**Abstract**

Refrigeration systems have the priority in design for residential and industrial applications. The chapter includes five major refrigeration systems: vaporcompression refrigeration; ammonia-water absorption refrigeration; gas refrigeration where standard air is the most popular refrigerant; multi-pressure refrigeration including multistage, cascade, and multipurpose refrigeration system; and heat pump systems. Energy and exergy analysis has been presented for most of the systems. The energetic and the exergetic COP for each system are presented. Renewable energy sources are also discussed including geothermal, solar, and wind energy, a with combination with refrigeration systems in different industrial and residential applications. The overall efficiency of the renewable systems is achieved to be more than 50% providing promising solutions for energy use and having a low environmental impact.

**Keywords:** refrigeration systems, absorption cooling system, heat pump, geothermal energy, solar energy, wind energy

## **1. Introduction**

The primary application of refrigeration system is to transfer heat from a lower temperature region to a higher temperature one. A refrigeration cycle consists of a source at low temperature, a sink at high temperature, and a device to produce the work done to transfer heat from the source to sink. For the complete circulation, the refrigeration cycle should have an expansion device to circulate the refrigerant to the source.

Major refrigeration systems include vapor-compression refrigeration system (VCRS), heat pump (HP), gas refrigeration system (GRS), multi-pressure refrigeration systems (MPRS), and absorption refrigeration system (ARS), as presented in **Figure 1**. These systems are combined with renewable sources, such as geothermal, solar, and wind energy sources.

#### **2. Vapor-compression refrigeration system**

The vapor-compression refrigeration cycle (VCRS) is the most widely used cycle for refrigerators, air-conditioning systems, and heat pumps [1, 2]. It consists of four processes, as shown in **Figure 2**:

1-2 Isentropic compression in a compressor

2-3 Constant-pressure heat rejection in a condenser


destruction. For the given system of **Figure 2**. The refrigerant mass flow rate is constant through the cycle and denotes as *m*\_ in kg/s, *h* is the specific enthalpy of each state point in kJ/kg, *exi* is the specific exergy of a state point in kJ/kg and defined as *exi* ¼ ð Þ� *hi* � *h*<sup>0</sup> *T*0ð Þ *si* � *s*<sup>0</sup> , and *s* is the specific entropy of the refrigerant at each state point, and its unit is kJ/kg.K. The change in kinetic and potential energy is negligible for each component and the entire system. The energy balance equation (EnBE) of the evaporator considers the rate of heat removal by the evaporator, *Q*\_ *<sup>L</sup>* which is released from a low-temperature environment and determined by Eq. (1) [5]. The exergy balance equation (ExBE) of the evaporator is given as Eq. (2). Also, the thermal exergy rate due to the heat transfer from the evaporator is

EnBE *<sup>Q</sup>*\_ *<sup>L</sup>* <sup>¼</sup> *m h* \_ ð Þ <sup>1</sup> � *<sup>h</sup>*<sup>4</sup> (1) ExBE *<sup>m</sup>*\_ <sup>4</sup>*ex*<sup>4</sup> <sup>þ</sup> *Ex*\_ *Q,evap* <sup>¼</sup> *<sup>m</sup>*\_ <sup>1</sup>*ex*<sup>1</sup> þ þ*Ex*\_ *des,evap* (2)

> *T*<sup>0</sup> *TL* � 1

The power input to the compressor, *W*\_ *comp*, can be determined from Eq. (4), the

*<sup>W</sup>*\_ <sup>¼</sup> *<sup>h</sup>*2*<sup>s</sup>* � *<sup>h</sup>*<sup>1</sup> *h*<sup>2</sup> � *h*<sup>1</sup>

(3)

(9)

(5)

*Ex*\_ *Q,evap* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>*

*<sup>η</sup>comp* <sup>¼</sup> *<sup>W</sup>*\_ *in*

destruction of the compressor can be given as Eq. (6) [6]:

condenser can be given as Eqs. (8) and (9) [6]:

transfer and work done in the throttling process [6]:

**247**

isentropic efficiency of an adiabatic is defined as in Eq. (5) [5], and the exergy

EnBE *<sup>W</sup>*\_ *comp* <sup>¼</sup> *m h* \_ ð Þ <sup>2</sup> � *<sup>h</sup>*<sup>1</sup> (4)

ExBE *<sup>m</sup>*\_ <sup>1</sup>*ex*<sup>1</sup> <sup>þ</sup> *<sup>W</sup>*\_ *in* <sup>¼</sup> *<sup>m</sup>*\_ <sup>2</sup>*ex*<sup>2</sup> <sup>þ</sup> *Ex*\_ *des,comp* (6)

The heat rejection rate from the condenser, *Q*\_ *<sup>H</sup>*, to the environment can be written as Eq. (7) [5], while the exergy destruction and thermal exergy rate of the

EnBE *<sup>Q</sup>*\_ *<sup>H</sup>* <sup>¼</sup> *m h* \_ ð Þ <sup>2</sup> � *<sup>h</sup>*<sup>3</sup> (7) ExBE *<sup>m</sup>*\_ <sup>2</sup>*ex*<sup>2</sup> <sup>¼</sup> *<sup>m</sup>*\_ <sup>3</sup>*ex*<sup>3</sup> <sup>þ</sup> *Ex*\_ *Q,cond* <sup>þ</sup> *Ex*\_ *des,cond* (8)

*Ex*\_ *Q,cond* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>H</sup>* <sup>1</sup> � *<sup>T</sup>*<sup>0</sup>

The energy and exergy balance equations for the expansion valve can be expressed as Eqs. (10) and (11), respectively. The expansion valves are considered to be decreasing the pressure adiabatically and isentropically, which means no heat

EnBE *mh*\_ <sup>3</sup> ¼ *mh*\_ <sup>4</sup> (10) ExBE *<sup>m</sup>*\_ <sup>3</sup>*ex*<sup>3</sup> <sup>¼</sup> *<sup>m</sup>*\_ <sup>4</sup>*ex*<sup>4</sup> <sup>þ</sup> *Ex*\_ *des,* exp (11)

The energy balance for the entire refrigeration system can be given as [5]:

The coefficient of performance (COP) of the refrigeration system is defined as the ratio of useful energy, which is the rate of heat removal by the evaporator to the

*TH*

*<sup>Q</sup>*\_ *<sup>H</sup>* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>* <sup>þ</sup> *<sup>W</sup>*\_ *comp* (12)

defined as Eq. (3) [6].

*Energy and Exergy Analysis of Refrigeration Systems DOI: http://dx.doi.org/10.5772/intechopen.88862*

#### **Figure 1.**

*The classifications of refrigeration systems and renewable sources.*

#### **Figure 2.** *Schematic and T-s diagram for the ideal VCRS.*

The refrigerant enters the compressor from state 1 at saturated vapor to be isentropically compressed from low pressure of state 1 to high pressure and temperature of state 2, which is at the superheated region. Then, the refrigerant of state 2 enters the condenser to reject heat to the warm environment and exits at the saturated liquid as state 3. The refrigerant enters an adiabatic throttling or expansion valve to drop the pressure, which equals the pressure at the compressor inlet of state 1. The refrigerant temperature at state 1 is very low so that it absorbs heat from the refrigerated space at the evaporator and heated to be saturated vapor again. The vapor refrigeration system is a closed cycle where it starts and ends at state 1. This type of refrigeration system can be used for refrigerators, inside the air conditioners as split air conditioners, and separate as in radiant cooling systems [3, 4] and air-to-air systems [1].
