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Boiler oversizing factor--Siegenthaler recommends max 10% (!!)
@fentonc has very informative thread going on his efforts to optimize efficiency of a very oversized hot water boiler. We're in a similar situation where we have cold-start cast iron boilers that are 3x oversized for our heat load.
I'm just starting to read Siegenthaler's "Modern Hydronics" bible from which some of the boiler efficiency curves in @fentonc's thread were taken (from Chapter 3.9 Efficiency of Boilers). One thing I just came across in that chapter is Siegenthaler's statement on the bottom of pg 77 (in 4th edition of Modern Hydronics Heating & Cooling) where he says that:
" to keep the boiler cycle efficiency as high as possible, do not needlessly oversize the boiler. The author suggests a maximum oversizing factor of 10% of the (properly calculated) heating load. Minimum oversizing allows the boiler to run for longer periods, and thus attain higher efficiency."
I've never heard anyone here quote Sigenthaler's recommendation of only 10% oversize, so I'm mentioning that as an interesting data point in the ongoing discussion/debate about how to properly size hydronic boilers. For now I'm stuck with the boilers I have, but in future I do hope to replace with a properly-sized boiler (or two), and the recommended sizing factors I'm aware of have varied from the 40% oversize recommended by ASHRAE to the various other numbers recommended by the pros here. But I can't recall anyone recommending only 10%.
Obviously you want to be very sure of your design heat loss number if you're only going to oversize by 10%, and I doubt any pro is going to want to cut it that close with a customer. As an engineer who has run the numbers many times, many ways for our 4-unit condo building, I'd be willing to trust my numbers and go only 10% oversize, but if I were a heating contractor I wouldn't feel comfortable installing less than, say, a 25% oversized boiler, and 50% over would make me sleep better. And I doubt many pro's here would want to go less than 40-50% oversize either unless they were very confident that the design heat loss number was very accurate. Usually that can only happen if the homeowner has reliable energy consumption data for several years, and if the building envelope has remained unchanged over that time.
jesmed1
Re: Boiler oversizing factor--Siegenthaler recommends max 10% (!!)
that’s aggressive but mostly moot. Cast irons don’t come in enough sizes to get within 10% that often and modulating boilers can be oversized easily.
Re: Taming an Oversized Boiler - eliminating short-cycling and improving efficiency
What were the things that were tried and didn't work well?
- Adding a 'mild purge', where the circulator was only run until the aquastat differential of 20F was about to kick in. This probably helped a tiny amount, but not in a satisfying way. For thermal purging, go big or go home.
- "Zone Synchronization" - What if you try to solve short-cycling by getting all of your zones to line up their calls for heat? It barely helped the short cycling issue, and made the thermostat control way less predictable because it tied together floors with different heat losses and radiation:heat-loss ratios. Tekmar tried to commercialize this, but there's a reason this didn't catch on. Also, it's very upsetting to other people in the household when turning up a thermostat does not result in immediate action on the part of the heating system.
- "Freeze Protection" - I read about a device on here that would make sure each zone would call for heat periodically to prevent potential pipe freezes when water sits for a long time when it's cold out. I experienced a pipe freeze once, so I tried having each zone run for at least 5 minutes out of every hour, and the result was terrible overheating. There's relatively few BTUs moving around during a post-call purge cycle, but enabling a zone for 'freeze protection' when other zones are actively calling for heat resulted in immediate and significant overheating. Like 4-5F overheating. I think this lasted for like 4 days before I disabled it.
- Lowering the SWT. I can actually heat my house just fine with 140F-120F water, but it did little to address the short-cycling or getting the BTUs out of my boiler after a call for heat. It probably would actually help with the latter if I measured things carefully, as this is what 'outdoor reset' schemes are taking advantage of to increase efficiency, but I never tried lower than 160F-140F, and the purging was a much more effective way to accomplish the same thing.
What other things did work well?
- Heat Pump Water Heaters - I replaced my gas water heater (co-located in the mechanical room next to the boiler) with a heat pump water heater. In the summer it provides 'free' air conditioning and dehumidification in the basement, and in the winter it pulls BTUs out of the oversized CI boiler and stuffs them in an insulated tank with very low loss. The gas water heater not only had lower efficiency than the boiler, but it also came with an always-open flue as well. Whenever HPWH's are discussed, someone usually mentions 'but it's just taking BTUs from the boiler!' - this can really be a feature when the boiler is oversized.
