Free PE Mechanical Engineering: HVAC and Refrigeration Practice Questions

Sample Practice Questions

Try these 10 sample questions from the PE Mechanical Engineering: HVAC and Refrigeration practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1An engineer is beginning the ACCA design sequence for a detached house. Which publication provides the procedure for calculating its heating and cooling loads?

   1. A. ACCA Manual D
   2. B. ACCA Manual J
   3. C. ACCA Manual S
   4. D. ACCA Manual T

   Answer: B

   Explanation: The DOE guide states, "Manual J Version 8 provides the detailed steps required to calculate the heating and cooling loads." Manual S addresses equipment selection, Manual T outlets, and Manual D ducts.

   Reference: Strategy Guideline: Accurate Heating and Cooling Load Calculations — Executive Summary, p. ix

2. 2A rectangular supply duct has inside dimensions 16 in. by 12 in. and carries 1,600 cfm. What is its average air velocity?

   1. A. 8.33 ft/min
   2. B. 100 ft/min
   3. C. 1,200 ft/min
   4. D. 1,600 ft/min

   Answer: C

   Explanation: DOE states, "The volumetric flow rate can be calculated as the product of the crosssectional area (A) for flow and the average flow velocity (v)." Area is 16(12)/144 = 1.333 ft², so velocity is 1,600/1.333 = 1,200 ft/min. The other values omit one or both length conversions or omit area.

   Reference: DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 3 — Continuity Equation, Volumetric Flow Rate, p. 9, Eq. 3-1

3. 3An evaporative cooling tower receives water at 95°F and discharges it at 85°F while the entering-air wet-bulb temperature is 78°F. What is the tower approach?

   1. A. 7°F
   2. B. 10°F
   3. C. 17°F
   4. D. 78°F

   Answer: A

   Explanation: EnergyPlus defines approach as "the outlet water temperature minus the inlet air wet-bulb temperature". Thus approach = 85−78 = 7°F. Ten degrees is the water range, 17°F uses entering water, and 78°F is the air reference itself.

   Reference: EnergyPlus Engineering Reference—Cooling Towers and Evaporative Fluid Coolers — Variable-Speed Cooling Tower, Model Description, Equation 16.32 definitions

4. 4A steam humidifier remains enabled but its moisture demand is zero. In the specified control model, its internal humidifier fan stops and only the 20-W standby circuit remains energized. What electric energy does the humidifier use over 8 hours in this state?

   1. A. 0.020 kWh
   2. B. 0.160 kWh
   3. C. 0.00250 kWh
   4. D. 160 kWh

   Answer: B

   Explanation: For zero water addition while scheduled on, the reference sets "Whum=Wstby". Standby consumption is 20 W × 8 h / 1,000 = 0.160 kWh. Omitting duration, dividing by duration, or omitting the watts-to-kilowatts conversion produces the alternatives.

   Reference: EnergyPlus Engineering Reference: Air System Humidifiers — Electric and Gas Steam Humidifier—Component, zero-water-addition case

5. 5A detached-house heating calculation follows the Manual J assumptions described in the DOE load-calculation guide. How should solar and internal heat gains be treated when estimating the peak heating load?

   1. A. Credit the coincident solar and occupied internal gains.
   2. B. Credit the solar gains but omit occupied internal gains.
   3. C. Omit the solar gains but credit occupied internal gains.
   4. D. Omit both solar gains and occupied internal gains.

   Answer: D

   Explanation: The guide states, "No credit is taken for solar gains or internal loads in calculating the heating load because the peak heat loss occurs at night during periods of occupant inactivity." Under the specified calculation assumptions, neither gain offsets the peak heating requirement.

   Reference: Strategy Guideline: Accurate Heating and Cooling Load Calculations — Peak Heating Load, p. 7

6. 6An installer selects flexible duct for a fixed straight routed distance. At the same airflow and diameter, which ratio of installed length to the selected piece's fully extended length minimizes the friction penalty from duct compression?

   1. A. 0.55
   2. B. 0.70
   3. C. 0.85
   4. D. 1.00

   Answer: D

   Explanation: The DOE guide explains that "installing flexible duct in its compressed form can increase the friction rate exponentially". A ratio of 1.00 means the piece is fully extended instead of carrying excess compressed length; the smaller ratios leave progressively greater compression.

   Reference: Advanced Strategy Guideline: Air Distribution Basics and Duct Design — Section 2.1.2, Ductwork Materials and Configuration, pp. 4–5, Fig. 3

7. 7An engineer evaluates the limiting temperature for an ideal direct-contact evaporative cooling tower supplied with unsaturated outdoor air. With no external refrigeration or desiccant stage, which entering-air property sets the ideal lower limit for the leaving-water temperature?

   1. A. Dry-bulb temperature
   2. B. Wet-bulb temperature
   3. C. Dew-point temperature
   4. D. Mean radiant temperature

   Answer: B

   Explanation: The cooling-tower effectiveness relation uses the "wet-bulb temperature of the inlet air" as the limiting reference. As effectiveness approaches unity, leaving water approaches that temperature. Dry bulb applies to dry sensible heat rejection; dew point and mean radiant temperature are not this evaporative limit.

   Reference: EnergyPlus Engineering Reference—Cooling Towers and Evaporative Fluid Coolers — Model Description, Equation 16.7 and definitions

8. 8A refrigeration design specifies an A2L refrigerant under ASHRAE Standard 34. What does this classification indicate?

   1. A. Lower toxicity and low burning velocity
   2. B. Higher toxicity and low burning velocity
   3. C. Lower toxicity and no flame propagation
   4. D. Higher toxicity and high flammability

   Answer: A

   Explanation: The ASHRAE factsheet states that A2L refrigerants "are of lower toxicity and have low burning velocity." A identifies lower toxicity; 2L indicates limited flammability with low burning velocity. It does not mean nonflammable or higher toxicity.

   Reference: UNEP/ASHRAE Factsheet 1—Update on New Refrigerants Designations and Safety Classifications — Page 2—Hazard Classification, A2L

9. 9A residential cooling-load report gives 24,000 Btu/h of sensible load and 6,000 Btu/h of latent load at the same design condition. What total cooling load must the engineer use?

   1. A. 18,000 Btu/h
   2. B. 24,000 Btu/h
   3. C. 30,000 Btu/h
   4. D. 48,000 Btu/h

   Answer: C

   Explanation: The guide explains, "Cooling loads are made up of the sensible and latent heat gains." Thus the total is 24,000 + 6,000 = 30,000 Btu/h. Subtraction, omitting latent load, or doubling sensible load gives the competing values.

   Reference: Strategy Guideline: Accurate Heating and Cooling Load Calculations — Peak Cooling Load, p. 8

10. 10A ceiling supply jet stays attached to the nearby ceiling surface and travels farther into the room than a comparable free jet. Which named effect explains the surface attachment?

    1. A. Stack effect
    2. B. Coanda effect
    3. C. Venturi effect
    4. D. Joule–Thomson effect

    Answer: B

    Explanation: The guide defines "Coanda effect – The tendency of moving air to attach itself to a surface and flow along it." This attachment increases the reach of a ceiling supply jet.

    Reference: Advanced Strategy Guideline: Air Distribution Basics and Duct Design — Section 2.2.2, Throw, p. 6