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NVQ L4 Refrigeration & AC study materials
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NVQ L4 Refrigeration & AC practice questions

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Question 1Health, safety and environmental compliance in refrigeration and air conditioning work

Why should refrigerant cylinders be stored upright and secured?

  1. To allow the cylinder to be rolled away quickly.
  2. To keep the pressure-relief device in the vapour space. Correct answer.
  3. To stop the valve outlet pointing at the wall.
  4. To keep the cylinder label visible for inspection.

Explanation

Cylinders are designed so the pressure-relief device vents vapour. If a cylinder lies on its side, liquid refrigerant can reach the device and be discharged as a large, very cold release, and an unsecured cylinder can fall and shear the valve.

Question 2Health, safety and environmental compliance in refrigeration and air conditioning work

Which PPE is required as a minimum when decanting liquid refrigerant from one cylinder to another?

  1. Welding gauntlets and tinted goggles.
  2. Ear defenders and a disposable dust mask.
  3. Face shield, insulated cryogenic gloves and an apron. Correct answer.
  4. Cotton overalls and thin nitrile gloves.

Explanation

Liquid refrigerant boils at very low temperature and can cause severe cold burns or frostbite on contact with skin, and can splash into the eyes. A face shield, insulating gloves rated for low temperature, and a protective apron are the minimum protection.

Question 3Health, safety and environmental compliance in refrigeration and air conditioning work

Which gas must never be used to pressure-test a refrigeration system?

  1. Helium.
  2. Dry nitrogen.
  3. Argon.
  4. Oxygen. Correct answer.

Explanation

Oxygen under pressure reacts violently with oil and grease and can detonate, so it must never be used for strength or leak testing. Dry nitrogen is the standard test gas because it is inert and dry.

Question 4Health, safety and environmental compliance in refrigeration and air conditioning work

Which statement about refrigerant removed from a system is correct?

  1. It may be released outdoors when the wind is strong.
  2. It may be discharged through the vacuum pump to save time.
  3. It must be recovered into a suitable container and not released to atmosphere. Correct answer.
  4. It may be released if the system holds less than 3 kg.

Explanation

Deliberately releasing controlled refrigerants to the atmosphere is prohibited, whatever the charge size. Refrigerant must be recovered into a suitable container so that it can be recycled, reclaimed or disposed of correctly.

Question 5Health, safety and environmental compliance in refrigeration and air conditioning work

For how long must an operator keep F-gas leak-check and service records for a system?

  1. At least 1 year.
  2. At least 5 years. Correct answer.
  3. At least 10 years.
  4. At least 3 years.

Explanation

Operators must keep records of leak checks, repairs and refrigerant added or recovered for a minimum of five years, and make them available to an inspector on request.

Question 6Health, safety and environmental compliance in refrigeration and air conditioning work

Why is a leak of carbon dioxide refrigerant into a basement plant room particularly dangerous?

  1. It is lighter than air and collects at ceiling level.
  2. It is flammable and can ignite at low level.
  3. It has a strong smell that warns occupants in good time.
  4. It is heavier than air and can displace the oxygen at low level. Correct answer.

Explanation

Carbon dioxide is denser than air, so in a pit, basement or low-lying plant room it collects and displaces breathing air, causing rapid asphyxiation. It is odourless, so there may be no warning before collapse.

Question 7Health, safety and environmental compliance in refrigeration and air conditioning work

What is the correct way to move a large refrigerant cylinder across a workshop?

  1. Carry it on your shoulder for short distances.
  2. Drag it by the valve cap.
  3. Use a purpose-made cylinder trolley and secure the cylinder to it. Correct answer.
  4. Roll it along the floor holding the valve.

Explanation

Cylinders are heavy and awkward, so manual lifting is a significant injury risk and a dropped cylinder can shear the valve. A cylinder trolley with the cylinder secured is the safe handling method.

Question 8Health, safety and environmental compliance in refrigeration and air conditioning work

Which statement about safety data sheets on site is correct?

  1. They are kept locked in the manager's office and issued only on request.
  2. They are only needed for substances used in large quantities.
  3. They may be replaced by the manufacturer's advertising leaflet.
  4. They must be available to everyone who uses or handles the substance. Correct answer.

