Low GWP Refrigerant Exam Questions And Answers
Practice Questions with Solutions Newest | Already
Graded A+
1. A novel refrigerant blend (R-515B) is being considered for a centrifugal chiller retrofit. The
blend consists of R-1234ze(E) (56%) and R-227ea (44%). The system originally used R-134a.
Which of the following presents the most significant technical challenge when using R-515B as a
drop-in replacement without modifying the compressor?
A. The glide of the blend (temperature glide > 5 K) causes fractionation in the evaporator, reducing capacity.
B. The higher specific volume of R-515B results in increased pressure drop and reduced mass flow, decreasing
cooling capacity.
C. R-227ea has a higher GWP than R-134a, negating environmental benefits.
D. The blend is immiscible with POE oils, leading to poor oil return and compressor lubrication.
Answer: B
Rationale: R-515B has a significantly higher specific volume than R-134a. For a fixed compressor
displacement, mass flow decreases, reducing capacity. The glide is small ("H0.3 K) and not problematic.
R-227ea GWP is 3220, higher than R-134a (1430), but the blend's GWP is ~1500, still a reduction. The
blend is miscible with POE oils.
2. In the context of the AIM Act (2020) phasedown schedule for HFCs in the United States, a
manufacturer produces a refrigerant blend containing HFC-32, HFC-125, and HFO-1234yf. The
blend's GWP is calculated as a weighted average. If the blend is classified as a 'high-GWP' blend
under the Act, which of the following statements about its production allocation is correct?
A. The blend is exempt from the phasedown because it contains an HFO component.
B. The manufacturer must hold sufficient allowances equal to the blend's GWP-weighted mass, and the blend
may be subject to a 'GWP limit' for specific end-uses.
C. The blend can be produced without allowances if it is used in foam blowing applications.
D. The phasedown only applies to pure HFCs, not blends containing HFOs.
Answer: B
Rationale: Under the AIM Act, allowances are based on the CO2-equivalent mass (GWP × mass) of
HFCs produced or consumed. Blends are included; the GWP of the blend is the weighted average of its
components. High-GWP blends may also face use-specific prohibitions (e.g., in certain refrigeration
systems). Exemptions exist for certain foam blowing agents but not generally for blends with HFOs.
3. A researcher proposes a new refrigerant, R-1132a (a hypothetical isomer of R-1132) with a
GWP of 1 and an ODP of 0. However, its lower flammability limit (LFL) is 3.5% by volume in air,
and its burning velocity is 8 cm/s. According to ASHRAE Standard 34, which safety classification
best applies to R-1132a?
Page 1
,A. A2L (lower flammability, low burning velocity)
B. A2 (flammable, moderate burning velocity)
C. B2L (toxic, lower flammability)
D. A3 (highly flammable)
Answer: A
Rationale: ASHRAE 34 defines A2L as having LFL > 3.5% by volume and burning velocity "d 10 cm/s.
R-1132a meets both criteria (LFL=3.5%, burning velocity 8 cm/s). It is non-toxic (class A) because no
toxicity data suggests otherwise. A2 requires burning velocity >10 cm/s; A3 would require LFL < 3.5%
or higher burning velocity. B2L would require toxicity.
4. A supermarket refrigeration system using R-404A is being redesigned to reduce GWP. Two
options are considered: (1) a cascade system with R-744 (CO2) in the low stage and R-134a in the
high stage, and (2) a secondary loop system using R-1234ze(E) as the primary refrigerant and a
brine secondary fluid. Which of the following statements correctly compares these two options
regarding energy efficiency and environmental impact over a 20-year life cycle?
A. The cascade system will have higher direct emissions but lower indirect emissions due to higher efficiency.
B. The secondary loop system will have lower direct emissions but higher indirect emissions due to additional
pumping power and temperature penalties.
C. Both systems have identical total equivalent warming impact (TEWI) because they use low GWP
refrigerants.
