Bypass for a Buderus G115/3 boiler?
After looking at a lot of boilers as potential replacements for our oversized WGO-5's, I'm leaning towards two Buderus G115/3's for our 4-unit condo building. The building is set up with two cast iron gravity conversion systems fed by two boilers, and although we could heat the entire building with one G115/4, the other owners like the idea of keeping two boilers so that, even if one goes down, we still have heat in the other half of the building. Plus, our heating oil company has experience with Buderus and likes them, so they would do a good job on the install, I think.
So we will probably go with two G115/3's. Although the WGO-5's are still doing fine, I'm trying to plan the G115/3 installs and get a BOM together for pricing when the time comes.
The major concern is going to be return water temp. We have high water volume (100+ gallons in each system), and the relatively low output of the G115/3 at 85,000 BTU/hr gross is going to take a very long time (probably 45 minutes or more) to raise the average water temperature from 65 deg cold start to 120 degrees average, the point at which return water temperature starts getting high enough that condensation isn't a concern. (The Buderus manual specifies 122 F, or 50 C, as the minimum desired return temp).
Even though our WGO-5's have been running for 30+ years with low return water temps with no observable ill effects, I don't want to take that chance with a brand-new lower mass boiler. So I would rather plan for overkill on the return water temp protection. The Buderus manual requires a bypass for high water volume systems like ours, but their piping diagram shows only a 3/4" valved bypass, which I don't think is going to be good enough.
@Ron Beck has a new website (see below) with a good explanation of boiler bypasses. He mentions an ESBE Thermic valve that might be a good solution for us.
The ESBE spec sheet has a number of different schematics showing different applications. The one that's relevant for us is for gravity conversion systems, as shown below.
It looks to me like this is basically a primary-seconday arrangement. The ESBE valve has different thermal cartridges you can select based on your application. A 131 F (55 C) degree cartridge would stay closed for about the first 5 minutes of boiler cold start, until the 10 gallons or so of boiler water heated up to 131 F. Then it would begin to open, keeping the mixed return at or above 131. The valve is designed to open fully at an 18 degree F (10 C) delta, so fully open at 149 F (65 C). But since our water is never going to get that hot, the valve will never fully open.
Meanwhile, the secondary loop circulator circulates water that's cold at first, but which starts heating up at around 5 minutes when the ESBE valve begins to crack open. allowing some hot supply water to flow to the radiators and to return to the boiler through the ESBE.
So in this scenario, the boiler would reach safe return water temp of 131 F within 5 minutes (Buderus manual requires within 10 minutes) and will never drop below 131. Meanwhile, the colder water in the secondary loop slowly heats up but will most likely never exceed 120 degrees average because of the high water volume, and the massive amount of cast iron radiation.
Does this sound like a good plan?
Comments
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YES
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Thanks Ed. I see you're getting paid by the word today. 😄
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I'm sure @hot_rod will be able to provide some good advice.
Perhaps a hydro separator could work? The boiler will have its own circulator and the zone circulators will only be energized when the temperature is above 130-135⁰.
Maybe a variable speed injection pumping setup would work as well?
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The hydro separator might work, but the zone circulator (only one zone) might run very stop-start every time a slug of cold water from the secondary loop hit it and reduced the water temperature?
The thing I like about the ESBE schematic is that the secondary circulator runs continuously regardless of temperature, which means there will always be a very even distribution of BTU's throughout the secondary loop, no matter what the primary loop is doing.
The variable speed injection pump could work too, but a Taco variable speed controller is $500, and I don't like the idea of relying too much on electronics for the bypass protection. I like the ESBE valve because it's all mechanical, and should be very reliable. So all I need is the ESBE valve and a second circulator. Both circulators run continuously, and there are no electronics involved, which appeals to me on the KISS principle.
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If you want a sure fix I would use a motorized 3 way valve (like a Belimo) with an accurate control (like a Johnson A350) with a sensor on the boiler return water. Its a few bucks more $ but is a bulletproof fix.