Explanation

Safety data sheets give the hazard, first-aid, spill and disposal information needed to work safely, and must be accessible to the people using the substance. They support the COSHH assessment for lubricants, refrigerants, fluxes and cleaning chemicals.

Question 9Health, safety and environmental compliance in refrigeration and air conditioning work

Under F-gas rules, how often must an operator leak-check a system containing between 5 and 50 tonnes CO2 equivalent when no fixed detection system is fitted?

  1. At least every 24 months.
  2. At least every 3 months.
  3. At least every 6 months.
  4. At least every 12 months. Correct answer.

Explanation

The standard leak-check frequencies rise with charge: at least every 12 months for 5 to 50 tonnes CO2e, every 6 months for 50 to 500 tonnes, and every 3 months at 500 tonnes and above.

Question 10Health, safety and environmental compliance in refrigeration and air conditioning work

A system contains 60 tonnes CO2 equivalent and has a fixed leakage detection system that is verified each year. What is the maximum interval between manual leak checks?

  1. Every 3 months. Correct answer.
  2. Every 6 months.
  3. Every 12 months.
  4. Every 24 months.

Explanation

A charge of 60 tonnes CO2e falls in the 50 to 500 tonne band, giving a base interval of six months. Where a fixed leakage detection system is installed and checked annually, the interval between manual checks may be halved, giving three months.

Question 11Health, safety and environmental compliance in refrigeration and air conditioning work

Why is dry nitrogen flowed through pipework while brazing joints?

  1. To draw moisture out of the filler rod.
  2. To raise the pressure inside the pipe while brazing.
  3. To cool the joint so the filler metal sets faster.
  4. To prevent oxidation and scale forming on the inside of the pipe. Correct answer.

Explanation

Heating copper in the presence of air forms oxide scale inside the pipework, which later contaminates the refrigerant circuit and can block strainers and damage the compressor. A slow nitrogen purge displaces the air and prevents this.

Question 12Health, safety and environmental compliance in refrigeration and air conditioning work

A hot work permit is issued for brazing in a plant room. What does good practice require when the torch is switched off?

  1. Post a warning sign and take no further action.
  2. Spray the area with water and sign the permit back immediately.
  3. Maintain a fire watch in the area for a set period after work finishes. Correct answer.
  4. Leave the area at once and return at the end of the shift.

Explanation

Smouldering material such as insulation or dust can take time to develop into a fire after the torch is extinguished. The permit should require a fire watch, commonly at least 30 to 60 minutes, with the area checked before the permit is closed.

Question 13Health, safety and environmental compliance in refrigeration and air conditioning work

Which of these refrigerants has the highest global warming potential?

  1. R134a.
  2. R32.
  3. R404A. Correct answer.
  4. R410A.

Explanation

R404A has a GWP of about 3922, the highest of these, which is why its use in new equipment has been restricted under the F-gas phase-down. For comparison, R410A is around 2088, R134a around 1430 and R32 around 675.

Question 14Health, safety and environmental compliance in refrigeration and air conditioning work

An engineer gets liquid refrigerant on the back of the hand. What is the correct first-aid response?

  1. Rub the area briskly with a warm cloth.
  2. Apply ice directly to the frozen skin.
  3. Flush with plenty of tepid water, remove affected clothing and obtain medical help. Correct answer.
  4. Warm the area quickly with hot water or a heat lamp.

Explanation

Liquid refrigerant evaporates rapidly and freezes tissue on contact. The affected area should be flushed with plenty of tepid water, clothing that may be frozen to the skin should not be pulled away, and medical help must be sought.

Question 15Health, safety and environmental compliance in refrigeration and air conditioning work

A strong smell of ammonia is detected coming from a plant room. What is the correct immediate action?

  1. Stay in the area and use a hose to dilute the gas.
  2. Enter with a dust mask and close the main valve.
  3. Raise the alarm, move upwind and keep people out until trained staff with breathing apparatus attend. Correct answer.
  4. Wait nearby until the smell clears, then enter without protection.

