Modelling, simulation and analysis of solar absorption power-cooling systems

Accepted Manuscript Modelling, simulation and analysis of solar absorption power-cooling systems Jesús López-Villada, Dereje S. Ayou, Joan Carles Bruno, Alberto Coronas

PII:

S0140-7007(13)00296-X

DOI:

10.1016/j.ijrefrig.2013.11.004

Reference:

JIJR 2669

To appear in:

International Journal of Refrigeration

Received Date: 11 July 2013 Revised Date:

31 October 2013

Accepted Date: 4 November 2013

Please cite this article as: López-Villada, J., Ayou, D.S., Bruno, J.C., Coronas, A., Modelling, simulation and analysis of solar absorption power-cooling systems, International Journal of Refrigeration (2013), doi: 10.1016/j.ijrefrig.2013.11.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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MODELLING, SIMULATION AND ANALYSIS OF SOLAR ABSORPTION POWER-COOLING SYSTEMS Jesús López-Villada, Dereje S. Ayou*, Joan Carles Bruno, Alberto Coronas

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Universitat Rovira i Virgili, CREVER – Group of Applied Thermal Engineering, Avda. Paisos Catalans, 26, 43007 – Tarragona (Spain)

Corresponding author (E-mail: [email protected])

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*

Abstract

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The main objective of this paper is to simulate different solar absorption power-cooling systems that uses ammonia based working fluid mixture to simultaneously produce cooling and mechanical power with a single system. The power and cooling cycles through absorption are of great interest because they can use low temperature thermal energy sources as solar energy with a higher versatility than the separated production of power and cooling

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(refrigeration) to cover the typical variable cooling and power demands of the building. In this study we have considered several system configurations based on the Goswami and singlestage combined absorption power and cooling cycles and different solar thermal technologies:

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evacuated tube, parabolic trough and linear Fresnel solar collectors. To compare the configurations we have performed the energy and exergy analysis for a specific case located

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in Sevilla (Spain) with a coordinates of 37°22′38″N 5°59′13″W using TRNSYS software as simulation tool.

Keywords: Solar thermal energy; Combined power-cooling; Absorption; Ammonia Mots clés: L'énergie solaire thermique; Combiné puissance de refroidissement; absorption; ammoniac

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Nomenclature Abbreviations

Variables and Parameters

1 ... 27

E

Thermodynamic state points

Solar energy received by solar

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collectors in a defined period [kW·h] Absorber

Ex

Exergy [kW·h]

APC

Absorption Power and Cooling

h

Specific enthalpy [kJ·kg-1]

C

Cooler

mɺ

Mass flow rate [kg·s-1]

CON

Condenser

Q

Thermal energy [kW·h]

DES

Desorber

Qɺ

Thermal power [kW]

ETC

Evacuated Tube Collector

EVA

Evaporator

EXP

Expander

FPC

Flat Plate Collector

H2O

Water

LFC

Linear Fresnel Collector

LiBr

Lithium bromide

LiNO3

Lithium nitrate

MIX

Mass flow stream mixer

II

Second law

NaSCN

Sodium thiocyanate

APC

Absorption power and cooling

NH3

Ammonia

cw

Cooling water or dissipated heat

Parabolic Through Collector

chw

Chilled water

Rectifier

e

Mechanical power

REV

Refrigerant Expansion Valve

heat

Hot water

RSC

Refrigerant Sub-Cooler

hs

Heat source

REC

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Solar fraction [-]

t

Temperature [ºC]

T

Temperature [K]

W

Mechanical work [kW·h]

Wɺ

Mechanical power [kW]

z

Ammonia mass fraction [kg.kg-1]

