In this study, we analyzed VWV system control and theoretically demonstrated the effect of minimum differential pressure control in a VWV System. Constant differential pressure control or Predictive system curve control or Constant differential pressure control is widely adopted for variable flow control. Since the resistance of a complicated flow passage cannot be specified, even with an extremely small load, it is set as a constant differential pressure and the predictive differential pressure on the safe side, so the differential pressure reduction margin is large. When there is uneven flow rate or when a plurality of branched piping systems are connected, there is a possibility that piping resistance fluctuates and the flow rate becomes insufficient besides assuming terminal end. There is a possibility to greatly reduce differential pressure. In this research which optimally controls the head by the control valve monitoring, after reporting on the actual results where the annual WTF is 125 or more, we also reported a research example that was applied to a building. The control (minimum differential pressure control) to lower the pump differential pressure until one of the flow control valves is monitored, and one of them is close to the fully open state which is unlikely to cause a flow shortage at the full load and is carried by the minimum differential pressure indicating that power reduction can be achieved. By modeling the change of the theoretical power of each variable flow control system by a case study, it is shown that there is an influence due to the uneven distribution of flow rate, where the localized influence becomes small at the distribution range of flow uneven distribution and low load, and the effect of controlling to minimum differential pressure is indicated. We reported that the transportation power is cold water heating so the cooling heat transportation power reduction has the effect of reducing the cold heat load, and the actual performance of WTF 125 is sufficiently higher than the other energy transport efficiencies. We studied the change of the theoretical power of each variable flow control system by a case study, and showed the influence of the uneven distribution of flow rate and showed the effect where the localized influence becomes small at the low range and the low load due to the uneven flow rate, and the effect to control to the minimum differential pressure. Based on a case study in which variable flow control is applied to an office building, we compare the annual theoretical power including the influence of the pump, electric motor, and inverter performance reduction, and the WTF of minimum differential pressure control becomes 157, the reduction of constant flow rate pump ratio is 93 %, a 74% reduction in differential pressure constant control ratio, 52% decrease in estimated differential pressure ratio, 41% decrease in terminal differential pressure constant control ratio and WTF was 216 when the actual maximum water volume was 10% lower than the design value, and reported that design margin has the effect of further reducing power. We showed that the lower limit speed affects energy saving performance, and the WTF improved by more than 190 by lowering the lower limit value and controlling the number of units. In order to improve the stability of the differential pressure variation flow control, we showed an improvement method such as automatically judging the control valve that erroneously requests the maximum flow and the applicability to the commissioning. We showed high applicability to DHC because of a few control valves, and the necessity to analyze the possibility that the WTF exceeds 290 due to the expansion of the temperature difference with a small differential pressure.