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Variable speed injection pumping - a success story
In November I found evidence of flue gas condensation in my chimney base. I'm sure this is the result of everything I have done to maximize efficiency, outdoor reset, downfiring the burner, heating with low supply water temperature on my Peerless WBV-03. I could have solved this problem by sacrificing some efficiency but that's no fun so I decided to research other solutions.
I decided that primary secondary piping and better control over supply and return water temperature was the answer. I considered installation of a hydro separator or a Taco I series mixing valve but I decided on another solution, variable speed injection mixing.
The boiler loop is 1-1/4" pumped by a Taco Viridian VT2218, I also added a wye strainer and thermometer to keep an eye on return water temperature. The crossover bridge piping has another VT2218 as the injection pump with a Caleffi QuickSetter balancing valve and flow check valve on the return side of the crossover bridge, all 1" copper.
For the secondary I decided to keep the existing zone valves and Grundfos Alpha circulator. I piped the manifolds reverse return, with the supply manifold piped downward to prevent gravity flow and heat traps on the return manifold. The indirect tank is the first priority zone, followed by the two pipe Venturi tee cast iron baseboard zone for the first floor and cast iron radiatior zone for the basement.
I'll attach pictures so suggestions for improvements can be made, although it's working great. I can easily heat with low supply temps without the return dropping below 140 degrees. Short cycling has been eliminated. On a near design temperature days circulation is nearly constant with the burner cycling 1-2 times an hour at most.
I plan on adding a dirtmag next and eventually installing a Tekmar control. Any other suggestions for improvements would be appreciated.