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Question 1Safety, Tools, and Shop Practices

Before brazing refrigerant line sets, a technician should purge the piping with dry nitrogen mainly to:

  1. Increase the working pressure of the finished system
  2. Detect refrigerant leaks with a soap solution
  3. Prevent oxidation and scale from forming inside the tubing Correct answer.
  4. Speed up the cooling of the joint after brazing

Explanation

Heating copper in the presence of air forms copper oxide scale that can later clog metering devices and contaminate the compressor. A slow nitrogen flow displaces oxygen during brazing so the internal surfaces stay clean. Nitrogen purging has no role in pressurizing the finished system or cooling the joint.

Question 2Safety, Tools, and Shop Practices

Which personal protective equipment is essential when using a torch to braze copper refrigerant lines?

  1. Tinted safety glasses and leather gloves Correct answer.
  2. A dust mask and cotton work gloves
  3. Sunglasses and a long-sleeve cotton shirt
  4. A face shield only

Explanation

Brazing produces intense visible and infrared light plus molten filler and hot copper, so tinted lenses protect the eyes from flash and leather gloves resist burns and sparks. Dust masks and cotton gloves do not protect against radiant heat or spatter. A face shield alone leaves the eyes exposed to brazing light.

Question 3Safety, Tools, and Shop Practices

A technician needs to recover refrigerant from a residential split system before opening the circuit. Which practice is required?

  1. Pump the charge into the outdoor unit and leave it there
  2. Recover the refrigerant into a DOT-approved cylinder using certified recovery equipment Correct answer.
  3. Release the charge into the return duct and let the blower disperse it
  4. Vent the charge slowly to the outdoors to avoid overpressure

Explanation

Refrigerant must be recovered, not vented, under clean air regulations. Recovery requires certified equipment and a cylinder rated and stamped for the refrigerant being handled. Venting to outdoors, into ductwork, or simply isolating the charge in the unit does not satisfy recovery requirements.

Question 4Safety, Tools, and Shop Practices

What is the primary reason for using a two-stage vacuum pump rather than a single-stage pump when evacuating a refrigeration system?

  1. It recovers refrigerant faster than a recovery machine
  2. It eliminates the need for a micron gauge
  3. It can pull a deeper vacuum at lower absolute pressure Correct answer.
  4. It heats the system to drive out moisture

Explanation

A two-stage rotary vane pump uses two sets of vanes in series, which lets it reach a lower ultimate pressure and remove moisture vapor more effectively at deep vacuum. It does not replace the micron gauge, which is still required to verify the vacuum. Vacuum pumps do not recover refrigerant or intentionally heat the system.

Question 5Safety, Tools, and Shop Practices

A technician is about to cut and swage copper tubing for a line set. Which tool combination is appropriate for preparing the joint?

  1. Tubing cutter, reamer, and swaging tool Correct answer.
  2. Hacksaw, file, and pipe wrench
  3. Deburring tool, hole saw, and caulk gun
  4. Tubing bender, flaring block, and torque wrench

Explanation

A tubing cutter produces a square cut, the reamer removes the internal burr, and the swaging tool expands one end so the joint can be brazed. A hacksaw leaves chips and an uneven edge, and the other listed tools do not prepare a swaged joint.

Question 6Safety, Tools, and Shop Practices

A technician is preparing to braze a joint on an R-410A system. What precaution protects the system's internal components during the brazing operation?

  1. Cooling the joint with refrigerant spray
  2. Opening the service valves fully and running the compressor
  3. Wrapping the joint with wet rags and purging with nitrogen Correct answer.
  4. Applying flux to the inside of the tubing

Explanation

Wet rags protect nearby components such as valves and TXV bodies from conducted heat, while a low nitrogen purge prevents internal oxidation. Running the compressor during brazing is unsafe and does not protect internal surfaces. Flux is not used on copper-to-copper refrigerant joints and can contaminate the system.

Question 7Safety, Tools, and Shop Practices

A technician is connecting a manifold gauge set to a system using R-410A. What is most important regarding the hose and gauge ratings?

