Milestone-Proposal:Inverter-driven residential air conditioner 1981

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Docket #:2019-06

This Proposal has been approved, and is now a Milestone

To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:


Title of the proposed milestone:

Inverter Air Conditioners, 1980-1981

Plaque citation summarizing the achievement and its significance:

Toshiba developed and mass-produced the world’s first split-type air conditioners with inverter-driven compressors for commercial and residential applications in 1980 and 1981, respectively. Compact and robust inverters using power electronics technologies allowed variable-speed control of the compressors for optimized air-conditioning operations, with significantly improved comfort and energy efficiency. These innovations led to widespread use of inverter air conditioners across the world.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

In what IEEE section(s) does it reside?


IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Senior Officer Name: Jun Sato

IEEE Organizational Unit(s) arranging the dedication ceremony:

Senior Officer Name: Jun Sato

IEEE section(s) monitoring the plaque(s):

IEEE Section Chair name: Naohiro Hozumi

Milestone proposer(s):

Proposer name: Shingo Naito
Proposer email: Proposer's email masked to public

Proposer name: Takahisa Endo
Proposer email: Proposer's email masked to public

Proposer name: Mikiko Kato
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

336 Tadehara, Fuji-Shi, Shizuoka-Ken, 416-8521 Japan, GPS; 35.147448, 138.663803

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. Fuji Operations of Toshiba Carrier Corporation, is the intended site of the milestone plaque, as it is where the world first inverter air conditioner was developed and manufactured and is the ultimate choice for the plaque to be displayed.

Are the original buildings extant?

Yes; the original buildings in which development and manufacturing were performed for the achievement are extant.

Details of the plaque mounting:

The plaque is to be displayed together with the actual product of the achievement in the “history section” of our internal exhibition place called the Air Conditioning System Center (AIRS), situated on the third floor of one of the buildings at Fuji Operations, the intended plaque site.

How is the site protected/secured, and in what ways is it accessible to the public?

Fuji Operations has its security control office at the entrance of the campus and has its security personnel to manage the access record to the campus. The exhibition place is publicly accessible with a prior appointment and no admission required. (Contact: AIRS, Fuji Operations, Toshiba Carrier Corporation; Phone: +81 545 62 5555) 

Who is the present owner of the site(s)?

Toshiba Carrier Corporation: A joint venture established in 1999 between Toshiba Corporation and Carrier Corporation; the Toshiba HVAC business has been transferred from Toshiba Corporation to the joint venture and has been operated by the joint venture since the foundation of the JV.

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

The achievement is about the world first inverter split air conditioners developed and commercialized by Tokyo Shibaura Electric Co., Ltd. or Toshiba, as known as Toshiba Carrier Corporation today [2]. Toshiba manufactured 100 units and 10,997 units for commercial and residential use, respectively, during the first year after the product launch in Japan in 1980 and 1981, respectively [1] [5]. Inverter split air conditioners have been widely used around the world since then to address global needs for air conditioning and have brought a breakthrough to the HVAC industry for triggering evolutions in later generations in terms of improved energy efficiency and comfort of the HVAC products.[7] [9 ; p.40, p.72]

The air conditioner has its origin in the United States as seen in an ice machine patented for the invention of Dr. John Gorrie in 1851 and the first modern air conditioning unit invented by Dr. Willis Carrier in 1902. Once considered a luxury, the air conditioner is essential and vital to maintain economy and daily lives around the world. [10]

In the early 70s, which is before the emergence of the inverter air conditioner, cooling/heating (i.e. heat pump) type air conditioners had a limited heating capacity and most of them needed auxiliary electric heaters in their indoor units to complement their heating capacity. As energy-saving awareness rose in the wake of the 1973 oil crisis, the emergence of new technology was long awaited for reducing energy loss by a continuous control of compressor capacity so that the conventional on-off control for temperature adjustment was to be replaced. Japanese HVAC manufacturers stood up to develop such new technology, as Japan, a nation scarce with key natural resources such as oil, was one of the countries hardest hit by the oil crisis and was desperate to address a nationwide call for energy conservation. [9 ; p.4]

