By DaveBoyer
Date 03-09-2008 05:36
Edited 03-09-2008 05:39
I like to use an air scoop on any hydronic system, because the sooner You get the air out of the liquid stream the better as far as circulation air lock problems go. The automatic vent could be eliminated by a standpipe going higher than the highest point in the system.
An open system needs a vented expansion resivor mounted above the highest point in the system, the capacity depends on the total liquid volume. The one on My solar setup is a foot long section of 4"diameter PVC pipe with a loosely fitted cap, the bottom of which is at the same elevation as the highest point in the pipe run. It tees off the return pipe GOING DOWN A FOOT then into a return bend and up to the proper elevation. This prevents thermo syphoning, and the tank and it's contents remain cool.
If the firebox has a chimney there will be draft, so You may need to actually close the air intake to controll the fire. A guy I worked with built a wood fired boiler that had a 1,000 gallon insulated storage tank burried in His yard. He could fire the stove at maximum capacity, as the temperature of that much water [it was a fresh water system] doesn't change rapidly.
As You probably know already, You are much better off burning wood vigorously than roasting it. If You burn a hot fire with secondary air entering above the fire, all the stuff that makes stack deposits [creosote] will be burned up.
Pallets are a great source of wood, that is what the guy I mentioned used.
The closed loop will work, and might be simpler if You have a multi story house, but even the low pressure of a closed system and the cyclical loading from temperature change requires carefull engineering of a tank for it to last.