CEM Certified Energy Manager Motors and HVAC 4

Question 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?

Accepted Answer

$104

Answer

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.

Question 2

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

Accepted Answer

Four-pipe fan coil unit system

Answer

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

Question 3

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

Accepted Answer

Electrical power input per ton of cooling output

Answer

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

Question 4

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

Accepted Answer

Maintaining original winding geometry and conductor cross-section

Answer

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

Question 5

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

Accepted Answer

Reducing duct static pressure setpoint as terminal box dampers open less

Answer

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

CEM - Certified Energy Manager Practice Test

CEM - Certified Energy Manager Practice Test

CEM Certified Energy Manager Motors and HVAC 4