Explanation

Ammonia is acutely toxic and can incapacitate a person very quickly, so unprotected entry is life-threatening. The correct response is to alarm, evacuate, approach from upwind and let trained responders wearing breathing apparatus isolate the leak.

Question 16Health, safety and environmental compliance in refrigeration and air conditioning work

Before working on the electrical supply to a condensing unit, what must be done?

  1. Isolate the supply, lock off, and prove the circuit is dead. Correct answer.
  2. Switch off at the local isolator and start work at once.
  3. Rely on the stop button on the control panel.
  4. Ask a colleague to stand by the switch while you work.

Explanation

The safe isolation procedure is to identify and isolate the supply, lock off and tag the point of isolation, then prove the conductors are dead with a test instrument before touching them. A colleague watching a switch is not a substitute for lock-off.

Question 17Health, safety and environmental compliance in refrigeration and air conditioning work

What is the correct route for refrigerant recovered from a decommissioned system?

  1. Pour it into the workshop drain with plenty of water.
  2. Burn it in a workshop heater to recover the energy.
  3. Transfer it to a registered waste carrier as hazardous waste with the correct documentation. Correct answer.
  4. Store it in an unlabelled container for the general waste collection.

Explanation

Recovered refrigerant is controlled waste that must be handled under the duty of care, transferred only to a registered carrier and accompanied by the correct waste documentation. Reuse is only possible where it has been reclaimed or recycled to the required standard.

Question 18Health, safety and environmental compliance in refrigeration and air conditioning work

Which method is acceptable for pinpointing a suspected leak on a flare joint?

  1. Pressurise the joint with oxygen and listen for a hiss.
  2. Feel the pipe by hand to find a cold spot.
  3. Hold a lighted gas torch near the joint.
  4. Use an electronic leak detector or apply soap solution to the joint. Correct answer.

Explanation

An electronic refrigerant detector or a soap solution applied to the joint will show a leak safely. Flame testing produces toxic decomposition products and is never acceptable, and oxygen must never be used to pressurise a system.

Question 19Health, safety and environmental compliance in refrigeration and air conditioning work

What hazard arises when air and moisture are left inside a system that is subsequently run?

  1. The refrigerant becomes flammable.
  2. The lubricating oil turns into a harmless wax.
  3. Acids form that can burn the skin and damage the compressor. Correct answer.
  4. The system pressure rises automatically to a dangerous level.

Explanation

Moisture and air in a refrigeration circuit react with refrigerant and oil to form acidic compounds, which corrode windings and pipework and can burn the skin when a system is opened. This is why evacuation and dehydration are essential before charging.

Question 20Health, safety and environmental compliance in refrigeration and air conditioning work

Why must a pressure-reducing regulator be fitted when nitrogen from a cylinder is used for pressure testing?

  1. To reduce the high cylinder pressure to a controlled test pressure. Correct answer.
  2. To allow the cylinder to be laid on its side during the test.
  3. To add moisture to the gas so leaks are easier to see.
  4. To stop nitrogen condensing inside the pipework.

Explanation

A full nitrogen cylinder is at very high pressure, far above any test pressure, and uncontrolled delivery can burst pipework or fittings. A regulator reduces the outlet pressure and allows the test pressure to be set and controlled.

Question 21Health, safety and environmental compliance in refrigeration and air conditioning work

Why is oxygen especially dangerous when used to pressurise a system that contains refrigerant oil?

  1. Oxygen dissolves the oil and destroys lubrication.
  2. Oxygen freezes the oil and blocks the pipework.
  3. Oxygen and oil can form an explosive mixture under pressure. Correct answer.
  4. Oxygen reacts with copper to form a toxic gas at low pressure.

Explanation

Pressurised oxygen combined with oil or grease can ignite spontaneously and detonate, which is why only inert gases such as dry nitrogen are used for strength and leak testing. The risk exists even at moderate pressures.

Question 22Health, safety and environmental compliance in refrigeration and air conditioning work

Why must the refrigerant charge be recovered and the pipework purged before brazing a joint on an existing system?

  1. Heat can break the refrigerant down into toxic and corrosive compounds. Correct answer.
  2. The refrigerant speeds up brazing so the joint is hard to control.
  3. The refrigerant acts as a flux and weakens the joint.
  4. The refrigerant freezes the pipe and prevents the joint forming.

