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World's First Household Inverter Air ConditionerWorld

Development started with complete modification of compressor for use with inverter.
Engineers gave up summer holidays and worked naked in the heat, making prototypes and checking their performance.

World's First Household Inverter Air Conditioner

Cooling/heating-type air conditioners sold in the early 70s had low heating capacity and most of them had to incorporate auxiliary heaters in their indoor units.

As energy-saving awareness rose in the wake of the 1973 oil crisis, people wanted to reduce energy loss with a compressor that was controlled continuously, rather than having to adjust the room temperature with the on-off control. Many had predicted that the use of an inverter, or frequency converter, would satisfy the necessary requirements, but inverters were too large and expensive at the time to be built into air conditioners.

Toshiba used a state-of-the-art high-power transistor and microcomputer-controlled sine wave approximate pulselength modulation to complete the world's first commercialuse inverter air conditioner, and the size and weight were significantly reduced to one-sixth that of a conventional inverter. The product was put on the market in October 1980.

Toshiba hoped to improve the capacity of household inverter air conditioners through application of commercial inverter technology, and began development started in December 1980. The biggest problem was the price and size of the inverter, an electric circuit used to control rotation of the compressor, but the engineers also had to solve another problem. The compressor, which until that time was the heart of an air conditioner, was made to rotate at a constant speed, but the engineers had no idea how and where faults would occur when compressor speed was controlled by the inverter.

So, the engineers started by modifying the compressor. The first problem was that under high-speed rotation, an excessive amount of lubricant oil flowed out from the working part of the compressor, while under low-speed rotation, lubrication was insufficient. The second problem was in the delivery valves; they all broke down under frequent jolting when roller speed increased. Those jolts also caused inordinate vane wear. The third problem was the abnormal noise the machine made under operation. The engineers worked hard to overcome the problems one by one.

Since household air conditioners operate on AC 100V, the voltage doubler method was utilized to convert the power into AC 200V for supply to the converter. To reduce the size of the compressor, a larger transistor was needed. The transistor was an important component used by the computer to control a circuit connecting the compressor and inverter, and development of that component was done in cooperation with the engineers in the semiconductor division.

The compressor and inverter were nearly complete by the end of August 1981. The inverter was reduced to one-third the size of a commercial inverter, installed above the compressor in household air conditioner outdoor units, and cost was reduced to 40% of the original value. The engineers also had a hard time developing the refrigeration cycle. They gave up their summer holidays and worked naked in the heat (as power in the factory had been stopped due to renovations then underway), making their prototypes, and checking the performance.

The product was finally completed in September of 1981, and received a great response after a press release on December 12, 1981. The household inverter air conditioner was revolutionary in the history of air conditioner development, and Toshiba won the Ichimura Industrial Award in 1984 from the New Technology Development Foundation for its development. The product was one of the first registered as a “Cornerstone of Electrical Technology” by the Institute of Electrical Engineers of Japan in 2008.

Inverter Circuit

Inverter Circuit

Awarded the "One Step on Electro-Technology" prize by the Institute of Electrical Engineers of Japan

Awarded the "One Step on Electro-Technology" prize by the Institute of Electrical Engineers of Japan

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