Your FREE PE Mechanical (Principles and Practice of Engineering) Practice Test 2026 – 160+ Q&A

PE Mechanical Practice Questions

1. On a standard psychrometric chart, which property is read along the horizontal axis?
   • Dry-bulb temperature
   • Relative humidity
   • Humidity ratio
   • Enthalpy

   Correct answer: Dry-bulb temperature

   Dry-bulb temperature is the property plotted on the horizontal (x) axis of the psychrometric chart, with humidity ratio on the vertical axis. Relative humidity appears as curved lines, and enthalpy is read on diagonal scales outside the chart body.

2. Which statement correctly describes the dew-point temperature of a sample of moist air?
   • The temperature read by a thermometer with a wetted wick under forced airflow
   • The average of the dry-bulb and wet-bulb temperatures
   • The temperature at which the air becomes fully saturated when cooled at constant pressure and moisture content
   • The temperature at which relative humidity reaches 50 percent

   Correct answer: The temperature at which the air becomes fully saturated when cooled at constant pressure and moisture content

   The dew-point temperature is the temperature at which moist air, cooled at constant pressure and constant humidity ratio, first reaches saturation and water begins to condense. The wetted-wick reading describes wet-bulb temperature, not dew point.

3. For air at a fixed dry-bulb temperature, how does relative humidity change as the humidity ratio increases?
   • Relative humidity stays constant
   • Relative humidity decreases
   • Relative humidity drops to zero
   • Relative humidity increases

   Correct answer: Relative humidity increases

   Relative humidity increases as humidity ratio rises at a fixed dry-bulb temperature, because more water vapor is present while the saturation capacity stays the same. Relative humidity is the ratio of actual vapor pressure to saturation vapor pressure at that temperature.

4. What is the defining ratio expressed by the sensible heat ratio (SHR) of a cooling coil process?
   • Sensible load divided by total load
   • Sensible load divided by latent load
   • Latent load divided by sensible load
   • Total load divided by latent load

   Correct answer: Sensible load divided by total load

   Sensible heat ratio is the sensible load divided by the total (sensible plus latent) load. It sets the slope of the coil process line on the psychrometric chart and ranges between 0 and 1.

5. An air handler delivers 5,000 CFM and must raise the supply air dry-bulb temperature by 20F. Using the standard sensible heat relation, approximately what sensible heating capacity is required?
   • 216,000 BTU/hr
   • 27,000 BTU/hr
   • 108,000 BTU/hr
   • 54,000 BTU/hr

   Correct answer: 108,000 BTU/hr

   The required capacity is about 108,000 BTU/hr, found from q = 1.08 × CFM × ΔT = 1.08 × 5,000 × 20. The 1.08 factor combines air density, specific heat, and unit conversion at standard conditions.

6. A space requires 80,000 BTU/hr of sensible cooling with supply air delivered 18F below the room dry-bulb. Approximately what airflow is needed?
   • About 2,500 CFM
   • About 1,800 CFM
   • About 4,115 CFM
   • About 6,200 CFM

   Correct answer: About 4,115 CFM

   About 4,115 CFM is required, found by rearranging q = 1.08 × CFM × ΔT to CFM = 80,000 / (1.08 × 18). The sensible relation links airflow, temperature difference, and sensible capacity.

7. Which formula correctly gives the latent cooling load of an airstream using airflow and the moisture change expressed in grains of water per pound of dry air?
   • Q = 0.68 × CFM × Δgrains
   • Q = 1.08 × CFM × Δgrains
   • Q = 0.24 × CFM × Δgrains
   • Q = 4.5 × CFM × Δgrains

   Correct answer: Q = 0.68 × CFM × Δgrains

   The latent load equals 0.68 × CFM × Δgrains, where Δgrains is the change in humidity expressed in grains of water per pound of dry air. The 1.08 factor applies to sensible load, while 4.5 applies to total load when using enthalpy.

8. A 6,000 CFM system removes moisture such that the humidity ratio drops by 15 grains of water per pound of dry air. Approximately what latent load is being handled?
   • About 97,200 BTU/hr
   • About 61,200 BTU/hr
   • About 40,800 BTU/hr
   • About 405,000 BTU/hr

   Correct answer: About 61,200 BTU/hr

   The latent load is about 61,200 BTU/hr, computed from q = 0.68 × CFM × Δgrains = 0.68 × 6,000 × 15. The grains-based latent equation captures the heat associated with condensing the removed moisture.

9. Two airstreams are mixed adiabatically: 3,000 CFM at 75F and 9,000 CFM at 95F. Neglecting density differences, what is the approximate mixed-air dry-bulb temperature?
   • 95F
   • 85F
   • 90F
   • 80F

   Correct answer: 90F

   The mixed temperature is about 90F, found from a flow-weighted average: (3,000 × 75 + 9,000 × 95)/12,000. In adiabatic mixing the resulting state lies on the straight line connecting the two states, positioned by the relative airflows.

10. When two airstreams mix adiabatically on the psychrometric chart, where does the resulting mixed-air state lie?
    • At the saturation curve regardless of inlet states
    • Always at the colder of the two inlet states
    • Along a constant wet-bulb line through the warmer stream
    • On the straight line connecting the two inlet states

    Correct answer: On the straight line connecting the two inlet states

    The mixed-air state falls on the straight line drawn between the two inlet states, with its position set by the proportion of each airflow. This follows from simultaneous mass and energy balances on the combined stream.

11. In an ideal evaporative (adiabatic saturation) cooling process, which air property remains essentially constant?
    • Humidity ratio
    • Wet-bulb temperature
    • Dry-bulb temperature
    • Dew-point temperature

    Correct answer: Wet-bulb temperature

    Wet-bulb temperature stays essentially constant during ideal evaporative cooling, so the process follows a line of constant wet-bulb on the chart. Dry-bulb falls while humidity ratio rises as water evaporates into the airstream.

12. What does the coil bypass factor represent in a cooling coil analysis?
    • The fraction of refrigerant that bypasses the evaporator
    • The ratio of latent to total coil capacity
    • The percentage of design airflow lost to duct leakage
    • The fraction of air that effectively passes through unconditioned, leaving the coil unchanged

    Correct answer: The fraction of air that effectively passes through unconditioned, leaving the coil unchanged

    Bypass factor represents the fraction of air treated as if it leaves the coil at its entering condition, unconditioned. The remaining contact fraction is brought to the apparatus dew point, and the two combine to give the actual leaving-air state.

13. On the psychrometric chart, the apparatus dew point of a cooling coil is located at which point?
    • At the leaving-air dew-point temperature on the horizontal axis
    • At the intersection of constant enthalpy and 50 percent relative humidity
    • At the entering-air dry-bulb on the saturation curve
    • Where the coil process line, extended, intersects the saturation curve

    Correct answer: Where the coil process line, extended, intersects the saturation curve

    The apparatus dew point lies where the straight coil process line, extended, meets the saturation curve. It represents the effective coil surface temperature and anchors the bypass-factor calculation of the leaving-air state.

14. Which combination of independent properties is sufficient to fully fix the state of moist air at a known barometric pressure?
    • Dry-bulb temperature and wet-bulb temperature
    • Enthalpy and wet-bulb temperature
    • Humidity ratio and dew point temperature
    • Relative humidity and dew point alone without temperature

    Correct answer: Dry-bulb temperature and wet-bulb temperature

    Dry-bulb plus wet-bulb temperature fully fix the moist-air state at a known pressure, letting all other properties be read from the chart. Humidity ratio and dew point are not independent of each other, so that pairing does not uniquely locate the state.

15. The enthalpy of moist air on the psychrometric chart is most nearly the sum of which two contributions?
    • Latent heat of vaporization plus the dew-point temperature
    • Vapor pressure plus barometric pressure
    • Specific heat of water plus relative humidity
    • Sensible heat of the dry air plus the total heat of the associated water vapor

    Correct answer: Sensible heat of the dry air plus the total heat of the associated water vapor

    Moist-air enthalpy is essentially the sensible heat of the dry air plus the enthalpy (sensible and latent) of the water vapor it carries. This total-heat basis is why constant-enthalpy lines on the chart track combined sensible-plus-latent energy.

16. A cooling coil handles air entering at 38 BTU/lb and leaving at 25 BTU/lb at a mass flow of 30,000 lb/hr of dry air. What is the total cooling capacity?
    • About 780,000 BTU/hr
    • About 195,000 BTU/hr
    • About 390,000 BTU/hr
    • About 130,000 BTU/hr

    Correct answer: About 390,000 BTU/hr

    The total capacity is about 390,000 BTU/hr, from q = ṁ × Δh = 30,000 × (38 - 25). Using enthalpy difference captures both sensible and latent components of the coil load in a single energy balance.

17. A cooling load comprises 90,000 BTU/hr sensible and 30,000 BTU/hr latent. What is the sensible heat ratio?
    • 0.25
    • 0.33
    • 0.75
    • 0.67

    Correct answer: 0.75

    The sensible heat ratio is 0.75, computed as sensible divided by total: 90,000 / (90,000 + 30,000). A higher SHR indicates a process dominated by sensible heat and a flatter coil process line.

18. During a sensible-heating-only process (no moisture added or removed), how does the air state move on the psychrometric chart?
    • Along the saturation curve
    • Diagonally down a constant-enthalpy line
    • Vertically upward at constant dry-bulb
    • Horizontally to the right at constant humidity ratio

    Correct answer: Horizontally to the right at constant humidity ratio

    Sensible heating with no moisture change moves the state horizontally to the right at constant humidity ratio, since only dry-bulb temperature increases. Relative humidity falls along this path even though the moisture content is unchanged.

19. As moist air is cooled at constant humidity ratio toward its dew point, what happens to its relative humidity?
    • It first decreases then increases
    • It remains unchanged
    • It decreases toward zero
    • It increases toward 100 percent

    Correct answer: It increases toward 100 percent

    Relative humidity rises toward 100 percent as the air cools at constant moisture content, because the saturation capacity shrinks while the actual vapor pressure stays fixed. Saturation (100 percent) is reached at the dew point.

20. Why is the wet-bulb temperature of an unsaturated air sample always lower than its dry-bulb temperature?
    • The wick adds latent heat to the sensor
    • Evaporation of water from the wick removes heat, cooling the wetted sensor
    • Radiation from the surroundings warms the dry-bulb only
    • The wet-bulb sensor measures dew point directly

    Correct answer: Evaporation of water from the wick removes heat, cooling the wetted sensor

    Evaporative cooling at the wetted wick lowers the wet-bulb reading below the dry-bulb whenever the air is unsaturated. As water evaporates it absorbs latent heat from the sensor; only at saturation do the two temperatures coincide.

21. A heating load calculation for a wall uses $U = 0.08\ \text{BTU/(hr} \cdot \text{ft}^{2} \cdot {}^{\circ}\text{F)}$, area $400\ \text{ft}^{2}$, with indoor 70F and outdoor 10F. What is the conductive heat loss through the wall?
    • About 3,200 BTU/hr
    • About 1,920 BTU/hr
    • About 960 BTU/hr
    • About 19,200 BTU/hr

    Correct answer: About 1,920 BTU/hr

    The heat loss is about 1,920 BTU/hr, from $q = U \times A \times \Delta T = 0.08 \times 400 \times (70 - 10)$. Heating load calculations sum such conductive losses across the building envelope at the design temperature difference.

