return water temp control

kwilliams

I have 2 year old Crown CT-3 with a Riello 40 F5 oil gun. I am zoned with circ pumps, 3 fin tube baseboard zones and an indirect fired domestic water heater. A Taco SR 504 Exp controls the beast.I want to add a low temp zone (a small radiant floor zone) and a corn/wood pellet boiler to the mix. Presently I have a problem with low return water temp that is causing condensation on the inside of the boiler. I need to incorporate a system bypass of sorts, manual balancing valves won't work because of the variable loads with different rt's. that leaves electronic mixing controllers, mechanical mixing valves 3or 4 port. If I use a 4 port valve and boiler reaches temp, valve will be fully open and circ pumps will be pumping in series- not good. I have already resigned to the fact I have to build a new boiler board, but I want it to be the last one. Who has used what with success? Ideally I could snap an expansion board in the 504 mount the supply and return temp sensors and let it drive a 3 port mixing valve on the return line. I have not been able to find such offered from Taco without running on outdoor reset which doesn't work well with FT in upstate New York. Any advice would be appreciated!

icesailor

Low temp. control:

Have you tried using  Honeywell mixer with a circulator to mix your low temperature water?

You have overengineered and overthought this.

There's a drawing in the box on how to do it.