- Temperature setbacks. An oversized system can pump out heat when needed, so recovering from a deep setback is easy. Even with my 60F differential, I can easily recover from a 6F overnight setback in an hour or two. Temperature setbacks save heat by lowering the average room temperature (since the heat loss is proportional to the temperature difference between inside and outside), and this translates into real savings as long as your heating system doesn't get less efficient when trying to recover. With a giant gas boiler, this is not an issue. The all-zone purging scheme also means that water still circulates fairly often, which can prevent pipes freezing (this happened to my 1st floor baseboard loop during a cold-but-sunny day with a daytime temperature setback enabled).
fentonc
Re: Some minor conflicts.
I'm not quite sure where to begin…
First, as said above,, there is no protection for the wood boiler. Those things can, and will, get carried away from time to time. It needs to have its veery own dedicated circulator to the main buffer tank and back, and it also needs to have a gravity circulation dump zone. The buffer tank could be the dump zone, if it is big enough and if but only if, it is arranged with enough elevation difference for gravity circulation.
The way that is arranged is flat out dangerous.
Second, the heat pump also needs to feed the buffer tank. There is no particular reason why it couldn't be controlled by the buffer tank temperature with a simple aquastat set for the best performance from the heat pump.
Then the rest of the system can pull from the buffer tank. Since the wood boiler is quite unpredictable, however, you will need thermal mising valves and individual pumps for the various zones so that they get the water temperature they need.
Re: any risk associated with a properly executed TSP cleaning?
The boiler water chemistry presented in the thread is entirely valid with one major caveat:
Many sectional boilers of the type used for residential heating have, for the last 20-to-30 years, employed elastomer or other types of polymer compounds for sealing the sections together rather than the older "push nipple" approach where a tight metal-to-metal seal is established. The merits and detriments of this approach are discussed in other threads, but anyone considering an alkaline boiler water treatment program should first determine the type of seal present in the target boiler.
Hydroxide alkalinity will damage and eventually destroy any type of polymer seal and is only appropriate for push-nipple sealed boilers. The Weil McLain E-9 discussed above is a 50-year-old push-nipple boiler and can tolerate and benefit from a TSP and sodium hydroxide treatment, where perhaps a majority of newer boilers are gasket-seal boilers that would potentially be destroyed by such a water program.
With that in mind, it is likely that Steamaster Tablets as discussed are probably safe for use in gasket-seal boilers as the active ingredient is primarily of Sodium Nitrite. The formulation of Steamaster does not promote the high pH that results in a hydroxide alkalinity equilibrium. Observed Steamaster pH is in the vicinity of 9.0, below the aforementioned threshold. Sodium nitrite promotes the formation of a magnetite (black) iron oxide layer on the waterside surface which protects the metal from detrimental hematite (red) iron oxidation.
This posting is not meant to attract further comment but is intended as a warning to anyone who might come across this thread via a search engine such as Google.
Binnacle
Re: any risk associated with a properly executed TSP cleaning?
Starting with the results: Brilliant! Steam is much drier and the entire system sounds dramatically better. Sound of water boiling in the vessel is mellow and almost inaudible. Much less swooshing in the risers and radiators. Sound of steam entering the most troublesome radiator actually sounds dry, if such a thing is possible. Bouncing of level-gauge water is almost gone. Probably the planned spring opening of the skim port and skimming will move the boiler's behavior into the realm of perfection.
Now for the effort:
Let the boiler cool for three hours after a cycle, water temp was 130 degrees, then drained and filled it with fresh hot water via the top relief-valve union. Not much rust and other junk in the water due to earlier drains and fills and keeping the pH between 9 and 11 the last few weeks.
Added five ounces TSP and ended up with a pH of 10, P-alkalinity of 222, M-alkalinity of 660 leaving OH-alkalinity zero with a big P*2-M negative bias of 216.
