**6.1 Energy and exergy analysis of ammonia-water (NH3-H2O) ARSs**

The energy and exergy analysis for each component is presented according to **Figure 8**. The partial mass balance (PMBE) is also included to determine the concentration mass of ammonia and water in the absorber and generator. That is because the ARS has two fluids as refrigerant and absorbent and their composition at different points is different, particularly in the absorber and generator. The exergy analysis of ammonia-water ARSs is to determine the exergy destruction of each component and to determine the overall exergy efficiency based on the second law of thermodynamics. The exergy analysis (ExBE) for each component is stated below [5, 6]:

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

Absorber:

$$
\dot{m}\_1 \mathbf{E} \mathbf{E} \tag{50}
$$

$$
\dot{m}\_6 h\_6 + \dot{m}\_{12} h\_{12} = \dot{m}\_1 h\_1 + \dot{Q}\_{Aburber} \tag{50}
$$

$$\dot{m}\_{\text{WBE}} = \dot{m}\_{\text{ws}} X\_{\text{ws}} + \dot{m}\_{r} = \dot{m}\_{\text{us}} X\_{\text{us}} \tag{51}$$

$$\dot{\mathbf{E}} \mathbf{z} \mathbf{B} \mathbf{E} \qquad \qquad \dot{\dot{m}}\_6 \mathbf{c} \mathbf{x}\_6 + \dot{m}\_{12} \mathbf{c} \mathbf{x}\_{12} = \dot{m}\_1 \mathbf{c} \mathbf{x}\_1 + \dot{E} \dot{\mathbf{x}}\_{Q,A} + \dot{E} \dot{\mathbf{x}}\_{de,aber} \tag{52}$$

where *Q*\_ *Absorber* is the absorber head load in kW; *X* is the concentration of ammonia (refrigerant); *m*\_ *ws* is the mass flow rate of the weak solution in kg/s, which equals to *m*\_ 6; *m*\_ *ss* is the mass flow rate of the strong solution in kg/s, which equals to mass flow rate exiting from the absorber at *m*\_ 1; and *m*\_ *<sup>r</sup>* is the mass flow rate of pure ammonia (refrigerant) in kg/s, which flows from the generator at state 7 to state 12; *Ex*\_ *Q,A* is the thermal exergy rate of the absorber due to the heat transfer *Q*\_ *<sup>A</sup>* to the environment, and it is calculated as *Ex*\_ *Q,A* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>A</sup>*ð Þ <sup>1</sup> � *<sup>T</sup>*0*=Ts* . Here, state 1 is a saturated liquid at the lowest temperature in the absorber and is determined by the temperature of the available cooling water flow or air flow.

Solution pump:

$$
\dot{m}\_1 \mathbf{E}\_1 \tag{53}
$$

$$
\dot{m}\_1 h\_1 + \dot{W}\_{Pump} = \dot{m}\_2 h\_2 \tag{53}
$$

$$
\dot{\mathbf{E}} \mathbf{E} \mathbf{B} \mathbf{E} \tag{2.52}
$$

$$
\dot{\boldsymbol{m}}\_1 \mathbf{e} \mathbf{x}\_1 + \dot{\mathbf{W}}\_P = \dot{\boldsymbol{m}}\_2 \mathbf{e} \mathbf{x}\_2 + \dot{\mathbf{E}} \mathbf{x}\_{des, pump} \tag{54}
$$

Regeneration heat exchanger (HX1):

$$
\dot{m}\_2 \mathbf{E} \tag{55}
$$

$$
\dot{m}\_2 h\_2 + \dot{m}\_4 h\_4 = \dot{m}\_3 h\_3 + \dot{m}\_5 h\_5 \tag{55}
$$

$$
\dot{\mathbf{E}} \mathbf{E} \mathbf{B} \mathbf{E} \qquad \qquad \dot{\dot{m}}\_2 \mathbf{e} \mathbf{x}\_2 + \dot{\dot{m}}\_4 \mathbf{e} \mathbf{x}\_4 = \dot{\dot{m}}\_3 \mathbf{e} \mathbf{x}\_3 + \dot{\dot{m}}\_5 \mathbf{e} \mathbf{x}\_5 + \dot{\dot{E}} \mathbf{x}\_{\text{des},HX1} \tag{56}
$$