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PTC

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ABS

Subscripts

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SAPCS

Solar Absorption Power -

in

Inlet

Cooling System Superheater

out

Outlet

SEV

Solution Expansion Valve

ref

Refrigeration

SHX

Solution Heat exchanger

SAPCS

Solar Absorption Power-Cooling System

Solution Pump

x

SPLIT

Mass flow stream splitter

Greek symbols

SR

Split Ratio

η ε

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Absorption

Solar or effective first law efficiency

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Single-Stage Combined SSCA

Denotes heat, cold or dissipated heat

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SP

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SH

Effective exergy efficiency

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1. Introduction With rapid energy demand growth worldwide, human beings have to face more energy scarcity and environmental issues. The conventional technologies to produce useful energy

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products, such as electricity, normally results in considerable environmental pollution and non-renewable energy resource depletion. These interrelated challenges could be solved through the use of energy conversion enhancement, waste heat recovery and renewable

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energy resource utilization. In that sense, Solar Absorption Power-Cooling Systems (SAPCS) are a good example to improve significantly the energy utilization efficiency using solar

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energy (Fig. 1). The SAPCS are based on a thermodynamic cycle that was developed for the simultaneous production of power and cooling from low-grade energy sources such as solar thermal, geothermal and industrial waste heat. The combined power and cooling cycles through absorption are of great interest because they can use the low grade energy sources as solar energy with a higher versatility than the separated production of power and cooling

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(refrigeration) to cover the typical variable cooling and power demands of the buildings. In the particular case of the Mediterranean countries, this is especially important in spring and autumn, periods in which cooling demands could be very low and then most of the solar

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energy would be used to generate electricity.

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One of the first combined absorption cycle proposed by Goswami (1995), combines the Rankine and absorption refrigeration cycles to provide mechanical power and cooling (subproduct) as useful outputs. Erickson et al. (2004) proposed an ammonia/water absorption cycle configuration which produces power and refrigeration interchangeably. A novel form of absorption cooling cycles for combined production of power and refrigeration has been presented by Ziegler (2007). Three different cycle configurations (namely parallel, series and compound cogeneration configurations) for the combined production of power and

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refrigeration have been suggested by Zhang and Lior (2007). The authors developed the configurations through the integration of refrigeration and power generating systems based on ammonia/water working fluid mixture. And also, a detailed review of several cycle

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configurations proposed for the production of mechanical power and refrigeration, simultaneously and/or alternatively have been presented in the literature (Ayou et al., 2013a). Finally, Ayou et al. (2013b) proposed a new cycle based on a combination of absorption

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refrigeration and Kalina power cycles. The main advantage of these new cycle configurations is the possibility to use low grade energy such as solar energy or waste heat at low or medium

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temperature levels.

Ammonia/water (NH3/H2O) mixture, as working fluid, is commonly used in combined absorption power and cooling cycles except a few times where organic fluid mixtures have been used in Goswami Cycle (Vijayaraghavan et al., 2005 and Abed et al., 2013). Other types

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of fluid mixtures like ammonia (as absorbate) with inorganic salts such as lithium nitrate (LiNO3) or sodium thiocyanate (NaSCN) as absorbent can also be used. So far, these working fluid mixtures have been used in absorption cooling and/or heating cycles (Venegas et al.,

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2005 and Zhu et al., 2010). The main advantages of the NH3/LiNO3 and NH3/NaSCN mixtures in absorption cycles is that the need for the costly rectification process in the

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conventional NH3/H2O absorption cycles can be avoided by using these mixtures. This is mainly due to the non-volatility of the absorbent (LiNO3 or NaSCN) during the thermal separation process in the desorber.

In this paper we analyse the energetic and exergetic performance of the Goswami cycle (sensible cooling recovery) and the single-stage combined absorption (SSCA) power and cooling (latent cooling) cycle using several ammonia based working fluid mixtures with a

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maximum temperature up to 150 ºC, and considering three types of solar thermal collectors: evacuated tube (ETC), linear Fresnel (LFC) and parabolic through (PTC) collectors. Previously, the thermodynamic analysis of the Goswami and SSCA cycles with NH3/H2O

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working fluid mixtures haven been presented in the literature, e.g. Demirkaya et al. (2011a) and Jawahar et al. (2013) respectively. However, there is not any comparison done between these two cycles for a typical application using solar thermal collectors. Moreover,

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NH3/LiNO3 and NH3/NaSCN mixtures are not used in a combined absorption cycles. So it is used, for the first time, in a single-stage combined absorption cycles to produce power and

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cold simultaneously by integrating it with solar thermal collectors.