So it occurred to me that the two-cup prescription takes into account that much of the TSP will immediately react with oil and other contaminants and the high alkalinity seen with pure water and 0.25% TSP in a pot is not representative. Decided to go big and ended up adding 20 ounces (2.5 cups) of TSP in two increments. Ended up with
P 672
M 1665
OH 0
pH 11
which still has a substantial way to go before becoming caustic. Found a recommendation for cleaning with 5000 ppm TSP and 20oz in 20
gallons is 6000 ppm--not way off that
http://www.steamesteem.com/feedwater/boiling-out.html
What makes TSP safe for an old system is a) not supplementing TSP with caustic lye (sodium hydroxide) and b) monitoring the pH and not letting it get past 11 or so. What's happening here is that the boiler is, in effect, being washed out with mild detergent solution.
Kept the water at between 190 and 200 degree for two hours after the final TSP addition, and the entire cleaning ran for about four hours.
When draining saw virtually zero particles and no rust whatsoever--almost perfectly clean. Drain water had a dark tinge indicating, I believe, dissolved oil.
Discovered through recent reading that TSP is considered an excellent boiler water additive. Strong positive experience reported right here on HH:
http://www.heatinghelp.com/forum-thread/91982/Sodium-Nitrate-in-Steam-Boilers
The US Navy uses primarily TSP and some additional soda ash for all marine boilers, preferring to keep the pH close to 10.5 to minimize the risk of tiny eddies of caustic water in the nooks and crannies of their large boilers. I prefer a pH of 11 for the small low-pressure boiler here as do many others. Keeping the concentration of phosphate in the boiler at around 60 ppm does an excellent job of protecting the boiler from various forms of water-related nastiness.
After filling I added three ounces of Savogran to obtain about 60 ppm of phosphate (6.9g per 4oz noted on side of box) plus three Steamaster tables. After a day two teaspoons sodium hydroxide dissolved in a quart of water to bring the caustic up. Now have
P 342
M 600
OH 84
pH 11
and after another day plan on another teaspoon of sodium hydroxide or two to bring caustic into the 150-300 ppm range.
I've decide that sodium nitrate from the Steamaster tables is superfluous here since I will monitor the pH and anything over 9 or so completely inhibits oxidation regardless of how the pH is achieved. Also switching to pure TSP with the idea that total alkalinity can be kept lower with optimal phosphate and hydroxide alkalinity if the sodium nitrate and sodium sesquicarbonate are eliminated. So in a week or so I'll drain and refill again, adding just pure TSP (on order) and sodium hydroxide. Draining after running with some phosphate should knock down further any oil residual left behind by the cleaning. As I understand it the oil will end up as soap in solution and depart peaceably with the drainwater.
I would still highly recommend Steamaster tablets as the treatment of choice for the less-obsessed. The sodium nitrite works by scavenging dissolved oxygen in boiler water, thus inhibiting rust, and by biasing the pH to somewhere between 9 and 10, a reasonable range especially for the typical situation where no one is monitoring the water. However I agree with the HH consensus that one-to-two tablets per 100 MHB or 10 gallons of water is the correct dose and the Steamaster label directions are excessive.
A note for anyone who contemplates a similar approach: Even one teaspoon of sodium hydroxide dissolved in a quart of water results in a highly caustic solution with a pH up around 14. Even when pored into vessel and mixed with the existing boiler water, the concentration might still be high enough to do some damage. So one should always follow the addition of hydroxide solution with a fair amount of make-up water or recycled blow-down water to disperse the caustic solution quickly. Then immediately cycle the boiler to further disperse the hydroxide. The Navy considers it too risky to use sodium hydroxide for the aforementioned reasons. This makes sense considering the high capital cost of their equipment and the extreme rate of job assignment turnover in ranks as crew are trained for various tasks and rotated constantly. Too easy for inexperienced or careless crew members to damage a boiler.
