a central chiller not shown and each coil 12 14 and 16 will have a return line connected to the chiller the input to the proportional demand controller 40 is supplied by current transformer 50 which has inputs connected to power lines 51 entering the building and its outputs connected to output lines 52 which supply the power to the various loads within the building including the chiller or other type of condition controlling load output lines 52 supply all of the loads of the building while proportional demand controller 40 controls typically only loads which consume large amounts of power and which can be throttled downward without destroying their function such loads can include the building 39 s chillers and or other condition controlling equipment to show the manner in which power is saved with respect to chillers it may be assumed that the space supplied by the air flowing in duct 11 is a heavy load so that temperature sensor 33 requires valve 17 to be 100 open the space connected to duct 13 is a light load such that temperature sensor 34 requires valve 18 to be 50 open and the space connected to duct 15 is a light load resulting in temperature sensor 35 requiring valve 19 to be 40 open under these conditions if a seasonal peak load period does not exist such that the total current flowing through current transformer 50 is below level a shown in fig4 the percent load signal supplied from proportional demand controller 40 will be 100 such that valve 17 will be maintained at its 100 opened condition valve 18 will be maintained at a 50 opened condition and valve 19 will be only 40 open however if the total current flowing through current transformer.