Energy Fundamentals
What the exam expects
Candidates must move confidently among power, energy, heat rate, load factor, and efficiency. Know that power is instantaneous (kW) and energy is power over time (kWh); 1 kW = 3,412 Btu/h; 1 hp = 0.746 kW; 1 therm = 100,000 Btu; 1 MMBtu = 10 therms. Understand sensible versus latent heat, psychrometrics, combustion, HHV versus LHV efficiency, coefficient of performance, and the fan and pump affinity laws. Load factor is average load divided by peak load; diversity recognizes that not all loads peak together. Degree days normalize weather-driven consumption.
Traps
Mixing kW and kWh is the classic error, followed by using boiler combustion efficiency as seasonal efficiency. Chiller COP and kW/ton are reciprocals with a unit conversion. Fan laws are cubic for power, not linear. Do not apply nameplate kW without load and efficiency adjustments.
Worked example
A 100 hp motor runs at 75% load, 90% efficiency, for 8,000 hours. Input kW = 100 x 0.746 x 0.75 / 0.90 = 62.2 kW. Annual energy = 62.2 x 8,000 = 497,600 kWh. At $0.08/kWh, energy cost is about $39,800 per year.