New Boilers for Steam System Previously Converted to Hot Water

jjakucyk

Hi everyone, this is probably going to get fairly long, but it's a complicated situation, so please bear with me.



I live in a circa 1914 4-story walkup apartment building in Cincinnati, Ohio. The original heating system was 2-pipe steam, which I assume was a simple gravity system instead of vacuum. There's 34 units each of about 750 square feet with two main rooms and a sunroom that each have decent sized radiators. Plus there's a kitchen and bathroom with a tiny radiator, as well as one at the bottom of each front stairwell. The exterior walls are solid masonry, so insulation is almost nonexistent.



Sometime probably in the 1960s or 70s the system was converted to forced hot water and storm windows were added throughout. Few modifications have been made aside from replacing broken steam traps and valves, and adding bleed valves to all the radiators. There's a few radiators scattered around with oldish thermostatic valves, but those are the exception rather than the rule.



I got a chance to skulk around the boiler room one day and talk to the maintenance man about it. It's not a pretty situation. The natural gas boilers which I assume probably date from the switch-over are two blue refrigerator-sized forced downdraft units, with 1.5 million BTU input and 1.25 output. I don't recall the brand, but they've had some of their controls replaced, and the panels are all very loose. The draft from the horrendously loud blowers is also coming out through the switches on the front and any gaps in the panels. That's caused some shutdowns due to "low air" as the lights on the front panel indicate.



Needless to say, the boilers are on their last legs. The maintenance man told me the landlord is having contractors over to bid replacing the boilers and the domestic hot water heaters as well. There's two standard gas fired tank water heaters connected in parallel, and because of the size of the building there's continuous recirculation. I'll get back to that in a moment.



There's a few things that are definitely not right with the system, and I'd like to make recommendations to the landlord to question the heating contractors about. For one thing, there's a big problem with the current circulator pump. The old steam supply pipes in the boiler room are about 8" in diameter, but they quickly transition down to about 4" supplies as they branch out to the various parts of the building. The main return is about 4" in diameter too, but again, that shrinks down to 2" immediately upon branching out from the boiler room. The newer pipes feeding into and out of the boilers are 3-4" which is ok as well. The thing is, the last few feet of pipe feeding into and out of the circulator pump are only 1.5" in diameter at best, and there's no flexible connectors.



So the water just races through this pump, which vibrates enough that you can feel it in the concrete floor of the boiler room. It also transmits some vibration through all the pipes and there's a noticeable hum and a faint high-pitched whine in the whole building. Despite the disparity in pipe sizes in the boiler room, it still seems to move the water too fast through the whole system. If you close down radiator valves you hear a wooshing sound like a sink faucet, and if there's even the slightest bit of air in the radiator (the supply enters in the top on one side and leaves from the bottom on the other), the water gurgles inside.



There's also the issue of temperature control. The system is set up for constant recirculation with an outdoor reset, so kudos for best practice on that front. There appears to be an auxiliary thermostat somewhere in the building, but I don't think it works anymore, so it just relies entirely on the outdoor temperature to set the supply water temperature. This works OK, but of course if it's very windy, or cold but sunny, parts of the building overheat or underheat, as you'd expect. So here's what I want to know.



Aside from the obvious benefits of more efficient boilers, how can I best sell the landlord on installing new thermostatic valves on all the radiators, and replacing the few old ones that do exist? That's going to be very expensive as far as labor and potential for breaking old pipes. I know it will make a huge difference in comfort, and it will save more money on the heating bill, but can it realistically pay for itself if the overheating/underheating situation isn't all THAT bad? It would require a little extra plumbing around the pump as well, to prevent excessive pressure buildup when most valves are closed, so that adds yet another expense too. Is it worth the hassle?



What solutions are there for the pump? Based on how the building is piped, you could have four separate zones with their own individual pumps on the return lines, but would that be more expensive than a single larger pump? Would they have chosen a faster/more powerful pump with a small inlet and outlet pipe diameter because it's cheaper than one that can handle a larger/slower flow?



If four zones are created, that could also be a way to better control the temperatures in each apartment unit without having to install individual thermostatic valves on each radiator (4 per apartment unit). However, that could get complicated very fast with the need for mixing valves on the large supply pipes and remote thermostats in hard to reach places and who knows what else. Is this something worth suggesting?



Another thought regarding the pumping and water volumes and such. Have any steam to hot water conversions been done so that the hot water is pumped in reverse through the system? The problem is always about how to get the hot water through those large steam supply pipes, which then causes it to race through the rest of the system. What if the old condensate returns are made the supply? That way it doesn't matter how long it takes for the return water to lollygag its way back to the boiler room. The only problem I can think of with this would be that there's still many original steam traps that don't look like they have an access cover so you can just remove the guts. Would they even allow water to flow in the opposite direction in the first place?



