CEM Certified Energy Manager Motors and HVAC 3

Question 1

Which motor protection device guards against single-phasing in a three-phase motor?

Accepted Answer

Thermal overload relay with phase-loss sensitivity

Answer

A thermal overload relay with phase-loss sensitivity detects the current imbalance caused by single-phasing and trips before winding damage occurs.

Question 2

In a chilled water system, what is the benefit of increasing chilled water delta-T from 10°F to 14°F at the same cooling load?

Accepted Answer

Reduced chilled water flow rate and pump energy

Answer

A higher chilled water delta-T allows the same cooling load to be met with less flow, reducing pump energy consumption.

Question 3

What is the NEMA efficiency designation for a motor that meets or exceeds NEMA Premium efficiency levels?

Accepted Answer

NEMA MG1 Table 12-12

Answer

NEMA Premium efficiency motors meet or exceed the efficiency levels defined in NEMA MG1 Table 12-12.

Question 4

An economizer on an air handling unit uses outdoor air for free cooling when:

Accepted Answer

Outdoor dry-bulb or enthalpy is below the return air condition

Answer

An economizer brings in outdoor air when it is cooler (or has lower enthalpy) than return air, allowing mechanical cooling to be reduced or eliminated.

Question 5

Which parameter is used to evaluate the part-load efficiency of a chiller under real-world mixed operating conditions?

Accepted Answer

Integrated Part Load Value (IPLV)

Answer

IPLV (Integrated Part Load Value) is a weighted average efficiency metric that accounts for chiller performance at 25%, 50%, 75%, and 100% load.

CEM - Certified Energy Manager Practice Test

CEM - Certified Energy Manager Practice Test

CEM Certified Energy Manager Motors and HVAC 3