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Corn Fired / Fuel Oil Back-Up Primary Secondary Boiler System Concept - Please Check My Work?
I currently have an old school Triad fuel oil boiler that is plumbed / controlled old school as well. The boiler is plumbed directly to the zones (not primary secondary), has one pump that is controlled by aquastat, and the boiler is fired by one central thermostat. I have 10 zones, however its acts like one big zone as I have no zone valves. I have one large return manifold with a row of 10 gate valves to manually balance / throttle the loops. (Like I said, old school.)
What I want to do:
Since I live on a farm, I would like to plumb in a corn-fired boiler in parallel with my existing fuel oil. The fuel oil would be the back-up. I plan to use primary/secondary piping because the corn boiler does not like flue gas condensation. I also plan to have the zone circulator controlled by the thermostat and boilers controlled by aquastat the same way most modern systems are controlled.
Please take a look at the file I have attached.
I detail my piping, calculations, operation of the corn boiler, and the control system. (The fine folks at Tekmar are really helping me out.) I would like some general guidance as to whether I am missing components in my system or am on the wrong path. I have been reading the Dan Holohan books so I hope I am close.
My main questions include:
-Do I need additional bypass lines in my boiler loops to further protect against low return water temps? ESBE valve?
-Do I need a balancing line between my main zone supply and return lines if I choose to not add electric zone valves to my system? I think I can just use the existing manifold gate valves I have to throttle/balance to achieve target 40 delta T?
-If I chose to add zone valves, I would group my 10 loops into 3 sub groups with 3 "sub manifolds." I feel that one zone valve / thermostat per floor is sufficient. Would I then add a balancing line between the main supply and return? What valve would I put in this balancing line? Are gate valves suitable to balance with? I have seen expensive "circuit setters" with flow meters, but don't know much about them.
-Are my purge stations in the correct spot? Goal is to be able to purge zones separately from boiler/ primary loops.
-Do I need a ball valve to close off my zone loops when purging the primary loop? Or will the closely spaced Tees be enough to keep the purge in the primary loop?
Any help is appreciated!