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BPI AC/Heat Pump study materials
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BPI AC/Heat Pump practice questions

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Question 1Air Conditioning and Heat Pump Fundamentals

Which component of a vapor-compression air conditioner raises the pressure and temperature of the refrigerant vapor before it enters the condenser?

  1. The accumulator
  2. The expansion valve
  3. The evaporator coil
  4. The compressor Correct answer.

Explanation

The compressor is the pump of the cycle. It draws low-pressure vapor from the evaporator and discharges it at higher pressure and temperature, which allows the condenser to reject heat to outdoor air. The other listed parts either meter flow or exchange heat but do not raise pressure.

Question 2Air Conditioning and Heat Pump Fundamentals

In a standard split air conditioner, heat is rejected to the outdoors in which coil?

  1. The evaporator
  2. The metering device
  3. The condenser Correct answer.
  4. The suction line

Explanation

The condenser is the coil where high-pressure hot refrigerant vapor gives up heat and condenses to liquid. In cooling mode it is the outdoor coil. The evaporator does the opposite job indoors, absorbing heat from the conditioned space.

Question 3Air Conditioning and Heat Pump Fundamentals

A heat pump in heating mode reverses the refrigerant flow so that the indoor coil functions as which of the following?

  1. The receiver
  2. The evaporator
  3. The muffler
  4. The condenser Correct answer.

Explanation

A reversing valve swaps the roles of the two coils. In heating mode the indoor coil becomes the condenser, rejecting heat into the building, while the outdoor coil becomes the evaporator that gathers heat from outside air.

Question 4Air Conditioning and Heat Pump Fundamentals

What is the primary purpose of the metering device in a refrigeration circuit?

  1. To store excess refrigerant during low load
  2. To lubricate the compressor bearings
  3. To filter moisture from the refrigerant
  4. To reduce refrigerant pressure and regulate flow into the evaporator Correct answer.

Explanation

The metering device creates the pressure drop between the high side and low side and controls how much refrigerant enters the evaporator. That drop lets the refrigerant boil at a low temperature and absorb heat. Filtering, storage, and lubrication are handled by other components.

Question 5Air Conditioning and Heat Pump Fundamentals

Which refrigerant line in a typical split system is normally insulated because it is cold and prone to sweating?

  1. The discharge line
  2. The suction line Correct answer.
  3. The hot gas bypass line
  4. The liquid line

Explanation

The suction line carries cool low-pressure vapor from the evaporator back to the compressor, so its surface is below the dew point of surrounding air. Insulation prevents condensation and unwanted heat gain. Liquid and discharge lines are warmer and are not insulated for that reason.

Question 6Air Conditioning and Heat Pump Fundamentals

What does a ton of refrigeration capacity represent?

  1. A heat removal rate of 12,000 Btu per hour Correct answer.
  2. The weight of refrigerant in a full charge
  3. The power drawn by a one-ton compressor
  4. The airflow of 400 cubic feet per minute

Explanation

One ton of refrigeration equals 12,000 British thermal units per hour of heat removal, a rate inherited from the cooling effect of melting one ton of ice per day. It is a capacity rating, not a weight or an electrical rating.

Question 7Air Conditioning and Heat Pump Fundamentals

In the cooling mode of a heat pump, which coil is the evaporator?

  1. The indoor coil Correct answer.
  2. Both coils act as evaporators
  3. Neither coil acts as an evaporator
  4. The outdoor coil

Explanation

In cooling mode a heat pump behaves like an ordinary air conditioner. The indoor coil evaporates refrigerant and absorbs heat from the house, while the outdoor coil condenses refrigerant and rejects heat outside.

Question 8Air Conditioning and Heat Pump Fundamentals

Which of the following best describes sensible heat?

  1. Heat that changes the temperature of a substance without changing its phase Correct answer.
  2. Heat released only during condensation
  3. Heat that changes the phase of a substance without changing its temperature
  4. Heat measured exclusively in latent units

Explanation

Sensible heat produces a measurable temperature change in a substance, such as warming air across a coil. Latent heat, by contrast, is absorbed or released during a phase change at constant temperature. Both matter in coil performance.

