**Thermodynamics Assessment of the Multi-Generation Energy Production Systems**

Murat Ozturk

40 Clean Energy for Better Environment

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/51522

## **1. Introduction**

The efficiency of the solar multi-generation energy production system has great significance due to the limited supply of available energy from solar radiation as well as impact on sys‐ tem production performance, operation cost and environmental concerns. Thus, a good un‐ derstanding of the efficiency of the whole system and its components is necessary for the multi-functional system installation. In this regard, the First Law of Thermodynamics based efficiency also known as energy efficiency may lead to inadequate and also misleading con‐ sequences, since all energy transfers are taken to be equal and the ambient temperature is not taken into consideration. The Second Law of Thermodynamics defines the energy con‐ versation limits of this available energy based on irregularities between different forms of energies. The quality of the available energy is highly connected with the reference environ‐ ment, which is often modeled as the ambient environment, as well as the success level of this conversion capacity; and needs to be considered to prevent any incomplete and/or in‐ correct energy conversation results. Quality of the energy should be given as an examining the work potentials of the initial and final stages of an investigated system. Such analysis is called as exergy analysis, which gives the amount of an energy that may be totally converted into useful work. Exergy (also called as an available energy or availability) of an investigat‐ ed system is defined using the thermodynamics principles as the maximum amount of work which can be produced by a system or a flow of matter or energy as it comes to equilibrium with a reference environment [1-3]. It is well known that one of the important uses of the exergy analysis in engineering processes is to determine the best theoretical performance of the system.

The useful work potential of the system is reduced by the irreversibilities and the corre‐ sponding amount of energy becomes unusable [4]. The entropy generation give the effects of

© 2012 Ozturk; licensee InTech. This is an open access article 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, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. 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, provided the original work is properly cited.

these irreversibilties in the investigation system during a process and helps compare the each component in the system based on how much they contribute to the operation ineffi‐ ciencies of the whole system. Thus, entropy generations of the system components needs to be evaluated to determine the whole system efficiency. Even though energy analysis of the system is the most commonly used method for examining energy conversation systems, its only concerned with the conservation of energy, which neither takes the corresponding en‐ vironmental conditions into account, nor provides how, where and why the system per‐ formance degrades for the operated system. Also, the energy analysis of the system only measures the quantity of energy and does not reveal the full efficiencies of the process [5]. Thus, in this scientific study, the multi-generation system is examined with exergy analysis in order to give the true efficiency of the whole system and its components by determining the irreversibilities in the each process, and how nearly the respective performance ap‐ proach ideal conditions. By using the energy and exergy analysis, magnitude of the losses, and their causes and locations are identified by investigating the sites of exergy destruction in order to make improvements to the whole system and its components [6].

The by-product oxygen has relatively negligible energy and exergy content, and can be used

Thermodynamics Assessment of the Multi-Generation Energy Production Systems

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43

In this research, the general mass, energy and exergy balance equations to find the energy and exergy inputs and outputs, the rate of exergy decrease, the rate of irreversibility and the ener‐ gy and exergy efficiencies for the solar multi-generation energy production system are given.

where input and output gives to quantities entering and exiting through the system boun‐ dary, respectively, generation and consumption gives to quantities produced or consumed within the system, respectively and accumulation gives to potential build-up of the quantity within the system [7]. The general mass balance equation can be given in the rate form.

where *m*˙ is the mass flow rate, and the subscripts in and out shows inlet and outlet flows, respectively. Assuming the absence kinetic, potential and chemical exergy terms, the general

energy balance for the multi-generation system is formulated as follows;

*Input* + *Generation* - *Output* - *Consumption* = *Accumulation* (1)

∑ *m*˙ *in* =∑ *m*˙ *out* (2)

In general, thermodynamic balance equation for a quantity in a process can be given as

for the other purposes or can be sold.

**Figure 1.** The Solar multi-generation energy production system

**3. Thermodynamic Analysis**

### **2. System Description**

The whole system and its components are given for the solar multi-generation energy pro‐ duction system. This system can be divided into four subsystems; i-) parabolic trough collec‐ tor, ii-) organic Rankine cycle (ORC), iii-) electrolyzer and iv-) absorption cooling and heating. The schematic diagram of the multi-generation system is given in the Figure 1. The main outputs of the given system are electricity, hydrogen, oxygen, heating, cooling and hot water. Thermal energy of the solar radiation is collected and concentrated using a parabolic trough collector in order to produce electricity, heating-cooling and hot water from ORC, absorption system and hot water collection tank, respectively. Another important purpose of this solar multi-generation system is producing of hydrogen. Stored hydrogen can be used in a PEM fuel cell to produce power in the night time. Thus, electricity can be pro‐ duced continuously for 24 hours. A part of produced electricity from the organic Rankine cycle is used to run the PEM (proton exchange membrane) electrolysis system, which re‐ quires heat at nearly 80 °C and electricity as an input. The thermal energy is used in the PEM electrolysis to decrease the electricity demand of the electrolysis system. Heat require‐ ments of the PEM electrolyzer system are supplied from generator waste heat. The hydro‐ gen separator separates hydrogen from the steam by using hydrogen separation membrane. The produced hydrogen stream is then cooled to 40°C with the help of the cooling water. The produced hydrogen is compressed in a four-stage compressor, through intercooling to 40°C. The product gases (which is 99.9 wt% H2) exit from the store tank at 506.5 kPa and 85°C. When the weather conditions are not favorable or additional power is needed, the stored hydrogen can be used in order to generate power. In addition, the outputted oxygen from the high temperature electrolysis is stored in a separate storage tank. The produced oxygen from the high temperature electrolysis system is cooled to 45°C via the cooling wa‐ ter. Similarly, the cooling water used in the oxygen cooler has an exit temperature of 80°C, The by-product oxygen has relatively negligible energy and exergy content, and can be used for the other purposes or can be sold.

