Air conditioning
Adjusting the quality, change amount, speed, temperature and humidity of the air in a volume to the desired values within certain algorithms and limits is called air conditioning. Computer programs prepared according to international air conditioning standards, compare the values obtained from the sensors with the set values and actuate the actuators that control these parameters according to the error values obtained. Thanks to this continuous process, the desired air-conditioning values are continuously provided in the relevant space. A typical air conditioning system, provided on board commercial ships, consists of several main components which Marine Engineer on watch must know how to use, adjust the operating parameters and monitor the system performance.
Different air-conditioning processes are performed for people, foods, beverages, animals, plants and all kinds of materials keeping in closed spaces. Air conditioning processes and setting values of spaces, such as ship holds, living quarters, engine room, battery rooms, kitchen, closed car parking lots, hospitals, and theaters, are different.. For this reason, Marine Engineers have to know the air conditioning principles, system components, methods and operations applied especially in commercial ships. The best air-conditioning is possible by determining the most appropriate air conditioning conditions.
Psychometric is frequently used by Marine Engineers to determine the relationship between the temperature, pressure and humidity to be set and to adjust the setting values accordingly. Marine Engineers are responsible for knowing and applying the basis and usage of psychometric, which is a branch of science that studies the effects of temperature and humidity on various materials and people, helps to understand how different properties of air affect each other.
Properties of air, such as dry bulb, wet bulb, dew point temperatures and humidity are some of the parameters related to air conditioning. These values are adjusted to appropriate values manually or automatically via control panels, special machines and systems.
Air consists of large proportion of oxygen (O2) and nitrogen (N2) molecules, as well as water (H2O), in varying proportions as liquid and gas. These values are directly related to the temperature and pressure of the air. In order for Marine Engineers to operate the air conditioning system consciously, they must know these dominant parameters and use them in accordance with psychometric conditions.
Atmospheric Air Pressure (Pa) is measured with a barometer device. Partial Pressure (Pd) is exerted by the dry air in the air mixture. Saturated air pressure (Pw) is the partial pressure where the water vapor is maximum. So, Dalton’s law air pressure is P=Pd + Pw. Absolute humidity of the air is the total mass of water vapor present in the unit volume of air at any given condition of temperature. Relative Humidity of air (Rh) is the amount of water vapor in unit volume of unsaturated air divided by amount of water vapor in unit volume of saturated air. Relative humidity is expressed in percentage. It indicates the actual humidity present in the air at the prevalent temperature conditions and widely used by the air conditioning Engineers. Rh = (Pw /Pws) x 100.
In the literature, the air conditioning process consists of two stages in order. In the first stage, substances, harmful to health such as dust, feathers and hair suspended in the circulated air, are kept by various equipment called filters. Revitalizing the filtered air is the second step, consisting of heating, cooling, humidification and dehumidification in sequence. Areas that do not need air conditioning such as parking lots, engine rooms, battery rooms are ventilated with 100% fresh air with ventilation and exhaust fans operating according to the air quality values of the sensors. The illustrations below show a typical air conditioning system consisting of several integrated components and a component called Air Conditioning Processing Unit (AHU), respectively.