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Two different sized condensing boilers cascaded. Big problem?

mabo
mabo Member Posts: 20
edited October 2017 in THE MAIN WALL
Hi All,

We bought a house recently and in process of servicing our boilers: a cascaded Triangle Tube Prestige 110 and a Triangle Tube Prestige 175, the tech noted that they should have been put in with the same size. Manual says that they need to be equal size and that problems can happen if they aren’t. In practice and realistically, how much of an issue is this going to be? Is it to the point where we should up/downgrade one of the units so that they match? Up until now the second in line, the 175, has effectively been off due to a number of piping issues. Both boilers are on a common loop, servicing variety of hydro heat and dhw via an indirect tank. As I have learned the previous job here was almost completely fubar.

Also, Triangle Tube support suggested the settings below for the secondary boiler (the 175), in light of the situation. Could someone interpret conceptually what they mean?

Stage Delay = 60 sec.
Minimum Fire Rate= 27%
Maximum Fair Rate = 95 MBH
CH/DHW Boilers = 0
Automatic Rotation = Disabled
CH Proportional Gain = 7
CH Integral Gain = 245
DHW Proportional Gain = 7
DHW Integral Gain = 245

Thank you!

Comments

  • Leon82
    Leon82 Member Posts: 684
    Post some details about the house, construction square feet. Pictures of the near boiler piping from different angles. Any water tanks that are hooked up

    You may not need both of them.
  • Leon82
    Leon82 Member Posts: 684
    The rotation parameter is probably to rotate the first firing boiler so the one still the end of the Cascade gets some use instead of sitting for a long period of time.
  • mabo
    mabo Member Posts: 20
    edited April 2018
    House is in Southwestern Connecticut. Not counting unfinished attic and basement the house is 5300 square feet (including finished garage). I estimate house volume is approx 52k cubic feet (without attic and basement). All windows and doors were replaced about 4 years ago, and mostly there is new insulation resulting from that project. Heating system is propane, for both hydro heat and hot water.

    Below is a room by room breakdown. Right click open image in new tab to see it full size.



    Below is picture of how the boilers are piped (with panel off). Water flows into the 110 first, then into the 175. This piping was actually just redone because before this there was no pump for the 175, and it was just turned off because it was tripping a High Temperature code. It only occurred for me to check with Triangle Tube support when I looked at the finished work and noticed how the two boilers internally have different sized piping and sized pumps. And that's when I learned that stable cascade requires same size boilers. So now I am full stop until I figure out the exactly the right setup for this house and whether this setup can be salvaged.

    Right click open image in new tab to see it full size.


    Firm that originally installed the system definitely messed up huge. None of this just came out until I started working through maintenance items post moving into the house.

    The entire system is one loop with smaller loops for various zones: baseboards, radiant (with mixing/thermostatic valve), and for two water tanks (Triangle Tube Smart 80 and Smart 40). All zoning is controlled by a Taco board (as per below). I don't believe there is any direct communication from the Boiler and the hot water tanks.


  • Leon82
    Leon82 Member Posts: 684
    edited October 2017
    The csst piping can cause issues in some cases.

    I would take that data and plug it into the slant fin heat loss application. That will give you an idea of what you will need btu wise

    I would see if the small boiler will handle the heating on its own this winter before replacing the big one with another. If it struggles you can repipe with the big one and sell the small one

    With Cascade It probably should be piped with a low loss header to ensure the 175 is receiving it's minimum safe flow rate
  • mabo
    mabo Member Posts: 20
    edited April 2018
    Edited a response and whols post disappeared, so retyping it one more time.

    House is in Southwestern Connecticut. Total square footage is 5300, including finished garage. Total volume is approximately 52k cubic feet, not counting basement or attic. All doors and windows as well as insulation were redone about four years ago.

    Here are details for the house:


    Here is what the piping looks like (with covers off)


    Piping around boilers was just redone because the 175 was effectively off the whole time. It had no pump and was tripping a High Temp code. After this was done, I looked at the different pump sizes and internal pipe sizes and realized they looked very different. After checking with Triangle Tube support that's when I learned that cascade requires both of the boilers to be the same. So now I have stopped to make sure that any next steps are exactly right.