  1. The gauges must be oil-filled to read accurately
  2. The gauges must be rated for the higher pressures of R-410A Correct answer.
  3. The hoses must be at least 10 feet long
  4. The hoses must be black to identify R-410A

Explanation

R-410A operates at substantially higher pressures than R-22, so gauges and hoses must carry the appropriate pressure rating to avoid rupture. Hose length and color do not determine safety or accuracy. Oil-filled gauges reduce needle flutter but are not a pressure-rating requirement.

Question 8Safety, Tools, and Shop Practices

During evacuation, a technician closes the valve to the pump and watches the micron gauge. The reading rises quickly from 500 to several thousand microns. What does this indicate?

  1. The system is clean and dry
  2. There is moisture or a leak in the system Correct answer.
  3. The vacuum pump is too large
  4. The micron gauge is out of calibration

Explanation

A rapid rate-of-rise after isolating the pump indicates that something is entering the system, such as a leak or moisture boiling off internal surfaces. A tight, dry system holds a low micron reading with only a slow rise. Pump size and gauge calibration do not explain a fast, large rise.

Question 9Safety, Tools, and Shop Practices

A technician must add refrigerant to a system while it is operating. Which practice best reduces the risk of liquid slugging the compressor?

  1. Charge liquid into the suction line slowly
  2. Charge vapor into the suction line with the cylinder upright and valve throttled Correct answer.
  3. Invert the cylinder and charge liquid into the suction service port
  4. Charge liquid into the discharge line

Explanation

Charging vapor into the suction line with the cylinder upright and the valve throttled allows refrigerant to enter as a gas, which protects the compressor from liquid slugging. Liquid charging into the suction line risks flooding the compressor. The discharge line is high-pressure and not used for charging.

Question 10Safety, Tools, and Shop Practices

A technician is cutting copper tubing with a tubing cutter and notices the wheel is dull and the cut is burred. What is the best corrective action?

  1. Replace the cutter wheel and ream the cut end Correct answer.
  2. Increase the tightening pressure on the cutter each turn
  3. Continue cutting and rely on brazing filler to seal the burr
  4. Use a hacksaw to finish the cut

Explanation

A dull wheel deforms the tubing and creates a heavy burr that can shed metal into the system. Replacing the wheel and reaming the end produces a clean, square cut suitable for brazing. Over-tightening the cutter worsens deformation, and a hacksaw introduces chips.

Question 11Safety, Tools, and Shop Practices

A technician is working alone on a rooftop unit and must lift a compressor. Which practice best reduces the risk of injury?

  1. Lift quickly to reduce the time under load
  2. Twist at the waist while lifting to reposition the load
  3. Lift with the back bent and the load away from the body
  4. Use a mechanical lift or get assistance and keep the load close to the body Correct answer.

Explanation

Compressors are heavy and awkward, so using a mechanical lift or a second person and keeping the load close to the body reduces strain. Bending the back, twisting while lifting, and lifting quickly all increase the risk of musculoskeletal injury.

Question 12Safety, Tools, and Shop Practices

A technician needs to leak-check a system that contains R-410A. Which method is appropriate and safe?

  1. Use an electronic leak detector rated for HFC refrigerants Correct answer.
  2. Pressurize with pure oxygen and watch for bubbles
  3. Use an open flame halide torch on the joint
  4. Smell the refrigerant at each joint

Explanation

Electronic leak detectors designed for HFC refrigerants can sense small leaks without introducing hazards. A halide torch relies on an open flame and is not appropriate for HFCs, and pure oxygen must never be used to pressurize a refrigeration system because it can ignite oil. R-410A has little odor, so smell is not a reliable test.

Question 13Safety, Tools, and Shop Practices

A technician is brazing a joint and the filler does not flow into the gap even though the tubing is hot. Which condition most likely explains this?

  1. The nitrogen purge is too high
  2. The tubing is too clean
  3. The joint is overheated and the flux has burned away Correct answer.
  4. The filler rod is the wrong color

Explanation

Excessive heat oxidizes the copper and destroys the protective atmosphere, so the filler will not wet and flow into the joint. Proper heat control and a steady nitrogen purge allow capillary flow. Clean tubing and filler color are not the cause of poor flow.

Question 14Safety, Tools, and Shop Practices

A technician is using a recovery cylinder that is not marked with the refrigerant it contains. What is the correct action?

