Fundamentals Of HVAC


 Heat:- Heat is a form of energy that is a transfer from higher body to lower body temperature. Unit:- BTU/hr (British thermal unit), J or KJ. 

 British Thermal Unit:- It is defined as the amount of heat to be added to raise the temperature of 1 a pound of water by 1°F (Fahrenheit) 

Types of Heat 

1. Sensible Heat 

2. Latent Heat 

1) Sensible Heat:- The heat which can be sensitive, can be measured, it increases by raising body temperature. 

 OR 

Heat absorb or transmitted by a substance during a change of temperature is known as sensible heat. Eg.- Human body temperature can be measured using a thermometer. 

2) Latent Heat:- It can not be measured, it is rejected or absorbs during the phase change. 

 OR

 The heat required to convert a solid into liquid or vapor without changing temperature called latently heat. Eg. When water becomes vapor or when ice becomes liquid.

Modes of Heat Transfer 

1) Conduction 

2) Convection 

3) Radiation 

1) Conduction:- It is a mode of heat transfer through solid. 

2) Convection:- It is a mode of heat transfer through the liquid. 

3) Radiation:- It is a mode of heat transfer through a gaseous medium

 1 TON of Refrigeration: It is the amount of heat required to melt one ton of ice in 24hrs.

 Mathematically latent heat of ice is 335 KJ/KG 

1 Ton = 335 X 1000 Kg in 24 hr of refrigeration. 

1 Ton = 335 X1000 / 24 X 60 = 232.6 KJ/KG But in actual practice 

1TR= 210 KJ/Min = 3.51 KW

1TON= 12000 BTU/HR 

         = 200 BTU/MIN 

         = 3.51 KW 

         = 0.8 HP 

         = 3025.9 Kcal/J 

         = 400 Cfm (Cubic feet per Min) 

 Discharge(Q) = Area X Volume 

                          = A X V 

Unit:- m3/s, l/s, CFM, CMH 

1m3/s = 2119 CFM 

1L/s = 2.119 CFM 

1CMH= 1.7 CFM 

 Temperature:- It is degree of hotness and coldness. 

Hotness:- It is the addition of Heat. 

Coldness:- Removal of heat from a system called coldness. 

Unit:- °C, F, K 

F= 9/5 X C + 32 

C= 5/9 X [F- 32 ] (Note:- 1°C = 273 K) 

 Enthalpy:- It is sum of internal energy and product of pressure and volume this sum(U+PV) is known as Enthalpy (H).

 OR 

 The heat content of the body is called enthalpy. 

Units:- KJ/KG or BTU/hr 

 Types of temperature 

1) Dry Bulb Temperature – The temperature which is measured by an ordinary sling thermometer. 

2) Wet Bulb Temperature -The temperature which is measured by an ordinary thermometer whose bulb is cover with a wet cloth. 

3) Dew Point Temperature:- The temperature at which condensation starts. 

 Condensation:- Conversion of vapor to liquid is known as condensation.

 Evaporation:- Conversion of liquid to vapor is known as evaporation. 

 Humidity:- Amount of moisture content in the air. 

 Air:- It is a mixture of gases. 

1) Saturated air:- It contains 100% moisture in the air. 

2)Unsaturated air:- It contains 0% moisture in the air. 

 Types of Humidity 

1) Relative humidity[RH]:- It is the ratio of the amount of moisture present in a sample of air to the amount of moisture present in saturated air. ( Unit:- %)  

2) Specific Humidity/ Humidity ratio (W):- It is the number of grains of moisture present in a sample of air is called specific humidity. ( Unit:- Grains /lb)