We installed 3 Buderus MOD CONs to heat an outdoor Insulated 300,000 gallon water storage tank for fire protection water in a paper mill. that was previously heated by an old Bryant 1,500,000 input boiler with no return water temp protection.
We put in (3) 200,000 Buderus and set the return temp at 86 degrees. The condensate actually poured out of these boilers and most of the time only 1-2 boilers were needed.
So we had cut the boiler input from 1,500,000 to 400000. They used to keep the tank at 90 degrees as that was the lowest setting on the old aquastat. We kept the tank at 48-50 degrees and calculated that it would take a week before the tank would even start to ice over if all the boilers failed.
I think the job paid for itself in less than a year. We used 1 three way valve for all three boilers.
Each boiler had its own circulator. Came off the common supply header to the three way with the hot water. The common return to the three way and the mixed return to the boilers. The flow through the three way varied depending on how many boiler pumps were on.
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With a mix valve, you won't be able to do a shutdown thermal purge. I guess a motorized one could be configured to allow flow when the boiler is off.
I'm a fan of KISS, simple bypass. One pump, no valves, no electronics. You will need more than 3/4", I've run into this before where the bypass was not big enough and had to restrict to house feeds to get enough flow through it.
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Thanks, I didn't think about the thermal purge.
I would like to do a simple bypass as you suggest, but here's the problem. Buderus wants 122 degrees in the boiler within 10 minutes. If I set up a simple bypass to do that, it's about a 60 degree temperature rise (from a cold start of about 65 degrees) in 10 minutes. But because the simple bypass has only one "setting", the temperature rise is going to be roughly linear. So in another 10 minutes, the temperature in the boiler will rise another 60 degrees. Now it's 180 degrees, hitting the high limit after just 20 minutes.
But because we have such high water volume and this will be a relatively small output boiler, it's going to take 1+ hours for the Tstat to satisfy. So for the last 40 minutes of the boiler run, the boiler will be bouncing off the high limit, which doesn't sound like a good idea.
Maybe I'm missing something, but that's why it looks to me like we need some sort of active control over the bypass, be it the ESBE thermic valve or an eletronic valve control.
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You could simply use a hydrostatic with circulator hold off and/or a 3 way valve
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If that set up requires two circulators , Pipe primary secondary would make the system sing . If you have the room for the pipe work..
If you don't have the room .The return on the 115 is 1" , 3/4" system bypass will be fine.. You may not need it but still put it in ..
The system will run in long cycles and will only heat up to the temperature needed for that time ..
There was an error rendering this rich post.
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Thanks, my one concern is the tight space. We will have to get creative to find room for the second circ and bypass, but I think it is possible.
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@Kaos has the right idea. KISS
I would like to add to your KISS in order to make one boiler be able to heat all 4 condos.
The consensis of the owers of the 4 units is that having 2 boilers is better than having only one
I would add to that concept that having 2 boilers where one of them can heat all 4 units in the event that the other one goes inoperative at any time.
If you size both boilers to operate up to 70 to 75% of the load each, then you will have an even more efficient usage of resources. Only on the extreme cold days that make up 20% of the winter will the second boiler need to operate. If you ever have a situation where one boiler fails during extreme cold weather, the building can heat to 75% of the needs on one boiler, and that will protect the building from freezing pipes.
The benefits for this system would be
- You can use one smaller 115-3 to do the entire building for most of the winter
- Less wear and tear on the boilers since only one boiler at a time will be operating during most of the season.
- When the system is down for the installation you can repipe so each unit has it's own thermostat (optional)
- Spare parts are identical for both boilers
- Lower fuel consumption by staging the boilers
- If you elect to use only one thermostat for the entire building (optional) then you can keep the piping simple.
