Highly Efficient and Compact
Side-Air-Flow Type Multi-Air
Conditioner
SHINICHI ISOZUMI*1

SUSUMU YAMASHITA*1

TAKASHI KAWASHITA*1

HIROYUKI OTAKE* 1

JUNICHI YOSHIDA*1

MITSURU NAKAMURA*2

Mitsubishi Heavy Industries, Ltd. (MHI) has developed a new side-air-flow type multi-air conditioner for the
Chinese market. It is most suitable for high quality apartments and small offices. The volume of the outdoor unit has
been reduced by 22% and its COP (Coefficient Of Performance) has been increased by 40% compared to conventional
KX2 series air conditioners, thus realizing a remarkable reduction in both size and energy consumption. A fully
chargeless system that completely eliminates the need to charge refrigerant during installation has also been adopted
in order to improve workability and reliability. In addition, the indoor unit (FDT: Ceiling cassette 4-way blowout
model) and the wired remote controller have been completely redesigned.
size compared with the conventional KX2 series, and has
improved workability and serviceability.
An overview of the main features of the side-air-flow
type multi-air conditioner is presented here.

1. Introduction
China is currently enjoying a construction boom as the2008 Beijing Olympics and 2010 Shanghai Expo approach,with high quality apartments being constructed one after
another for foreigners and Chinese high-income earners.
Many of these apartments have a floor space ranging from100 to 150 m2 in which an air conditioner with a capacityof approximately 5 HP is required.
In response to this demand, MHI has put the KX2 series on the Chinese market with the aim of expanding therange of MHI products in the market. Since more growthin the market is expected in the future, MHI has developed and introduced a new side-air-flow 5 HP multi-air
conditioner for use in homes such as apartments. It has
marked energy-saving features, is remarkably reduced in

2. Features
The side-air-flow type multi-air conditioner and its indoor units are shown in Fig.1
Fig.1. The accompanying indoor
unit is standardized with that used in the LX series, andcan be directly connected, together with the pipes andcables, to the outdoor unit without any special interface.
Since the indoor unit is not designed for specific use, MHI
can always put the latest model on the market. The communication system succeeds conventional “Superlink” sothat multiple integrated control units such as SL-1 can beconnected and used easily.
Indoor unit:
Similar to that used with the LX series

Outdoor unit:
Side-air-flow type multi-air conditioner

SLA-1

FDUM

..

FDK

FDTW
FDE
Refrigerant pipe: Branch pipe system
Communication between indoor and outdoor units: Superlink system

FDT

FDR

FDTQ

FDQM

Fig. 1 The side-air-flow type multi-air conditioner and its indoor units
The indoor units are similar to the units of LX series. All pipes and cables can be connected directly to the system
as in the conventional system.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.41 No.2 (Apr. 2004)*1 Air-Conditioning & Refrigeration Systems Headquarters*2 Nagoya Research & Development Center, Technical Headquarters

1Increase in indication efficiency
Reduction of tip clearance throughadoption of high strength material
in scroll material
Increase in mechanical efficiency
Reduction in diameter of scroll

Reduction in scroll leakage loss
φ158 mm

Reduction in thrust bearing loss

Increase in efficiency of motor
Adoption of neodymium magnet
reluctance DC motor
Fig. 2 Structure of reluctance DC compressor
The scroll and motor have been modified, and the efficiency of the compressor unit could be increased by approximately 11%.

The side-air-flow type multi-air conditioner has the following five outstanding features that are not incorporated
in conventional units.
2.1 Notable energy-savings
The side-air-flow type multi-air conditioner is remarkably improved in terms of energy savings compared withthe 5 HP KX2 series. The COP for the outdoor unit of thesystem is increased by 40%, that is, from 2.57 to 3.61. Thisis due to the major impact of a newly developed high efficiency compressor fitted with a DC motor and a DC
converter to drive the compressor.
Fig. 2 shows the structure of the reluctance DC compressor. By optimizing the design of the scroll, leakage loss
and thrust bearing loss are reduced, and both indication

Large diameter propeller fan

DC motor-driven inverter
Adoption of highefficiency IPM

1 300 mm

1 450 mm

Air rate was increased
by approx. 15%
while suppressing
air blow noise.