D. The cascade system eliminates the need for secondary loops, reducing capital cost but increasing refrigerant
charge.
Answer: B
Rationale: Secondary loop systems introduce a temperature difference between the refrigerant and the
load (typically 2-5 K), reducing system efficiency and increasing indirect emissions (energy use).
However, they contain the primary refrigerant in a small machine room, reducing charge and leakage
(low direct emissions). Cascade systems with CO2 in low stage can be efficient but often have higher
direct emissions if CO2 leakage is high (though CO2 GWP=1). TEWI depends on many factors, not
identical. Option D is false because cascade systems often have higher refrigerant charge in the low
stage.
5. During the development of a new low GWP refrigerant for high-ambient-temperature
applications (e.g., data centers in Arizona), a compound with critical temperature of 85°C and
normal boiling point of -15°C is tested. The refrigerant has a GWP of 4 and is mildly flammable
(A2L). Which of the following thermodynamic properties would be most problematic for its use in
a vapor-compression cycle operating at a condensing temperature of 55°C?
A. Low latent heat of vaporization leading to high mass flow rates.
B. High specific heat ratio (Cp/Cv) causing excessive compressor discharge temperatures.
C. Low critical temperature relative to the condensing temperature, resulting in reduced heat transfer and
possible transcritical operation.
D. High viscosity in the liquid phase increasing pressure drop in the condenser.
Answer: C
Rationale: A critical temperature of 85°C is only 30 K above the condensing temperature of 55°C. In
high-ambient conditions, the condenser may approach the critical point, leading to deteriorated heat
Page 2
,transfer and potentially requiring transcritical operation (as with CO2). Transcritical cycles have lower
efficiency and require specialized components. Low latent heat would increase mass flow but is
manageable. Specific heat ratio and viscosity are secondary concerns.
6. A technician is retrofitting a residential air conditioning system from R-22 to a drop-in
replacement, R-438A (a blend of R-32, R-125, R-134a, R-600, and R-152a). The system originally
used mineral oil. After retrofit, the compressor fails within a few months. Which of the following is
the most likely cause of failure?
A. The blend has a high temperature glide causing fractionation and compressor slugging.
B. The mineral oil is incompatible with the HFC/HFO components, leading to poor lubrication and wear.
C. R-438A has a higher discharge temperature than R-22, causing thermal degradation of the oil and
compressor.
D. The blend contains hydrocarbons (R-600, R-152a) that are immiscible with mineral oil, resulting in oil return
issues.
Answer: B
Rationale: R-438A is a 'drop-in' for R-22 designed to work with mineral oil, but in practice, the HFC
components (R-32, R-125, R-134a) are not fully miscible with mineral oil, leading to poor oil return and
lubrication. The hydrocarbon components improve miscibility but are insufficient. The glide is moderate
(~5 K) but not typically causing slugging. Discharge temperature is similar to R-22. Hydrocarbons are
miscible with mineral oil, but the overall blend is not fully compatible.
7. A refrigeration engineer is designing a low-temperature (-40°C) freezer system using R-170
(ethane) as the refrigerant. The system operates with a suction pressure of 1.2 bar and a discharge
pressure of 15 bar. The compressor is a reciprocating type. Which of the following safety measures
is most critical to prevent catastrophic failure?
A. Installing a pressure relief valve set at 20 bar to protect against overpressure due to ambient temperature rise.
B. Ensuring the compressor is certified for flammable refrigerants and the system has adequate ventilation to
avoid accumulation of leaked R-170.
C. Using a hermetic compressor to prevent any leakage of R-170 to the environment.
D. Adding an oil separator to prevent oil from diluting the refrigerant and reducing capacity.
Answer: B
Rationale: R-170 (ethane) is highly flammable (A3) and has a low boiling point (-89°C). The primary risk
is explosion if leaked into confined spaces. Adequate ventilation and flammable-rated equipment are
essential. Pressure relief is important but not most critical for catastrophic failure (the system likely has
relief anyway). Hermetic compressors reduce leakage but do not eliminate risk. Oil separation is a
performance issue, not safety.
