CEM Sample Questions Answers

Thermal scans of electrical equipment are useful for:

Which type of lighting control technique operates in "manual on" and "auto-off mode, and can be used in situations where there is brief occupancy that do not need lights on?

Insulation has a thermal conductivity of 0.04 Watt/(m-°C). What is the R-value for this insulation when it is 5-cm thick?

Which of the following steam turbines will likely not provide steam output at a useable temperature for industrial processes?

A motor operates with a normal and constant load. The electric current is measured to be 25% of the motor's nameplate rating. What does this mean?

Using an interest rate of 15%, an energy project has a net-present value (NPV) of $3,500. Which statement is true about the project's internal rate of return (IRR)?

The International Performance Measurement and Verification Protocol (IPMVP) has how many categories (method options) to determine the performance of an energy- or water-consuming system?

What term describes the difference between the control signal value and the set point?

Which of the following is NOT a typical benefit of performance contracting from the building owner's perspective?

Which problems can be caused by poor power quality?

What is the definition of lamp life for a fluorescent lamp?

If outside air has a temperature of 30°C dry bulb and 20°C wet bulb, what is the dew point temperature?

A 75-kW induction motor operates at 80% partial load and 88% efficiency. A new high-efficiency 75-kW motor can be installed that will operate at 95% efficiency (also at 80% partial load). What is the reduction in electric power demand?

What is the Energy Use index (EUl) for a 4,000 m2 building that uses the following amountsof energy each year?

Which of the following controls can optimize the operation of lighting systems?

How does an enthalpy-based economizer control operate?

Which type of single-phase alternating-current motor has the highest efficiency?

If the initial design process includes group relamping, how can this reduce the number of lamps required to illuminate a space?

An air-conditioning unit delivers 10,000 kJ/h (thermal cooling). The equipment uses single-phase electrical power at 220-volt and 5.25 amps with a power factor of 100%. Calculate the coefficient of performance (COP).

A cooling tower delivers 29°C water to a central chilled water plant. The cooling tower is capable of delivering water to the chilled-water plant with a 6°C approach temperature to the ambient wet bulb temperature. Using this information, what type of control strategy would you recommend be added to the cooling tower operation to save additional energy?

A piece of equipment costs $250,000 to buy and install. The annual operating cost for the equipment is $50,000 per year. The equipment will last 15 years. After 15 years, the equipment will have no net salvage value. The annual interest rate is 10%. What is the present value of the life-cycle cost to own and operate the equipment? Use end-of-year annual cash flow analysis.

Which of the following is NOT included in commissioning documentation?

How can commissioning reduce the life-cycle cost to owners and operators?

What is the best type of heat exchanger to recover and transfer latent heat energy from one air stream to another?

A 55-kW motor at full load is used to drive a pump that generates 50 meters of head while pumping water at a rate of 5,000 liters per minute. Calculate the pump efficiency.

If the temperature difference across an external wall is 20°C and the heat flow across the wall is 2.5 Watts/m², calculate the insulation value of the wall (including inside and outside air films)?

A 100-kW electrical load has a power factor of 75%. What capacitance, in KVAR, will improve the power factor to 95%?

A gas-fired boiler is operating with 31.9% excess air. A feedwater economizer is used to reduce the stack temperature rise from 310°C to 160°C. Using the natural gas combustion efficiency tables in your workbook, find the energy savings from the economizer as a percentage of historical fuel consumption.

What is the purpose of top (or skimming) blowdown in a steam boiler?

If a boiler cycles on and off too frequently, what control can you adjust to reduce the number of times a boiler cycles on and off?

A heat pump water heater has an annual average coefficient of performance (COP) of 2.1 and heats water from 15°C to 50°C. Hot water use is 100 liters per day, 365 days/yr. The electricity cost is $0.10/kWh. What is the annual water heating cost? (The specific heat of water (C) is 4.2 kJ/kg-°C.)

An outdoor parking area has 25 light poles. Each pole has a 420 Watt (ballast included) high-pressure sodium (HPS) luminaire. The parking area lights are illuminated 4,500 hours per year and the electricity cost is $0.08/kWh. What is the annual energy cost reduction if each luminaire is replaced with a 220-Watt (driver included) LED luminaire?

Which pump system listed below is most likely the best application for converting to variable-speed drive?

What type of passive heat exchanger can wrap around an evaporator coil to precool entering air and reheat the air after the cooling coil without adding more moisture to the supply air stream?

A three phase, 380-volt system, has the following voltage measurements:

Va = 375 volts

Vb = 380 volts

Vc = 391 volts

Calculate the percent voltage imbalance.

You can buy air compressor A for $15,000 or air compressor B for $6,000. Compressor A will cost $10,000 per year to operate. Compressor B will cost $11,500 per year to operate. If both air compressors have a 10-year life and your required return on investment is 12%, which air compressor has the lowest total life-cycle cost?