COSC 325 Mechanical and Electrical Systems
Examination | University of Houston | 2026/2027
Edition | 110 Questions & Answers
SECTION I: HVAC FUNDAMENTALS – Psychrometrics, Heat Transfer &
Load Calculations (Q1–20)
1. On a psychrometric chart, which temperature measurement is read along the
horizontal (x) axis?
A. Dry-bulb temperature
B. Wet-bulb temperature
C. Dew point temperature
D. Relative humidity
Correct Answer: A. Dry-bulb temperature
Rationale:>>Dry-bulb temperature is plotted on the horizontal axis; wet-bulb lines
slope diagonally; dew point follows the saturation curve.
2. Air at 80°F dry-bulb and 67°F wet-bulb has approximately what relative
humidity?
A. 50% RH
B. 67% RH
C. 80% RH
D. 35% RH
Correct Answer: A. 50% RH
*Rationale:>>The 13°F wet-bulb depression at 80°F DB gives about 50% RH on
the psychrometric chart.*
3. What is the dew point of air at 75°F dry-bulb and 50% relative humidity?
A. 55°F
B. 65°F
C. 50°F
D. 60°F
,Correct Answer: A. 55°F
Rationale:>>From 75°F DB and 50% RH, move left horizontally to saturation
curve → dew point ≈55°F.
4. Which mode of heat transfer occurs primarily through electromagnetic waves
without requiring a medium?
A. Radiation
B. Conduction
C. Convection
D. Infiltration
Correct Answer: A. Radiation
Rationale:>>Radiant heat transfer (infrared) occurs via electromagnetic waves;
conduction and convection require matter.
5. The formula Q = U × A × ΔT is used to calculate:
A. Heat loss through a building envelope
B. Latent heat of vaporization
C. Sensible heat from infiltration
D. Cooling coil bypass factor
Correct Answer: A. Heat loss through a building envelope
Rationale:>>Q = U·A·ΔT is the basic conduction heat transfer equation through
walls, roofs, windows.
6. A wall has an R-value of 20 h·ft²·°F/Btu. If the temperature difference across the
wall is 30°F and area is 200 ft², what is the heat loss?
A. 300 Btu/hr
B. 600 Btu/hr
C. 1200 Btu/hr
D. 3000 Btu/hr
Correct Answer: A. 300 Btu/hr
*Rationale:>>Q = A·ΔT / R = (200×30)/20 = 6000/20 = 300 Btu/hr.*
7. On a psychrometric chart, the specific volume lines run:
A. Vertically
B. Horizontally
C. Diagonally (steep slope)
D. In concentric curves
, Correct Answer: C. Diagonally (steep slope)
Rationale:>>Specific volume lines (ft³/lb dry air) run diagonally with a steep
slope, slightly angled to the vertical.
8. The total heat content of air (enthalpy) includes:
A. Sensible heat only
B. Latent heat only
C. Both sensible and latent heat
D. Barometric pressure
Correct Answer: C. Both sensible and latent heat
Rationale:>>Enthalpy (Btu/lb dry air) is the sum of sensible and latent heat
content.
9. A cooling coil that reduces both dry-bulb and humidity ratio is performing:
A. Sensible cooling only
B. Dehumidification (total cooling)
C. Adiabatic cooling
D. Reheat
Correct Answer: B. Dehumidification (total cooling)
Rationale:>>When air is cooled below its dew point, moisture condenses, reducing
both DB and humidity ratio.
10. The summer outdoor design temperature used in load calculations is based on:
A. Average daily maximum
B. Extreme annual maximum
C. 1% or 0.4% dry-bulb temperature (ASHRAE)
D. Wettest month average
Correct Answer: C. 1% or 0.4% dry-bulb temperature (ASHRAE)
*Rationale:>>ASHRAE design conditions use statistical percentiles (e.g., 1% dry-
bulb) for peak loads.*
11. A building has a sensible heat ratio (SHR) of 0.75. This means:
A. 75% of the total cooling load is sensible
B. 25% of the total cooling load is sensible
C. The latent load is 75% of sensible
D. The supply air is 75°F
Examination | University of Houston | 2026/2027
Edition | 110 Questions & Answers
SECTION I: HVAC FUNDAMENTALS – Psychrometrics, Heat Transfer &
Load Calculations (Q1–20)
1. On a psychrometric chart, which temperature measurement is read along the
horizontal (x) axis?
