Pumps and Power Consumption

It is important for you to understand what happens with a water pump. This is because Koi ponds and their successful operation are far more intimately linked to actual flow rates than they are in a swimming pool.

Also, because your pump in your Koi pond will be running 24/7/365 the efficiency of your pump will make a big difference to your bottom line when paying the electricity bill each month.

At R1.088 per kWhr it will cost you R79.43 ex VAT each month for every 100W you put into your pond pump.

That statement is loaded. It states for every 100W you put into your pond pump. Pumps quote their power output in terms of watts delivered, not consumed!

Hence a pump that claims it is running at say, 90W might be consuming as much as 250W. In other words, you are paying 250W for an effective 90W delivery. In other words, the pump is inefficient in converting watts consumed into moving water.

This is common place amongst cheap pumps.

Swimming pool pumps that deliver 750 watts, or 0.75 kW or 1 HP are typically much better. They will consume around 900W to deliver 750. That's around R815 a month including VAT.

So be aware. Don't believe every thing you see on the label. Often the only way to be sure is to physically hook the pump up to a meter when it is up and running to test and see exactly what kind of power it is actually drawing.

What you should be after to minimise the costs of running your pond is maximising the volume of water delivered per watt you pay for. We use a figure of litres moved per hour per watt consumed. The higher this figure, the better.

For instance you get a chart that looks something like this - with a few of the pumps we have tested and measured with actual consumptions used, not those quoted on the box:


Pump Description     Quoted power      Actual power       Maximum flow rate         Litres per hr per watt

Submersible              250W                     360W                    18 000 l/hr                        50

Submersible              90W                        250W                    18 000 l/hr                       72

Submersible              160W                      220W                    20 000 l/hr                       90.1

Submersible               50W                       60W                      10 000 l/hr                       167!

External                       370W                     360W                     18 000 l/hr                       50

External                       750W                     900W                      24 000 l/hr                      26.67


So there is immediately a fair amount of variation - from 50 l/h/w to 167 l/h/w. That's significant.

However, there is a lot more than meets the eye to these equations. All of theser figures assume that the pump is capable of operating at its maximum flow rate. However, in the real world the flow rates are affected by many things and pumps react differently. Which is why each pump has it's own set of curves.