F-Gas English Low GWP
All questions
HFC | Flammable | CO₂ | NH₃
Easy questions |
Medium questions |
Difficult questions
1
Difficult
Why do CO₂ refrigeration systems require special attention when separating liquid and oil?
| CO₂ operates at high pressure, which increases the risk of compressor failure and leaks |
| CO₂ is flammable, so separators cannot be used |
| CO₂ does not require lubrication, so separators are unnecessary |
| CO₂ cannot be used in systems with sight glasses |
2
Difficult
What is the critical pressure of CO₂ (R744)?
| Approximately 10 bar |
| Approximately 31 bar |
| Approximately 74 bar |
| Approximately 120 bar |
3
Difficult
What characterises the transcritical process in CO₂ systems?
| Conventional condensation occurs |
| The system operates above the critical point and the refrigerant does not condense in the conventional manner |
| It is irrelevant to the operation of the system |
| It occurs only at low temperatures |
4
Difficult
What characterises the subcritical CO₂ process?
| The absence of evaporation |
| Operation above the critical point |
| The absence of condensation |
| The conventional condensation process below the critical point |
5
Difficult
What is the log(p)-h diagram for CO₂ used for?
| To detect leaks |
| For analysing thermodynamic processes in a refrigeration system |
| To measure temperature |
| To regulate pressure |
6
Difficult
What can be read from the log(p)-h graph?
| Pressure, enthalpy, temperature and state of the refrigerant |
| Only the temperature |
| Only the amount of refrigerant |
| Only the humidity |
7
Difficult
What are CO₂ saturation tables used for?
| To determine the relationship between temperature and pressure at saturation |
| To determine the oil quantity |
| To regulate the compressor |
| To measure humidity |
8
Difficult
What does the CO₂ saturation state mean?
| Dry ice state |
| A state of high pressure |
| Equilibrium between the liquid and vapour phases |
| A state in which the refrigerant is only a gas |
9
Difficult
When can dry ice (solid CO₂) form?
| During normal operation of the system |
| At high pressure |
| At high temperature |
| In the event of a sudden drop in pressure and temperature below the triple point |
10
Difficult
What risks are associated with the formation of dry ice in a CO₂ system?
| Improved efficiency |
| No risk |
| Pressure reduction |
| Blocked pipes and system damage |
11
Difficult
How does the CO₂ pressure change as the temperature rises?
| It decreases |
| Rises sharply |
| It first decreases, then increases |
| It remains the same |
12
Difficult
Why is understanding the log(p)-h graph particularly important for CO₂?
| As CO₂ systems operate in different modes (sub- and transcritical) and require detailed analysis |
| It doesn’t matter |
| It only applies to NH₃ |
| It is only used for design purposes |
13
Difficult
What happens to CO₂ above the critical point?
| It turns into a solid |
| It transitions to a supercritical state (no distinction between liquid and gas) |
| It turns into a liquid |
| It ceases to conduct heat |
14
Difficult
Why do CO₂ systems require precise pressure control?
| Because there are no valves |
| They do not require control |
| Due to significant pressure changes with temperature fluctuations |
| Due to low pressures |
15
Difficult
What is the main characteristic of R744 (CO₂) refrigeration systems?
| Very high operating pressures |
| Low energy efficiency |
| No need for regulation |
| Low operating pressures |
16
Difficult
What are the requirements for piping materials in CO₂ systems?
| They must be made exclusively from plastics |
| It does not matter |
| They must be able to withstand high pressures (e.g. high-grade steel) |
| They may be made of any material |
17
Difficult
How does a booster system work in CO₂ installations?
| It reduces the amount of refrigerant |
| It utilises two stages of compression (low and medium pressure) in a single system |
| It is used to store the refrigerant |
| It reduces the pressure in the evaporator |
18
Difficult
What is the function of high-pressure control valves in CO₂ systems?
| They regulate oil flow |
| They lower the evaporator temperature |
| They control the pressure on the high-pressure side and optimise system operation |
| They are used to store the refrigerant |
19
Difficult
Why is pressure optimisation in CO₂ systems crucial?
| It enables the system to achieve maximum energy efficiency |
| It reduces the ambient temperature |
| It doesn’t matter |
| It reduces the amount of refrigerant |
20
Difficult
What role do parallel-operating compressors play in CO₂ systems?
| They lower the ambient temperature |
| They increase energy consumption |
| They enable gas recovery from the medium-pressure stage and improve efficiency |
| It does not matter |
21
Difficult
How does an ejector work in a CO₂ system?
| It uses the energy of the higher-pressure refrigerant to raise the pressure of the refrigerant from the lower stage, which improves efficiency |
| Stores the refrigerant |
| It increases the amount of refrigerant |
| It lowers the evaporator temperature |
22
Difficult
What is the function of liquid ejectors in CO₂ systems?