22. In a peak cooling load calculation, why is solar heat gain through glazing typically treated as an instantaneous sensible gain that may peak at a different hour than conduction gains?
    • Solar gain depends on orientation and sun position, so different exposures peak at different times of day
    • Solar gain only contributes to nighttime heat loss
    • Solar gain is constant for all hours and orientations
    • Solar gain is entirely latent and unrelated to time

    Correct answer: Solar gain depends on orientation and sun position, so different exposures peak at different times of day

    Solar gain through glass varies with orientation and solar position, so east, south, and west exposures peak at different hours, which is why the design cooling load is evaluated for the hour producing the maximum total. Conduction gains driven by outdoor temperature peak later in the afternoon.

23. Which factor is included in a cooling load calculation but generally excluded from a winter heating load calculation?
    • Conduction through exterior walls
    • Internal heat gains from people, lights, and equipment as a credit
    • Outdoor design temperature
    • Building floor area

    Correct answer: Internal heat gains from people, lights, and equipment as a credit

    Internal heat gains from occupants, lighting, and equipment are counted in cooling loads but are conservatively excluded (not credited) in a design heating load, since they may be absent during peak heating. Conduction, design temperature, and area appear in both analyses.

24. For the same outdoor air conditions, an evaporative cooler is most effective at lowering dry-bulb temperature when the entering air has which characteristic?
    • A large difference between dry-bulb and wet-bulb temperatures
    • A relative humidity near 100 percent
    • A wet-bulb equal to its dry-bulb
    • A dew point equal to its dry-bulb

    Correct answer: A large difference between dry-bulb and wet-bulb temperatures

    Evaporative cooling works best when the dry-bulb to wet-bulb spread (the wet-bulb depression) is large, indicating dry air with capacity to absorb moisture. Near saturation the spread is small and little cooling is possible.

25. A cooling coil with an apparatus dew point of 52F has a bypass factor of 0.10. Entering air is 80F dry-bulb. What is the approximate leaving-air dry-bulb temperature?
    • About 54.8F
    • About 80F
    • About 52F
    • About 58F

    Correct answer: About 54.8F

    The leaving dry-bulb is about 54.8F, found from t_leave = ADP + BF x (t_enter - ADP) = 52 + 0.10 x (80 - 52). The bypass factor blends the apparatus-dew-point condition with the entering condition to give the actual leaving state.

26. Approximately how many grains of water are in one pound of moisture, a conversion frequently used when reading humidity ratio for latent load calculations?
    • 453.6 grains
    • 1,000 grains
    • 7,000 grains
    • 12,000 grains

    Correct answer: 7,000 grains

    There are 7,000 grains of water per pound, the standard conversion used to switch humidity ratio between pounds and grains per pound of dry air. This conversion underlies the 0.68 grains-based latent load factor.

27. Air at 75F dry-bulb has a humidity ratio of 0.0093 lb water per lb dry air. Approximately what is this humidity ratio expressed in grains of water per pound of dry air?
    • About 13 grains/lb
    • About 65 grains/lb
    • About 130 grains/lb
    • About 9.3 grains/lb

    Correct answer: About 65 grains/lb

    The humidity ratio is about 65 grains/lb, found by multiplying $0.0093\ \text{lb/lb}$ by $7{,}000\ \text{grains/lb}$. Engineers commonly convert to grains so the latent load equation $q = 0.68 \times \text{CFM} \times \Delta\text{grains}$ can be applied directly.

28. Two parallel air handlers discharge into a common plenum: 4,000 CFM at humidity ratio 0.008 and 4,000 CFM at humidity ratio 0.012. What is the mixed humidity ratio?
    • 0.004
    • 0.010
    • 0.012
    • 0.020

    Correct answer: 0.010

    The mixed humidity ratio is 0.010, the flow-weighted average of the two equal streams: $(0.008 + 0.012)/2$. Adiabatic mixing conserves total moisture, so the mixed humidity ratio is the mass-weighted blend of the inlets.

29. Outdoor air at 95F is mixed with return air at 75F in the ratio of 25 percent outdoor to 75 percent return by airflow. What is the mixed dry-bulb temperature entering the coil?
    • About 90F
    • About 85F
    • About 78F
    • About 80F

    Correct answer: About 80F

    The mixed dry-bulb is about 80F, from $0.25 \times 95 + 0.75 \times 75$. The mixed state used to size the cooling coil lies on the line between the outdoor and return states, weighted by the fraction of each airflow.

30. Why does a constant-relative-humidity line of 50 percent curve upward to the right on the psychrometric chart rather than running horizontally?
    • Humidity ratio is independent of temperature
    • Saturation vapor pressure rises with temperature, so holding RH constant requires more moisture at higher dry-bulb
    • The chart axes are logarithmic
    • Relative humidity decreases with added moisture

    Correct answer: Saturation vapor pressure rises with temperature, so holding RH constant requires more moisture at higher dry-bulb

    Because saturation vapor pressure climbs steeply with temperature, maintaining 50 percent relative humidity demands a higher humidity ratio as dry-bulb increases, so the RH line sweeps upward to the right. Relative humidity reflects the ratio to a temperature-dependent saturation value.

31. A total cooling load is 240,000 BTU/hr with a sensible heat ratio of 0.80. What is the latent portion of the load?
    • 300,000 BTU/hr
    • 60,000 BTU/hr
    • 48,000 BTU/hr
    • 192,000 BTU/hr

    Correct answer: 48,000 BTU/hr

    The latent load is 48,000 BTU/hr, since latent equals total minus sensible: $240{,}000 - (0.80 \times 240{,}000)$. An SHR of 0.80 means 20 percent of the total load is latent.

32. What does a steep (nearly vertical) process line on the psychrometric chart indicate about a coil's load?
    • A low sensible heat ratio with a large latent component
    • Pure sensible heating with no moisture change
    • An adiabatic mixing process
    • A sensible heat ratio of exactly 1.0

    Correct answer: A low sensible heat ratio with a large latent component

    A steep process line corresponds to a low sensible heat ratio, meaning a large share of the load is latent (moisture removal). A horizontal line, by contrast, represents pure sensible heat with SHR equal to 1.0.

33. In a heating load calculation, infiltration sensible loss is estimated as $q = 1.08 \times \text{CFM} \times \Delta T$. For 600 CFM of infiltration with a 60F indoor-to-outdoor difference, what is the sensible infiltration loss?
    • About 19,440 BTU/hr
    • About 64,800 BTU/hr
    • About 38,880 BTU/hr
    • About 6,480 BTU/hr

    Correct answer: About 38,880 BTU/hr

    The sensible infiltration loss is about 38,880 BTU/hr, from $1.08 \times 600 \times 60$. Infiltration introduces both sensible and latent loads; the sensible part uses the same 1.08 factor as supply-air heating.

34. Which property line on the psychrometric chart runs nearly parallel to, and is often approximated by, the lines of constant wet-bulb temperature?
    • Constant humidity ratio lines
    • Constant dew-point lines
    • Constant enthalpy lines
    • Constant dry-bulb lines

    Correct answer: Constant enthalpy lines

    Constant-enthalpy lines run nearly parallel to constant-wet-bulb lines, which is why evaporative (constant-wet-bulb) cooling is sometimes approximated as a constant-enthalpy process. The small divergence between them reflects the heat content of the added water.

35. When sizing supply airflow from the room sensible load and a chosen supply-to-room temperature difference, increasing the design temperature difference will do what to the required CFM?
    • Decrease the required CFM
    • Drive CFM to zero
    • Leave CFM unchanged
    • Increase the required CFM

    Correct answer: Decrease the required CFM

    A larger supply-to-room temperature difference decreases the required CFM, since $\text{CFM} = q_{\text{sensible}} / (1.08 \times \Delta T)$. Designers trade larger temperature differences for smaller airflow and duct sizes within comfort limits.

36. For a room held at 70F and 30 percent relative humidity in winter, the dew point is roughly 37F. What practical concern does this dew point most directly govern?
    • The surface temperature below which condensation forms on windows or cold surfaces
    • The boiler combustion efficiency
    • The maximum allowable supply airflow
    • The duct friction rate

    Correct answer: The surface temperature below which condensation forms on windows or cold surfaces

    The dew point sets the surface temperature at which condensation will form, so a 37F dew point means moisture condenses on any surface colder than about 37F, such as a poorly insulated window. Keeping surfaces above the dew point prevents condensation problems.

37. A coil cools and dehumidifies air from 80F dry-bulb / 67F wet-bulb to 55F dry-bulb / 54F wet-bulb. How can the total coil load be most directly determined from the psychrometric chart?
    • By multiplying CFM by the dry-bulb difference only
    • By multiplying mass flow of dry air by the enthalpy difference between entering and leaving states
    • By averaging the entering and leaving relative humidities
    • By dividing the humidity ratio change by the dew point

    Correct answer: By multiplying mass flow of dry air by the enthalpy difference between entering and leaving states

    The total load equals the dry-air mass flow times the enthalpy difference between the entering and leaving states read from the chart. Because enthalpy captures both temperature and moisture content, this single difference includes the sensible and latent portions.

38. At a given dry-bulb temperature, which condition corresponds to the maximum possible humidity ratio the air can hold?
    • Saturation, where relative humidity equals 100 percent
    • Wet-bulb equal to dew point minus 10 degrees
    • Relative humidity of 50 percent
    • Zero humidity ratio

    Correct answer: Saturation, where relative humidity equals 100 percent

    The maximum humidity ratio at a given dry-bulb occurs at saturation, where relative humidity is 100 percent and the air holds all the moisture it can at that temperature. Adding more moisture beyond this point produces condensation.

39. Why must the supply-air condition selected to meet a space load lie on the room's process (condition) line through the room state at the load's sensible heat ratio?
    • So the coil bypass factor becomes zero
    • So that supplying that air drives the room toward its design temperature and humidity simultaneously
    • So that the supply air is always saturated
    • So infiltration is eliminated

    Correct answer: So that supplying that air drives the room toward its design temperature and humidity simultaneously

    The supply air must lie on the room condition line whose slope equals the space SHR so that, as it absorbs the room's sensible and latent gains in the correct proportion, the room is held at its design dry-bulb and humidity. Choosing an off-line supply state would let one of the two conditions drift.

40. A space sensible load is 120,000 BTU/hr. Supply air enters at 58F to a 76F room. Using the sensible relation, what supply airflow is required?
    • About 3,200 CFM
    • About 6,173 CFM
    • About 8,000 CFM
    • About 4,000 CFM

    Correct answer: About 6,173 CFM

    About 6,173 CFM is required, from $\text{CFM} = 120{,}000 / (1.08 \times (76 - 58))$. The 18F supply-to-room difference and the sensible relation set the airflow needed to offset the space sensible gain.

