I Arrived in Banos at About 4 Pm

Date: October 31, 2010

PUMPING SYSTEM

Existing

Submersible Pump: about 218 GPM, 15 HP (11.2 KW), 4’’ piping

Holding Cistern, volume = 3300 gal.

Booster Pump: about 200 GPM, 60 HP (44.7 KW)

Findings:

Reducing the booster pump flow to 100 GPM saves 19% of power (16% with VFD); reducing the flow to 50 GPM saves 23% of power (20 with VFD).

At 100 GPM the instantaneous power consumption is 13.2 KW (17.6 HP); at 50 GPM 6.2 KW (8.3 HP).

At 100 GPM Tanks 1 and 3 will be filled in about 10 hrs without balancing valves; at 50 GPM in about 20 hrs with balancing valves (which will reduce power savings).

Option 1: add VFD (variable frequency drive to booster pump)

Assumptions:

1) VFD cost: $50/HP-$240/HP; $145/HP on the average

2) Motor cost: $100/HP (new motor may be required in case of VFD retrofit)

3) Apatut 5-HP pump costs $2,500 with the motor. It is used as a benchmark. The pump cost (with the motor) roughly scales with HP to the power of 1.6.

4) New flow of 100 GPM is assumed. Flow of 50 GPM saves little power but may extend the pump operation to around the clock, leaving no margin for increased water demand in the future or periods were the system is down for repairs and cleaning.

Calculations are attached separately.

At 100 GPM the VFD cost would be about $8,700; motor cost $6000. Total capital investment is about $14,700. There is a possibility that the old motor may be sufficient as it will draw less power.

At the same time the Submersible Pump flow would have to be reduced as well (3300 gal in a holding cistern gives only a 30-min buffer at 100 GPM, 1 hr at 50 GPM, not much.), either by another VFD or by pump replacement.

VFD with new motor would cost about $3,700.

Replacement pump at 100 GPM would draw about 6.9 HP (5.2 KW). It would cost about $3000.

It seems like replacing submersible pump makes more sense. The total capital investment of Option 1 is $17,700. Assuming the 30% installation cost, the total cost is about $23,000.

With the old booster motor and new submersible pump Option 1 installed cost would be $15,200.

Option 2: replace both Submersible and Booster pumps

At 100 GPM (17.6 HP) the Booster pump would cost about $5,300. The Submersible pump (6.9 HP) would cost about $3000 (as in Case 1). The total HP is 24.5. The total capital investment of Option 2 is $8,300. Assuming the 30% installation cost, the total cost is about $11,000. This is solely based on HP. One would need a quote for a possibly stacked pump (to develop enough head) to confirm it.

Option 3: replace both pumps with a single pump.

At 100 GPM the single pump would draw about 24.5 HP (18.3 KW) and cost about $6,500. The total capital investment of Option 3 is $6,500. Assuming the 30% installation cost, the total cost is about $8,500. This is solely based on HP. One would need a quote for a possibly stacked pump to confirm it.

Conclusion: replacing the two pumps with one (Option 3) makes most sense. It makes even more sense in view of unknown effect of the VFD on efficiency. Also, if we think Option 3 or 2 is the best there is no need to get more data on a booster pump.

The power required for all 3 options is 2.19 KWhrs/1000 gal at 100 GPM and 2.07 KWhrs/1000 gal at 50 GPM.