Due to the dynamic nature of demand, measures are necessary to regulate flow in the system. Traditionally, this is achieved with the aid of throttles (e.g. valves). However, adjusting the flow-rate by throttles can be likened to adjust the speed of your car by applying brakes while also giving full gas to your car's engine. Throttles are cheap and easy to operate, but as they regulate flow by increasing the pressure drop in the system, they result in significant wastage of energy. Therefore, alternative flow regulation strategies should be explored.
Alternative flow regulation approaches may include changing the impeller of the pump, installation fo a adjustable or variable speed drives, permanently reducing the pump's speed, and installing smaller and/or multiple pumps. These will have their own advantages and shortcomings – for example, a VSD will provide flexibility and fine-tuned response, but will only be feasible for systems that run long periods and that show significant fluctuations in demand. Impeller trimming may be a cheaper alternative, but will only serve effectively when the reduced demand conditions are lasting. Systems with relatively fixed changes, on the other hand, may be best served by multiple pump arrangements. Consequently, selection of the best strategy will require a thorough assessment of the system and alternatives.
See also: variable speed drives.