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OSAKA — With more and more heat-generating computers being used in workplaces, owners and tenants of office buildings are seeing their electricity bills shoot up.

This is especially true during the summer months, when constant air conditioning is an absolute necessity.

Osaka-based general contractor Takenaka Corp., however, is bidding to slash the cost of keeping office temperatures at comfortable levels through its new comprehensive air-conditioning system.

The system, recently installed in a new 14-story building in Osaka’s Chuo Ward, combines three conventional air-conditioning technologies.

These are the use of ice for cooling purposes, a coolant and hot water circulation system, and a floor cooling and heating system.

The new system, which takes full advantage of nighttime electricity fee discounts, can result in savings of 70 percent over conventional systems, according to Atsushi Kasuya, a Takenaka Corp. official.

While installing the system costs around 20 percent more than the average outlay for a conventional air-conditioning system, this disparity can eventually be recouped through savings on running costs, Kasuya said.

This is exactly why JTB Estate agreed to install Takenaka Corp.’s system in its building in Chuo Ward.

“The initial costs are higher, but we will be better off in the long run,” said Ikuo Kezuka of JTB Estate.

“We can save on running costs and that in turn can be a big selling point in wooing tenants.”

Kezuka, noting the building had only been completed in February, said it is still too early to judge whether his firm’s decision to install the system was the correct one.

“We’ll wait and see, but I don’t think we’re betting much because the technologies used in the system are not at all new,” he said.

Kasuya would not disclose the exact price of the system installed in the JTB building. Generally speaking, however, he said installing a new system in a new building of similar size would cost around 20 million yen more than installing a conventional system — an amount that can be paid off in three to five years.

He added that, apart from being a cost-saver, the new air-conditioning system is environmentally friendly.

He noted that total electricity consumption at an office building using the system can be cut by 14 percent, resulting in a 30 percent cut in carbon dioxide emissions.

Simply put, the system uses ice to refrigerate a coolant, which is then circulated around the building to cool its concrete floors.

More specifically, an ice machine and a 175-cu.-meter storage tank are set up on the roof to create and store ice, which is then used to refrigerate the coolant.

When its temperature falls below 7 degrees, the coolant liquefies and flows through pipes in the building’s walls to the spaces above each ceiling. A fan installed in the ceiling simultaneously blows air up toward the coolant pipes and to the concrete floors of the stories above.

This all takes place at night, when electricity costs are much lower. Kansai Electric Power Co. provides the electricity for the ice-making stage, which goes on from 10 p.m. to 8 a.m., at one-third of its daytime rate.

Once the concrete floors have been cooled to 21 or 22 degrees during the night, they can maintain this temperature until around noon the following day.

This helps to keep the temperature of the rooms above them at a comfortable level, according to Kasuya.

The fans in the ceiling spaces also blow air downward during the daytime, sending cool air into the rooms below. The air is cooled by the ice that was created and stored the previous night.

The coolant is circulated around the clock, although this flow consumes no energy in the daytime or at night.

The coolant evaporates and returns to the roof to be recooled once its temperature reaches 10 degrees.

During the winter, hot water is warmed by the heat from the ice-making machine and is circulated to heat up the air and the concrete floors in the building.

“We’ve had an air-conditioning system with ice, a coolant circulation system without power, and a system to keep room temperature by either cooling or heating floors,” Kasuya said. “But the combination of these three has created the ultimate air-conditioning system.”

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