Attached are a graph that show the fundamental pH chemistry of water (found at http://www.sprungtraining.com/messageboards/tabid/73/forumid/14/postid/175/view/topic/default.aspx) and Navy document showing the effects of pH in boilers. In addition here is a helpful paragraph from a Navy boiler operations manual. Much additional information may be found by searching on "COPHOS boiler".
https://www.google.com/search?q=COPHOS+boiler
-----
Boiler Water
The boiler acts as a concentrator for all the materials which the feed system pours into it. All contaminants remain in the boiler and produce damaging conditions. In order to minimize these, boiler water treatment programs have been established. The present standard Navy treatment is based on a regimen known as coordinate phosphate – pH control (more simply, COPHOS) to serve several purposes:
1. Maintain the pH and phosphate levels so that caustic corrosion cannot occur.
2. Maintain the pH sufficiently high to limit corrosion and to protect against acid-forming magnesium reactions by forming magnesium hydroxide (Mg(OH)2) sludge.
3. Maintain a phosphate residual in the water sufficient to precipitate calcium and magnesium as phosphate sludges which are less adherent than scale.
Binnacle
Re: 3 way valve stopping flow?
I think you are asking too much of the one mix valve. 3 low temps zones should = 3 mix valves.
Another option would be a Taco injection set up. This will allow a significant amount of more flow.
kcopp
Re: I'm getting solar panels. I'll let you know how it goes in this discussion thread.
I used one of those to get my annual usage numbers up prior to sizing! (And still have one of course)
Re: Let me try this again, this time with a 1" supply pipe. Surely that will cause trouble!
Thanks for all the replies everyone. I have a few of your questions to answer, I'll hit them all in one reply here
https://www.tfi-everhot.com/anti-surge-steam-separator.html
Does anyone ever recommend those to homeowners with surging problems? That might be less costly than replacing all the undersized/badly installed near-boiler piping. Because as you showed, if you have clean dry steam, pipe size doesn't matter much.
I personally wouldn't recommend this item. I find it unnecessary because every boiler can run cleanly without carryover if it's just piped with the manufacturer's recommendation. And as my videos are showing, you can be way below those recommendations and still be fine.
PhilKulkarniMember Posts:97December 24
I would appreciate if someone clarified what good water quality means. If it means no oil on the water surface and a PH above 7 then I have it in my 63-03 boiler.
To me, it means water that boils cleanly—no oil, and no other contaminants that would cause carryover.
The next term I seek clarity on is surging. If it means the water line fluctuates more than +/- 0.25” when the boiler is operating then I have no surging, but my water line is approx 2.5” from the bottom of the sight glass. Does this mean I have significant carryover? I do get a fair amount of rust despite using 8-way. I am using distilled water to refill after draining the rust once a month. Could the carryover be caused by suspended rust particles?
I think you should start another thread with your issues listed and your questions. There is kind of too much to unpack and address here in my thread. But I will say this: If your water line varies less than an inch during your call for heat, then you aren't surging/carrying over to a significant degree and you are probably OK. Don't drain your boiler once a month. I think carryover can occur due to too much "gunk" in your water. And why is your water line 2.5" from the bottom of the gauge glass? That is lower than I like to have it for sure.
EBEBRATT-EdMember Posts:19,553December 24
The Thermoflow thing is just a "slow place in the road" to let the steam rise and the water to drop out. Same thing a header does.
I have always felt that riser size may be more important than the header. Why use the header to separate the water and steam/? Keep the water in the boiler where it belongs.
This is a great point. It is my belief that if you pipe it as recommended, the header will never even be necessary. I have a ton of videos showing no water even getting into the risers, let alone the header. This is why tons of boilers don't even have headers and still work great.
ChrisJMember Posts:17,067December 24edited December 24
I've personally watched an improperly piped boiler (no header at all) blow a ton of water up into the main and shutdown on low water. Would this happen if it had a proper header and equalizer, or would it all return quick enough to prevent the LWCO from tripping?@ethicalpaulHave you tested that yet? I can't remember.
If the boiler was carrying over a bunch of water then my experiments show it had "bad water". In all my videos, we can see that when the water is OK there is nary a drop that appears in the supplies where my sight glasses begin. On my old boiler it could run with bad water getting carried over to the main and returning back via the return without triggering the LWCO, but depending on the amount of main and amount of water the LWCO could definitely trigger during heavy carryover.
jesmed1Member Posts:1,277December 24edited December 24
If headers are successful at removing water, why did Dan say in LAOSH that many of the steam guys he met were using anti-surge tanks? Maybe in theory headers were supposed to be removing all the water, but in practice apparently they weren't. Maybe the surging was so bad due to poor water quality that it would overwhelm even properly sized/designed risers and headers, and the anti-surge tank was just a band-aid for dirty water?