Question 9Air Conditioning and Heat Pump Fundamentals

A technician measures 72°F dry-bulb and 60°F wet-bulb air entering an evaporator coil. What does this entering air condition most directly indicate?

  1. The relative humidity of the return air Correct answer.
  2. The compressor is short-cycling
  3. The refrigerant charge is overcharged
  4. The coil is frosted

Explanation

A dry-bulb and wet-bulb pair fixes the psychrometric state of the air, from which relative humidity and enthalpy can be found. The wet-bulb depression of 12°F shows the air is not saturated. The other choices are equipment faults that cannot be read from a single air state.

Question 10Air Conditioning and Heat Pump Fundamentals

An R-410A system has a measured suction line temperature of 55°F and a suction saturation temperature of 40°F. What is the superheat?

  1. 95°F
  2. 55°F
  3. 40°F
  4. 15°F Correct answer.

Explanation

Superheat is the difference between the actual suction line temperature and the saturation temperature at the same pressure. Subtracting 40 from 55 gives 15°F. This value helps confirm the evaporator is properly fed with refrigerant.

Question 11Air Conditioning and Heat Pump Fundamentals

A liquid line saturation temperature is 110°F and the measured liquid line temperature is 100°F. What is the subcooling?

  1. 110°F
  2. 100°F
  3. 10°F Correct answer.
  4. 210°F

Explanation

Subcooling is the saturation temperature minus the actual liquid line temperature. Here 110 minus 100 equals 10°F, meaning the liquid has been cooled below its condensing point. Adequate subcooling confirms the condenser is holding a solid liquid seal.

Question 12Air Conditioning and Heat Pump Fundamentals

Why does a heat pump require a defrost cycle in cold weather?

  1. The reversing valve sticks in heating mode
  2. The indoor coil collects dust and must be cleaned
  3. The compressor oil thickens and must be warmed
  4. Frost on the outdoor coil blocks airflow and reduces heat absorption Correct answer.

Explanation

In heating mode the outdoor coil is the evaporator and runs below freezing, so moisture in the air can freeze on its fins. Frost insulates the coil and restricts airflow, cutting capacity. Defrost temporarily reverses the cycle to melt the frost.

Question 13Air Conditioning and Heat Pump Fundamentals

What is the function of the reversing valve in a heat pump?

  1. It bypasses the condenser during defrost only
  2. It regulates compressor oil return
  3. It switches the direction of refrigerant flow between heating and cooling Correct answer.
  4. It modulates refrigerant flow to the evaporator

Explanation

The reversing valve is a four-way valve that redirects discharge and suction gas so the roles of the indoor and outdoor coils swap. Energizing or de-energizing its solenoid selects heating or cooling. It does not meter refrigerant or control oil.

Question 14Air Conditioning and Heat Pump Fundamentals

A technician notices the indoor coil is iced over while the system runs continuously. Which condition most plausibly explains this?

  1. Low refrigerant charge or restricted airflow Correct answer.
  2. A liquid line that is too subcooled
  3. A thermostat set too high
  4. Excessive outdoor airflow across the condenser

Explanation

Ice on the evaporator signals that coil temperature has fallen below freezing, usually because low charge or restricted airflow reduces heat available to boil refrigerant. Both faults lower suction pressure and temperature. Correcting charge or airflow restores normal operation.

Question 15Air Conditioning and Heat Pump Fundamentals

Why is R-410A typically charged as a liquid rather than as a vapor?

  1. It has a very low critical temperature
  2. It is a zeotropic blend and liquid charging preserves the intended composition Correct answer.
  3. It is flammable as a vapor
  4. It contains no lubricant and would foam

Explanation

R-410A is a near-azeotropic blend of two refrigerants, and the components can fractionate if vapor is drawn from a cylinder. Charging liquid keeps the mixture at its designed ratio. Manifold gauges and throttling devices are used to charge safely as liquid.

Question 16Air Conditioning and Heat Pump Fundamentals

A heat pump delivers warm but insufficient heat on a cold day, and the auxiliary electric strip heat never energizes. Which item should be checked first?