41. How does a sensible-only heating process appear differently from an evaporative-cooling process when traced on the psychrometric chart?
    • Sensible heating moves along constant wet-bulb while evaporative cooling moves horizontally
    • Both follow the saturation curve
    • Both move vertically upward
    • Sensible heating moves horizontally at constant humidity ratio, while evaporative cooling moves up-and-left along a constant wet-bulb line

    Correct answer: Sensible heating moves horizontally at constant humidity ratio, while evaporative cooling moves up-and-left along a constant wet-bulb line

    Sensible heating traces a horizontal path at constant humidity ratio (dry-bulb rising), whereas evaporative cooling rises and moves left along a constant wet-bulb line as moisture is added and dry-bulb drops. The two processes have distinctly different directions and slopes on the chart.

42. Infiltration brings in 500 CFM of outdoor air, raising the space humidity ratio contribution by 20 grains per pound of dry air relative to the room. What latent load does this infiltration impose?
    • About 10,800 BTU/hr
    • About 3,400 BTU/hr
    • About 13,600 BTU/hr
    • About 6,800 BTU/hr

    Correct answer: About 6,800 BTU/hr

    The latent infiltration load is about 6,800 BTU/hr, from $q = 0.68 \times \text{CFM} \times \Delta\text{grains} = 0.68 \times 500 \times 20$. Infiltrating outdoor air adds moisture that must be removed, contributing to the space latent cooling load.

43. A return airstream at enthalpy 30 BTU/lb (12,000 lb/hr) mixes with outdoor air at enthalpy 42 BTU/lb (4,000 lb/hr). What is the mixed-air enthalpy?
    • About 39 BTU/lb
    • About 36 BTU/lb
    • About 33 BTU/lb
    • About 42 BTU/lb

    Correct answer: About 33 BTU/lb

    The mixed enthalpy is about 33 BTU/lb, the mass-weighted average: $(12{,}000 \times 30 + 4{,}000 \times 42)/16{,}000$. Adiabatic mixing conserves total energy, so enthalpy blends in proportion to each stream's dry-air mass flow.

44. During a cooling-and-dehumidifying coil process, why does the wet-bulb temperature of the air decrease even though the process is not purely evaporative?
    • Only dry-bulb changes while wet-bulb is fixed by definition
    • Both sensible heat and moisture (latent heat) are being removed, lowering total heat content
    • Wet-bulb tracks barometric pressure only
    • Moisture is being added to the airstream

    Correct answer: Both sensible heat and moisture (latent heat) are being removed, lowering total heat content

    In cooling and dehumidification both sensible heat and latent heat are removed, which lowers the air's enthalpy and therefore its wet-bulb temperature. Because wet-bulb closely follows enthalpy, removing total heat drives it down.

45. Reheat is applied after a cooling coil to control space humidity. On the psychrometric chart, the reheat step is represented by which movement?
    • A horizontal shift to a higher dry-bulb at constant humidity ratio
    • A move along the saturation curve toward higher enthalpy
    • A constant-wet-bulb move to lower dry-bulb
    • A vertical rise in humidity ratio at constant dry-bulb

    Correct answer: A horizontal shift to a higher dry-bulb at constant humidity ratio

    Reheat adds sensible heat only, so it shifts the state horizontally to a higher dry-bulb at constant humidity ratio. The moisture content set by the cooling coil is preserved while the supply temperature is raised to avoid overcooling.

46. In a direct-expansion (DX) refrigeration system, what is the primary function of the suction line connecting the evaporator to the compressor?
    • Carry low-pressure refrigerant vapor from the evaporator back to the compressor inlet
    • Deliver high-pressure liquid refrigerant to the metering device
    • Return condensate water to the cooling tower
    • Carry high-pressure discharge gas to the condenser

    Correct answer: Carry low-pressure refrigerant vapor from the evaporator back to the compressor inlet

    The suction line carries low-pressure refrigerant vapor from the evaporator outlet back to the compressor inlet. The discharge line carries high-pressure gas to the condenser, and the liquid line feeds the metering device.

47. Why must refrigerant suction lines that rise vertically be sized to maintain a minimum vapor velocity?
    • To prevent water hammer in the vapor line
    • To carry entrained compressor oil up the riser back to the compressor
    • To reduce the refrigerant charge required
    • To keep the discharge temperature below 100F

    Correct answer: To carry entrained compressor oil up the riser back to the compressor

    A minimum velocity in vertical suction risers is needed to entrain and return compressor oil up the riser to the compressor. If velocity is too low, oil collects in the riser and can starve the compressor of lubrication.

48. A two-pipe direct-return hydronic system tends to suffer from which distribution problem compared with a reverse-return arrangement?
    • Excessive air entrainment at the boiler
    • Reverse flow through the expansion tank
    • Unequal flow because terminals nearest the pump have the shortest, lowest-resistance circuit
    • Higher refrigerant migration during shutdown

    Correct answer: Unequal flow because terminals nearest the pump have the shortest, lowest-resistance circuit

    A direct-return system gives the closest terminal the shortest total circuit and least resistance, so it tends to be overflowed while far terminals are starved, requiring balancing valves. A reverse-return layout equalizes total path lengths to self-balance flow.

49. In a reverse-return two-pipe hydronic system, why does flow distribution among terminals become inherently more uniform?
    • The pump head is doubled at each terminal
    • The return water is reheated before each unit
    • Air is automatically vented at every terminal
    • Each terminal sees approximately the same total supply-plus-return path length and pressure drop

    Correct answer: Each terminal sees approximately the same total supply-plus-return path length and pressure drop

    Reverse return routes the return main so that each terminal has nearly the same combined supply-plus-return path length and therefore similar circuit resistance, making flow self-balancing. This reduces the need for extensive balancing valves compared with direct return.

50. What is the main purpose of a four-pipe fan-coil distribution system compared with a two-pipe system?
    • It allows simultaneous heating and cooling to different zones without seasonal changeover
    • It eliminates the need for a chiller
    • It uses refrigerant instead of water
    • It removes the need for a pump

    Correct answer: It allows simultaneous heating and cooling to different zones without seasonal changeover

    A four-pipe system supplies separate chilled-water and hot-water circuits to each coil, so any zone can heat or cool at any time without seasonal changeover. A two-pipe system shares one set of pipes and must switch the whole system between heating and cooling.

51. In a VRF (variable refrigerant flow) heat-recovery system, what allows one zone to be heated while another is simultaneously cooled?
    • Two separate water loops
    • Refrigerant is routed so heat rejected from cooling zones is delivered to heating zones
    • A cooling tower transfers heat between zones
    • Each indoor unit has its own compressor

    Correct answer: Refrigerant is routed so heat rejected from cooling zones is delivered to heating zones

    A VRF heat-recovery system routes refrigerant so heat extracted from zones in cooling mode is transferred to zones calling for heating, often through branch controllers. This simultaneous heating and cooling improves part-load efficiency in buildings with diverse loads.

52. An outdoor-air economizer in an air-handling system reduces mechanical cooling by doing what?
    • Increasing the chilled-water supply temperature
    • Recirculating return air at higher flow
    • Using cool outdoor air to meet some or all of the cooling load when conditions allow
    • Adding moisture to the supply air

    Correct answer: Using cool outdoor air to meet some or all of the cooling load when conditions allow

    An economizer brings in additional cool outdoor air to satisfy cooling needs when outdoor conditions are favorable, reducing or eliminating compressor operation. This free cooling lowers energy use during mild weather.

53. A differential enthalpy economizer control chooses outdoor air over return air based on what comparison?
    • Outdoor dry-bulb versus a fixed 65F setpoint
    • Outdoor relative humidity versus 50 percent
    • Outdoor wet-bulb versus a fixed 55F setpoint
    • Outdoor air total enthalpy versus return air total enthalpy

    Correct answer: Outdoor air total enthalpy versus return air total enthalpy

    A differential enthalpy economizer compares the total enthalpy of outdoor air with that of return air and admits outdoor air only when its enthalpy is lower. This accounts for both temperature and moisture, avoiding bringing in humid air that increases latent load.

54. What is the principal advantage of a low-temperature (cold-air) air distribution system using supply air near 45F instead of 55F?
    • It reduces required airflow and duct size for the same sensible load
    • It eliminates the need for dehumidification
    • It increases fan energy at part load
    • It removes the need for terminal boxes

    Correct answer: It reduces required airflow and duct size for the same sensible load

    Colder supply air carries more sensible cooling per unit of airflow, so the required CFM and duct sizes shrink for the same load. This lowers fan energy and first cost, though it pairs well with ice storage or low chilled-water temperatures.

55. In a dual-duct air system, how is the supply air temperature to a zone controlled?
    • By reheating a single supply stream at each zone
    • By blending air from a separate hot deck and cold deck at a mixing terminal
    • By varying the chilled-water flow to one coil per zone
    • By cycling the central fan on and off

    Correct answer: By blending air from a separate hot deck and cold deck at a mixing terminal

    A dual-duct system delivers separate hot-deck and cold-deck air to each zone, where a mixing box blends the two to meet the zone setpoint. This provides flexible simultaneous heating and cooling but uses more duct space.

56. A multizone air handler differs from a dual-duct system primarily in what way?
    • It uses water instead of air
    • It has no heating coil
    • Hot- and cold-deck air are blended at the central unit by zone dampers, then ducted separately to each zone
    • It cannot provide cooling

    Correct answer: Hot- and cold-deck air are blended at the central unit by zone dampers, then ducted separately to each zone

    In a multizone unit the hot and cold decks are mixed by paired zone dampers at the air handler itself, and a separate single duct then serves each zone. A dual-duct system instead carries both decks out to mixing boxes near the zones.

57. Why is a draw-through air-handler configuration (fan downstream of the cooling coil) more likely to produce condensation on the supply duct than a blow-through arrangement?
    • The fan adds moisture to the air
    • Draw-through units have no cooling coil
    • Blow-through fans run at higher speed
    • The fan heat is added after the coil, so the air leaving the fan is cooler and closer to its dew point than blow-through supply air

    Correct answer: The fan heat is added after the coil, so the air leaving the fan is cooler and closer to its dew point than blow-through supply air

    In draw-through, fan heat is picked up downstream of the coil but is small, so supply air leaves near the coil's cold leaving condition close to saturation, raising condensation risk on duct surfaces. Blow-through adds fan heat before the coil and the supply air is slightly warmer relative to its dew point.

58. In a fan-powered VAV terminal of the series type, how does the terminal fan operate relative to the primary air?
    • It runs continuously, drawing primary air plus induced plenum air through the box
    • It runs only when primary air is shut off
    • It runs only during economizer mode
    • It reverses to exhaust air

    Correct answer: It runs continuously, drawing primary air plus induced plenum air through the box

    A series fan-powered box has its fan in the primary airstream running continuously, mixing variable primary air with induced ceiling-plenum air to deliver a constant volume to the space. A parallel box instead runs its fan only on a call for heating to add plenum air.

