circulator control help please

[stokes79]

I just got my boiler (greenfire 130k) up and running, connected to 1000 gallon propane tank and here is my question:
I fill the boiler and it charges storage and supplies heat calls in my system, but then after the fire goes out the circulator on the boiler keeps running and I want a way to make it stop circulating if the boiler is not producing heat, because the way I have it piped it just circulates my storage and drains the heat from it

 

[Tarmsolo60]

Tekmar 156 differential controller

 

[Piker]

Timers work well too.

cheers

 

[jebatty]

You also might want to consider other differential controllers marketed for solar applications. I just installed one from Sunearth (aka Steca brand) bought off of ebay. Check the specs carefully because different controllers may have different specs and control options. I think the Tekmar has a few more control options, but I determined I did not need those and the controller I bought was less expensive.

As an example of use, here is how I installed mine. I have a plate hx separating the boiler from the storage tank (controller would work equally as well without a plate hx), and I put one sensor on the boiler input to the hx (boiler output to system) and the other on the line from the tank to the hx (tank return to boiler). I set the max temp at 190F for the line from the tank, which it never will reach, just to be sure that the tank can always operate also as an overheat sink, if needed. An aquastat powers on the boiler-hx circ at 155F, which also powers on the differential controller. The controller immediately powers on the tank circ, as boiler input to hx is much higher than the tank line to the hx (16F fixed differential of the controller). If the tank line temp rises to within 10F of the boiler line temp, the tank line circ shuts off (it comes back on when the differential is 16F). At a 10-16F differential between the two lines, very little effective heat transfer occurs with the plate hx, so shutdown of the tank circ is appropriate and efficient. The Tekmar may allow you to change these parameters, the Sunearth has these parameters fixed.

What happens that is useful is that as the boiler burns out and boiler output finally falls (not to rise again until refueling or relighting), boiler output does fall to within 10F of tank return line temp, and the tank circ shuts off, preventing the tank circ from continuing to run and heat the boiler when the boiler is not producing heat.

On my Tarm, the boiler circ will continue to run until the boiler itself falls to 190F in the firebox, and then the Tarm control shuts down the boiler circ. This assures complete burning of the wood load and also prevents a possible boiler overheat as the last coals burn down in the firebox.