The lie that high insulation will cause overheating

Renovation work on a day service center in Akashi City will soon be completed. (Steel-framed office building)
The cooling effect of the original ceiling air conditioner was quite poor, so we replaced it with a new one.
They had planned to do this, but instead carried out thorough insulation renovations.
What happened as a result?!
When the client came to the site, he said, "The air conditioning is too strong and it's cold!"
He said.
Until now, even with air conditioning, a lot of heat was coming in through the walls and windows.
The air conditioner just wasn't working, but after proper insulation repairs, it was no longer necessary.
The air conditioning became more effective.
So why is there such a simple fact in the housing and construction industry?
"If the insulation is significantly higher than the next-generation energy-saving standard, it will overheat in the summer."
Why are urban legends like this so prevalent?
I thought about it calmly and calculated the results.
Heat is a physical phenomenon, so it always flows from high to low.
Move
Next, the factors that determine the room temperature in summer are the outside temperature, insulation, airtightness,
Factors that play a major role include the amount of solar radiation obtained, the amount of internal heat generated, and the cooling capacity of the air conditioner.
The theory that "high insulation will cause overheating"
The premise is that the room temperature is always higher than the outside temperature.
"The surface temperature of the ceiling and interior walls is always higher than the surface temperature of the roof and exterior walls."
The point is that.
In these cases, the temperature inside the room is higher.
Heat tries to move from the inside to the outside. In this state,
The worse the insulation, the easier it is for heat to move out (escape).
So the argument that "low insulation makes it less likely to overheat"
It will probably come out.
However, the reality is quite different.
First of all, the surface temperature of the roof exceeds 50°C, let alone 60°C, during the day.
No matter how you look at it, heat tends to move from outside to inside.
Even on the exterior walls, the surface temperature of the exterior walls during the daytime is about 40 degrees Celsius.
In other words, it is definitely higher than the outside temperature and the average temperature of the exterior wall.
In this case, as with the roof, heat transfer is from outside to inside.
Clearly, the more insulation there is, the more comfortable it is.
Also, the temperature of the exterior wall in the shade is roughly the same as the outside temperature.
Since the temperature difference between the room temperature and the room temperature is not that large, there is little heat transfer in the first place.

While it is true that the human body and electrical appliances do generate internal heat, the amount of heat generated is not significant.
Even in a highly insulated building, if the building is properly protected from sunlight, the room temperature will not rise rapidly.
Not at all.
Furthermore, if you are running just one air conditioner in your attic, as our customers often do,
In such a situation, the temperature of the entire house will definitely be lower than the outside temperature.
Heat does not move from the inside to the outside. This means that the higher the insulation, the better.
This clearly means that "it becomes more difficult for outside heat to enter."
If this urban legend is relatively true, it is because of the next generation energy-saving technology that provides almost no protection from sunlight.
I think it's a building like this.