When building a new house, many owners may be wondering what kind of air conditioning system to use. There are two main methods for air conditioning a house. One is whole house air conditioning and the other is individual air conditioning for only the rooms and zones that are being used.
When deciding whether to use whole house or individual air conditioning, owners should consider the air conditioning method that suits each living environment and operation pattern, taking into account aspects such as cooling and heating capacity, comfort, noise, design, product price, the installation cost, and the operating costs.This passage is going to discuss from the perspective of housing and comfort vs operating costs.
Depending on the structure, materials, and the floor plan of the house, there are suitable air conditioning methods and operation patterns. Walls, floors, and ceilings of houses have different thermal conductivities or heat insulation properties, and heat capacities depending on the materials, and the differences affect the effectiveness of air conditioning.
Stone and brick houses tend to have higher heat capacity and thermal conductivity than wooden houses. Houses in regions with severe cold winters such as Europe have often been made of stone since ancient times.
In stone houses without insulation, the surface temperature of the stone wall does not rise easily even when the air conditioner offers heating in winter. It also takes quite a long time to raise the room temperature. Therefore, in a stone house, stopping the air conditioner when no-one is present may significantly reduce comfort, and it can be said that individual air conditioning is not suitable for stone houses.
On the other hand, homes in temperate and tropical regions such as Japan, Southeast Asia, and Latin America are often made of wood.
Since a wooden house has a low heat capacity and low thermal conductivity, the surface temperature of the wooden wall and floor rises faster than that of a stone wall and floor, and therefore the temperature of the room air also rises faster. In a wooden house, even if the air conditioner is stopped when there is no-one in a room, a comfortable temperature can be achieved within a short time if the air conditioning is restarted when a person returns to the room. Therefore, individual air conditioning is suitable for the wooden house.
In a well-insulated house, a comfortable temperature range will be achieved by continuous operation with almost any type of air conditioning system. For example, in heating operation, the temperatures of the floor, walls, and ceilings approach the room air temperature, so there is little temperature difference in the upper and lower parts of the room, and a comfortable state is achieved. On the other hand, a house with poor heat insulation tends to have a difference in temperature between the upper and lower parts of the room.
Comfort vs Operating Costs
A comfortable indoor environment condition is realized by achieving an appropriate air temperature, wall temperature, and humidity in the room, and the airflow of 0.5 m/ s or less. In addition, a comfortable temperature condition is almost realized with a total homogeneity of room temperature and a temperature difference of 2ºC or less between walls/floors and the room.
As mentioned above, since whole house air conditioning is basically operated 24 hours, a day comfort is maintained, but operating costs are high. In the case of individual air conditioning, the room temperature fluctuates if the air conditioner is on and off each time a person enters or leaves the room in order to reduce operating costs. Since the air conditioner operates at high capacity when it starts up, this is disadvantageous both in terms of comfort and operating costs. According to Daikin’s research, it is economical, depending on the conditions, if there is no-one in the room for 30 minutes or more, the individual air conditioning is stopped, and if the person returns to the room within 20 to 30 minutes, the operation is continued.
As described above, at present, one has to put up with high electricity bills in order to be comfortable at all times, and conversely, comfort has to be sacrificed to some extent in order to reduce electricity bills. From now on, the trend is heading toward reduced operating costs while still ensuring comfort. There is a limit to the energy savings that can be achieved by the air conditioner alone, so it is important to save energy in the whole house. In other words, it becomes important to reduce the energy consumption of the whole house by controlling not only the air conditioner, but also other systems such as the ventilation fan, air purifier, humidifier, dehumidifier, hot water supply, solar hot water supply and power generation, and gas equipment.
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