If the new boilers are also going to provide domestic hot water, what's the best way to handle that? I'm concerned because of the recirculation. Almost none of the domestic water lines in the building are insulated, and even if they wanted to, they could only probably get to about half of them since many are buried inside walls. So there's a constant load on the domestic water heaters. I'd be very worried that the boilers in the summer would short-cycle constantly to try to maintain the temperature set point for the domestic hot water. How is this avoided, or what should I suggest the landlord question the contractors about?



So yeah, that did get pretty long, sorry. I hope I've explained everything well enough though. Thanks for any input you can give.

sreja

trvs

i can't help answer most of your questions, but i can just underline your comments about Thermostatic Radiator Valves improving the lives of residents.



About 2 years ago we had TRVs put on all of the radiators in this 14 unit building (about 80 radiators i think).



The difference in comfort has been HUGE -- it turns out there were quite a few units whos valves never opened or closed properly, people were overheating and underheating, etc.  The TRVs seem to have solved all of that (we also replaced all the traps), and the difference has been dramatic.



I can't really address whether it will save you money though -- theoretically it should -- some people who used to open windows will stop doing so, etc.  But if you're building is like ours you might not save that much money if it turns out that you are now heating rooms that people didn't heat before due to broken radiator valves/traps.

Tony_23

pump

The pump issue is well-corrected by installing a Wilo Stratos ECM PD circulator.



Combine that with TRV's and the proper boiler control strategy and mod/cons and your world will be a better place.



That is, of course, assuming they find the right contractor to do the job.

icesailor

You could do a lot:

You could do a lot to improve this but it depends on how much the owners of the building are willing to spend.

If it is a committee doing the deciding, there will be one or two really cheap skates that will be enthralled with the lowest bid which will be to just change the boilers with something like. Everyone else wasted their time.

If you are trying to bid this job, I suggest that you take everything from doing little (change the boilers) to the whole nine yards. Break it up into increasing steps with what you will gain and why. It might overwhelm the cheapskates. Not usually though. Unless you can spend a small amount on the building and it directly effects them and no one else.

There are so many things you can do that don't cost that much and are innovative. You just don't get the opportunity to to them.

Steamhead

I'd look at changing it back to steam

You're probably looking at a situation where the return lines are too small to move the amount of water needed. The volume difference between steam and water is 1700- so when steam condenses back to water, it shrinks 1700 times. That's why the returns in a steam system can be so small. But such a small return was never sized for water. Hence the huge, vibrating pump using a lot of electricity trying to force the water thru.



This is one of many reasons we don't convert steam to hot-water.



This system will probably never work well on hot-water. The typical landlord really doesn't care if it works or not, and we'd run away from such a job. But if yours is an exception, this is what I'd propose.

jjakucyk

No Steam

Converting back to steam is really a non-starter. For one thing, even a vacuum/vapor system that would allow it to steam at a lower temperature would still cost more to operate than hot water. Plus, whether a traditional low pressure steam or a vacuum system, it would require checking and most likely replacing every steam trap in the building, which have probably been gutted or are at least "broken" in the open position. There's 140 by my estimation, plus new vents and such at the end of the supply mains. That's money and effort much better spent on some TRVs, which would probably be needed anyway.



Also, I really do suspect that the current pump is oversized. Since the horizontal supply mains are still insulated, if the flow rate was reduced, there shouldn't be much temperature drop at the farthest point from the boiler room (about 150' away horizontal and 40' vertical). Even if there was, this would be a good argument for adding TRVs throughout the building. With the system set to a slightly higher water temperature, most TRVs would be nearly closed, thus forcing more heat to the remote radiators that need it most.



Here's something I have been puzzling over. With the supply pipes mostly (except in the stairwells) entering the top of the radiator, would it make sense to suggest installing TRVs at the outlet in place of the steam traps, rather than at shutoff valve? I'd be concerned that heat from the supply riser would mess with the TRV. On the other hand, putting it at the outlet might make it susceptible to drafts along the floor, and the pipes might need more modification. What's the best strategy there?

Steamhead

"would still cost more to operate than hot water"

We keep hearing people say that, but where are the numbers?



Where is the scientific study where two systems, one steam and one hot-water, both in peak condition, are tested in the same building?



So far, it hasn't turned up anywhere. All we see are broken-down steam systems compared to new hot-water systems. This is typical of school buildings where nothing is maintained. It would be interesting to see how those new systems fare under such total neglect, but again, no one talks about that.



There were a bunch of discussions about this several years ago, and the challenge to produce the numbers went unanswered. I can post the links if anyone's interested.



The notion that a steam system must always cost more to operate than a hot-water system is a myth, unless the proper study is done. And if it's been done and is out there, we can't find it.

jjakucyk

Steam

That newly converted hot water systems are usually compared to old broken down steam systems is a fair point. I would posit however that the lack of high efficiency steam boilers is a big factor. 86% seems to be about the max efficiency for steam, and condensing hot water boilers can achieve 95%+ efficiency. In residential or small commercial and multi-family situations, that 10% efficiency increase is more than enough to offset the additional electricity usage of a circulator pump and draft fan. I don't know if a condensing boiler would be possible in my building's situation considering the usually high return water temperature. It would also require a new chimney liner, which would be a huge job, as the chimney is practically a smoke stack. Still, electricity is relatively cheap here compared to gas, so the extra cost of operating pumps is less of a factor compared to the boiler's BTU input/output.



