Post-002: Basic Concept of HVAC

Below are some basics, which can help you to understand properties of moist air and psychometric chart.

  • Dry bulb temperature: It is nothing but normal temperature we measure using ordinary thermometers.
  • Wet bulb temperature: Temperature of moist air.
  • Dew point temperature: A temperature at which air becomes saturated with moisture.
  • Relative Humidity: A saturated air has 100% relative humidity. That means it is the ratio of water vapor in air to the water vapor in saturated air.
  • Humidity ratio: Suppose you have a sample of air like air in one close room. This room will have a mixture of dry air and moisture. The ratio of water vapor in room to the ratio of dry air in room is called humidity ratio.

There are many other terms but you will confuse if you learn everything at once. This is the basic information.

Let us learn some process now:

Sensible heating or Cooling: a psychometric process that involves the increase or decrease in the temperature of air without changing its humidity ratio. If you open a psychometric chart (P. Chart), you will find that humidity ratio lines are represented by horizontal lines parallel to x-axis. So the sensible heating process can be shown on P. Chart using a straight line moving in right side parallel to x-axis, as dry bulb temperature will increase. For cooling, same line will move to left from starting point.

sensible heating

Heating With Humidification: A psychometric process that involves the simultaneous increase in both humidity ratio and dry bulb temperature of the air.


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