**Figure 1.** The Solar multi-generation energy production system

## **3. Thermodynamic Analysis**

for Better Environment

42 Clean Energy

**2. System Description**

these irreversibilties in the investigation system during a process and helps compare the each component in the system based on how much they contribute to the operation ineffi‐ ciencies of the whole system. Thus, entropy generations of the system components needs to be evaluated to determine the whole system efficiency. Even though energy analysis of the system is the most commonly used method for examining energy conversation systems, its only concerned with the conservation of energy, which neither takes the corresponding en‐ vironmental conditions into account, nor provides how, where and why the system per‐ formance degrades for the operated system. Also, the energy analysis of the system only measures the quantity of energy and does not reveal the full efficiencies of the process [5]. Thus, in this scientific study, the multi-generation system is examined with exergy analysis in order to give the true efficiency of the whole system and its components by determining the irreversibilities in the each process, and how nearly the respective performance ap‐ proach ideal conditions. By using the energy and exergy analysis, magnitude of the losses, and their causes and locations are identified by investigating the sites of exergy destruction

in order to make improvements to the whole system and its components [6].

The whole system and its components are given for the solar multi-generation energy pro‐ duction system. This system can be divided into four subsystems; i-) parabolic trough collec‐ tor, ii-) organic Rankine cycle (ORC), iii-) electrolyzer and iv-) absorption cooling and heating. The schematic diagram of the multi-generation system is given in the Figure 1. The main outputs of the given system are electricity, hydrogen, oxygen, heating, cooling and hot water. Thermal energy of the solar radiation is collected and concentrated using a parabolic trough collector in order to produce electricity, heating-cooling and hot water from ORC, absorption system and hot water collection tank, respectively. Another important purpose of this solar multi-generation system is producing of hydrogen. Stored hydrogen can be used in a PEM fuel cell to produce power in the night time. Thus, electricity can be pro‐ duced continuously for 24 hours. A part of produced electricity from the organic Rankine cycle is used to run the PEM (proton exchange membrane) electrolysis system, which re‐ quires heat at nearly 80 °C and electricity as an input. The thermal energy is used in the PEM electrolysis to decrease the electricity demand of the electrolysis system. Heat require‐ ments of the PEM electrolyzer system are supplied from generator waste heat. The hydro‐ gen separator separates hydrogen from the steam by using hydrogen separation membrane. The produced hydrogen stream is then cooled to 40°C with the help of the cooling water. The produced hydrogen is compressed in a four-stage compressor, through intercooling to 40°C. The product gases (which is 99.9 wt% H2) exit from the store tank at 506.5 kPa and 85°C. When the weather conditions are not favorable or additional power is needed, the stored hydrogen can be used in order to generate power. In addition, the outputted oxygen from the high temperature electrolysis is stored in a separate storage tank. The produced oxygen from the high temperature electrolysis system is cooled to 45°C via the cooling wa‐ ter. Similarly, the cooling water used in the oxygen cooler has an exit temperature of 80°C,

In this research, the general mass, energy and exergy balance equations to find the energy and exergy inputs and outputs, the rate of exergy decrease, the rate of irreversibility and the ener‐ gy and exergy efficiencies for the solar multi-generation energy production system are given. In general, thermodynamic balance equation for a quantity in a process can be given as

$$\text{Input} \newline + \text{Generation} \newline - \text{Output} \newline - \text{Consumption} \newline = \text{Accumulation} \newline \tag{1}$$

where input and output gives to quantities entering and exiting through the system boun‐ dary, respectively, generation and consumption gives to quantities produced or consumed within the system, respectively and accumulation gives to potential build-up of the quantity within the system [7]. The general mass balance equation can be given in the rate form.

