Two Boiler into a Primary Boiler Loop

GW

I have this commercial account where the original installer did a less than stellar job with the radiant system (no consrant circ); the building is 10,000 sq feet or so. Anyway, there are two Burnahm Revolution boilers piped just how the install book shows. But, on the primary loop above the boilers they installed a Grunfos 2699; it's a honking huge circ with nothing but 2" copper and 4 90* elbows, and some close-space tees to pick up the boilers and the heating systems.

After I fixed a boiler circ that puked, I had both boilers running. The place was cold because one boiler was off (bad circ). So, with the cold building the radiant was drinking up the heat as fast as the two boilers could make it, which is nice to see.

So, after the radiant system piping grabbed the heat from the primary, the other close tee is obviuosly taking return water back from the radiant system. So the 2" primary piping is cool to the touch at this point. What perplexes me is that the two boiler supplies (and the two returns for that matter) tie in together BEFORE they meet up with the 2" pri loop. What I'm trying to spit out is that the return water going into the two boilers is HOT. I'm obviously backfeeding at the two close-space boiler injection tees. Would it be practical to assume I should not see back-flow on this 2" main pri loop? I fail to see how 100% of the boiler energy is making it to the system. Thanks for any input. I'm guessing a smaller circ would help.


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Gary

If you could post a sketch of what you have there it would help in identifying the problem. Twinning up the piping in parallel is the method we recommend in the I&O manual so that each boiler gets the same temperature of return water. From your description, it sounds as if the common supply and returns from the boiler might be connected in backwards in respect to the primary main flow or "reverse injection". If you can't post a drawing then try to fax one to me at (401) 789-1899.


Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.

GW

Glen

Thanks for the reply. But yes, that's what I'm saying. The boilers are piped according to the drawings. I'll see if I can get a picture.

There's actually a ball valve on the 2" primary between the supply and return boiler injection tees (is injection the right word). When I start to close off the 2" ball valve, the primary main begins to get very hot after the radiant take-offs.

Gary

Gary

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What size load and boilers?

If you have two 200K Revolutions, yes the primary loop needs to move about 34 gpm at a 20° delta T. This would require 2" loop and the primary pump is correct for this flow.

The 26-64 or 96 fall short.

I would pipe them parallal also. You want the boiler to see the lowest temperature to keep the efficiency highest.

The Revs will protect themself return temperature wise, down to 70 return.

hot rod

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