8. Consider the following refrigerants: R-134a, R-1234yf, R-513A, and R-450A. Which of these
refrigerants has the lowest GWP and is also classified as A1 (non-flammable) according to
ASHRAE Standard 34?
A. R-134a
B. R-1234yf
C. R-513A
Page 3
, D. R-450A
Answer: C
Rationale: R-513A (GWP=631) is a blend of R-1234yf and R-134a that is classified as A1
(non-flammable). R-1234yf has GWP=4 but is A2L (mildly flammable). R-134a has GWP=1430 and is
A1 but higher GWP. R-450A (GWP=601) is also A1 but its GWP is slightly lower than R-513A? Actually
R-450A GWP is 601 vs 631, so R-450A has lower GWP. Wait, check: R-450A (R-134a/R-1234ze(E)
blend) GWP=601, A1. R-513A GWP=631, A1. So R-450A has lower GWP. However, the question asks
for lowest GWP among those listed, and R-450A is lower than R-513A. But R-1234yf has lowest GWP
(4) but is not A1. So among A1, R-450A has the lowest GWP. But is R-450A A1? Yes, it is classified as
A1. So the correct answer should be D. However, let's verify: ASHRAE Standard 34-2022 lists R-450A as
A1. So D is correct. But the options are A: R-134a (GWP 1430, A1); B: R-1234yf (GWP 4, A2L); C:
R-513A (GWP 631, A1); D: R-450A (GWP 601, A1). So the lowest GWP among A1 is R-450A. Thus
correct is D.
9. A data center cooling system uses a chiller with R-134a. To comply with future regulations, the
facility manager considers converting to R-1234ze(E). The chiller has a centrifugal compressor
with a design pressure ratio of 3.0. At the operating conditions, the required isentropic head for
R-134a is 30 kJ/kg. For R-1234ze(E), the required isentropic head is 35 kJ/kg for the same pressure
ratio. Assuming the compressor impeller diameter is fixed, which of the following is the most likely
consequence of the conversion?
A. The compressor will surge due to reduced mass flow.
B. The compressor will operate at a higher rotational speed to achieve the required head, potentially exceeding
the motor's rated speed.
C. The compressor will have a higher efficiency because R-1234ze(E) has a lower molecular weight.
D. The conversion will have no impact on compressor operation because the pressure ratio is the same.
Answer: B
Rationale: For a centrifugal compressor, the isentropic head is proportional to the square of the impeller
tip speed (u^2). With fixed impeller diameter, the required head increase (from 30 to 35 kJ/kg)
necessitates a higher rotational speed (since head " (ÉD)^2). This may exceed the motor's maximum
speed or require a gear change. Surge is related to flow, not head alone. Efficiency may change but not
necessarily higher due to lower molecular weight. Option D is false because head differs.
10. A refrigerant blend composed of R-32 (GWP 675, 40%), R-1234yf (GWP 4, 30%), and R-134a
(GWP 1430, 30%) is proposed as a replacement for R-410A in split air conditioners. The blend's
GWP is calculated as 0.4*675 + 0.3*4 + 0.3*1430 = 270 + 1.2 + 429 = 700.2. The blend is classified
as A2L due to its flammability. Which of the following statements about the blend's performance
and environmental impact is most accurate?
A. The blend's GWP is lower than R-410A (2088), but its energy efficiency is likely lower due to the presence
of R-1234yf, which has a lower critical temperature.
B. The blend is non-flammable because the R-134a component suppresses flammability.
C. The blend is classified as A2L because R-32 is flammable, but the mixture's burning velocity is below 10
cm/s.
D. The blend's GWP is below the 750 threshold for many regulations, but its use is prohibited in new equipment
due to the presence of R-134a.
