Refrigeration, HVAC, and Auxiliary Systems
Core concepts
Know the vapor-compression refrigeration cycle: compression, condensation, expansion, evaporation - and where each occurs on a pressure-enthalpy diagram. Understand refrigerants, their properties, and the phase-out of ozone-depleting substances. Familiarize yourself with the components: compressor, condenser, expansion valve, evaporator, and receiver. For HVAC: sensible vs. latent heat, dry-bulb and wet-bulb temperatures, relative humidity, and the psychrometric chart. Know auxiliary systems such as compressed air, cooling water, and ventilation.
Traps to watch
- Confusing the condenser (rejects heat) with the evaporator (absorbs heat).
- Mixing dry-bulb and wet-bulb - RH depends on both.
- Forgetting superheat and subcooling as diagnostic indicators.
- Assuming all refrigerants behave identically - glide and pressure differ.
- Overlooking ventilation requirements for refrigerant leak safety.
Worked example / rule of thumb
A chiller with 5 kW compressor power and 20 kW evaporator load has COP = 20/5 = 4. Rule of thumb: COP for a well-run chilled-water plant is typically 3–5; lower values suggest inefficiency or fouling.