$$
\Sigma \,\dot{m}\_{in} = \Sigma \,\dot{m}\_{out} \tag{2}
$$

where *m*˙ is the mass flow rate, and the subscripts in and out shows inlet and outlet flows, respectively. Assuming the absence kinetic, potential and chemical exergy terms, the general energy balance for the multi-generation system is formulated as follows;

$$\mathbf{Q} + \sum\_{i} \dot{\mathbf{m}}\_{\text{in},i} \left( \mathbf{h}\_{i} + \frac{\mathbf{V}\_{i}^{2}}{2} + \mathbf{g} \mathbf{z}\_{i} \right) = \sum\_{\text{e}} \dot{\mathbf{m}}\_{\text{out},\text{e}} \left( \mathbf{h}\_{\text{e}} + \frac{\mathbf{V}\_{\text{e}}^{2}}{2} + \mathbf{g} \mathbf{z}\_{\text{e}} \right) + \mathbf{W} \tag{3}$$

where *Q*˙ and *W*˙ represents the heat and work rates, respectively, and h is the specific en‐ thalpy at the chosen state. Considering a system at rest relative to the environment, kinetic and potential terms can be ignored,

$$\dot{\mathbf{Q}} + \sum\_{\text{i}} \dot{\mathbf{m}}\_{\text{in},\text{i}} \mathbf{h}\_{\text{i}} = \sum\_{\text{e}} \dot{\mathbf{m}}\_{\text{out},\text{e}} \mathbf{h}\_{\text{e}} + \dot{\mathbf{W}} \tag{4}$$

The entropy balance can also be expressed on a time rate basis as

$$
\dot{\mathbf{S}}\_{in} + \dot{\mathbf{S}}\_{gen} = \dot{\mathbf{S}}\_{out} \tag{5}
$$

*ex ph* ,*<sup>i</sup>* =(*hi* - *ho*) - *To*(*si* - *so*) (12)

Thermodynamics Assessment of the Multi-Generation Energy Production Systems

The difference being the rate of exergy destruction (or lost work) within the boundary due to associated irreverisibilities which can be calculated based on Gouy-Stodola theorem. The

where ∆*Si*,*net* is the specific entropy change for the process. The exergy loss ratio of the sys‐ tem components is given as follows to compare of these components by using exergy analy‐

where *E*˙ *xD*,*com* is exergy destruction of the system components and *E*˙ *xD*,*sys* is the exergy de‐ struction of the overall system. The exergy destruction rate for the each component and over‐ all of the multi-generation system is given in the Table 1 according to given above procedure.

*<sup>E</sup>*˙ *xLR* <sup>=</sup> *<sup>E</sup>*˙ *xD*,*com E*˙ *x <sup>D</sup>*,*sys*

*<sup>E</sup>*˙ *xi* <sup>=</sup>*m*˙ *exi* (13)

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45

*<sup>E</sup>*˙ *xD*,*<sup>i</sup>* <sup>=</sup>*To* <sup>∆</sup>*Si*,*net* (14)

(15)

The exergy rate of a material flow is given as follows.

sis view point.

exergy destruction in the component i should be given as follows;

**Table 1.** Exergy destruction rates for the multi-generation energy production system

$$
\dot{\mathcal{S}}\_{\mathcal{S}^{\text{gen}}} = \dot{m} \, \Delta \, \mathcal{S} \tag{6}
$$

where *S*˙ is the entropy flow or generation rate. The amount transferred out of the boundary must exceed the rate in which entropy enters, the difference being the rate of entropy gener‐ ation within the boundary due to associated irreversibilities.

The system components irreversibility and also recommended ways to improve the efficien‐ cies of them can be evaluated by using exergy analysis. The exergy balance of the multi-gen‐ eration system components is given as follows;

$$
\nabla \cdot \dot{\mathbf{E}} \mathbf{x}\_{\text{in}} = \nabla \cdot \dot{\mathbf{E}} \mathbf{x}\_{\text{out}} + \dot{\mathbf{E}} \mathbf{x}\_{\text{D}} \tag{7}
$$

$$\sum\_{i} \dot{m}\_{i} \boldsymbol{e} \boldsymbol{x}\_{i} + \dot{\boldsymbol{E}} \boldsymbol{x}\_{Q} = \sum\_{e} \dot{m}\_{e} \boldsymbol{e} \boldsymbol{x}\_{e} + \dot{\boldsymbol{E}} \boldsymbol{x}\_{W} + \dot{\boldsymbol{E}} \boldsymbol{x}\_{D} \tag{8}$$

where subscripts i and e are the specific exergy of the control volume inlet and outlet flow, *E*˙ *x* is the exergy rate, *E*˙ *xQ*and *E*˙ *xW* are the exergy flow rate associated with heat transfer and work, *ex*is the specific flow exergy of the process and *E*˙ *xD* is the exergy destruction rate.

$$\dot{\mathbf{E}} \propto\_{\mathcal{Q}} = \left(\mathbf{1} \cdot \frac{T\_o}{T\_i}\right) \dot{\mathbf{Q}}\_i \tag{9}$$

$$
\dot{E} \propto\_W = \dot{W} \tag{10}
$$

$$e\mathbf{x} = e\boldsymbol{\alpha}\_{ke} + e\boldsymbol{\alpha}\_{pe} + e\boldsymbol{\alpha}\_{ph} + e\boldsymbol{\alpha}\_{ch} \tag{11}$$

where *exke* is the kinetic exergy, *ex pe*is the potential exergy, *ex ph* is the physical exergy and *exch* is the chemical exergy. Since the variation of the kinetic, potential and chemical exergy is considered negligible in this study. The physical exergy

