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Hydronic Air Design

Hi guys, I could use some professional opinions before I have the Pro's come in and give me their idea/bids. Our system is 7 years old and consists of:

- Buderus GB142

- Air Handler zone

- DWH arm tank (Amtrol 80 gal)

- Wirsbo zone in basement slab

- Wirsbo zone in garage slab

For the most part the system has been great, the boiler seems overworked and I've kept up with annual cleanings, replaced the normal stuff (condensate trap, burner gasket, ignitor, etc). There is a current problem with the unit where it will not reach over 150 degrees for heating, the DHW reaches 180+....we've checked the delta T and that is not the problem, so not sure exactly what is up with it. I do not have the AM10 outdoor reset since it was installed in 05' (I bought one, have not had it installed yet). There are no mixing valves on the heating zones, they have their on stat and valve opening. If zones call for heat at or during another, the high mass concrete slab zones take longer of course to heat up as compared to my air handler zone...so they are mixing basically.

My question is I would like to offload the boiler with either a gas water heater for DHW or perhaps even a used boiler for the Arm tank and two wirsbo zones.....or any ideas you guys have. I like the concept of my setup overall but I don't think it was fully setup the correct way due to no mixing valves and other things. Thoughts and thanks in advance.


  • Zman
    Zman Member Posts: 7,468
    Thermal depression

    I am glad to hear your buderus is running well. That model can be a challenge.

    Check out this article from one of the industry greats http://www.radiantandhydronics.com/Articles/Glitch_and_Fix/BNP_GUID_9-5-2006_A_10000000000001216751

    You slab should absolutely be mixed. It should be done in a way that limits the btu's it will take, particularly when it first calls for heat. I would look to Tekmar controls for a solution.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Ironman
    Ironman Member Posts: 7,181

    What is the KW or Btu rating of the GB142? What is the heat loss of your house?

    I would not try to use a gas water heater in place of what you have. The smallest Gb142 has an 84k btu input, that's twice what a water heater would have.

    You need to install the AM10 reset control and have the curve properly setup. The 142 will automatically give priority to DHW if the 10k ohm sensor that came with it is placed in the indirect's well and it's connected to the "FW" terminals on the boiler.

    There may be an aquastat on the system that's connected to the boiler's "EV" terminals that's set @ 150* to limit the temp to the slab. That also may cause poor performance from the AHU's.

    The system needs to be setup as per Siggy's drawing that Carl posted. You can use an electronic mixing valve like Taco's "I" series or use injection mixing with a Tekmar 356 control. Then remove the aquastat (if present) and jumper the "EV" terminals.

    Go to www.buderus.us and download the applications manual for the GB142 to see how to wire the controls to the boiler. The AM10 connects to the "RC" terminals. If you have an "RC1020" room control, that may also be limiting the water temp. The AM10 will replace that, but you'll have to install a regular heating T'stat in place of the RC1020.

    I've included a Tekmar essay on how to control the slab.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mplsavant
    Mplsavant Member Posts: 20

    Thanks for the input guys, I appreciate it. I have the 142/24 with the 84k BTU. The setup today has DHW priority with the Buderus which works good, but again, with that, and the 3 heating zones, it's a lot. I had 3 bids when we installed, went with the one with the detailed heat calc which I dont have currently but they did the whole thing because they needed window sizes, direction house was facing, insulation type, etc, etc.

    The "EV" connection today is jumpered and "FW" has the Arm tank sensor connected to it. I don't have the RC1020. I have a standard wirsbo brand tstat in bsmt and one in the garage. I have aprilaire tstats for air handler zones (which are split zones btw). I spoke with Buderus support the other day specific to the air handler zone not heating past 150 even though the dial is set to 170, they believe the delta t and pump is not allowing it to get to dial temp. It used to reach past 150, this year it does not. I since read up on my First Co air handler coil, I am not sure my pump is sized for it appropriately cause the total round trip distance is over 24 feet and I have a stand grundfos 15-42 pump. This is all without any call from heat from the either slab zone.

    I was actually thinking of putting in a gas water heater for DHW and leaving the air handler and two wirsbo zones connected to the Buderus and install the AM10 as well as electronic or thermostatic valves for the slab heating zones. The unit gets so much work up here in cold Minnesota that I was thinking of off loading the DHW.
  • Ironman
    Ironman Member Posts: 7,181
    edited December 2012
    No Advantage, Only Disadvantage

    Again, there's no advantage to what you're considering. The space heating load has nothing to do with the domestic. If there's a domestic call, the boiler pump stops and all of the boiler's capacity is directed to the indirect. If the domestic call continues for more than one hour (shouldn't happen), then it reverts to space heating. You cannot have space heating and domestic at the same time if the tank sensor is used. It's "either or" but not both. What then would be the advantage of putting the domestic back to a tank heater with 1/2 the capacity? You're not gonna "over-work" the boiler as long as there's good maintenance on it.

    Installing the reset and mixing controls will allow the boiler water temp to be lowered a significant amount of time. THAT will due far more to reduce wear and energy consumption than what you're proposing.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Ironman
    Ironman Member Posts: 7,181
    edited December 2012

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mplsavant
    Mplsavant Member Posts: 20
    Makes sense

    Yes, that is exactly how the system works today, it heats up the 80 gal Amtrol in a short amount of time, puts the heating side on hold if neeeded, once DHW is satisfied, the heating then takes over.....the more I have been thinking about it and what you have stated, it seems to make more and more sense to stay with the high efficiency I am getting from the Buderus with concentric venting, continue to maintain and put in the am10 and the mixing valves......I printed off the am10 instructions, planning to set that up or ask my heating guy to do so....will post where I end up in a couple weeks.
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