This is a simple calculation indicating how much each piece of equipment is carrying for either the heating or cooling load of the home.

If you have one heating system, it carries 100% of the heating load.

If you have two heating systems, maybe a furnace and a few rooms with baseboard heating, the furnace might carry 80% of the load, and the baseboards 20% of the load.

The percentages must add up to 100% for the heat loads.

For cooling, a central a/c unit would carry 100% of the load.

If you also had one or two window a/c units maybe in a hot upstairs - the central a/c might carry 80% of the load, and the windows units carry 20% of the load. So together they carry 100% of the load.

In some homes, you might find only a couple of window a/c units or an evaporative cooler and no central system. In that case you would estimate what percentage of the home they cool. That might be 30% of the home has cooling.

You are not required to have the cooling units add up to 100% of load - only the heating systems. Heating systems are assumed and required by most programs.