boiler return tempering

[CRIV911]

I was thinking that instead of a thermostatic tempering valve, I could use a normally open [automag] zone valve. When the boiler fires, the hot out would cycle to the return. An aquastat in the return line would power the valve closed at proper temperature.
I think this might work fairly well, and cost much less.

 

[Hunderliggur]

The problem is that you need a return tempering valve. You want to maintain a minimum return temp (mine is 140F) which requires a mix of the boiler output (my circulator is set for 170F) and the return water temp (anywhere from 80F to 160F in my case). A basic on/off valve does not give you this control. There are many ways to solve this problem with mixing valves (I use a Danfoss valve), variable controllers, circulators, etc. Don't skimp on this important piece of the puzzle.

 

[maple1]

The problem with a zone valve is that it is either open or closed - one extreme or another. I think to maintain an even proper return temperature a variable flow valve is needed for good mixing.

 

[timberr]

I went about this in a basic fasion and it seems to work fine for me. I put a "T" on my supply side with a ball valve connected to my return and I have a TEMP probe on my return. I manually open the ball valve and and close down as the system temps come up. I only have to do this a couple of times per year; usually when I fire up the system for the season and when I return from a weekend away or vacation.

I considered a Danfos but had read a few post about folks no reilizeing theirs had failed. I have traded the set it a forget it it option for bomb proof and manual.

Good Luck

 

[Gasifier]

I was thinking that instead of a thermostatic tempering valve, I could use a normally open [automag] zone valve. When the boiler fires, the hot out would cycle to the return. An aquastat in the return line would power the valve closed at proper temperature.
I think this might work fairly well, and cost much less.

I would highly suggest that you do not use a zone valve for this application. I used a Danfoss (140 °F ) valve ($180 + tax) and a ball valve above it. After I had a few small fires to dry out the ceramics in my boiler I started trying to bring boiler and tank up to temp. Was not working the way I wanted it to. I had to tweak the ball valve several time to get the tank to come up to the temp I wanted. What a difference it made to throttle back the ball valve about 30%. Now the tank and boiler seem to pretty much remain the same temp. It is nice to have the ability to adjust if you want.

My opinion, spend the money and put the protection bypass valve in with the ball valve. Timberr also has the ability to make adjustments with his as well. Hope all goes well for you.

 

[CRIV911]

Danfoss make two versions. The ESBE TV, and ESBE VTC. I don't know the difference, but the TV recommends a balancing valve, and the VTC does not. Anyone know the difference? My other question is on the pump supplying the boiler. Would the Taco 007 with Delta-T make a difference. I could install the sensors on the supply and return. It doesn't have an ECM motor, but it would ramp up as return temps increased. I plan on using a B&G Eco-circ auto for the zones, that one uses Delta-P.

 

[ewdudley]

A two-pump solution is working well for me, one pump recirculates boiler supply to return, and another injects system return into the loop with a PID controller and bang-bang modulation.

Return temperature control is accomplished by injecting into a boiler recirc loop with an injection pump under PID bang-bang control. With an 80 second cycle, 105 degF system return water, and a 160 degF return temperature setpoint I’m seeing a 10 degF swing in return temperature with boiler discharge temperature steady at 170 degF. Push a button and you can set the return temperature anywhere you want it. Pumps were salvage, controller $40, relay with pedestal $12.

https://www.hearth.com/econtent/index.php/forums/viewthread/68776/