Buffer shunt pipe triggered by boiler's burner ?

Dave Carpentier

So, I'd like to go with plan "B" (in diagram) but having the boiler circ run during all the zone calls is going to destroy separation in the buffer when the burner isn't running.
What I came up with is possibly a dumb idea, so please let me know if it is.

What if I put a powered valve between the upper port of the buffer tank and the return to the boiler, and control it with the burner circuit. It would have to be NO. During a zone call, the TT would start the boiler's circ and the boiler would be sensing the temperature of the top of the buffer tank, but not mixing it too much. Once the boiler sees temp drop below setpoint (minus some delta), the burner kicks on and closes the shunt valve and the tank heats fully.

Or maybe a powered 3-way valve so that during a burn all of the water is exiting the buffer on the bottom left, but when its not burning all of the water is exiting the tank on the upper right port ?

mattmia2

Why would the boiler pump be running when the boiler isn't firing?

EDIT: Ok, i see your question. I was sort of thinking is there a way to run the boiler so it is using the buffer as a reserve of cold water, it just pulls from the tank and heats to whatever the zone needs then when hot water starts coming out of the tank it shuts off until everything has dropped say 15 or 20 degrees then it starts firing again. Ideally you could have multiple calls on the boiler itself and the one that needs the highest temp determines the setpoint. I think some Viessman stuff can do this and maybe some Lochinvar stuff or an external control with a 0-10v input to the boiler.

Dave Carpentier

I did find the Viessman 200W has a remote sensor that installs in a low-loss header tank. If the boiler can turn its circ pump off while the tank sensor is satisfied AND there's a call for heat , then that would work good. I couldnt find this in the IM or the OM. The Lochinvar Night seems the same.. it does have a tank/system sensor that controls the burner but doesnt specify what happens to the internal circulator.
Technically, it doesnt seem too difficult of a task.. if the remote sensor is below setpoint, turn on it's circ and burner, if the remote sensor is above setpoint, turn them both off (perhaps a little post-burn circ is good to cool down).
It shouldnt be a default mode, but at least an option would be good.
Maybe I'll call Lochinvar and/or Viessman support tomorrow to verify.

mattmia2

Or another control that only calls the boiler when the water needs to be heated. I guarantee you will never increase the efficiency enough to pay for anything but the simplest control here but odr can make it a lot more even.

Dave Carpentier

Ya an ODR aquastat would work, but is silly to pay for that on top of a fancy modcon boiler that already has ODR.