Thermodynamics & Heat Transfer
Heat transfer methods, enthalpy, latent and sensible heat, BTU calculations, psychrometrics, and the laws of thermodynamics.
- Identify the three methods of heat transfer and apply them to HVAC systems
- Distinguish between latent heat and sensible heat
- Define enthalpy and explain its role in refrigeration calculations
- Explain how pressure changes affect the boiling point of liquids
- Use a sling psychrometer to determine relative humidity
Lesson 1
Conduction, Convection & Radiation
The Three Methods of Heat Transfer
Heat always travels from a warmer object to a cooler object. This is the second law of thermodynamics, and it governs everything in HVAC. The exam tests three methods of heat transfer:
Conduction
Heat transfer through direct contact between molecules. Example: heat moving through a copper pipe wall from hot refrigerant to cooler air.
Rate depends on material conductivity, thickness, and temperature difference.
Convection
Heat transfer through fluid movement (air or liquid). Example: warm air rising from a furnace register and cool air sinking to the return.
Can be natural (gravity) or forced (fan/pump).
Radiation
Heat transfer through electromagnetic waves. Example: infrared heat from the sun warming a rooftop condensing unit.
Does not require a medium - works through vacuum.
The exam may ask "Heat is NOT transmitted in which manner?" The answer would be any method not listed above. Heat cannot be transmitted by sound or by magnetic fields - only by conduction, convection, and radiation.
Heat always travels from hot to cold - never the other way. A refrigeration system does not "add cold" to a space; it removes heat from the space and rejects it outdoors.
Heat transfers by conduction (contact), convection (fluid movement), and radiation (electromagnetic waves). Heat always travels from hot to cold - this principle drives every HVAC system.