Analyzing the four major air conditioners and how to choose an efficient product③

Problems with too much capacity and too little capacity
There is one thing you need to keep in mind when choosing an air conditioner. It is not as simple as "it's fine as long as the maximum capacity is just enough." It depends on the outside temperature and the model, but when heating, it works most efficiently when operating at around 0.7 to 0.9 of the rated capacity. The more you push it beyond that (the more you choose an air conditioner with a capacity that is too small for the room), the more it will operate in the area to the right of 1.0 on the graph, and the worse the efficiency will be.

Graph showing the relationship between rated capacity and efficiency (Source: Kazuya Matsuo)）
However, as we mentioned last time, in most homes, the operating range is only to the right of 1.0 immediately after the switch is turned on. If more than an hour has passed since the operation, most homes are operating at 1 or less (the range to the left of 0.5 on the graph).
According to measurements taken in an experimental house by the Building Research Institute (Tsukuba City), a national research and development corporation, the longest period of time was when the air conditioner was operating at about 20% of its rated capacity. The average COP in this case was about 2.5, which was far from the figures of around 7 from the companies introduced at the beginning. This also shows that losses caused by choosing an air conditioner that is too large are a very big problem.
Also, in the case of a system that operates only when people are present in a house with poor insulation, it is possible that the unit will operate at close to maximum capacity for the first few minutes. In such cases, there are so many uncertainties that it becomes even more difficult to select the appropriate capacity.