| They reduce atmospheric pressure |
| They increase the amount of oil |
| They raise the refrigerant temperature |
| They assist with liquid recovery and improve evaporator feed |
23
Difficult
What are the characteristics of partially flooded systems in CO₂ systems?
| The absence of liquid in the evaporator |
| Low operating pressure |
| Lack of regulation |
| The presence of liquid in the evaporator, which improves heat transfer and efficiency |
24
Difficult
What is the main risk associated with static pressure in CO₂ systems?
| Increased efficiency |
| A drop in temperature |
| A rise in pressure resulting from the refrigerant heating up whilst at rest |
| A decrease in refrigerant quantity |
25
Difficult
How can standstill pressure in CO₂ systems be reduced?
| By increasing the temperature |
| By using parallel compressors and external cooling systems |
| By shutting down the system completely |
| By increasing the refrigerant charge |
26
Difficult
What does ‘stagnation’ of a refrigeration system mean in the context of CO₂?
| A drop in temperature |
| Improved efficiency |
| A lack of refrigerant flow, which can lead to increased pressure and safety risks |
| Normal system operation |
27
Difficult
Why do CO₂ systems require more advanced automation than traditional systems?
| Due to the need for precise control of pressure and temperature |
| Because there are no valves |
| They do not require automation |
| Due to low pressures |
28
Difficult
Which safety class applies to R744?
| A1 |
| A3 |
| B2L |
| A2 |
29
Difficult
In an R744 system operating in supercritical mode, the refrigerant entering the evaporator expansion valve is...
| Saturated vapour at intermediate pressure |
| A supercritical fluid |
| A two-phase mixture at intermediate pressure |
| A subcooled liquid |
30
Difficult
In R744 supercritical systems, the gas cooler outlet valve controls:
| The inlet temperature to the gas cooler |
| The gas cooler fans |
| The pressure in the gas cooler |
| The outlet temperature of the gas cooler |
31
Difficult
What is the main reason for using K65 copper tubing in some R744 systems?
| They have good low-temperature performance |
| They bend easily |
| They come in a wider range of diameters |
| They can withstand higher pressures |
32
Difficult
Which of the following statements is correct regarding the installation of Schrader valves?
| Schrader valves must not be used in R744 systems |
| Hydrocarbons leak through Schrader valves |
| When brazing the valve body to the system, the core must be removed, then refitted and tightened to the correct torque |
| All Schrader valve cores are suitable for all refrigerants |
33
Difficult
Which refrigerant can be detected using phenolphthalein paper?
| R717 |
| R1270 |
| R1234ze |
| R744 |
34
Difficult
How does a refrigerant shortage affect the high-pressure side of the system (without discharge pressure regulation)?
| Discharge pressure will be higher, and the degree of subcooling will be higher |
| The discharge pressure will be lower, and the subcooling will be lower |
| Discharge pressure will be lower, subcooling will be higher |
| Discharge pressure will be higher, and the degree of subcooling will be lower |
35
Difficult
What is the benefit of using helium as a tracer gas in nitrogen during a pressure test?
| It has smaller molecules and diffuses more easily |
| It has a distinct odour |
| It has a higher pressure than pure nitrogen |
| It is non-flammable |
36
Difficult
Why should an R744 system that has been drained be initially charged with the refrigerant in gaseous form?
| To prevent the drain valve from opening |
| To ensure that R744 is charged slowly |
| To prevent damage to the compressor |
| To prevent the formation of dry ice |
37
Difficult
If an R744 system contains moisture because it has not been properly drained, what is the likely consequence?
| The formation of hydrogen fluoride, which will decompose into hydrofluoric acid and damage the compressor |
| The formation of carbonic acid, which will cause damage to the system |
| Reduced cooling capacity |
| Excessively high discharge pressure |
38
Difficult
The pressure of R744 at a saturation temperature of 20 °C is approx.
| 90 bar g |
| 25 bar g |
| 14 bar g |
| 56 bar g |
39
Difficult
At an ambient temperature of 25°C, the standby pressure in the low-pressure stage of an R744 cascade system will typically be…
| 27.5 bar g |
| Higher than the maximum permissible pressure in the low-pressure stage |
| The same as the high-pressure setting on the pressure switch |
| The same as the pressure set on the relief valve |
40
Difficult
What is the correct definition of critical temperature?
| The temperature at which the vapour pressure of a liquid is equal to the ambient pressure surrounding the liquid |
| The temperature at which, for certain substances, electrical resistance is zero |
| The temperature above which there are no distinct liquid and gaseous phases |
| The temperature at which a substance changes from a gaseous to a solid state |
41
Difficult
In a supercritical system, under supercritical conditions, the working fluid in the gas cooler
| it loses heat when its pressure drops |
| loses heat at constant temperature and pressure |
| it loses heat as its temperature drops |
| loses heat during a phase change |