Your second to the last post question:
The model used is basically a pump model and is valid for any plumbing system. For a specific plumbing system and RPM value, there is only one value of GPM and Watts that the model produces. This why knowledge of the actual plumbing system is not required. Three equations and four variables are used in the model:
Pump Watts = Fw(RPM, GPM) - Determined from CEC data
Pump Head = Fh(GPM) - Determined from CEC or published head curve data
Plumbing Head = Fh'(GPM) - Generally unknown and is an output
Each spreadsheet uses the above equations to turn known inputs to the unknown outputs:
Watts2GPM
Inputs: RPM, Watts
Outputs: GPM, Head, Plumbing Curve
Head2GPM
Inputs: RPM, PSI, Suction
Outputs: GPM, Head, Watts, Plumbing Curve
PSI2GPM (Cost# sheets as well)
Inputs: RPM, PSI, Suction plumbing description
Outputs: GPM, Head, Watts, Plumbing Curve
All of the sheets require RPM as an input since this is always known. Also, all of the sheets calculate the plumbing system curve which is unique to each plumbing system and is generally not known.
Your last post question:
First, the filter pressure only gives you an indication of return head not total head. You need a suction measurement to get that. Second, the elevation of the pump/filter will affect the filter pressure and needs to be taken into account. Third, low flow rates generate low pressure and pressure/vacuum gauges lose accuracy at the low end of scale much like the flow meters. Most pressure gauges have a 1 PSI accuracy so if it reads 1 PSI, it could be anywhere from 0-2 PSI.
What was the actual filter pressure on the gauge (not feet of head)?
Also, what is the elevation of the pump relative to the water level?