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To buffer or not to buffer

Hey, Hot Rod. As you know I've advocated use of condensing water heaters for radiant heat for the past 15 years. They are now available with modulation. HTP makes them. I think Polaris is now modulating but I'm not sure. From the operational point of view, modcon storage type water heaters are the perfect choice. From the economic point of view, I'm still not sure. How long will they last? What is the life-cycle cost? Clear as mud.

Bill

Comments

  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    that is the question

    I had this job all thought out and ready to go and the HO throws me 2 curves, at the very last minute. I had a radiant floor with a few supplemental panel rads at 90,000 btuh at 10 degrees design. Around here is 15 design but I fudge a little. I also had a nice 50 gallon indirect in the proposal. A Prestige solo with 110,000 input was a perfect fit. Then the Homeowner wants to upgrade to a 100 gallon indirect and a snowmelt that requires 45,000 btuh. So I bump up to the next size boiler at 175,000 input. Plenty of capacity, but what about the mild days. The lower firing range of this boiler, will be 40,000 btu's. When the smow melt is not being used and there's no hot water being asked for 40000 is going to be way too much. I'm afraid of short cycling. I was thinking buffer tank but I read in Siggys Modern Hydronics text that you shouldnt need to buffer a high mass zone. Where do you guys draw the line? How do you deal with divergent needs in capacity? WW

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  • Ray M
    Ray M Member Posts: 94
    buffer tank

    Hi,
    Wayne i think you have some diverisity with your system. Meaning that i would not add up all the load's to size the boiler. Use a smaller boiler as the DHW is priorized and not all the loads will be on all the time. Just my .2 cent's.

    Thanks

    Ray M
  • Perry_2
    Perry_2 Member Posts: 381
    Interesting question...

    I had the same one when trying to find a mod/con for my house.

    For now I have been watching the Vitodens 200 cycle on and off - even at 30 F.

    I wonder when will it reach a state of constant firing.

    Perry
  • Ray M
    Ray M Member Posts: 94


    Perry,
    Are you useing constant ciculation? I have learned after 27 years in the bussiness the you need less capacity than you might think. The problem is the mod-con available here in the states are SOMETIMES to big. Buderus has a 15KW unit in europe but not here. Just a though.
    Thanks
    Ray M
  • Perry_2
    Perry_2 Member Posts: 381
    The Vitodens controls the secondary circulator... but yes..

    I have a Low Loss Header configuration, cast iron baseboard on a Monoflo T system. I have the RS remote temperature sensing and control module as well so their is house temperature feedback to the Vitodens.

    The Vitodens controls the secondary circulator. Essentially, unless the house is way to warm the circulator runs constantly - even when the boiler itself is not firing. If the house is way to warm the secondary circulator is shut down. It is also shutdown for Domestic Hot Water prioritization.

    I concure with your comment about to large Mod/cons in the US. I think Viessmann should also make a 3-12, and a 4-16 model below the 6-24 (I have the 6-24). It would not matter much if the boilers cost about the same - the real savings is in fuel economy.

    Perry
  • Ray M
    Ray M Member Posts: 94


    It all come down to "DELTA T" providing the correct amount of heat to match the load and providing a LARGE differental a the heat source. Hard to do with the equipment available, no one want's to be caught with thier pant's down at design temp's.

    Thanks
    Ray M
  • Paul Rohrs_5
    Paul Rohrs_5 Member Posts: 134
    Siggy's Radiant Precision

    My "Radiant Precision" book is at the office but there is a diagram of Siggy's of buffer tanks piped as a parallel loop with it's own circulator. The buffer tank could be brought on line with the specific load of your choosing, or with a 2nd stage controller. That might be more condusive to your application.

    I might be able to sketch something on Visio later today.

    Regards,

    PR

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  • hr
    hr Member Posts: 6,106
    Or a buffer in series!

    This Munchkin package includes a 52 gallon buffer piped in series, and the primary loop is the stand for the Munchkin. It handles micro zones very well.

    Although if you stand back it looks "hydrauliclly speaking" a lot like a Polaris or any other tank style condensing heat sourse.

    Hense my request for a modulating tank type mod con, say about 50- 65 gallons 5-80 K modulating range.

    hot rod

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  • Paul Rohrs_5
    Paul Rohrs_5 Member Posts: 134
    Makes a guy wish...

    I look forward to the future technology and what's in store for boilers down the road.

    We already have mod/cons that have built in outdoor reset. Separate contacts for DHW with priority. Why not a mod/con with a singular combustion chamber but more S/R headers with separate contacts for Low temp AND high temp? As long as the cumulative load is still within the output capacity of the boiler, who cares if it is low and high temp.

    New variable speed circulators and differential pressure circs should handle the necessary algorithms for optimum delta t.

    Just a thought.

    Paul

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  • Perry_2
    Perry_2 Member Posts: 381
    But the biggest issue I see...

    Is the lack of small mod/cons.

    If you heat load is less than the minimum firing rate - the boiler still cycles - regardless of the ciculation temperature. No fancy technology will fix that problem.

    Perry
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Hor Rod

    Does your water Supply go into the bottom of the tank and out the top. I was thinking the opposite might be better since it would draw the hot water down to the bottom of the tank or is my intuition mistaken. I'm having a little trouble tracing the flow from your picture. Do you have a conceptual drawing of the piping? Thanks for your help. WW

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  • hr
    hr Member Posts: 6,106
    Howdy Bill

    nice to see you around again. I had to do a Polaris warranty a couple weeks back. They have done some nice upgrades to that unit. Much quieter, cleaned up that rat's nest underneath. I understand the price has jumped considerably.

    I have about 10 out in the field with up to 8 years run time. A couple ignitors and the one warranty leaker. Not so bad. I've had a lot more mod con call backs than that :)

    Are you thinking of the HTP Phoenix? Is it a modulating burner with coil inside for radiant?

    You've heard the all steel Bradford CombiCor will be un-eiled at ASHRAE in January. 1-1/4" diameter steel coil, all enameled more sizes and an oil fired version due.

    I think Bradford White/ Laars owes some of the originial "on the bandwagon" contractors out there a freebie. Yourself included.

    hot rod

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  • jp_2
    jp_2 Member Posts: 1,935
    yes, hot rod,

    I too am curious as to the piping diagram?
  • hr
    hr Member Posts: 6,106
    There is one slight of hand

    in the piping. Can you guess what and where?

    hot rod
  • Bob Sweet
    Bob Sweet Member Posts: 540
    Placement of the pri loop pump?

    How are you getting flow through the primary loop?
    Are you getting it through the pressure drop of the closely spaced tees on the pri loop

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