Heating, Ventilation, and Air Conditioning Systems and Equipment
Core concepts
A candidate must be able to describe how each major system moves heat and air, and when each is appropriate. Know the difference between a gas-fired forced-air furnace, an electric resistance air handler, a hydronic boiler with terminal units, a heat pump (air-source and ground-source), and packaged rooftop equipment. Understand the refrigeration cycle as it applies to cooling and the reversing valve role in heat pumps. Be able to discuss ventilation: exhaust-only, supply-only, balanced (HRV/ERV), and the role of outdoor air in indoor air quality and building pressure.
Traps in questions
- Confusing efficiency ratings: AFUE is for combustion heating, SEER/SEER2 for cooling, HSPF for heat pump heating, and COP is a dimensionless instantaneous ratio.
- Heat pump balance point versus auxiliary/emergency heat: questions often ask which comes on first and why.
- Latent versus sensible capacity - a unit can be "the right tonnage" but fail to control humidity.
- Short cycling causes: oversized equipment, low airflow, bad thermostat placement, or refrigerant charge issues.
Worked example / rule of thumb
A common rule of thumb is roughly 400–600 CFM per ton of cooling (about 350–450 CFM/ton in humid climates for better latent removal). For a 3-ton system in a humid NC climate, target about 1,050–1,200 CFM to balance sensible and latent capacity. If measured airflow is 1,400 CFM on that system, expect a higher sensible heat ratio and poorer humidity control.
Study guidance
Trace the path of refrigerant and air through each system type, and practice explaining why a component exists rather than just naming it.