I want to have a cool house in the summer

Those who think that "ventilation is important" to keep cool in the summer may have noticed that 20 years ago, ventilation may have been enough to keep the temperature down to a certain extent, but now it is "absolutely" impossible. 2019 was the only year in the past 10 years that was relatively cool. In other years, temperatures over 35°C have become common every year. If you rely on ventilation to keep the temperature down, even if there is wind blowing, the wind is not cold, but only warm air at 35°C, which is very close to the temperature of the warm air from an air conditioner. What's worse, this warm air is not dry like air conditioners, but contains a lot of moisture, which makes it even worse. For reference, I will show you a thermal image of a house built in a rural area in the summer. What surprised me the most was that the water surface of the rice field was 39°C. Even in a rural area like this, we live in an age like this.

When you use an air conditioner to cool your home, it lowers the temperature and at the same time condenses a large amount of water vapor, turning it into water. The resulting moisture is then dumped outside through the drain pipe. In this way, you pay for electricity and input it into the air conditioner, only to finally dump the heat and moisture outside... This is what an air conditioner does to cool your home. Despite this, many people leave their air conditioners on until the evening, and then turn them off at night and open the windows. If you do this, at that moment you end up taking in the heat and moisture that you previously spent money on dumping outside.

That doesn't mean ventilation is a complete waste, though. Ventilation in the summer is a no-no, but in May and October it feels really nice and is recommended. However, in May, people with hay fever will find it very uncomfortable to open the windows. These days, at least one person in every family has hay fever. With that in mind, there may be many houses where it's difficult to open the windows in May as well.

This is a long digression, but if ventilation is not an important measure, then what is? There are two major points. One is perfect sun protection from the windows. For the east, west, and north sides, use heat-insulating Low-E glass. This is something that is often done by any housing company. However, this alone will not make the house cooler.

"For windows facing the east, west and north, each side of a room should be no more than 0.5 mXNUMX."

Doing this much will be just right. It is rare to see a house that adheres to this rule.

For south-facing windows, you need to install eaves with a height of 10 and a projection of 3. Or you need to install an external sun-blocking product called an outer shade. If the south-facing side is within about 20 degrees of due south, eaves will be effective. If it is more than that, an outer shade is an effective solution.

Another important measure is roof insulation. This is insufficient in the vast majority of cases. For glass wool, you want at least 180mm. The thicker it is, the less likely it is that the high heat of the roof will be transmitted.

The above two points are the most important, but most companies fail to do so. However, there is another important point that has recently become more common. That is black exterior walls. The surface temperature of a black exterior wall is more than 2°C higher than a light exterior wall. This has a significant negative impact. Considering that the earth will continue to warm in the future, we strongly recommend that you avoid using black exterior walls as much as possible.

Furthermore, if these measures are taken properly and the air conditioning is designed and operated appropriately, even if you run the air conditioning 8 hours a day in August and keep the temperature in the house at 24°C, your monthly air conditioning bill will be around 27 yen. This may seem unlikely for an average home, but it is true.