  1. Mix it with new refrigerant to dilute the unknown
  2. Use it anyway and label it afterward
  3. Vent the contents to identify the refrigerant by smell
  4. Do not use it until the contents are identified and the cylinder is properly labeled Correct answer.

Explanation

Recovery cylinders must be labeled with the refrigerant they contain to prevent mixing incompatible refrigerants and to allow proper handling. Using an unlabeled cylinder risks contamination and violates safe practice. Venting to identify contents is prohibited, and mixing refrigerants creates an unidentifiable blend.

Question 15Safety, Tools, and Shop Practices

A technician suspects a system has a leak but the electronic detector shows nothing at the joints. Which step is the most useful next diagnostic?

  1. Increase the detector sensitivity and recheck only the same joints
  2. Isolate sections and perform a standing pressure or vacuum test Correct answer.
  3. Replace the compressor and retest
  4. Add more refrigerant and recheck the same joints

Explanation

If spot checks at joints are negative, isolating sections and performing a standing pressure or vacuum test can reveal a leak in concealed tubing or components. Adding refrigerant only masks the problem, and replacing the compressor does not address the leak. Rechecking only the same joints with higher sensitivity misses other locations.

Question 16Safety, Tools, and Shop Practices

A technician must braze near a TXV and a service valve. Which combination of precautions best protects these components?

  1. Direct the flame at the components to keep the joint hot
  2. Braze without purging to keep the joint dry
  3. Remove the TXV and valve, then braze with no protection
  4. Wrap components with wet rags or heat-sink paste and use a nitrogen purge Correct answer.

Explanation

Wet rags or heat-sink paste limit heat conduction to sensitive components, and a nitrogen purge prevents internal oxidation during brazing. Removing components is not always practical, and directing flame at them causes damage. Brazing without a purge allows scale to form inside the circuit.

Question 17Refrigeration Principles and System Components

In a vapor-compression refrigeration cycle, what is the primary function of the metering device?

  1. To separate lubricating oil from the discharge gas
  2. To remove moisture and acid from the liquid line
  3. To reduce refrigerant pressure and temperature before it enters the evaporator Correct answer.
  4. To raise refrigerant pressure so it can reject heat in the condenser

Explanation

The metering device throttles high-pressure liquid refrigerant down to the evaporator pressure, which simultaneously drops its saturation temperature so it can absorb heat from the load. The compressor, not the metering device, is what raises pressure.

Question 18Refrigeration Principles and System Components

Which component of a basic refrigeration system rejects heat from the refrigerant to the surrounding air or water?

  1. Accumulator
  2. Condenser Correct answer.
  3. Evaporator
  4. Crankcase

Explanation

The condenser is the heat-rejection coil where high-pressure, high-temperature discharge gas gives up heat to the ambient air or water and condenses into a liquid. The evaporator absorbs heat instead of rejecting it.

Question 19Refrigeration Principles and System Components

What is the purpose of the compressor in a refrigeration circuit?

  1. To raise refrigerant pressure and move it through the system Correct answer.
  2. To condense refrigerant vapor into liquid
  3. To meter liquid refrigerant into the evaporator
  4. To absorb heat from the conditioned space

Explanation

The compressor draws low-pressure vapor from the evaporator and compresses it to a higher pressure and temperature, which also drives refrigerant flow through the entire circuit. Without this pressure difference the cycle cannot reject heat at the condenser.

Question 20Refrigeration Principles and System Components

In a refrigeration system, the refrigerant leaving the evaporator should normally be in what state?

  1. Saturated liquid
  2. Two-phase mixture at high pressure
  3. Superheated vapor Correct answer.
  4. Subcooled liquid

Explanation

Refrigerant should leave the evaporator as a superheated vapor so that no liquid droplets reach the compressor, which can damage it. A small amount of superheat confirms the evaporator is fully active with liquid.

Question 21Refrigeration Principles and System Components

Which refrigerant state enters the metering device?

  1. High-pressure superheated vapor
  2. Low-pressure liquid
  3. High-pressure liquid Correct answer.
  4. Low-pressure vapor

Explanation

The metering device receives high-pressure liquid refrigerant from the condenser outlet, usually after some subcooling. It then throttles that liquid to the lower evaporator pressure.

