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Thread: Variable speed - or not?

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    chumbley's Avatar
    Join Date
    Jun 2007
    Doylestown, PA

    Variable speed - or not?

    I have another more generic thread on this topic, but wanted to get some input specifically on the applicability of a VS pump in my pool.

    As background, I'm replacing all of my pool pad equipment (old, worn out, noisy, leaking, etc.) in my ~25K gunnite pool / spillover spa pool. I will also be adding solar, and I am planning to use SWCG. The pool has a 1.5" main drain and 2 x 1.5" skimmers, and two returns (from a single 1.5" pipe) with eyeballs. It also has a dedicated 1.5" line for a pool cleaner (haven't decided whether I want pressure or vacuum yet). The spa has a 2" main drain and 5 jets from a 2" line, plus an air blower. The solar will be about 10' up and about 50' from the pad. And some basic automation will be implemented.

    The current pump is 1.5HP, but is leaking, and screaming, and old and not terribly effective. So I can't tell much from what's installed. Electricity here is about $0.09/kwh.

    I have been leaning towards a VS pump, since:
    1) I don't believe a two speed pump on low will support the solar, and suspect it will run on solar a good bit of the time given the average temperatures and my preference for warmer water.
    2) I'm also not sure it will support SWCG on low (to get the necessary flow rates).
    3) And both together would be more of a challenge (I am guessing).
    4) I would like more "oomph" for the spa mode.
    5) I have no idea what two speed pump I should get because I can't effectively measure head with the current system issues.

    My options really are get a VS pump (ePump or IntelliFlo), OR get a ~1HP 2 speed pump (knowing I will run it on high most of the time) and separate jet pump (which gets me right back to the same relative cost as a VS pump), OR get a single ~2HP 2 speed pump and hope it supports SWCG and solar on low. The latter is most risky, but least cost.

    28K free form IG pool, pebble finish, spillover spa, Pentair IntelliFlo VS, IntelliChlor IC40, Easy Touch 8 PS, Quad 60 DE, Aquabot Supreme, Hayward LP heater

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    mas985's Avatar
    Join Date
    May 2007
    Pleasanton, CA

    Re: Variable speed - or not?

    1 - A 10' solar rise will still require a fairly high flow rate from either a VS or two speed pump. But you do have a lot more flexibility with a VS on setting flow rates. To maintain efficiency, the flow rate should be determined by the size of the panels (~0.1 GPM/sq-ft).

    2 - As for the SWG, most work down to 15 GPM so that is usually not an issue.

    3 - Running both solar and SWG is not really an issue. Solar will be the constraint.

    4 - The biggest problem with the one pump solution is that you are forcing high rate of water through the pad equipment so a lot of the pump efficency is lost with a VS OR two speed pump. The best way to get high power jets is with a separate pump on a separate loop.

    5 - This depends on if you go with a two pump or single pump solution. The single pump would need to be bigger to compensate for the loses in the equipment pad plumbing. So your current pump may be big enough if it bypassed the equipment but you may need a larger pump if you continue to go through the equipment.

    The biggest advantage of a VS pump over a two speed is the flexibilty rather than energy saving. A two speed will capture most of the energy savings but it isn't adjustable. At $0.09/kwh, the lifetime cost of the two speed will probably be much less than the VS.
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater, ThePoolCleaner

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