The HVAC industries inside and outside Japan in fact had already started earlier to study various options for such new technologies. Many had predicted that the use of an inverter, or frequency converter, would be an optimal choice to serve the purpose, but inverters in those days were too large and expensive to be built into air conditioners [4]. Despite these challenges, Toshiba, with a state-of-the-art high-power transistor and microprocessor-controlled sinusoidal pulse width modulation, achieved a significant downsizing in its inverters. An inverter whose size and weight was only one-sixth that of a conventional inverter, was instrumental in Toshiba’s mass-production of 100 units and launch of the world’s first air conditioner for commercial use in October 1980 [2][11].

Toshiba’s next quest was to apply this inverter technology to residential air conditioners in the hope that the technology would also allow flexible capacity changes for residential air conditioners. The development started in December 1980. The biggest challenge was the price and size of the inverter. Given the size of residential air conditioning units, which are far smaller than commercial units, considerable effort for additional downsizing of inverter was necessary with a minimized cost. Through numerous trials and errors especially with developing the compressor and inverter for nearly two years, however, the residential split air conditioners were finally complete in September 1981 for mass-production and product launch in Japan. The size of the inverter was reduced to one-third that of a commercial inverter, which was small enough to be mounted above the compressor inside the outdoor unit, and the cost was reduced to 40% of the commercial air conditioners. Toshiba mass-produced 10,997 units of the residential air conditioners in Year 1 after the product launch. The energy efficiency of the inverter residential air conditioners saw approximately 40% improvement from that of the conventional fixed-speed models. [6][11][Photo1][Photo2].

The product received a rave review after a press release on December 12, 1981. Other HVAC players, who were reluctant to the challenging development of downsized inverters and lower costs and initially skeptical on Toshiba’s move, eventually followed suit of Toshiba after seeing Toshiba expanded its inverter lineup the following year. These circumstances have driven the ownership ratio of residential inverter air conditioners in Japan ahead of other countries by far and have also boosted Japanese HVAC manufacturers to a leading position in the world. In addition, the technologies used for the achievement, including drive control and downsizing, were also instrumental in promoting innovation of other various inverter-driven home appliances such as refrigerators and washing machines.

The inverter air conditioner, whose origin is Japan, is nowadays widely used throughout the world and is considered to have become the global standard of air conditioners. In 2018, countries and regions such as Japan, China, Europe, and Oceania saw a high inverter air conditioner ratio at 100%, 74%, 82%, and 100%, respectively. The inverter ratio in North America was notably low at 13%, because the inverter split air conditioning technology is relatively new in a long air conditioning history of North America; however, the inverter split air conditioner segment including residential ductless split air conditioners and variable refrigerant flow systems (VRF) has been recently growing faster than the entire heating, ventilation, and air-conditioning (HVAC) market in North America, and almost all U.S. based major HVAC manufacturers have added residential ductless split air conditioners and VRF to their product portfolio. The inverter ratio in regions such as the Middle East and Asia except for Japan and China are relatively low at 20% and 40%, respectively. However, as a part of efforts to tackle global environment issues and mitigating climate changes, many countries in the world including emerging countries are tightening their regulations on energy label and are shifting from conventional non-inverter fixed-speed air conditioners to inverter variable-speed air conditioners [7]. In addition, the inverter air conditioner is generally considered to bring better comfort to the humanity compared to the fix-speed air conditioner and as a result is contributing to improved human health, economy, and daily lives. [9 ; p.40]

As for historical significance in electrical engineering and science, the advent of the inverter split air conditioner has also made a significant contribution in the evolution of heat pump air conditioners. Heat pumps as a mechanism to pump up heat for both cooling and heating operations of air conditioners have existed for many years, however, in its early days the mechanism was mainly used not for both cooling and heating but for cooling only because of the low heating efficiency of heat pumps and the low fuel prices, which gave the edge to combustible heating systems using oil or gas. In order for heat pumps to be comparable to combustible heating systems in terms of energy efficiency, it was essential for heat pumps to attain 3 in Coefficient of Performance (COP, defined by the ratio of the output thermal energy to the input power).[9 ; p.72]