This is the ultimate KISS piping design
But I suggested this when you first joined our little club. You are not trying hard enough to convince the other owners.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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looks to me like the circs are in series. Why wouldn’t the second circ just pull from the boiler not the bypass when the valve starts to open. And when the 3 way is wide open, or closed to bypass, seems you just have two circs doubling the head?
I don’t see it being a P/S piping? Why do you need two circs on a low pressure drop boiler on a low pressure drop gravity system. Seems like it will be grossly over-pumped piped like that.
Bypass piping alone has no way of knowing or responding to temperature changes. That’s the whole point of a 3 way thermostatic, it has the intelligence to do the right blend.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
@jesmed1 that why I like the Belimo valve with the Johnson A350 control. It can put out 0-10v or 4-20MA. On start up with cold boilers that valve will modulate the return temp to 120 or whatever you set it at. It will take a while to heat on a cold start. I would use a two-stage thermostat to control the boilers or maybe 2 Ecobees if you can switch them to alternate the lead boiler and keep 1 boiler on lag.
After a little adjusting of the modulation rate in the 350 control this will track perfectly smooth, This works great with MOd Cons.
As long as your not going to exceed the temp rise from the return to the supply that the boiler MFG wants.
The only way to really do boiler protection is to have a valve with a sensor on the return water. Johnson makes a well for the 350 control sensor or you can strap it on the pipe.
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What @HydronicMike mike said. Bypass with circulator hold off. Use a digital aquastat for thermal purge as those can be set with high differential. Circ turns on at say 150F, off at 80f. Heat call resets circ aquastat.
Bypass is set so when circ is running with your expected low RWT (probbly around 80F), the boiler sees 130F. That will get you a supply swing from 150F to 180F and return swing from 80F to 110F. This gets you quick boiler warmup and should keep it from bouncing off the high limit.
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@hot_rod… Getting the boiler hot enough to close the mix to the return does not seem like that is going to happen with the way @jesmed1 explains the current system. So I don't believe that the individual pumps will ever be pulling from a closed valve. And each boiler has its own pump so the boiler that is not operating will not get any return water from the system or the other boiler as long as there is a IFC in each pump. (not shown)
The system will operate by gravity past the boiler. If there are no zone valves to separate the units and the system is balanced properly (some valves may be needed to do that) then I see no reason for any other components. If @jesmed1 wants to keep the existing expansion tank with the Airtrol® tank fitting, all he will need is a central location to remove the air from the two boilers to direct it into the PONPC tank. I thinks this is very simple. The pumps are parallel to each boiler separately, not in series. The only time both pumps will operate is when there is extreme low temperatures. There may be a lot less cycling of the burner and the circulator(s) with this simple design.
The oil burner(s) should operate less with smaller firing rates that the existing. This is the KISSest of all KISS designs.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Trying to absorb 5 different plans from 5 different heating pros is like trying to catch 5 footballs at the same time…and I can't run that fast. 😅
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If you are trying to catch footballs, you need to talk to @Mad Dog_2
First thing you need to do is decide if the two boilers are going to stay separate to each pair of condos. one boiler for each side, (which is silly for several reasons) or one system with 2 boilers that are staged to the load as needed.
If you can do the whole building with one of the WGO5s I would look at doing that before you even need a new boiler. Using 2 oversize boilers at the same time when all you need is to add a few pipes and valves this summer, to cut your oil usage by as much as 20% next year, would be worth it. That is my first step if I were in your shoes. Then when you actually need a new boiler in 2 or 10 years, the piping is already done.
The next step is to see what it will cost to remove some of that big piping in the basement. Decide which radiators are first floor and which radiators are second floor and set up two different smaller diameter mains to feed each group of radiators. The scrap value of the 3" iron pipes will pay for more than half of the new piping, and it can be done in 1" PEX with 1/2" branches to each radiator. Use a reverse return design. (now you are getting into a bigger expense to zone each condo) Losing all that water will reduce some of the heating expense wasted on all the extra water. Now each owner can be comfortable with their own thermostat.