Generator:

refrigerant) is heated in the high-pressure generator. This produces refrigerant vapor off the solution at state 7. The hot pure ammonia vapor is cooled in the condenser at state 8 and condenses at state 9 by passing through the HX2 before entering a throttling valve into the low pressure at state 10. Then the refrigerant liquid passes through the evaporator to remove the heat from refrigerated medium and leaves at low-pressure vapor phase of state 11. The pure ammonia is heated by the HX2 to enter the absorber and mixed with the absorbent water. The weak solution (about 24% ammonia concentration) flows down from the generator at state 4 through the regeneration heat exchanger HX1 at state 5 through a throttling valve and enters the absorber at state 6. Therefore, the weak refrigerant is absorbed by the water because of the strong chemical affinity for each other. The absorber is cooled to produce a strong solution at low pressure at state 1. The strong solution is obtained and pumped by a solution pump to the generator passing through HX1, where it is again heated, and the cycle continues. Then, the water absorbs the ammonia in the absorber at the condenser temperature supplied by the circulating water or air, and hence a strong solution (about 38% ammonia concentration) occurs. For ammonia-water ARSs, the most suitable absorber is the film-type absorber because of high heat and mass transfer rates, enhanced overall perfor-

**6.1 Energy and exergy analysis of ammonia-water (NH3-H2O) ARSs**

The energy and exergy analysis for each component is presented according to **Figure 8**. The partial mass balance (PMBE) is also included to determine the concentration mass of ammonia and water in the absorber and generator. That is because the ARS has two fluids as refrigerant and absorbent and their composition at different points is different, particularly in the absorber and generator. The exergy analysis of ammonia-water ARSs is to determine the exergy destruction of each component and to determine the overall exergy efficiency based on the second law of thermodynamics. The exergy analysis (ExBE) for each component is stated

mance, and large concentration rates [11].

below [5, 6]:

**256**

**Figure 8.**

*Ammonia absorption refrigeration cycle.*

*Low-temperature Technologies*

$$
\dot{m}\_{\text{BE}} = \dot{m}\_{\text{3}} h\_{\text{3}} + \dot{Q}\_{\text{gen}} = \dot{m}\_{\text{4}} h\_{\text{4}} + \dot{m}\_{\text{7}} h\_{\text{7}} \tag{57}
$$

$$\mathbf{PMBE} \tag{58}$$

$$\dot{m}\_{\text{uv}} X\_{\text{uv}} + \dot{m}\_{r} = \dot{m}\_{\text{ts}} X\_{\text{ts}} \tag{58}$$

$$
\dot{\mathbf{E}} \mathbf{E} \mathbf{B} \mathbf{E} \qquad \qquad \dot{\dot{m}}\_3 \mathbf{e} \mathbf{x}\_3 + \dot{\mathbf{E}} \mathbf{\dot{x}}\_{Q, \text{gen}} = \dot{m}\_4 \mathbf{e} \mathbf{x}\_4 + \dot{m}\_7 \mathbf{e} \mathbf{x}\_7 + \dot{\mathbf{E}} \dot{\mathbf{x}}\_{\text{de}, \text{gen}} \tag{59}
$$

where *<sup>Q</sup>*\_ *gen* is the heat input to the generator in kW; *<sup>m</sup>*\_ *ws* <sup>¼</sup> *<sup>m</sup>*\_ <sup>4</sup> and *<sup>m</sup>*\_ *ss* <sup>¼</sup> *<sup>m</sup>*\_ 3; *Ex*\_ *Q, gen* is the thermal exergy rate of the generator due to the heat transfer *Q*\_ *gen* to the environment, and it is calculated as *Ex*\_ *Q, gen* <sup>¼</sup> *<sup>Q</sup>*\_ *gen*ð Þ <sup>1</sup> � *<sup>T</sup>*0*=Ts* .