efficiency and mechanical efficiency are increased. In addition, neodymium magnets are buried in the core of the
motor rotor in order to increase its efficiency up to the low
speed rotation region through the combined effects ofFleming’s force and reluctance torque. In addition, the compressor minimizes loss as an inverter through the adoptionof a highly efficient Intelligent Power Module (IPM) and ahigh voltage drive motor.
In addition to the above, remarkable energy savings
could be realized by the adoption of a large diameter propeller fan and a reduction in unit pressure loss bystreamlining airflow, as can be seen in Fig. 3
3.
2.2 Reduction in size
A comparison of the outer dimensions of the KX2 series
and the side-air-flow type multi-air conditioner is shown
4 The volume of the unit could be reduced by 22%
in Fig. 4.
by renovating the external design and changing the air blow
direction of the fan from a diagonal to a side direction. In
particular, since the depth dimension has been reduced
from 600 to 370 mm, the unit can be easily installed in a
restricted space such as the verandas of apartments.
The weight has also been reduced from 150 to 125 kg.
The reduction in weight and size of the unit results in easyload handling and transportation to installation.

Reductionby 22 %

High-pressure receiverHigh efficiency compressor

Excess refrigerant accumulated
in the heat exchanger is retained
to improve heat exchange loss.

The DC motor is driven by ahigh voltage to reduce current
so as to suppress resistance loss.

Fig. 3 Improvements in unit
Overall COP has been increased by 40%, from 2.57 to 3.61 comparedwith the existing 5 HP KX2 series.

690 mm0.600 m3

600mm

970 mm370mm

0.467 m3

Fig. 4 Comparison in size between new and old models of outdoor unit
The direction of air blowout was changed from the diagonal to the side
direction in order to reduce the volume of the outdoor unit by 22%.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.41 No.2 (Apr. 2004)2

2.3 Fully chargeless system
A major feature of the side-air-flow type multi-air conditioner described here is the fully chargeless system, which
completely eliminates the need to charge the refrigerantat the time of installation. It not only reduces the costs
associated with both the refrigerant cost and construction,such as charging operation, but also serves to prevent any
difficulties due to an excess or deficiency of refrigerant,
thereby improving reliability. MHI believes that the system is indispensable to facilitate the penetration of its
products into the Chinese market where the infrastructures for new refrigerant HFC410A are not so maintained.
In order to realize this goal, a method for processing
excess refrigerant had to be established, since the side-airflow type multi-air conditioner needs a large amount ofrefrigerant to operate properly.
The excess refrigerant produced by eliminating charge
is stored in a high pressure area through the adoption ofsuperheat control in the electronic expansion valve and anincrease in the capacity of the high pressure receiver. This
leads to a reduction in heat exchange loss by preventing
the accumulation of refrigerant in the heat exchanger anda reduction in suction pressure loss by eliminating a lowpressure accumulator, thereby contributing to an increasein efficiency.
The high-pressure receiver is not installed in the machine chamber but rather is installed in the fan chamberin the double-split state. To cope with the increase in capacity, the compact machine space is effectively utilized.
In addition, it has been confirmed that air flow noise is notaffected.
2.4 Good workability and serviceability(1) Adoption of new refrigerant HFC410A
HFC407C was used in conventional multi-air conditioners as a new refrigerant that does not destroy theozone layer. In the side-air-flow type multi-air conditioner, a high-pressure and high-density refrigerant,
HFC410A, has been newly adopted following on use inroom air conditioners. This refrigerant is convenient for
reducing pressure loss and increasing efficiency. Since
HFC410A is a pseudo-azeotropic refrigerant, any gas
leak that might occur can be remedied simply by adding additional charge. There is no need to replace theentire amount of HFC410A refrigerant, whereas
HFC407C must be fully replaced.
(2) Adoption of single-phase power
A single-phase power supply has been adopted basedon the assumption that the side-air-flow type multi-air
conditioner will be used in homes such as apartments.
In addition, a passive filter formed of a reactor and acapacitor was newly designed to suppress the occurrenceof higher harmonics. Considering the situation regarding electric power in China, an optimum start pattern
was determined from the power voltage and refrigerant
equalizing level, and applied to the DC inverter com-pressor to ensure that the system can be started at awide range of voltage levels.
(3) Acquisition of operational data by personal computer
A function is added to acquire operation data fromthe outdoor circuit board using a general personal computer but not a special checker. Should the side-air-flow
type multi-air conditioner stop abnormally, data on operation of the system for the thirty minutes prior to theoccurrence of the abnormality can be stored automatically for use in quickly investigating the cause of the
problem and taking appropriate countermeasures.
(4) Improvement of 7-segment display function
High- and low-pressure sensors and an suction pipe
temperature sensor have been newly added to the sideair-flow type multi-air conditioner. Consequently, thedata on high-pressure, low-pressure and suction superheat, can also be displayed in 7-segments on the outdoor
circuit board which was installed in conventional models. As a result, the operation points of the system canbe detected without a gauge manifold.
2.5 New type of indoor unit and wired remote controller
Not only the outdoor unit but also the ceiling cassette
4-way blowout indoor unit (FDT) and wired remote controller were redesigned as well during the course ofdeveloping this system.
With regards to the FDT, contamination of the ceilinghas been reduced by improving the panel blowout port
Fig.5
(Fig.5
Fig.5), and efficiency increased by improving the inside
air route and increasing the capacity of the heat exchanger.
A louver peripheral structure has been adopted that allows
blown-out airflow to be easily separated from the panel surface, and an air blowing method has also been adopted thatmakes it more difficult for mold and dust to be adhere to theceiling. In addition, fan input has been reduced by 20% ofthat of conventional machines by modifying the structure