59. What is the main reason interior zones of a large building usually require cooling year-round?
    • They have the largest exterior wall area
    • Internal gains from lights, equipment, and people dominate while there is little envelope heat loss
    • They receive the most solar gain
    • They have the highest infiltration

    Correct answer: Internal gains from lights, equipment, and people dominate while there is little envelope heat loss

    Interior zones are isolated from the envelope, so they have minimal heat loss but steady internal gains from lighting, equipment, and occupants, requiring cooling even in winter. Perimeter zones, in contrast, swing between heating and cooling with the weather.

60. A cooling tower rejects heat from a water-cooled chiller condenser primarily by which mechanism?
    • Conduction through the tower walls
    • Radiation to the night sky
    • Evaporation of a small portion of the circulating water into the air
    • Compression of the condenser water

    Correct answer: Evaporation of a small portion of the circulating water into the air

    A cooling tower rejects most heat by evaporating a small fraction of the circulating water, which carries away latent heat and cools the bulk water. Sensible heat transfer to the air is secondary to this evaporative effect.

61. The approach of a cooling tower is defined as which temperature difference?
    • Entering minus leaving condenser water temperature
    • Entering minus leaving air dry-bulb temperature
    • Condenser water minus refrigerant condensing temperature
    • Leaving water temperature minus entering-air wet-bulb temperature

    Correct answer: Leaving water temperature minus entering-air wet-bulb temperature

    Cooling-tower approach is the leaving water temperature minus the entering-air wet-bulb temperature, and a smaller approach means a larger, more effective tower. The range, by contrast, is the entering-minus-leaving water temperature difference.

62. Why can a cooling tower never cool the condenser water below the entering-air wet-bulb temperature?
    • The wet-bulb temperature is the thermodynamic limit for evaporative cooling of the water
    • Because the pump adds heat to the water
    • Because the fan recirculates warm air
    • Because the water flow is too high

    Correct answer: The wet-bulb temperature is the thermodynamic limit for evaporative cooling of the water

    The entering-air wet-bulb temperature is the lowest temperature evaporative cooling can theoretically reach, so the leaving water always remains some approach above it. Real towers leave water several degrees above the wet-bulb due to finite size and contact time.

63. What distinguishes an air-cooled condenser from a water-cooled condenser in a refrigeration plant?
    • An air-cooled condenser uses chilled water
    • An air-cooled condenser rejects heat directly to ambient air without a cooling tower
    • An air-cooled condenser requires a larger pump
    • An air-cooled condenser operates at lower condensing temperatures than water-cooled

    Correct answer: An air-cooled condenser rejects heat directly to ambient air without a cooling tower

    An air-cooled condenser rejects heat directly to ambient air with fans, eliminating the cooling tower, condenser-water pump, and water treatment. Water-cooled condensers generally achieve lower condensing temperatures and higher efficiency but need that supporting water loop.

64. In a primary-secondary chilled-water system, the decoupler (common pipe) allows what operating condition?
    • Constant flow through both loops at all times
    • Refrigerant to bypass the chiller
    • The primary (production) loop and secondary (distribution) loop to operate at different flow rates hydraulically isolated from each other
    • The cooling tower to bypass the condenser

    Correct answer: The primary (production) loop and secondary (distribution) loop to operate at different flow rates hydraulically isolated from each other

    The decoupler pipe hydraulically separates the constant-flow primary chiller loop from the variable-flow secondary distribution loop, letting each run at its own flow. Excess or deficit flow passes through the common pipe without forcing the two loops to match.

65. What problem can occur in a primary-secondary chilled-water system if secondary flow exceeds primary flow?
    • The expansion tank overflows
    • The chiller trips on low refrigerant
    • The cooling tower freezes
    • Warm return water mixes backward through the decoupler, raising supply temperature to the coils

    Correct answer: Warm return water mixes backward through the decoupler, raising supply temperature to the coils

    When secondary demand exceeds primary production, return water flows backward through the decoupler and blends with chiller supply, raising the chilled-water temperature delivered to the coils. This loss of supply temperature reduces coil capacity and is a sign more chiller flow is needed.

66. A constant-volume reheat system controls space temperature in cooling-dominated buildings by doing what?
    • Cooling all supply air centrally, then reheating it at each zone to meet the zone load
    • Varying the supply airflow to each zone
    • Cycling the cooling coil on and off per zone
    • Mixing hot and cold decks at the zone

    Correct answer: Cooling all supply air centrally, then reheating it at each zone to meet the zone load

    A constant-volume reheat system cools all the air to a low central temperature for the highest load, then adds reheat at each zone terminal to avoid overcooling lighter-load zones. It provides excellent control but is energy-intensive because it cools then reheats.

67. Why does a single-zone constant-volume system provide poor comfort when serving multiple rooms with different loads?
    • It has no cooling coil
    • It supplies one common air temperature and volume controlled from a single thermostat
    • It uses too little outdoor air
    • It reheats every zone independently

    Correct answer: It supplies one common air temperature and volume controlled from a single thermostat

    A single-zone system delivers one supply temperature and airflow set by one thermostat, so rooms with loads different from the control point are over- or under-conditioned. Multiple-zone systems add terminal control to address differing loads.

68. In a thermal energy (ice) storage system, why is ice typically made at night?
    • Outdoor air is more humid at night
    • Compressors cannot run during the day
    • To shift the cooling-generation electrical demand to off-peak hours and lower demand charges
    • Daytime water is too cold

    Correct answer: To shift the cooling-generation electrical demand to off-peak hours and lower demand charges

    Ice storage charges at night using off-peak, lower-cost electricity and then melts the ice during the day to meet cooling loads, shifting demand off the peak period. This reduces peak electrical demand charges and can downsize daytime chiller capacity.

69. What is the function of a duct smoke detector in a supply air system?
    • Measure supply air temperature
    • Control the economizer dampers
    • Balance the airflow between zones
    • Sense smoke in the airstream and shut down the air handler to limit smoke spread through ductwork

    Correct answer: Sense smoke in the airstream and shut down the air handler to limit smoke spread through ductwork

    A duct smoke detector senses products of combustion in the airstream and signals the unit to shut down so the HVAC system does not distribute smoke through the building. It is a life-safety control required by code on many air-handling systems.

70. A fire damper in a duct that penetrates a fire-rated wall performs what action during a fire?
    • Closes to maintain the fire-resistance rating of the barrier the duct penetrates
    • Increases airflow to pressurize the space
    • Opens fully to vent smoke
    • Modulates to control temperature

    Correct answer: Closes to maintain the fire-resistance rating of the barrier the duct penetrates

    A fire damper closes automatically, typically when a fusible link melts, to restore the integrity of the rated wall or floor the duct passes through. This prevents fire from spreading through the duct opening in the barrier.

71. In a laboratory exhaust system, why must the exhaust ductwork downstream of a fume hood generally be kept under negative pressure?
    • To increase the fan efficiency
    • So any leaks draw room air inward rather than leaking contaminated air into occupied spaces
    • To reduce the duct size
    • To allow heat recovery

    Correct answer: So any leaks draw room air inward rather than leaking contaminated air into occupied spaces

    Keeping contaminated lab exhaust ductwork under negative pressure ensures that any leakage is inward, preventing hazardous exhaust from escaping into occupied areas. This is why the exhaust fan is located at the discharge end, downstream of the duct run.

72. What is the main purpose of a high-plume (high-velocity) laboratory exhaust stack discharge?
    • To reduce fan energy
    • To dehumidify the exhaust
    • To project exhaust high enough to avoid re-entrainment into building air intakes
    • To recover heat from the exhaust

    Correct answer: To project exhaust high enough to avoid re-entrainment into building air intakes

    A high-plume stack discharges exhaust at high velocity to loft the plume above the building's recirculation zone, preventing contaminated air from being drawn back into outdoor-air intakes. Dilution with bypass air often accompanies this to manage capture concerns.

73. Demand-controlled ventilation typically modulates outdoor air based on what measured indicator of occupancy?
    • Supply air temperature
    • Duct static pressure
    • Chilled-water flow
    • Indoor carbon dioxide concentration

    Correct answer: Indoor carbon dioxide concentration

    Demand-controlled ventilation uses indoor CO2 concentration as a proxy for occupancy to modulate outdoor-air intake, supplying more ventilation when more people are present. This saves conditioning energy during low occupancy while maintaining indoor air quality.

74. Under ASHRAE Standard 62.1 ventilation-rate procedure, the required outdoor air for a zone is based on which combination?
    • A per-person rate plus a per-unit-floor-area rate
    • Supply air temperature and humidity
    • Duct velocity and length
    • Cooling load and fan power

    Correct answer: A per-person rate plus a per-unit-floor-area rate

    The ventilation-rate procedure sums a people-based outdoor-air component and an area-based component to set the breathing-zone outdoor airflow. These two terms account for occupant-generated and building-generated contaminants respectively.

75. Why is a relief (barometric or powered) air path required when an air handler operates in economizer mode at high outdoor-air fractions?
    • To add humidity to the space
    • To exhaust the excess air introduced so the building does not become over-pressurized
    • To preheat the outdoor air
    • To increase chilled-water flow

    Correct answer: To exhaust the excess air introduced so the building does not become over-pressurized

    When large quantities of outdoor air are admitted in economizer mode, an equal amount of air must be relieved or exhausted to avoid over-pressurizing the building. Relief dampers or powered exhaust fans maintain the building pressure balance.

76. A radiant floor heating system delivers heat to a space primarily by which mode?
    • Forced convection from supply diffusers
    • Evaporative cooling
    • Radiant and natural-convective heat transfer from a warm floor surface
    • Conduction through the building envelope

    Correct answer: Radiant and natural-convective heat transfer from a warm floor surface

    A radiant floor warms occupants and surfaces mainly by thermal radiation from the heated floor, supplemented by gentle natural convection. This allows comfort at a lower air temperature because mean radiant temperature is raised.

77. A chilled-beam system provides space cooling mainly through what process at the beam?
    • Compression refrigeration at each beam
    • Direct evaporative cooling of room air
    • Electric resistance cooling
    • Room air is cooled by a water coil and circulated by buoyancy (passive) or induced primary air (active)

    Correct answer: Room air is cooled by a water coil and circulated by buoyancy (passive) or induced primary air (active)

    Chilled beams cool room air with a water coil; passive beams rely on natural convection while active beams induce room air using primary supply air. Because they move heat with water and modest airflow, they reduce fan energy and duct size.

78. Why must chilled-beam and radiant-cooling surface temperatures be kept above the space dew point?
    • To prevent condensation from forming on the cooling surface
    • To increase cooling capacity
    • To reduce pump energy
    • To raise the room humidity

    Correct answer: To prevent condensation from forming on the cooling surface

    If the cooling surface drops below the room dew point, moisture condenses on it, causing dripping and potential damage. Designers keep chilled-water temperature high enough, and control space humidity, so surfaces stay above dew point.

