I recently came from an install that had a Franklin Variable Speed pump system. The pump is located about 60 feet down and is set to 60 psi for the home. There is two heat pumps. One is a single stage water to water and the other is a two stage water to air. There is a single taco geothermal valve on the water to water and two taco geothermal valves on the water to air (2 different flow rates for the 2-speed). The amp draw while all valves are open (10.25 gpm) is 4.75 (230V pump) this seems acceptable. The amp draw with one valve open (4.5 gpm) is 4.25, this seems high. Does anyone have any experience with different brands of variable speed pumps? Does the Grundfos efficiency track better according to gpm? Is there changes that could be made to improve the pump efficiency on the Franklin system? Note: No other water was being used in the house while the test was being done. System maintained pressure with pump off (no leaks). Thanks in advance for suggestions.
In general I've thought of vfd's as more of a flow management device vs. energy savings device. That is just based on results such as what you are indicating and on what I've seen on larger devices. Hopefully there is an expert on their electro mechanics here. Off to read the wiki.
I like to think of vfd's as perpetual motion machines. They achieve the desired result= variable flow rates, but they consume electric as indicated, yet they consume less electric and are more long lived than a traditional set up at higher flow rates. You can rarely get it all. Most open systems are still grossly oversized in regard to gpm and pressure. The only way to reduce the pumping cost is to move less water at a lower pressure for the geo. No, the grundfos will not consume any less than the franklin, it is a symptom of the solution the problem of variable flow rates. Eric
This is pure conjecture, but... Amp draw may not tell the whole story...at low freqs power factor may decline so that amp draw is an inaccurate indicator of Wattage. Residential customers don't typically pay for apparent power, just actual power in kWh, so a load with low power factor assessed via just a current measurement may look far worse than it is. What's needed is an actual power measurement. A variety of instrumentation is available to do this. TED5000 and possibly Welserver are worth a look.
Thanks for the info. I have some TED metering devices on my shelf that I can use to accurately check it.
