The challenge: finding the best switching combinations
The binary pumps are not all running constantly. In fact, these four pumps can be switched on or off in 16 different combinations to provide the required amount of water. The calculations get even more complicated when the inverter pump is added to the mix. Here’s an example. If you need a flow rate of 3,500 m3, you would run three of the four binary pumps and have the inverter pump provide the rest. At least in theory.
The reality is a bit more complicated. For one thing, the binary pumps do not simply provide their nameplate capacity. Their actual output depends on a number of factors such as pipe routes, location, condition and age. This increases the variety of possible combinations, which in turn places different demands on the inverter pump. Also, running the inverter pump at full capacity fails to optimize energy use – as does running it at an overly low flow rate. In addition, the relationship between energy consumption and flow rate is not linear.
The challenge, then, is to determine how to pump a given amount of water while consuming as little energy as possible. At the same time, you want to wear the individual pumps at the same rate. That means all pumps have to be utilized approximately evenly. So the math problem is this: Which combination of pumps consumes the least amount of energy with the least amount of wear? And how long will each combination run while maintaining a constant flow rate?