UH COSC 325 — Mechanical & Electrical Systems Exam — 2026/2027
UNIVERSITY OF HOUSTON COSC 325
MECHANICAL AND ELECTRICAL SYSTEMS EXAM
2026/2027 Comprehensive Study Set
75 Questions | Complete Q&A | Verified A+ Solutions | UH Construction Science Aligned
Exam Structure: 75 multiple-choice, calculation-based, and scenario questions
Testing Time: 120–150 minutes | Scientific calculator permitted
Passing Score: 70–75% (53–56/75 correct) per UH undergraduate program policy
Core References: IMC, IECC, NEC (2023), ASHRAE 90.1, NFPA 13
SECTION I: HVAC FUNDAMENTALS — Psychrometrics, Heat Transfer & Load Calculations
(Q1–10)
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
Rationale: The dry-bulb temperature is plotted along the horizontal axis of a standard
psychrometric chart. Dry-bulb temperature represents the sensible temperature of air as measured
by a standard thermometer, unaffected by moisture content. Wet-bulb temperature lines slope
diagonally upward from left to right, dew point is read along the horizontal saturation line, and
relative humidity curves arc across the chart from lower-left to upper-right.
2. Air at 80°F dry-bulb and 67°F wet-bulb temperature has approximately what relative
humidity?
A. 50% RH
B. 67% RH
C. 80% RH
D. 35% RH
Rationale: Using a psychrometric chart, the intersection of 80°F dry-bulb and 67°F wet-bulb
temperatures falls approximately on the 50% relative humidity curve. The wet-bulb depression (the
difference between dry-bulb and wet-bulb temperatures) is 13°F, which at 80°F dry-bulb corresponds
to roughly 50% RH. This is a common psychrometric calculation tested in COSC 325.
3. What is the dew point temperature of air at 75°F dry-bulb and 50% relative humidity?
A. Approximately 55°F
B. Approximately 65°F
C. Approximately 50°F
D. Approximately 60°F
Rationale: On the psychrometric chart, moving horizontally left from the intersection of 75°F dry-
bulb and 50% RH until reaching the saturation curve (100% RH line) gives the dew point. For air at
75°F and 50% RH, this value is approximately 55°F. The dew point represents the temperature at
which moisture would begin to condense from the air if cooled at constant pressure.
4. Which mode of heat transfer occurs primarily through electromagnetic waves without
requiring a medium?
A. Radiation
B. Conduction
C. Convection
D. Infiltration
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, UH COSC 325 — Mechanical & Electrical Systems Exam — 2026/2027
Rationale: Radiation is the transfer of thermal energy through electromagnetic waves (infrared
radiation). Unlike conduction (molecular contact transfer through solids) and convection (fluid
circulation transfer), radiation does not require a physical medium and can occur through a vacuum.
This is why solar heat reaches Earth through space, and why radiant heating systems can warm
surfaces without directly heating the air.
5. A wall assembly has the following layers: exterior siding (R-0.5), 2×4 framing with R-13
cavity insulation, and ½-inch drywall (R-0.45). What is the total R-value of this assembly,
approximately?
A. R-14.0
B. R-16.5
C. R-13.0
D. R-11.5
Rationale: The total R-value of an assembly is the sum of individual layer R-values. R-0.5 (siding) +
R-13.0 (cavity insulation) + R-0.45 (drywall) = R-13.95, which rounds to approximately R-14.0. Note
that in more detailed calculations, thermal bridging through the framing members would reduce the
effective R-value, but for basic COSC 325 problems, summing the component R-values is the standard
approach.
6. A building wall has a total R-value of 19. What is its U-factor?
A. 0.053
B. 0.19
C. 1.9
D. 19.0
Rationale: The U-factor is the reciprocal of the total R-value: U = 1/R. Therefore, U = 1/19 = 0.0526,
which rounds to approximately 0.053 Btu/h·ft²·°F. The U-factor represents the rate of heat transfer
through a building assembly per unit area per unit temperature difference, and lower U-factors
indicate better insulating performance.
7. A window assembly measures 4 ft × 5 ft and has a U-factor of 0.65. If the indoor
temperature is 70°F and the outdoor temperature is 20°F, what is the heat loss through the
window in Btu/h?
