Japan Sustainable Building Database

Natural energy use system

Natural energy use system

As technical elements of natural energy use and air conditioning load reduction suitable for a subtropical climate, Solar Shading, photovoltaic power generation, natural ventilation and daylight use are employed.

Solar shading:
In Itoman City Hall, the shapes of external louvers were studied to block solar radiation efficiently. Horizontal louvers were provided on southern side of the hall and pre-cast concrete screens were provided on eastern and western side. Vertical louvers were provided on northern side. Horizontal louvers were provided on the roof as a shelter.

Natural ventilation:
In Itoman City Hall, the air-conditioning system is stopped from November to May next year. The natural ventilation was designed to maintain the indoor thermal environment at acceptable level during those seasons. External louvers block the solar radiation effectively and the large windows could be applied to all external walls to provide the natural ventilation without additional air-conditioning load. The natural ventilation route in Itoman City Hall is formed with the large sliding windows on the external walls, sliding doors and windows facing two courtyards in the centre of the building.

Natural lighting:
Direct solar ray is block by external louvers, thus the sky light with little unpleasant glare are used as lighting sources. And two courtyards also introduce natural light into the hall. Automatic lighting controls with illumination sensors were provided at perimeter zone of office area in northern wings, to reduce power consumption for lighting.

Photovoltaic power generation

City Hall bird's view

The solar cells are on southern horizontal louvers and horizontal louvers of roof shelter. The total capacity of the solar cells is 195.6[kW]. For the effective operation, the photovoltaic power generation system (PV system) was designed to interact with power utility so that excess power can be reversed. In the weekends and holidays, surplus power is sold to Okinawa Power Company.

The PV system consists of power conditioners, power collectors and multi-crystalline silicon solar cells. An auxiliary 200[Ah] battery is installed in the system to operate during the power failure in case of disaster.

As the Itoman City Hall is in the coastal area, consideration on corrosion protection against briny air had been taken. The solar cells are protected with two layers of tempered glass provided on both of front and back sides to have self-washing effect by rainwater.

Traditional passive design

Space created by eaves to shield from strong sunlight

Itoman City Hall was designed as a low energy building in sub-tropical climate based on observations and studies of the traditional and modern house in Okinawa. The deep eaves and room layout to have good ventilation were studied and reflected to southern external louvers and floor plan of the hall. And solar screens in modern houses were reflected to the eastern and western side PC concrete screens of the hall.

In the building design work, it is important to consider the features observed in the local buildings as well as the latest technologies. And it is also important to integrate architectural design and building service engineering to suit the building with the local climate in order to realize high performance building.