Thermodynamics Assessment of the Multi-Generation Energy Production Systems http://dx.doi.org/10.5772/51522 45

$$\mathbf{e} \times\_{ph\\_i} = \begin{pmatrix} \mathbf{h}\_i \ -\mathbf{h}\_o \end{pmatrix} - T\_o \begin{pmatrix} \mathbf{s}\_i \ -\mathbf{s}\_o \end{pmatrix} \tag{12}$$

The exergy rate of a material flow is given as follows.

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44 Clean Energy

Q˙ + ∑ i m˙ in,i (hi <sup>+</sup> Vi 2 <sup>2</sup> + gzi

and potential terms can be ignored,

) =∑ e m˙ out,e

Q˙ + ∑ i m˙ in,i hi=∑ e

The entropy balance can also be expressed on a time rate basis as

ation within the boundary due to associated irreversibilities.

*exi* <sup>+</sup> *<sup>E</sup>*˙ *xQ* <sup>=</sup><sup>∑</sup>

*e*

*<sup>E</sup>*˙ *xQ* =(1 -

eration system components is given as follows;

∑ *i m*˙ *i*

is considered negligible in this study. The physical exergy

where *Q*˙ and *W*˙ represents the heat and work rates, respectively, and h is the specific en‐ thalpy at the chosen state. Considering a system at rest relative to the environment, kinetic

where *S*˙ is the entropy flow or generation rate. The amount transferred out of the boundary must exceed the rate in which entropy enters, the difference being the rate of entropy gener‐

The system components irreversibility and also recommended ways to improve the efficien‐ cies of them can be evaluated by using exergy analysis. The exergy balance of the multi-gen‐

where subscripts i and e are the specific exergy of the control volume inlet and outlet flow, *E*˙ *x* is the exergy rate, *E*˙ *xQ*and *E*˙ *xW* are the exergy flow rate associated with heat transfer and work, *ex*is the specific flow exergy of the process and *E*˙ *xD* is the exergy destruction rate.

> *To Ti*

where *exke* is the kinetic exergy, *ex pe*is the potential exergy, *ex ph* is the physical exergy and *exch* is the chemical exergy. Since the variation of the kinetic, potential and chemical exergy

(he <sup>+</sup> Ve 2 <sup>2</sup> + gze

) + W˙ (3)

<sup>m</sup>˙ out,ehe <sup>+</sup> <sup>W</sup>˙ (4)

*<sup>S</sup>*˙ *in* <sup>+</sup> *<sup>S</sup>*˙ *gen* <sup>=</sup>*S*˙ *out* (5)

*<sup>S</sup>*˙ *gen* <sup>=</sup>*m*˙ <sup>∆</sup>*<sup>S</sup>* (6)

<sup>∑</sup> <sup>E</sup>˙ xin <sup>=</sup><sup>∑</sup> <sup>E</sup>˙ xout <sup>+</sup> <sup>E</sup>˙ xD (7)

*<sup>m</sup>*˙ *<sup>e</sup>exe* <sup>+</sup> *<sup>E</sup>*˙ *xW* <sup>+</sup> *<sup>E</sup>*˙ *xD* (8)

)*Q*˙ *<sup>i</sup>* (9)

*<sup>E</sup>*˙ *xW* <sup>=</sup>*W*˙ (10)

*ex* =*exke* + *ex pe* + *ex ph* + *exch* (11)

$$
\dot{E}\,\alpha\_i = \dot{m}e\alpha\_i\tag{13}
$$

The difference being the rate of exergy destruction (or lost work) within the boundary due to associated irreverisibilities which can be calculated based on Gouy-Stodola theorem. The exergy destruction in the component i should be given as follows;

$$
\dot{E} \propto\_{D,i} = T\_{\,o} \Delta S\_{i,net} \tag{14}
$$

where ∆*Si*,*net* is the specific entropy change for the process. The exergy loss ratio of the sys‐ tem components is given as follows to compare of these components by using exergy analy‐ sis view point.

$$
\dot{E} \propto\_{LR} = \frac{E \times\_{D,con}}{E \times\_{D,sys}} \tag{15}
$$

where *E*˙ *xD*,*com* is exergy destruction of the system components and *E*˙ *xD*,*sys* is the exergy de‐ struction of the overall system. The exergy destruction rate for the each component and over‐ all of the multi-generation system is given in the Table 1 according to given above procedure.


