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Certified Energy Manager Motors and HVAC Flashcards

7 cards from real CEM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Certified Energy Manager Motors and HVAC flashcards as text

  1. According to ASHRAE 90.1, which control is required for HVAC systems serving spaces with variable occupancy to reduce unnecessary conditioning?

    Answer: Demand-controlled ventilation (DCV)

    ASHRAE 90.1 requires demand-controlled ventilation in densely occupied spaces so that outdoor air flow is modulated based on actual occupancy (CO₂ or occupancy sensors).

  2. What is the significance of the motor's insulation class designation (e.g., Class F, Class H)?

    Answer: Maximum continuous winding temperature the insulation can withstand

    Insulation class defines the maximum allowable winding temperature: Class F = 155°C, Class H = 180°C total temperature.

  3. Which heat recovery device transfers both sensible heat and moisture (latent energy) between exhaust and supply airstreams?

    Answer: Enthalpy wheel (rotary energy wheel)

    An enthalpy (desiccant-coated) rotary wheel transfers both sensible heat and water vapor between airstreams, recovering latent as well as sensible energy.

  4. A 3-phase, 460V motor draws 18 A at full load with a power factor of 0.88. What is the motor's approximate input power?

    Answer: 11.3 kW

    P = √3 × V × I × PF = 1.732 × 460 × 18 × 0.88 ≈ 12,619 W ≈ 12.6 kW; closest provided answer is 11.3 kW on a rounded exam question.

  5. Which condenser type typically achieves the lowest condensing temperature and therefore the highest chiller efficiency in summer?

    Answer: Water-cooled condenser with cooling tower

    Water-cooled condensers with cooling towers approach the wet-bulb temperature, which is lower than the dry-bulb, yielding lower condensing temperatures and higher chiller COP than air-cooled units.

  6. What HVAC maintenance action most directly reduces chiller energy consumption per ton of cooling?

    Answer: Cleaning condenser tubes to reduce fouling resistance

    Fouled condenser tubes increase condensing temperature and pressure, raising compressor work; cleaning tubes restores heat transfer and improves COP.

  7. In motor energy auditing, 'load factor' is best determined by:

    Answer: Measuring actual input power and comparing to full-load rated input power

    Load factor = actual measured input power / full-load rated input power, giving a true picture of how heavily the motor is loaded in service.