79. In a steam heating distribution system, what is the primary purpose of a steam trap at the end of a coil or main?
    • Increase steam pressure
    • Discharge condensate and air while preventing the passage of live steam
    • Add water to the boiler
    • Reduce the steam temperature

    Correct answer: Discharge condensate and air while preventing the passage of live steam

    A steam trap automatically removes condensate and noncondensable air from the system while holding back live steam so energy is not wasted. Proper trap operation keeps coils full of steam and free of waterlogging.

80. Why is condensate returned to the boiler in a steam system rather than discharged to drain?
    • It is contaminated and must be diluted
    • It increases the steam pressure
    • It is hot, treated water, so returning it conserves energy and treated makeup water
    • It cools the boiler

    Correct answer: It is hot, treated water, so returning it conserves energy and treated makeup water

    Condensate is already hot and chemically treated, so returning it to the boiler saves the heat and the treated water that would otherwise be lost. This improves overall steam-system efficiency and reduces makeup water treatment.

81. A dedicated outdoor air system (DOAS) is typically paired with parallel sensible cooling devices because the DOAS handles which part of the load?
    • All of the sensible load
    • Only the radiant heat gain
    • Only the duct friction losses
    • The ventilation air and most of the latent (dehumidification) load

    Correct answer: The ventilation air and most of the latent (dehumidification) load

    A DOAS conditions and dehumidifies the outdoor ventilation air, taking on most of the latent load, while separate equipment such as chilled beams or fan coils handles the space sensible load. Decoupling ventilation from sensible cooling improves humidity control and efficiency.

82. What is the purpose of a balancing valve in a hydronic terminal branch?
    • Add resistance so the branch receives its design flow rather than too much
    • Stop reverse flow
    • Vent air from the branch
    • Reduce the water temperature

    Correct answer: Add resistance so the branch receives its design flow rather than too much

    A balancing valve adds adjustable resistance to a branch so it draws its intended design flow instead of being over- or under-supplied relative to other branches. Balancing distributes flow correctly across all terminals in the loop.

83. Why are air separators and high-point vents installed in closed hydronic loops?
    • To pressurize the expansion tank
    • To remove entrained and dissolved air that would otherwise cause noise, corrosion, and poor heat transfer
    • To add chemical treatment
    • To increase pump head

    Correct answer: To remove entrained and dissolved air that would otherwise cause noise, corrosion, and poor heat transfer

    Air separators and high-point automatic vents collect and expel air that becomes trapped in the loop, since air pockets cause flow noise, corrosion, and reduced coil performance. Removing air also prevents air-bound circuits that block flow.

84. In a variable-flow chilled-water system using two-way control valves, how does plant flow respond as coil loads drop?
    • Flow stays constant
    • Three-way valves bypass all water
    • Two-way valves throttle, reducing system flow so variable-speed pumps can slow down
    • Flow increases to maintain temperature

    Correct answer: Two-way valves throttle, reducing system flow so variable-speed pumps can slow down

    As loads fall, two-way coil valves throttle and reduce total system flow, allowing variable-speed pumps to slow and save energy. This is the basis of variable-primary or variable-secondary flow distribution.

85. Why does replacing three-way coil valves with two-way valves improve pumping energy in a distribution system?
    • Two-way valves bypass water at part load
    • Two-way valves increase the head loss to the pump
    • Two-way valves require larger pipes
    • Two-way valves reduce flow at part load, letting pump power fall, whereas three-way valves keep flow nearly constant

    Correct answer: Two-way valves reduce flow at part load, letting pump power fall, whereas three-way valves keep flow nearly constant

    Two-way valves cut flow as loads decrease, so a variable-speed pump can reduce speed and power, while three-way valves maintain near-constant flow by bypassing, wasting pump energy. Variable flow with two-way valves captures the affinity-law savings.

86. What does a building automation system (BAS) most directly provide for HVAC distribution systems?
    • Centralized monitoring and control of equipment, setpoints, and schedules
    • Mechanical refrigeration
    • Structural support for ductwork
    • Water treatment chemicals

    Correct answer: Centralized monitoring and control of equipment, setpoints, and schedules

    A BAS centrally monitors and controls HVAC equipment, adjusting setpoints, schedules, and sequences for efficient operation. It enables strategies like optimum start, demand control, and economizer logic across the distribution system.

87. An optimum-start control sequence saves energy by doing what?
    • Running equipment continuously overnight
    • Delaying equipment start to the latest time that still reaches setpoint by occupancy, based on conditions
    • Starting all equipment at full capacity at midnight
    • Shutting off ventilation during occupancy

    Correct answer: Delaying equipment start to the latest time that still reaches setpoint by occupancy, based on conditions

    Optimum start computes the latest time the system can begin warming up or cooling down and still reach setpoint by the occupied period, minimizing unoccupied run time. It adapts the lead time to building conditions and outdoor weather.

88. Why is supply-air temperature reset used on a VAV air-handling system at part load?
    • To increase humidity
    • To lower the chilled-water flow to zero
    • To raise supply temperature when cooling demand is low, reducing reheat and improving comfort
    • To increase duct static pressure

    Correct answer: To raise supply temperature when cooling demand is low, reducing reheat and improving comfort

    Supply-air temperature reset raises the supply temperature when zone cooling demand drops, which reduces simultaneous cooling and reheat energy and improves ventilation distribution. The reset is limited so the highest-load zone is still satisfied.

89. Duct static-pressure reset on a VAV system lowers fan energy by doing what?
    • Increasing the static-pressure setpoint at all times
    • Closing all VAV boxes simultaneously
    • Bypassing the supply fan
    • Reducing the duct static-pressure setpoint until the most-open VAV box is nearly fully open

    Correct answer: Reducing the duct static-pressure setpoint until the most-open VAV box is nearly fully open

    Static-pressure reset lowers the duct pressure setpoint until at least one VAV damper is near fully open, ensuring the fan produces only the pressure actually needed. Because fan power rises steeply with pressure, this saves significant energy at part load.

90. In a refrigeration system, the liquid line should be sized to avoid which condition that would impair the metering device?
    • Flash gas forming from too much pressure drop or subcooling loss in the liquid line
    • Excessive oil return
    • Water hammer
    • Excessive superheat

    Correct answer: Flash gas forming from too much pressure drop or subcooling loss in the liquid line

    If the liquid line has too much pressure drop or the liquid is not adequately subcooled, refrigerant can flash to vapor before the metering device, reducing capacity and causing erratic feeding. Proper sizing and subcooling keep the line full of liquid to the expansion device.

91. A double suction riser in a refrigeration system is used to address what part-load problem?
    • Excessive condensing pressure
    • Maintaining adequate vapor velocity for oil return when the system unloads to low capacity
    • Preventing liquid slugging at the condenser
    • Reducing compressor superheat

    Correct answer: Maintaining adequate vapor velocity for oil return when the system unloads to low capacity

    A double suction riser provides a small riser that maintains velocity at minimum load for oil return, while a larger parallel riser carries the added vapor at full load with acceptable pressure drop. This keeps oil moving back to the compressor across the capacity range.

92. Why are perimeter heating elements such as baseboard or fin-tube placed along exterior walls and under windows?
    • To reduce the supply airflow
    • To dehumidify the space
    • To counteract downdrafts and offset envelope heat loss where it is greatest
    • To provide ventilation air

    Correct answer: To counteract downdrafts and offset envelope heat loss where it is greatest

    Perimeter heat placed under windows and along exterior walls counters the cold downdraft and offsets the heat loss concentrated at the envelope, improving comfort. This placement neutralizes the coldest surfaces directly at their source.

93. What is the main distribution benefit of a constant-volume single-duct system with zone reheat over a basic single-zone system?
    • Lower energy use
    • Elimination of the cooling coil
    • No need for a fan
    • Independent temperature control of multiple zones from one air handler

    Correct answer: Independent temperature control of multiple zones from one air handler

    Adding zone reheat to a single-duct constant-volume system lets each zone hold its own setpoint from a single central air handler, unlike a single-zone system serving one control point. The tradeoff is higher energy from cooling then reheating.

94. In a refrigeration system serving multiple evaporators at the same temperature, why is an evaporator pressure regulator (EPR) used on a warmer coil?
    • To raise that coil's pressure and keep it from running colder than the others
    • To increase the compressor discharge pressure
    • To meter liquid into the coil
    • To remove oil from the coil

    Correct answer: To raise that coil's pressure and keep it from running colder than the others

    An evaporator pressure regulator holds a minimum pressure on a warmer evaporator so it does not cool below its setpoint while sharing a compressor with colder coils. It throttles the suction from that coil to maintain the desired higher saturation temperature.

95. A building exhaust system removing 8,000 CFM with only 6,000 CFM of supply makeup air will tend to create what condition?
    • A net positive building pressure
    • A net negative building pressure that draws in uncontrolled infiltration
    • Perfectly balanced pressure
    • No effect on building pressure

    Correct answer: A net negative building pressure that draws in uncontrolled infiltration

    Exhausting more air than is supplied creates a net negative building pressure, which pulls in uncontrolled infiltration through cracks and doors. Proper makeup air must be provided to balance the exhaust and maintain intended pressurization.

96. In a vapor-compression refrigeration cycle, which component raises the refrigerant pressure and temperature between the evaporator and condenser?
    • Compressor
    • Expansion valve
    • Condenser
    • Receiver

    Correct answer: Compressor

    The compressor raises the refrigerant from low evaporator pressure to high condenser pressure, also increasing its temperature so heat can be rejected in the condenser. The expansion valve performs the opposite pressure-reducing role.

97. What is the function of the metering (expansion) device in a refrigeration system?
    • Compress the refrigerant vapor
    • Reduce the high-pressure liquid to low pressure, causing it to begin boiling in the evaporator
    • Reject heat to the surroundings
    • Separate oil from the refrigerant

    Correct answer: Reduce the high-pressure liquid to low pressure, causing it to begin boiling in the evaporator

    The metering device drops high-pressure subcooled liquid to the low evaporator pressure, where the refrigerant flashes and begins absorbing heat. It also regulates the refrigerant flow into the evaporator.

98. A thermostatic expansion valve (TXV) controls refrigerant flow to maintain what condition at the evaporator outlet?
    • Constant subcooling
    • Constant condensing pressure
    • Constant superheat
    • Constant mass flow regardless of load

    Correct answer: Constant superheat

    A TXV modulates refrigerant flow to hold a relatively constant superheat at the evaporator outlet, ensuring the coil is well used without flooding the compressor with liquid. The sensing bulb at the suction line drives this control.

99. Refrigerant superheat is best defined as which quantity?
    • The temperature of the liquid below its saturation temperature
    • The difference between condensing and evaporating temperature
    • The pressure drop across the compressor
    • The temperature of the vapor above its saturation temperature at that pressure

    Correct answer: The temperature of the vapor above its saturation temperature at that pressure

    Superheat is the number of degrees the refrigerant vapor is above its saturation (boiling) temperature at the existing pressure. It confirms the refrigerant has fully evaporated, protecting the compressor from liquid.

