Nursery Efficient Pumping Solutions - Variable Speed Pumps

Due to increasing shortages of available water supplies and ever rising electricity prices nursery industry operators are currently investigating ways to reduce water usage, increase nursery efficiencies as well as conserving money. With variable speed pumping now more affordable and reliable than ever we have addressed some commonly asked  questions and myths.

How many ways can you save with variable speed pumping?

1.        Energy consumption : This is the primary saving with many nursery pump installations, savings of between 30% and 50% are  achievable in many installations utilizing Variable Speed Drive Technology. Typical payback period ranges from 6-12 months depending upon system size with ongoing cost savings

2.        Constant pressure : Variable speed drives can maintain a constant pressure on the entire system limiting pressure fluctuations  to around 10%. (Therefore should a low flow say via a garden hose be used the pressure will be exactly the same as the main nursery irrigation block watering.) Variable speed pumping  reduces the effect of water hammer commonly attributed to standard pumps cycling on pressure switch control thus avoiding premature component failure and enabling the same pressure at every block in your nursery (Subject to System Design)

3.         Improved System Reliability : Any reduction in speed achieved by using a VSD has major benefits in reducing pump wear in components (such as bearings and seals) extending required time period between maintenance or breakdown. Reductions in motor amp draw on start up are also reduced resulting in power savings.

I have heard they are expensive?

Variable speed pumping has become more common and is now considered a standard industry practice, consumer demand has forced more suppliers to offer variable speed pumping alternatives. This means more competition which for the nursery owner / operator results in more affordable prices, that is should your Irrigation & Pump Supplier Pass it On!. On average a 4.0kw (5.5hp) Variable speed single pump set complete  is around $6k - $7k while a standard pump / pressure switch / pressure tank arrangement being around $4k - $5k. This represents an investment of an extra $2k to have all the control benefits, power saving and cost efficiencies associated with variable speed pumping with a payback period of 6 to 12 months with ongoing savings are achieved.

Somebody told me to stay away from variable speed pumps, as they can have electrical problems, Is This True ?

Variable speeds drives and associated components are like most electronics circuits utilized currently in nurseries, - Irrigation controllers, computers etc  are sensitive to voltage spikes and surges, therefore it is recommended that upon any installation of any variable speed system, surge protection / phase failure to be installed by your electrician on your incoming power supply.

Can variable speeds be fitted to my existing pump unit ?

Yes, a variable speed can be fitted to any existing pump system, however every site needs to be individually inspected by your reputable pump supplier which is fully versed in all aspects pertaining  to variable speed pumping. This ensures that you get the right variable speed drive to suit your application and that the investment warrants the operational savings, Ask your pump supplier for a demonstrated payback period!

What benefits does a variable speed pump have over a Standard Pressure System?

Since a conventional pump can only operate along its fixed speed performance curve (regardless of the given flow requirement) the system must always involve other components in order to regulate the supply of water in the nursery ie constant pressure / sustaining valves etc, With variable speed systems large pressure tanks / valves are not normally required as constant even pressure is maintained via modulating the pump speed. Other benefits such as the following are typical of variable speed installations  -

1.        Pump(s) shut down in a case of loss of prime or no supply water

2.        Pump(s) shut down in case of a burst pipeline, ie excessive flow rate 

3.        Protection of the motor from over voltage, under voltage, overload and Phase Failure

4.        Can send out a signal for remote monitoring of pressure & flow rate

5.        Can be wired up to SMS your mobile / UHF communications in the event of a pump fault

6.        LED display for pump operation, status and any fault conditions which allows you to easily identify if the system has failed and for what reason ie – Low power, No Water, Burst pipe etc

7.        Flow rate calculation for instantaneous and totalized flow indication or for flow control rather than pressure

8.        Selectable options for additional pump & valve control (dosing, filter backwashing etc) and external communications

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