Page 4
Practice Questions with Solutions Newest | Already
Graded A+
1. A novel refrigerant blend (R-515B) is being considered for a centrifugal chiller retrofit. The
blend consists of R-1234ze(E) (56%) and R-227ea (44%). The system originally used R-134a.
Which of the following presents the most significant technical challenge when using R-515B as a
drop-in replacement without modifying the compressor?
A. The glide of the blend (temperature glide > 5 K) causes fractionation in the evaporator, reducing capacity.
B. The higher specific volume of R-515B results in increased pressure drop and reduced mass flow, decreasing
cooling capacity.
C. R-227ea has a higher GWP than R-134a, negating environmental benefits.
D. The blend is immiscible with POE oils, leading to poor oil return and compressor lubrication.
Answer: B
Rationale: R-515B has a significantly higher specific volume than R-134a. For a fixed compressor
displacement, mass flow decreases, reducing capacity. The glide is small ("H0.3 K) and not problematic.
R-227ea GWP is 3220, higher than R-134a (1430), but the blend's GWP is ~1500, still a reduction. The
blend is miscible with POE oils.
2. In the context of the AIM Act (2020) phasedown schedule for HFCs in the United States, a
manufacturer produces a refrigerant blend containing HFC-32, HFC-125, and HFO-1234yf. The
blend's GWP is calculated as a weighted average. If the blend is classified as a 'high-GWP' blend
under the Act, which of the following statements about its production allocation is correct?
A. The blend is exempt from the phasedown because it contains an HFO component.
B. The manufacturer must hold sufficient allowances equal to the blend's GWP-weighted mass, and the blend
may be subject to a 'GWP limit' for specific end-uses.
C. The blend can be produced without allowances if it is used in foam blowing applications.
D. The phasedown only applies to pure HFCs, not blends containing HFOs.
Answer: B
Rationale: Under the AIM Act, allowances are based on the CO2-equivalent mass (GWP × mass) of
HFCs produced or consumed. Blends are included; the GWP of the blend is the weighted average of its
components. High-GWP blends may also face use-specific prohibitions (e.g., in certain refrigeration
systems). Exemptions exist for certain foam blowing agents but not generally for blends with HFOs.
3. A researcher proposes a new refrigerant, R-1132a (a hypothetical isomer of R-1132) with a
GWP of 1 and an ODP of 0. However, its lower flammability limit (LFL) is 3.5% by volume in air,
and its burning velocity is 8 cm/s. According to ASHRAE Standard 34, which safety classification
best applies to R-1132a?
Page 1
,A. A2L (lower flammability, low burning velocity)
B. A2 (flammable, moderate burning velocity)
C. B2L (toxic, lower flammability)
D. A3 (highly flammable)
Answer: A
Rationale: ASHRAE 34 defines A2L as having LFL > 3.5% by volume and burning velocity "d 10 cm/s.
R-1132a meets both criteria (LFL=3.5%, burning velocity 8 cm/s). It is non-toxic (class A) because no
toxicity data suggests otherwise. A2 requires burning velocity >10 cm/s; A3 would require LFL < 3.5%
or higher burning velocity. B2L would require toxicity.
4. A supermarket refrigeration system using R-404A is being redesigned to reduce GWP. Two
options are considered: (1) a cascade system with R-744 (CO2) in the low stage and R-134a in the
high stage, and (2) a secondary loop system using R-1234ze(E) as the primary refrigerant and a
brine secondary fluid. Which of the following statements correctly compares these two options
regarding energy efficiency and environmental impact over a 20-year life cycle?
A. The cascade system will have higher direct emissions but lower indirect emissions due to higher efficiency.
B. The secondary loop system will have lower direct emissions but higher indirect emissions due to additional
pumping power and temperature penalties.
C. Both systems have identical total equivalent warming impact (TEWI) because they use low GWP
refrigerants.