100. Refrigerant subcooling at the condenser outlet refers to which condition?
     • Liquid cooled below its saturation temperature at that pressure
     • Vapor above saturation temperature
     • A two-phase mixture at the metering device
     • Vapor at the compressor discharge

     Correct answer: Liquid cooled below its saturation temperature at that pressure

     Subcooling is the number of degrees the liquid leaving the condenser is below its saturation temperature at that pressure. Subcooling ensures solid liquid reaches the metering device and prevents premature flashing.

101. The coefficient of performance (COP) of a refrigeration cycle in cooling mode is defined as which ratio?
     • Heat rejected divided by compressor work
     • Refrigeration effect (heat absorbed) divided by compressor work input
     • Compressor work divided by heat absorbed
     • Condenser heat divided by evaporator heat

     Correct answer: Refrigeration effect (heat absorbed) divided by compressor work input

     Cooling COP equals the useful refrigeration effect absorbed in the evaporator divided by the compressor work input. A higher COP means more cooling per unit of energy consumed.

102. A chiller has a cooling capacity of 200 tons while consuming 240 kW. Approximately what is its efficiency in kW per ton?
     • 0.83 kW/ton
     • 2.0 kW/ton
     • 1.2 kW/ton
     • 0.6 kW/ton

     Correct answer: 1.2 kW/ton

     The efficiency is 1.2 kW/ton, found by dividing 240 kW by 200 tons. Lower kW/ton indicates a more efficient chiller, and this metric is widely used to compare large cooling equipment.

103. One ton of refrigeration is equivalent to which rate of heat removal?
     • 3,412 BTU/hr
     • 1,000 BTU/hr
     • 33,475 BTU/hr
     • 12,000 BTU/hr

     Correct answer: 12,000 BTU/hr

     One ton of refrigeration equals 12,000 BTU/hr, the rate of heat needed to melt one ton of ice in 24 hours. This unit is standard for rating cooling equipment.

104. A centrifugal chiller compressor is best suited for which application compared with a reciprocating compressor?
     • Large-capacity cooling with high flow and relatively low compression ratio
     • Very small residential systems
     • High compression ratio at very low flow
     • Variable refrigerant flow only

     Correct answer: Large-capacity cooling with high flow and relatively low compression ratio

     Centrifugal compressors excel at large cooling capacities with high refrigerant flow and moderate compression ratios, making them common in big chiller plants. Reciprocating compressors suit smaller capacities and can handle higher compression ratios.

105. What characteristic distinguishes a scroll compressor from a reciprocating compressor?
     • It uses pistons and valves
     • It compresses refrigerant between two interleaved spiral scrolls with few moving parts
     • It requires a cooling tower
     • It cannot be hermetically sealed

     Correct answer: It compresses refrigerant between two interleaved spiral scrolls with few moving parts

     A scroll compressor uses one orbiting and one fixed spiral scroll to progressively compress refrigerant, with fewer moving parts and smoother, quieter operation than a reciprocating piston unit. This improves reliability and efficiency at typical comfort-cooling capacities.

106. A screw compressor controls capacity at part load most commonly by which means?
     • Cycling on and off
     • Throttling the suction with a damper
     • A slide valve that varies the effective compression length
     • Adding refrigerant charge

     Correct answer: A slide valve that varies the effective compression length

     Rotary screw compressors use a slide valve to vary the effective rotor compression length, providing smooth capacity modulation at part load. This avoids the inefficiency of frequent on-off cycling.

107. In an absorption chiller, what drives the refrigeration effect instead of a mechanical compressor?
     • An electric resistance heater only
     • A cooling tower fan
     • A centrifugal pump alone
     • A heat source (such as steam or hot water) that regenerates the absorbent solution

     Correct answer: A heat source (such as steam or hot water) that regenerates the absorbent solution

     An absorption chiller uses a thermal energy source to boil refrigerant out of an absorbent solution in the generator, replacing the mechanical compressor with a heat-driven process. Common pairs are lithium bromide and water, or water and ammonia.

108. In a lithium-bromide absorption chiller, which fluid serves as the refrigerant?
     • Water
     • Lithium bromide
     • Ammonia
     • R-134a

     Correct answer: Water

     In a lithium-bromide absorption machine, water is the refrigerant and lithium bromide is the absorbent. The water evaporates at very low pressure to provide cooling and is then reabsorbed into the salt solution.

109. What is the primary purpose of an evaporator coil in a DX air-conditioning system?
     • Reject heat to outdoor air
     • Absorb heat from the air being conditioned as the refrigerant boils
     • Raise the refrigerant pressure
     • Subcool the liquid refrigerant

     Correct answer: Absorb heat from the air being conditioned as the refrigerant boils

     The evaporator coil absorbs heat from the conditioned airstream as low-pressure refrigerant boils inside the tubes, cooling and often dehumidifying the air. This is where the useful refrigeration effect occurs.

110. Why are heat-transfer coils fitted with fins on the air side?
     • To reduce refrigerant charge
     • To strengthen the tubes
     • To increase the air-side surface area and improve heat transfer where the air film resistance is high
     • To reduce the water-side pressure drop

     Correct answer: To increase the air-side surface area and improve heat transfer where the air film resistance is high

     Fins greatly expand the air-side surface area to compensate for the air's poor heat-transfer coefficient, boosting overall coil performance. The dominant resistance is on the air side, so adding air-side area is most effective.

111. A counterflow heat exchanger generally achieves what compared with a parallel-flow exchanger of the same size?
     • A smaller log-mean temperature difference and less heat transfer
     • Identical performance
     • No temperature change in either stream
     • A larger effective temperature difference and greater heat transfer

     Correct answer: A larger effective temperature difference and greater heat transfer

     Counterflow maintains a more uniform and larger temperature difference along its length, yielding a higher log-mean temperature difference and better heat transfer than parallel flow for the same area. This is why counterflow is preferred in most HVAC heat exchangers.

112. The log-mean temperature difference (LMTD) is used in heat-exchanger sizing because temperature difference between streams does what along the exchanger?
     • Varies along the length, so an averaged driving force is needed
     • Stays constant
     • Drops to zero immediately
     • Reverses direction

     Correct answer: Varies along the length, so an averaged driving force is needed

     Because the temperature difference between the two streams changes along the exchanger, the LMTD provides the correct effective average driving force for the q = U × A × LMTD relation. Using a simple arithmetic average would misstate the heat transfer.

113. A shell-and-tube heat exchanger transfers q = U × A × LMTD. If fouling builds up on the tubes over time, what happens to U and the heat transfer?
     • U increases and heat transfer rises
     • U decreases and heat transfer falls for the same area and LMTD
     • U is unaffected
     • LMTD drops to zero

     Correct answer: U decreases and heat transfer falls for the same area and LMTD

     Fouling adds thermal resistance, lowering the overall heat-transfer coefficient U and reducing heat transfer for the same area and temperature difference. This is why fouling factors are included in design and why tubes are cleaned periodically.

114. What is the main function of a refrigerant receiver in a system?
     • Compress the vapor
     • Reject heat to the air
     • Store liquid refrigerant to accommodate charge variation between operating conditions
     • Meter refrigerant into the evaporator

     Correct answer: Store liquid refrigerant to accommodate charge variation between operating conditions

     A receiver stores liquid refrigerant downstream of the condenser, accommodating charge differences as operating conditions change and ensuring a solid liquid supply to the metering device. It acts as a reservoir for the high side of the system.

115. A suction-line accumulator protects the compressor by performing what function?
     • Adding superheat to the discharge gas
     • Storing high-pressure liquid
     • Increasing condensing pressure
     • Trapping liquid refrigerant from the suction line so it does not slug the compressor

     Correct answer: Trapping liquid refrigerant from the suction line so it does not slug the compressor

     A suction accumulator catches any liquid refrigerant returning in the suction line and meters it back as vapor, preventing liquid slugging that can damage the compressor. It is common on heat pumps where flooded returns can occur.

116. A filter-drier installed in the liquid line serves which two purposes?
     • Remove moisture and filter out particulate contaminants
     • Add oil and superheat
     • Increase pressure and flow
     • Cool and subcool the refrigerant

     Correct answer: Remove moisture and filter out particulate contaminants

     A filter-drier removes moisture, which can form acids or freeze at the metering device, and traps solid contaminants that could plug valves. It protects the system from the damaging effects of water and debris.

117. In a heat pump, what is the purpose of the reversing (four-way) valve?
     • Meter the refrigerant
     • Reverse refrigerant flow so the indoor coil serves as evaporator in cooling and condenser in heating
     • Remove moisture from the refrigerant
     • Store excess liquid

     Correct answer: Reverse refrigerant flow so the indoor coil serves as evaporator in cooling and condenser in heating

     The reversing valve switches the refrigerant flow direction so the same coils swap roles between cooling and heating modes. This lets one machine provide both functions by changing which coil rejects and which absorbs heat.

118. An air-source heat pump's heating capacity drops as outdoor temperature falls primarily because of what?
     • The reversing valve fails
     • The indoor fan slows down
     • Lower outdoor temperature reduces evaporator suction pressure and refrigerant mass flow
     • The compressor oil thins

     Correct answer: Lower outdoor temperature reduces evaporator suction pressure and refrigerant mass flow

     As outdoor air cools, the outdoor coil (acting as evaporator in heating) sees lower suction pressure, reducing refrigerant density and mass flow, so heating capacity falls just as the building load rises. Supplemental heat is often needed at low temperatures.

119. Why does an air-source heat pump require a defrost cycle in cold, humid weather?
     • To dehumidify the indoor air
     • To increase refrigerant charge
     • To cool the compressor
     • Frost forms on the cold outdoor coil and must be melted to restore heat transfer

     Correct answer: Frost forms on the cold outdoor coil and must be melted to restore heat transfer

     When the outdoor coil operates below freezing, moisture from the air frosts on it, insulating the coil and reducing capacity, so a periodic defrost cycle melts the frost. Defrost typically reverses to cooling mode briefly while energizing supplemental heat.

120. A centrifugal fan with backward-inclined blades is generally selected over forward-curved blades when which characteristic is important?
     • Higher efficiency and a non-overloading horsepower characteristic
     • Lowest possible first cost
     • Smallest physical size
     • Lowest tip speed

     Correct answer: Higher efficiency and a non-overloading horsepower characteristic

     Backward-inclined fans are more efficient and have a non-overloading power curve, so brake horsepower does not run away as airflow increases. Forward-curved fans are smaller and cheaper but less efficient and can overload at high flow.

121. What does the brake horsepower of a fan represent?
     • The air power delivered to the airstream only
     • The actual shaft power input required to drive the fan, including its inefficiency
     • The motor nameplate power
     • The static pressure times area

     Correct answer: The actual shaft power input required to drive the fan, including its inefficiency

     Brake horsepower is the shaft power the motor must deliver to the fan, equal to the useful air power divided by the fan efficiency. It is always greater than the air power because of fan losses.

