CEM Certified Energy Manager (CEM) Questions and Answers

Which of the following best describes a thermally-light building?

Which is the best application for variable-speed drives?

A concentrating solar thermal system collects 5 GJ/h of thermal heat, which is delivered to a 94% efficient hot water generator. The hot water generator is used to raise the water temperature from 15°C to 65°C. The specific heat of water (Cp) is 4.2 kJ/kg-°C. What flow rate (liter/second) of hot water can be delivered from the hot water generator?

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

A desk lamp is located inside a windowless office. The office is heated during the winter and cooled during the summer. When the lamp is switched on, how much of the energy consumed by the lamp becomes heat in the office space?

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?

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.

A new energy-efficient boiler costs $60,890 to buy and install. The new energy-efficient boiler will save $15,400 per year and last for 20 years. What is the internal rate of return (IRR) of the project?

Exhaust gases from an industrial furnace flow through a heat-recovery steam generator, which generates medium-pressure steam. This steam is used in a steam turbine to generate shaft power driving a fan. Which type of combined heat and power (CHP) cycle does this process describe?

What is the uniform series present worth factor (P/A, i%, n) for an annual interest rate of 15% and a lifetime of 20 years?

Air is heated from 10°C (dry bulb temperature) and 80% relative humidity to 32°C (dry bulb temperature). What is the new relative humidity?

What is a common method to reduce the impact of voltage imbalance?

Using a degree-day base of 18°C, calculate the number of cooling degree days (CDD) if the outside temperature is a uniform 25°C throughout the year (365 days/year).

In a chilled water thermal energy storage system, chilled water is stored at 4°C and used for supply water. Chilled water return is 14°C. Calculate the storage capacity required to hold 50 GJ of thermal cooling. (The specific heat of water (C) is 4.2 kJ/kg-°C. Assume no system losses.)

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)?

If outside air has a temperature of 25°C dry bulb and 15°C wet bulb, what is the enthalpy of the air?

A facility replaces a natural gas heating system rated at 10,000 kJ/h and 80% efficiency with an electric heat pump rated at 10,000 kJ/h and a coefficient of performance (COP) of 2.3. Will this project also reduce the annual energy utilization index (EUI) for the facility?

A new lighting system costs $60,000. The new lighting system has a 15-year life and the minimum required rate of return (MARR) is 15%. How much must the new lighting system save to be life-cycle cost effective?

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

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

In a PID control system, what is the purpose of the Proportional Gain?

A controller has a signal output that can range from 4 to 20 mA (milli-amperes). The controller regulates the output temperature from a three-way mixing valve from 5°C to 15°C. What is the control gain?

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?

Which of the following is NOT included in commissioning documentation?

Why do electric utility companies transmit power at high voltages?

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A facility has a monthly peak power demand of 1,000 kW and an average power factor of 80%. The facility pays a demand charge of $7.50/kVA-month. What is the additional cost per month because the power factor is less than 100%?

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

What does a manometer measure?

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

Using the lumen method, calculate the number of luminaires (fixtures) required to light a room to 200 lux. Each luminaire has 2 fluorescent lamps, 3,000 lumens per lamp. The room is 20 meters by 30 meters. The total light loss factor (LLF) is 0.70 and the luminaire coefficient of utilization (CU) is 0.80.

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

A compressed air system has a total volume of 247,500 liters. During a 30-minute break in production (air compressor system turned off and no production demand for compressed air), the system pressure drops from 7 bar, gauge (700 kPa, gauge) to 5 bar, gauge (500 kPa, gauge). Calculate the leakage rate in the compressed air system.

What instrument is NOT used to measure temperature?

How does an enthalpy-based economizer control operate?

Which heat recovery device listed below can be used to preheat boiler make-up water using the heat energy from skimming blowdown?