F-Gas English Low GWP
Všetky otázky
HFC | Flammable | CO₂ | NH₃
Ľahké otázky |
Stredne ťažké otázky |
Ťažké otázky
1
Ťažká
What is the main difference between a dry evaporator and a flooded evaporator?
| A dry evaporator is filled with refrigerant liquid, whilst a flooded evaporator is filled with gas |
| A dry evaporator allows the entire refrigerant to evaporate in the pipe upstream of the compressor; in a flooded evaporator, part of the refrigerant remains in a liquid state within the evaporator |
| A dry evaporator does not require an expansion valve, whereas a flooded one does |
| A dry evaporator has a lower operating pressure than a flooded one |
2
Ťažká
What is the typical pressure in deep-freezing systems (below −40 °C) for an evaporator in a system using R717?
| A pressure varying between 10 and 20 bar |
| Positive pressure, in the range of 5–10 bar |
| Atmospheric pressure, approximately 1 bar |
| Negative pressure (vacuum), below 0 bar |
3
Ťažká
Why are PFAS substances formed as a result of the decomposition of certain F-gases problematic?
| They cause rapid cooling of the atmosphere |
| They are readily biodegradable, so they only pollute the environment for a short time |
| They are persistent, accumulate in the environment and may be toxic |
| They are climate-neutral |
4
Ťažká
What is the basic requirement when charging a system with R717 (NH₃)?
| Charging must only take place at temperatures below 0°C |
| Charging should take place in a well-ventilated area using appropriate personal protective equipment |
| Charging can be carried out without personal protective equipment |
| NH₃ can be charged together with air |
5
Ťažká
How should oil be handled in systems using R717?
| Oil can be mixed with any refrigerant |
| Oil has no effect on the system’s operation |
| The oil should be checked regularly and any excess removed from the lower parts of the units to prevent reduced heat transfer and leaks |
| The oil does not require any monitoring |
6
Ťažká
What is the correct procedure for recovering R717 from a system?
| The gas can be released into the atmosphere |
| Recovery is not required |
| The refrigerant must be recovered into suitable, leak-proof tanks designed for NH₃ |
| The refrigerant can be drained into the sewer system |
7
Ťažká
How should R717 (NH₃) be stored?
| In any open containers |
| In sealed, labelled containers, in a cool and well-ventilated place |
| Near heat sources |
| In unmarked plastic containers |
8
Ťažká
What should be done in the event of R717 contamination?
| Continue to use without restriction |
| Add water to dilute it |
| Release into the atmosphere |
| The refrigerant must be purified or sent for disposal in accordance with regulations |
9
Ťažká
What is the main hazard associated with an R717 leak during maintenance work?
| No risk whatsoever |
| Increased cooling efficiency |
| Toxic to humans and may cause chemical burns |
| Damage to electrical equipment only |
10
Ťažká
What action should be taken if an NH₃ leak is detected?
| Close your eyes and carry on working |
| Increase the pressure in the system |
| Ignore it and carry on working |
| Evacuate personnel immediately and remove the source of the leak, if it is safe to do so |
11
Ťažká
What role do scrubbers play in NH₃ systems?
| They are used to measure temperature |
| They increase the pressure in the system |
| They store the refrigerant |
| Neutralises ammonia through absorption in a liquid (e.g. water) |
12
Ťažká
How should the system be prepared before filling with R717?
| The pressure must be increased above the standard level |
| There is no need to check it |
| Simply start it up |
| Check for leaks, remove air and moisture, and create a vacuum |
13
Ťažká
What are the transport requirements for R717?
| Transport is not subject to regulations |
| Must be transported in suitable, labelled containers in accordance with ADR regulations |
| It can be transported in open containers |
| It can be transported without labelling |
14
Ťažká
What personal protective equipment is required when working with NH₃?
| No requirements |
| Workwear only |
| Only a safety helmet |
| Safety goggles, gloves and respiratory protective equipment |
15
Ťažká
Which statement best describes the behaviour of R717 and mineral compressor oil?
| R717 mixes very well with compressor oil and easily returns to the compressor |
| R717 does not mix with compressor oil, so the oil remains in the system on the low-pressure side as a layer beneath the R717 |
| In an R717 system, a return oil line cannot be used because the oil is too hot |
| R717 does not mix with compressor oil, so the oil remains in the system on the high-pressure side as a layer above the R717 |
16
Ťažká
Which system may require manual oil recovery?
| R744 cascade system |
| Supercritical ‘booster’ system using R744 |
| Secondary system using R744 |
| An R717 system |
17
Ťažká
Which refrigerant is lighter than air?