A. 650 Btu/h
B. 1300 Btu/h
C. 260 Btu/h
D. 585 Btu/h
Rationale: Heat loss is calculated using Q = U × A × ΔT, where A = 4 × 5 = 20 ft² and ΔT = 70 − 20 =
50°F. Therefore, Q = 0.65 × 20 × 50 = 650 Btu/h. This fundamental heat transfer calculation is
essential for HVAC load estimating in construction science.
8. Sensible heat is defined as heat that causes a change in:
A. Temperature without a change in state
B. Moisture content without a change in temperature
C. Both temperature and moisture content simultaneously
D. Latent heat of vaporization
Rationale: Sensible heat causes a change in the temperature of a substance without changing its
phase or state (solid, liquid, or gas). For example, heating air from 70°F to 80°F involves sensible heat
only. Latent heat, by contrast, causes a change in state (such as water evaporating into vapor)
without a change in temperature. In HVAC load calculations, both sensible and latent heat
components must be accounted for.
9. Latent heat in HVAC load calculations is primarily associated with which of the following?
A. Moisture removal (dehumidification)
B. Temperature change of supply air
C. Air filtration efficiency
D. Fan motor heat gain
2
, UH COSC 325 — Mechanical & Electrical Systems Exam — 2026/2027
Rationale: Latent heat in HVAC design refers to the heat energy associated with moisture changes—
primarily the energy required to condense moisture from the air (dehumidification). In cooling load
calculations, the latent heat component accounts for the energy needed to remove humidity from the
conditioned space. Sensible heat relates to dry-bulb temperature changes, while latent heat relates to
moisture removal and dew point control.
10. The coefficient of performance (COP) of a heat pump is 3.5. If the heat output is 42,000
Btu/h, what is the electrical power input in watts?
A. 3,516 W
B. 12,000 W
C. 1,200 W
D. 10,500 W
Rationale: COP = Heat Output (in consistent energy units) / Work Input. First, convert 42,000
Btu/h to watts: 42,000 Btu/h ÷ 3.412 Btu/h per watt = 12,306 W. Then, Work Input = Heat Output /
COP = 12,.5 = 3,516 W. The COP dimensionless ratio indicates how many units of heating or
cooling energy are delivered per unit of electrical energy input.
SECTION II: HVAC EQUIPMENT & SYSTEMS — AHU, Chillers, Boilers, Cooling Towers (Q11–
16)
11. Which component of an air handling unit (AHU) is responsible for removing moisture
from the supply air stream during cooling mode?
A. Cooling coil
B. Heating coil
C. Supply fan
D. Filter bank
Rationale: The cooling coil (typically a chilled water or direct expansion refrigerant coil) removes
both sensible heat and latent heat (moisture) from the air stream during cooling operation. As warm,
humid air passes over the cold coil surface (below the air dew point), moisture condenses on the coil
and is drained away. The heating coil adds heat, the supply fan moves air, and the filter bank
removes particulates—none of these remove moisture.
12. In a vapor compression refrigeration cycle, at which component does the refrigerant
absorb heat from the conditioned space?
A. Evaporator
B. Condenser
C. Compressor
D. Expansion valve
Rationale: The evaporator is the component where the refrigerant absorbs heat from the
conditioned space or air stream. In the evaporator, low-pressure liquid refrigerant evaporates by
absorbing latent heat from the surrounding environment, thereby producing the cooling effect. The
condenser rejects heat to the outdoors, the compressor raises refrigerant pressure and temperature,
and the expansion valve reduces pressure—completing the refrigeration cycle.
13. Which type of chiller uses a heat source (such as steam or natural gas) rather than a
mechanical compressor to drive the refrigeration cycle?
A. Absorption chiller
B. Centrifugal chiller
C. Reciprocating chiller
D. Scroll chiller
Rationale: An absorption chiller uses a thermal energy source (steam, hot water, or natural gas
combustion) to drive the refrigeration cycle instead of a mechanical compressor. Absorption chillers
use a refrigerant-absorbent solution pair (typically lithium bromide-water or water-ammonia). The
heat source drives the refrigerant out of solution in the generator, replacing the work of a
compressor. Centrifugal, reciprocating, and scroll chillers are all vapor compression cycle machines.