122. A pump operating far to the right of its best-efficiency point on its curve is likely to experience which problem?
     • Excessive head and overheating
     • Zero flow
     • Low NPSH margin and possible cavitation along with low efficiency
     • Reverse rotation

     Correct answer: Low NPSH margin and possible cavitation along with low efficiency

     Running far right of the best-efficiency point means high flow and low head, which raises NPSH required and can cause cavitation, plus the pump operates inefficiently. Selecting near the best-efficiency point improves reliability and energy use.

123. Two identical pumps connected in series produce what combined characteristic compared with one pump?
     • Same head, double the flow
     • Half the head
     • No change in head or flow
     • Approximately double the head at a given flow

     Correct answer: Approximately double the head at a given flow

     Pumps in series add their heads at a given flow, roughly doubling the head capability for identical pumps. Pumps in parallel instead add flows at a given head.

124. What is the primary purpose of a boiler economizer?
     • Recover heat from the flue gas to preheat the boiler feedwater and improve efficiency
     • Reduce the boiler water level
     • Increase the stack temperature
     • Add chemicals to the water

     Correct answer: Recover heat from the flue gas to preheat the boiler feedwater and improve efficiency

     A boiler economizer extracts heat from the outgoing flue gas to preheat feedwater, reducing the fuel needed to make steam or hot water. Lowering the stack temperature recovers energy that would otherwise be lost.

125. A condensing boiler achieves higher efficiency than a conventional boiler mainly because it does what?
     • Burns fuel at higher temperature
     • Condenses water vapor in the flue gas, recovering latent heat of vaporization
     • Operates at higher water pressure
     • Uses no combustion air

     Correct answer: Condenses water vapor in the flue gas, recovering latent heat of vaporization

     A condensing boiler cools the flue gas enough to condense its water vapor, recovering the latent heat that a conventional boiler sends up the stack. This requires low return-water temperatures to keep the heat exchanger below the flue-gas dew point.

126. Why must condensing boilers be supplied with relatively low return-water temperatures to realize their efficiency advantage?
     • To prevent the burner from overheating
     • To raise the stack temperature
     • Return water must be below the flue-gas dew point for the vapor to condense on the heat exchanger
     • To reduce the combustion air requirement

     Correct answer: Return water must be below the flue-gas dew point for the vapor to condense on the heat exchanger

     Condensation, and the latent heat recovery it provides, only occurs when the heat-exchanger surface is below the flue-gas dew point, which requires low return-water temperatures. High return temperatures keep the boiler out of the condensing regime and its efficiency falls.

127. Excess air in a combustion process is provided for what main reason?
     • To increase the flame temperature
     • To reduce the stack temperature
     • To eliminate carbon dioxide formation
     • To ensure complete combustion of the fuel beyond the stoichiometric requirement

     Correct answer: To ensure complete combustion of the fuel beyond the stoichiometric requirement

     Excess air above the stoichiometric amount ensures complete combustion, minimizing unburned fuel and carbon monoxide. Too much excess air, however, carries heat up the stack and lowers efficiency, so it is optimized.

128. A high-efficiency particulate air (HEPA) filter is defined by removing what minimum fraction of the most penetrating particle size?
     • 99.97 percent of 0.3-micron particles
     • 85 percent
     • 50 percent
     • 99.97 percent of 10-micron particles

     Correct answer: 99.97 percent of 0.3-micron particles

     A HEPA filter removes at least 99.97 percent of particles at the most-penetrating 0.3-micron size, making it suitable for cleanrooms and critical filtration. The 0.3-micron size is used because it is the hardest to capture.

129. The MERV rating of an air filter indicates what?
     • Its pressure drop only
     • Its minimum particle-removal efficiency across defined particle size ranges
     • Its physical dimensions
     • Its airflow capacity

     Correct answer: Its minimum particle-removal efficiency across defined particle size ranges

     MERV (Minimum Efficiency Reporting Value) rates a filter by its minimum efficiency at capturing particles in standardized size ranges, with higher numbers capturing smaller particles. It lets designers compare filters on a consistent basis.

130. As an air filter loads with dust during service, what happens to its pressure drop and the fan it serves?
     • Pressure drop falls and airflow rises
     • Pressure drop is unaffected
     • Pressure drop rises, increasing fan energy or reducing airflow until the filter is changed
     • The fan stops automatically

     Correct answer: Pressure drop rises, increasing fan energy or reducing airflow until the filter is changed

     Dust accumulation increases the filter's resistance, raising pressure drop, which forces the fan to work harder or reduces delivered airflow until the filter is replaced. Final pressure drop is the usual trigger for filter changeout.

131. A humidifier that injects steam directly into the supply air provides humidification with what effect on dry-bulb temperature?
     • A large drop in dry-bulb temperature
     • A large rise in dry-bulb temperature
     • A drop to the dew point
     • Little change in dry-bulb temperature, essentially isothermal humidification

     Correct answer: Little change in dry-bulb temperature, essentially isothermal humidification

     Steam humidification adds moisture that already carries its latent heat, so it raises humidity ratio with little change in dry-bulb temperature, nearly isothermal on the chart. Evaporative (water-spray) humidification, by contrast, cools the air as it humidifies.

132. What is the main purpose of a variable-frequency drive (VFD) on a fan or pump motor?
     • Vary motor speed to match output to load and save energy at part load
     • Increase the motor voltage
     • Convert AC to DC permanently
     • Eliminate the need for a motor starter

     Correct answer: Vary motor speed to match output to load and save energy at part load

     A VFD adjusts the motor's frequency and speed so a fan or pump delivers only the flow needed, capturing the cubic energy savings of the affinity laws at part load. It also provides soft starting and reduces inrush current.

133. A cooling-coil's apparatus dew point being higher than the required leaving condition usually indicates what about the coil selection?
     • The coil has too many rows or too low a surface temperature
     • The coil cannot achieve the required dehumidification and needs more rows or colder water
     • The coil is oversized for sensible cooling
     • The bypass factor is zero

     Correct answer: The coil cannot achieve the required dehumidification and needs more rows or colder water

     If the achievable apparatus dew point is too high to reach the required leaving humidity, the coil lacks sufficient surface and must be selected with more rows, more fin area, or colder coolant. This lowers the surface temperature and the apparatus dew point to meet the latent load.

134. An electronic (electrostatic) air cleaner removes particles by which principle?
     • Mechanical straining through dense media
     • Adsorbing gases onto carbon
     • Charging particles and collecting them on oppositely charged plates
     • Condensing moisture on the particles

     Correct answer: Charging particles and collecting them on oppositely charged plates

     An electrostatic precipitator charges incoming particles in an ionizing section, then collects them on oppositely charged plates downstream. This captures fine particles with low airflow resistance compared with dense media filters.

135. An activated-carbon filter in an air system is used primarily to remove what?
     • Large dust particles
     • Water droplets
     • Bacteria by straining
     • Gaseous contaminants and odors by adsorption

     Correct answer: Gaseous contaminants and odors by adsorption

     Activated carbon adsorbs gaseous pollutants and odors onto its large internal surface area, addressing contaminants that particulate filters cannot capture. It is used where gas-phase or odor control is required.

136. A packaged rooftop unit (RTU) integrates which set of components in a single cabinet?
     • Compressor, condenser, evaporator, and supply fan as a self-contained air conditioner
     • Boiler and cooling tower only
     • Only a heating coil
     • Chiller and pumps

     Correct answer: Compressor, condenser, evaporator, and supply fan as a self-contained air conditioner

     A packaged rooftop unit combines the compressor, condenser, evaporator coil, and supply fan, and often heating, in one weatherproof cabinet, providing complete air conditioning from the roof. This contrasts with split systems whose components are separated.

137. In a water-source heat pump loop serving many units, the central loop temperature is typically maintained within a moderate range by what equipment?
     • Only individual compressors
     • A boiler to add heat and a cooling tower or fluid cooler to reject heat
     • A single expansion valve
     • Outdoor air dampers

     Correct answer: A boiler to add heat and a cooling tower or fluid cooler to reject heat

     A water-source heat pump loop uses a boiler to add heat when the loop gets too cold and a cooling tower or fluid cooler to reject heat when too warm, keeping the common loop within a usable range. Individual units then heat or cool by exchanging with this loop.

138. A geothermal (ground-source) heat pump achieves higher efficiency than an air-source unit mainly because of what?
     • It uses no compressor
     • It requires no refrigerant
     • The ground provides a more stable, moderate temperature source and sink than outdoor air
     • It needs no electricity

     Correct answer: The ground provides a more stable, moderate temperature source and sink than outdoor air

     Ground temperatures are more stable and moderate than outdoor air across seasons, so a ground-source heat pump operates against smaller temperature lifts, improving COP. This stability avoids the capacity loss air-source units suffer in extreme weather.

139. Why is a hot-gas bypass sometimes used on a refrigeration compressor?
     • To increase condensing pressure
     • To remove moisture
     • To raise the refrigerant charge
     • To provide artificial load at low demand, preventing evaporator frosting and short cycling

     Correct answer: To provide artificial load at low demand, preventing evaporator frosting and short cycling

     Hot-gas bypass routes discharge gas to the evaporator to create a false load at very low demand, keeping suction pressure up to prevent coil frost and reduce compressor short cycling. It allows stable operation below the minimum step of unloading.

140. A pressure-enthalpy (P-h) diagram is used to analyze the refrigeration cycle because it directly shows what?
     • The pressures and enthalpies at each state point, allowing refrigeration effect and work to be read
     • Fan airflow
     • Duct friction
     • Pump head

     Correct answer: The pressures and enthalpies at each state point, allowing refrigeration effect and work to be read

     The pressure-enthalpy diagram plots refrigerant states, so the enthalpy changes across the evaporator (refrigeration effect) and compressor (work) can be read directly. This lets engineers evaluate cycle capacity and COP.

141. On a pressure-enthalpy diagram, an increase in compressor discharge pressure with the same suction pressure does what to the compressor work per pound of refrigerant?
     • Decreases it
     • Increases it, lowering the cycle COP
     • Leaves it unchanged
     • Drives it to zero

     Correct answer: Increases it, lowering the cycle COP

     A higher discharge pressure increases the compression work per pound while the refrigeration effect changes little, so COP drops. This is why high condensing temperatures (for example, dirty condensers) hurt efficiency.

142. What is the primary function of an oil separator on a refrigeration compressor discharge?
     • Add refrigerant to the system
     • Reduce the discharge pressure
     • Capture compressor oil entrained in the discharge gas and return it to the compressor
     • Condense the refrigerant

     Correct answer: Capture compressor oil entrained in the discharge gas and return it to the compressor

     An oil separator removes lubricating oil carried out with the hot discharge gas and returns it to the compressor crankcase, keeping the heat-exchanger surfaces free of fouling oil. This protects the compressor from oil loss and maintains coil performance.

143. A flooded evaporator differs from a direct-expansion evaporator in what way?
     • It has no refrigerant
     • It rejects heat to outdoor air
     • It uses no metering device at all
     • It keeps the tubes surrounded by liquid refrigerant with a controlled level, rather than feeding metered refrigerant that fully evaporates inside

     Correct answer: It keeps the tubes surrounded by liquid refrigerant with a controlled level, rather than feeding metered refrigerant that fully evaporates inside

     A flooded evaporator maintains a liquid refrigerant level so the heat-transfer surfaces stay wetted, improving heat transfer, with a float or level control feeding refrigerant. A DX evaporator instead meters refrigerant that evaporates and superheats inside the tubes.