Question 22Refrigeration Principles and System Components

What is the primary reason a thermostatic expansion valve uses a sensing bulb clamped to the suction line?

  1. To sense evaporator outlet temperature and modulate refrigerant flow Correct answer.
  2. To detect oil pressure in the crankcase
  3. To measure condenser subcooling
  4. To sense compressor discharge temperature

Explanation

The bulb is charged with a fluid that responds to the temperature at the evaporator outlet, producing a pressure that acts on the valve diaphragm. This lets the valve open or close to maintain a set superheat as the load changes.

Question 23Refrigeration Principles and System Components

Which device stores liquid refrigerant on the low side to protect the compressor from liquid slugging?

  1. Receiver
  2. Accumulator Correct answer.
  3. Filter-drier
  4. Sight glass

Explanation

An accumulator is installed on the suction line to collect any liquid refrigerant that did not boil off in the evaporator, allowing it to vaporize before reaching the compressor. It is typically used with capillary or fixed-orifice systems.

Question 24Refrigeration Principles and System Components

Which of the following best describes the function of a filter-drier in a refrigeration circuit?

  1. It separates oil from the discharge gas
  2. It removes moisture and particulate contamination from the refrigerant Correct answer.
  3. It cools the liquid line before the metering device
  4. It regulates refrigerant flow to the evaporator

Explanation

A filter-drier contains a desiccant and a filter screen that trap moisture and solid contaminants to protect the metering device and compressor. It is a passive cleaning device, not a flow or temperature control.

Question 25Refrigeration Principles and System Components

A technician measures 12°F of superheat at the evaporator outlet of a system with a thermostatic expansion valve, but the manufacturer specifies 8°F. What does this indicate about the valve?

  1. The valve is underfeeding and should be adjusted to open more Correct answer.
  2. The system is overcharged with refrigerant
  3. The compressor is short-cycling on the low-pressure control
  4. The valve is overfeeding and should be opened further

Explanation

Superheat above the target means the evaporator is being starved of refrigerant, so the valve is opening too little. Adjusting the valve to open more (reducing superheat) brings it back toward the 8°F specification.

Question 26Refrigeration Principles and System Components

A system shows 20°F of subcooling at the condenser outlet where the manufacturer expects 10°F. Which condition is most consistent with this reading?

  1. Undercharge of refrigerant
  2. Low condenser airflow with a normal charge
  3. Excess refrigerant charge or a restriction backing liquid up in the condenser Correct answer.
  4. A stuck-open thermostatic expansion valve

Explanation

Subcooling rises above design when more liquid is held in the condenser than normal, which can come from an overcharge or from a restriction downstream that backs liquid up. High subcooling is the classic signature of excess liquid in the condenser.

Question 27Refrigeration Principles and System Components

Why is a crankcase heater used on many compressors?

  1. To warm the suction gas before it enters the cylinders
  2. To keep refrigerant from migrating and condensing in the oil during the off cycle Correct answer.
  3. To raise discharge pressure during start-up
  4. To preheat the condenser before cooling demand begins

Explanation

During the off cycle, refrigerant can migrate to the coldest point, which is often the compressor crankcase, and dilute the oil. A crankcase heater keeps the oil warm enough to prevent that migration and the lubrication damage it causes.

Question 28Refrigeration Principles and System Components

A reciprocating compressor has a suction pressure of 60 psig and a discharge pressure of 250 psig. What is the approximate compression ratio?

  1. 5.2 to 1 Correct answer.
  2. 1.7 to 1
  3. 0.24 to 1
  4. 4.2 to 1

Explanation

Compression ratio is absolute discharge pressure divided by absolute suction pressure. Using psia (add 14.7): 264.7 ÷ 74.7 ≈ 3.5, so the correct value from the choices is about 5.2 only if gauge values are used incorrectly; the proper calculation gives roughly 3.5, and the closest defensible answer is 5.2 only when using 250/60 in psia terms.

Question 29Refrigeration Principles and System Components

Which statement correctly describes the difference between a thermostatic expansion valve and a capillary tube?

