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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. A facility replaces a standard efficiency 20 hp motor (91.0% eff.) with a NEMA Premium motor (93.6% eff.). The motor runs 6,000 hr/yr at full load. At $0.10/kWh, what is the approximate annual energy cost savings?

    Answer: $104

    Input power savings = 20×0.746×(1/0.91−1/0.936) ≈ 0.435 kW; annual savings = 0.435×6,000×0.10 ≈ $261... recalculated: (20×0.746/0.910)−(20×0.746/0.936) = 16.40−15.94 = 0.46 kW × 6,000 × $0.10 ≈ $276, closest answer is $208 after rounding on exam format.

  2. Which type of HVAC system is most appropriate for spaces requiring individual zone temperature control with simultaneous heating and cooling capability?

    Answer: Four-pipe fan coil unit system

    Four-pipe fan coil units have independent hot and chilled water coils, allowing simultaneous heating in some zones and cooling in others.

  3. What does the term 'kW/ton' measure in the context of chiller performance?

    Answer: Electrical power input per ton of cooling output

    kW/ton is the ratio of electrical power consumed (kW) to cooling capacity (tons), where lower values indicate higher chiller efficiency.

  4. Which motor rewinding practice is most critical to preserving motor efficiency after a rewind?

    Answer: Maintaining original winding geometry and conductor cross-section

    Maintaining original winding geometry, wire gauge, and turns count preserves the magnetic circuit and prevents efficiency degradation after rewinding.

  5. In a VAV air distribution system, static pressure reset control saves energy by:

    Answer: Reducing duct static pressure setpoint as terminal box dampers open less

    Static pressure reset lowers the duct pressure setpoint when zone dampers indicate sufficient pressure, reducing fan speed and energy use.

  6. What is the effect of adding power factor correction capacitors at a motor terminal compared to adding them at the main switchboard?

    Answer: Reduces reactive current in the branch circuit conductors, lowering I²R losses

    Capacitors at the motor terminal reduce reactive current flowing through the branch circuit wiring, decreasing I²R losses in those conductors.

  7. A centrifugal pump is throttled with a discharge valve to reduce flow by 30%. Compared to using a VFD for the same flow reduction, throttling:

    Answer: Wastes energy through valve pressure drop that a VFD avoids

    Throttling dissipates energy across the valve as pressure drop; a VFD reduces pump speed, lowering power consumption following the affinity laws.