    The entire system is one loop with smaller loops off it for zones: baseboard heating, radiant, and two hot water tanks (TT Smart 80 and Smart 40). Zones are controlled by a Taco board and the tanks are not communicating directly with the boilers. The zone boards are as below:




  • STEVEusaPA
    STEVEusaPA Member Posts: 5,724
    edited October 2017
    I'll post the same thing as I did on the other site:
    First step is a proper heat loss. I think you would be better off with a properly sized mod-con who's upper range covers just your heat loss on the coldest day.
    So you probably will only need one boiler, if one of those is properly sized
    You could also go with 2 smaller boilers, who's combined maximum btu's will cover you for the coldest day. Then you'll be able to take advantage of the turndown of both units combined.
    steve
    Ironman
  • mabo
    mabo Member Posts: 20
    STEVEusaPA: I moved this post here since it seemed like a more appropriate place.

    I am working with my current tech on the detailed heat loss using the above data. The approx calculators are yielding 150k BTU



    Rule of thumb calculators are getting to 200k BTU.

    So it seems that the small unit really is by itself quite undersized.
  • Leon82
    Leon82 Member Posts: 684
    New havens design day is 7 degrees If I recall. there is a chart somewhere on the internet
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,724
    edited October 2017
    A room by room heat loss may be more accurate. I assume for cubic feet you fudged the numbers so they would yield a result of square footage X ceiling height? For rule of thumb, you're at about 31btu's per sq ft. If you're well insulated and consider 25btu's you would be at 132.5k total.
    If your heat loss is accurate, the 175 will be too big 98% of the year, but 2 smaller 80k's, properly piped and installed, would give you a range of about 14k-160k. And they can be staged and rotated. You'll be condensing and saving money.
    Or like mentioned earlier, run the smaller boiler. If it can't keep up, turn it off and run the larger boiler. But if the smaller one keeps up on the coldest day, then at least you know it's the right size.
    Or, add snow melt, you have the boiler capacity....:)
    Too bad you can't find out the history of the 2 boiler install.

    edit: If you only use the heater in the garage to keep the temperature in the 50's, just curious as to what happens to a detailed heat loss if you remove it from the equation. If it's a shop and you want to be in there in your t shirt when its 5° outside, that's a different story.
    steve
  • Ironman
    Ironman Member Posts: 6,890
    Can you post some more pics that show all the near boiler piping, including the primary loop, zone connections and indirect tanks?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • mabo
    mabo Member Posts: 20
    Dumb question, but are the Prestige Solo boilers not modulating?

    https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Prestige Solo 110 Trimax Submittal-ProdO.pdf

    From description "Full modulation from 25% to rated input" for both the 110 and 175.
  • Leon82
    Leon82 Member Posts: 684
    Yes they modulate but how well depends on how much radiation per zone and proper piping.

    Is there a cable linking the boilers so they can communicate?

    If the manual says use the same boilers and they guy didn't he may not have input the proper Cascade settings called out in the manual
  • mabo
    mabo Member Posts: 20
    Wiring between the two is missing so are all the sensors. That would need to be remedied as well.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,139
    Those are piped in series. Are they supposed to be piped that way?
  • mabo
    mabo Member Posts: 20
    edited April 2018
    Ironman, here goes my attempt at explaining the system. Mind you, it's already been called a "murder scene" and other colorful things. So I am trying to make the best of it for now and planning on how to make it right in the medium term.

    At a high level this was a hydronic system for a 60's house with piping to match. When house was renovated and expanded a few years ago, it seems that things were tacked on, rather than fully redone with a holistic design in mind.

    Snapshot of the whole system:


    The two boilers are setup in serial on a loop that connects to the main loop. The boilers:


    Closeup of connection of boiler loop to the main loop:


    The supplies are all at the top of the picture. Close-up below. For the three radiant zones there are mixing valves to regulate temperature.


    The returns are in the middle. Close-up below. Circulators are driving water flow on the return pipes. Each circulator is driven by a zone on the Taco board, which is in turn driven by a two wire connection to a thermostat.


    The two water tanks are setup such that the cold water T's out to the two tanks and hot water T's back into domestic hot water supply. I have been told that the smaller tank is unnecessary and that the 80g tank should be more than sufficient for this size house. I have been told that the T-ing of the hot water tanks is also not correct. I haven't focused on it much since there is bigger fish to fry.
  • Ironman
    Ironman Member Posts: 6,890
    What I'm seeing is that with all that zoning, even the smaller boiler would severely short cycle just running by itself.