Condenser:

$$
\dot{m}\_{\uparrow}\mathbf{B}\mathbf{E}\tag{60}
$$

$$
\dot{m}\_{\uparrow}h\_{\uparrow} = \dot{Q}\_{H} + \dot{m}\_{\ $}h\_{\$ }\tag{60}
$$

$$\dot{\mathbf{E}} \mathbf{E} \mathbf{B} \mathbf{E} \qquad\qquad \dot{\dot{m}}\_{7} \mathbf{ex}\_{7} = \dot{\mathbf{E}} \dot{\mathbf{x}}\_{Q\_{c} \text{cond}} + \dot{\boldsymbol{m}}\_{8} \mathbf{ex}\_{8} + \dot{\mathbf{E}} \dot{\mathbf{x}}\_{\text{des}, \text{cond}} \tag{61}$$

where *Ex*\_ *Q,cond* is the thermal exergy rate of the condenser due to the heat transfer *<sup>Q</sup>*\_ *<sup>H</sup>* to warm environment and is calculated as *Ex*\_ *Q,cond* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>H</sup>*ð Þ <sup>1</sup> � *<sup>T</sup>*0*=Ts* .

Heat recovery heat exchanger (HX2):

$$
\dot{m}\_1 \mathbf{E} \mathbf{B} \tag{62}
$$

$$
\dot{m}\_8 h\_8 + \dot{m}\_{11} h\_{11} = \dot{m}\_9 h\_9 + \dot{m}\_{12} h\_{12} \tag{62}
$$

$$\mathbf{\dot{x}} \mathbf{z} \mathbf{B} \mathbf{\dot{z}} \qquad \qquad \dot{m}\_{\theta} \mathbf{e} \mathbf{x}\_{\theta} + \dot{m}\_{11} \mathbf{e} \mathbf{x}\_{11} = \dot{m}\_{\theta} \mathbf{e} \mathbf{x}\_{\theta} + \dot{m}\_{12} \mathbf{e} \mathbf{x}\_{12} + \dot{E} \mathbf{x}\_{\text{des}, \text{HX2}} \tag{63}$$

Expansion valves:

$$
\dot{m}\_5 \mathbf{E} \tag{64}
$$

$$
\dot{m}\_5 \hbar\_5 = \dot{m}\_6 \hbar\_6 \Rightarrow \hbar\_5 = \hbar\_6 \tag{64}
$$

$$
\dot{m}\_{\theta}h\_{\theta} = \dot{m}\_{10}h\_{10} \Rightarrow h\_{\theta} = h\_{10} \tag{65}
$$

The ARS is a heat-driven system, which requires heat pump instead or required power by a compressor. That means the ARS is a combination of a heat pump and a refrigeration cycle without a compressor. Therefore, the maximum (reversible) of an ARS can be achieved by a reversible heat engine and a reversible refrigerator, as shown in **Figure 9**. A reversible heat pump is operating by absorbing the heat from a source at and rejecting heat to an environment of to produce a work output from the heat engine. This work is defined as the reversible efficiency of the heat pump multiplied by the heat absorber from the source, which is the heat transfer from the generator in the ARS. This work output is used by the reversible refrigerator to keep a refrigerated space at *TL* while rejecting heat to the environment at *T0*. Therefore, the reversible COP of ARS can be obtained by the thermal efficiency of a reversible

*<sup>W</sup>*\_ <sup>¼</sup> *<sup>η</sup>th,revCOPrev* <sup>¼</sup> <sup>1</sup> � *<sup>T</sup>*<sup>0</sup>

The temperature of the heat source is taken as the average temperature of geothermal water. Then the second-law efficiency of this absorption system is

*COPex,abs* <sup>¼</sup> *<sup>η</sup>II,abs* <sup>¼</sup> *COP*

The refrigeration systems require an input work to release the heat from the refrigerated space to the environment, which is called as a work-driven system. The absorption refrigeration system is based on external heat transfer from an external source, which can be classified as a heat-driven system. For industrial refrigeration systems, energy demand is high and should be provided in a secure and eco-friendly approach to reduce environmental pollution. This can be executed by fossil-based fuels such as oil, natural gas, and coal, which produce substantial carbon monooxide and dioxide emissions that affect global warming and climate change.

