believable as a universal truth, that you have just put all the mod-con manufacturers out of business?

A HW CI boiler can be considered on par for efficiency (electric excluded) with a steam system.

Why would anyone install a mod-con to get 4%?????????????????

This is $64.000 question. I think we need to consider efficiency of the boiler and efficiency of the heating system. Of course standby losses of mod con are lower, But again,ability to deliver proper amount of heat at the proper time to any part of the heating system to compensate losses is the key to high efficiency of the system, and efficiency of the boiler plays lesser role in the total efficiency. This is my 2 cents.

gennady

Middle of the winter job, where we had to fix whole set of heating issues on existing heating system. As part of the job we installed I-series taco valve, with outdoor reset, removed thermostat and set system to continuous circulation.
I think client saved probably 30% off the heating bills, might be more. Hope there will not be plumber later on who will remove all these unknown thingis. So, here we have old CI boiler with outdoor reset down to whatever, imitating mod (non con). Local heating supply house had no idea what I-series outdoor reset valve is. Nobody uses them in the hood.

Jamie Hall

Actually, @Hatterasguy , there is a theoretical consideration here. Although it would be just lovely to have real world data, it's kind of hard to come by. One needs to look at the comparison between the higher heating value of the fuel, which basically includes the heat released by condensing the water created during combustion, and the lower heating value, which does not. The difference will be the maximum possible gain in efficiency between a condensing boiler, condensing to the intake air temperature (higher heating value) and a non-condensing boiler.

The percentage is different for different fuels. For natural gas and propane, the ratio is about the same: 0.79. For #2 oil, it is higher: 0.82. Examining these numbers, one can conclude that the maximum possible gain, involving equipment to recover all of the higher heating value, could be as high as about 20% for gas fired appliances, and 18% for oil fired (note, parenthetically, that the maximum practical efficiency for electricity is about 40% for fuel-fired generators -- somewhat higher for some modern supercritical steam boilers and turbines). Is this achievable in practice? Probably not. In principle, though, a hydronic system operating with a return water temperature equal to the air temperature of the combustion air could could come very very close. So might a steam system with the same condensate return temperature; I haven't run the numbers -- it would be limited by the relatively small volume of condensate. Both systems would require either forced or induced draught, since with the stack gas at ambient, there would be no natural draught. Both systems would require rather sophisticated counterflow air to water heat exchangers.

In the real world, however, so long as it is operating in condensing mode, I find it quite reasonable to suppose that a condensing hot water boiler could return 95% of the higher heating value, provided the return water temperature is below about 140 F. A well designed and piped steam boiler should be able to recover slightly more than the lower heating value, but in my judgement it would be hard to recover more than, say 85% of the higher heating value (a little more with oil fired boilers). Either a condensing or non-condensing hot water boiler operating with a return flow at a temperature of more than 140 F or thereabouts is limited to the lower heating value.

Where does that leave us? Clearly a hydronic system with a low return temperature will have a definite advantage -- this is one of the attractions of radiant systems (although they do have other problems!). But before one gets too enthusiastic about mod-cons in general, remember that return temperature limit: to gain the reputed advantage in efficiency, that return temperature absolutely must be kept low, and at this point the evaluation has to turn from theoretical considerations to more practical matters such as the overall cost of the boiler and the installed radiation and controls.

And, of course, all the numbers go out the window if the system isn't maintained!

gennady

attraction of radiant system not in the low water temperature, but in the fact:
1. that floor temperature is too low to initiate convection of the air. hot air does not rise to the ceiling where temperature becomes too high, delta t between air temperature under the ceiling and outdoor air temperature is maxed out and heat loss is at maximum.
2. heat exchange is done via direct heating rays from floor to firm bodies in the room, without heating room air.
3. air temperature in the room with radiant heat is less than one with convection heating (especially under ceiling). therefore infiltrations have lesser effect on heat loss.

radiant heating system produces less losses of the heat.

Bottom line: radiant system is more efficient than steam or convection hot water.

but still convection hot water modulating system and steam systems with trv are very close in efficiency.
My 2 cents.

Paul S_3

@gennady just for my knowledge are you using that 2way iseries as a "injection valve" into the constant circulation loop with the red pump? The valve would provide boiler protection for CI boiler too......how do you size the valve ? Same way i would size injection piping? High delta T...low GPM =smaller piping?

Jamie Hall

@Hatterasguy -- I was consciously simplifying with that fixed temperature -- it is a curve, of course! But it looks, on the whole, as though you and I are pretty much on the same page -- and real world gains of much more than 5% just aren't realistic.

Me, I'll stick with the CI boiler -- but I'm really a steam guy at heart anyway, and @Charlie from wmass keeps Cedric humming happily along at about 85%!

gennady

Paul S said:

@gennady just for my knowledge are you using that 2way iseries as a "injection valve" into the constant circulation loop with the red pump? The valve would provide boiler protection for CI boiler too......how do you size the valve ? Same way i would size injection piping? High delta T...low GPM =smaller piping?

yes, it provides cold water protection and also warm weather shutdown. Cv 8.9. boiler is set to 180 constant temperature. I was tempted to install tekmar 256 to modulate boiler temperature as well, but decided not to overcomplicate the job.

Paul S_3

Thank you @gennady ....i will try this

Charlie from wmass

Guys you need to account for additional maintenance and electrical costs for hot water also. If it is steam or vapor I keep it that way. If it is hot water I use the best efficiency I can find for that system. One size never fits all.

SWEI

Hatterasguy said:

I simply wish one of the manufacturers would step up and use siliconized cast iron together with a two stage gas valve.

I'm assuming you'll want good combustion numbers for both of those firing rates. If there's to be any meaningful turndown ratio, you'll need a two stage air system to go with. A commodity 80+ induced draft furnace train should be relatively easy to re-purpose.