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Comparison of ERDs

The tables below are a representation of the main factors used in deciding the feasibility of an ERD in an RO system. The HPB and the HP-HEMI provide the best solution for any RO system.

Capital Costs	HPB	HP-HEMI	Isobaric Chambers	Pelton Turbines
HP Feed Pump	Lowest	Lowest	Medium	Highest
HP Booster Pump	N/A	N/A	Yes	N/A
HP Flow Meters	N/A	N/A	Yes	N/A
Sampling ports, TDS measurements, etc.	N/A	N/A	Yes	N/A
ERD HP Piping Manifolds	N/A	N/A	Yes	N/A
Additional Instrumentation	N/A	N/A	Extensive	N/A
Floor Space	Minimal	Minimal	Extensive	Moderate
Cost Ranking	1	2	4	3

System Complexity	HPB	HP-HEMI	Isobaric Chambers	Pelton Turbines
Auxiliary Equipment	None	None	Extensive	Some
HP Booster Pump	No	No	Yes	No
HP Flow Meters	No	No	Yes	No
Sampling ports, TDS measurements, etc.	No	No	Yes	No

Energy Efficiency	HPB	HP-HEMI	Isobaric Chambers	Pelton Turbines
Feed Pump Efficiency	Highest	Highest	Reduced	Highest
Size of Pump and Motor	Reduced	Reduced	Reduced	Full Size
Parasitic Losses	No	No	Yes	Sometimes
Brine Intrusion into Feed	No	No	Yes	No
Specific Energy Consumption (ranking)	2	1	2	3

Pressure Controls	HPB	HP-HEMI	Isobaric Chambers	Pelton Turbines
Feed Pressure Control	Partial	Yes	None	None
Brine Pressure Control	Yes	Yes	Yes	Yes
Brine Discharge Pressure	Unlimited	Unlimited	Limited	= zero
Brine Discharge Controlled by LP Feed Pressure	No	No	Yes	No

Sensitivity to System Upsets	HPB	HP-HEMI	Isobaric Chambers	Pelton Turbines
Air Bubbles	No	No	Yes	No
Flow Spikes/Variations	No	No	Yes	No
Bio Fouling	No	No	Yes	No
Minor Debris	No	No	Yes	No
Changes in LP Feed Pressure	No	No	Yes	No

Life Cycle Cost Factors	HPB	HP-HEMI	Isobaric Chambers	Pelton Turbines
Capital Costs	Lowest	Low	Very High	Medium
Installation/ Foundations	Lowest	Lowest	Very High	High
Energy Savings	High	Highest	High	Moderate
Training	Low	Low	High	Low
Auxiliary Equipment Maintenance	None	Low	High	Low
Downtime	Low	Low	Moderate	Low
LCC Ranking	1-2	1-2	3	3

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