  1. The liquid line filter drier
  2. The outdoor fan capacitor
  3. The condenser fan blade pitch
  4. The auxiliary heat sequencer or relay and its control wiring Correct answer.

Explanation

If auxiliary strip heat does not stage on, the control path feeding its sequencer or relay is the logical first check. That includes the thermostat's auxiliary heat signal and low-voltage wiring. Coil and fan components would not prevent strip heat from energizing.

Question 17Air Conditioning and Heat Pump Fundamentals

What does the term balance point mean for a heat pump system?

  1. The outdoor temperature at which heat pump output equals the building heat loss Correct answer.
  2. The indoor humidity level at which the coil stops condensating
  3. The point where subcooling equals superheat
  4. The refrigerant pressure at which the system is fully charged

Explanation

The balance point is where the heat pump's capacity curve crosses the structure's heat loss curve. Below that outdoor temperature, the heat pump alone cannot hold setpoint, so auxiliary heat makes up the difference. It is a system design concept, not a refrigerant measurement.

Question 18Air Conditioning and Heat Pump Fundamentals

An air-source heat pump's rated heating capacity falls as outdoor temperature drops. What is the main physical reason?

  1. Refrigerant mass flow increases in cold weather
  2. The lower outdoor temperature reduces the temperature difference available for heat absorption Correct answer.
  3. The compressor slows down automatically
  4. The indoor coil loses surface area in cold weather

Explanation

Heating capacity depends on the difference between the outdoor air and the cold evaporating refrigerant. As outdoor air cools, less heat is available per pound of refrigerant, and lower suction density reduces mass flow. Both effects cut capacity.

Question 19Air Conditioning and Heat Pump Fundamentals

What is the purpose of the accumulator in a heat pump system?

  1. To store liquid refrigerant and prevent it from reaching the compressor Correct answer.
  2. To provide a reservoir of liquid for the metering device
  3. To separate oil from discharge gas
  4. To increase discharge pressure during heating

Explanation

The accumulator sits on the suction side and traps any liquid refrigerant that did not boil off, releasing it gradually as vapor. This protects the compressor from slugging. Liquid reservoirs for the metering device belong on the high side.

Question 20Air Conditioning and Heat Pump Fundamentals

A technician finds a 20°F temperature drop between the return and supply air across the indoor coil with low airflow. What is the most reasonable interpretation?

  1. The system has too much refrigerant
  2. The low airflow is exaggerating the temperature split, so airflow must be corrected before judging charge Correct answer.
  3. The compressor is oversized
  4. The charge is definitely correct

Explanation

A temperature split is only meaningful when airflow is within design range. Low airflow lets the same coil cool less air more deeply, inflating the split. Airflow and filter condition should be corrected before charge is evaluated by superheat or subcooling.

Question 21Air Conditioning and Heat Pump Fundamentals

Which statement correctly distinguishes a heat pump from a cooling-only air conditioner?

  1. A heat pump has a larger compressor in all cases
  2. A heat pump can reverse refrigerant flow to provide heating as well as cooling Correct answer.
  3. A heat pump rejects heat indoors in both modes
  4. A heat pump does not use a metering device

Explanation

The defining feature of a heat pump is the ability to reverse the refrigeration cycle so the indoor coil can act as either evaporator or condenser. A cooling-only unit rejects heat indoors only in the sense of cooling the space; it cannot supply heat by reversing flow.

Question 22Air Conditioning and Heat Pump Fundamentals

A heat pump in heating mode shows very high head pressure and high subcooling while outdoor fan operation is normal. Which fault is most consistent with these readings?

  1. A suction line that is too short
  2. Low indoor airflow in heating mode
  3. A failed reversing valve solenoid coil only
  4. An overcharge of refrigerant or a restriction in the indoor metering path Correct answer.

Explanation

High head pressure with elevated subcooling points to excess liquid backing up in the condenser, caused by overcharge or a restriction downstream of the condenser. In heating mode the indoor coil is the condenser, so its metering path matters. Low airflow would raise pressures too but would not raise subcooling in the same way.

Question 23Air Conditioning and Heat Pump Fundamentals

Why do some cold-climate heat pumps use vapor injection or economizer circuits?

