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Posted By webfish,
Dec 16, 2014 at 8:36 AM
Wish this had been here when I first set up my system, MUST READING FOR ANYONE PUTTING IN OR MODIFYING THIER SYSTEM. I could have saved lots of cash, time, and had a much better system. I've redone my system several times and looks like I need to make some more changes.
Readers should take note that most storage tanks in the document are shown with ports somewhere into the sides of the tank. All volume above and below the ports is lost for the purpose of heat storage, which can reduce the effective size of the tank by more than a third in many cases.
The problem can be avoided by using vertical ports with diffusers at high/low points of the tank domes, but this can complicate the plumbing, and it can make the tanks too tall in many cases.
Another option would be to use double-tapped bushes and add internal riser/dip tubes that deliver flow up/down to top/bottom of the tanks.
True to a point EW but you have to remember that perfect stratification does not exist unless there is no circulation within the tank.
A small percentage of usable volume may be lost but currents from pumping and natural convective flow in the tank keep fluid above the tappings blended pretty well.
I observed one of the more mindless things I have seen in a tank battery a couple weeks ago however.......
The ports were arranged on the sides of the tank about 12" from the top and absolutely no provision at all was left in the system to remove air trapped above them. No air vent, no manual valve, not even an opening in the tank. A good 10-15% of the tank was wasted space. This system was spec'd and drawn by an engineer.
So just put two ports in the middle of the tank and let let convective flow take care of the rest.
Where having the boiler supply at the top of the tank is when flow is reversed when the boiler is off and you are drawing from the tank. More capacity available. On my measly 120 gallon vertical buffer tank I can see a 20-30 degree difference from the top and a point 1/3 down from the top when supplying a load from the tank. Since the boiler is triggered by that second system, this gives, like a ten or 15 minute lead time for the boiler to get up to temp.
I've seen a number of real horror stories where engineers simply did not understand thermal stratification at all. In my experience there's a *huge* performance advantage to be gained in most (not all) storage applications if you can minimize mixing and maximize stratification. This document does a nice job of emphasizing stratification and other key concepts that are often missed.
It's also good to see lots of alternatives to primary/secondary systems. They're great for commercial installations, but they don't easily accomplish a good delta T between supply and return when heating from storage. Conventional wisdom used to be that primary/secondary was the holy grail.
The author of the slides John Siegenthaler has a few online course on Heatspring.com including what appears to be the one that the slides were developed for.
I took the course when it was launched. Saved the day many times.
Although I forgot about how to pipe the vertical storage tanks properly. It caused mixing and didn't stratify. Side ports into the water storage tanks would have solved that. And the initial hicccups of releasing the trapped air on top of the tanks...
If some folks think the course is too much, then buy the textbook. Its worth every penny.
one idea I like is to use the very top port as a supply to an indirect water heater only (and an air vent, of course). It is often the case that the lowest usable supply temperature coming from the tank is a function of indirect water heater performance, not space heating. This is especially true with low-temp systems like radiant floors. You might, for example, have to re-charge the thermal storage once it gets down to 120F in order to be able to make domestic hot water. However, if you have radiant floors, you might be able to heat well with 100F supply. By leaving the hottest water "stranded" at the top of the tank, it is available for domestic hot water production while the rest of the tank can continue to be drawn down by space heating.
NYSERDA is offering a free webinar training at 13:00 EST, Titled: Outdoor Wood Boilers Done Right.
The webinar uses the presentation that the OP linked for us in the first post. The link below will take you to the registration if you can make it in time.
Replacing an outdoor wood furnace with a cordwood gasification boiler - Design and installation considerations.
This webinar presents what installers need to know based on the requirements of the Renewable Heat NY program. Specific topics include: Thermal Storage requirements, boiler venting, evaluating existing buried piping, evaluating the balance of system, wiring considerations, and operating the cordwood gasification boiler.