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I have a split-type inverter air conditioning unit in one room placed near the ceiling. Assume that the cooling capacity is met, and I'm using the correct CFM of fans. I would like to share this air conditioner with the adjacent rooms. My plan is to install two fans for each room to be cooled. There will be four fans in all.

Questions: Are the following implementations correct?

  1. I install one exhaust fan to blow cold air from the colder room near the floor to the living room (hotter). This is because cold air tends to settle to the floor and this makes it easier for cold air to be moved from one room to another.
  2. I put one exhaust fan at the higher point (directly in front of split type air con) which is pulling hot air from the other room back to the colder room. My thinking is that in the other room which is hotter originally, hot air rises. So putting the exhaust fan at the higher point makes it easier to move hot air from the hot room to the colder room.

Thus, #1 and #2 complete the heat exchange cycle and cools the other room. I repeat the same implementation for the other room. What do you think, does this make sense?

Some people suggest the reverse. This way putting the exhaust fan to pull cold air to the hotter on the top (near the ceiling) instead of near the floor. Since its easier for cold air to falls to the floor thus more efficient. Is this a better scenario?

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I suspect that the reverse method is more efficient.

Assumptions:

  • Efficiency is energy required to reach a certain thermostat temperature. A lower amount of energy required to reach the desired thermostat temperature means a more efficient design.
  • Like most households, the thermostat is at head height.
  • The direction of the fans does not impact energy used at a given airflow rate.
  • The air-conditioned room is room A and the unconditioned room is room B
  • Your first scenario, with the lower going from A->B and the upper going from B->A is scenario (1). The reverse is scenario (2).
  • Room A is always uniformly at the thermostat temperature because the cool air from the air conditioning unit is at the top of the room and as the cooled air sinks it mixes evenly.

In scenario (1), Room A is at a uniform temperature and Room B has a temperature gradient. The magnitude of the temperature gradient will be related to the fan airflow. A higher airflow will create a lower gradient. In scenario (2), Room A and Room B are both (the same) uniform temperature throughout because the falling cool air mixes throughout the room.

In order to achieve a desired thermostat temperature in Room B, scenario (1) will need a lower thermostat temperature in Room A or a higher fan airflow rate than in scenario (2) because the temperature gradient will mean the thermostat in Room B will always be hotter than in Room A for scenario (1).

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