Heating, Ventilation & Air Conditioning Systems
What this domain tests
HVAC questions cover efficiency metrics, part-load behavior, ventilation, and the interaction between chillers, boilers, fans, and pumps.
Core rules
- COP = cooling output ÷ power input (both in kW); EER = Btu/h ÷ watts; kW/ton = 12 ÷ EER.
- SEER and HSPF are seasonal ratings; do not substitute them for EER in a peak calculation.
- Economizers save when outdoor air enthalpy is below return air; they need commissioning and dampers that actually close.
- Fan and pump power follow the affinity laws: flow ∝ speed, power ∝ speed³ (with no static head).
- Boiler combustion efficiency is measured with a flue-gas analyzer; 80–85% is typical for non-condensing units.
Worked example
A 300-ton chiller runs at 0.60 kW/ton for 2,000 equivalent full-load hours. Energy = 300 × 0.60 × 2,000 = 360,000 kWh. A retrofit to 0.50 kW/ton gives 300,000 kWh, saving 60,000 kWh/yr. At $0.10/kWh, savings are $6,000/yr - before any chiller plant pump or cooling tower fan savings.
Traps
Mixing EER and SEER; ignoring fan and pump energy; assuming ideal economizer operation; and using full-load efficiency to predict part-load performance.