After you make the decision to make 4 zones with a common boiler for all, 2 zones with a common boiler for all, or leave it as 2 systems, then you can choose the best near boiler piping design. Sometimes getting the numbers together from a professional to do 3 different things will be difficult. No one wants to do that much homework for free. So perhaps you can draw up the specifications yourself using what you have learned here and using accepted engineering principles you can offer these specifications out for bid. Once you have the bids back you can look over what it will cost to do each of the ideas. Then assign a savings in fuel usage for each job and amortize it out for 3 to 5 years and see if it makes sense to do the zoning the right way. or leave it as is.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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the drawings I have seen in the past from ESBE with that bypass, .always have a throttling valve the bypass to do some flow balancing , as I recall
The thermal purge, complicates the use of the thermostatic valve, as does 4 zone pumps, if that is your current thinking?
Tekmar has a boiler staging control that brings ODR into the mix in addition to multiple way to stage and rotate boiler run times.
I don’t have an issue with KISS as long as it covers all your objectives.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
I like the Tekmar stuff for ODR and boiler staging. But I didn't suggest it for the KISS reason. If it were me in @jesmed1 situation, I would look at using that stuff. They are pretty simple once you understand what each device is doing.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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I like your plan for the cross-strapping. If we do eventually change to the Buderus G115/3, each of those has a gross output of 85,000 BTU/hr, and the entire building's heat loss is only 100,000 BTU/hr, so one G115/3 would already handle 85% of the design load, which is most of the heating days in the season.
Also, I like that we wouldn't have to do primary/secondary, which is a pain both for complexity and real estate. We already have 6 supply branches and 6 return branches coming together above two boilers side-by-side, so there just is not a lot of room for adding more circulators, etc. So if we could just continue using one circ per boiler, on the return, that would solve a lot of problems.
And, just FYI, I finally broke down and took out the plain steel tank and the Airtrol that I installed two years ago, and installed an SX-40V with Caleffi Minicals on the air separator ports of the WGO-5's. The SX-40V now handles both boilers, and is working great. I have the pressure set at 15 psi, and it never gets above 18 psi even with both boilers hot. So that is one more step towards the modern age. 🙂 I figured when we install new boilers we can put in "real" air separators, but for now the Minicals should work.
We do need to keep the two sides of the building zoned separately, with one thermostat per side. I know you made a diagram before showing that, so I just have to go back and find that. So we'd need a zone valve on each side. But I assume the bypass with the ThermoProtec would work the same way.
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In order to sell the idea to the other 3 owners, you need to have hard numbers that say
Spend $$$ for the control and save $$$ on the oil usage.
Spend $$$ on individual thermostats and zoning. Save $$$ on oil usage and have better comfort control
Spend $$$ on replacement boiler. save $$$ on oil usage
Spend $$$ on combining the system so one boiler can do the whole building. Save $$$ on fuel costs.
Without having hard numbers to sell the project then you have no way to promote the plan of action that is in their best interest. One hard number could be. Don't do anything and spend $$$ on oil like we already are doing, then when the boiler breaks down, that side of the building will spend $$$$ on frozen pipes and inconvenience and dealing with insurance company cleanup and possible loss of coverage when the insurance company drops you after that claim.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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to add more confusion, perhaps. Take a read through the possibilities with the 261
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Thanks, Bob. You guys are way ahead of me, as usual!
The biggest problem here is that I may be moving in a year or two, and once I'm gone, the other owners have no interest in or understanding of the heating system, so it has to be as simple as possible. It's taken me several years of learning from you guys just to get to a level of basic competence, and I was an engineer to start with. So while I would love to do all this stuff if I had more time and $$, for the good of the other owners I just need to focus on doing the bare minimum for simplicity and reliability.