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UNIVERSITY OF HOUSTON COSC 325
MECHANICAL AND ELECTRICAL SYSTEMS EXAM
2026/2027 Comprehensive Study Set
75 Questions | Complete Q&A | Verified A+ Solutions | UH Construction Science Aligned
Exam Structure: 75 multiple-choice, calculation-based, and scenario questions
Testing Time: 120–150 minutes | Scientific calculator permitted
Passing Score: 70–75% (53–56/75 correct) per UH undergraduate program policy
Core References: IMC, IECC, NEC (2023), ASHRAE 90.1, NFPA 13
SECTION I: HVAC FUNDAMENTALS — Psychrometrics, Heat Transfer & Load Calculations
(Q1–10)
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
Rationale: The dry-bulb temperature is plotted along the horizontal axis of a standard
psychrometric chart. Dry-bulb temperature represents the sensible temperature of air as measured
by a standard thermometer, unaffected by moisture content. Wet-bulb temperature lines slope
diagonally upward from left to right, dew point is read along the horizontal saturation line, and
relative humidity curves arc across the chart from lower-left to upper-right.
2. Air at 80°F dry-bulb and 67°F wet-bulb temperature has approximately what relative
humidity?
A. 50% RH
B. 67% RH
C. 80% RH
D. 35% RH
Rationale: Using a psychrometric chart, the intersection of 80°F dry-bulb and 67°F wet-bulb
temperatures falls approximately on the 50% relative humidity curve. The wet-bulb depression (the
difference between dry-bulb and wet-bulb temperatures) is 13°F, which at 80°F dry-bulb corresponds
to roughly 50% RH. This is a common psychrometric calculation tested in COSC 325.
3. What is the dew point temperature of air at 75°F dry-bulb and 50% relative humidity?
A. Approximately 55°F
B. Approximately 65°F
C. Approximately 50°F
D. Approximately 60°F
Rationale: On the psychrometric chart, moving horizontally left from the intersection of 75°F dry-
bulb and 50% RH until reaching the saturation curve (100% RH line) gives the dew point. For air at
75°F and 50% RH, this value is approximately 55°F. The dew point represents the temperature at
which moisture would begin to condense from the air if cooled at constant pressure.
4. Which mode of heat transfer occurs primarily through electromagnetic waves without
requiring a medium?
A. Radiation
B. Conduction
C. Convection
D. Infiltration
1
, UH COSC 325 — Mechanical & Electrical Systems Exam — 2026/2027
Rationale: Radiation is the transfer of thermal energy through electromagnetic waves (infrared
radiation). Unlike conduction (molecular contact transfer through solids) and convection (fluid
circulation transfer), radiation does not require a physical medium and can occur through a vacuum.
This is why solar heat reaches Earth through space, and why radiant heating systems can warm
surfaces without directly heating the air.
5. A wall assembly has the following layers: exterior siding (R-0.5), 2×4 framing with R-13
cavity insulation, and ½-inch drywall (R-0.45). What is the total R-value of this assembly,
approximately?
A. R-14.0
B. R-16.5
C. R-13.0
D. R-11.5
Rationale: The total R-value of an assembly is the sum of individual layer R-values. R-0.5 (siding) +
R-13.0 (cavity insulation) + R-0.45 (drywall) = R-13.95, which rounds to approximately R-14.0. Note
that in more detailed calculations, thermal bridging through the framing members would reduce the
effective R-value, but for basic COSC 325 problems, summing the component R-values is the standard
approach.
6. A building wall has a total R-value of 19. What is its U-factor?
A. 0.053
B. 0.19
C. 1.9
D. 19.0
Rationale: The U-factor is the reciprocal of the total R-value: U = 1/R. Therefore, U = 1/19 = 0.0526,
which rounds to approximately 0.053 Btu/h·ft²·°F. The U-factor represents the rate of heat transfer
through a building assembly per unit area per unit temperature difference, and lower U-factors
indicate better insulating performance.
7. A window assembly measures 4 ft × 5 ft and has a U-factor of 0.65. If the indoor
temperature is 70°F and the outdoor temperature is 20°F, what is the heat loss through the
window in Btu/h?