**Table 1.** Exergy destruction rates for the multi-generation energy production system

#### **3.1. Energy efficiency**

The energy efficiency of the process is defined as the ratio of useful energy produced by the process to the total energy input. In this paper, energy efficiencies for five different systems are considered: parabolic trough collector, organic Rankine cycle, hydrogen production, ab‐ sorption cooling and heating sub-system, overall multi-generation system as shown below

$$
\eta\_{\rm PTC} = \frac{Q\_1 + Q\_5}{Q\_{solar}} \tag{16}
$$

*<sup>ψ</sup>absorption* <sup>=</sup> *<sup>E</sup>*˙ *xcooling*

*<sup>ψ</sup>system* <sup>=</sup> *<sup>W</sup>*˙ *org* ,*Rankine* <sup>+</sup> *<sup>E</sup>*˙ *<sup>x</sup> <sup>H</sup>* <sup>2</sup> <sup>+</sup> *<sup>E</sup>*˙ *xcooling*

system should be formulated in forms of the exergetic COP.

**Table 2.** Exergy efficiency equations for the system components

*<sup>Q</sup>* <sup>+</sup> *<sup>E</sup>*˙ *xheating Q*

*<sup>Q</sup>* <sup>+</sup> *<sup>E</sup>*˙ *xheating*

*<sup>Q</sup>* <sup>+</sup> *<sup>E</sup>*˙ *xhotwater Q*

Thermodynamics Assessment of the Multi-Generation Energy Production Systems

*<sup>Q</sup>* (26)

*<sup>Q</sup>* (27)

(25)

47

http://dx.doi.org/10.5772/51522

*E*˙ *x HEX* -*<sup>I</sup> <sup>Q</sup>* <sup>+</sup> *<sup>W</sup>*˙ *<sup>P</sup>* -*III*

*E*˙ *x PTC*

The exergy efficiency equations for the solar-based multi-generation energy production sys‐ tem components are given in the Table 2. The exergetic performance of the absorption sub-

> *Q W*˙ *pump*-*III* + *E*˙ *x gen*

*COPex* <sup>=</sup> *<sup>E</sup>*˙ *xcooling*

$$\text{mg}\_{org\text{-}Rankine} = \frac{\dot{W}\_{net\text{-}org\text{-}Rankine}}{\dot{Q}\_{whole}} \tag{17}$$

$$
\ln \eta\_{hydroget} = \frac{m\_{H\_2} LHVH\_2}{Q\_{Gm} + W\_{Turbine}} \tag{18}
$$

$$\eta\_{absorption} = \frac{Q\_{cooling} + Q\_{heating}}{Q\_{HE\\_l} + W\_{P\\_III}} \tag{19}$$

$$\eta\_{sgssteur} = \frac{\dot{W}\_{avg-Rainic} + \dot{m}\_{H12} LHVH\_2 + \dot{Q}\_{cooling} + \dot{Q}\_{heating} + \dot{Q}\_{heaturbr}}{\dot{Q}\_{PIC}} \tag{20}$$

A coefficient of performance (COP) term can be used to expressing of the energetic perform‐ ance of the absorption sub-system.

$$\text{COP} = \frac{\text{Q}\_{\text{cooling}}}{\text{W}\_{\text{pump}\text{-}ill} + \text{Q}\_{\text{gen}}} \tag{21}$$

where *W*˙ *<sup>p</sup>* is the pumping power requirement, and it is usually neglected in the COP calcu‐ lations and *Q*˙ *gen* is the rate of heat inputted to the generator.

#### **3.2. Exergy Efficiency**

The exergy efficiency of the process is the produced exergy from the system output that is divided by the exergy system input and it can also be expressed by the aforementioned subsystems as follows;

$$
\psi\_{PTC} = \frac{\triangle x\_1^Q + \triangle x\_2^Q}{\triangle x\_{solar}^Q} \tag{22}
$$

$$
\hat{\Psi}\_{org\text{ -}Rankine} = \frac{\dot{W}\_{org\text{ -}Rankine}}{\hat{\mathbb{E}} \, x\_{bubble}^{Q}} \tag{23}
$$

$$
\psi\_{hydrogent} = \frac{\mathbb{E}\,x\_{H2}}{\mathbb{E}\,x\_{Gm}^Q + W\_{Turbine}} \tag{24}
$$

Thermodynamics Assessment of the Multi-Generation Energy Production Systems http://dx.doi.org/10.5772/51522 47

$$\text{V}\,\begin{aligned} \text{V}\,\begin{array}{c} \text{V}\,\text{a}\,\text{s}\_{\text{cooling}} = \frac{\text{E}\,\text{x}^{\text{Q}}\_{\text{cooling}} + \text{E}\,\text{x}^{\text{Q}}\_{\text{heating}}}{\text{E}\,\text{x}^{\text{Q}}\_{\text{PEX}\,-\text{I}} + \text{V}\,\text{V}\,\text{P}\_{\text{P}\,-\text{III}}} \end{aligned} \tag{25}$$

$$\psi\_{system} = \frac{W\_{avg,Rankine} + E \ge\_{H.2} + E \ge\_{cooling}^{Q} + E \ge\_{heating}^{Q} + E \ge\_{photon}^{Q}}{E \ge\_{PC}^{Q}} \tag{26}$$

The exergy efficiency equations for the solar-based multi-generation energy production sys‐ tem components are given in the Table 2. The exergetic performance of the absorption subsystem should be formulated in forms of the exergetic COP.

for Better Environment

ance of the absorption sub-system.