*Ts TL*

ð Þ 1 � *T*0*=Ts* ð Þ *TL=*ð Þ *T*<sup>0</sup> � *TL*

<sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>=Q*\_ *gen*

*COPabs,rev*

*T*<sup>0</sup> � *TL*

(72)

(73)

(74)

heat engine and the COP of a reversible refrigerator as in Eq. (72) [10]:

*Q*\_ *L*

<sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>*ð Þ *<sup>T</sup>*0*=TL* � <sup>1</sup> *<sup>Q</sup>*\_ *gen*ð Þ <sup>1</sup> � *<sup>T</sup>*0*=Ts*

*Renewable sources for refrigeration systems: (a) work-driven and (b) heat-driven source.*

*COPabs,rev* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>*

determined to be [10]:

**Figure 10.**

**259**

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

*Q*\_ *gen*

*Ex*\_ *Q, gen*

<sup>¼</sup> *<sup>W</sup>*\_ *Q*\_ *gen*

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

**7. Renewable sources for refrigeration system**

$$
\dot{\mathbf{x}} \mathbf{E} \mathbf{B} \mathbf{E} \tag{66}
$$

$$
\dot{\mathbf{m}}\_{\xi} \mathbf{e} \mathbf{x}\_{\xi} = \dot{\mathbf{m}}\_{6} \mathbf{e} \mathbf{x}\_{6} + \dot{\mathbf{E}} \dot{\mathbf{x}}\_{\mathrm{de}, \mathrm{EX1}} \tag{66}
$$

$$
\dot{m}\_{\theta}e\mathbf{x}\_{\theta} = \dot{m}\_{10}e\mathbf{x}\_{10} + \dot{E}\dot{\mathbf{x}}\_{\text{de},EX1} \tag{67}
$$

Evaporator:

$$
\dot{m}\_{10}\mathbf{E}\tag{68}
$$

$$
\dot{m}\_{10}h\_{10} + \dot{Q}\_{L} = \dot{m}\_{11}h\_{11}\tag{68}
$$

$$\dot{\mathbf{ExBE}} \tag{15.20} \qquad \dot{m}\_{10}\mathbf{ex}\_{10} + \dot{\mathbf{Ex}}\_{Q,evap} = \dot{m}\_{11}h\_{11} + \dot{\mathbf{Ex}}\_{des,enap} \tag{69}$$

where *Ex*\_ *<sup>Q</sup> ,evap* is the thermal exergy rate of the evaporator due to the heat

transfer *<sup>Q</sup>*\_ *<sup>L</sup>* from refrigerated space and is calculated as *Ex*\_ *Q,evap* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>*ð Þ *<sup>T</sup>*0*=TL* � <sup>1</sup> . For the entire system, the overall energy balance of the complete system can be

written as follows, by considering that there is negligible heat loss to the environment:

$$
\dot{\mathcal{W}}\_P + \dot{\mathcal{Q}}\_{gen} + \dot{\mathcal{Q}}\_L = \dot{\mathcal{Q}}\_A + \dot{\mathcal{Q}}\_H \tag{70}
$$

The COP of the system then becomes:

$$\text{COP} = \frac{\dot{Q}\_L}{\dot{W}\_P + \dot{Q}\_{gen}} \cong \frac{\dot{Q}\_L}{\dot{Q}\_{gen}}\tag{71}$$

where *W*\_ *<sup>P</sup>* is the pumping power requirement, and it is usually neglected in the COP calculation.

**Figure 9.** *The maximum COP of an absorption refrigeration system.*

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

Expansion valves:

*Low-temperature Technologies*

Evaporator:

COP calculation.