Explanation

Heating refrigerant in the presence of a flame and air produces hydrogen fluoride and other toxic, corrosive breakdown products, and some older refrigerants can form phosgene. The charge must be recovered and the section purged or vented to a safe place before heat is applied.

Question 23Health, safety and environmental compliance in refrigeration and air conditioning work

Which statement about the refrigerant R22 is correct?

  1. It is an HFC with zero ozone depletion potential.
  2. It is an ozone-depleting HCFC and must be recovered rather than vented. Correct answer.
  3. It has a GWP of zero and is outside the F-gas rules.
  4. It can be vented to atmosphere because it is an old refrigerant.

Explanation

R22 is a hydrochlorofluorocarbon with a measurable ozone depletion potential, and its supply for new equipment and for maintenance has been phased out. Any R22 recovered from an existing system must be recovered and handled as controlled waste, never vented.

Question 24Health, safety and environmental compliance in refrigeration and air conditioning work

A system holds 10 kg of R410A, which has a GWP of 2088. What is the charge in tonnes CO2 equivalent, and what is the minimum leak-check interval?

  1. About 2.1 tonnes CO2e, so no leak checks are required.
  2. About 20.9 tonnes CO2e, so a check at least every 12 months. Correct answer.
  3. About 209 tonnes CO2e, so a check at least every 6 months.
  4. About 20.9 tonnes CO2e, so a check at least every 3 months.

Explanation

Tonnes CO2e equals mass in kilograms multiplied by GWP, divided by 1000, so 10 x 2088 / 1000 = 20.9 tonnes CO2e. That falls in the 5 to 50 tonne band, which requires a leak check at least every 12 months when no fixed detection system is fitted.

Question 25Health, safety and environmental compliance in refrigeration and air conditioning work

An engineer is injured at work and cannot carry out their normal duties for more than seven days. What does health and safety law require?

  1. Reporting is required only if refrigerant was also released.
  2. The incident need only be noted in the engineer's personal notebook.
  3. The employer must report the incident to the enforcing authority. Correct answer.
  4. Reporting is required only if the customer requests it.

Explanation

Employers must report specified injuries and injuries that keep a worker off normal duties for more than seven days to the enforcing authority under RIDDOR, and keep an incident record. The duty sits with the employer, not with the customer or the injured person.

Question 26Health, safety and environmental compliance in refrigeration and air conditioning work

An engineer is about to decant liquid refrigerant from one cylinder into another. Which personal protective equipment is required for this task?

  1. Eye protection and loose-fitting impervious gloves Correct answer.
  2. A dust mask and standard cotton overalls
  3. Cotton work gloves and safety footwear only
  4. No special equipment, provided the valve is opened slowly

Explanation

Liquid refrigerant boils at very low temperature, so contact with skin causes cold burns and splashes can permanently damage eyes. Impervious gloves with loose cuffs are specified because trapped liquid inside a tight glove would continue to freeze the skin and the glove must be removable quickly.

Question 27Health, safety and environmental compliance in refrigeration and air conditioning work

How should refrigerant cylinders be kept in a workshop storage area?

  1. Upright, secured and valve-capped in a ventilated store Correct answer.
  2. Standing on the floor with the valves left open to relieve pressure
  3. Laid flat on shelving so they cannot topple during handling
  4. Chained together in a locked cupboard beside the boiler to keep them dry

Explanation

Cylinders are pressure vessels and must be stored upright and restrained so they cannot fall, with valve caps fitted to protect the valve in the event of a knock. The store must be ventilated and kept clear of heat sources and ignition risks so that any leakage disperses rather than accumulating.

Question 28Health, safety and environmental compliance in refrigeration and air conditioning work

An operator keeps the F-gas equipment records for a split system. Which item must the record contain?

  1. The cylinder colour code used by the supplier for that refrigerant
  2. The quantity and type of refrigerant charged or recovered Correct answer.
  3. The name of the training provider that issued the engineer's certificate
  4. The ambient temperature in the plant room on the day of the visit

Explanation

Records for equipment containing F-gas must show the type and quantity of refrigerant involved, the quantity recovered, the dates of the work and details of the certified company or engineer. This allows the charge history, leakage and recovery performance of the system to be audited.

