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SuperStor SSC-80 as buffer tank?

tc60045
tc60045 Member Posts: 31
I currently have an indirect-fired 80-gallon DHW tank and am building a new system.

What do you guys see as the pros / cons are to using this already-paid-for glass-lined tank as a buffer tank for a radiant system.

Pros that I see: redundancy. On the new radiant system, it is merely a passive buffer, but I can heat this tank with a different source should the boiler go down. More on this later, depending on the feedback I get.

Cons: standby losses. I realize I may lose around 9,000 BTU a day in standby losses with this tank, but (a) that is only in winter, versus all-year today, (b) the heat in this room keeps a crawlspace warmish, (c) I could always blanket-insulate to reduce those losses, and (d) some will say that the drop-down in temperature helps ensure I stay in condensing range with radiant system boiler.

Thoughts, please -- and thank you!

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 16,320
    Why not use it? Is it inside a conditioned space? If so, then that standby loss isn't really a loss, is it?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 14,836
    what type of boiler? Zoo you hav a lot of zones and small micro zones?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • tc60045
    tc60045 Member Posts: 31
    edited July 2018
    Updating this thread and hoping for peoples' thoughts:
    hot rod said:

    what type of boiler? Zoo you hav a lot of zones and small micro zones?

    4 zones (2 hydronic air handlers; 2 small zones), going eventually to 10 zones (2 hydronic air handlers; 8 small zones)

    I have a 12 year-old Munchkin 200K BTU boiler. Came with the house; "finicky," no longer made, and parts are hard to get.

    Today, Munchkin does DHW via Indirect + heat for 5,000 ft2 old house. So 200K BTU - 80 gallon DHW = 200K BTU x 20 hours a day, I figure, or 167K BTU of nominal heating capacity. Oh, and zero redundancy, so when it goes down in January, family goes to hotel and I start burning propane heaters to keep pipes warm.

    Would love thoughts on this..
    This year:
    - Take Munchkin off DHW duty
    - Convert Ultra-Stor to Buffer Tank (wait for it)
    - Add Navien NCB-240 for DHW with...
    - Navien accessory heater connected as heating source to UltraStor tank, giving me 120K BTU of heat if Munchkin fails
    - I get redundancy + heating capacity + decent DHW

    2019:
    - Replace Munchkin with Navien NFB Boiler (200K BTU)

    2020:
    - If needed, add either another NCB or a Navien NPE to have more DHW supply

    Again, thanks for your thoughts.
  • Zman
    Zman Member Posts: 6,710
    I sure would not trade a munchy with an indirect for a navien combi. The combi is a huge compromise and will rarely run at optimal cycle lengths and efficiency. Munchkins can be finicky if not installed and maintained properly. Is the lack of parts a local issue?

    After reading your other post and hearing your desire for redundancy, why not go with 2 modcons cascaded with 10 to 1 turndown each and keep your indirect?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • tc60045
    tc60045 Member Posts: 31
    Zman said:

    I sure would not trade a munchy with an indirect for a navien combi. The combi is a huge compromise and will rarely run at optimal cycle lengths and efficiency. Munchkins can be finicky if not installed and maintained properly. Is the lack of parts a local issue?

    After reading your other post and hearing your desire for redundancy, why not go with 2 modcons cascaded with 10 to 1 turndown each and keep your indirect?

    Really good feedback, Zman -- thank you -- and you blew my mind with this design thought above. More on that in a sec.

    Availability of parts is my biggest concern for Munchy -- I can't predict what will go wrong but I have heard horror stories about waits for draft blowers, and in Chicagoland winter, having to get a hotel room(s) is a possibility. Redundancy is key. I could get some electric coils for my air handler in a pinch, but I hate doing that.

    Re: long cycle times -- Munchy ran for the entire months of January and February *continuously*. When I add basement heat to its workload, I have to subtract something, as 200K BTU is not enough. I will give it a break by adding hydronic (staple up) under the family room, so we will be supplying heat directly to the coldest room, rather than going through the air handler, which heats the whole first floor (yes, I could re-zone....and should consider that).

    2 modcons would definitely do the trick for my DHW (one is going to cause trouble with my kids). But I think the 240K BTU they put out on accessory heating might be light when I add some zones / heat to the basement.

    Now, you really bent my mind with thinking about keeping the indirect -- with the modcons! I can wrap my head around this part: keep Munchy (for this season) + 1 modcon, with modcon providing DHW directly into the top of the indirect, yet also having the job of keeping that tank warm indirectly (warming it to 140 to kill legionella) -- and then also having a "help munchy" role/zone on the accessory side. But with one modcon, I rate limit the DHW supply to the 5GPM that it can replenish the tank. Two modcons gives me 10GPM replenish rate, but then if i can deliver 10 GPM of DHW directly, why hold it in a tank?

    Would love to know more of your thoughts on this. Thanks again!
  • Brewbeer
    Brewbeer Member Posts: 616
    Where does the 200,000 BTU/hr load number come from?

    For redundancy, at my house I have a gas fired, fireplace insert that will provide heat to the house even if the power goes out.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
    tc60045
  • flat_twin
    flat_twin Member Posts: 289
    Don't assume your dhw production is doubled because you have two modcons. You still only have one indirect.
  • Zman
    Zman Member Posts: 6,710
    When you are producing water DHW on demand, you need far more available BTUs than with a storage configuration. The 80 gallons of buffer that the indirect provides will greatly reduce the amount of DHW production you will need. It looks like the indirect you have can absorb 91,000 btu. according to the manufactures limited specs. It will likely do a bit more than that.

    Phasing the boiler upgrade will save you a little money upfront now but the boilers will not cascade (talk) to each other and the labor cost will be much higher to do 2 installs.

    If this where mine, I would install the new version of these. http://www.lochinvar.com/_linefiles/WHN-05.pdf
    Depending on your heat loss, you would be looking at (2) 110's or (2) 86's. It is not 1 for each function, it is 2 boilers working in unison.
    They will do antilegionella cycles, DHW priority, Web alerts, you name it.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • tc60045
    tc60045 Member Posts: 31
    Closing this out nearly a year later.... Munchkin failed in December, and I installed 2x Navien NFB-200 as Lochinvars were just too loud (YMMV). I had installed a NFB-200 in September in an apartment we have, and it did well.

    Having 2 units cascaded as @Zman suggested is indeed the best way to fly... We re-plumbed the system on 2" through a Caleffi Hydro Cal and everything works so well. At worst of Polar Vortex in Chicagoland (-22F), we needed 300K BTU when all zones (except DHW) were calling, IIRC, but steady-state in that cold was probably more like 220K - 240K. More than we had previously, but we could have limped along with just 200, so I indeed have redundancy running these 2 units.

    Many thanks to @Zman and @hot_rod for your help. Oh, and I got a kick out of seeing you, hot_rod, demonstrating the awesome Caleffi hydro cal. I sure do love mine!
    Zman