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The right system circulator with a Viessmann WB2B 35

I have a Mono Flo single main system designed in the mid 50's that I am installing a WB2B 35 into. The original system has a 2" main that splits into two 1 1/4" branch mains. The branches are currently zoned with B&G 100 circulators installed on the returns which then tee back to a 2" return main. The branches are balanced with a pair of gate valves with thermometers located in front of The circulators.

The Viessmann is designed not to have zones and I do not need them. I am reworking my near boiler piping to Viessmanns System layout 2 using the Viessmann low loss header and recommended Grundfos boiler and DHW circulators. I am planing to do away with the B&G's and use a single system circulator on the 2" main supply.

My question concerns the system circulator. I have a calculated head loss of 4.8 ft and flow of 8.2 gpm @ a 25 deg delta. I am interested in using a Taco Bumblebee to maintain a constant delta t across the reset curve. My concerns are weather I should use a delta t circulator and with the varying flow will I be able to balance the system by throttling the existing gate valves or should I do it another way?

I have about 1800 sq ft of emitters with a design heat loss of about 109,000 BTUH so I only need about 125 deg for a design temp. We only hit the design temp here a few days a year so if I can hit a delta T of 25 Deg I should be condensing almost all of the time. I really don't care about anything beyond consistent comfort and economy so what ever circulator I need to do that with will be fine. I was just thinking that a variable speed pump would likely give me a nice consistent room temp across the reset curve. I have put a lot into calculating my head loss so I hope it is correct. Compensating for head loss is another atractive advantage of the Bumblebee. I also think it is cool that it displays the current flow.

As usual I would appreciate any thoughts you guys have and I do not mind learning I am wrong. That is how I got this far.




  • Rich_49
    Rich_49 Member Posts: 2,766
    edited November 2013
    Bumble Bee

    The bumble bee should work just fine with your system requirements . Just watch your calculations and head  109,000 @ 25 Delta is 8.72 GPM if 100% water . If you increased the Delta to 35 that would put you right in the middle of the curve 2 & 3 for the Bumble Bee and would take you farther into the efficiency be it ever so slight . 

    Would using 2 Bumble Bees be out of the question ? Then both 1 1/4 circuits would remain as is , balancing would be at a minimum , considering whether it was balanced well to begin with and you would operate at 22 watts as opposed to 32 on design day . 1 at 32 or 2 at 44 and ultimate control .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Canecreek
    Canecreek Member Posts: 21

    Thanks Rich,

    I have no problem using 2 circulators. I can connect both to the same terminals on the Viessmann pump control with no electrical load issues. I would need to install them on the 1 1/4" returns but do not see that as a problem with the expansion tank on the other side of the LLH. The two branches are similar. I was not thrilled with the idea of throttling one of the branches to get a good balance but was unsure about how well 2 circs would work together.
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