Control Panel Cooling units Technical Information
3-9. Enthalpy
Enthalpy and psychrometric chart are essential knowledge for air conditioning technology.
In everyday life, many people often use the terms cooling capacity and dehumidification capacity of air conditioners.
The knowledge of "enthalpy and psychrometric chart" is important for each of the cooling capacity and dehumidification capacity.
As interest in environmental issues such as global warming and ozone depletion increases year by year, new technologies for cooling and dehumidifying capabilities of air conditioners are evolving day by day.
Cooling capacity and dehumidifying capacity are intimately related, and if you do not understand the meaning and content of each, you will miss the true meaning of cooling capacity and dehumidifying capacity.
To understand the close relationship, we can not talk without the most important "enthalpy and psychrometric chart".
We would like to introduce basic knowledge about "enthalpy and psychrometric chart" so that even those who are not engineers of air conditioners can understand.
* The psychrometric chart contains numerical values that represent the state of the air, such as enthalpy.
Enthalpy
The amount of heat (energy) possessed by air, which is the combination of internal energy and energy for expansion and contraction (fluid energy).
Units are expressed in kJ.
*Represents total energy including flow energy that does not remain as temperature rise.
Enthalpy [kJ] = Internal energy [kJ] + Pressure [kPa] x Volume [m3]
Specific enthalpy
Enthalpy per unit mass is called specific enthalpy.
(Represents how many kJ of enthalpy per 1 kg of dry air)
The unit is [kJ/kg(DA)].
Air
Moist air that contains water vapor.
It is a familiar gas that is essential to our daily lives.
Composition of dry air
| Name of gas | Symbol | Volume percentage |
|---|---|---|
| Nitrogen | N2 | 78.09 |
| Oxgen | O2 | 20.95 |
| Argon | Ar | 0.93 |
| Carbon dioxide | CO2 | 0.03 |
*Air is a mixture of various substances and has a certain composition.
Moist air
What is usually called air is "moist air" which is a mixture of dry air and water vapor.
The state of "moist air" can be expressed by "dry bulb temperature", "wet bulb temperature", "dew point temperature", "relative humidity", "absolute humidity", etc.
An example of moist air classification
| Classification | Content |
|---|---|
| Saturated air | Something that reaches the limit of what air can contain as water vapour. |
| Unsaturated air | Something that is not reaching saturated air |
| Air with frost | Water vapor in the air exists as small water droplets |
| Air with snow | Water vapor in the air exists as ice crystals |
The specific enthalpy of "moist air" is the total of the enthalpy of 1 kg of "dry air" and the specific enthalpy of xkg of water vapor.
Previous item: 3-8. Relationship between static electricity and humidity
Next item: 3-10. Psychrometric Chart
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