That's why I'm trying to pre-plan for the boiler replacements, because once I'm gone, the other owners are at the mercy of whatever our oil company tells them, and I just want to make sure we get the boiler sizing, type, and bypass plans right, which seem to be the major factors that could get screwed up.
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@EdTheHeaterMan said:
"If you can do the whole building with one of the WGO5s I would look at doing that before you even need a new boiler. Using 2 oversize boilers at the same time when all you need is to add a few pipes and valves this summer, to cut your oil usage by as much as 20% next year, would be worth it. That is my first step if I were in your shoes. Then when you actually need a new boiler in 2 or 10 years, the piping is already done."
I may be able to get that done this spring. But as I mentioned above to Bob, I may not be here for much longer (may be moving) so while all your other ideas about removing the large-diameter pipes, etc, would be great, I don't think I'll have time for all that. So first I'm just trying to get a "KISS" plan for boiler replacement in case I'm not around. So at a minimum I just want a fallback plan with two G115/3's piped basically the same way as the WGO-5's, which I know is not optimum, but unfortunately it doesn't look like I'm going to have the time to do much more.
But if I can sell the other owners on repiping the WGO-5's this spring, and if I'm still here to manage it, that would be a sensible next step.
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You are moving?
Why bother with the system at all? It won't be your problem after a while.
You just need to find someone like the other owners that will love the place as is. The heating system is just one of those things that is there and will need to be addressed as needed. People look at Kitchens and bathrooms and the number of bedrooms.
Think about proper staging of your unit in order to sell it a the profit you deserve for the work you did so far. That stuff you did for the heating plant will not make you any $$$ on your resale value.
Remember there is no profit in being a nice guy. It just makes you feel better about yourself and your life. I help here for the fun of it, not for the profit. But you need to concentrate on your next move and that is going to cost $$$ for the new place and the movers and the settlement costs and the like.
And of course, you will be looking at the heating plant of the new home with the additional knowledge you learned here. You are a better person for your time here. Good luck with your new place.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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According to Buderus, you can't shock the block, and it isn't effected by low return water temps. 1.25" supply, 1" return. Some kind of silicone infused CI. And most Buderus packages come with the Hydrostat 3250 Plus or the Beckett Aquasmart. Both offer condensate protection.
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Thanks Ed. Let me qualify. I'm hoping to buy a fixer-upper house and move within the next year or so, but I haven't found the right house yet, so it's still somewhat speculative.
The "why bother" answer is that my sister is one of the other owners, and I consider the other two owners friends. So I want to help them out as best I can before I leave. Also, I've spent all this time learning how the system works, and I don't want that time and effort to go to waste. So if I can at least leave them with a good plan that they can hand to the boiler installers when the time comes, that will make me feel better.
No, there is no profit in being the "nice guy." But I have all I need in life, and when I go, I can't take anything with me except the satisfaction of a life well lived, which to me means having used my abilities to help the people around me. And I suspect you think the same way, or you wouldn't be generously giving of your time to strangers like me.
I am definitely a better person for having been here and learned so much from you and many others. Thank you!!! I will continue to hang around and learn as long as I'm still breathing. 🙂
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Thanks, I'm not worried about shocking the block, but I am worried about condensation after having been warned against it so many times.
The problem is that we have a large water volume system (100+ gallons), and an aquastat can't change the physics that says it will take 45+ minutes for a G115/3 to raise all that water from room temp to 120-130 degrees. So we need a bypass, and then the question is how to do the bypass. So far it seems there are 3 options: (1) thermal mixing valve, (2) active control of motorized valve, or (3) aquastat set for circulator hold-off.
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An ODR control is not needed on this system . The high mass radiation and proper size boiler the boiler temperature will find its own sweet spot . The only time it will reach limit is the coldest day of the year … Buderus insulation instructions also points this out .
There was an error rendering this rich post.
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I understand now @jesmed1, you are stuck with this place until your sister moves out…. Never work for Family…. UGH! …at least don't expect to be paid for that work …LOL
So we will be looking at your progress for some time after you move out.