Aside from that, steam systems seem to require more babysitting than hot water, especially in big buildings. One clogged air vent or broken steam trap can cause all sorts of problems that someone who isn't living on-premesis and isn't familiar with everything won't be able to diagnose quickly or at all. Dirty boiler water can cause uneven heating, building settling or removed/changed radiators, replace piping, etc. are much less forgiving with steam than with hot water.



Also, without upgrades that should really be done anyway, such as adding TRVs across the board, and because of the building's asymmetry about the boiler room (that 150' run in one direction is countered with a mere 50' run in the other), I simply can't imagine that an intermittently fired steam system could ever heat the building as evenly as constantly circulated hot water. I have little doubt that's why it was converted in the first place, and the apartment leases even have an old clause stating that units farthest from the boiler room may be required to provide supplementary heat.



I do appreciate the idea, but I just feel that it will require too much investment, too much risk, and too little potential for improvement, since the current system works fairly well considering the circumstances.

nicholas bonham-carter

steam to hot water

if those boilers are 1.50 mbtu each, then perhaps they were over-sized. most likely, they were sized according to the old steam boiler.

i doubt if the landlord will have the temerity and smarts to at least consider the possibility of steam, unless he were to consider the cost of repiping the under-sized returns! in fact i wonder if anyone will think of doing a heat survey.

the clause in the lease which "excuses" poor heating performance could be against the landlord tennant laws in many states.--nbc

The Steam Whisperer (Formerly Boilerpro)

True efficiencies and operating costs......

I think you have already touched on some of the issues re efficiency but have not assembled the complete picture and are missing some data.  When comparing the published efficiencies of boilers, they only take into account the efficiency of fuel use, not electricity.  You have pointed out that a very large, power hungry pump must be used for hot water system flow.  This pump is unnecesary for steam operation.  You probably also have additional pumps for the boilers to circulate this water.  Most high efficiency hot water boilers have very small water flow passages, require constant flow that systems with trv's cannot provide,  that require very large power hungry pumps. Next depending on the type of steam boiler (especially when comparing gas boilers), you also eliminate virtually all electrical usage required for draft fans that are needed for "high efficiency" hot water boilers.  I wouldn't be a bit surprised if the total electrical comsumption of the current system is between 3 to 5 kw per hour or 2200 to 3600 kw per month.  Figure out your energy usage costs.  Then most commercial buildings also have demand charges, which for the above loads probably are about $90 to $150 per month of operation.  Add this cost in too.  Now start factoring in these costs and that wonderful 95% efficiency fuel efficiency isn't so great after all. 

Oh, and don't forget that most high efficiency gas boilers are quite complex, with lots that can go wrong, so maintenance costs are much larger than simplier, less fuel efficient designs

Steam boilers do not need to be, and if anyone involved in the design process is using some sense, primitive on/off designs.  Modulating or stage fired steam boilers  have been around for decades.  Combining this type of boiler with TRV's and/ or radiator supply valve orifices offer a tremendously efficient system that provides modulating heat output to every radiator without the potential for freeze ups that hot water systems have.  Again this technology is about 100 years old, so it is nothing new.  And no traps are necessary at the radiators and possibly anywhere on the system,  depending on the sizing of the radiators.

I have high efficiency hot water in my own home and my fuel usage is incredibly low.  However, when moving from my old simple cast iron boiler (like many basic steam boilers today) to a high tech high efficiency boiler, my winter electrical usage has jumped substancially and so have my maintenance and repairs.

Lastly, 90% plus efficiency steam boilers are available on a very limited basis at this time, but more are on the way.

Dismissing steam as inefficient and not cost effective is not based on facts, but on lack of knowledge.  As Steamhead said, no one has ever come up with comparable statistics that show that steam is inherently more costly than hot water.

Steamhead

Your quote

"because of the building's asymmetry about the boiler room (that 150' run in one direction is countered with a mere 50' run in the other), I simply can't imagine that an intermittently fired steam system could ever heat the building as evenly as constantly circulated hot water. I have little doubt that's why it was converted in the first place, and the apartment leases even have an old clause stating that units farthest from the boiler room may be required to provide supplementary heat."



is, again, not based on fact. We have the ability to vent the air from these asymmetrical steam mains based on their cubic capacity, so the steam reaches the ends of all the mains at about the same time, and within a couple minutes of the point at which the steam first leaves the boiler. From the boiler to the ends of all the mains in a couple minutes- that makes a very quick, balanced system. 



Look at the photo in my signature at the bottom of the post- it's a group of five vents forming one of eleven venting stations on a one-pipe steam system in a 32-unit apartment building. That's how it's done. We've cut their fuel consumption by a third so far, and hope to have more-impressive numbers at the end of this season.



That provision in the lease is quite interesting. I've never seen anything like it before- and it shows that system was misunderstood and knuckleheaded for a long, long time.