**Figure 9.**

**258**

The COP of the system then becomes:

*The maximum COP of an absorption refrigeration system.*

EnBE *m*\_ <sup>5</sup>*h*<sup>5</sup> ¼ *m*\_ <sup>6</sup>*h*<sup>6</sup> ) *h*<sup>5</sup> ¼ *h*<sup>6</sup> (64)

ExBE *<sup>m</sup>*\_ <sup>5</sup>*ex*<sup>5</sup> <sup>¼</sup> *<sup>m</sup>*\_ <sup>6</sup>*ex*<sup>6</sup> <sup>þ</sup> *Ex*\_ *des,EX*<sup>1</sup> (66)

EnBE *<sup>m</sup>*\_ <sup>10</sup>*h*<sup>10</sup> <sup>þ</sup> *<sup>Q</sup>*\_ *<sup>L</sup>* <sup>¼</sup> *<sup>m</sup>*\_ <sup>11</sup>*h*<sup>11</sup> (68) ExBE *<sup>m</sup>*\_ <sup>10</sup>*ex*<sup>10</sup> <sup>þ</sup> *Ex*\_ *Q,evap* <sup>¼</sup> *<sup>m</sup>*\_ <sup>11</sup>*h*<sup>11</sup> <sup>þ</sup> *Ex*\_ *des,evap* (69)

where *Ex*\_ *<sup>Q</sup> ,evap* is the thermal exergy rate of the evaporator due to the heat transfer *<sup>Q</sup>*\_ *<sup>L</sup>* from refrigerated space and is calculated as *Ex*\_ *Q,evap* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>*ð Þ *<sup>T</sup>*0*=TL* � <sup>1</sup> . For the entire system, the overall energy balance of the complete system can be written as follows, by considering that there is negligible heat loss to the environment:

*COP* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>L</sup>*

*<sup>W</sup>*\_ *<sup>P</sup>* <sup>þ</sup> *<sup>Q</sup>*\_ *gen*

where *W*\_ *<sup>P</sup>* is the pumping power requirement, and it is usually neglected in the

*m*\_ <sup>9</sup>*h*<sup>9</sup> ¼ *m*\_ <sup>10</sup>*h*<sup>10</sup> ) *h*<sup>9</sup> ¼ *h*<sup>10</sup> (65)

*<sup>m</sup>*\_ <sup>9</sup>*ex*<sup>9</sup> <sup>¼</sup> *<sup>m</sup>*\_ <sup>10</sup>*ex*<sup>10</sup> <sup>þ</sup> *Ex*\_ *des,EX*<sup>1</sup> (67)

*<sup>W</sup>*\_ *<sup>P</sup>* <sup>þ</sup> *<sup>Q</sup>*\_ *gen* <sup>þ</sup> *<sup>Q</sup>*\_ *<sup>L</sup>* <sup>¼</sup> *<sup>Q</sup>*\_ *<sup>A</sup>* <sup>þ</sup> *<sup>Q</sup>*\_ *<sup>H</sup>* (70)

(71)

ffi *<sup>Q</sup>*\_ *<sup>L</sup> Q*\_ *gen*

The ARS is a heat-driven system, which requires heat pump instead or required power by a compressor. That means the ARS is a combination of a heat pump and a refrigeration cycle without a compressor. Therefore, the maximum (reversible) of an ARS can be achieved by a reversible heat engine and a reversible refrigerator, as shown in **Figure 9**. A reversible heat pump is operating by absorbing the heat from a source at and rejecting heat to an environment of to produce a work output from the heat engine. This work is defined as the reversible efficiency of the heat pump multiplied by the heat absorber from the source, which is the heat transfer from the generator in the ARS. This work output is used by the reversible refrigerator to keep a refrigerated space at *TL* while rejecting heat to the environment at *T0*. Therefore, the reversible COP of ARS can be obtained by the thermal efficiency of a reversible heat engine and the COP of a reversible refrigerator as in Eq. (72) [10]:

$$\text{COP}\_{abs, rev} = \frac{\dot{Q}\_L}{\dot{Q}\_{gen}} = \frac{\dot{W}}{\dot{Q}\_{gen}} \frac{\dot{Q}\_L}{\dot{W}} = \eta\_{th, rev} \text{COP}\_{rev} = \left(1 - \frac{T\_0}{T\_s}\right) \left(\frac{T\_L}{T\_0 - T\_L}\right) \tag{72}$$