  1. To eliminate the need for a defrost cycle
  2. To lower the compressor's compression ratio to zero
  3. To reduce the refrigerant charge required
  4. To increase heating capacity and discharge temperature at low outdoor temperatures Correct answer.

Explanation

Vapor injection adds intermediate-pressure vapor to the compression process, increasing mass flow through the evaporator and raising capacity and supply temperature in cold weather. It does not remove the need for defrost, and a compression ratio cannot be reduced to zero.

Question 24Air Conditioning and Heat Pump Fundamentals

A heat pump system in cooling mode has normal suction pressure but the liquid line is warm and the evaporator is starved. Which condition best fits a restricted liquid line drier?

  1. Low head pressure with high superheat at the compressor
  2. A frosted suction line with normal subcooling
  3. High subcooling at the condenser with a pressure drop across the drier Correct answer.
  4. A temperature drop across the drier with low subcooling at the condenser outlet

Explanation

A restriction holds liquid back at the condenser, so subcooling rises upstream of the restriction. Downstream, pressure and temperature drop, starving the evaporator. Measuring temperature or pressure across the drier confirms the restriction.

Question 25Air Conditioning and Heat Pump Fundamentals

A building's heat loss is 40,000 Btu/h at 20°F outdoor design temperature. The installed heat pump delivers 26,000 Btu/h at that condition. What does this indicate about the design?

  1. The balance point is above 20°F and no backup is needed
  2. A supplemental heat source of about 14,000 Btu/h is needed at design conditions Correct answer.
  3. The heat pump alone is adequate and auxiliary heat is unnecessary
  4. The heat pump is oversized by about 14,000 Btu/h

Explanation

Subtracting the heat pump capacity from the building load gives the shortfall that backup heat must cover. Here 40,000 minus 26,000 equals 14,000 Btu/h. Auxiliary heat is sized to make up that difference at design conditions.

Question 26Air Conditioning and Heat Pump Fundamentals

Which physical change occurs in the refrigerant as it passes through the condenser of a system operating in the cooling mode?

  1. It absorbs heat and boils from a low-pressure liquid to a low-pressure vapor.
  2. It increases in pressure while remaining entirely a superheated vapor.
  3. It releases heat and condenses from a high-pressure vapor to a high-pressure liquid. Correct answer.
  4. It drops in pressure and temperature while remaining entirely a liquid.

Explanation

The condenser is the heat-rejection coil, so the hot high-pressure discharge vapor gives up sensible heat to the outdoor air and then latent heat as it changes phase into a liquid. Because the coil is on the high-pressure side, the pressure stays high across it while enthalpy falls.

Question 27Air Conditioning and Heat Pump Fundamentals

A technician measures a supply air temperature of 58°F and a return air temperature of 76°F across an evaporator coil. What is the temperature split?

  1. 18°F Correct answer.
  2. 14°F
  3. 34°F
  4. 22°F

Explanation

Temperature split is the difference between the entering (return) air and the leaving (supply) air. Subtracting the smaller value from the larger gives 76 minus 58, which equals 18°F. This value is then compared with the manufacturer's expected range for the measured indoor conditions.

Question 28Air Conditioning and Heat Pump Fundamentals

What is the primary function of the metering device in a heat pump or air conditioning circuit?

  1. To raise the pressure of the refrigerant vapor before it enters the condenser.
  2. To remove moisture and acid from the refrigerant as it circulates.
  3. To store excess liquid refrigerant during low-load operation.
  4. To reduce refrigerant pressure and regulate flow into the evaporator. Correct answer.

Explanation

The metering device creates the pressure drop between the high side and the low side and controls how much refrigerant enters the evaporator. That drop lowers the saturation temperature so the coil can absorb heat from the conditioned air.

Question 29Air Conditioning and Heat Pump Fundamentals

Which statement best explains why airflow across an evaporator coil matters for capacity?

  1. Reduced airflow limits heat transfer to the refrigerant, lowering capacity and suction pressure. Correct answer.
  2. Reduced airflow lowers the coil temperature, which shortens compressor run time.
  3. Reduced airflow raises the suction pressure, which increases the mass flow of refrigerant.
  4. Reduced airflow lowers the heat content of the air, which decreases the load on the coil.

