Residential Use Air-Conditioner
with anti-Allergy Function
KENICHI MIYAZAWA* 1
HIROSHI KANBARA* 1
YASUHIRO NAITO* 1
DAISUKE TANAKA* 2
TAKAYUKI SUZUKI* 2
YUJI NAKAJIMA* 3

Improvement of the basic performance of air-conditioners remains an important task demanded by the revised
Energy Conservation Law of Japan. Recently, improvement of indoor air quality (IAQ) is another requirement,
together with differentiation from competitors. Mitsubishi Heavy Industries, Ltd. (MHI) has developed a filter fordecomposing and suppressing allergens causative factors of allergy, and has manufactured an air-conditioner
incorporating this filter.

1. Introduction

6.5

Average COP of cooling and heating

Against the background of recent mounting concern
about the environment and health, air-conditioners arerequired to have various extra functions aside from thebasic performance of air conditioning.
As the basic performance of wall mounted separate
type of 4.0 kW or less, upgrading of performance is required by the Energy Conservation Law that becomes
effective in 2004. According to this law, performance isdefined by the average COP (coefficient of performance:
the capacity divided by the power consumption) of cooling and heating, and products exceeding the limit values(for example, in the case of 2.8 kW class, COP 4.90) cannot be sold.
As extra functions, improvements of IAQ are being
proposed by manufacturers as a means of differentiation. Filters having functions such as ventilating
functions are considered, including the "Negative ion"boom of recent years.

: High class models: Standard class models
5.96

6.0

5.96

5.89
5.80
5.5
5.06
5.07

5.0

Statutory level of 4.90
(2.8 kW class)
4.5

4.90 4.90

4.55
4.10

4.0
3.79111213141516

Refrigeration year
Fig. 1 History of COP
High class models have already satisfied the statutory levels.

2. MHI's policy

3. Development of allergen clear filter

2.1 Basic performanceFig. 1 shows the history of development of COP in
the 2.8 kW class (high and standard class) of MHI. In
the case of high class models, the COP is already above
the limits, and equal to the high end of other manufacturers. Further enhancement is an immediate goal.
2.2 Extra functions
Extra functions of the high class models to differentiate them from competitors' models include (1) the world's
first filter for decomposing allergens by the power of enzyme (called allergen clear filter), (2) ventilation function
for expelling indoor air to the outside, (3) internal cleaning function, and (4) remote control by using the Internet("e-@ir").

3.1 Concept
Indoor air contaminants include gaseous matter causing the "sick house syndrome" and malodor, particulatematter such as cigarette smoke and house dust, microorganisms such as floating bacteria and mold spores, andmany others. To eliminate all such contaminants, individual properties must be studied, and appropriatetechnologies must be selected or developed. Biologic airborne allergens, which are present in the living
environment and possibly cause serious diseases, arestudied, and technologies for eliminating them are being developed. Such biologic airborne allergens include
mite allergens, pollen, pet allergens, and insect allergens (cockroaches, mosquitoes, etc.). They are inhaled*1 Air-Conditioning & Refrigeration Systems Headquarters*2 Nagoya Research & Development Center, Technical Headquarters*3 Advanced Technology Research Center, Technical Headquarters

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.41 No.2 (Apr. 2004)1

Table 1. Test allergens
OriginAllergenDer f 1

Dermatophagoides farinae

Dirt-derived cysteine proteaseDer f 2

Dermatophagoides farinae

Insect-derived epididymis-related protein

Der p 1

Dermatophagoides pteronyssinus

Dirt-derived cysteine protease

Cry j 1

Cryptomeria japonica

Pollen surface particulate

Fel d 1

Felis domesticus

Epithelial protein

100

3.3 Performance
Enzyme and urea were carried on a nonwoven fabricof special fibers, and a filter was prepared and presented
for the allergen inactivation test. Allergens shown in
Table 1 were used in the test. These are air-borne allergens commonly found in Japan. They (dust allergens)were made to adhere to the allergen clear filter, and theinactivation capability was evaluated.
Fig. 2 shows the inactivation rate of mite allergens
and other allergens. The inactivation rate varies withallergens. This is because the properties of allergens aredifferent and also because this enzyme is effective witha wide variety of allergens, and inactivates various allergens present in the indoor environment. In addition,
since this enzyme is designed to act on proteins, it iseffective not only for allergens but also for viruses, bacteria and mold. For example, influenzae can beinactivated by 99.9% in one hour, and staphylococcus
aureus can be sterilized (not only is growth suppressed,
but the number of cells is also decreased).
3.4 Unit operation control
For obtaining the maximum capacity of the filter performance, the temperature and humidity of the filter
environment are important. The ideal environment isrealized in the developed model by using the basic function of the air-conditioner. That is, moisture in the indoor
atmosphere is captured in the heat exchanger by cooling
operation, and the condensed water is evaporated again
in heating operation. In this way, the optimum environment is always realized around the filter. These
operations are realized by the control system for changing the operation cycles depending on the environmental
conditions by using sensors incorporated in the unit.
3.5 Unit system configuration
Fig. 3 shows the configuration of the allergen clear
system in the developed model. The filter is installedin the unit before the heat exchanger. Allergens floating in the environment are sucked in together with theindoor air from the air-inlet grille during operation, andthey are captured on the filter. The allergens captured
on the filter are inactivated (decomposed) by the enzyme. As a result, even if the substance captured on
the filter is released again from the unit, allergy is nolonger caused.
The developed model has a mechanism for control-

93.6
83.5

80

Inactivation rate (%)

