Development of a new indoor unit with propeller fan system for room air conditioner


In order to protect the global environment, the energy saving law of “Top Runner Approach” has been enforced. Manufactures have been striving to improve energy saving performance of room air conditioners, which consume much electricity at home.

In addition to the efficiency improvement, we are developing technologies to provide comfortable living environment by controlling air flow depending on the room temperature distribution detected by a sensor. To further reduce power consumption and improve comfort, we developed a new indoor unit (Fig.1) for air conditioners whose internal structure was renewed for the first time in nearly half a century. We also successfully improved comfort by controlled air flow with full use of the feature of a new fan configuration.

Fig.1 Developed Indoor Unit



As shown in Fig.2 (left), a cross-flow fan has been used in conventional indoor units, where air is taken from the front (the left side in the figure) and exhausted downward. However, in recent years, the front side is used for a design surface and is not available for air intake, which means the air passage is not suitable for cross-flow fans. To solve this issue, we drastically changed the air passage structure and developed a high-efficiency fan that matches the new structure.

We adopted a propeller fan that can take in and exhaust the air in the same direction along with air flow pass in the indoor unit. Propeller fans generally provide higher efficiency as compared with cross-flow fans, and thus the use of a propeller fan can reduce power consumption of the indoor unit. By locating the fan at the upper position, heat exchangers can be densely installed in the area where a cross-flow fan is located in conventional indoor units.

Fig.3 shows a propeller fan developed for indoor unit of the new structure. We developed a low-profile and high performance fan in order to mount as many heat exchangers as possible. The fan efficiency is degraded as the fan thickness decreases when a traditional method is used where the chord length is shortened and the number of blades is increased. We optimized the fan thickness and fan efficiency by conducting CFD as well as experiments on blade shapes and bell-mouth shapes.

We also applied stator blades for the stays supporting a drive motor to recover static pressure from the pressure loss induced by the rotation-directional velocity component.

As shown in Table 1, these changes reduced the power consumption of an indoor unit by 31% and improved the energy saving performance by 13.3% as compared with the previous year model. A new indoor unit accommodates multiple fans that can create two different temperature distribution in one room by controlling fans’ speed individually.

Fig.2 Conventional type(left), Developed new type(right)


Fig.3 Developed Propeller Fan


Table.1 Comparison of Power Consumption and APF*3

*3 Comparison between 2016 model MSZ-ZW565S and MSZ-FZ5616S

APF (Annual Performance Factor)



We developed an indoor unit for room air conditioners whose structure was completely renewed from conventional one, and achieved significant improvement in energy saving performance as well as comfort. We will continue to develop air conditioning equipment aiming for further energy saving by higher efficiency, thereby contributing to global environmental protection.

Tomoya Fukui*1

Kenichi Sakoda*1

Shoji Yamada*1

Akira Takamori*2

Takashi Matsumoto*2

*1 Member, Mitsubishi Electric Corporation

(8-1-1, Tsukaguchi-hommachi. Amagasaki 661-8661, Japan)

*2 Mitsubishi Electric.Coporation

(18-1, Oshika, Suruga-ku, Shizuoka 422-8528, Japan)