The temperature of the heat source is taken as the average temperature of geothermal water. Then the second-law efficiency of this absorption system is determined to be [10]:

$$\text{COP}\_{\text{ex},abs} = \frac{\dot{\text{Ex}}\_{Q,emap}}{\dot{\text{Ex}}\_{Q,gen}} = \frac{\dot{Q}\_L(T\_0/T\_L - \mathbf{1})}{\dot{Q}\_{gen}(\mathbf{1} - T\_0/T\_s)} = \frac{\dot{Q}\_L/\dot{Q}\_{gen}}{(\mathbf{1} - T\_0/T\_s)(T\_L/(T\_0 - T\_L))}\tag{73}$$

$$\text{COP}\_{\text{ex, abs}} = \eta\_{\text{II, abs}} = \frac{\text{COP}}{\text{COP}\_{\text{abs, rev}}} \tag{74}$$

#### **7. Renewable sources for refrigeration system**

The refrigeration systems require an input work to release the heat from the refrigerated space to the environment, which is called as a work-driven system. The absorption refrigeration system is based on external heat transfer from an external source, which can be classified as a heat-driven system. For industrial refrigeration systems, energy demand is high and should be provided in a secure and eco-friendly approach to reduce environmental pollution. This can be executed by fossil-based fuels such as oil, natural gas, and coal, which produce substantial carbon monooxide and dioxide emissions that affect global warming and climate change.

**Figure 10.** *Renewable sources for refrigeration systems: (a) work-driven and (b) heat-driven source.*

Another example, a small-scale system, is designed to provide an electrical load to residential buildings [13]. This system utilizes, as shown in **Figure 12**, photovoltaic solar system (PV) to provide electrical power. This electric power is used for a water electrolyzer system to split the water electrochemically to produce hydrogen and oxygen gases. The hydrogen gas enters high-temperature solid oxide fuel cells (SOFC) to produce electricity and heat. The heat is transferred to an absorption cooling system by heat recovery generator. The PV system may generate excess electricity more than the demand during off-peak hours. This system is designed for a detached house in Toronto city, Canada. The PV solar system delivers maximum power of 3.35 kW. The water electrolyzer can produce 0.792 and 0.538 kg/day of gaseous hydrogen in summer and winter seasons. The SOFC fuel cell supplies 8.43 kWh per day in summer season. The maximum energy and exergy efficiencies of the photovoltaic system are 17 and 18.3%, respectively, while the maximum total energy and exergy efficiencies are obtained to be 55.7 and 49.0%, respectively.

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

In a similar study, a hybrid renewable system was designed to produce electricity and clean fuel such as hydrogen gas and provide cooling for a residential building in two locations Egypt and Saudi Arabia in summer season [14]. The cooling loads for a house are 18.06 and 19.3 kW in Egypt and Saudi Arabia, respectively. This system, as shown in **Figure 13**, depends on the photovoltaic solar system and wind turbines to provide excess electricity more than the electric grid. The excess electricity is delivered to a water electrolyzer to produce pure oxygen and hydrogen gases stored in tanks for clean fueling services. Part of the hydrogen gas is used for a proton-exchange membrane (PEM) fuel cell that can produce heat and electricity through an electrochemical process without any mechanical parts. The heat generated from the fuel cell can be utilized by a generator of an ammonia-water ARS to provide cooling. The hybrid renewable system can operate in a significant performance with water mass flow rate of 1.8 kg/s to produce hydrogen with a mass flow rate of 0.2 kg/s and ammonia mass flow rate of about 0.2 kg/s to produce cooling load between 40 and 120 kW more than the design cooling load of one house. The energy and exergy efficiencies are obtained to be about 67 and 68%, respectively.

Therefore, this hybrid system can be sufficient for more than one house.

