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Variable speed injection pumping - a success story

SuperTechSuperTech Posts: 1,146Member
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.


  • STEVEusaPASTEVEusaPA Posts: 3,819Member
    edited December 2018
    Why the Tiger loop? At the very least lower it about 6-8" so the supply/return lines have a little play in them.
    You'll have to keep track of DDays and oil usage and let us know the results.
    Also I hope you replaced that door gasket...looks like some scorching.
  • SuperTechSuperTech Posts: 1,146Member
    > @STEVEusaPA said:
    > Why the Tiger loop? At the very least lower it about 6-8" so the supply/return lines have a little play in them.
    > You'll have to keep track of DDays and oil usage and let us know the results.

    The tiger loop was a freebie from years ago I don't have an air problem but I figured it couldn't hurt anything. I have to redo the flex lines at some point but I can still open the combustion chamber.

    I'm keeping track of oil usage, with this weather it doesn't look like I'm going to see a design temperature day anytime soon. The burner cycles are definitely longer but much less frequent. I've been very pleased with the ability control primary and secondary loop temperature with this setup. I expected more problems given that I have never attempted something like this before.
  • STEVEusaPASTEVEusaPA Posts: 3,819Member
    Looks like you're having fun!

    I've gone thru multiple re-pipings of my boiler, just to see how it performs (my wife thinks I have a problem).

    I've tried primary/secondary, even reversed them, just for kicks.

    I ended up with a buffer tank w/ODR and injection mixing for all the zones off the buffer, and an indirect.

    I think I'm done, but I'm considering a solar storage tank to replace the buffer and indirect. Just haven't figured out how I want to control everything.
  • SuperTechSuperTech Posts: 1,146Member
    edited December 2018
    Hahahaha, you and I have the same problem, this is my second repipe in three years. I am having fun with it! Can I see a picture of your system? It sounds really cool. I was thinking about doing a buffer tank. That electric water heater is just sitting there doing nothing...
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,879Member
    I've repiped my boiler twice and got rid of my New Yorker WC130 wood/coal and replaced it with a wood Gasification boiler. Also removed and sold my backup oil tank/boiler and installed a mod/con as backup.

    I've reworked my control system a couple of times and gotten rid of an injection system and FPHX. I could never sell a system like this as the labor would be astronomical!

    My wife says I have a problem, but i dont believe her!

    May i ask why you didn't consider going with a mod/con to leverage those nice cold return temps to your advantage? I bought my own 500 gallon LP tank (and refurbished it) and the savings of shopping around worked out much better than oil.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperTechSuperTech Posts: 1,146Member
    edited December 2018
    LP isn't an option due to the cost of fuel/BTU output of propane. I know a couple of customers who have regretted converting to LP, even with properly installed mod cons.

    I'm certainly not in love with the existing Peerless WBV-03, I am looking at options for three pass boilers. I've been looking at indoor and outdoor wood boilers, they would go in nicely now that I have primary secondary piping. I've seen a couple of oil and wood combo boilers, they look good but something tells me I'd be better off with two separate boilers.

    I'm starting to regret insulating my near boiler piping now, I'm bound to be ripping it off and making more modifications soon!
  • SuperJSuperJ Posts: 575Member
    Nice revision, I have a similar problem always tweaking my setup.
    Can you expand on what settings you used in the VT2218 pumps?
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,879Member
    If you go with a wood boiler, go with indoor gasification. Outdoor boilers are forest eater smoke dragons. There are a few exceptions.

    I cut my wood consumption by 30% just by switching boilers. I ran my WC130 with storage as efficiently as possible before too. Storage is key in making burning wood both efficient and convenient. Only one fire a day supplies 100% of DHW and heat. Your primary/secondary will lend itself very well to keeping return temps up. Your cast iron will also lend itself very well to storage and wood. Outdoor reset will work even better!

    I can expound further if/when you go in the wood direction.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperJSuperJ Posts: 575Member
    Agree with @Solid_Fuel_Man about storage and outdoor boilers, if you don't have storage even the most efficient high tech wood boilers waste tons of wood keeping things hot when there is no load.
    Outdoor boilers lose a lot of heat before it even makes it inside. I know a couple people locally who switched from wood boiler to high efficiency indoor wood stoves and have cut their annual wood consumption in half (l have a Blaze King Ashford).

    I can't stand it when my neighbour reloads his with like 100lbs of wet wood. It smokes so bad I can't see his house sometimes. We all burn wood on my road, but the outdoor wood boiler guys give us wood burners a bad reputation, it almost like rolling coal in a diesel truck (gives good tech a bad name).
  • SuperTechSuperTech Posts: 1,146Member
    @SuperJ I've operated my boiler pump on Delta T mode trying both 15-20 degree settings. I now have it on setpoint heat mode, set to 185 degrees which it will only see when the burner shuts off during DHW production and on design temperature days.
    The injection pump is also on setpoint heat, set to 160 degrees. This slows down recovery time on the indirect tank, but I have priority control on it so that doesn't concern me too much at the moment. I could always change things.
    It's a nice setup to be able to play around and see how flow and temperature affect heat transfer. I got the opportunity to show my apprentice the boiler yesterday, he was fascinated by it.
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,879Member
    There are few who appreciate good boiler rooms. I bet the vast majority of those folk are here on HH!
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperJSuperJ Posts: 575Member
    Where do you have your injection pump's sensors installed (I'm guessing Supply on the secondary supply pipe, and return on the boiler return pipe?).

    I suspect you should just run your boiler pump in a constant speed mode. Your current setpoint mode, will cause the pump to run at full speed most of the time (wasting a bit of power), unless it gets over 185F and slows down. Might not matter too much since your boiler doesn't modulate, and is high mass.
    But, you might have some control loop interactions between the boiler pump and injection pump if they are both in temperature responsive modes.
    IMHO, let your injection pump do all the work of set point control and boiler protection, the boiler pump just has to move water around in a circle and can do that at a constant speed.

    It's too bad the VT2218 can't accept an outdoor sensor, to give a ODR in setpoint mode.
  • SuperTechSuperTech Posts: 1,146Member
    Thanks for the advice @SuperJ . Yes the sensors are where you thought they were. And yes the boiler pump does run at full speed. I probably will switch it to fixed speed, I just like the temperature display on setpoint mode, but that is no big deal.

    They should make the VT2218 work with ODR like the I series mixing valve, that would be great.
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,879Member
    @SuperTech I've been thinking the same thing. The VT2218 with ODR....

    @Joe Mattiello
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
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