The advent of the inverter heat pump air conditioner drastically changed such landscape in Japan. In the early 1990’s, the evolution of inverter drive and power semiconductor device technologies played a major role to raise the energy efficiency of residential air conditioners above 3 in COP. In 1999, as Japan introduced the “Top Runner Program”, under which energy efficiency targets are set to be achieved within a given number of years on the basis of the most efficient model on the market, it propelled the competition among the HVAC manufacturers in Japan for improving its heat pump systems with the key inverter technology as well as other technologies such as inverter field oriented control, the use of rare earth permanent magnets and concentrated stator windings for compressors, and improved cooling fans and heat exchangers. As a result, the heat pump air conditioners witnessed a dramatic improvement in energy efficiency as the COP value in 2006 reached well above 6 for residential use and was able to run at the half the cost of combustible heating systems in a similar capacity [9 ; p.17, 39, 72].

Engineering efforts with inverter air conditioning technology have also raised the position of heat pumps to another level. In Japan, triggered by electric power shortage resulting from the nuclear power plant shutdown in the wake of the Great East Japan Earthquake in 2011, the national government has been promoting the J-Credit Scheme, under which the government certifies the amount of greenhouse gas emissions reduced or removed by carbon dioxide sinks through efforts to introduce energy-saving devices as credit, and high efficiency heat pumps and high efficiency air conditioning facilities are included in this program [12]. In EU, heat pumps have been recognized as a renewable energy technology since 2006 and the aerothermal energy captured by heat pump is counted in its energy-related statistics. [9 ; p.54][13] In Japan, heat pumps have been positioned as a renewable energy technology by the Act for Enhancement for Energy Supply Structure of Japan since 2010. [14 ; p.3, p.9]

In such respects, the technology of inverter air conditioners, after almost 40 years since the first product was brought to the world, remains to be one of the key technologies. For its revolutionary innovation in the history of air conditioning technologies, the achievement has been bestowed with some of the highest honors in Japan: the Ichimura Prize in Industry for Distinguished Achievement in 1984 from the New Technology Development Foundation and the First “One-Step on Electro-Technology” in 2008 by the Institute of Electrical Engineers of Japan [1][11].

What obstacles (technical, political, geographic) needed to be overcome?

There are three major technical obstacles that needed to be overcome during the development:

(i) Breaks and wears caused in compressors and refrigerant cycle parts such as valves due to the change in compressor operation from a fixed speed to variable speeds

(ii) Decrease in the lubricant oil level in the compressor as a part of the refrigeration cycle and vibration of the pipes resulting from variable speed operation

(iii) Development of the drive circuit for inverter’s power transistor and the microprocessor-controlled sinusoidal pulse width modulation

Japan is known as a nation scarce with key natural resources such as oil. In the wake of the second oil crisis in 1979, the Japanese government was pressed to tighten the 1976 Act of the Rational Use of Energy or so-called Energy Conservation Law of Japan and call on industry to introduce products complying with newly established high energy efficiency standards. Under this difficult circumstance from a political viewpoint, Toshiba accelerated its development and saw its launch of the inverter split air conditioners in the market within a short time frame ahead of other HVAC players.

As to a geographical obstacle, Japan is one of a few countries in the world where two different power supply frequencies exist in the same country: 50Hz in Eastern Japan and 60Hz in Western Japan. This unique geographical challenge led to extra effort and costs for appliances and adapters as well as testing procedures to ensure the quality of the new developments.

Through the efforts of engineers at Toshiba to overcome these obstacles with their technical expertise, assure reliability through technology development, and also attain downsizing and lower costs, the achievement was accomplished in a timely and successful manner [4] [11].

