Heating, Ventilating and Air Conditioning Systems
Core concepts
Understand the refrigeration cycle: compressor, condenser, expansion device, evaporator. Know coefficient of performance (COP), energy efficiency ratio (EER), and seasonal energy efficiency ratio (SEER), plus the relationship EER ≈ COP × 3.412. Candidates should understand chillers (air- and water-cooled, with kW/ton as a common metric where lower is better), air handling units, variable air volume (VAV) systems, economizers, and energy recovery ventilation.
Controls and operations
Know temperature reset, static pressure reset, demand-controlled ventilation (DCV) using CO₂ sensors, and optimal start/stop. Understand that simultaneous heating and cooling is a major waste and that reheat should be minimized. Familiarity with part-load performance and variable speed drives on fans and pumps is essential.
Traps to watch
Questions often confuse EER (a single rating point) with SEER (seasonal). Another trap is assuming a higher-efficiency chiller always saves energy - part-load performance and staging matter. Watch for confusion between sensible and latent cooling, and between dry-bulb and wet-bulb temperature. Economizer questions often hinge on the changeover setpoint and on whether the damper actually works.
Worked example
A chiller provides 400 tons of cooling while drawing 280 kW. Efficiency = 280/400 = 0.70 kW/ton. A typical high-efficiency water-cooled centrifugal chiller runs near 0.55 kW/ton at design, so this unit is a candidate for review. Annual energy = 280 kW × 2,000 equivalent full-load hours ≈ 560,000 kWh.
Practical guidance
Commission and retrocommission; verify economizer operation, sensor calibration, and scheduling before considering equipment replacement.