Working toward the Realization of Comfortable and Energy Efficient Spaces with Climate and Landscape-Utilizing Radiant Heating and Cooling

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When planning a building, it is necessary to examine the building site and formulate a plan rooted in the climate and landscape. This is a necessary process toward realizing sustainable buildings. There are no two building plans with identical building site conditions, and the same can be said for facility designs.

The radiant heating and cooling plan devised by Nikken Sekkei for the new Densan main office building is closely linked to the architectural plan, the lighting plan, the climate, and the landscape. Based on the example of the new Densan main office building, information will be presented here on logical radiant heating and cooling plans that make use of the climate and landscape.


What Kind of Equipment is a Radiant Heating and Cooling System?

Before explaining radiant heating and cooling systems, an explanation of the mechanisms and distinguishing features of air conditioning equipment in general will be provided.
Within a given thermal environment, individuals perceive comfort based on six elements. These are temperature, humidity, airflow, radiance, the amount of clothes being worn, and the rate of metabolism. Currently the most common kind of air conditioner is the convection current air conditioner. These air conditioners make use of airflow. Convection current air conditioners use a mechanism in which they blow cold or hot air to cool or heat the air in the room. Out of the six elements listed this mechanism controls temperature, humidity and airflow. However, they have issues including blower noise, convection current drafts, and uneven room temperatures.
Let’s turn our attention to one of the six elements that compose the thermal environment, that of radiance. Radiance is a phenomenon in which heat is carried as electromagnetic waves. Electromagnetic waves are emitted by the object possessing heat, and the object receiving the electromagnetic waves is affected. As this does not involve air or airflow as is the case with convection currents, the electromagnetic waves will reach the target as long as nothing is blocking the waves between the two objects.
For example, even if you are not directly touching a hot skillet you can still feel the heat on your skin. This is radiant heat. Radiant air conditioners make use of this “radiant” mechanism. The radiant surface cooled or heated by the air or water is installed indoors and this surface controls the thermal environment. As the environmental control is performed with radiant heat, it is quiet with few unpleasant drafty sensations. From the standpoint of comfort it is an exceptional system. Possessing these kinds of features they are even used by medical facilities.

Making Use of Nagano’s Natural Potential in Radiant Surfaces

The Densan main office building is located in Nagano City, Nagano Prefecture. This is an area blessed with cold outside air and plentiful ground water. In this project we focused our attention on the outside air and ground water characteristic of the Nagano region and effectively utilized these in radiant surfaces.
We used ground water for the ceiling radiant surface. This ground water maintains a temperature of 15oC year-round due to geothermal energy. This cool water is perfectly adequate for use in radiant cooling.
Outside air is used for the floor radiant surface. In the summer and interim periods when the outside air becomes warm, the air is cooled through geothermal heat as it is cooler than the outside air. This is done through a cooling and heating trench that utilizes seismic isolation layers. The cooled air is then sent into the floor. In the winter when the air becomes cold, the temperature of the geothermal heat is higher than the outside air. The use of geothermal heat is how we give consideration to energy efficiency.

Flow chart of the radiant heating and cooling system using natures’ potential
Water radiation from the ceiling and air radiation from the floor due to outside air and geothermal heat.
Due to the plentiful natural resources in Nagano, it is possible to create a pleasant and relaxing space that is energy efficient.

Nagano City, Nagano Prefecture is blessed with the natural potential of its outside air, geothermal energy and ground water. In focusing our attention on these resources we were able to realize a comfortable cooling and heating system that is energy efficient and gentle on the human body.

Maximizing the Effects of Radiant Heating and Cooling in the Radiant Surface Plan

In radiant heating and cooling the percentage of the space taken up by radiant surfaces is important. Controlling the radiant environment with larger surfaces makes it possible to realize a comfortable space. In this project we utilized ceiling surface radiance, floor surface radiance and window surface radiance as our radiant surfaces.

Radiant heating and cooling system concept for Densan ShinHonsha building

For floor surface radiance we chose a “Floor Seep Air Conditioner,” which seeps air emitted by the air conditioner through the OA floor surface. This pushes the air in the entire space upward from the bottom of the floor and efficiently introduces fresh air into the office area. Compared to traditional air conditioners, this system limits air conditioning unevenness resulting from the distance to the air conditioning vent as well as discomfort resulting from the emitted air. In cooling the entire floor surface with the emitted cold air, effective radiant cooling is possible. In many instances vents and grills are installed into the ceiling. As it is possible to reduce the number of these, the facility design also gives consideration to design.
The window surfaces are called the perimeter zone, and are considered to be a very important area of the thermal environment. Larger surface areas impart a greater effect upon the radiant environment. For this reason we implemented a number of contrivances into the window surfaces.
In winter the radiant environment is controlled through the use of Low-E exothermic glass. In the summer and interim periods eaves and blinds are controlled automatically to provide shade against direct sunlight. Air circulation is created at the windows by running an air barrier fan.
Through these radiant environment control technologies we have prepared a radiant environment in which individuals can spend the entire year in comfort.

Reducing Thermal Loads through Lighting Plans

The heat emitted by lights is hardly noticed as they are often installed into the ceiling. However, within the thermal environment it is impossible to ignore the heat emitted by lights. It also bears a relation to air conditioner energy consumption. In skillfully processing the heat emitted by lights, it is possible to realize a comfortable and energy efficient office space.
In this project radiant cooling is performed by running heat-exchanged cool water through the perforated aluminum ceiling. Lights affixed to the ceiling were installed to have their illuminating portion on the inside of the room, and their heat-generating portion on the inside of the ceiling. In this we aimed to create a comfortable office space.

Screen light

  • Heat distribution image (New Headquarters)
    The ceiling surface is cooled and the space is enclosed in radiant heat. The heat generating part of the lighting fixtures are disguised inside the ceiling to reduce variation in heat radiation.

  • Heat distribution image (Former Headquarters)
    The heat generating part of the lighting is hot and the outlet of the air conditioning is cold showing wide variation in the radiated heat environment.

In order to make the office space one in which people can easily concentrate, we took the idea of “keeping one’s head cool and one’s feet warm” into account. We decided to make the ceiling radiance only a cooling effect, and designed the system to suspend ceiling radiance when the building is being heated.
We took into account radiant surfaces together with the light and heat emission of the lighting, and carefully designed the lighting on the inside of the ceiling. In doing so we were able to realize a comfortable living environment and at the same time give consideration to energy efficiency.

Deriving Optimal Air Conditioning System Solutions in Consideration of Climate, Landscape and the Wishes of the Building Owners

Just as there are no two identical building sites, building plans once made are not used on other projects. This project required the building to have the functionality of a main office building, a comfortable office space, and thorough environmental consideration. We took into account the location of Nagano City, Nagano Prefecture and the wishes of the building owners. Our approach was to derive optimal solutions within the heating and cooling facility design, and this approach led to our proposing a radiant heating and cooling system that uses ground water and outside air.
Every project differs in every one of its conditions. At Nikken Sekkei we do not simply apply given technologies and knowledge to our projects. We seek out optimum solutions for each project by integrating all of the variables, such as the unique characteristics of the building site. Our company is a comprehensive design firm. As such we believe our strengths lie in our steadfast environmental and equipment technology capabilities and our ability to make proposals that integrate the building with environmental technologies that address the conditions of the project.

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