A. Dry-bulb temperature
B. Wet-bulb temperature
C. Dew point temperature
D. Relative humidity
Correct Answer: A. Dry-bulb temperature
Rationale:>>Dry-bulb temperature is plotted on the horizontal axis; wet-bulb lines
slope diagonally; dew point follows the saturation curve.
2. Air at 80°F dry-bulb and 67°F wet-bulb has approximately what relative
humidity?
A. 50% RH
B. 67% RH
C. 80% RH
D. 35% RH
Correct Answer: A. 50% RH
*Rationale:>>The 13°F wet-bulb depression at 80°F DB gives about 50% RH on
the psychrometric chart.*
3. What is the dew point of air at 75°F dry-bulb and 50% relative humidity?
A. 55°F
B. 65°F
C. 50°F
D. 60°F
,Correct Answer: A. 55°F
Rationale:>>From 75°F DB and 50% RH, move left horizontally to saturation
curve → dew point ≈55°F.
4. Which mode of heat transfer occurs primarily through electromagnetic waves
without requiring a medium?
A. Radiation
B. Conduction
C. Convection
D. Infiltration
Correct Answer: A. Radiation
Rationale:>>Radiant heat transfer (infrared) occurs via electromagnetic waves;
conduction and convection require matter.
5. The formula Q = U × A × ΔT is used to calculate:
A. Heat loss through a building envelope
B. Latent heat of vaporization
C. Sensible heat from infiltration
D. Cooling coil bypass factor
Correct Answer: A. Heat loss through a building envelope
Rationale:>>Q = U·A·ΔT is the basic conduction heat transfer equation through
walls, roofs, windows.
6. A wall has an R-value of 20 h·ft²·°F/Btu. If the temperature difference across the
wall is 30°F and area is 200 ft², what is the heat loss?
A. 300 Btu/hr
B. 600 Btu/hr
C. 1200 Btu/hr
D. 3000 Btu/hr
Correct Answer: A. 300 Btu/hr
*Rationale:>>Q = A·ΔT / R = (200×30)/20 = 6000/20 = 300 Btu/hr.*
7. On a psychrometric chart, the specific volume lines run:
A. Vertically
B. Horizontally
C. Diagonally (steep slope)
D. In concentric curves
, Correct Answer: C. Diagonally (steep slope)
Rationale:>>Specific volume lines (ft³/lb dry air) run diagonally with a steep
slope, slightly angled to the vertical.
8. The total heat content of air (enthalpy) includes:
A. Sensible heat only
B. Latent heat only
C. Both sensible and latent heat
D. Barometric pressure
Correct Answer: C. Both sensible and latent heat
Rationale:>>Enthalpy (Btu/lb dry air) is the sum of sensible and latent heat
content.
9. A cooling coil that reduces both dry-bulb and humidity ratio is performing:
A. Sensible cooling only
B. Dehumidification (total cooling)
C. Adiabatic cooling
D. Reheat
Correct Answer: B. Dehumidification (total cooling)
Rationale:>>When air is cooled below its dew point, moisture condenses, reducing
both DB and humidity ratio.
10. The summer outdoor design temperature used in load calculations is based on:
A. Average daily maximum
B. Extreme annual maximum
C. 1% or 0.4% dry-bulb temperature (ASHRAE)
D. Wettest month average
Correct Answer: C. 1% or 0.4% dry-bulb temperature (ASHRAE)
*Rationale:>>ASHRAE design conditions use statistical percentiles (e.g., 1% dry-
bulb) for peak loads.*
11. A building has a sensible heat ratio (SHR) of 0.75. This means:
A. 75% of the total cooling load is sensible
B. 25% of the total cooling load is sensible
C. The latent load is 75% of sensible
D. The supply air is 75°F