Just because Dan said many steam guys were using anti-surge tanks doesn't mean those tanks were necessary or a good idea.
If the water is good, the header doesn't even see any water. My videos have been showing this for several years, since I installed my new boiler. Those guys were either experiencing, or were afraid of bad water causing carryover. In my video where I added a little cutting oil into my boiler, the carryover was pretty bad (not bad enough to overwhelm my drop header's ability to separate the water). If the water is REAL bad, like sudsy or really oily, it can definitely overwhelm a manufacturer-specified header with carryover. In my opinion, all those guys had to do was properly wash out and skim every new boiler and they wouldn't have any problem.
jesmed1Member Posts:1,277December 24@ChrisJ
I was commenting on@PhilKulkarni's third paragraph where he was commenting on the effect of using a 3-inch riser vs. the 2-inch spec, and he said "Yet, despite a 55.6% reduction in exit steam velocity, I get wet steam- steam that is not 100% vapor."
I saw that and forgot to mention it. My question to @PhilKulkarni would be: how do you know you get wet steam that is not 100% vapor? As I hope you all know, I do not like the term "wet steam"—please state the behavior or phenomenon that you are observing instead of this term that is at best a catch-all and at worst, completely erroneous.
EastmanMember Posts:968December 24
Great video. What's next?
Thank you but dang it's Christmas haha
EBEBRATT-EdMember Posts:19,553December 24
I just remember the Weil McLain video with the glass piped boiler that is still (probably) circulating on you tube it's probably 15-20 years old. That thing was throwing a lot of water.
It is a mystery I have seen horribly piped boilers with no kind of water treatment or blow down work absolutely fine. You stare at them and say it can't work but it does.
The Weil-McLain guys were just putting on a show. They ran the PSI up to 5 or 10 and then threw open the exit valve. No boiler could ever avoid carryover with that practice. When the interior of the boiler went from whatever pressure it was to atmospheric pressure, all the water in there which was well above 212F more or less instantly flashed to steam and shot out.
I think if there were a sight glass on those poorly-piped boilers, you'd see that there was simply no water being thrown up the supply just like we see on my boiler.
STEAM DOCTORMember Posts:2,509December 24
Need to be totally honest. I didn't watch the video (yet). I have long wondered about the 15 ft per second rule. That rule was "established" in a previous generation, when steam boilers had humongous steam chests. If those boilers needed piping that would sustain 15 ft per second, then what would our boilers, with their relatively tiny steam chest, need. 10 ft per second, 5 ft per second..... We all know that's not the case. I think a lot of the old rules of thumb, were instituted to cover all types of situations. The idea is basically give blanket rules for everything, and then you will always be safe. Will cover for bad water quality, overfired boilers, under piped or poorly boilers, undervented systems, tiny residential and humongous commercial and everything in between. Sort of like the speed limits. They don't always make sense. We all know that when it's 2:00 in the morning and the roads are totally empty and clear and straight, the rush hour speed limit doesn't make much sense. But it's one blanket rule to cover all scenarios.
This exactly matches my thinking. I think their engineers were quite conservative in order to give everything the best possible chance to work. And when the water is good, we see boilers with even crazy bad piping work. When the water is pretty bad, boilers still work. Only when the water is really bad (oily, sudsy, gunky) do we see carryover that is bad enough to make the level in the gauge glass drop.
Re: Heating and Cooling Options for 1850s Greek Revival New York
Cedric's home is a 7,000 livable square foot house, built originally around 1780 as a pretty typical post and beam four square and added onto as recently as 1893. It is on the National Register of Historic Places — which is both a plus and a minus. Mostly plus.
Steam heat (1930, Hoffman Equipped, mostly unaltered) plus a minisplit in an apartment. Mostly uninsulated, as it just isn't practical. Almost all windows are original; in one small area some top end modern windows were installed about 30 years ago. They have already failed; won't make that mistake again.
Someone up there mentioned spray foaming a rock and mortar basement wall. Be careful. If you have any water intrusion, yo may regret it.