Explanation

The evaporator can only absorb heat that the air stream delivers to its fins and tubes. When airflow falls, less heat is available per unit of coil surface, so the refrigerant evaporates less completely, suction pressure drops, and net capacity falls.

Question 30Air Conditioning and Heat Pump Fundamentals

A heat pump operating in heating mode has a suction pressure that is lower than expected and a suction line that is frosted at the outdoor coil. Which condition is most consistent with these readings?

  1. A shorted outdoor fan motor running too fast
  2. An overcharge of refrigerant in the system
  3. A failed reversing valve stuck in cooling mode
  4. A restricted or blocked outdoor coil airflow path Correct answer.

Explanation

In heating mode the outdoor coil is the evaporator, so restricted airflow across it starves the coil of heat and drives suction pressure down while frost forms. Low load on the coil produces exactly the frosted suction line and low pressure described.

Question 31Air Conditioning and Heat Pump Fundamentals

A technician measures a suction line temperature of 62°F with a suction saturation temperature of 45°F. What is the superheat?

  1. 27°F
  2. 62°F
  3. 45°F
  4. 17°F Correct answer.

Explanation

Superheat is the difference between the actual suction line temperature and the saturation temperature at the same pressure. Subtracting 45 from 62 gives 17°F of superheat, which confirms vapor has fully formed before leaving the coil.

Question 32Air Conditioning and Heat Pump Fundamentals

Why does a heat pump's heating capacity decrease as the outdoor air temperature falls?

  1. The smaller outdoor-to-refrigerant temperature difference reduces heat absorbed by the outdoor coil. Correct answer.
  2. The compressor speed is reduced by the outdoor thermostat at low ambient.
  3. The indoor coil becomes the condenser and cannot reject heat efficiently.
  4. The refrigerant charge is deliberately reduced to protect the compressor.

Explanation

Heating capacity depends on the temperature difference between the outdoor air and the colder refrigerant in the outdoor coil. As outdoor air cools, that gap shrinks, fewer Btu per pound of refrigerant are absorbed, and capacity declines.

Question 33Air Conditioning and Heat Pump Fundamentals

During a defrost cycle, which sequence of actions typically occurs in a heat pump?

  1. The compressor unloads, the metering device closes fully, and the indoor blower slows down.
  2. The reversing valve stays in heating, the outdoor fan reverses, and the indoor coil defrosts.
  3. The compressor stops, the outdoor fan runs at high speed, and the indoor blower shuts off.
  4. The reversing valve shifts to cooling, outdoor fan stops, and auxiliary heat energizes indoors. Correct answer.

Explanation

Defrost temporarily puts the system back into cooling mode so hot discharge gas flows through the outdoor coil and melts frost. The outdoor fan is stopped to keep the coil warm, and indoor auxiliary heat runs so the space does not blow cold air.

Question 34Air Conditioning and Heat Pump Fundamentals

A heat pump in heating mode has a suction pressure that is too high and a suction line that is warm and sweating at the compressor. Which fault best fits these symptoms?

  1. A dirty indoor coil with low airflow
  2. An undercharge of refrigerant
  3. A restricted liquid line filter drier
  4. A reversing valve leaking internally between suction and discharge Correct answer.

Explanation

An internal leak in the reversing valve lets hot discharge gas bypass into the suction side, raising suction pressure and warming the suction line. The compressor then handles dilute, warmer vapor, which shows up as the described readings.

Question 35Air Conditioning and Heat Pump Fundamentals

What is the purpose of the auxiliary (supplemental) electric resistance heat in a heat pump system?

  1. To cool the compressor during long heating cycles.
  2. To raise the refrigerant suction pressure during cold starts.
  3. To replace the compressor entirely once outdoor temperature drops below freezing.
  4. To make up capacity when the heat pump alone cannot meet the building load and to temper defrost air. Correct answer.

Explanation

A heat pump's capacity falls with outdoor temperature, so resistance elements stage on to cover the gap between heat pump output and building load. They also run during defrost to prevent cold supply air from reaching the occupants.

