Those who have newer air conditioners bought in recent years will notice that there is an additional button in the remote controller. This button is called "Dry Mode". Some like it as they claimed it could save energy; some just ignore it completely. This button is not available in the older models. What is this button and how does it work to provide cooling?
Why The Button?
Our body is sensitive to temperature as well as humidity. When the temperature is hot or cold, our bodies can feel it immediately. When the humidity is high or low, we might not feel it immediately but over time, our body will react to it.
This is because 1/2 to 3/4 of our bodies are full of water. When water evaporates fast enough from our bodies, we will feel the sensation. The feeling is just like we are under a fan. The air blowing towards us evaporates vapor from our bodies. The faster the airflow, the higher the evaporation, the better will be the cooling.
The air conditioner is also an air dehumidifier but not as efficient as a real dehumidifier. When it cools the air, it also removes water vapors from the air. This is a natural cooling process. The dry mode button will instruct the air conditioner to operate more like a dehumidifier.
The dry mode will be particularly useful in tropical countries where humidities are usually high. The dry mode can help to lower humidity in the room more quickly than the normal cooling mode.
How Does it Work?
As a simple illustration of how airconditioning and dry mode works, if the air conditioner's airflow is strong, it is working as an air conditioner; on the other hand, if the airflow is reduced, it is working as a dehumidifier. It appears that the airflow is forcing the air conditioner to change from air conditioning mode to dry mode.
Slow Fan Speed Not Freeze Coil?
Of course, its controls are not so simple. The control involves also the speed control of the compressor. There is also a need to make sure the cooling coil will not freeze when the airflow is reduced. This is why the dry mode button is not always available in older models that have fixed-speed compressor motors.
This is one possible control strategy:
The Best Design Strategy for Dry Mode?
Dry Mode slows down the fan speed so that the evaporator coil can condense more vapor out of the air when the air passes through the coil. It will use some energy and be able to lower the humidity faster than usual to an acceptable and comfortable level.
Different manufacturers have different design strategies for dry mode; some adjusted also temperature as well as the airflow in their cooling strategies. The idea is to achieve a desired comfortable cooling condition.
It has been commonly accepted by researchers that the most comfortable room cooling condition is 25oC@ 55% humidity. This is the room condition that most manufacturers are using to design their air conditioners. For the angle of saving more energy, there is a tendency for the professional to pick 65% humidity level as the new comfortable humidity level.
Anyway, different people might have different feelings and reactions towards temperature and humidity. For this reason, most manufacturers will still allow users to adjust the temperature in the dry mode. If temperature adjustment is available in dry mode, most users will still use 25oC as the setpoint temperature. This does not necessarily save energy. This is because the energy to maintain the room at the comfortable setting of 25oC@ 55% humidity will more or less remain the same.
Will Dry Mode Save Energy?
The dry mode lowers the fan speed allowing moisture in the air that flows through the evaporator coil to be removed more quickly. It still consumes about the same energy to maintain the room's humidity at the desired comfort level of 55%. However, if one finds it comfortable to allow the room temperature to be set higher than the usual 25oC, one will be able to save some energy.
Operating an air conditioner at econ cooling mode or auto mode will save more energy as the air conditioner is always set to run at the most efficient designed load capacity under this operating mode. Depending on the design, the airconditioner's efficiency can vary a lot at different load capacities.
Difference between Cool, Dry, and Econ Modes?
The newer air conditioner having an inverter or otherwise to control the speed of the compressor motor allows 2 additional modes of control, namely Dry Mode and Econ Mode. The differences between them are briefly described in this table:
| Mode | Mode Description | Usage | Energy Saving |
| Cool Mode | Default mode | in hot and humid weather to maintain constant temperature control | Saving Depend on selected temperature; |
| Dry Mode | New Function | In not too hot weather or raining season to lower humidity to achieve comfort cooling | Save energy if the temperature can be allowed to be set higher. |
| Econ Mode | New Function | In not so hot weather to run the air conditioner at a most efficient level | Prevent excessive low-temperature cooling to lower electricity bills |
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