With reference to Marine Air Conditioning Systems, explain EACH of the following expressions: (a) wet bulb temperature(2) (b) dry bulb temperature;(2) (c) comfort zone;(2) (d) psychrometric chart;(2) (e) relative humidity.(2)
(a) Wet Bulb Temperature (2 marks)
The temperature indicated by a thermometer whose bulb is covered with a wet wick and exposed to moving air.
It represents the cooling effect due to evaporation of water and is always lower than or equal to the dry bulb temperature.
(b) Dry Bulb Temperature (2 marks)
The temperature of air measured by an ordinary thermometer freely exposed to the air but shielded from radiation.
It is the actual air temperature without considering humidity.
(c) Comfort Zone (2 marks)
The range of temperature, humidity, and air movement in which most people feel comfortable.
Typically around 20–25°C with 40–60% relative humidity in marine accommodation spaces.
(d) Psychrometric Chart (2 marks)
A graphical representation of the thermodynamic properties of moist air (temperature, humidity, enthalpy, dew point, etc.).
Used in air conditioning to calculate and visualise changes in air condition during cooling, heating, humidification, or dehumidification.
(e) Relative Humidity (2 marks)
The ratio of the actual water vapour present in the air to the maximum amount of vapour the air could hold at the same temperature, expressed as a percentage.
Indicates how close the air is to saturation (100% = fully saturated).