Question 36Air Conditioning and Heat Pump Fundamentals

A heat pump in cooling mode has normal suction pressure, but the indoor coil is only partly cold and the suction line is not sweating along its full length. Which condition most likely explains this?

  1. A restricted metering device or distributor Correct answer.
  2. A condenser fan running too fast
  3. A failed indoor blower motor
  4. An overcharge of refrigerant

Explanation

A restriction at the metering device or distributor limits refrigerant flow, so only part of the evaporator circuit receives liquid and becomes cold. Suction pressure can look near normal while the coil is partially starved, which matches the described pattern.

Question 37Air Conditioning and Heat Pump Fundamentals

Which pressure relationship correctly describes a normally operating system?

  1. Discharge pressure is higher than suction pressure because the compressor raises vapor pressure. Correct answer.
  2. Suction pressure equals the saturation pressure of the liquid line.
  3. Suction pressure is higher than discharge pressure during the cooling cycle.
  4. Suction and discharge pressures are equal across the compressor at steady state.

Explanation

The compressor takes low-pressure vapor from the evaporator and compresses it, so discharge pressure is always higher than suction pressure in a running system. That pressure ratio is what allows the condenser to reject heat at a temperature above outdoor air.

Question 38Air Conditioning and Heat Pump Fundamentals

A building has a design heat loss of 45,000 Btu/h at 15°F outdoor temperature. The selected heat pump delivers 28,000 Btu/h at that temperature. What is the required auxiliary heat capacity, ignoring defrost allowance?

  1. 73,000 Btu/h
  2. 17,000 Btu/h Correct answer.
  3. 45,000 Btu/h
  4. 28,000 Btu/h

Explanation

Auxiliary heat must cover the difference between the building load and the heat pump output at design conditions. Subtracting 28,000 from 45,000 leaves 17,000 Btu/h of supplemental capacity needed to hold the indoor setpoint.

Question 39Air Conditioning and Heat Pump Fundamentals

A heat pump is installed in a climate where the balance point is 30°F, but the building's heat loss at 30°F exactly equals heat pump output. What happens to auxiliary heat as outdoor temperature rises above 30°F?

  1. It stages on progressively more to maintain setpoint.
  2. It runs continuously to protect the compressor from short cycling.
  3. It remains locked out because the heat pump alone meets the load. Correct answer.
  4. It cycles on and off in step with the compressor.

Explanation

Above the balance point the heat pump's output exceeds the building load, so no supplemental capacity is needed and the auxiliary stages stay off. Auxiliary heat only becomes necessary when outdoor temperature falls below the balance point.

Question 40Air Conditioning and Heat Pump Fundamentals

A technician calculates that a system's suction line superheat is 2°F at the compressor while the evaporator is flooded and the compressor is sweating. Which conclusion is most defensible?

  1. Liquid refrigerant is reaching the compressor, risking slugging and oil dilution. Correct answer.
  2. The system is undercharged and needs additional refrigerant.
  3. The metering device is restricted and should be replaced.
  4. The evaporator airflow is excessive and should be increased.

Explanation

Very low superheat at the compressor means vapor is still carrying liquid droplets instead of being fully boiled off in the evaporator. That condition can dilute compressor oil and cause mechanical damage, so charge or metering should be corrected before continued operation.

Question 41System Design and Sizing

A heat pump is rated at 36,000 BTU/h. What is its nominal capacity in tons?

  1. 4 tons
  2. 1.5 tons
  3. 6 tons
  4. 3 tons Correct answer.

Explanation

One ton of refrigeration equals 12,000 BTU/h, so dividing the rated capacity by 12,000 yields the tonnage. Here 36,000 divided by 12,000 equals 3 tons, which is the standard way to express residential heat pump capacity.

Question 42System Design and Sizing

Which quantity expresses how much heating or cooling a system actually delivers to the conditioned space at design conditions?

  1. Net capacity Correct answer.
  2. Nominal capacity
  3. Gross capacity
  4. Standby capacity

Explanation

Net capacity subtracts defrost losses, fan heat, and duct losses from the gross refrigeration effect, giving the load actually met at the space. Designers size equipment against net capacity so that the building load is truly satisfied on the coldest or hottest day.