    I'd recommend that you use the smaller indirect tank as a buffer tank. This would prevent short cycling and allow both boilers to be utilized as needed. There are several ways it could be piped to do this. I'll try and post one later or you can look up the IDronics issue that addresses it very succinctly.

    Maybe @hot rod will chime in.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 16,543
    I'm not sure why they are series piped? An unfired boiler is always seeing flow and becoming a radiator, of sorts.

    ( pumps also seems like an over kill.

    I wonder that one 175,000 would carry the heating load of 5300 sq ft?

    I'm not sure how deep you want to get into it? I'll bet two or three circulators and some re-pipe would make it a state of the art system. a bit of buffer tank would help lessen cycling.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mabo
    mabo Member Posts: 20
    edited April 2018
    Ideally I would love to be able to have a system that has any shot of the efficiency that the equipment is capable for. But it sure seems like its configured to just be an old-style boiler. Control panel settings are to maintain a constant temperature. This is what the temperature display reads. Very hot water in and out. Should the temp target be this high (174deg)? How does this get setup to modulate? Most time of the year when everyone is out of the house, there is almost no demand, or at most some from the hot water tank. Whatever is happening seems very inefficient.


    Here is my diagram of the system, in case it's helpful. The zones that I drew out are representative of the three types that are hooked up.


    Also, from the manual, the cascade is setup as below. It seems that's what is actually done here. But perhaps my eyes are playing tricks on me? It also seems that I can just shut off valves to either one of them on the supply and return side, preventing that "radiator" effect that you speak of. I was, of course, trying to have both of these boilers be usable in this system.



    About the pumps:
    All the pumps are Grundfos 15-58 FRC or 15-55 FR (Alpha). The only exception is the pump for the 175 boiler, which was installed as 26-99F. When I saw it installed, it was a case of "this one is not like the other, why?". That is what ultimately led me to figure out that the boilers should have been the same size to be per cascade spec. But I wondered why the tech installed a larger pump on the 175.

  • hot_rod
    hot_rod Member Posts: 16,543
    Here is how I like to see multiple boilers piped. The green hydraulic separator replaces those closely spaced tees. It also is the air purger, dirt separator and magnetic removal device, so 4 functions in one.

    But, like others I think the one large boiler would be sufficient, get or have a detailed heat load calc to be sure.

    Here is how you could add a buffer to a single boiler.

    This happens to show a pellet boiler input also, the gas fired boiler as back up. Same piping, ignore the pellet input.

    If in fact the load is around 150,000, one or two circulators should easily handle that, get rid of maybe 7 pumps that are working well below their optimum range. Possibly too many mixing valves also.

    You would be talking a major repipe to upgrade all this.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mabo
    mabo Member Posts: 20
    edited October 2017
    So would I ideally need a low loss header as well as a buffer tank or just one of those?

    Conceptually, how can the Smart 40 be used as a buffer tank?

    If there are too many circulators, what would I use instead of circulators? Is there another device that triggers water flow without pumping it?
  • unclejohn
    unclejohn Member Posts: 1,757
    You do not have a cascade system you have two boilers. You also have enough domestic hot water for the whole block, some where around 500 gallons per hour. Call TT back and ask them to tell you who the rep. is for your area and have him come out and he should get some one who can set you straight.
  • mabo
    mabo Member Posts: 20
    I sent an email to get in touch with the rep. Will let you know what I find out. On the topic of cascade system, of course it is not since it’s not wired that way. But it seems to be piped that way. What’s preventing it from being in a cascade once the wiring is complete?
  • lchmb
    lchmb Member Posts: 2,997
    someone correct me if I'm wrong. The venting on the 175 does not appear to have any primer used on it (pipe to the right on the unit) and black lettering is still showing in the fitting on top of the unit. I also notice some discoloration so that has me concerned...
  • Leon82
    Leon82 Member Posts: 684
    > @lchmb said:
    > someone correct me if I'm wrong. The venting on the 175 does not appear to have any primer used on it (pipe to the right on the unit) and black lettering is still showing in the fitting on top of the unit. I also notice some discoloration so that has me concerned...