Since blowout airstream flows
along the panel, it easilyadheres to the ceiling.

Forming the structure so that theblowout airstream is easily
separated from the ceiling makes
it difficult for the airstream toadhere to the ceiling.

Fig. 5 Reduction in contamination of ceiling
The structure of the panel blowout part of the system was improved so thatthe blowout airstream can be separated easily from that part.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.41 No.2 (Apr. 2004)

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Cooling capacity (kW)14.6

Heating capacity (kW)16.6

HFC 410 A
220-240 V, 50 Hz

Height (mm)1 300

Width (mm)970

Depth (mm)370

3Volume (m )Noise value (dB(A))

0.467
53 dB(A)

Refrigerant pipe
specifications

Refrigerant
Power supply

Exterior
dimensions

Quantity of connected units

2 to 8 / 2 to 6

Volume of connected units

80-130%/80-150%

Average of coolingand heating 3.61

COP

Outdoor unit

Indoorunit

Table 1 Basic specifications of side-air-flow type multi-air conditioner for export

Max. length

(m)

70

Overall length

(m)

100

Head
difference

Atmospherictemperature
lower limit value

so that the blowout port flow passage is increased, and theheat exchange performance was increased by 30% throughthe adoption of a high performance heat exchanger tube.
6 the operation data display of
As can be seen in Fig. 6,
the wired remote controller was increased in size throughthe adoption of a dot liquid crystal to improve visibility.
Further, the function of the timer was improved by installing a weekly schedule timer as a standard reference inaddition to the conventional 24-hour timer. Accordingly,
even at the end of the week when living patterns tend todiffer from each other, individual timer operations can be
set. In addition, models are available that use pictographic
plus alphanumeric or Chinese character displays to provide product specifications best suited to a given market
anywhere in the world.

Indoor-indoor
distance
(m)

4

o

-5

o

-15

In cooling time ( C)In heating time ( C)

the side-air-flow type multi-air conditioner have been remarkably improved compared with the conventional KX2
series. MHI plans to expand the sale of the side-air-flow
type multi-air conditioner primarily in the apartment market of China, where remarkable market growth of thesystem can be expected in the future.
At the same time, MHI believes that there is also a needfor the side-air-flow type multi-air conditioner in European
and Japanese markets as well as in the Chinese market,
although the scales of such systems will differ from eachother. The company is currently moving ahead with preparations to develop a three-phase powered version of theside-air-flow type multi-air conditioner system.
The global air condition market is expected to expand
further largely in the future and, concurrently, a variety ofneeds will also be produced. In this regard, MHI has its
antennae raised high to grasp these trends quickly andwith keen insight, and develop successive new productsthat best meet these wide ranging needs.

The basic specifications of the side-air-flow type multiair conditioner for export are summarized in Table 1
1. Theconnectable capacity of the indoor unit is up to 150%. As aresult, the initial investment cost per unit air conditioning
area can be reduced in residential apartments, where theload factor and simultaneous operation ratio are rather
small. In terms of refrigerant pipe specifications, a total
length of up to 100 m of pipes can be installed without theneed for charging, which is sufficient for homes and small
offices.

4. Conclusion
Development of the side-air-flow type multi-air conditioner was mainly focused on use in residences such asapartments. As a result, product specifications were determined by placing emphasis on realizing energy savings,
reduction in size, and improved reliability. All phases ofSusumu Yamashita

Outdoor unit
(Up: 30/Down: 15)

Fig. 6 New type of wired remote controller
System visibility and operability were improved
with the adoption of dot liquid crystals and theimprovement of the timer function.

3. Outline Summary

Shinichi Isozumi

Indoor-outdoor
distance(m)

Takashi Kawashita

Hiroyuki Otake

Junichi Yoshida

Mitsuru Nakamura

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.41 No.2 (Apr. 2004)

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