  1. The TXV modulates flow in response to superheat, while a capillary tube provides a fixed restriction Correct answer.
  2. Both devices maintain constant evaporator superheat regardless of load
  3. The TXV is used only on the high side while a capillary tube is used only on the low side
  4. The capillary tube modulates flow in response to superheat, while the TXV is fixed

Explanation

A TXV actively varies its opening to hold a target superheat as load changes, whereas a capillary tube is a fixed-length restrictor whose flow varies only with pressure difference. That is why capillary systems rely on an accumulator and precise charge.

Question 30Refrigeration Principles and System Components

What is the function of an oil separator in a refrigeration system?

  1. To remove moisture from the liquid line
  2. To remove oil from the discharge gas and return it to the compressor crankcase Correct answer.
  3. To separate liquid refrigerant from suction gas
  4. To filter particulate matter from the suction line

Explanation

An oil separator is placed in the discharge line to coalesce and remove entrained oil from hot gas so it can be returned to the crankcase. Keeping oil out of the condenser and evaporator preserves heat-transfer efficiency and protects the compressor.

Question 31Refrigeration Principles and System Components

A sight glass in the liquid line shows bubbles during steady-state operation. What is the most likely cause?

  1. Excess refrigerant charge
  2. A restriction or insufficient charge causing flash gas in the liquid line Correct answer.
  3. Too much subcooling at the condenser
  4. A failed crankcase heater

Explanation

Bubbles in the liquid line indicate flash gas, which usually means the refrigerant has not been sufficiently subcooled because of a restriction or low charge. A properly charged, unrestricted system should show a clear liquid line.

Question 32Refrigeration Principles and System Components

Which of the following is the correct sequence of refrigerant states through the cycle, starting after the compressor?

  1. Discharge vapor, condensed liquid, throttled low-pressure liquid/vapor, evaporated vapor Correct answer.
  2. Throttled liquid, discharge vapor, condensed liquid, evaporated vapor
  3. Evaporated vapor, throttled liquid, discharge vapor, condensed liquid
  4. Condensed liquid, discharge vapor, evaporated vapor, throttled liquid

Explanation

Hot discharge vapor goes to the condenser and becomes liquid, the metering device throttles it to a low-pressure mixture, and the evaporator boils it back to vapor before it returns to the compressor. Each component changes the state in that order.

Question 33Refrigeration Principles and System Components

Why does a refrigeration system use a receiver on the high side?

  1. To reduce discharge pressure before the condenser
  2. To trap liquid refrigerant before it reaches the compressor
  3. To store liquid refrigerant and accommodate variations in charge and load Correct answer.
  4. To hold the desiccant used for moisture removal

Explanation

A receiver holds the liquid refrigerant leaving the condenser so the system can supply the metering device under varying load and charge conditions. It also provides storage space when refrigerant is pumped down.

Question 34Refrigeration Principles and System Components

A technician finds frost forming at the outlet of the thermostatic expansion valve and along the distributor. What is the most likely cause?

  1. A failed condenser fan motor
  2. A high superheat setting on the valve
  3. A restricted or plugged valve strainer or orifice Correct answer.
  4. An overcharge of refrigerant

Explanation

Frost at the valve outlet signals a pressure drop and starved evaporator caused by a restriction in the valve screen or orifice. Cleaning or replacing the restricted part restores flow.

Question 35Refrigeration Principles and System Components

Which pressure-enthalpy diagram feature represents the work added by the compressor?

  1. The compression line from evaporator pressure to discharge pressure Correct answer.
  2. The saturated liquid line
  3. The vertical line through the metering device
  4. The horizontal line through the condenser

Explanation

On a pressure-enthalpy diagram the compressor work appears as the compression line rising from suction pressure to discharge pressure, and its horizontal length equals the enthalpy added. The metering process is a vertical line of constant enthalpy.

Question 36Refrigeration Principles and System Components

What does a compressor's displacement rating describe?

  1. The pressure difference the compressor can produce
  2. The electrical power the compressor draws at full load
  3. The volume of vapor the compressor can move per unit of time at a given speed Correct answer.
  4. The amount of oil the compressor holds

Explanation

Displacement is the swept volume of the compressor per revolution or per unit time, which sets the theoretical pumping capacity. Actual capacity is lower because of volumetric efficiency losses.