A. 650 Btu/h
B. 1300 Btu/h
C. 260 Btu/h
D. 585 Btu/h
Rationale: Heat loss is calculated using Q = U × A × ΔT, where A = 4 × 5 = 20 ft² and ΔT = 70 − 20 =
50°F. Therefore, Q = 0.65 × 20 × 50 = 650 Btu/h. This fundamental heat transfer calculation is
essential for HVAC load estimating in construction science.
8. Sensible heat is defined as heat that causes a change in:
A. Temperature without a change in state
B. Moisture content without a change in temperature
C. Both temperature and moisture content simultaneously
D. Latent heat of vaporization
Rationale: Sensible heat causes a change in the temperature of a substance without changing its
phase or state (solid, liquid, or gas). For example, heating air from 70°F to 80°F involves sensible heat
only. Latent heat, by contrast, causes a change in state (such as water evaporating into vapor)
without a change in temperature. In HVAC load calculations, both sensible and latent heat
components must be accounted for.
9. Latent heat in HVAC load calculations is primarily associated with which of the following?
A. Moisture removal (dehumidification)
B. Temperature change of supply air
C. Air filtration efficiency
D. Fan motor heat gain
2
, UH COSC 325 — Mechanical & Electrical Systems Exam — 2026/2027
Rationale: Latent heat in HVAC design refers to the heat energy associated with moisture changes—
primarily the energy required to condense moisture from the air (dehumidification). In cooling load
calculations, the latent heat component accounts for the energy needed to remove humidity from the
conditioned space. Sensible heat relates to dry-bulb temperature changes, while latent heat relates to
moisture removal and dew point control.
10. The coefficient of performance (COP) of a heat pump is 3.5. If the heat output is 42,000
Btu/h, what is the electrical power input in watts?
A. 3,516 W
B. 12,000 W
C. 1,200 W
D. 10,500 W
Rationale: COP = Heat Output (in consistent energy units) / Work Input. First, convert 42,000
Btu/h to watts: 42,000 Btu/h ÷ 3.412 Btu/h per watt = 12,306 W. Then, Work Input = Heat Output /
COP = 12,.5 = 3,516 W. The COP dimensionless ratio indicates how many units of heating or
cooling energy are delivered per unit of electrical energy input.
SECTION II: HVAC EQUIPMENT & SYSTEMS — AHU, Chillers, Boilers, Cooling Towers (Q11–
16)
11. Which component of an air handling unit (AHU) is responsible for removing moisture
from the supply air stream during cooling mode?
A. Cooling coil
B. Heating coil
C. Supply fan
D. Filter bank
Rationale: The cooling coil (typically a chilled water or direct expansion refrigerant coil) removes
both sensible heat and latent heat (moisture) from the air stream during cooling operation. As warm,
humid air passes over the cold coil surface (below the air dew point), moisture condenses on the coil
and is drained away. The heating coil adds heat, the supply fan moves air, and the filter bank
removes particulates—none of these remove moisture.
12. In a vapor compression refrigeration cycle, at which component does the refrigerant
absorb heat from the conditioned space?
A. Evaporator
B. Condenser
C. Compressor
D. Expansion valve
Rationale: The evaporator is the component where the refrigerant absorbs heat from the
conditioned space or air stream. In the evaporator, low-pressure liquid refrigerant evaporates by
absorbing latent heat from the surrounding environment, thereby producing the cooling effect. The
condenser rejects heat to the outdoors, the compressor raises refrigerant pressure and temperature,
and the expansion valve reduces pressure—completing the refrigeration cycle.
13. Which type of chiller uses a heat source (such as steam or natural gas) rather than a
mechanical compressor to drive the refrigeration cycle?
A. Absorption chiller
B. Centrifugal chiller
C. Reciprocating chiller
D. Scroll chiller
Rationale: An absorption chiller uses a thermal energy source (steam, hot water, or natural gas
combustion) to drive the refrigeration cycle instead of a mechanical compressor. Absorption chillers
use a refrigerant-absorbent solution pair (typically lithium bromide-water or water-ammonia). The
heat source drives the refrigerant out of solution in the generator, replacing the work of a
compressor. Centrifugal, reciprocating, and scroll chillers are all vapor compression cycle machines.
3