| R1270 |
| R1234ze |
| R744 |
| R717 |
18
Ťažká
R717 is highly corrosive to
| stainless steel |
| titanium |
| aluminium |
| copper |
19
Ťažká
What is the effect of repeatedly opening the relief valve?
| The valve remains fully open continuously |
| The valve will not open |
| The relief pressure rises |
| The relief pressure drops |
20
Ťažká
What is the relationship between the pressure (P) and temperature (T) of nitrogen at the start (1) and end (2) of the leak test?
| P2 = T2/(P1 × T1) |
| P2 = (P1 × T2)/T1 |
| P2 = (P1 × T1)/T2 |
| P2 = T1/(P1 × T2) |
21
Ťažká
What is the recommended alarm level for fixed leak detection systems for R717?
| 50,000 ppm |
| 5,000 ppm |
| 500 ppm |
| 500,000 ppm |
22
Ťažká
Why are compressors with a separate electric motor most commonly used in R717 (NH₃) refrigeration systems?
| Because NH₃ reacts with the motor windings and hermetic compressors are not used |
| To increase the amount of refrigerant in the system |
| To reduce the condensing pressure |
| Because compressors with a separate motor are cheaper |
23
Ťažká
Which type of compressor is most commonly used in large ammonia systems?
| A reciprocating or screw compressor |
| Diaphragm compressor |
| Rotary vane compressor |
| Hermetic scroll |
24
Ťažká
How is the capacity of a piston compressor regulated in NH₃ systems?
| Solely by adjusting the oil volume |
| By increasing the condensing pressure |
| By reducing the refrigerant charge |
| By unloading the cylinders or changing the rotational speed |
25
Ťažká
How is the capacity of a screw compressor most commonly controlled?
| By closing the suction valve |
| By using a slide valve |
| By changing the type of oil |
| By adjusting the oil level |
26
Ťažká
When is two-stage compression used in NH₃ systems?
| Exclusively in small systems |
| At very low vapour pressures and high pressure differentials |
| At small temperature differences |
| Only with water-cooled condensers |
27
Ťažká
What is the advantage of two-stage compression over single-stage compression?
| No need for a separator |
| Higher efficiency and lower discharge temperature |
| Lower efficiency |
| Higher energy consumption |
28
Ťažká
How does an evaporative condenser used in NH₃ systems work?
| Operates without a fan |
| It transfers heat only to the air |
| It utilises the evaporation of water to increase cooling efficiency |
| It does not require a water supply |
29
Ťažká
What is the function of the liquid separator in an NH₃ system?
| It prevents liquid from entering the compressor |
| Regulates the condensing pressure |
| It separates oil from the refrigerant |
| Increases the discharge temperature |
30
Ťažká
What is the purpose of monitoring the liquid level in the separator?
| To increase the oil volume |
| To maintain the correct refrigerant level and prevent the compressor from flooding |
| To control the condenser fan |
| To reduce the condensing temperature |
31
Ťažká
What is the role of the float switch in NH₃ systems?
| It controls the fan’s operation |
| It regulates the condensation temperature |
| It is used to detect leaks |
| It monitors the liquid level in the tank or separator |
32
Ťažká
What is a thermosiphon in NH₃ systems?
| A type of evaporator |
| A defrosting device |
| An oil circulation system utilising differences in pressure and temperature |
| A type of safety valve |
33
Ťažká
Why are oils that are immiscible with the refrigerant used in NH₃ systems?
| To increase the amount of refrigerant |
| To reduce the pressure |
| Because NH₃ does not mix with most compressor oils |
| Because the oil mixes only with water |
34
Ťažká
What is the main function of an oil separator in NH₃ systems?
| Removing moisture from the system |
| To lower the condensation temperature |
| To increase fan efficiency |
| To separate the oil from the refrigerant and return the oil to the compressor |
35
Ťažká
Which NH₃ system features direct evaporation of the refrigerant in the evaporator?
| Direct expansion (DX) system |
| Glycol system |
| Indirect system |
| Thermosiphon system |
36
Ťažká
What is the characteristic feature of a flooded evaporator system?
| No level control is required |
| The evaporator contains a large amount of liquid, which improves heat transfer |
| No separator is used |
| The evaporator is filled exclusively with vapour |
37
Ťažká
What is the main difference between a direct and an indirect system?
| In an indirect system, NH₃ cools an intermediate medium (e.g. glycol), which in turn cools the load |
| In an indirect system, no compressor is used |
| In a direct system, there is no evaporator |
| In an indirect system, NH₃ flows directly into the space being cooled |