Mitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)15

Development of Lightweight, Compact Inverter-type
Room Air conditioner which Cleared
New EU Energy-saving Regulations
YASUHIRO NAITO*1

HIRONORI MORI*1

JYUN AKITA*2IKUO ESAKI*1

SHINICHI TAKAHASHI*3

With the growing global trend of awareness about reducing environmental burden, demandis increasing for a replacement for the system of air conditioning for households to room
air-conditioners, which promise safe and efficient heating and cooling. Furthermore, in ourprimary market of Europe, new energy-saving regulations on air conditioners were enacted inJanuary, 2013. Mitsubishi Heavy Industries, Ltd. (MHI) placed on the market an inverter-typeroom air-conditioner complying with the new European energy-saving regulations, which is thehighest class in the industry in terms of its lightness and compactness.

|1. Introduction
At present, room air-conditioners are in the process of establishing their position as aheating-cooling combination appliance throughout the year. At the same time, they require highenergy saving efficiency because they are one of the home appliances consuming the largest
amount of energy in a typical household. This holds true of not only high-end appliances, but also
cheaper models, and it is hard to improve the efficiency of lowest price level, constant-speed
models unable to change their capacity, depending upon the air conditioning loads. Constant-speed
appliances can also barely meet the new energy-saving regulations enacted in Europe. In theEuropean market, therefore, air-conditioner manufacturers are hastily switching tohigher-efficiency inverter types. But inverter types are more expensive – although higher inenergy-saving efficiency than constant-speed types. It is important to place cheaper inverter types
on the market for the creation of comfortable living spaces and for the future response to a global
increase in energy demand, as well as for the concurrent expansion of our market share.

|2. Environment surrounding our company
2.1

European market environment

The scale of European market demand for room air-conditioners was around 4 million to 6
million units annually in 2007 through 2012, although variable due to abnormal weather andintense heat. Due to an increase in summer demand for cooling triggered by global warming anddemand to replace hot water and other radiant heating units, the area is likely to witness robust
sales of room air-conditioners in the future.

2.2

Energy-saving regulations

Conventionally, as an indicator to compare energy conservation, the value of rated capacity
to heating or cooling divided by the rated input power has been used to represent efficiency,
suggesting that the larger this value, the higher energy-saving efficiency. In the actual
environments where room air-conditioners are used, however, air conditioning loads continuously
change and, therefore, it cannot always be said that previous indicators correctly predict energy
conservation throughout the year. Hence, since January, 2013, periodic efficiency (ErP Directives:Energy Related Products) (Figure 1), into which the summated capacity necessary during the*1

Air-Conditioner Designing & Engineering Department, Air-Conditioning & Refrigeration Division,*2

Engineering Division, Aircraft Integration Department, Mitsubishi Aircraft Corporation*3

Nagoya Research & Development Center, Technology & Innovation Headquarters

Machinery, Equipment & InfrastructureMitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)16

cooling and heating seasons throughout the year is divided by the total power consumption during
the seasons, has been adopted for evaluation in terms of energy efficiency throughout the year. For
air-conditioners with a cooling capacity of 12kW or less, periodic capacity and periodic power
consumption are calculated in accordance with the LOT 10 Enforcement Regulations of the ErP
Directives.

Figure 1

Cooling (Heating) Season Period Efficiency|3. Popular inverter-type appliance
Our air-conditioner lineup for Europe consists of inverter-type quality, standard, and popularappliances. Among them, popular inverter types realize requirements from both the perspectives ofperformance and price on a minimum level and are the main models shipped in large quantities. In
the previous developments for popular inverter types, the functions of standard or upper-grade
models were only narrowed down. Although this has the advantage of easy extension toward avariety of destinations available through the narrowing-down of functions, it also has problems
including unit sizes that are just a little too large and costliness for inverter types due to thedevelopment based on upper-grade models. Determining that if we followed such conventional
development we would be unable to introduce any competitive models, we addressed the drastic
reduction in the size and weight of the popular inverter-type units.

|4. Efforts toward lighter weight/compactness
4.1

Efforts for outdoor units

Figure 2 contains an exploded perspective view of the outdoor unit and a graph showing theweight ratios. Many of the panels making up the framework of an outdoor unit are metal plates,
accounting for the largest proportion of the weight, with the heat exchanger/piping also as theheaviest component, which is followed by the compressor.

