Johnson Controls-Hitachi Air Conditioning’s PAM Inverter Room Air Conditioner (RAS-501HX2), originally released by Hitachi in 1997, has been registered as an Essential Historical Material for Science and Technology by Japan’s National Museum of Nature and Science.
The Essential Historical Materials for Science and Technology is a registration system launched in 2008 by the National Museum of Nature and Science to preserve, recognise, and make the best use of prominent scientific and technological achievements worthy of being passed on to future generations and materials that have had significant impact on Japan’s lifestyles, economy, society and culture.
By the 1990s, inverter room air conditioners, in which it was possible to control the speed of the compressor motor, had appeared on the market.
But as demand for heating functionality in air conditioning units grew, it became necessary to equip them with high-power heating capabilities, which at the time could only be achieved by operating compressor motors with high-speed.
This meant that when the compressor motor was operated at a low speed, especially when the room temperature was stable, the energy-saving capability was reduced.
The PAM (Pulse Amplitude Modulation) inverter solved this problem by making it possible to control the compressor’s rotation across a wide range of speeds.
With a PAM inverter, the voltage delivered to the compressor could be increased as needed, resulting in increased rotation speed. Once the temperature stabilized, the voltage could be lowered and the compressor could be operated efficiently at low speeds.
The PAM inverter also made it possible to control the waveform of the input current so that it approximated a sine wave, increasing the maximum power factor to 99 percent and allowing more effective use of the electric current drawn from the outlet.
The PAM inverter room air conditioner was an epoch-making product in air conditioning technology history that made it possible to achieve both high power and low energy consumption.
Its high power heating capabilities won it acclaim even in cold climate regions, where the heating function of conventional inverter air conditioners had been considered insufficient. It also contributed to the wide-spread use of heat pump heating.
PAM inverter technology is still being used in air conditioning systems that offer comfort year-round.
The technology has also been implemented in other home appliances, including refrigerators, providing a significant contribution to their increased energy saving performance and efficiency.