Basics of HVAC This article is just the second part of the complete Heating Ventilation and Air Conditioning. We will Study Heating Ventilation and Air Conditioning from Basic to Advance level. So, Let's Start.. 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). BTU (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 = TR (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 ...