Running Pentair Intelliflow Pumps in Parallel

[71SoCal]

I have a 12,000 gal. IG pool with an IntelliFlo pump. I've read that running the pump around 1000 rpm is most efficient, but my salt generator complains about flow rate unless I run the pump at least 2000 rpm (especially if solar is on).

Is it possible to run two IntelliFlo pumps in-parallel, both at half-ish the rpm, but effectively doubling the flow rate? It seems to me that as long as it is plumbed evenly (and efficiently), it should work???

I don't completely understand dynamic head pressure, but is seems to me that there shouldn't really be a difference between say one pump at 2000 rpm, and two pumps at 1000 rpm, again assuming they are in parallel and not in series.

Does anyone have experience with something like this? Thanks...

[PoolDoc]

1. Running pumps in parallel is tricky. It can be done, but all sorts of problems can arise. Worse, it's unlikely to be efficient.

2. Pump output is non-linear: depending on dynamic head pressure (resistance to flow), two pumps at 1,000 rpm might produce a small fraction of the flow (GPM) of a single pump at 2,000 rpm.

3. Fully valid considerations of energy efficiency consider not only the energy cost of operation, but also the energy cost of manufacture and installation. (This is why Al Gore's claims to be 'green' are so bogus -- he may have bought 'energy credits' for the cost of OPERATING his 10,000 sft house, but there's no way he's bought sufficient credits to offset the energy-cost to manufacture and construct that monstrosity! Like many environmental crusaders, he's all "Do as I say, not as I do!".)

From an environmental point of view, once the energy cost of manufacture is considered, you'll probably more efficient with a single old 1-speed pump, than with (2) VSR pumps installed in parallel. (Of course, a SINGLE variable speed pump will be more efficient than either.)

4. Regarding your SWCG -- most salt systems use a flow switch that is dependent on the 'shape' of the flow into the cell. Often, the switch can be arranged to activate properly by piping the upstream side of the cell with 1.5" pipe, instead of 2" pipe. Depending on your pool's layout, it may be necessary to install a bypass on the cell, with a check valve having a 1 lb spring on the bypass. This allows 100% of flow to go through the cell, at low flow, but allows the bypass to open at higher flow rates.

[mas985]

When you run two pumps in parallel on the same plumbing, you don't get anywhere close to twice the flow rate. This is because the head loss seen by each of the pumps is due to the combined flow rates. For example, on typical 2" plumbing, dual pumps will increase the flow rate by only 6% but the energy consumption increase by over 2x so efficiency is much worse. Compare that to increasing the RPM of a single pump by 6% for a 6% increase in flow rate, the energy increase is only 9%.

The most efficient way to increase flow rate is with RPM.

Here is the effective head loss curve with two pumps in parallel and at two different speeds. The parallel pumps (noted by (P)) has the head curve extended to the right but max head does not change. I also plotted plumbing Curve-C over the head curves so you can see how the operating point changes for a single pump to a dual pump.