In the next section is described the main components of the two power and cooling cycles followed by a description of the models and of the energetic and exegetic performance parameters. Finally, a complete analysis of the proposed SAPCS is performed for a specific

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case located in Sevilla (Spain). Although only the Goswami cycle with ammonia/water working fluid pair has been experimentally tested at a laboratory scale (Demirkaya, 2011b) and no other operational data was available to validate the model, the results presented in this

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paper are representative of the potential application of these systems.

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2. Solar Absorption Power-Cooling Systems (SAPCSs) This system consists of four main components: the absorption power-cooling subsystem (i.e. the thermodynamic cycles), the solar thermal subsystem, the conventional heating subsystem and the recooling subsystem (Fig. 1). The SAPCSs considered in this work are based on the Goswami and Single-Stage Combined Absorption (SSCA) cycles that use ammonia based working fluid mixtures. In this study an NH3/H2O working fluid mixture is used for both cycle configurations whereas NH3/LiNO3 and NH3/NaSCN working fluid mixtures are only

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used in the SSCA cycles. Figs. 2 and 3 (a, b) shows the flow schematics of the Goswami and the SSCA cycles, respectively, analysed in this work.

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2. 1 Goswami cycle The operational characteristics and configuration of the Goswami cycle have already been described in detail by Demirkaya et al. (2011a and 2011b). In this cycle (Fig. 2) a mixture of

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ammonia and water, basic solution, is pumped to a high pressure (state 2) and partially boiled in the desorber (DES). The desorbed vapour (state 4) consists of mostly ammonia. A rectifier

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(REC) is used to increase the concentration of ammonia in the vapour by partially condensing water out of the vapour stream from the DES. The resulted purified vapour (state 6) may be superheated (state 7) in the superheater (SH) and expanded in the expander (EXP) to low pressure and temperature (state 8). This low-temperature vapour, below the ambient, can be used to obtain cooling (states 8-9) by incorporating a sensible heat exchanger (cooler, C). The

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weak solution in ammonia from the desorber (state 10) is passed through a solution heat exchanger (SHX) to recover heat from it and throttled back to the absorber (ABS) along with the rejection of heat from the cycle. The condensed liquid in the rectifier is also re-mixed

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with basic liquid solution coming from the absorber, after recovering heat from the weak solution coming from the DES in this schematic. The heat of rectification is used internally to

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preheat part of the basic solution.

2. 2 Single-Stage Combined Absorption (SSCA) cycles Figs. 3 (a) and (b) illustrated the follow schematic of the SSCA cycles with NH3/H2O and NH3/salts (NH3/LiNO3 or NH3/NaSCN) working fluid mixtures respectively. The SSCA cycles considered in this study are based on the modification of the basic single-stage absorption cooling cycle. These cycles consists of absorber (ABS), condenser (CON),

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desorber (DES), evaporator (EVA), expander (EXP), solution heat exchanger (SHX), superheater (SH), refrigerant sub-cooler (RSC), and rectifier (REC) for the case of an NH3/H2O mixture based cycle (Fig. 3 (a)). The cycles operate at two pressure levels and to

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sustain the necessary pressure difference between the high and low pressure side components in the cycle a solution pump (SP), refrigerant and solution expansion valves are included (REV and SEV, respectively). The basic absorption cooling cycle is modified by including a

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power sub-cycle (states 16-17-18 in Fig. 3 (a) and states 14-15-16 in Fig. 3 (b)) in parallel of the cooling (refrigeration) sub-cycle (states 8A-9-10-11-12-13-14-15 in Fig. 3 (a) and states 8-

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9-10-11-12-13 in Fig. 3 (b)) with the splitting of the vapour stream leaving the DES.

