A sprinkler installation is basically a water-filled pipe system with spray nozzles and a large sprinkler pump. If the pump supplies pressure, the same amount of water will not come from every sprinkler head.
That mainly depends on the pipe resistance between the sprinkler head and the pump and the height difference between the highest and lowest sprinklers. A sprinkler head near the pump (located low) will deliver more water than a sprinkler head that is located at a great distance (higher).
It is important that every sprinkler head supplies enough water. But often the amount of fire extinguishing water is limited and you do not want much difference between the yield of a low-lying sprinkler and a high-lying sprinkler.
If you match the size of the pump to the lower-lying sprinklers, much more water will come out than the sprinklers located above. After all, more pressure is available because the water needs to be raised less.
Due to the large difference in yield between the sprinklers you will have to build up a much more expensive water supply because of the sprinkler head with a high yield. The pump will then also be larger and therefore more expensive.
For clarification see the image below:
It is clear in the image above that the distance between the water pump and the first layer of sprinklers is smaller than the higher-lying sprinklers.
With a hydraulic calculation you make clear what is the difference between the highest and the lowest yield per sprinkler head for a given pipe network. This takes into account, among other things, flow properties of the liquid, pipe length and bends, the pump characteristic and the passage of the sprinkler heads.
By designing the pipe network so that the pipe resistance is approximately the same in all cases, you ensure that the sprinkler heads all have approximately the same output and that the installation is hydraulically balanced. An additional advantage is that the installation functions as well as possible, but is also cost-effective.
To perform hydraulic calculations for complex situations, specialized programs are available such as HASS.