Still haven't decided on a design yet. I followed jackel440's thread after I found it on a google search.
http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=642.0Then I stumbled on peacmar's build here and read it with great interest:
http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=2132.30Then read his collection of information here:
http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=1182.0Question is this, is peacmar's research flawed? When running my numbers for tube diameter and length for the secondary heat exchanger, every commercial unit I've compared my numbers to are undersized according to the formulas in peacmar's thread.
When comparing how much area I would need on just a vertical heat exchanger for easier cleaning (like Central Boiler or Heatmaster) I come up with a incredibly large number of vertical tubes required or do the turbolaters work that well? According to the formulas in his thread I would depending on the size of the tube need up to 28 vertical tubes, or basically enough to take the place of the horizontal tubes in a P&M design. Vertical tubes are only half as efficient at transferring heat compared to a horizontal tube, unless of course using turbolaters doubles the efficiency of a vertical tube, if so then I'm back to a quite reasonable number of vertical tubes only which would greatly simplify cleaning. Vertical tubes only also greatly simplify adding a bypass.
Fan size, for the 8 hour btu's I'm looking at I need about 63 CFM, or according to peacmar's thread would need 150% of that or roughly 95 CFM. I see some use up to a 500 CFM fan. From looking at some videos of the newer Optimizer I'm guessing from the dimensions of the fan (narrow but large diameter) and the sound of it running that they use a higher speed blower that is capable of producing the required air flow but at higher static pressure than most squirrel cage fans can produce. A standard squirrel cage fan when the static pressure starts getting much over one half inch the performance drops off drastically. The one thing that's not mentioned anywhere in the thread is what kind of static pressure if any to expect.
Going with a scotch design and the required cleaning doesn't really bother me that much,
but the wife and I both like to travel in the winter. Normally if I cleaned it before I left it would be fine till I got back. However, about every other or every third year we travel to the UK to visit the wife's mothers side of the family. She doesn't have hardly any family left on her side here, but over their she has aunt's, an uncle, and a metric ton of cousins. When traveling that far it's not worth the hassle to stay for less than three weeks. When we travel Dad tends the boiler now as he has to come out every day to check the cattle anyways and I'm sure I can get him retrained to load a gasifier properly, but actually convincing him that it might need cleaned before we get home is something else entirely.