The entire cyclic processes in Figs. 3 (a) and (b) is described as follows. A basic solution (strong in NH3) leaves the ABS as saturated liquid. It is then pumped to the cycle's high pressure using the solution circulation pump (SP) and then recovers heat internally in the

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SHX (and REC for the cycle with NH3/H2O working fluid mixture, Fig. 3 (a)). After the internal heat recuperation, the strong solution is further heated and partially boiled in the DES by using an external heat input (hot water at pressure in this study). Then the desorbed vapour

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split into two streams by a split ratio (SR) for the power and cooling sub-cyclic processes. The SR is defined as the ratio of the vapour mass flow rate that follows the power sub-cycle to the

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total vapour from the DES. In the power sub-cycle, the ammonia vapour is first superheated in the SH (if any) and then expanded in the EXP for generating the mechanical power before mixed with the vapour from the cooling sub-cycle at the vapour inlet of the ABS. This expander provides the mechanical power output of the cycle after covering the power requirement for circulating the working fluid mixture in the cycle (i.e. after covering SP power consumption). The processes of the cooling sub-cycle are identical to the common absorption cooling cycle: the vapour that follows the cooling sub-cycle first totally condensed

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to saturated liquid in the CON and then further sub-cooled in the RSC before throttling to the EVA pressure using the REV. The heat of condensation is rejected to the heat sink medium (water in this case). The cooling effect is obtained in the EVA by absorbing heat from the

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external water circuit, in general any secondary fluid, to be chilled. The weak (in NH3) saturated solution leaving the DES returns to the ABS through the SHX and SEV for absorbing the vapour from power and cooling sub-cycles followed by the rejection of heat of

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absorption to the sink. This regenerate the basic solution and then it complete the entire cyclic

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process.

The external cooling water circuit (from the cooling tower) for the ABS and CON are connected in series arrangement being first the ABS. In the case of the NH3/H2O cycle, solution cooled rectifier is used. The minimum heat source fluid inlet temperature is dependent on the working fluid used in the cycle as well as the operating condition of the

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cycle (cooling water and chilled water inlet temperatures). And also, the maximum heat source fluid inlet temperature is limited by the property correlation range and crystallization

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phenomena for NH3/LiNO3 and NH3/NaSCN working fluid mixtures.

Dealing with the solar thermal field, we considered three cases according to the technology

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evaluated: evacuated tube (ETC), linear Fresnel (LFC) and Parabolic Through Collectors (PTC). We discarded flat-plate collectors (FPC) because of the relatively high temperatures needed to drive the SAPCS. In the three configurations we have considered some available commercial collectors suitable to be installed on the flat roof of the buildings with a total aperture area of 600 m2, a tilt angle of 20º and an azimuth of 0º. Also, as could be seen in Fig.1, the solar subsystem integrates a hot water buffer tank of 36 m3. Finally the recooling subsystem has a cooling tower of a maximum dissipation capacity of 350 kW. The useful

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thermal power of the conventional heating system depends on the solution type of the power and cooling cycle, being 400 kW for Goswami cycle and 600 kW for NH3/H2O, 850kW for

3. Modelling, simulation and performance parameters

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NH3/NaSCN and 900kW for NH3/LiNO3 single-stage absorption cycles.

The SAPCS is simulated in Transient System Simulation Tool (TRNSYS, 2004), which is a

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software commonly used to simulate solar thermal systems. Fig. 4 shows a schematic of the main components and the corresponding TRNSYS types with their description. It is important

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to remark that we have used the new type 1288 to model the solar thermal collectors according to the quasi-dynamic model described in the standard EN-12975. The parameters of the solar collectors for the quasi-dynamic model are shown in Table 1. For the simulation of the combined absorption power-cooling cycle we created a specific type based on the linear correlations that could be obtained from the simulation of the thermodynamic model of the

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absorption cycles (Goswami and SSCA cycles in this study) in Engineering Equation Solver (EES, from the F-chart Software Company). The thermodynamic modelling of the Goswami and SSCA cycles is described in section 3.1 below. The correlations express the driving heat

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input, dissipated heat, cooling capacity and net mechanical power output of the cycle as a function of the three temperatures: namely heat source (ths,in), cooling water (tcw,in) and chilled

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water (tchw,in) inlet temperatures. The correlations are given in Eq. 1 and Eq. 2.

