The blessings of the sun, the soft wind and the natural heat form the earth will not be depleted in the future. By making good use of these great natural forces, while relying on special building equipment as little as possible, it is possible to create a pleasant environment inside the rooms of the building. By using natural energy, it is possible not only to limit the use of fossil fuel, but also to save in many ways on the costs of coping with the effects of the surrounding environment.
 
 

Cross-section and exterior view from North

Cross-section and exterior view from South

Preserving cool air inside a building
In urban areas with problems such as noise and air pollution, bringing outside air directly into a building by means of natural ventilating methods is far from being an ideal solution. The energy strategy of the building is based on a mixture of natural ventilation and air conditioning, together with a combination of natural daylight and artificial light. Cool air is drawn in under the windows and enters the floor via diffusers, which serves to cool the concrete parts of the structure and lower energy consumption of air-conditioning. It is extracted both through the light fittings and through the atrium. Floors can be either open to the atrium or closed off by roller shutters. As a result of the increased use of electronic office equipment in recent years, it has become necessary to run the cooling and heating systems all year round. This approach to the use of cool outside air has come to be highly valued.

Underfloor air conditioning system An underfloor air conditioning system was introduced in this building. Compared with conventional ceiling diffuser system, not only promotes exhaust heat removal with higher efficiency but also increase the use of natural energy. The air column of the underfloor air-conditioning system can be controlled in either manual or automatic mode. In manual mode, occupants can directly control the air-conditioning to meet their personal requirements. Automatic mode is selected by the building operator during cool-down operations. Furthermore, automatic mode is selected over manual mode when the room temperature is abnormally high or low.  Personalized Air Conditioning through Integration with Furniture Several types of personal systems are available in this building. Type A is a typical system that diffuses the conditioned air from the floor plenum. Type B is a system that exhausts heat through the partition. This prevents discomfort caused by high-temperature air from a pedestal computer. The idea is to catch the heated air at its source and discharge it efficiently through the exhaust openings at the top of partitions. Type C has the partition connected to the underfloor fan unit via a duct. The diffuser of the floor unit is removed to allow connection to the furniture outlet. The air from the floor plenum is mixed with room air to control supply air temperature from the partition outlet.  In the underfloor air-conditioning system, significant beneficial impacts of directly removing exhaust heat can be achieved which means that the cooling load to be processed in the occupied area can be decreased. Consequently, higher temperature supply air is delivered at the time of cooling compared with a conventional ceiling-based air-conditioning system, assuming the same amount of conditioned air is supplied. Experimental results led to the assumption that the underfloor air-conditioning system allows the temperature of supply air to be approximately 4oC higher than that of the ceiling based air-conditioning system. When the climatic conditions of Tokyo are taken into account, the potential amount of cooling energy savings that can be achieved is estimated to approach 30%. Thermal Storage Effects of Floor Slab During the night, cool outside air is introduced into the underfloor plenum. and the thermal mass of the floor slab is cooled down. The cool storage of the floor slab is subsequently utilizer during the day to reduce the temperature of the supply air in the underfloor plenum, thus reducing mechanical cooling energy use. As this building is subjected to air-cooling loads throughout the year, this slab heat storage system is a highly effective solution for utilizing natural energy and reducing peak cooling energy use and electricity costs. The ventilation volume of underfloor plenum varies depending on the outdoor wind direction and velocity as well as the indoor/outdoor air temperature difference, the overall average ventilation air change rate was measured to be 0.5 to 3.5 times per hour, based on the volume of the office space. The results confirmed that an estimated energy savings of 186 Wh/day/m2 could be achieved through the night purge operation utilizing the floor slab thermal storage.  Energy Saving Effect Effect of night purge

 

Daylight enters the atrium through a relatively narrow space at roof level, where it passes through an arrangement of prisms, and through the east facade. Reflecting mirrors secured to the north edge of the top light introduce sunshine to the atrium floor in winter, to create a subdued effect. A further 104 panels of circular mirrors reflect artificial light into the atrium. (See the section for the system of natural lighting and ventilation)

 The floor-vented air conditioning system

The building was expected to generate extremely high-density thermal loads that would change position or increase frequently. This situation made it very important to install a comfortable, flexible air conditioning system that would also be cost effective. Research by the structural engineers led to the idea of floor-vented air conditioning. The validity of such a system was extensively tested using a verity of simulations and experiments.

This kind of floor vented air conditioning has a number of advantages. It functions perfectly as an individual air conditioning resource for people. One floor vent is allocated to each occupant and fans produce a pleasant air movement with the feeling of a natural breeze.

Night cooling by Outside Air

At night, ventilation using outside air is increased to eliminate heat that has accumulated inside the building during the day. the chilled night air also cools the concrete floor slabs, which in turn act like a form of air conditioning during the day. this is an energy-saving technique that successfully operates on the theory of cold storage. 

Ceiling and floor air conditioning system

Ambient air conditioning for inhabited areas Ambient air conditioning was planned for the outer edge of the personal space. Separate floor vents were added for the ambient air conditioning, allowing temperature adjustment in the inhabited areas of the entire space. In this case, the inhabited area is the volume to about 1.8m above the floor level. Temperatures in all occupied areas was deemed sufficient if the air was maintained at comfortable degree for human activity. Effective Use of free cooling in local heat extraction The floor-vented air conditioning system can effectively extract the heat generated within a room from people and equipment by utilizing the buoyancy created. When resulting updraughts are drawn into the ceiling without mixing them with other air and then expelled, the room-cooling load is substantially reduced, allowing highly effective air conditioning. Compared to ceiling-vented systems, this system can use free cooling by outdoor air for a much longer part of the year, achieving an energy saving factor of approximately 30%. The proven benefits of the floor-vented air conditioning system at the Panasonic Centre open up a wide range of possiblities for creating more flexible and heterogeneous environments in modern buildings.

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