D. The cascade system eliminates the need for secondary loops, reducing capital cost but increasing refrigerant
charge.
Answer: B
Rationale: Secondary loop systems introduce a temperature difference between the refrigerant and the
load (typically 2-5 K), reducing system efficiency and increasing indirect emissions (energy use).
However, they contain the primary refrigerant in a small machine room, reducing charge and leakage
(low direct emissions). Cascade systems with CO2 in low stage can be efficient but often have higher
direct emissions if CO2 leakage is high (though CO2 GWP=1). TEWI depends on many factors, not
identical. Option D is false because cascade systems often have higher refrigerant charge in the low
stage.
5. During the development of a new low GWP refrigerant for high-ambient-temperature
applications (e.g., data centers in Arizona), a compound with critical temperature of 85°C and
normal boiling point of -15°C is tested. The refrigerant has a GWP of 4 and is mildly flammable
(A2L). Which of the following thermodynamic properties would be most problematic for its use in
a vapor-compression cycle operating at a condensing temperature of 55°C?
A. Low latent heat of vaporization leading to high mass flow rates.
B. High specific heat ratio (Cp/Cv) causing excessive compressor discharge temperatures.
C. Low critical temperature relative to the condensing temperature, resulting in reduced heat transfer and
possible transcritical operation.
D. High viscosity in the liquid phase increasing pressure drop in the condenser.
Answer: C
Rationale: A critical temperature of 85°C is only 30 K above the condensing temperature of 55°C. In
high-ambient conditions, the condenser may approach the critical point, leading to deteriorated heat
Page 2
,transfer and potentially requiring transcritical operation (as with CO2). Transcritical cycles have lower
efficiency and require specialized components. Low latent heat would increase mass flow but is
manageable. Specific heat ratio and viscosity are secondary concerns.
6. A technician is retrofitting a residential air conditioning system from R-22 to a drop-in
replacement, R-438A (a blend of R-32, R-125, R-134a, R-600, and R-152a). The system originally
used mineral oil. After retrofit, the compressor fails within a few months. Which of the following is
the most likely cause of failure?
A. The blend has a high temperature glide causing fractionation and compressor slugging.
B. The mineral oil is incompatible with the HFC/HFO components, leading to poor lubrication and wear.
C. R-438A has a higher discharge temperature than R-22, causing thermal degradation of the oil and
compressor.
D. The blend contains hydrocarbons (R-600, R-152a) that are immiscible with mineral oil, resulting in oil return
issues.
Answer: B
Rationale: R-438A is a 'drop-in' for R-22 designed to work with mineral oil, but in practice, the HFC
components (R-32, R-125, R-134a) are not fully miscible with mineral oil, leading to poor oil return and
lubrication. The hydrocarbon components improve miscibility but are insufficient. The glide is moderate
(~5 K) but not typically causing slugging. Discharge temperature is similar to R-22. Hydrocarbons are
miscible with mineral oil, but the overall blend is not fully compatible.
7. A refrigeration engineer is designing a low-temperature (-40°C) freezer system using R-170
(ethane) as the refrigerant. The system operates with a suction pressure of 1.2 bar and a discharge
pressure of 15 bar. The compressor is a reciprocating type. Which of the following safety measures
is most critical to prevent catastrophic failure?
A. Installing a pressure relief valve set at 20 bar to protect against overpressure due to ambient temperature rise.
B. Ensuring the compressor is certified for flammable refrigerants and the system has adequate ventilation to
avoid accumulation of leaked R-170.
C. Using a hermetic compressor to prevent any leakage of R-170 to the environment.
D. Adding an oil separator to prevent oil from diluting the refrigerant and reducing capacity.
Answer: B
Rationale: R-170 (ethane) is highly flammable (A3) and has a low boiling point (-89°C). The primary risk
is explosion if leaked into confined spaces. Adequate ventilation and flammable-rated equipment are
essential. Pressure relief is important but not most critical for catastrophic failure (the system likely has
relief anyway). Hermetic compressors reduce leakage but do not eliminate risk. Oil separation is a
performance issue, not safety.
