FREE CEM Test HVAC Systems & Building Envelope Questions and Answers

Question 1

An energy manager is evaluating the thermal performance of a building's wall assembly. The wall consists of several layers with a combined thermal resistance (R-value) of 25 hr·ft²·°F/Btu. What is the overall heat transfer coefficient (U-value) for this wall assembly?

Accepted Answer

0.04 Btu/hr·ft²·°F

Answer

The U-value (or U-factor) is the mathematical reciprocal of the total R-value (U = 1/R). A high R-value indicates good resistance to heat flow, while a low U-value indicates that a material or assembly is a good insulator. In this case, U = 1 / 25 = 0.04 Btu/hr·ft²·°F.

Question 2

A facility's centrifugal chiller is rated at 400 tons and consumes 240 kW at full load. What is the chiller's full-load energy efficiency rating in kW/ton?

Accepted Answer

0.60 kW/ton

Answer

Chiller efficiency is calculated by dividing the power input (kW) by the cooling capacity (tons). A lower kW/ton value indicates higher efficiency. The calculation is: 240 kW / 400 tons = 0.60 kW/ton.

Question 3

In a hot, sunny climate, which of the following window properties is most critical for reducing solar heat gain and thus minimizing cooling loads?

Accepted Answer

A low Solar Heat Gain Coefficient (SHGC)

Answer

The Solar Heat Gain Coefficient (SHGC) measures the fraction of solar radiation admitted through a window. A lower SHGC is desirable in cooling-dominated climates to reduce the amount of solar heat entering the building, which in turn reduces the load on the air conditioning system.

Question 4

A building's air handling unit (AHU) in a temperate climate is equipped with an air-side economizer. Under which condition should the economizer be fully utilized to provide 'free cooling'?

Accepted Answer

When the outdoor air is cool and dry enough to meet the cooling demand without mechanical refrigeration.

Answer

An air-side economizer provides 'free cooling' by using cool, low-humidity outside air instead of running the mechanical cooling (compressor) system. This is most effective when the outdoor air conditions are favorable (e.g., low temperature and/or low enthalpy) to cool the space directly, reducing or eliminating the need for mechanical refrigeration.

Question 5

What is the primary negative impact of uncontrolled air infiltration on a building's energy consumption in a cold climate?

Accepted Answer

It increases heating loads by allowing cold, unconditioned air to enter the building.

Answer

In a cold climate, uncontrolled air infiltration allows cold outdoor air to leak into the building envelope. This forces the heating system to work harder to maintain the desired indoor temperature, thereby increasing heating energy consumption and utility costs.

(CEM) Certified Emergency Manager Practice Test

(CEM) Certified Emergency Manager Practice Test

FREE CEM Test HVAC Systems & Building Envelope Questions and Answers