*Schematic diagram of a hybrid renewable system (adopted from [14]).*

**Figure 13.**

**261**

A multigeneration system is designed by [15] and powered by geothermal energy assisted with solar energy to produce five outputs: heating air for residential building, hot domestic water, drying food, refrigeration for industry, and electricity. This multigeneration system, as shown in **Figure 14**, consists of a heat pump

#### **Figure 11.**

*Schematic diagram of the integrated solar thermal power plant, absorption refrigeration system, and MED cycle (adopted from [12]).*

Massive efforts point to renewable sources such as geothermal energy, solar energy, and wind energy, which promise a potential solution to provide the clean energy needed as work or heat to operate the refrigeration. Schematic diagram of **Figure 10** shows possible ways of renewable sources for work-driven and heat-driven refrigeration system.

An integrated system of a concentrated solar power plant integrated with desalination process and absorption refrigeration cycle is utilized to supply power, freshwater, and refrigeration [12]. The system, as shown in **Figure 11**, consists of concentrated solar collectors connected with steam turbine power plant, a multieffect desalination process with a parallel feed of seawater, and a single-stage ammonia-water absorption refrigeration system. The solar collectors provide thermal energy 21,030 kW to the steam power plant to deliver an electric power of 4632 kW. The refrigeration load from the absorption cooling system is 820.8 kW. The desalination system can also provide 22.79 kg/s freshwater. This cycle has obtained overall energy and exergy efficiencies to be 80.70% and 66.05%, respectively.

#### **Figure 12.**

*Schematic of the photovoltaic-fuel cell CHIP system for residential applications (adopted from [13]).*

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

Another example, a small-scale system, is designed to provide an electrical load to residential buildings [13]. This system utilizes, as shown in **Figure 12**, photovoltaic solar system (PV) to provide electrical power. This electric power is used for a water electrolyzer system to split the water electrochemically to produce hydrogen and oxygen gases. The hydrogen gas enters high-temperature solid oxide fuel cells (SOFC) to produce electricity and heat. The heat is transferred to an absorption cooling system by heat recovery generator. The PV system may generate excess electricity more than the demand during off-peak hours. This system is designed for a detached house in Toronto city, Canada. The PV solar system delivers maximum power of 3.35 kW. The water electrolyzer can produce 0.792 and 0.538 kg/day of gaseous hydrogen in summer and winter seasons. The SOFC fuel cell supplies 8.43 kWh per day in summer season. The maximum energy and exergy efficiencies of the photovoltaic system are 17 and 18.3%, respectively, while the maximum total energy and exergy efficiencies are obtained to be 55.7 and 49.0%, respectively.

In a similar study, a hybrid renewable system was designed to produce electricity and clean fuel such as hydrogen gas and provide cooling for a residential building in two locations Egypt and Saudi Arabia in summer season [14]. The cooling loads for a house are 18.06 and 19.3 kW in Egypt and Saudi Arabia, respectively. This system, as shown in **Figure 13**, depends on the photovoltaic solar system and wind turbines to provide excess electricity more than the electric grid. The excess electricity is delivered to a water electrolyzer to produce pure oxygen and hydrogen gases stored in tanks for clean fueling services. Part of the hydrogen gas is used for a proton-exchange membrane (PEM) fuel cell that can produce heat and electricity through an electrochemical process without any mechanical parts. The heat generated from the fuel cell can be utilized by a generator of an ammonia-water ARS to provide cooling. The hybrid renewable system can operate in a significant performance with water mass flow rate of 1.8 kg/s to produce hydrogen with a mass flow rate of 0.2 kg/s and ammonia mass flow rate of about 0.2 kg/s to produce cooling load between 40 and 120 kW more than the design cooling load of one house. The energy and exergy efficiencies are obtained to be about 67 and 68%, respectively. Therefore, this hybrid system can be sufficient for more than one house.

