HVACR Core Knowledge and Skills Study Guide
This domain, HVACR Core Knowledge and Skills, tests the foundation the other four domains assume: safety, thermodynamics, heat-transfer math, pressure–temperature relationships, tools, and refrigerant handling. Expect questions that combine a formula with a field decision-converting gauge to absolute pressure, separating sensible from latent heat, or selecting the right instrument for a measurement.
Core rules and concepts
- Gauge pressure (psig) plus atmospheric pressure (about 14.7 psi at sea level) gives absolute pressure (psia). PT charts and gas-law calculations use absolute pressure.
- Sensible heat changes dry-bulb temperature; latent heat changes moisture state without a dry-bulb change. Total heat is the sum.
- For standard air, sensible Btu/h ≈ 1.08 × CFM × ΔT°F; latent Btu/h ≈ 0.68 × CFM × Δgrains; total Btu/h ≈ 4.5 × CFM × Δh in Btu/lb.
- Brazing requires a nitrogen purge to prevent internal oxidation. Evacuation removes moisture and non-condensables, and a micron gauge-not manifold gauges-verifies it.
- Use appropriate PPE and recovery equipment; never vent refrigerant.
Worked example
A 1,200-CFM air stream is heated from 65°F to 85°F. Sensible heat = 1.08 × 1,200 × 20 = 25,920 Btu/h. If the same air also picks up 10 grains of moisture per pound, latent load = 0.68 × 1,200 × 10 = 8,160 Btu/h. The total coil load is not simply the sensible number; add latent and any fan heat.
Traps
Using psig in a PT chart; applying the 1.08 constant to nonstandard air or a wet coil without correction; confusing superheat with temperature rise; skipping nitrogen purge; trusting manifold-gauge vacuum readings.