Certified Energy Manager (CEM) Test

FREE Certified Energy Manager: Steam, Industrial and Thermal Storage Questions and Answers

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A manager of energy is comparing the running expenses of two boilers. One uses natural gas and has a 75% efficiency, while the other uses electricity and has a 97% efficiency. Electricity is $0.095/kWh and natural gas is $0.92/therm. Calculate the price per MMBtu for each system's water heating.

Correct! Wrong!

Storing Thermal Energy Latent heat storage is the main method for employing ice as a storage medium.

Correct! Wrong!

More Btu can be stored (or released) in energy storage systems thanks to the "phase change" energy.

Consider a process that consumes 10,000 MMBtu per year and is powered by a 50 percent efficient, old oil-fired boiler that burns leftover fuel oil #6. What energy savings might you expect if you upgrade to an 80% efficient natural gas-fired boiler?

Correct! Wrong!

To determine the savings, we need to compare the fuel consumed before and after the retrofit.
Before the retrofit, if the boiler is only 50% efficient, then the fuel supplied to the boiler will be more than the 10,000 MMBtu needed for the process. Thus, the fuel input will be 10,000/.5
= 20,000 MMBtu per year.
After the retrofit, the new boiler is 80% efficient and the fuel input will be 10,000/.8
= 12,500 MMBtu per year.
The Savings would be:
= 20,000 MMBtu – 12,500 MMBtu
= 7,500 MMBtu per year.

An ESCO finds chances for energy savings in the new building's design (which has not been built yet). Which of the following M&V Approaches would be the best fit to take into account the "avoided cost" (resulting from the energy savings) inside the new structure?

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Because there are no energy performance statistics for the new portion of the building, IPMVP Option D is helpful in this situation. Option D enables simulation in order to determine baseline and "avoided expenses" associated with making energy improvements.

In general, if cooler air enters a compressor, the compressor's efficiency is:

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Because colder air is denser and dryer, it requires the compressor to operate less and is therefore more efficient.

What does enthalpy equal at 400 degrees Fahrenheit for saturated steam?

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Enthalpy in the gaseous state (hg), which is equal to 1201 Btu/lb, may be calculated using the Saturated Steam tables.

Heat recovery systems (also known as heat exchangers) are unable to lower temperatures below the hot gas's dew point.

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Flue gas temperatures that fall below the dew point will cause condensation. (Let's hope your boiler is a condensing one.