Question 29Health, safety and environmental compliance in refrigeration and air conditioning work

A risk assessment for replacing a compressor in a plant room identifies manual handling injury as a significant risk. Applying the hierarchy of control, which measure is the most effective?

  1. Issuing back support belts to the technicians doing the lift
  2. Providing manual handling training to all technicians on site
  3. Rotating the lift between several technicians to spread the load
  4. Rigging a hoist to lift the compressor into position Correct answer.

Explanation

The hierarchy of control ranks measures by effectiveness: eliminate the hazard, substitute it, apply engineering controls, then administrative controls, then PPE. A hoist removes the manual handling entirely and therefore controls the risk at source, whereas training, rotation and belts only rely on people behaving correctly.

Question 30Health, safety and environmental compliance in refrigeration and air conditioning work

A split system using an A2L flammable refrigerant is to be installed in a small office. Which factor determines the maximum charge that may be present in that room?

  1. The room volume and the refrigerant's flammability limit Correct answer.
  2. The seasonal ambient temperature range recorded for the site
  3. The diameter of the interconnecting pipework supplied with the kit
  4. The manufacturer's warranty terms for the outdoor unit

Explanation

For flammable refrigerants the charge in an occupied space is limited so that a complete leak could not reach a concentration approaching the lower flammability limit. The permitted charge is therefore calculated from the room volume and the flammability characteristics of the specific refrigerant, and additional measures such as ventilation or a refrigerant detector are needed where the limit is exceeded.

Question 31Design and specification of refrigeration and air conditioning systems

Under ASHRAE Standard 34, which refrigerant classification indicates lower toxicity and no flame propagation?

  1. B1
  2. A1 Correct answer.
  3. A3
  4. A2L

Explanation

The letter denotes toxicity class, with A being lower toxicity and B higher toxicity. The number denotes flammability, with 1 meaning no flame propagation, 2L lower flammability and 3 higher flammability. A1 therefore combines lower toxicity with no flame propagation.

Question 32Design and specification of refrigeration and air conditioning systems

In a direct-expansion system, superheat is the number of degrees the refrigerant vapour is:

  1. above its saturation temperature at the evaporating pressure Correct answer.
  2. above the condensing temperature at the compressor discharge
  3. below the entering air temperature at the evaporator
  4. below its saturation temperature at the evaporating pressure

Explanation

Superheat is measured at the evaporator outlet and is the difference between the actual suction line temperature and the saturation temperature corresponding to the suction pressure. A positive value confirms that no liquid is leaving the evaporator. It is a temperature difference at one pressure, not a comparison with air or condensing conditions.

Question 33Design and specification of refrigeration and air conditioning systems

Which of the following represents a latent heat load in an occupied space?

  1. Heat conducted through the wall
  2. Sweat evaporating from occupants Correct answer.
  3. Solar radiation through glazing
  4. Heat from lighting fixtures

Explanation

Latent loads change the moisture content of the air without changing its dry-bulb temperature, and evaporation of moisture from people is a classic example. Conduction, lighting and solar gain all raise the dry-bulb temperature and are sensible loads.

Question 34Design and specification of refrigeration and air conditioning systems

Which refrigerant is normally piped in steel rather than copper?

  1. R-134a
  2. R-32
  3. R-410A
  4. R-717 (ammonia) Correct answer.

Explanation

Ammonia attacks copper and its alloys, particularly in the presence of moisture, so steel pipe and steel components are used. The HFC and HFO refrigerants listed are routinely installed in copper. Material selection is therefore a fundamental part of the pipework specification.

Question 35Design and specification of refrigeration and air conditioning systems

A plant room ventilation rate is specified as six air changes per hour. This means:

  1. Six cubic metres of air enter per hour
  2. The volume is replaced six times per hour Correct answer.
  3. The grille velocity is six metres per second
  4. The room is held six pascals below atmosphere

Explanation

Air changes per hour express the number of times the whole room volume of air is replaced in one hour. It is a volume-based rate, obtained by dividing the supply airflow by the room volume. It says nothing about velocity, absolute flow or room pressure.