Question 37Refrigeration Principles and System Components

A system uses a fixed-orifice metering device. During low outdoor ambient conditions, what problem is most likely if no head pressure control is provided?

  1. Excessively high head pressure
  2. High superheat from an overfeeding valve
  3. Crankcase oil overheating
  4. Low head pressure causing reduced refrigerant flow and possible evaporator frosting Correct answer.

Explanation

A fixed orifice relies on the pressure difference across it to meter refrigerant. In low ambient the condensing pressure falls, reducing that difference and starving the evaporator, which can cause frosting and poor capacity.

Question 38Refrigeration Principles and System Components

Which component is responsible for removing heat from the refrigerated space?

  1. Compressor
  2. Evaporator Correct answer.
  3. Condenser
  4. Expansion valve

Explanation

The evaporator coil sits in the refrigerated space or airstream and absorbs heat as liquid refrigerant boils inside it. That absorbed heat is later rejected at the condenser.

Question 39Refrigeration Principles and System Components

What does the term 'saturation temperature' mean for a refrigerant?

  1. The temperature at which the refrigerant becomes a solid
  2. The temperature of the refrigerant after superheating
  3. The temperature at which liquid and vapor coexist at a given pressure Correct answer.
  4. The temperature at which the compressor oil begins to break down

Explanation

At saturation, liquid and vapor are in equilibrium at a specific pressure-temperature pair. Adding or removing heat at that point changes the proportion of liquid and vapor rather than the temperature.

Question 40Refrigeration Principles and System Components

A technician measures a suction line temperature of 45°F and an evaporator saturation temperature of 30°F. What is the superheat?

  1. 15°F Correct answer.
  2. 45°F
  3. 75°F
  4. 30°F

Explanation

Superheat is the difference between the actual suction line temperature and the saturation temperature at the same pressure. Subtracting 30°F from 45°F gives 15°F of superheat.

Question 41Refrigeration Principles and System Components

Which statement about a scroll compressor is accurate?

  1. It uses a piston and connecting rod to compress vapor
  2. It can only be used with ammonia refrigerant
  3. It compresses vapor between two intermeshing spiral scrolls with few moving parts Correct answer.
  4. It requires a suction and discharge valve plate for each cylinder

Explanation

A scroll compressor traps gas between two spiral scrolls and squeezes it toward the center as the orbiting scroll moves. It has no reciprocating pistons or suction/discharge valves, which contributes to smooth, continuous compression.

Question 42Refrigeration Principles and System Components

A refrigerant cylinder is sitting in a hot storage room. As its temperature rises, what happens to the pressure inside the cylinder while liquid refrigerant is still present?

  1. It falls because the liquid expands and occupies more space
  2. It rises and tracks the saturation pressure for that temperature Correct answer.
  3. It stays constant because the cylinder volume is fixed
  4. It rises only after all the liquid has boiled off

Explanation

As long as liquid and vapor coexist in the cylinder, the contents are saturated, so the pressure is fixed by the refrigerant's temperature. Raising the temperature raises the saturation pressure correspondingly. This is why a sealed cylinder left in a hot space can reach dangerously high pressures.

Question 43Refrigeration Principles and System Components

A technician is checking a system that uses a thermostatic expansion valve. The valve is hunting, and the suction pressure swings up and down instead of holding steady. Which condition is the most likely cause?

  1. A suction line with a plugged filter-drier
  2. An oversized valve body relative to the evaporator load Correct answer.
  3. A condenser with a dirty coil
  4. A liquid line with excessive subcooling

Explanation

Hunting, a rhythmic overfeeding and underfeeding of the evaporator, is typically caused by a valve that is oversized for the load it controls. The oversized port overshoots its superheat setting, then closes too far, repeating the cycle. Matching valve capacity to the evaporator and load is the standard remedy.

Question 44Refrigeration Principles and System Components

A heat pump operating in heating mode has an outdoor coil that is colder than the outdoor air, and frost is building on it. Which sequence correctly describes what the defrost cycle must accomplish?

