Tremendous energy savings can be achieved by replacing balancing and control valves in HVAC systems with variable-speed pumps. As these pumps adjust performance due to actual demands, the system is automatically well-balanced and the tedious process of manually balancing is a thing of the past. It sounds nearly too good to be true. Can variable-speed pumps control air handling units… with the same efficiency and authority as valves?

The answer is yes, they can. To prove this,… we have made a simulation consisting of a chiller, a primary pump, and a riser that supplies four air handling units (AHUs), each controlled by secondary pumps. Each AHU has a capacity of 64 tonnes of refrigeration and should receive 27 cubic metres per hour, equivalent to 7.5 litres per second, at full load.

Now, let's run the simulation. We'll start by letting all secondary pumps run at full speed. As you can see, all the AHUs lie very close to the target flow of 7.5 litres per second. Now, let's try switching off the first pump.

You can see that the first AHU now gets zero flow while the three others are still close to the target flow. Now, we will switch the first pump on again and turn off the second pump. Again, you can see that the corresponding AHU now gets no flow, while all others are very close to 7.5 litres per second. So, as the simulation demonstrates, AHUs can be relied upon to be efficiently controlled with variable pumps in distributed pumping systems.