Researchers at Shanghai Maritime University has come up with a new air-conditioning system that uses power at night, when rates and demand are low, to cool down an office or home during the day.

If used on a large-scale basis, the system could significantly reduce power demand during the day in the summer, when the city faces massive shortages that have forced some factories to change production schedules or take extra vacations.

The system freezes large amounts of water over nights, and then allows the ice to melt during the day, cooling down air that is then circulated through a building or home.

As the price of electricity is 50 percent lower at night than during the day in Shanghai, the system could cut energy costs by 20 percent, researchers said.

"The biggest significance of this system lies in that it could effectively balance the city's power load gap between daytime and night," said Zhang Xuelai, a professor at SMU's thermal storage research institute and director of the project.

During prolonged heat waves in the summer, the city faces a shortage of about 4 million kilowatts of power. To balance the power load gap, the city ordered about 500 companies to shift their production to night hours or weekends to avoid peak load time from June to September last year.

Residential electricity price in the city drop from 0.61 yuan (7 US cents) a kilowatt-hour during the day to 0.31 yuan overnight - from 10:00 PM to 6:00 AM.

The system produces 30 percent less heat than ordinary air-conditioners, which could help to solve the heat island effect in the city, Zhang added. The effect refers to the increase in temperature downtown, caused by heat from thousands of air conditioners.

The system could go on sale in the city within a year.

(Shanghai Daily March 1, 2006)