**3.2. Exergy Efficiency**

systems as follows;

The energy efficiency of the process is defined as the ratio of useful energy produced by the process to the total energy input. In this paper, energy efficiencies for five different systems are considered: parabolic trough collector, organic Rankine cycle, hydrogen production, ab‐ sorption cooling and heating sub-system, overall multi-generation system as shown below

(16)

(17)

(18)

(19)

(20)

(21)

(24)

*<sup>η</sup>PTC* <sup>=</sup> *<sup>Q</sup>*˙ <sup>1</sup> <sup>+</sup> *<sup>Q</sup>*˙ <sup>5</sup> *Q*˙ *solar*

*<sup>η</sup>org*-*Rankine* <sup>=</sup> *<sup>W</sup>*˙ *net*,*org* -*Rankine*

*<sup>η</sup>hydrogen* <sup>=</sup> *<sup>m</sup>*˙ *<sup>H</sup>* <sup>2</sup>*LHV <sup>H</sup>*<sup>2</sup>

*<sup>η</sup>absorption* <sup>=</sup> *<sup>Q</sup>*˙ *cooling* <sup>+</sup> *<sup>Q</sup>*˙ *heating*

*<sup>η</sup>system* <sup>=</sup> *<sup>W</sup>*˙ *org* -*Rankine* <sup>+</sup> *<sup>m</sup>*˙ *<sup>H</sup>* <sup>2</sup>*LHV <sup>H</sup>*<sup>2</sup> <sup>+</sup> *<sup>Q</sup>*˙ *cooling* <sup>+</sup> *<sup>Q</sup>*˙ *heating* <sup>+</sup> *<sup>Q</sup>*˙ *hotwater Q*˙ *PTC*

*COP* <sup>=</sup> *<sup>Q</sup>*˙ *cooling*

*<sup>ψ</sup>PTC* <sup>=</sup> *<sup>E</sup>*˙ *<sup>x</sup>*<sup>1</sup>

*<sup>ψ</sup>org*-*Rankine* <sup>=</sup> *<sup>W</sup>*˙ *org* -*Rankine*

*<sup>ψ</sup>hydrogen* <sup>=</sup> *<sup>E</sup>*˙ *<sup>x</sup> <sup>H</sup>* <sup>2</sup> *E*˙ *x Gen*

lations and *Q*˙ *gen* is the rate of heat inputted to the generator.

*Q*˙ *boiler*

*Q*˙ *Gen* + *W*˙ *Turbine*

*Q*˙ *HEX* -*<sup>I</sup>* + *W*˙ *<sup>P</sup>* -*III*

A coefficient of performance (COP) term can be used to expressing of the energetic perform‐

*W*˙ *pump*-*III* + *Q*˙ *gen*

where *W*˙ *<sup>p</sup>* is the pumping power requirement, and it is usually neglected in the COP calcu‐

The exergy efficiency of the process is the produced exergy from the system output that is divided by the exergy system input and it can also be expressed by the aforementioned sub-

> *<sup>Q</sup>* <sup>+</sup> *<sup>E</sup>*˙ *<sup>x</sup>*<sup>2</sup> *Q*

> > *E*˙ *xboiler*

*<sup>Q</sup>* <sup>+</sup> *<sup>W</sup>*˙ *Turbine*

*<sup>Q</sup>* (22)

*<sup>Q</sup>* (23)

*E*˙ *xsolar*

**3.1. Energy efficiency**

46 Clean Energy

$$\text{LCOP}\_{ex} = \frac{\triangle x\_{\text{cooling}}^{Q}}{\dot{W}\_{\text{pump-ill}} + \triangle x\_{\text{gen}}^{Q}} \tag{27}$$


**Table 2.** Exergy efficiency equations for the system components

## **4. Result and Discussion**

A software code in EES (Engineering Equation Solver) [8] is created to analyze a baseline model with respect to the balance equations given in Table 2. The ambient conditions are assumed to be 25 °C and 100 kPa for the analysis. A widely used refrigerant R134a is used in the absorption cooling system and water in the other sub-systems. The assumptions for the analysis are given as follow.

**Exergy destruction rate (kW)**

Evaporator 56.31 1.40 40.84 571.1 Absorber 98.25 2.43 21.42 696.2 Pump-III 8.24 0.20 34.41 12.92 Throttling valve 1.16 0.03 96.58 17.34 HEX-II 6.72 0.17 56.53 109.1

**Table 3.** Thermodynamic analysis data of the multi-generation energy production system devices

which results in more entropy generation between the inlet and outlet streams.

**Figure 2.** Exergy efficiencies of the multi-generation energy production system components

sonably good agreement are found.