Qɺ x = a xt hs , in + bxtcw, in + cxtchw, in + d x

(1)

Wɺ e = ae t hs ,in + be t cw,in + ce t chw,in + d e

(2)

where Qɺ x : (kW) x = in driving heat provided to the cycle (i.e. the heat supplied to the DES and SH (if any)), x = cw heat dissipated in the ABS (and CON in the case of the SSCA cycles), x = cold cooling capacity of the cycle; Wɺe : (kW) net mechanical power output; a, b,

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c, d: (a, b and c in kW·ºC-1 and d in kW) are the correlation parameters showed at Table 2. For the case of the SSCA cycles the correlation parameters are dependent on the split ratio (SR).

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3. 1 Thermodynamic model for absorption power-cooling (APC) cycles The developed thermodynamic models for the Goswami and SSCA cycles are based on the thermodynamic properties of the working fluid mixtures, steady-state mass and energy

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balances for each component of the cycle and some model assumptions. The following model assumptions were made in the thermodynamic model of the Goswami and SSCA cycles: • Thermal and pressure losses are neglected.

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• The solution and refrigerant expansion valves are isenthalpic.

• Isentropic pump and expander (turbine) efficiencies are 80% and 85%, respectively. • A minimum expander exit vapour mass fraction (dryness) of 90% is set. • Minimum approach temperature of 5 K is set for the absorber, condenser, cooler, desorber,

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evaporator, and superheater.

• Minimum pinch temperature of 10 K is set in the solution heat exchanger and refrigerant sub-cooler.

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• Counter flow desorber for NH3/H2O SSCA cycle is considered whereas co-current flow desorber for Goswami and NH3/Salt (LiNO3 or NaSCN) SSCA cycles are considered.

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• Concentration of the rectified vapour leaving the rectifier of NH3/H2O SSCA cycle is 0.999 and 0.996 for the Goswami cycle. • Saturated pure ammonia vapour leaving the evaporator of the NH3/Salt SSCA cycles. • Partial vaporization is allowed in the evaporator of the NH3/H2O SSCA cycle. • A constant mass flow rate of 5 kg/s is assumed for the external heat source fluid circuit of the Goswami and SSCA cycles. The mass flow rates of the external cooling and chilled water circuits are also assumed constant.

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The constant mass flow rates of the external cooling and chilled water circuits of the Goswami cycle are calculated by operating the cycle at a typical operating conditions: cooling water and chilled water inlet/outlet temperatures of 30/38 ºC and 12/7 ºC, respectively. A unit

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mass flow rate of the basic NH3/H2O solution through the SP is considered. Regarding the SSCA cycles, the constant mass flow rates of the external cooling and chilled water circuits are calculated by operating the cycle in cold mode of operation (to obtain the peak cooling

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demand of the system 175 kW) at the typical operating conditions. At this mode of operation the EXP power output only cover the power consumption of the SP. The heat source inlet

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temperature is fixed at the minimum acceptable heat source inlet temperature to achieve a steady COP. Accordingly, the cooling water, chilled water and basic solution mass flow rates are determined as follows.

- For NH3/H2O SSCA cycle: mɺ cw = 13.33 kg/s, mɺ chf = 8.34 kg/s and mɺ 1 = 0.55 kg/s. - For NH3/LiNO3 SSCA cycle: mɺ cw = 14.69 kg/s, mɺ chf = 8.34 kg/s and mɺ 1 = 0.90 kg/s.

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- For NH3/NaSCN SSCA cycle: mɺ cw = 14.13 kg/s, mɺ chf = 8.34 kg/s and mɺ 1 = 1.04 kg/s.