Early in my career, I have converted a 4 unit building from a single boiler system to a system where each unit paid their own gas bill. At first the owner of the building purchased 3 gas boilers and I connected them to the perspective radiators while capping off the unused branches of the original system. The furthest and hardest system to disconnect stayed connected to the old gravity piping system and retained the old oil fired boiler. When the three tenants with low gas bills compared their bills with the amount of oil the one tenant was using, that caused the landlord to add the 4th gas boiler the following year.. Go Figure!
I guess that natural gas is not an option at your location, since there is no mention of using that option in the time you have been with us.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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@EdTheHeaterMan LOL, about working for family! I think we've all been there…but I'm happy to do it.
Also LOL about the gas conversion. I did look into converting about 2 years ago. You may have missed that episode…we would have needed a new chimney liner, and then the plumbers I called gave us ridiculous numbers to run 20 feet of new gas piping from the meter in the basement to the boilers, and then no HVAC company wanted to give me numbers on swapping burners, because everyone wanted to sell me a new boiler. So it never went anywhere.
As it turns out, probably a good thing, because the gas companies here in the Boston area had a major rate hike this winter to cover infrastructure costs, and some people had their gas bills double from $300 to $600/mo, so it was a big deal. The gov got involved and forced the gas companies to backtrack somewhat, but it's still a big hit for gas users. And heating oil prices have been dropping, to the point that we're now at price parity for heating oil BTU's vs. natural gas BTU's.
So it's a good thing I didn't convince the other owners to spend $10k+ on gas conversion!
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I think you were commenting on the ESBE valve diagram I put in my first post, not on @EdTheHeaterMan's diagram with two boilers? Below is a slight mod to the ESBE diagram, which hopefully clarifies how that ESBE piping was supposed to work.
To explain where this came from, I first read about the ESBE valve on @Ron Beck 's website comfort-calc.com. He has a diagram on his site that he made of the ESBE valve piped primary/secondary. His diagram is basically the same as what I've showed below by slightly modifying the ESBE diagram to add closely spaced tees. I didn't want to poach Ron's diagram, but this is basically the same thing.
Hopefully that clears up the confusion about what I meant when I said the ESBE diagram appeared to be a primary-seconday arrangement. They just left out the closely spaced tees, which I've added below.
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I don't know that your system wants or needs P/S, but here is an option w
ith a 4-1 sep.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
@hot_rod OK thanks.
Is this a "4-1" separator? I assume the "1" is the end port for the air eliminator?
https://www.supplyhouse.com/Caleffi-548007A-1-1-4-NPT-Union-Hydronic-Separator
I don't think we have room for a vertically mounted. What is the benefit of the hydro sep vs. closely spaced tees, which would be easier for us to fit?
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Post a few photos of the boiler room ..
p
There was an error rendering this rich post.
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For your viewing pleasure. Two WGO-5's, each heating half the building through gravity conversion cast iron rads. Each system has 100+ gallons water. Boilers currently set up for 1.2 gph input each, or about 168,000 BTU/hr input, but because our heat loss is so low, we only need 50,000 BTU/hr per boiler on a design day.
Because of high water volume and large radiation (about 500 sq ft per boiler), boiler will typically run 30-45 minutes once every 3-6 hours, with average water temp of 130 or so when Tstat satisfies.
Boilers are piped identically, with returns on left and supplies on right. Each supply feeds up into 3-4 large-diameter gravity conversion branches, and each return comes down from the same number of large-diameter return branches.
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A 4 in 1 sep gives you air, dirt, magnetic and hydraulic separation in one device.
I don't see any air removal other than the auto vents?
These show as mod cons, but same piping concept for multiple boilers into a hydraulic separator. With zone pumps.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
PS piping and hydraulic separation makes sense if you need zoning, otherwise you are installing an extra pump for no reason.
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