a tall well insulated chimney would sort that out, and flow velocity (and hence mass flow) in chimney can be accurately inferred from temperature given column pressure differential caused by air density difference. Calorimetry with just two thermocouples to measure inlet and outlet air temps!
On 13 October 2014 09:13, Steve High <[email protected]> wrote: > Well I spent an hour or so in the HVAC world and sure enough Jed was > right. Apparently the standard for measuring air flow in a round > duct involves checking wind speed in 18 locations along three separate > axes, which is probably not practical when you are trying to assess air > flow in a dynamic system. On the other hand I think it is safe to assume > that the purveyors of natural gas have worked out a way to know precisely > how much petroleum is flowing through their pipes. In the lung doctors > office you can blow into a tube that will show precisely how much air your > lungs are moving. So if there was a monetary reason to efficiently know > how much air is moving through a system we would probably have a reliable > means of doing so. > > On Sun, Oct 12, 2014 at 4:19 PM, Jed Rothwell <[email protected]> > wrote: > >> I have had wretched experiences trying to do air-flow calorimetery. It is >> done by HVAC installers on a daily basis, so it does work, although I >> gather it is imprecise. I know it is hard to do right. >> >> The hard parts are determining the flow rate of air, and finding the >> temperature, which varies in the stream even when you go to great lengths >> to mix the air. >> >> - Jed >> >> >