Description

83.5

81.5
72.7

60
40200
Der f 1

Der f 2

Der p 1

Cry j 1Fel d 1

Fig. 2 Inactivation rate of allergens
The inactivation rate varies with allergens, but various allergens
are inactivated.

into the respiratory system of the body and cause sneezing, inflammation, and diseases. Unlike microorganisms,
they are not metabolized by the activity of living cells,
but their molecular structure itself disturbs the immunity of the respiratory system, and inactivation requires
advanced reaction. The principal components of allergens are proteins, and they are stable chemically byhigher order structure. It has been difficult to inactivate them without using high heat or strong chemicals.
MHI has selected an enzyme as a means of inactivating
the allergens, establishing the conditions for functioning in the air-conditioner, and finally developing a filter.
The history of the development is given below.
3.2 Selection of filter material
The selected enzyme has the property of promotinghydrolysis. Therefore, moisture is required for promoting the reaction of the enzyme and allergen (to inactivate
the allergen). To supply moisture for activating the enzyme on the filter, two methods may be considered.
(1) Supplying water from a tank into filter fibers.
(2) Moistening the filter with moisture contained in theair (moisture absorption).
Considering simplification of structure, ease of maintenance by users, and versatility, the second method isselected. For higher moisture absorbing capacity of thefilter, special fibers that absorb moisture more readily
than cotton or wool are used. These fibers have hydroxyl
group on the surface, and their use makes it easy to immobilize the enzyme.

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

Allergen clear filter

Allergen clear filter

Exhaust duct (exhaust route)

Indoor control

Suction ofIndoor air

Hot, damp air

Ventilation fanFig. 4 Exhaust mechanism
Hot, damp air is discharged outdoors through an exhaust duct installed
next to the filter.

Air blowing
Heat exchanger

Exhaust to outdoors

Exhaust duct

Fig. 3 Concept of unit system
Filter is installed in front of heat exchanger. Sucked-in allergens arecaptured on filter (right half: air-inlet grille detached).

carbon dioxide, formaldehyde or other gases present in
the room. The new air-conditioner has a fan for ventilation, which operates together with the sensor to detect
concentration of gases for discharging the contaminatedindoor air to the outside. The ventilation function hasbeen attracting attention as a means of enhancing IAQ
recently, and other manufacturers are also attempting
to develop it.
In this model, the ventilation function does not work
alone, but is combined with unit drying operation andothers, and has been developed as part of compound functions.
4.2 Internal cleaning function
After long operation of the air-conditioner, dust andstains are collected inside, and moisture and mold also
accumulate in the unit. Such deposits not only lower theoperating capacity of the air-conditioner, but also cause
malodor. Accordingly, to remove moisture in the unit, unit
drying operation is combined with the ventilation function, and a fan using antimold agent is also operated toremove dirt and mold.
In addition, to remove the collected dirt and mold,the air-outlet grille is designed as a detachable unit to
be cleaned directly, and various needs of users are satisFig. 5
fied (Fig.
5).

ling the capacity of the enzyme to the correct degree.
For the allergen clear filter, atmosphere of high temperature and high humidity is desired, whereas for the unit
such atmosphere is not desired from the viewpoints ofair conditioned comfort, contamination and mold growth.
Accordingly, a duct for releasing the unit air to the outside is installed next to the filter, the air is released
outside after optimum condition operation by the fan for
ventilation, and stagnation of hot, damp air in the unit
Fig. 4is prevented (Fig.
4).

4. Other functions
When an air-conditioner is purchased, the price andperformance are vital, but extra functions such as air
purifying and ease of cleaning are also important. The
new air-conditioner is distinguished from others by various features as well as the allergen clear filter, including(1) ventilation function, (2) unit internal cleaning functions, and (3) remote control function by use of theInternet.
4.1 Ventilation function
Usually, the filter of an air-conditioner cannot remove

Remove the detachable section.

Clean the inside.

Fig. 5 Detachable cleaning mechanism
Air-outlet grille is detachable to facilitate direct cleaning of the inside of the unit.

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

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Wireless unit
(remote unit)
Cellphone

Telephone
Wireless unit
Personal (remote unit)
computerInternetTelephone
circuitAir-conditioner
Wireless unit (base unit)

CellphoneserverProvider(Exclusive software installation)

Fig. 6 Concept of "e-@ir"Wireless communication of air-conditioner and personal computer simplifies the installation.

4.3 Internet communication function
The concept of this system is shown in Fig. 6. Bycommunication between the air-conditioner and a personal computer, two-way communication is realized
from outside by use of cellphone or e-mail, and the airconditioner can be operated and monitored from aremote location.
By combining with the ventilation function (especiallyin summer), hot air in the room can be discharged beforehand from the outside by operating the ventilation
function, and the cooling operation can be started efficiently when the user returns home. In this way, power
consumption is saved, and the time required to reach adesired temperature is reduced by 20 percent as compared with the existing model.

Kenichi Miyazawa

Hiroshi Kanbara

5. Conclusion
The new air-conditioner has achieved the average COPof 5.96 (122% of the specified level) as compared with
the new statutory level of 4.90 in class 28, and this performance is the highest in the industry. In addition, theIAQ improving functions include the allergen clear filter and ventilation function.
Henceforth, MHI will continue to develop new products with higher basic function and new functions suited
to the needs of users.
References(1) Miyazawa, K. et al., High-Efficiency Residential-Use Air-Conditioner, Mitsubishi Juko Giho Vol. 39 No. 2 (2002) p. 60

Yasuhiro Naito

Daisuke Tanaka

Takayuki Suzuki

Yuji Nakajima

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

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