Question 43System Design and Sizing

A house has a design heating load of 48,000 BTU/h at 5°F outdoor and 70°F indoor. What nominal heat pump capacity should be selected if the unit is to meet the full load?

  1. 60,000 BTU/h
  2. 24,000 BTU/h
  3. 36,000 BTU/h
  4. 48,000 BTU/h Correct answer.

Explanation

Equipment is matched to the design load so that capacity equals demand at the coldest expected outdoor temperature. Selecting 48,000 BTU/h balances the two, though many designers add a small margin or pair the unit with supplemental heat instead of oversizing.

Question 44System Design and Sizing

Which load component is typically the largest sensible cooling load in a well-insulated residence?

  1. Duct conduction loss
  2. Solar gain through windows Correct answer.
  3. Infiltration sensible load
  4. Internal latent load from occupants

Explanation

Solar radiation through glazing can drive the peak sensible load, especially on west and south exposures in summer. Manual J treats fenestration solar gain as a dominant block, which is why shading and glass selection matter so much.

Question 45System Design and Sizing

What does the balance point of a heat pump represent?

  1. The point where defrost terminates
  2. The outdoor temperature where heat pump capacity equals building load Correct answer.
  3. The refrigerant pressure at which the compressor unloads
  4. The indoor temperature at which the thermostat is satisfied

Explanation

As outdoor air cools, heat pump capacity falls while building load rises; their intersection is the balance point. Below that temperature the unit can no longer meet the load alone and supplemental heat must make up the difference.

Question 46System Design and Sizing

Which factor most directly increases the required supplemental heat capacity in a cold-climate heat pump design?

  1. Higher indoor humidity setpoint
  2. Lower design outdoor temperature Correct answer.
  3. Shorter refrigerant line set
  4. Larger return air duct

Explanation

Supplemental capacity is sized to cover the gap between heat pump output and building load at the design outdoor temperature. A colder design temperature widens that gap because capacity drops and load climbs simultaneously.

Question 47System Design and Sizing

What is the primary purpose of a Manual J load calculation in system design?

  1. To estimate the heating and cooling loads the system must meet Correct answer.
  2. To select refrigerant line sizes
  3. To determine equipment efficiency ratings
  4. To set thermostat schedules

Explanation

A room-by-room load calculation quantifies sensible and latent gains and losses so equipment can be sized to the building. Sizing from rules of thumb instead often leads to oversizing and comfort problems.

Question 48System Design and Sizing

A heat pump has a rated cooling capacity of 30,000 BTU/h and a sensible heat ratio of 0.75. What is its sensible capacity?

  1. 22,500 BTU/h Correct answer.
  2. 15,000 BTU/h
  3. 30,000 BTU/h
  4. 7,500 BTU/h

Explanation

Sensible capacity equals total capacity multiplied by the sensible heat ratio, so 30,000 times 0.75 equals 22,500 BTU/h. The remaining 7,500 BTU/h is latent capacity used for dehumidification.

Question 49System Design and Sizing

Why should a heat pump be sized close to the design load rather than significantly oversized?

  1. Oversizing causes short cycling and poor latent removal Correct answer.
  2. Oversizing eliminates the need for a defrost cycle
  3. Oversizing reduces first cost
  4. Oversizing improves low-temperature heating output

Explanation

An oversized unit reaches setpoint quickly and shuts off before removing enough moisture, so the space feels clammy and equipment wears from frequent starts. Modest sizing with proper airflow keeps run times long enough for dehumidification and stable temperatures.

Question 50System Design and Sizing

A duct system delivers 1,200 CFM with a 0.10 in. w.c. external static pressure. Which design change most directly reduces static pressure without changing airflow?

  1. Increase duct cross-sectional area Correct answer.
  2. Reduce return grille free area
  3. Add a tighter filter
  4. Increase blower speed

Explanation

Static pressure falls with the square of velocity for a fixed airflow, so enlarging duct area lowers velocity and pressure drop. Reducing restrictions such as filters or grilles raises static pressure and should be avoided.