    The UPC is still clear. I would think the glue would have distorted it. I wonder how well it is sealed
  • hot_rod
    hot_rod Member Posts: 16,543
    Looks like the boiler on the left is valved out of the system, is it always like that. Maybe it is intended as a spare :)

    Here is how a Smart tank could be piped. Notice one pump for the boiler, one for the building.

    You may need to get a complete load calc and design to get started down the best path. I'm not sure why 3 thermostatic valves are needed? It sort of needs to be reverse engineered now, what are the heat emitters, can they run on one or two temperatures, etc.

    Possibly the rep can help some, but it is not generally their job to do a complete design, or sort out a unusual system.

    Some wholesalers offer design service and send out a well documented drawing for the installers to pipe and wire to.

    Before you spend any more $$ on the system, get a workable design and plan.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mabo
    mabo Member Posts: 20
    edited October 2017
    The 175 is currently valved off and turned off. The original install on the 175 was definitely bungled: no pump, no cascade wire, nothing really. After I bought the house I noticed that the 175 was just off, and when turned on it would error our on a code. After digging into that, a plumber installed the pump and isolation valves so that the boiler could be turned on/off and easily serviced. It now seems to work without codes. Obviously I have run only one of them at a time. My plan was to just put them into cascade mode (110 master and 175 the slave), but then realized that this isn't to spec. Looking deeper into this sent me down this rabbit hole. Ultimately tech support said that without rotation enabled, the cascade will work. It's just not an ideal setup.

    The 3 thermostatic valves are for each of the three radiant floor heat zones, which correspond to three parts of the house.

    Also, from a piping point of view, the slightly confusing part is that the supply/return pipes on the 110 and 175 have them on opposite sides. So from initial view it looks like one of them is done backwards, but having looked at it a dozen times it seems right.

    I am measuring everything in the house now, just windows left at this point. Then I will be able to do the heat loss calculations, by room and zone. But with that info, I am not sure where to take it. I have been through 4 different hvac/heating firms, and have gotten nowhere productive. Deep knowledge doesn't seem to be there. I would certainly appreciate a referral to someone who can do a proper system review and design in my area (Southwestern Connecticut).
  • mabo
    mabo Member Posts: 20
    edited April 2018
    Hi All, I wanted to give an update on my hydronic saga. The hydro tech recommended that I see how it goes with just the one boiler. I ran with the 110 and it was ok until it dipped below 25 and then it couldn’t ever satisfy the target temperature of 174 and just ran all the time. I then switched to just the Solo 175 and it was keeping up with the demand.

    Now that it is warmer and there is less heat demand I noticed what seems like cavitation in the boiler pump for the 175. Here is the video link:



    It sounds like a washing machine and a rush periodically. This happens when the boiler is either in post pump and no zone is calling (that’s only one minute), and more frequently when only the indirect tank is calling. The indirect tank is by far the shortest loop that I have in the system.

    The boiler pump is a grundfos up26-99f, so a big’un without speed control too.

    When the normal heating zones start calling, the rushing sound disappears.

    I can see a solution for this by wiring the DHW so that into doesn’t try to heat the water so high when it’s just the tank calling. Right now it’s just being treated as a heating zone. Combined with an outdoor reset, the temperature should not be too hot unless some heating zones are calling. But that’s a bandaid ain’t it?

    That being said, should I scale down the pump? Or replace with one that has speed control? How do I calculate what size boiler pump I should have? Given the vastly changing heating demand, would one of the Grundfos Alpha auto adjusting pumps be suitable? All the zones have their own individual pumps, one size down and also have 3 speed control.

    Thanks!
  • Zman
    Zman Member Posts: 7,355
    Does the noise happen only at high or low fire?
    It sound like a combustion noise to me. Has a combustion analysis been done on it? I would have one done and be sure they check it at both high and low fire.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mabo
    mabo Member Posts: 20
    Interesting. In both of the examples I have it seems the boiler is on low fire (there is a little fire icon on screen). I am away from home until tomorrow night and I will see if I can spot the noise when the burner is off. Perhaps I can set the postpump time much higher and see if noise happens. To understand better, what could cause combustion noise? How much of a problem is it?
  • Zman
    Zman Member Posts: 7,355
    Boilers need to be tuned. They don't just come out of the box with perfect combustion.
    The combustion analysis should be done on every boiler startup and then at service intervals. Most systems never see a combustion analyser at all.
    Get the boiler properly tuned and the will run more efficiently and last longer.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    GordyTinman