The term "Blockload" is used to express the net simultaneous room sensible room heat gain. This load is only the room sensible load and does not include system factors such as ventilation load, fan heat, etc. It can be any load that may exist in any room or group of rooms that the system sees as a whole at any given time. If the block room load is a net heat loss, its value is negative.

The factor (Th - Trm} in the numerator suggests that the cold flow rate will increase if the hot duct temperature is increased. At the same time, however, the factor (Th - Tc} in the denominator suggests that the cold flow would decrease upon an increase in Th. In any case, it is hard to guess what will happen to what when looking at the equation.

None the less, it is the equation, and while the warm flow rate can be similarly expressed, it is generally easier to obtain the warm flow by simply subtracting cold flow from the total. Having established both flow rates, it is relatively easy to calculate the 'operating loads incurred ih both paths from the statepoint change that takes place from the fan discharge to the final conditions in each duct or plenum.