9 TEWI Assessment of Conventional and Solar Powered Cooling Systems
157
Condensation Temperature
The assessment has been performed for the summer season when the ambient temperature is around 30 °C. The condensation temperature is always higher than the
ambient temperature so that heat exchange can occur naturally. In this assessment,
the condensation temperature is considered constant (40 °C).
Selected Refrigerants and Their Environmental Impact
Global warming potential (GWP) is the quantity of heat that a greenhouse gas can
grasp in the atmosphere for a specific duration, relative to CO 2 . Each refrigerant has a
certain amount of GWP when released to the environment. Previously used CFCs and
HCFCs have very high GWP. Those refrigerants are also responsible for ozone layer
depletion (ODP), which is located at the lower portion of the stratosphere. ODP value
of a fluid is the measure of destructive effects compared to the reference substance
R11 (or CFC-11 or CCl 3 F or Trichlorofluoromethane). HFC based refrigerants are
used in modern domestic air-conditioning and refrigeration systems. Most frequently
used refrigerants for room air-conditioning systems are R134a and R32. However,
R22 is still used in room air-conditioning system in some developing and underdeveloped countries. Besides, HFC blend R404A and R410A are predominantly used
in commercial refrigeration systems and low-temperature applications. Hence, these
three refrigerants (R32, R134a and R404A) are selected for the assessment. Analysis
with R22 (for room air-conditioning application) and R410A (for medium and low
temperature applications) are also presented in the appendix section for the readers’
convenience.
Cooling Load
The cooling load is the quantity of heat energy that needs to be removed from
the cooling space (evaporation surroundings) to maintain the target temperature.
Usually, a standard 20 m
2 room (typical height −2.44 m) can be cooled with a
5 kW air-conditioner (Quick calculations for walk-in coolers and freezers 2019).
A typical two-room house with 10 kW air-conditioning cooling load is considered
for this assessment. Medium temperature (MT) and low temperature (LT) cooling
loads are also considered 10 kW. Since, MT and LT loads are mostly used for food
preservation; the cooled space is smaller compared to room air-conditioning system.
Superheat and Subcool
A certain degree of superheating is applied after the evaporator to ensure that the
liquid refrigerant is completely vaporized before it reaches the suction line of the
compressor. Likewise, subcooling is performed after condenser to confirm that the
157
Condensation Temperature
The assessment has been performed for the summer season when the ambient temperature is around 30 °C. The condensation temperature is always higher than the
ambient temperature so that heat exchange can occur naturally. In this assessment,
the condensation temperature is considered constant (40 °C).
Selected Refrigerants and Their Environmental Impact
Global warming potential (GWP) is the quantity of heat that a greenhouse gas can
grasp in the atmosphere for a specific duration, relative to CO 2 . Each refrigerant has a
certain amount of GWP when released to the environment. Previously used CFCs and
HCFCs have very high GWP. Those refrigerants are also responsible for ozone layer
depletion (ODP), which is located at the lower portion of the stratosphere. ODP value
of a fluid is the measure of destructive effects compared to the reference substance
R11 (or CFC-11 or CCl 3 F or Trichlorofluoromethane). HFC based refrigerants are
used in modern domestic air-conditioning and refrigeration systems. Most frequently
used refrigerants for room air-conditioning systems are R134a and R32. However,
R22 is still used in room air-conditioning system in some developing and underdeveloped countries. Besides, HFC blend R404A and R410A are predominantly used
in commercial refrigeration systems and low-temperature applications. Hence, these
three refrigerants (R32, R134a and R404A) are selected for the assessment. Analysis
with R22 (for room air-conditioning application) and R410A (for medium and low
temperature applications) are also presented in the appendix section for the readers’
convenience.
Cooling Load
The cooling load is the quantity of heat energy that needs to be removed from
the cooling space (evaporation surroundings) to maintain the target temperature.
Usually, a standard 20 m
2 room (typical height −2.44 m) can be cooled with a
5 kW air-conditioner (Quick calculations for walk-in coolers and freezers 2019).
A typical two-room house with 10 kW air-conditioning cooling load is considered
for this assessment. Medium temperature (MT) and low temperature (LT) cooling
loads are also considered 10 kW. Since, MT and LT loads are mostly used for food
preservation; the cooled space is smaller compared to room air-conditioning system.
Superheat and Subcool
A certain degree of superheating is applied after the evaporator to ensure that the
liquid refrigerant is completely vaporized before it reaches the suction line of the
compressor. Likewise, subcooling is performed after condenser to confirm that the