144. A unit ventilator used in classrooms provides what combination of functions in one cabinet?
     • Outdoor-air ventilation plus heating and often cooling for a single room
     • Only cooling
     • Only dehumidification
     • Central plant pumping

     Correct answer: Outdoor-air ventilation plus heating and often cooling for a single room

     A unit ventilator combines an outdoor-air intake, filter, fan, and heating (and often cooling) coil in one cabinet to ventilate and condition a single room such as a classroom. It delivers controlled ventilation along with space conditioning at the perimeter.

145. What does the integrated part-load value (IPLV) describe for a chiller?
     • Its full-load capacity
     • A weighted efficiency representing performance across a range of part-load conditions
     • Its refrigerant charge
     • Its physical weight

     Correct answer: A weighted efficiency representing performance across a range of part-load conditions

     IPLV is a single number that weights chiller efficiency at several part-load points to represent typical seasonal operation, since chillers spend most time below full load. It complements full-load efficiency for realistic comparisons.

146. A desiccant dehumidifier removes moisture from air by which mechanism?
     • Cooling the air below its dew point on a coil
     • Compressing the air
     • Adsorbing or absorbing water vapor onto a desiccant material, then regenerating it with heat
     • Filtering out water particles

     Correct answer: Adsorbing or absorbing water vapor onto a desiccant material, then regenerating it with heat

     A desiccant dehumidifier passes air over a desiccant such as silica gel that captures water vapor directly, and a separate heated airstream regenerates the desiccant. This can achieve very low humidity without cooling the air below its dew point.

147. Why is a desiccant dehumidification system often selected over cooling-based dehumidification when very low dew points are required?
     • It uses less floor space
     • It needs no energy input
     • It cannot be regenerated
     • It can dry air below the dew points practically achievable by chilled coils without risk of coil frosting

     Correct answer: It can dry air below the dew points practically achievable by chilled coils without risk of coil frosting

     Desiccant systems can reach very low humidity levels that would require coil temperatures near or below freezing if done by cooling, where frost would form. This makes desiccants the practical choice for low-dew-point industrial and process applications.

148. An economizer-equipped DX rooftop unit with low refrigerant charge will most likely show which symptom at the evaporator?
     • Low suction pressure and high superheat
     • High suction pressure and low superheat
     • High subcooling at the condenser
     • Excessive liquid floodback

     Correct answer: Low suction pressure and high superheat

     An undercharged DX system starves the evaporator, producing low suction pressure and abnormally high superheat because the refrigerant fully evaporates early in the coil. These paired symptoms are a classic indicator of low charge.

149. A two-stage (compound) refrigeration system with an intercooler is used to improve performance under what condition?
     • Small temperature lift between evaporator and condenser
     • Large temperature lift requiring a high overall compression ratio
     • Systems with no compressor
     • Constant load operation only

     Correct answer: Large temperature lift requiring a high overall compression ratio

     Compound systems split a large compression ratio into two stages with intercooling between them, reducing discharge temperature and improving efficiency for high-lift, low-temperature applications. A single stage would suffer high discharge temperatures and poor efficiency at such large lifts.

150. Within the supportive-knowledge area for HVAC and refrigeration engineering, what is the primary role of an engineering code of ethics regarding public welfare?
     • It holds paramount the safety, health, and welfare of the public
     • It ranks client profit above all other considerations
     • It applies only to academic researchers
     • It governs only marketing claims

     Correct answer: It holds paramount the safety, health, and welfare of the public

     Engineering codes of ethics state that engineers must hold paramount the safety, health, and welfare of the public above other interests. This duty guides professional decisions even when they conflict with client or employer preferences.

151. An engineer is asked to seal HVAC drawings for work outside their area of competence. What does professional practice require?
     • Seal the drawings to keep the client satisfied
     • Perform services only in areas of their competence, or obtain qualified assistance
     • Seal the drawings if the fee is adequate
     • Refer the matter to marketing

     Correct answer: Perform services only in areas of their competence, or obtain qualified assistance

     Professional engineering practice requires engineers to perform services only in their areas of competence and to associate qualified experts for work outside their expertise. Sealing work one is not competent in violates professional obligations.

152. In project cost analysis, the simple payback period of an energy-efficiency measure is calculated as which ratio?
     • Annual savings divided by initial cost
     • Initial cost multiplied by interest rate
     • Initial cost divided by annual savings
     • Annual savings multiplied by project life

     Correct answer: Initial cost divided by annual savings

     Simple payback equals the initial incremental cost divided by the annual savings, giving the number of years to recover the investment. It ignores the time value of money but is a quick screening tool.

153. A high-efficiency chiller costs $40,000 more than a standard unit but saves $8,000 per year in energy. What is its simple payback period?
     • 2 years
     • 8 years
     • 10 years
     • 5 years

     Correct answer: 5 years

     The simple payback is 5 years, found by dividing the $40,000 added cost by the $8,000 annual savings. This screening metric shows how quickly the premium is recovered through energy savings.

154. Life-cycle cost analysis of HVAC systems differs from simple payback by including which factor?
     • The time value of money and ongoing costs over the system's life, discounted to present value
     • Only the first cost
     • Only the annual maintenance
     • Only the salvage value

     Correct answer: The time value of money and ongoing costs over the system's life, discounted to present value

     Life-cycle cost analysis discounts future energy, maintenance, replacement, and salvage cash flows to present value, accounting for the time value of money over the system life. This gives a more complete economic comparison than simple payback.

155. When converting an HVAC heating rate, 1 BTU is approximately equal to which amount of energy in joules?
     • 10.6 J
     • 1,055 J
     • 100 J
     • 4.18 J

     Correct answer: 1,055 J

     One BTU equals about 1,055 joules, the standard conversion between English and SI energy units. Engineers use this factor when converting heating and cooling rates between unit systems.

156. How many watts are approximately equivalent to one ton of refrigeration?
     • 1,000 W
     • 746 W
     • 3,517 W
     • 12,000 W

     Correct answer: 3,517 W

     One ton of refrigeration equals about 3,517 watts, derived from 12,000 BTU/hr converted to SI power. This conversion is used when comparing cooling capacity across unit systems.

157. For HVAC equipment selection, an engineer must apply a manufacturer's capacity rating with caution because catalog data are based on what?
     • Arbitrary values
     • The lowest possible performance
     • Field conditions identical to every project
     • Specific rated test conditions that must be corrected for actual operating conditions

     Correct answer: Specific rated test conditions that must be corrected for actual operating conditions

     Catalog capacities are published at standardized rating conditions, so the engineer must apply correction factors for the actual entering temperatures, flows, and altitude on the project. Using uncorrected ratings can lead to mis-sized equipment.

158. At higher altitude, standard air density decreases, which means a fan moving a fixed volumetric airflow (CFM) will do what to the mass flow and heat-carrying capacity?
     • Reduce mass flow and heat-carrying capacity, requiring correction of the 1.08 and similar factors
     • Increase both mass flow and capacity
     • Leave them unchanged
     • Eliminate the need for correction

     Correct answer: Reduce mass flow and heat-carrying capacity, requiring correction of the 1.08 and similar factors

     Lower air density at altitude reduces the mass flow for a given CFM, so the heat carried per CFM falls and the standard 1.08 sensible factor must be corrected downward. Ignoring this overestimates capacity at high elevations.

159. An HVAC project schedule shows the critical path. What does the critical path represent?
     • The least expensive sequence of tasks
     • The longest sequence of dependent tasks that determines the minimum project duration
     • The tasks with the most float
     • The optional tasks

     Correct answer: The longest sequence of dependent tasks that determines the minimum project duration

     The critical path is the longest chain of dependent activities, setting the shortest possible project duration, and tasks on it have zero float. Delays to any critical-path task directly delay the project.

160. Why must an HVAC engineer coordinate ductwork and piping layouts with the structural and electrical disciplines during design?
     • To increase the equipment cost
     • To eliminate the need for drawings
     • To resolve physical conflicts and ensure systems fit and are supported within the building
     • To avoid using a building code

     Correct answer: To resolve physical conflicts and ensure systems fit and are supported within the building

     Coordination among disciplines resolves spatial conflicts so ducts, pipes, beams, and conduit fit and are properly supported, preventing costly field clashes. Interdisciplinary review is part of competent professional practice.

161. A mechanical engineer must verify that selected HVAC equipment meets the minimum efficiency requirements of which type of document?
     • The manufacturer's marketing brochure
     • An unrelated plumbing code
     • The contractor's bid form
     • Applicable energy codes and standards such as ASHRAE Standard 90.1

     Correct answer: Applicable energy codes and standards such as ASHRAE Standard 90.1

     Equipment must meet the minimum efficiency levels mandated by adopted energy codes and standards such as ASHRAE Standard 90.1. Verifying compliance with these documents is part of responsible HVAC design.

162. In an HVAC economic comparison using present worth, a future cost is converted to present value by doing what?
     • Discounting it using a present-worth factor based on the discount rate and number of years
     • Multiplying by the interest rate
     • Adding the inflation rate
     • Ignoring the time value of money

     Correct answer: Discounting it using a present-worth factor based on the discount rate and number of years

     A future cost is brought to present value by multiplying it by a present-worth factor that discounts for the interest (discount) rate over the number of years. This lets cash flows occurring at different times be compared on a common basis.

163. Why does an engineer apply a safety factor or design margin when sizing HVAC equipment from calculated loads?
     • To guarantee the smallest possible equipment
     • To account for uncertainties in loads, future changes, and modeling assumptions
     • To eliminate all redundancy
     • To reduce the equipment cost

     Correct answer: To account for uncertainties in loads, future changes, and modeling assumptions

     A reasonable design margin covers uncertainties in load estimates, future load growth, and modeling simplifications so the system performs reliably. Excessive oversizing, however, harms efficiency and part-load performance, so margins are kept reasonable.

164. When an engineer discovers a design error after construction documents are issued, professional responsibility requires what action?
     • Conceal it to avoid liability
     • Wait until the warranty expires
     • Promptly disclose and correct it to protect public safety and the client
     • Blame the contractor

     Correct answer: Promptly disclose and correct it to protect public safety and the client

     Professional ethics require an engineer to promptly disclose and correct discovered errors, since concealment can endanger the public and breaches the duty of honesty. Acting transparently to fix the issue upholds the engineer's obligations.

165. Commissioning of a newly installed HVAC system is performed primarily to accomplish what?
     • Market the building
     • Replace the design calculations
     • Eliminate the need for maintenance
     • Verify that systems are installed and perform according to the design intent and owner requirements

     Correct answer: Verify that systems are installed and perform according to the design intent and owner requirements

     Commissioning systematically verifies that HVAC systems are installed correctly and operate according to the design intent and the owner's project requirements. It catches deficiencies before turnover and documents proper performance.