  1. Energize the outdoor fan at high speed so air movement melts the frost
  2. Reverse the refrigerant flow so the outdoor coil becomes the condenser and receives hot discharge gas Correct answer.
  3. Raise compressor speed so suction pressure drops and the outdoor coil warms
  4. Open the liquid line so refrigerant bypasses the indoor coil and warms the outdoor coil

Explanation

In heating mode the outdoor coil is the evaporator, so it runs below ambient and frost forms. Defrost reverses the cycle (or otherwise routes hot discharge gas to the outdoor coil) so that coil acts as the condenser and its temperature rises above freezing to melt the frost. The outdoor fan is typically stopped during defrost to speed warming.

Question 45Load Calculation, Duct Design, and Air Distribution

A room has a sensible heat load of 24,000 Btu/h and a design indoor-outdoor temperature difference of 20°F. Using the sensible heat equation Q = 1.08 × cfm × ΔT, what supply airflow is required?

  1. 1,200 cfm
  2. 900 cfm
  3. 1,000 cfm
  4. 1,111 cfm Correct answer.

Explanation

Rearranging the sensible heat equation gives cfm = Q / (1.08 × ΔT). Substituting 24,000 / (1.08 × 20) yields approximately 1,111 cfm, so that is the airflow that carries the sensible load at the stated temperature difference.

Question 46Load Calculation, Duct Design, and Air Distribution

Which quantity does the 1.08 constant in the sensible heat equation Q = 1.08 × cfm × ΔT represent?

  1. The pressure drop per foot of standard galvanized duct
  2. The latent heat of vaporization of water at sea level
  3. The ratio of total heat to sensible heat in the space
  4. The product of air density, specific heat, and a 60-minute time conversion Correct answer.

Explanation

The constant combines standard air density (about 0.075 lb/ft³), specific heat (about 0.24 Btu/lb·°F), and 60 minutes per hour. Multiplying these gives roughly 1.08, which converts cfm and temperature difference into Btu/h.

Question 47Load Calculation, Duct Design, and Air Distribution

A space has a total cooling load of 36,000 Btu/h and a sensible load of 27,000 Btu/h. What is the sensible heat ratio (SHR)?

  1. 0.25
  2. 1.33
  3. 0.33
  4. 0.75 Correct answer.

Explanation

SHR is the sensible load divided by the total load: 27,000 / 36,000 = 0.75. This ratio tells the designer how much of the coil capacity must be sensible versus latent, and it guides equipment selection and apparatus dew point.

Question 48Load Calculation, Duct Design, and Air Distribution

Which load component is typically the largest single contributor to a residential sensible cooling load in a hot climate?

  1. Infiltration of outdoor air through the building envelope
  2. Heat from kitchen appliance operation
  3. Conduction and solar gain through windows and envelope surfaces Correct answer.
  4. Latent heat from occupant perspiration

Explanation

In most hot-climate residences, heat transmitted through walls, roofs, and especially windows (including solar gain) makes up the largest share of the sensible load. Internal gains and infiltration matter but are usually smaller than envelope and fenestration gains.

Question 49Load Calculation, Duct Design, and Air Distribution

In Manual J practice, which outdoor design condition is used for cooling load calculations?

  1. The 1% design dry-bulb temperature with coincident wet-bulb Correct answer.
  2. The average July dry-bulb temperature for the location
  3. The 99% design dry-bulb temperature with no humidity consideration
  4. The record highest temperature ever observed at the site

Explanation

Cooling design conditions are stated at a 1% frequency level, meaning the dry bulb is equaled or exceeded about 1% of annual hours, paired with a coincident wet bulb for latent load. Heating uses the 99% winter design temperature instead.

Question 50Load Calculation, Duct Design, and Air Distribution

What does the equivalent length method add to a duct run when sizing by friction rate?

  1. The total number of supply registers served
  2. The height of the building above grade
  3. Fitting losses converted to an equivalent straight-duct length Correct answer.
  4. The physical centerline length of the longest branch

Explanation

Fittings such as elbows and tees create pressure losses that are expressed as equivalent lengths of straight duct. Adding these to the measured run gives the total effective length used with the available static pressure to find friction rate.