Figure 2 Exploded Perspective View of Outdoor Unit and Weight Ratio(Exploded view of a model for reference)(1)

Weight saving of panels
We conducted topography optimization, a technology by which thinning and weight
reduction are realized while maintaining rigidity. As an outdoor unit example, Figure 3compares an analytical result and the actual product shape:
The continuous base gathering in its longitudinal direction is an important point forachieving a level of rigidity equivalent to that of conventional plate thickness. The ultimate
shape based on the above finding and taking into consideration the drainage of condensationwater, the fit of each of the parts and the workability, is indicated on the right in the figure.
Other panels also underwent similar analysis and equivalent rigidity could successfully beobtained even though the plate thickness was reduced by as much as 20 percent.

Mitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)
17Figure 3 Topographical Base Analysis Result and Developmental Appliance’s
Product Shape(2)Weight saving of compressor
Figure 4 shows a compressor installed in our 2.5kW to 3.5kW-class air-conditioner. Acompressor with a motor incorporated inside is the heaviest component in an outdoor unit.
Focusing on the motor, which accounts for most of the weight, aluminum wire, which has aweight cost lower than copper, was used in the stator section, where copper wire is normallyused, in an attempt to make the motor’s cost reduction compatible with the lightening of themotor. As a result, the weight was reduced by about 10% while securing the requiredperformance.

Figure 4

Compressor and StatorThe part that appears bronze-colored due to varnishing is aluminum wire

(3)

Smaller controller
Since conventional controllers are made capable of expansion in consideration of
supposed functions specific to each destination, this has resulted in the unnecessarily large
substrate area of models that don’t need expansion like the developmental appliance.
For the developmental appliance, roughly the following three points were embodied:・Compactness of the circuit pattern design through the narrowing-down of functions
・Reduction of current capacity through expansion function curtailment
・Simplification of the compressor drive system
As a result, as Figure 5 shows, a reduction of the substrate area by some 15% and,
therefore, compactness of the substrate-housed control box size could be achieved. In addition,a revised current capacity has realized the compactness and cost reduction of the radiation fins
as well as the mounted components.
(4) Smaller outdoor unit
The interior of an outdoor unit can be roughly divided into the draft air duct and themachine room. The draft air duct consolidates components which play a role in heat exchange
and air draft including the heat exchanger and propeller fan. On the other hand, the machineMitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)18

room puts together a controller, a compressor, piping and other parts to circulate refrigerant into
the unit and control them. As for the developmental appliance, the machine room wassubstantially downsized by limiting efforts to small-capacity models to eliminate any surplus
space for the installation of a large-capacity compressor, while smaller and taller blades in thedraft air duct helped develop a fan which, despite its compactness, could secure the necessaryamount of supplied air flow, realizing a 22% reduction in volume from conventional appliances
as mentioned later.

Figure 5 Outdoor Unit’s Stand-alone Substrate of Existing (Left) and DevelopmentalAppliances (Right)

4.2

Efforts for indoor units

Figure 6 contains an exploded perspective view of the indoor unit and a graph showing theweight ratios.
In the case of indoor units, partly because their framework is made up mainly of plastic parts,
about 50 percent of total weight is accounted for by such parts. Plastic parts were, therefore,
subjected to parts count curtailment, as well as to wall thinning/weight reduction.

Figure 6 Exploded Perspective View of Outdoor Unit and Weight Ratio(Exploded view of a model for reference)(1)

Parts count curtailment
As an example of parts count curtailment, see Figure 7: Difference in Filter Pull-out
Mechanism. Indoor units have an air filter arranged in front of the heat exchanger to prevent
dust from entering the unit during operation. Existing appliances are designed so that the front
panel can be opened and closed and their structure does not allow the air filter to be removeduntil the panel is opened.

Mitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)
19The developmental appliance has integrated the front panel with the frontal structure tocurtail the parts count. Simple integration, however, raises problems such as being unable toremove the air filter. For the developmental appliance, this problem has been solved byunifying the top surface grid and the air filter. The grid on the top surface of the frontal
structure and the filter net were monolithically molded and made removable. The employmentof such a structure has enabled the air filter to be easily removed just be moving it toward thisside, thereby not only reducing the parts count, but also reducing user effort in opening thedesign panel. Moreover, since the front panel surface is now free from any unevenness orparts-mating notches, the cleaning of the panel has become easier.