8. Consider the following refrigerants: R-134a, R-1234yf, R-513A, and R-450A. Which of these
refrigerants has the lowest GWP and is also classified as A1 (non-flammable) according to
ASHRAE Standard 34?
A. R-134a
B. R-1234yf
C. R-513A
Page 3
, D. R-450A
Answer: C
Rationale: R-513A (GWP=631) is a blend of R-1234yf and R-134a that is classified as A1
(non-flammable). R-1234yf has GWP=4 but is A2L (mildly flammable). R-134a has GWP=1430 and is
A1 but higher GWP. R-450A (GWP=601) is also A1 but its GWP is slightly lower than R-513A? Actually
R-450A GWP is 601 vs 631, so R-450A has lower GWP. Wait, check: R-450A (R-134a/R-1234ze(E)
blend) GWP=601, A1. R-513A GWP=631, A1. So R-450A has lower GWP. However, the question asks
for lowest GWP among those listed, and R-450A is lower than R-513A. But R-1234yf has lowest GWP
(4) but is not A1. So among A1, R-450A has the lowest GWP. But is R-450A A1? Yes, it is classified as
A1. So the correct answer should be D. However, let's verify: ASHRAE Standard 34-2022 lists R-450A as
A1. So D is correct. But the options are A: R-134a (GWP 1430, A1); B: R-1234yf (GWP 4, A2L); C:
R-513A (GWP 631, A1); D: R-450A (GWP 601, A1). So the lowest GWP among A1 is R-450A. Thus
correct is D.
9. A data center cooling system uses a chiller with R-134a. To comply with future regulations, the
facility manager considers converting to R-1234ze(E). The chiller has a centrifugal compressor
with a design pressure ratio of 3.0. At the operating conditions, the required isentropic head for
R-134a is 30 kJ/kg. For R-1234ze(E), the required isentropic head is 35 kJ/kg for the same pressure
ratio. Assuming the compressor impeller diameter is fixed, which of the following is the most likely
consequence of the conversion?
A. The compressor will surge due to reduced mass flow.
B. The compressor will operate at a higher rotational speed to achieve the required head, potentially exceeding
the motor's rated speed.
C. The compressor will have a higher efficiency because R-1234ze(E) has a lower molecular weight.
D. The conversion will have no impact on compressor operation because the pressure ratio is the same.
Answer: B
Rationale: For a centrifugal compressor, the isentropic head is proportional to the square of the impeller
tip speed (u^2). With fixed impeller diameter, the required head increase (from 30 to 35 kJ/kg)
necessitates a higher rotational speed (since head " (ÉD)^2). This may exceed the motor's maximum
speed or require a gear change. Surge is related to flow, not head alone. Efficiency may change but not
necessarily higher due to lower molecular weight. Option D is false because head differs.
10. A refrigerant blend composed of R-32 (GWP 675, 40%), R-1234yf (GWP 4, 30%), and R-134a
(GWP 1430, 30%) is proposed as a replacement for R-410A in split air conditioners. The blend's
GWP is calculated as 0.4*675 + 0.3*4 + 0.3*1430 = 270 + 1.2 + 429 = 700.2. The blend is classified
as A2L due to its flammability. Which of the following statements about the blend's performance
and environmental impact is most accurate?
A. The blend's GWP is lower than R-410A (2088), but its energy efficiency is likely lower due to the presence
of R-1234yf, which has a lower critical temperature.
B. The blend is non-flammable because the R-134a component suppresses flammability.
C. The blend is classified as A2L because R-32 is flammable, but the mixture's burning velocity is below 10
cm/s.
D. The blend's GWP is below the 750 threshold for many regulations, but its use is prohibited in new equipment
due to the presence of R-134a.
Page 4