A multigeneration system is designed by [15] and powered by geothermal energy assisted with solar energy to produce five outputs: heating air for residential building, hot domestic water, drying food, refrigeration for industry, and electricity. This multigeneration system, as shown in **Figure 14**, consists of a heat pump

**Figure 13.** *Schematic diagram of a hybrid renewable system (adopted from [14]).*

Massive efforts point to renewable sources such as geothermal energy, solar energy, and wind energy, which promise a potential solution to provide the clean energy needed as work or heat to operate the refrigeration. Schematic diagram of **Figure 10** shows possible ways of renewable sources for work-driven and heat-driven refrig-

*Schematic diagram of the integrated solar thermal power plant, absorption refrigeration system, and MED cycle*

An integrated system of a concentrated solar power plant integrated with desa-

lination process and absorption refrigeration cycle is utilized to supply power, freshwater, and refrigeration [12]. The system, as shown in **Figure 11**, consists of concentrated solar collectors connected with steam turbine power plant, a multieffect desalination process with a parallel feed of seawater, and a single-stage ammonia-water absorption refrigeration system. The solar collectors provide thermal energy 21,030 kW to the steam power plant to deliver an electric power of 4632 kW. The refrigeration load from the absorption cooling system is 820.8 kW. The desalination system can also provide 22.79 kg/s freshwater. This cycle has obtained overall energy and exergy efficiencies to be 80.70% and 66.05%,

*Schematic of the photovoltaic-fuel cell CHIP system for residential applications (adopted from [13]).*

eration system.

*(adopted from [12]).*

*Low-temperature Technologies*

**Figure 11.**

respectively.

**Figure 12.**

**260**

by wind turbines (83.24 kWh) and fuel combustion (258.97 kWh), cooling load of 2.56 kW, and mass flow rate of hot water of 1.82 ton per day hot. The energy

The refrigeration systems are applied in our life for preserving food, cooling air, and other industrial applications. Most refrigeration systems require external power or external heat to release the heat from the refrigerated space. Many industrial applications involve large cooling energy, which can be operated by multi-pressure refrigeration system, which requires a large amount of external power. The chapter has presented some applications with renewable sources to replace the fossil fueldriven energy with an environmentally friendly energy source such as geothermal, solar, and wind energy so-called hybrid or integrated systems. In addition to cooling load, the hybrid systems can produce electricity, heating load, and clean fuel such as hydrogen fuel. The absorption refrigeration system is mostly-combined with hybrid

system to use the heating load from solar or geothermal energy to produce

efficiency of the system is achieved to be 53.94%.

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

**8. Conclusion**

cooling load.

**Author details**

Shaimaa Seyam

**263**

Faculty of Engineering, Benha University, Benha, Egypt

shaimaa.abdelhamid@bhit.bu.edu.eg

provided the original work is properly cited.

\*Address all correspondence to: shaimaa.seyam@mail.utoronto;

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

#### **Figure 14.**

*Schematic diagram of the multigeneration system powered by the solar and geothermal energy (adopted from [15]).*

#### **Figure 15.**

*Schematic diagram of gas power cycle with wind turbine, CAES, ORC, and ARS (adopted from [16]).*

system, a single flash geothermal cycle, an absorption cooling system, thermal energy storage connected with auxiliary steam turbine and concentrated solar collectors, hot water system, and drying system. The system has achieved overall energy and exergy efficiencies to be 69.6 and 42.8%, respectively. The first and second steam turbines have the power of 10,043 and 9886 kW. The *COP* and *COPex* are 0.678 and 0.253 for the absorption cooling system and 2.029 and 0.1826 for heat pump system, respectively. The refrigeration load is 1787 kW. The overall energy and exergy efficiencies for the whole system are 69.6 and 42.8%, respectively.

A wind system is combined with a refrigeration system, as shown in **Figure 15**. Wind energy is coupled with compressed air energy storage (CAES) systems to store wind energy for long-term usage [16]. The integrated system consists of a combined gas power cycle, including compressors, intercooling heat exchangers, and gas turbine, an organic Rankine power cycle (ORC), and an absorption refrigeration system (ARS). The system objective is to provide electricity, domestic hot water, and cooling load. The system can generate electricity of 33.67 kW provided

by wind turbines (83.24 kWh) and fuel combustion (258.97 kWh), cooling load of 2.56 kW, and mass flow rate of hot water of 1.82 ton per day hot. The energy efficiency of the system is achieved to be 53.94%.
