Background 
 

Nagano Precfecture is stituated at the centre of the island of Honshu, Japan's most populated landmass. The region possesses great natural beauty witha majestic alpine range formed by the Hida, Kiso and Akaishi Mountains. The clam grandeur of the Japanese Alps conceals many geological forces. Several of the snow-covered peaks are actually dormant or semi-active volcanoes that provide steam heat for volatile geysers and numerous hot spring spas (onsen) throughout the area. The region is also home to six national parks that offer year-round recreational activities. The 1998 Winter Olympics brought the Shinkansen (bullet train) to the area.

 
 

A house to catch wind

In keeping with its mountain surroundings, Iizuna House was designed as an airy sequence of open and closed spaces, a place that would literally 'catch the wind'. The project's energy mandate aimed at a substantially reduced environmental impact, restrained consumption of fossil fuels, and minimal reliance on artificial cooling and heating systems. Set deep in a thick stand  of trees, the composition of facility comprises a building for guest lodging and a separate unit that house a large kitchen and other public quarters. These two areas are connected by a common lounge that has large moblie glass screens, which gives the room spatial adaptability. 

Channelling Heat from the Earth

Just as volcanic heat boils the fumaroles and hot springs of Mt. Chubu, Iizuna House also successfully exploits geothermal energy via earth tunnel that's incorporated into the design. This heat and ventilation pathway uses outside air that's been slightly precooled, channels it through a subterranean heat-storage unit and disperses the chilled flow into living areas. With solar galre much reduced by the broad eaves above the windows, and the room properly insulated from exterior heat, there's very little load on the innovative cooling system.

Capturing the Wind and Sun

The flexibility of an Airflow Roof.  Solar heat is the main energy source for the villa and its use is expressed in the addition of a double-layered airflow roof whose crests create a harmonious effect juxtaposed against the triangular contours of surrounding pines. The airflow roof has dynamic insulating and conductive properties. It was installed to collect solar thermals via special glass panels for heating water and inhabited spaces, and prevent energy loading on the cooling system. The heating/cooling tube on roof is also to conserve energy consumption.

During summer, air passes through the two-layered roof and is carried away with exhausted air. The heat form the roof is used to heat water. This method maintains even interior temperatures. The forces of land, sun, mountain winds, sheltering forests and heat from the earth's belly are built into the very fabric of Izuna House. The villa is a simple but sublime example of architects thoroughly understanding the site of their design, and how utilizing natural elements can bring life to a building. 

In winter, fresh sun-warmed air is captured by the southern eave and by the air ducts in the earth tunnel then supplied to various rooms. When bringing the outside air into the building for ventilating purposes, the solar heat and the heat from the heating / cooling tube are used to raise its temperature, which also cuts down on heating expenses. Depending on the weather, the performance of the solar heat collector on the roof will vary. However, the temperature of the earth is stable. Therefore, air that has a temperature of 30oC in mid-summer can be changed to a cool breeze of 24oC. In winter, even if the temperature outside is 7-10oC, it is possible to obtain a flow of warm air from the earth. 
 
 
 

In summer, outside air conditioned using a subterranean air duct system. Heat from the roof is used to heat water.	Cold winter air is preheated using the solar energy collector on the roof and the subterranean air duct system.

     Reference:

• FACT - Nikken Sekkei 
• Sustainable Design Guide, Japan Institute of Architects 
• Building Future Japan 2000 
• Sustainable architecture in Japan