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Buffer Tank on Vitodens...

heatboy
heatboy Member Posts: 1,468
in THE MAIN WALL
especially on a system with multiple low load zones. While the Vitodens does modulate, it cycles frequently during moderate weather and small loads. If a buffer tank is to be used, install it between the LLH and boiler. It will keep the burner running and may also lower return temps since the LLH can elevate return temps under partial loads. The internal pump on the smaller 6 - 24 & 8 - 32 is large enough to handle what little head a buffer tank would have.

hb

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Comments

  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
    Buffer Tank on Vitodens...

    I have multiple small radiant floor zones on a Vitodens system and I would like to add a buffer tank for more volume.Would it make sense to add the buffer tank between the low loss header and the vitodens, or would you install it on the secondary side of the low loss header? Since the sensor in the low loss header is feeding back to the Vitodens, it would seem logical to add the buffer tank to the primary side of the low loss header. Has anyone ever tried this? Thanks for your help...
  • Unknown
    Unknown
    why?

    Mike,

    With all the controls, variable speed pumps and LLH.... Why would you want to do this?

    Did you use a Viessmann 3 way with Vitronic motor?

    Which model Vitodens?

    wheels
  • Paul Pollets
    Paul Pollets Member Posts: 3,663
    Huh??

    What do you mean you need more "volume"? If you have a low loss header, the system should have been designed for flowrates above 7gpm. Are you using a 3way mixing valve for the RFH circuit or just setting the curve in the LLH? The LLH is a "buffer" and decouples the boiler circuit from the radiant circuits. Low loss headers are available in several sizes, depending upon flowrate design. Adding a buffer tank would be unnecessary.

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  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
    Lowering the fuel bill..

    Hi Paul,
    I was trying to think of a way where the Vitodens (11-44) would not fire-up as often as it does. I am using the Viessmann motorized 3-way mixing set up with it's
    own heating curve for the radiant. I also am using the high
    temp circuit for an air handler which has it's own heating curve. Since the 11-44 can only modulate down to 55K BTU, what happens when a small zone of 5k btu's is the only active zone at that time? As soon as the 3-way mixing valve starts working and the temperature drops in the LLH, will the 11-44 not fire up right away? I do, by the way, have the lager LLH. I'm trying to figure out how to save the customer money on his natural gas bill. Since there is constant circulation between the LLH and the Vitodens, I
    suppose the one other thing that I can do to improve the
    efficiency would be to insulate the copper piping in the
    mechanical room. By using a storage tank that the 3-way mixing valve could draw from, I was hoping that I would decrease the number of times that the 11-44 fired.Do you have any other suggestions? Thanks for now...
  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
    Thanks heatboy...

    That's exactly what I am dealing with.I have multiple small zones and the 11-44 can only modulate down to 55K btu's. I am also going to adjust the heating curve down on the high temp cicuit and insulate as much as I can in the mechanical room.It is amazing how much heat can be given off of that copper. We have had an extremely cold January and I am about 100 miles north of Ottawa, Ontario. Cheers..
  • Unknown
    Unknown
    Yo HB

    Why not remove the LLH all together and use the buffer tank to decouple??
  • S Ebels
    S Ebels Member Posts: 2,322
    Yeh!

    My thoughts exactly. In effect, the buffer would become the LLH. BUT! One would have to be careful of flow patterns through the buffer or you could wind up with some wierd stratification and/or wacky temps supplied to the system.
  • heatboy
    heatboy Member Posts: 1,468
    I'm sure you could.....

    as long as there was a centralized place for the sensor. I use the LLH as my primary air removal for the system by changing out the manual vent with a 1/2" automatic vent. I think the buffer would work better in between the boiler and the LLh. In essence, just become a part of the boiler instead of the entire deal. Not sure if it would matter, though.

    hb

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  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
    Viessmann thoughts...

    I have also contacted my Viessmann rep. to see what their comments might be on adding the buffer tank. I would always get Viessmann's approval before proceeding. I have added buffer tanks to many other system with small loads and it has made a huge difference. Thanks for all of your help and I'll let you know what Viessmann recommends.
  • hr
    hr Member Posts: 6,106
    A sweet setup

    for that is the HTP 20 gallon buffer tank. It has 4 large taps so you could feed the boiler in and out, then use the second set of taps for the "load' loop. Sort of like a large volume Caleffi HydroLink or low loss header.

    Step back and it starts to look like a modulating tank style water heater :)

    Love to see Voyager or Polaris offer their tanks with modulating burners. This may be the "most ideal" heat source for micro, multi zoned radiant applications.

    Here is one I have been tinkering with in my shop. A 90K MZ bolted right onto a 120 gallon HW storage tank. since the MZ does not modulate I plan to charge the tank from 100- 145° and injection mix off it.

    hot rod

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  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
    Thanks hot rod...

    I didn't know that HTP had buffer tanks. I checked out their site and it look's like "Gas Solutions" is their Canadian rep. Hopefully, we should be able to order the tanks. Thanks for the picture....
  • hr
    hr Member Posts: 6,106
    I use HTP's 20's with cast iron sometimes

    to help buffer multi zoned jobs. This is a few years old, Crown Cabos, Megastore and HTP 20 buffer feeding a Danfoss zone panel. Six zones as I recall. It's the small master bathroom zones that relly benefit from some capacitance :)

    The indirect is close coupled to the boiler for best flow and minimun summertime piping loss.

    hot rod

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  • Paul Pollets
    Paul Pollets Member Posts: 3,663
    Air Handler

    If the air handler is constantly calling, than the boiler won't modulate very much. Are using the XX terminals to fire the external circuit? Or Switching Module V?


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  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
    Re: Zones

    I just have the one high temp circuit supplying the air handler.There is no external demand. Whenever the A.H. calls, the circulator turns on and starts drawing water from the LLH. The A.H. is not running excessively. The Vitodens also controls the 79 gallon Vitocell. As far as the low temp circuit, I just have the 3-way motorized mixing valve controlling 12 radiant floor zones.(using 12 zone valves and one circulator with a differential pressure bypass). Ther are no external demands from any of the space heating circuits. The Vitodens basically controls as to when it will turn on and for how long. Thanks for now...
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