Every indoor unit attached will operate at a random, self-regulated capacity, based on the actual demand it measures from the zone it is serving (Between 30% to 100% of its rated capacity or OFF). Outdoor unit will also self-regulate its output capacity, based on the total demand it reads from all of the simultaneously running indoor units at any given moment.
With multi split systems, the total demand from the outdoor unit, shall seldomly exceed 77% of the total available capacity of the combined indoor unit group due to load fluctuations. Although very seldom, if and when the total demand from the combined indoor group exceeds the rated capacity of the outdoor unit, the capacity of each indoor unit will be annotated accordingly.
For high demand heating applications, max loading limits may need to be reduced by 10-15 % to avoid underperformance risks at some extreme conditions.