Options

Design Options

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.

** HOLDING CISTERN **

For Pump Options 2 and 3 Booster pump can be fed directly off the Submersible pump, or with the Holding Cistern in between.

Advantages: 1) Possibility of water treatment (is it necessary?) 2) A buffer between Submersible and Booster pumps 3) ?

Disadvantages: 1) Possibility of contamination 2) ?

** SOLAR PANELS **

They can supplement grid power on sunny days. The total size would be approximately 18.3 KW at 100 GPM.

Brain suggests 10 HP may be more realistic. 10 HP (7.5 KW) roughly corresponds to 41 GPM for both submersible and booster pump (or combined pump). The filling time of Tanks 1 and 3 would be 24 hrs (pump working around the clock). However, assuming water demand of 30 gal/person/day, the water would be used up in 16 hrs. Also, this gives no margin for population growth. In addition, the pipeline from the pumps to the tank located next to the clinic is shared with the water system for another village (~9:00 -11:00 each morning; both systems are run 2-3 times a week) so the availability for Las Delicias is further reduced. But the analysis doesn't take into the account water from the spring to Tanks 2 and 3 (still unknown). Maybe we can get away with water supply of 50-75 GPM w/ power consumption of about 12-18 HP. 30 gal/person/day may be too conservative. It seems that currently the village receives between **8 and 12** gallons/person/day (Brian also estimated 8).

It would be interesting to know the **capacity of the pump supplying the other village** and, therefore, the approximate demand.

Solar panels may augment grid power or, with excess power available, add power to the grid for credit.

Brian points out that if we were to install a well near tank 1 we would probably only need a 10 HP pump.

Dawn have looked into the 7.5-kW solar panel system and found a kit of thirty six (36) 210 Watt Kyocera photovoltaic panels with inverter (DC->AC) and racking system for $31,500. We need to find out if the grid can be fed into it or if we need a battery bank.

Example solar panels:

Sunforce 39305 650-Watt High-Efficiency Polycrystalline Solar Power Kit, **0.65 KW, $4000**: []

Sunforce Products ProSeries Solar Backup Power System, **1.3 KW, $10,000**: []

Those don’t produce enough power (they can be stacked) and are expensive.

** TANK LEVEL CONTROL **

Float switch from EWB project in Thailand: []

New float valve idea: http://ewbelsalvador.wikispaces.com/Ideas

** ADDITIONAL WELL **

There is a possibility of drilling another well closer to the tanks. We would like to install a well that produces 50 GPM. This would produce **25 gal./person/day**.

The 150-m installed well cost quoted by the local company was **$20,000**, including the filtration system, excluding the pump. A 10-HP pump would cost **$4,000, $5,000** installed.

Therefore, the total cost would be about **$25,000**.

The Apatut team estimated the cost of 96-GPM, 40-60 m well at **$25,000**. They assumed the well installation (?) cost at **$10,200** so the total cost is about **$35,000** (have to confirm this). The numbers are in the ballpark.

Installing the new well near Tank 1 would only allow pumping to Tank 1 (35,000 gal) which will provides about **12 gal./person/day (24 gal/person/12 hours)**. The elevation is necessary for gravity distribution.

A 50 GPM pump would have to **operate continuously**. If it is located next to Tank 1 then filled Tank 1 will provide the 12-hour buffer for pump maintenance. A 100 GPM pump could operate 50% of the time using Tank 1 as temporary storage.

Installing the well next to Tank 1 will not allow using the gravity distribution system from Tank 3 (with the old well decommissioned for Las Delicias). Does the spring provide enough water for the distribution system from Tank 3?

Installing the well next to Pedronas crossing will allow filling both Tanks 1 and 3 but will not save much compared to using the existing well. Combined volume of Tanks 2 and 3 is 60,250 gal so they can provide **20 gal./person/day** (excluding the spring).

** WELL vs. PUMP REPLACEMENT **

** Table 1 **

Table 1 shows installed cost comparison. It looks like the new single pump at the old well is a winner. Stacked pump cost has to be further refined.