The energy consumption of the systems used in the heating, refrigerating, and air-conditioning field continues to increase. This necessitates improvements to the efficiency of these systems. However, in Japan, the performance of heating, refrigerating, and air-conditioning systems has already been improved greatly owing to the considerable efforts of manufacturers, the government, and academia. Therefore, it will not be easy to further decrease energy consumption simply by improving the efficiency of each system. In order to adhere to the demands of the worldwide energy saving policy, we need to investigate the best combinations and total energy management schemes for heating, refrigeration, and air-conditioning systems. To this end, simulation holds greater promise than actual field-testing because it is not easy to carry out such experiments on actual large-scale systems. High-precision simulation models are necessary for these investigations. Hence, we are developing simulation models for a heat pump, room air-conditioner, desiccant dehumidifier, indirect evaporative cooler, fuel cell, solar panel, and so on. This paper describes high-accuracy simulation models for a $CO_2$ heat pump, absorption heat pump, and desiccant dehumidification system. We also discuss the simulator that we have developed, based on those models. This simulator is called "Energy Flow + M". It is very easy to use because it has a user-friendly GUI. It has already been made available worldwide through the Internet. It is expected to be used to decrease the energy consumed by heating, refrigeration, and air-conditioning systems.