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Md. A. Islam and B. B. Saha
refrigerant is completely liquefied before entering the expansion device. Superheating and subcooling of the refrigerant prevent damage of the components and increase
the efficiency of the system. The typical value of superheating and subcooling is in
the range of 5–10 K. In this assessment, superheating has been considered 8 K and
subcooling is 5 K.
Isentropic Efficiency
When a thermodynamic process is adiabatic and completely reversible, the process
is called isentropic. Isentropic efficiency of an ideal compressor is hundred-percent.
An ideal compressor has to be frictionless, and there should be no heat transfer
during the operation. In reality, there is no ideal compressor, and we consider a certain value for the isentropic efficiency. In principle, the compression ratio increases
when the difference between the evaporation temperature and condensation temperature increases. Therefore, the isentropic efficiency of the compressor is lower
for low-temperature applications. Hence, isentropic efficiency values are different in
Table 9.3, depending on the application.
Refrigerant Charging
Initially, each cooling system requires a certain amount of refrigerant charging. The
actual initial charging amount depends on the evaporator cooling capacity, condenser
capacity, evaporator and condenser heat exchanger size, heat transfer coefficients,
operating conditions, refrigerant type, and so forth. Approximately, the required
refrigerant amount can be expressed in terms of cooling capacity. For domestic
cooling systems, the amount is 0.24–1 (in kg) times of the cooling load (kW). For
medium and low-temperature applications, the amount is higher (2–3.4 times) (Poggi
et al. 2008). In order to simplify the calculation, a certain amount of refrigerant charge
has been considered and shown in Table 9.3.
Leakage Rate
Although the compressor is hermetically sealed, 15–20% of the charged refrigerant might be leaked from joints and seals, mechanical failure or during servicing
(Tassou and Grace 2005; Francis et al. 2016). This leakage will lead to performance
degradation and will increase energy consumption. Modern refrigeration system
manufacturers claim that their system has a very low leakage rate, which could be
as low as 5% per year. Hence, the sensitivity of direct emission with the leakage rate
is presented in the appendix section.
Md. A. Islam and B. B. Saha
refrigerant is completely liquefied before entering the expansion device. Superheating and subcooling of the refrigerant prevent damage of the components and increase
the efficiency of the system. The typical value of superheating and subcooling is in
the range of 5–10 K. In this assessment, superheating has been considered 8 K and
subcooling is 5 K.
Isentropic Efficiency
When a thermodynamic process is adiabatic and completely reversible, the process
is called isentropic. Isentropic efficiency of an ideal compressor is hundred-percent.
An ideal compressor has to be frictionless, and there should be no heat transfer
during the operation. In reality, there is no ideal compressor, and we consider a certain value for the isentropic efficiency. In principle, the compression ratio increases
when the difference between the evaporation temperature and condensation temperature increases. Therefore, the isentropic efficiency of the compressor is lower
for low-temperature applications. Hence, isentropic efficiency values are different in
Table 9.3, depending on the application.
Refrigerant Charging
Initially, each cooling system requires a certain amount of refrigerant charging. The
actual initial charging amount depends on the evaporator cooling capacity, condenser
capacity, evaporator and condenser heat exchanger size, heat transfer coefficients,
operating conditions, refrigerant type, and so forth. Approximately, the required
refrigerant amount can be expressed in terms of cooling capacity. For domestic
cooling systems, the amount is 0.24–1 (in kg) times of the cooling load (kW). For
medium and low-temperature applications, the amount is higher (2–3.4 times) (Poggi
et al. 2008). In order to simplify the calculation, a certain amount of refrigerant charge
has been considered and shown in Table 9.3.
Leakage Rate
Although the compressor is hermetically sealed, 15–20% of the charged refrigerant might be leaked from joints and seals, mechanical failure or during servicing
(Tassou and Grace 2005; Francis et al. 2016). This leakage will lead to performance
degradation and will increase energy consumption. Modern refrigeration system
manufacturers claim that their system has a very low leakage rate, which could be
as low as 5% per year. Hence, the sensitivity of direct emission with the leakage rate
is presented in the appendix section.