Cycling and modulation. How a stage with too much capacity unloads: a fixed-speed compressor runs flat out for part of the hour, an inverter or a valve turns down. Cycling and modulation.
A fixed-speed compressor has two outputs, all and nothing, so it meets a part load by running part of the hour — cycling — and pays for every start: AHRI 340/360's cycling degradation, and the fans and pumps in its condenser section that stop with it. An inverter compressor slows instead, and at part load runs at lower pressure ratios, which is where a scroll's COP is best; over a year that is worth about 15 % of a rooftop's electricity on a real map.
Which one a machine does is a fact about the machine, not a setting, which is why HVAC Builder's default is the conservative reading — it cycles — and an inverter must say so. Valves modulate too: a chilled-water coil fed from outside its graph unloads by its valve, continuously, and a coil that cannot get low enough shuts and cycles. A chiller on a trickle cycles on its freeze cutout rather than on water it cannot make.
Open the builder — the examples in the Design tab's sources list include a machine of this kind, and the Simulate tab runs it against a year of weather.
DOAS — dedicated outside-air system · SZVAV — single-zone variable air volume · VAV terminal box · Economiser · Waterside economiser · Demand-controlled ventilation · Face-and-bypass · Head-pressure control · Humidity ceiling and floor · Coupling · Priority · Category · Nested system · Design point and TMY year