On Sun, Dec 22, 2024 at 07:47 AM, Jonathan Smith wrote:
Flow x pressure = horsepower
The formula oversimplifies reality, as horsepower is directed through impeller designs with different efficiencies.? And even for a given impeller design, the efficiency of pushing air is affected by atmospheric pressure.? Or to put it another way, you need a constant factor added into the equation that accounts for impeller design and atmospheric pressure.? A few hundred feet of elevation one way or the other doesn't make enough of a difference to worry about.? But here in Lake Tahoe, the ~1950m elevation makes a material difference.
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Any dust collector manufacturer worth dealing with will publish a fan-curve chart for the collector's performance at the inlet, which will allow one to avoid the need for test equipment to measure the static pressure of the collector, but those fan curve charts will be calculated for something close to sea level.? Better manufacturers will be able to supply a fan curve chart adjusted for a specific altitude.? For example, here's what Al-Ko has provided me for an 160P, with the sea-level and 2000m curves showing the drop in performance at my altitude:
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Not every vendor will offer that personal service, so the alternative is finding a reference for a static pressure adjustment factor for a given altitude.? Al-Ko's standard fan-curve is calculated at 400m altitude, while their adjusted chart shows a drop of about 500 Pa at my altitude.? Using the reference book adjustment factor of 1.27 increase in static pressure for my elevation, and you get a result that pretty closely matches their adjusted chart.? With either approach, it's then reasonable to use something like Bill Pentz's spreadsheet to estimate ductwork static pressure, and have a good chance of designing a dust collection system that will function as expected once purchased and installed.? I'm a one man operation, so the simplicity of planning for a single tool at a time works for me.? Bill's spreadsheet won't work for anyone designing a multi-tool collection system, as he acknowledges.? Even his advice for calculating dust collection for a single tool with multiple dust ports is a bit questionable.? Were I looking at a multi-tool collection system, I'd just bite the bullet and pay a professional to do the more complex math needed.