Figure 7
Difference in Filter Pull-out Mechanism between
Conventional (Left) and Developmental (Right) Appliances
A conventional appliance’s filter needs to be removed after the design panel isopened while the developmental appliance’s one can be removed only if drawn
toward this side.

(2)

Wall thinning/weight reduction of plastic parts
Plastic parts were also subjected to thinning like metal plate components. One problem isthe worsening fluidity of plastics. To solve this, plastics fluidity was analyzed for key large
parts through the calibration of manufacturing facilities and temperature conditions to identify
places of poor fluidity and then improve the fluidity by rectifying the gate position and/oraltering the shape for the embodiment of thinning. The cooling velocity was also analyzed toreduce the cycle time for concurrent enhancement of productivity (Figure 8).

Figure 84.3
(1)

Analytical Results of Plastics’ Fluidity and Cooling Velocity

Comparison with existing appliances
Weight reduction and compactness
Figure 9 shows the developmental appliance’s weight reduction ratio and volume ratiowith reference to existing appliances.

Figure 9

Developmental Appliance’s Weight Reduction/Downsizing Result

Mitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)20

Regarding the weight, a weight reduction of 18% was achieved for outdoor units and14%, for indoor units. With regard to the size, outdoor units were successfully compacted by
22% in volume ratio. The volume of indoor units remains unchanged from that of existing
appliances partly because of the design requirements.
(2) Energy conservation
Figure 10 shows the results of a comparison between the electric utility fee of existing
constant-speed appliances, assumed as 1.0, and that of developmental ones, into which
respective periodic cooling/heating power consumptions are converted, to prove the energy
saving efficiency of the developmental appliances. For the calculation of electric utility fees,
the new energy-saving regulations (LOT 10 Enforcement Regulations of the ErP Directives)
were used as a base for conversion. The above improvement is calculated to save about 40
percent during the cooling season and about 30 percent during the heating season, proving thatboth its user advantages and the effect of environmental loading reduction are great.

Figure 10 Comparison of Conventional Constant-Speedand Developmental Appliances’ Period Efficiencies

4.4

Comparison with another company’s product

Table 1 shows the results of a catalog value-based comparison with a competitor’s productfor a key 3.5kW-class model.
Regarding the performance, every company has a similar level of cooling/heating capacity.
MHI has the highest periodic cooling-season efficiency, but finds itself trailing Company A inperiodic heating-season efficiency. The capacity is, however, higher than Company A and for MHI,
this is an appealing point. As far as the size and weight of a unit are concerned, MHI’s indoor units
are compact and the lightest. As for outdoor units, we are just behind Company B but, sinceCompany B downsizes/lightens them by lowering their capacity and periodic consumption
efficiency, it may well be said that if capacity/periodic consumption efficiency is included for
examination, our products are more appealing to users.
Table 1Cooling
Heating
Size andweight

Comparison with Competitors (in catalog value)

Capacity
Period efficiency
Capacity
Period efficiency
Indoor unit

Outdoor unit

kWkW
HeightWidth
Depth
WeightHeightWidth
Depth
Weightmm
mmmm
kg
mm
mmmm
kg

MHI
3.2
6.15
3.6
4.00
262
769
230
7.2
540
645
275
27Company A
3.3
5.66
3.5
4.14
283
770
198
8.0
550658275
30Company B
3.155.103.6
3.80
290
799
232
9.0
53069924925

Mitsubishi Heavy Industries Technical Review Vol. 51 No. 2 (June 2014)21|5. Conclusion
The latest developmental appliance has started to be mass-produced at Mitsubishi Heavy
Industries-Mahajak Air Conditioners Co., Ltd. of Thailand since February, 2013, and also at
Mitsubishi Heavy Industries-Jinling Air-Conditioners Company, Ltd. of China around the sametime. With products being widely deployed as a global strategic item in Europe, CIS, southeast
Asia, China and Japan, praise has already begun to be heard about our compactness/weight saving.
The present development was not simply carried out in pursuit of weight and cost reduction, butalso has many features to be directly evaluated by users such as the design and a new filter
structure, and awaits future additional appraisal in the marketplace. Furthermore, what wasaddressed in this development can be extended laterally to future developmental appliances, and is
not just confined to popular inverter types. We intend to continuously develop competitive products
for extensive introduction to the market in the future.