What features set this work apart from similar achievements?

Some attempts were made in around 1980 to adopt inverter technologies in the social infrastructure field such as train systems for variable speed drive motor control and chiller systems, in which chilled water is created, as seen in the case developed in 1977 by York, which retrofitted an external inverter unit for chiller units already in operation [8].

The achievement by Toshiba (i.e. inverter air conditioner split type) is a totally different system from the chiller system in terms of the product categories in the following points:

(i) The split inverter air conditioning system consists of an indoor unit and an outdoor unit; heat transfer between the indoor unit and outdoor unit is made through refrigerant for cooling and heating operations.

(ii) Toshiba’s inverter unit mounted inside the air conditioner is significantly smaller than York’s inverter unit installed on the floor separately from the chiller unit.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

[1] The First “One Step on Electro-Technology” Prize, by the Institute of Electrical Engineers of Japan (IEEJ): Inverter Air Conditioner, IEEJ 2009 (original text in Japanese with an English translation) //File: 1 The Journal of the IEEJ, Vol 129-2.pdf

[2] Kenji Iida; Capacity Control with Frequency Modulation System, REFRIGERATION journal, Japanese Association of Refrigeration, 1981 (original test in Japanese with an English Translation) //File: 2 REFRIGERATION", June 1981 Vol. 56, No. 644.pdf

[3] Ushimaru, Wilfert; Japanese Power Electronics Inverter Technology and Its Impact on the American Air Conditioning Industry, Pacific Northwest National Laboratory for U.S. Department of Energy, 1990 //File: 3 US Department of Energy.pdf

[4] Muir, Griffith; Capacity Modulation for Air Conditioning and Refrigeration Systems, Air Conditioning, Heating & Refrigeration News 1979 //File: 4 Air Conditioning, Heating & Refrigeration News.pdf

[5] Kuroda, Kitagaki; Energy Saving by Compressor Capacity Control of Air Conditioners, Toshiba Review Vol. 36, No.9, p.p. 849-852 1981 //File: 5 Toshiba Review Vol. 36, No. 9.pdf

[6] Ide, Shimma, Sugiyama; Air Conditioners Incorporating Variable-Capacity Control Inverter, Toshiba Review Vol. 37, No. 7, p.p. 635- 638 1982 //File: 6 Toshiba Review Vol. 37, No. 7.pdf

[7] World AC Market & Inverter Ratio, Toshiba Carrier Corporation and The Japan Refrigeration and Air Conditioning Industry Association //File: 7 World AC Market & Inverter Ratio.pdf

[8] YORK Centrifugal Compressors, A Brief History, p.p. 7-8 1996 //File: 8 York be_vsd_history.pdf

[9] Heat Pump & Thermal Storage Technology Center of Japan; Heat Pumps – Long-awaited Way Out of the Global Warming, 2007 //File: 9 Heat Pumps – Long-awaited Way Out of the Global Warming.pdf

[10] Department of Energy; History of Air Conditioning //File: 10 History of Air Conditioning.pdf

[11] World’s First Residential Inverter Air Conditioner, Toshiba Science Museum //File: 11 Toshiba Science Museum Toshiba Firsts of Their Kind.pdf

[12] Ministry of Economy; Trade and Industry (METI), J-Credit Scheme, 2020 //File: 12 J credit.pdf

[13] European Commission; Energy for heating/ cooling from renewable sources //File: 13 energy-heating-cooling-renewable-sources.pdf

[14] Act of Sophisticated Methods of Energy Supply Structures; Agency of Natural Resources and Energy of Japan, 2010 //File: 14 Act of Sophisticated Methods of Energy Supply Structures 2010 w translation.pdf

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to Please see the Milestone Program Guidelines for more information.

File name; Photo1 RAS-225PKHV.jpg Summery; Photo of World First Inverter Air conditioner Split type for Residential use

File name; Photo2 RAS-225PKHV Inverter.jpg Summery; Photo of Inverter Unit

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