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Heating Ventilation and Air Conditioning Full Course - HVAC Course (Part 4)


HVAC - Properties of Air (Psychrometry)

This is the 4th part of the complete HVAC course. Lets start..

  Types of RCP's (Reflected Ceiling Plan / False Ceiling Plan) :

            There are three main types of false ceiling, Flat or plain false ceiling, Step false ceiling and Tiles false ceiling.

* Flat or Plain False ceiling :

            It can be used in cinema halls, waiting halls, theaters, seminar halls, function halls, supermarkets etc.

* Step False ceiling :

        This type of false ceiling is used in Seminar halls, conference rooms etc.

* Tiles False ceiling :

        Tiles false ceilings are used in offices, etc.

Psychrometry :

        It is the science dealing with physical loss of air and water mixture. (or) 

Atmospheric air that surround us is a mixture of dry air and water vapor called moist air. Because this gas mixture is conditioned in AC system, it is necessary to understand how it behaves ? It is the name given to the study of air water vapor mixture. We will use the word air to refer the air water vapor mixture i.e; in the atmosphere.

        Some of the properties of air are, Dry Bulb Temperature (DBT), Wet Bulb Temperature (WBT), Dew Point Temperature (DPT), Humidity Ratio or specific humidity (w), Relative Humidity (RH), Saturated Air, Unsaturated Air, Enthalpy of Air, etc.

* Dry Bulb Temperature (DBT) :

            It is the temperature of air which can be sensed or measured by an ordinary normal thermometer. This temperature is known as Dry Bulb Temperature (DBT). It will measure the sensible heat of air, normal temperature of a particular location. i.e; Outside environmental air temperature or ambient air temperature or outside air atmospheric temperature or room temperature is nothing but Dry Bulb Temperature (DBT), which is measured by using a normal thermometer.

* Wet Bulb Temperature (WBT) :

            Temperature sensed by thermometer who's bulb is wrapped with water soaked wick/cloth in rapid moving air is known as Wet Bulb Temperature (WBT) and thermometer (ordinary) which measures the temperature of wet bulb is known as Wet Bulb Thermometer. (or)

Wet bulb temperature which is measured by ordinary thermometer when its bulb is covered by wet cloth and exposed to atmospheric air is known as Wet Bulb Temperature (WBT). Basically, it is an ordinary thermometer only, to which wet cloth or wick soaked and rinsed in water wrapped around the bulb of the thermometer, where it is rotated in atmospheric air gives the Wet Bulb Temperature (WBT). Basically, through Wet Bulb Temperature (WBT) we get the presence of humidity content present in the atmospheric air. It is less than DBT.

* Dew Point Temperature (DPT) :

                                Temperature at which the condensation process begins, is known as Dew Point Temperature (DPT). (or)

It is the temperature at which moisture leaves air and condenses object in the form of dew point drops on grass / plants / leaves / wind shield of vehicles is known as Dew Point Temperature (DPT). On the contrary, Evaporation is defined as the temperature at which liquid starts to evaporate.

* Humidity Ratio or Specific humidity (w) :

            It is also called as specific moisture or humidity content, is the mass of the water vapor present in 1 kg of dry air and is generally expressed in terms of grains/kg of dry air in metric system or S.I system and grains/lb in terms of dry air in English system.

Psychrometric Chart :

The different lines shown in the image above represents the different characteristics of air, as shown in the image above. By knowing any two characteristics one can easily find the third characteristic of air, with the help of a psychrometric chart.

* Saturated Air :

The air that contains greatest measure of dampness that it can hold at specific temperature is called as saturated air.

        Air quality can be measured in two ways; either by measuring the oxygen content or by the measurement of carbon dioxide content. Oxygen is measured using the standard test method provided at the National Institute for Occupational Safety and Health (NIOSH). Carbon dioxide is measured using the same methods but subtracting out the amount of oxygen present. A higher level of oxygen is good for us and our health while a high level of carbon dioxide can cause respiratory issues. In regards to air quality and HVAC systems, what type of condition we have can affect how long the system lasts. If the air that is being circulated through the home has a lower than normal oxygen concentration, the components within the HVAC system will wear down faster and need to be replaced more often.

                 Humidity levels are directly related to air quality. When humidity levels are too low, air quality suffers due to condensation forming on indoor surfaces like walls and windows. This is especially common in areas where temperature extremes are experienced throughout the year. At this point, moisture will start to collect and drip onto objects causing mold to form and mildew to take hold. 

* Unsaturated Air :

                        Unsaturated air is something contrary to saturated air, it contains less measure of water vapors, Which means it can hold more water vapors.

        Unsaturated Air (U -Air) is the term used to describe air that has not been saturated with water vapor. An unsaturated environment contains more oxygen than a saturated one. 

        Well guys, here completes the 4th part of the full HVAC course.. Hope you got to learn something from this article.. Stay tuned for more parts of this course  to come.. Keep learning .. keep Growing.. 

Access Previous parts of this course, if you have missed it, by clicking Below..

Part 1 -- Click Here!!

Part 2 -- Click Here!!

Part 3 -- Click Here!!

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