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# Basics of Heating Ventilation and Air Conditioning

Physics used in HVAC System :

Heat :

Heat is a form of energy which transfers due to change in temperature or temperature difference. In S.I or Metric system unit is KJ (Kilo joules), in Imperial or English System the unit is BTU (British Thermal Units).

British Thermal Units :

It is defined as the amount of heat to be added to raise the temperature of 1 pound of water by 1 °F (Fahrenheit).

1 Pound (lbs) = 0.450 kgs

1 kgs = 2.2 lbs

Unit of Refrigeration = Ton or Tons of Refrigeration

TR (Tons of Refrigeration) :

One Ton of Refrigeration is characterized as how much cooling impact created by uniform dissolving of 1 ton or 1000kg of ice from 0 °C in 24 hours.

(or)

Energy required to melt 1000kg of ice in 24 hours thereby giving standard cooling effect / chilling effect. Cooling effect produced by it is known as 1 ton of refrigeration or 1 TR.

Mathematically Latent heat of ice is 335 kJ/kg.

1 Ton of Refrigeration = 335 x 1000kg in 24 hours.

1 TR = (335 x 1000) / (24 x 60)

=  232.6 kJ / kg.

But in Actual Practice,

1 TR = 210 kJ / min

1 TR = 3.5 kw.

Units :

Concepts such as Length, Area, Volume, Temperature concepts are called as Physical quantities. Physical characteristics are measured by standard quantities and are known as Units. For example, "metre" is used to measure length.

US and S.I Units :

There are two types of units or system of units which are used in HVAC industry. One is called "Inch-pound" (I.p) or US Imperial or English system or FPS (Foot-Pound-system). The second system that is used in the industry is called S.I system (International system or System de Internationale) or Metric system.

Examples for  US system or FPS or Imperial system are :

* Distance - Feet or inches

* Area - Square feet or square inches

* Volume of air - CFM (Cubic Feet per Minute)

* Temperature - ° F (Fahrenheit)

Examples for  S.I system or Metric system are :

* Distance - meters or mm, km, cm etc.

* Area - Square meters.

* Volume of air - LS (Liters per second)

* Temperature - ° C (Celsius)

Conversions of Equivalent :

Units have fixed numerically in relationship with each other called equivalence or conversion factor.

* Length or Distance :

1 m = 3.28 ft

1 m = 100 cm = 1000 mm

1 ft = 0.304 m

1' / 1 ft = 12" or 12 inches

1" / 1 inch = 2.54 cm = 25.4 mm

1' / 1 ft = 300 mm = (Round off of 304.8 mm)

1 m = 39 °

1 yard = 3 feet

* Area :

1 sq m = 10.76 sq ft

1 sq ft = 0.093 sq m

1 sq ft = 144 sq inch

1 sq yard = 9 sq ft

* Tonnage / Tons of Refrigeration :

1 Ton (TR) = 210 kJ / min

1 Ton = 3.5 kw

1 Ton = 12000 BTU / hr

1 Ton = 400 CFM approx

1 Ton = 2.4 GPM (Gallon Per minute)

1 Ton = 3000 kCal / hr

1 US Gallon = 3.786 Liters

1 CFM = 1.8 CMH

1 CFM = 2118 cubic meter per second (CMS)

1 CFM = 2.119 Litre / second

Thumb Rule For Tonnage :

* 1 Ton will cover 100 sq ft  (9 sq m) - For exposed zone for 2 or more.

* 1 Ton will cover 130 sq ft (12 sq m) - For partition area / zone

Temperature :

It is the degree of hotness or coldness measured by ordinary dry bulb thermometer (DBT).

(or) It is the measure of Thermal activity / intensity in a body. units are ° C or ° F.

Temperature scale / conversion factor :

* For Degree centigrade or degree celsius:

° C = (° F - 32 ) / 1.8

* For Degree Fahrenheit:

° F = 1.8 °C + 32

So, here Fahrenheit scale lies between 32 °F to 212 °F i.e, 180 divisions.

Example : As according to ASHRAE human comfort zone criteria is 24 °C / 76 °F with respect to temperature.

° F = 1.8 °C + 32

(C = 24 °C / 76 °F)

= 1.8 (24) + 32

= 76 °F

(or)

° C = (° F - 32 ) / 1.8

= (76 - 32) / 1.8

= 24 °C

Hotness : It is the addition of heat.

Coolness : It is the removal of heat from a system.

There are mainly two types of heat. They are Sensible heat and Latent heat.

Sensible Heat :

The heat which we can sense or we can measure by using an ordinary or dry bulb thermometer is known as Sensible heat. (or)

Heat absorbed or transmitted by a substance during change of temperature is known as sensible heat. For example, Human body temperature can be measured using thermometer.

Latent Heat :

Heat required to convert a solid into liquid or vapor without change in temperature is called Latent heat. (or)

Heat occurred or released during the change of phase without change in temperature is known as Latent heat. For example, When water becomes vapor or ice becomes liquid, when water kept in a mud pot is always cold, it is because of the latent heat concept.

Well here we complete the second part of the Full HVAC course. Hope you guys have learnt something about HVAC from this article.. Stay tuned for the next part of this course. Till then, Keep Learning. Keep Growing.

Access the Part 1 if you have missed it by clicking Below..