The COP and COPex of the single effect absorption refrigeration system are calculated as 0.7586 and 0.3321, respectively. The COPex is lower than COP, due to the considerable irre‐ versibilities occurring in the absorption cycle. Energy and exergy efficiency results for the absorption system components are compared to the experimental studies [9-11] and a rea‐

Parametric studies have also been conducted, by analyzing the changes in exergy efficien‐ cies of the system components with respect to changes in the ambient temperature. The exergy efficiencies for the ambient temperature ranges of 10 °C to 30 °C can be seen in

Based on the baseline analysis, the exergy efficiencies associated with the system and whole system are given in the Fig. 2. As seen in the Fig. 2, the solar parabolic trough collector and condenser are calculated to have the lowest exergy efficiency as 17 and 22%, respectively. This is associated with concentrating losses, high temperature differences and phase chance

**Exergy destruction ratio (%)**

**Exergy efficiency (%)**

Thermodynamics Assessment of the Multi-Generation Energy Production Systems

**Power or heat transfer rate (kW)** 49

http://dx.doi.org/10.5772/51522


The values for the exergy destruction rates (kW), exergy destruction ratio (%), exergy effi‐ ciency (%) and the power or heat transfer rate of the solar multi-generation energy produc‐ tion system are given in the Table 3. Exergy destruction rate indicates the reduction in energy availability; however, it cannot be used to investigate the energy and exergy utiliza‐ tion performance of the system processes. The exergy efficiencies of the system components are more useful for determining exergy losses.



**Table 3.** Thermodynamic analysis data of the multi-generation energy production system devices

for Better Environment

A software code in EES (Engineering Equation Solver) [8] is created to analyze a baseline model with respect to the balance equations given in Table 2. The ambient conditions are assumed to be 25 °C and 100 kPa for the analysis. A widely used refrigerant R134a is used in the absorption cooling system and water in the other sub-systems. The assumptions for the

**•** Steady-state conditions with no chemical or nuclear reactions are assumed for all compo‐

**•** Heat loss and pump work as well as kinetic and potential energies are considered negligi‐

**•** Expansion valve and throttling valve are assumed to be isenthalpic and the heat transfer and pressure drops in the tubes connecting the components are neglected since there are

The values for the exergy destruction rates (kW), exergy destruction ratio (%), exergy effi‐ ciency (%) and the power or heat transfer rate of the solar multi-generation energy produc‐ tion system are given in the Table 3. Exergy destruction rate indicates the reduction in energy availability; however, it cannot be used to investigate the energy and exergy utiliza‐ tion performance of the system processes. The exergy efficiencies of the system components

> **Exergy destruction ratio (%)**

**Exergy efficiency (%)**

**Power or heat transfer rate (kW)**

**4. Result and Discussion**

analysis are given as follow.

are more useful for determining exergy losses.

**Exergy destruction rate (kW)**

Parabolic trough collector 1892 46.89 34.21 18798 Boiler 564.1 13.98 90.92 18798 HEX-I 337.6 8.37 82.89 3351 Hot water tank 310.2 7.69 28.19 2593 Pump-I 45.11 1.12 56.03 74.37 Turbine 259.3 6.43 93.6 3792 Condenser-I 81.67 2.02 25.71 12734 Pump-II 114.7 2.84 58.77 175.5 PEM electrolysis system 202.4 5.02 37.03 781.5 Generator 37.03 0.92 75.42 750 Condenser-II 19.91 0.49 21.94 604.87 Expansion valve 0.15 0.00 97.36 1.69

nents in the cycle.

ble.

48 Clean Energy

short.

Based on the baseline analysis, the exergy efficiencies associated with the system and whole system are given in the Fig. 2. As seen in the Fig. 2, the solar parabolic trough collector and condenser are calculated to have the lowest exergy efficiency as 17 and 22%, respectively. This is associated with concentrating losses, high temperature differences and phase chance which results in more entropy generation between the inlet and outlet streams.

**Figure 2.** Exergy efficiencies of the multi-generation energy production system components

The COP and COPex of the single effect absorption refrigeration system are calculated as 0.7586 and 0.3321, respectively. The COPex is lower than COP, due to the considerable irre‐ versibilities occurring in the absorption cycle. Energy and exergy efficiency results for the absorption system components are compared to the experimental studies [9-11] and a rea‐ sonably good agreement are found.

