MUJI House is a passive house designed for optimal indoor comfort
We use energy in the home to keep the indoor temperature comfortable: not too hot, not too cold, even if it is scorching or freezing outside. According to the U.S. Energy Information Administration, space heating and air conditioning uses up about 50% of the total energy consumption in the residential sector. Recognizing this significant fact, it’s becoming increasingly common to couple the goal of achieving optimal indoor temperature with reductions in energy consumption.
And it’s not surprising that conscious living-oriented MUJI is committed to achieving comfortable indoor thermal quality by relying only on minimum amount of energy possible. But this is not achieved in the way you would imagine.
Comfort is something you create. It’s important that you have a clear idea what it takes to achieve a comfortable house BEFORE you start building it. There are things your house can do to blend with nature, that the ambient environment can do, and that you can do to help achieve optimal indoor thermal comfort. (MUJI report on optimal thermal comfort (快温シュミレーション報告書) Translation by Mihoyo Fuji)
While the MUJI house attempts to achieve optimal thermal comfort with the least possible amount of energy, it does not rely entirely on energy efficiency – which is probably the most common tool to reduce energy consumption in the home. Actually, it goes one step further and suggests that there is a factor more elemental than energy efficiency, and that has to do with how a house is designed. MUJI goes on to state:
The comfort of a house cannot be determined solely by meeting certain standards for performance/efficiency. While measures such as insulation improvements or energy consumption management are important, MUJI also focuses on incorporating a design philosophy that leverages the power of nature in order to optimize indoor thermal comfort.
For example, you may want to shield the interior from sunlight during the summer, but in the winter allow in as much light as possible. In order to accommodate these contradicting needs to keep your house comfortable, the design needs to carefully analyze/understand the site’s macroclimate conditions. Such an approach that takes advantage of ambient natural elements (such as sunlight, breeze or vegetation) is called passive design. (MUJI report on optimal thermal comfort (快温シュミレーション報告書) Translation my Mihoyo Fuji)
For MUJI, energy efficiency achieved by appliances and devices is probably a secondary priority. The prerequisite to achieve optimal indoor comfort is to design a house that accommodates the natural conditions that determine the flow of energy – heat or cool breeze – in the surrounding environment. Whereas energy efficiency is essentially a symptomatic therapy, house design approaches, such as the “passive house” can address potential root causes and reduce the need for energy in the first place.
What are some fundamental elements of passive design? Because thermal comfort is largely affected by the amount of heat that is stored inside the house, and since the heat is generated by the sun, the most important thing is to orient the house, taking into account how the sunlight affects it during the day, and throughout the seasons. And since heat can be moved by the flow of air, especially by cool breeze, it’s also important to create pathways through which the wind/breeze can travel. Last but not least, it’s also critical to remember that the need for sunlight and breeze changes as the seasons change.
During winter, the sun shines on the earth at a lower angle. If you have tall/wide windows facing south, you could take in more warmth from the sun, especially because a low-hanging sun can penetrate deep into your rooms. Once the warmth is inside, it’s important to keep it there as long as possible: this is where good insulation comes into play.
Also, warm air travels upwards. Your design could be strategic and take advantage of the warmth that rises and lingers on the higher floor(s).
During summer, the sun shines on the earth at a higher angle. The same sunlight that provided pleasant warmth during winter is now a painful source of excessive heat. In order to avoid this, it is important to furnish the house with some sun-shielding devices. For example, it is very effective to plant large deciduous trees on the south side of the house so that they can block strong sunlight. The beauty of deciduous trees is that they loose leaves when it gets cold, so you don’t have to worry about missing precious warmth and brightness during the winter.
Taking advantage of the breeze or ensuring uninterrupted air flow becomes critical during the summer. You need to orient your house and place windows strategically to make sure you secure pathways for cooling breezes.
Writing this, I couldn’t fail to notice that that my house, built in the 70’s, does almost the opposite of the passive house. Large windows face west just because they look out on the back yard, letting strong sunlight penetrate into the house when it’s 100 degrees outside. There are few openings on the north and south sides of the house, so it’s difficult to secure air flow. As a result, on any summer day, most of our neighbors, who have similar house designs and orientation, keep their windows shut and run air conditioners all day, even after the sun sets and a nice breeze kicks in. It’s such a shame because our neighborhood is located by a river that is blessed with a nice delta breeze. Unfortunately, we are locked in a house that cuts us off from the outside environment.
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