[Vol. 2] An important part of environmental design for residential areas involves predicting temperature changes by simulating wind flows. Conventional environmental design practices used to primarily depend on the designers’ experience and intuition. Misawa Homes Institute of Research and Development Co., Ltd. (MHIRD) has implemented the micro-climate design concept, which considers the effects of both the climate and the natural features of each site. In micro-climate design, thermal fluid analyses are performed using computer simulations that result in high-performance residential house designs with enhanced living comfort. MHIRD was one of the first in industry to recognize the significance of including natural environmental conditions in the simulations. Dr. Yukari Hirayama (Picture 1), Chief Researcher at the MHIRD Environmental Energy Center, describes the role of simulations as a means to help create comfortable residential houses and cities of the future.
One application of 'passive cooling technology' worth highlighting is the application to cooling louvers (Figure 1). MHIRD designed and manufactured the cooling louvers in-house. “Splashing water onto road surface cools the temperature around the feet, but we are most sensitive to heat around our faces. By incorporating cool louvers around on the exterior of a terrace, chilled cool louver surfaces are allocated at the face level. The temperature of the chilled cool louver can be as much as 5 or 6 °C lower than the air temperature,” explains Dr. Hirayama (Picture 3 and 4).
Water is injected on the vane-shaped louver, and flows slowly from the top layer to the bottom, gradually covering the entire surface. Surface heat dissipates as the water evaporates. As wind flows over the chilled louver faces, a cool breeze is generated. MHIRD ran extensive experimental tests to identify the ideal louver material and shape. They decided to use aluminum for the core component because it could be easy shaped and sized. MHIRD also discovered that they could increase the amount of water that spread across the louver surface by applying a porous paint containing photocatalyst to the louver. Positive results can be achieved by injecting water for two hours in the morning and evening. Approximately 1 to 2 liters of water are used each hour.
To evaluate the macro-scale impact of the cooled louvers, MHIRD used scSTREAM to simulate air temperatures and wind directions and velocity distribution around residential houses (Figure 2). ThermoRender was used to simulate the surface temperature distribution (Figure 3). “To save calculation time, we used porous media model as an alternative to generating fine mesh elements. This means the computational model was like a box containing solid and fluid. We specified the property value and porosity ratio of the solid material, and defined flow resistance as a function of wind velocity after we separately calculated the resistances as a function of the velocities,” says Dr. Hirayama. Analysis results show lower air temperatures around the cooled louvers and the gradual diffusion of the cool air. To accurately capture surface shapes and surface temperature, MHIRD used SC/Tetra, which enables analyses with hybrid mesh, as well as scSTREAM. Regarding the effectiveness of the cooled louvers, “we got the effect we hoped for,” says Dr. Hirayama with confidence.
Commenting on ways to visualize heat, which is obviously invisible, Dr. Hirayama says that thermal fluid analysis tools, such as scSTREAM, can be an effective means of communication. “We can simulate the surface temperature by using the heat balance calculation in ThermoRender and then import the analysis results directly into scSTREAM. This enables us to visually see how the air temperature decreases around plants and the cool louvers, and also where heat is likely to accumulate. It helps us communicate with our designers.” Dr. Hirayama recalls that the tool was useful when communicating with the design team about whether the cool louvers prevented sunlight when located around the terrace. Did this contribute the feeling of cold during winter? How close should the cool louvers be located near windows? Using scSTREAM to visualize the simulation results helped resolve these issues. “The designers saw that the impact of improving the design of one residential house, on the entire town section, was greater than they had assumed. As a result, the designers were motivated to implement cool louvers effectively in their house designs,” says Dr. Hirayama.
According to Dr. Hirayama, scSTREAM offers many more benefits apart from just being an effective means of visual communication. “During measurement of the thermal environment, multiple factors can influence the results at the same time which confound the results. Simulations make it easier to identify root cause. It can also be used to assess the effectiveness of countermeasures for a specific problem. I feel that we can design much better products when we use simulation tools,” says Dr. Hirayama.
|Main businesses||General research on residential home and living, evaluation, and system development services|
|Head office||Suginami-ku, Tokyo (Japan)|
|Representative||Haruo Sato (President and CEO)|
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