Water Pump Efficiency and Redundancy
Tech Talk 75
We know what you're thinking ... here they go again, talking about efficiency. Yes, and we'll keep doing it. The problem is that, in the US, electricity is so cheap, we all but ignore it. Then, when we get the power bill, we complain about how high it is!
Here is a note on energy efficiency from our 1981 Aeration Handbook and Catalog: "... one kilowatt-hour is equivalent to about two days of hard work by one man." A man's labor for 5¢ per day–that's cheap!
As efficiency relates to aquaculture, pumping and aeration are the two biggest consumers of electricity. After feed costs and labor, electricity is probably the next highest overhead expense. Be careful when selecting a pump. Do not compare them by horsepower alone. Often, a cheap pump has an undersized motor that must work very hard to do the job. This may be an appropriate pump selection for temporary or noncritical applications, but not where the lives of your animals are concerned. Often, pool type pumps, when used for low-pressure aquaculture applications, keep the motor in a continuous overload condition.
Operating an undersized motor in the duty range of its service factor is acceptable from the pump manufacturer's point of view, but not a fish farmer's point of view. It lowers the pump's cost (which looks good when you are comparing pumps), but increases energy consumption and operating temperature. Higher operating temperature shortens motor life.
We've painstakingly selected and tested all of our pumps for power consumption. We've illustrated ratings, specifications and power consumption clearly. We use the term "aquaculture duty," to indicate long-term reliability and efficiency in humid, industrial applications.
Multiple water pumps provide redundancy.
Bigger may not be better when it comes to pumping water. For example, to pump 300 gallons per minute (gpm) to a height of 20', you could use one large 300-gpm pump, two 150-gpm pumps, three 100-gpm pumps, four 75-gpm pumps, five 60-gpm pumps, etc. To determine which is best for your application, consider the following options.
Large pumps may only be available with 3-phase motors. If 3-phase power is not available, an expensive, power-robbing phase converter must be used, or multiple single-phase pumps. Even if one large pump can be used, another one must be available as a back up, if the pumping need is critical.
Consider multiple pumps. If one pump moves 100 gpm, two of the same pumps together will move 200 gpm, three will move 300 gpm, and so on. If less than 300 gpm is ever needed, multiple smaller pumps will save electricity, as they can be individually turned on or off as needed (installing a check valve on each pump will prevent water from flowing back when that pump is not in use). Also, multiple pumps may be preferred, as then only a portion of the total water flow would be lost when one pump fails. The cost of having a small pump on hand for backup is much less than a large one. For a "ready-to-go" backup, extra pumps could be plumbed into the main line (put the pumps on separate circuit breakers) so that the reserve pump is ready when needed. Alternate the use of the pumps to keep them exercised.
Simplify the backup and spare parts inventory at your facility by using multiples of the same pump instead of several single-purpose pumps. Similar multiple redundancy can be used with air blowers, heaters, chillers, filters, etc.
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