AA130FIREMAN wrote:The largest zone is the best for the dump zone, something that the output is close to the boilers. I use 2 dump zones, set 5-10 degrees apart. If one fails, the other takes over and I can switch aquastat settings to change zones from summer to winter, excess goes to my garage in the summer. I like the idea of the dump zone, and it doesn't overwelm the house, pay me now or pay me later. Like was said, if the expansion tank is large enough it's not needed. But my opinion, the warmer the boiler is, the more btu's lost, put them where you want them.
I assume the basic purpose for a dump zone is for a over run temperature condition. Ideally a fail safe design. How well does your design work when there's no electricity? Lets say you just had a large heat demand, the combustion blower has the coal burning hot and now you have a power failure. What happens? Does your PRV release? Do you loose boiler water? How much? Lets assume you do and the power now comes back on. Does the impeller of your pumps have water to pump? Can the automatic fill valve replenish the lost water? Do so without manual venting? What happens if the coal is still blazing hot when the power returns. Does it make steam because the trickle of flow from the automatic fill valve isn't fast enough to fill the boiler? The only fail safe design I can come up with is one that has sufficient expansion tank volume to fully absorb the boiler water during run away temperatures. I don't see how you can depend on any pump.
I agree getting the heat out of the house in the summer is a good idea, but your design still needs to be fail safe.