J F Graham wrote:Sunny Boy, IMHO, I feel you kinda said it all. I've been using MPD's for many years with wood, and most recently with a Harman boiler. Even though Harman does not recommend one I put one in thinking worst case scenario I could just leave it open. initially, with MPD open the heat was there, but the coal was gone. Now with a mano, and adjusting the MPD till I get a reading of .05 to .06 I can easily go 12 hrs between loads even in this weather. No different than cruising in a boat, you gotta find the sweet spot.
True, for best economical cursing , you find the boat's sweet spot by using a vacuum gauge and a tachometer, then swap props of different pitch until you find the one that gives the highest vac readings at the engine manufacturer's recommended cruising rpms. Then, that's the most economical set up for that hull's drag.
It does make a difference. But, like different boat hull shapes, I won't be surprised to see that difference likely will vary quite a bit with stove/stack differences.
Like the vacuum gauge and tach, manos and temp gauges can show what affect the MPD is having on stove output.
My RN girl friend reminds me that manometers are for showing low pressure of gases, and she's correct. There's a mano on the wall over every hospital bed as part of the oxygen system.
But, with the mano gauge hooked up "backwards" as we use it (tube to the "low" connection), that actually turns it into a vacuum gauge - like you would use to tune a gas engine. The mano is just way more sensitive than an automotive vacuum gauge.
I found the sweet spot for my stove/stack combo by using the same setting for the primary damper and then checking the mano readings as I experimented with different MPD angles. Each time, I change the MPD angle, I checked stove and stack temps with my IR gun.
I found I was wasting about a pound or two of coal a day by not using the MPD at it's optimum setting. To someone with a large coal furnace, or boiler, that may not sound like much, but with my small kitchen range averaging 30 pounds a day, that pound or two is a pretty good percentage saved. Using the MPD is like I just got a free day worth of coal every month. If a large stove could save a day worth of coal each month that adds up to some real money. Then the mano would be paid for in the first month, or two, just by the savings on coal.