About accuracy error

I am wondering whether accuracy error of pressure is 0.25% of full scale (25 in H2O). When I used this as my accuracy error of pressure, error of everything becomes so large that it's almost impossible.

Yes, the 0.25% is the full-scale accuracy error. This will end up being a pretty large percentage of your measurement at very low differential pressures, as this device is not very accurate close to zero differential pressure.

the accuracies are so large for the pressure transducer at low RPM and open valve position that sometimes they are 6-8 times as large as the measurement itself. also josh, regarding precision error, I was wondering if we are supposed to be using the standard deviation or standard deviation of the mean in the output file?

That is one of the chief reasons why you probably will not want to use your data at the lowest blower speed setting (the other being that you will probably get negative efficiencies because the correlation overpredicts Wloss).

In general, you should probably go with the standard deviation of the mean for your precision uncertainties.