Parametric studies have also been conducted, by analyzing the changes in exergy efficien‐ cies of the system components with respect to changes in the ambient temperature. The exergy efficiencies for the ambient temperature ranges of 10 °C to 30 °C can be seen in

the Fig. 3 to 5 for the parabolic trough collector, organic Rankine cycle and absorption cool‐ ing-heating cycle, respectively.

generally inversely proportional properties. The variations of the exergy destruction rate and also exergy efficiency in concern with the ambient temperature for the organic Ran‐

Thermodynamics Assessment of the Multi-Generation Energy Production Systems

http://dx.doi.org/10.5772/51522

51

**Figure 5.** Exergy destruction rate and exergy efficiency of the absorption cooling and heating system depending on

In the present study, a solar multi-generation system for electricity, hydrogen, oxygen, heat water production and space heating and cooling is proposed and examined with respect to exergy analysis in order to determine the magnitude of losses, and their causes and loca‐ tions by determining the irreversibility in each cycle and the whole system. In addition to that, exergy efficiency of the system components is evaluated to show how the system reaches a real operating condition. Some parametric studies are given in order to investigate

Department of Physics, Faculty of Art and Sciences, Suleyman Demirel University, 32260, Is‐

the effects of varying operating conditions such as ambient temperature.

Address all correspondence to: muratozturk@sdu.edu.tr

kine cycle are given in the Fig. 4.

ambient temperature changes

**5. Conclusions**

**Author details**

Murat Ozturk\*

parta, Turkey

**Figure 3.** Exergy destruction rate and exergy efficiency of the parabolic trough collector (PTC) depending on ambient temperature changes

**Figure 4.** Exergy destruction rate and exergy efficiency of the organic Rankine cycle (ORC) depending on ambient temperature changes

Although ambient temperature increases, exergy destruction of the parabolic trough col‐ lector and absorption system are increases and exergy efficiencies of these compo‐ nents decreases. The variations of exergy destruction rate and exergy efficiency of these components according to the ambient temperature remain almost linear. These results are expected since the exergy destruction rate and exergy efficiency of the process are generally inversely proportional properties. The variations of the exergy destruction rate and also exergy efficiency in concern with the ambient temperature for the organic Ran‐ kine cycle are given in the Fig. 4.

**Figure 5.** Exergy destruction rate and exergy efficiency of the absorption cooling and heating system depending on ambient temperature changes

## **5. Conclusions**

for Better Environment

ing-heating cycle, respectively.

50 Clean Energy

temperature changes

temperature changes

the Fig. 3 to 5 for the parabolic trough collector, organic Rankine cycle and absorption cool‐

**Figure 3.** Exergy destruction rate and exergy efficiency of the parabolic trough collector (PTC) depending on ambient

**Figure 4.** Exergy destruction rate and exergy efficiency of the organic Rankine cycle (ORC) depending on ambient

Although ambient temperature increases, exergy destruction of the parabolic trough col‐ lector and absorption system are increases and exergy efficiencies of these compo‐ nents decreases. The variations of exergy destruction rate and exergy efficiency of these components according to the ambient temperature remain almost linear. These results are expected since the exergy destruction rate and exergy efficiency of the process are In the present study, a solar multi-generation system for electricity, hydrogen, oxygen, heat water production and space heating and cooling is proposed and examined with respect to exergy analysis in order to determine the magnitude of losses, and their causes and loca‐ tions by determining the irreversibility in each cycle and the whole system. In addition to that, exergy efficiency of the system components is evaluated to show how the system reaches a real operating condition. Some parametric studies are given in order to investigate the effects of varying operating conditions such as ambient temperature.

## **Author details**

Murat Ozturk\*

Address all correspondence to: muratozturk@sdu.edu.tr

Department of Physics, Faculty of Art and Sciences, Suleyman Demirel University, 32260, Is‐ parta, Turkey

## **References**

[1] Moran, M. J. (1982). Availability analysis: A guide to efficiency energy use. *Englewood Cliffs, NJ: Prentice-Hall*.

**Chapter 4**

**Multi-Level Mathematical Modeling of Solid Oxide**

In recent years, numbers of questions concerning energy generation have arisen. Emission levels, delivery security, and diversification of the portfolio of technologies have been exten‐ sively discussed. Well-established generation based on fossil fuels in large-scale power sta‐ tions is criticized for big environmental impacts, and limited sustainability due to high fraction of process losses. Not only emissions, but also extraction of resources, alternation of the landscape, transmission and distribution inefficiencies are often pointed as the main downside. As a solution for rapidly increasing energy consumption, and emerging threat of current resources depletion, distributed generation based on highly efficient micro- and small-system was proposed. Moreover, combined heat and power (CHP) units with high achievable efficiency are seen as possible substitutes for stand-alone electricity generators. Most of technologies from that group are currently under development, however selected systems are already reaching market availability. In 2004 European Commission indicated selected systems, with guidelines for promotion and development of highly efficient co-gen‐ erative units [1]. List of technologies, which can provide high electrical and overall efficiency

> © 2012 Kupecki et al.; licensee InTech. This is an open access article 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, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

© 2012 The Author(s). Licensee InTech. 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,

**Fuel Cells**

Jarosław Milewski

**1. Introduction**

http://dx.doi.org/10.5772/50724

Jakub Kupecki, Janusz Jewulski and

Additional information is available at the end of the chapter

with limited environmental impacts, includes the following:

**•** Combined cycle gas turbine with heat recovery

**•** Steam backpressure turbines

**•** Gas turbines with heat recovery

**•** Steam condensing extraction turbines