Question 36Design and specification of refrigeration and air conditioning systems

On a pressure–enthalpy diagram, the refrigeration effect per kilogram of refrigerant is the enthalpy difference between the:

  1. compressor discharge and condenser outlet
  2. compressor suction and discharge
  3. condenser outlet and evaporator inlet
  4. evaporator outlet and TEV outlet Correct answer.

Explanation

The refrigeration effect is the heat absorbed in the evaporator, that is the enthalpy at the evaporator outlet minus the enthalpy entering the evaporator after expansion. Because expansion is isenthalpic, the TEV outlet enthalpy equals the condenser outlet enthalpy. The larger figure is therefore the useful cooling obtained per kilogram circulated.

Question 37Design and specification of refrigeration and air conditioning systems

On a cold refrigerant suction line, the vapour barrier of the insulation should be fitted:

  1. on the outer surface of the insulation Correct answer.
  2. no vapour barrier is needed on cold lines
  3. between the pipe and the insulation
  4. on the inside surface next to the pipe

Explanation

Water vapour diffuses from warm moist air towards the cold pipe, so the barrier must be on the warm side, which is the outer surface. Sealing the outer jacket keeps moisture out of the insulation. A barrier placed on the cold side traps water against the pipe.

Question 38Design and specification of refrigeration and air conditioning systems

Which defrost method is normally specified for a low-temperature ammonia evaporator?

  1. Hot gas defrost Correct answer.
  2. Off-cycle air defrost
  3. Electric resistance heaters
  4. Warm water spray

Explanation

Hot gas defrost uses compressor discharge vapour to melt frost from inside the coil and is standard practice on industrial ammonia plant. It is efficient at low temperatures where air defrost cannot work and avoids electric heaters in the refrigerated space.

Question 39Design and specification of refrigeration and air conditioning systems

A suction line reads 3 °C while the saturation temperature at the measured suction pressure is −5 °C. What is the superheat?

  1. 8 K Correct answer.
  2. 11 K
  3. −8 K
  4. 2 K

Explanation

Superheat is the actual line temperature minus the saturation temperature at the same pressure. Here 3 °C − (−5 °C) = 8 K. The pressure must be the pressure at the point where the temperature is taken.

Question 40Design and specification of refrigeration and air conditioning systems

Oversizing a suction line is undesirable mainly because:

  1. velocity falls and oil may not return Correct answer.
  2. flash gas appears in the liquid line
  3. it raises the pressure drop and lowers capacity
  4. it raises the condensing pressure

Explanation

Suction lines must be small enough to keep the gas velocity above the value needed to drag oil back to the compressor. Oversizing reduces velocity, especially at part load, so oil can lodge in traps and risers. Pressure drop and liquid line behaviour are affected by other parts of the pipe design.

Question 41Design and specification of refrigeration and air conditioning systems

A chiller evaporator is specified with a smaller approach temperature than an alternative design. The main consequence is:

  1. less compressor power but a bigger heat exchanger Correct answer.
  2. no change in compressor power or size
  3. lower first cost and lower capacity
  4. higher compressor power and a smaller heat exchanger

Explanation

A small approach brings the evaporating temperature close to the chilled water temperature, raising suction pressure and reducing compressor power. The penalty is more heat transfer surface, so the evaporator is larger and more expensive. Approach and surface area trade off against running cost.

Question 42Design and specification of refrigeration and air conditioning systems

On a pump-down system, the liquid receiver must be large enough to:

  1. hold half of the total system charge
  2. hold only the evaporator charge as vapour
  3. store the entire charge as liquid Correct answer.
  4. match the condenser internal volume

Explanation

Pump-down moves the whole charge out of the low side and stores it as liquid in the receiver. The receiver must therefore have sufficient volume for the full charge at the highest expected ambient temperature, when liquid specific volume is greatest. Sizing it for part of the charge risks overfilling and high discharge pressures.

