Two size 130 coal guns would certainly be the optimum system but also very expensive installed solution. Oil and propane are my alternate back up fuels, but after combustion effiency calcs, both run in the $35 to $37 per million btu's range. Depending on where coal price settle in after this winter, I expect coal to run at $11 to $14 per million btu's. In my final system design, I anticipate a propane boiler in the house with a backup emergency. An oil boiler exists in the workshop and will be used for backup out there. I currently use wood as primary fuel and would be my cheapest source but is labor intensive. I need fewer hobbies, so I can pursue other interests. I have many years of HVAC design experience and system design is not my problem. I do not have experience with coal fire appliances however.
My problem is that I have house load at peak of 100 MBTUH and a workshop load at approx. 150 MBTUH peak. The workshop is used some nights for 2-3 hours and on weekends. Heat is turned completly off otherwise. This lopsided load presents the design challange.
I know as with any boiler, oversizing will result in loss system operating efficiency. The solution now becomes one of economics. How much do I spend on equipment verses how much higher cost fuel do I buy? I can figure this out if I enough info on the operation of the coal boiler I am looking at.
As far as the thermoash not firing the boiler, I understand this concept. It will shake the grate only if the grate ash gets cold, not bring on the draft fan. If the boiler does not have enough load, one of two things will happen: A. The boiler will overheat and require a dump zone or B. If the boiler is air tight enough, the fire will go out.
I have an option B that may turn out to be a better economic option. This would be installing a s130 with a large thermal storage tank that would charge during lighter load times such a nights and workdays when no one is home. However, the sizing and operation of thermal storage with large fluctuating loads can be somewhat tricky.
So, with all of that said, the bottom line is that I am trying to figure out coal operation and consumption during low loads and what is defined at a low load for a coal-gun boiler.