Pump Efficiency

[chem geek]

Mark,

Thanks again for your wisdom and great advice. Before I got your response, I took a look at the IntelliFlow pump curves and came up with the following formula that tracks very, very well with the curves:

Head = (RPM/350)^2 - (GPM^2)/470

This essentially reduces to the formula you gave, if comparing two different Head/RPM combinations, assuming that the GPM is 0. The above is more accurate when there is a non-zero GPM, but because the curves are relatively flat this isn't a huge difference at low GPM.

For the 4x160, I intentionally wanted to use different flow rates for solar on and off since the solar on required 48 GPM for its solar panel efficiency while the solar off had no such requirement so could use a lower GPM of 33 worst-case (i.e. 8-hours) and this lower GPM (and RPM) should result in lower power and energy cost. This assumed that I always ran the pump for 8 hours since that is how long the solar could effectively be used to heat the pool. I understand that a single flow rate is simpler, but it's also (somewhat) more expensive.

For the full IntelliFlow, I can see how setting a single flow rate is easy (and I wouldn't need the IntelliComm in that case) and that the IntelliFlow can cut the runtime to only do a single turnover, but there could be a case where it goes for 5.5 hours without the solar and then turns off (because that's one turnover with the 48 GPM rate that I must have to make the solar efficient in case it comes on), but then the sun comes out and there won't be any solar heating because the pump is off. That's why I wanted to hook in to the solar as a "feature" to be able to force the pump on. So while I had two situations anyway (solar on and solar off), I figured to minimize the energy usage in the most extreme cases with two different GPM rates.

I understand the simplicity of a single flow rate, but thought I'd get away with lower flow in the solar off times because, well, because I can. In fact, I don't have to limit myself to 8 hours in that case and can have the pump "enabled" for the full 24 hours since I know the solar won't get triggered except during the day while the pump could use a VERY low GPM over up to 24 hours until one turnover is achieved. What I don't know (yet) is at what point a low GPM becomes less energy efficient where the longer time takes more energy than is saved by the lower GPM (and lower frictional losses). I don't have a good formula for the "power" curves except that it's about 50% of output power (proportional to product of GPM and Head) above about 40 GPM at low RPM and above 80 GPM at the highest RPM (at very low RPM, efficiency goes to hell regardless of GPM -- probably due to electrical and motor efficiency losses, so clearly using a very low GPM does not make much sense).

A leaf trap to the vacuum line -- BRILLIANT! Jeez, I wish I had thought of that, but am glad you did. It seems that the requirements for a vacuum unit are much less stringent (it would appear that they require 25 GPM) and I could probably then have an automatic valve switch to use the vacuum cleaner on suction (instead of the skimmer) and the flow rate could be set to whatever is needed for that feature (hopefully, the same 48 GPM that the solar uses would be sufficient, though this is cut down due to sharing the suction with the floor drains which are on a separate line until we get close to the pump; also, the line to the cleaner is 1.5" instead of 2" so the losses will be greater than on the floor drain line). If I wanted to figure out approximate flow rates for these two lines that are branched together at the suction side of the pump, how do I do that? I can estimate friction losses from the pipe, but how do I know what losses or restrictions there are at the floor drains and skimmer? I know that the negative pressure at the pump side must be the same between the two lines (though their GPM will clearly be different due to different line sizes) and can calculate the less negative pressure as I move through the line, but do I just assume no resistance at the opening to the pool and just assume the flow rates are related to the size of the line (i.e. assume the suction loss is the same in both lines and work backwards to calculate the GPM in each line that would make that happen)?

In terms of using a robotic cleaner, I don't think I can get away with having a cord on our hardscape to go into the pool -- my wife is picky about those things. And removing the robot might be more of a pain, though maybe it's about the same as pulling out the pressure (or vacuum) cleaner -- right now we just put the line that was in the pool over onto our coping and keep the sweeper unit in the corner at the deep end while we use the pool. What problems do you have with your vacuum cleaner or using a vacuum line?

Thanks for the explanation of priming. That makes perfect sense to me.

I feel like breaking out singing, "I'm so excited....and I just can't hide it....I know, I know, I know, I know, I know I want IntelliFlo...I want IntelliFlo". OK, so my rhythm sucks.

Richard