Question 43Design and specification of refrigeration and air conditioning systems

A room has a large west-facing window. Its peak summer cooling load from solar gain will occur:

  1. just after sunrise
  2. late afternoon Correct answer.
  3. at solar noon
  4. early morning

Explanation

West glazing receives direct sun in the afternoon, so the peak solar load arrives late in the day, often two to three hours after noon. East glazing peaks in the morning and a north-facing roof peaks around midday. Orientation therefore determines when the block load coincides.

Question 44Design and specification of refrigeration and air conditioning systems

The equal-friction method of duct sizing is used to:

  1. keep the total pressure constant along the run
  2. size each branch from the room load alone
  3. hold a constant pressure loss per metre Correct answer.
  4. hold the same air velocity in every section

Explanation

Equal friction sizes each successive section for the same pressure drop per unit length, which simplifies design and gives a naturally tapering system. Velocity falls along the run as the volume decreases. It is not the same as the constant-velocity method.

Question 45Design and specification of refrigeration and air conditioning systems

The approach temperature of an evaporative condenser is measured between the condensing temperature and the:

  1. entering air dry-bulb
  2. entering air wet-bulb Correct answer.
  3. spray water temperature
  4. leaving air dry-bulb

Explanation

An evaporative condenser rejects heat mainly by evaporation, so its performance is tied to the entering air wet-bulb temperature. The condensing temperature is normally 4 to 6 K above entering wet-bulb. Dry-bulb is the reference for air-cooled condensers, not evaporative ones.

Question 46Design and specification of refrigeration and air conditioning systems

When sizing central plant that serves many fan coil units, diversity is applied to:

  1. the individual fan coil capacities at design
  2. the refrigerant pipe diameters
  3. the outdoor air ventilation rate
  4. the coincident block load of the plant Correct answer.

Explanation

Diversity allows for the fact that not every terminal reaches its design load at the same moment. The plant is therefore sized on the coincident block load rather than the sum of connected capacities. Pipe sizes and each terminal's own duty are still based on their individual design figures.

Question 47Design and specification of refrigeration and air conditioning systems

A thermostatic expansion valve with an MOP charge is specified in order to:

  1. maintain a constant superheat at all part loads
  2. prevent liquid floodback at full load
  3. limit suction pressure during pull-down Correct answer.
  4. reduce condensing pressure in winter

Explanation

An MOP charge closes the valve as suction pressure rises above a set value, which holds the compressor within its motor rating during and after pull-down. Once the pressure falls back the valve modulates normally on superheat. It does not control condensing pressure and does not fix superheat at all loads.

Question 48Design and specification of refrigeration and air conditioning systems

A cooling coil has a bypass factor of 0.2. This means:

  1. 20 % of the air leaves at coil surface temperature
  2. 80 % of the air bypasses the coil
  3. 20 % of the air misses the coil face Correct answer.
  4. the coil removes 20 % of the sensible load

Explanation

Bypass factor is the fraction of air that passes through the coil without contacting the fin surface and therefore without being cooled to the apparatus dew point. A factor of 0.2 means 80 % of the air is treated and 20 % is effectively untreated. It is a characteristic of coil geometry and face velocity.

Question 49Design and specification of refrigeration and air conditioning systems

Flash gas appearing at the expansion valve inlet is most likely caused by:

  1. excessive subcooling at the condenser outlet
  2. pressure drop or heat gain in the liquid line Correct answer.
  3. too much superheat at the evaporator outlet
  4. an undersized suction line

Explanation

Liquid must arrive at the valve with enough subcooling to absorb line pressure drop and any heat picked up on route. If subcooling is lost or the drop is too large, part of the liquid flashes and valve capacity falls. Suction line and evaporator superheat are on the low side and cannot cause this.

Question 50Design and specification of refrigeration and air conditioning systems

An air-cooled condenser has to operate reliably at low winter ambient. A head pressure controller is needed because:

  1. the compressor motor would overspeed
  2. the expansion valve charge would be lost
  3. a low condensing pressure can starve the TEV Correct answer.
  4. the evaporating temperature would rise sharply at low load

Explanation

In cold weather the condensing pressure falls, so the pressure difference across the TEV becomes too small to deliver the required liquid flow, and the valve can hunt or starve the evaporator. Oil return and compressor lubrication can also suffer. Holding a minimum condensing pressure avoids both problems.