The generic equations based on mass and energy conservation laws for each component of the

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combined absorption cycles can be expressed as follows: Global mass balance:

− ∑ mɺ out = 0 ,

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∑ mɺ

in

(3)

where mɺ is the mass flow rate and the subscript in and out indicates the inlet and outlet streams of the component respectively. Ammonia mass balance:

∑z

in

mɺ in − ∑ zout mɺ out = 0 ,

where z is ammonia mass fraction.

(4)

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Energy balance:

∑h

in

mɺ in − ∑ hout mɺ out + Qɺ − Wɺ = 0 ,

(5)

where h is the specific enthalpy. Qɺ and Wɺ are the heat transfer and work interaction rates of

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the component respectively. The mechanical work interaction rate only appears in the energy balance of the SP and EXP. The trivial mass and energy balances of the external heat

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transferring fluids have been done in a similar manner.

The thermodynamic properties of the binary mixture NH3/H2O and pure ammonia properties

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are obtained from the work of Ibrahim and Klein (1993) and Baehr and Tillner-Roth (1994) respectively. For NH3/LiNO3 and NH3/NaSCN binary mixtures, the properties are taken from Libotean et al. (2007 and 2008) and Chaudhari et al. (2011) respectively. The properties of water that is used as external heat transferring fluids are given by Wagner and Pruss (1993).

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3. 2 Performance parameters

To evaluate the performance of the SAPCS we could use the energy (first law) and exergy efficiencies. In the first case we need to know the energy balances between the different

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components of the configurations in a defined time period. It is necessary to calculate the energy received by the solar collectors, useful energy from the collector field and energy

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inputs and outputs of the absorption power-cooling unit. In the second case, apart from the energy balances, it is necessary to perform the exergy balances. A detailed explanation of this procedure could be found in Baghernejad and Yaghoubi (2010) and in Ayou et al. (2013a and 2013b) for combined absorption power-cooling cycle's efficiency definitions and terminologies. In our case Eq. 6 to Eq. 8 defined the energetic efficiencies and Eq. 9 and Eq. 10 the exergetic efficiencies.

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η APC =

Qsolar E solar We +

(6) Excold

η II ,ref

(7)

Qin

η SAPCS =

(We +

Excold

η II ,ref ) ⋅ SF

E solar

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η solar =

(8)

= η solar ⋅η APC

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where

Esolar : Solar energy received by the solar collectors in a defined period (kW·h).

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η solar : Energy efficiency of the solar subsystem.

η APC : Effective first law (energy) efficiency of the absorption power-cooling subsystem. η SAPCS : Energy efficiency of the solar absorption power-cooling system. Excold : Exergy change in the chilled water circuit (kW·h).

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η II ,ref : Second law efficiency for the conventional vapour compression refrigeration cycle, which is assumed to be 30% in this work (Vijayaraghavan and Goswami, 2003). SF: Solar fraction of the driving heat provided to the absorption power-cooling subsystem.

Exin

(We +

η II , ref

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Excold

Excold

η II ,ref ) ⋅ SF

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ε APC =

We +

ε SAPCS =

Ex solar

ε APC : Effective exergy efficiency of the absorption power-cooling subsystem. ε SAPCS : Effective exergy efficiency of the solar absorption power-cooling system. Ex solar : Solar exergy received by the collectors (kW·h). Exin : Exergy change in the heat source fluid (kW·h).

(9)

(10)

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A controversial aspect of the exergy analysis is the reference temperature when the ambient temperature fluctuates during the studied period. According to Pons (2009), the reference temperature must be kept constant in the whole period. However, other authors consider that

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is better applying a dynamic reference environment (Angelotti and Caputo, 2007). In this study we decided to have a constant reference temperature.

The exergy analysis in this paper covers only the entire system (cycle) not the component

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exergy analysis in order not to extend the length of the paper. In addition to this, substantial work already done on exergy analysis of the Goswami cycle with ammonia/water working

4. Results and discussion

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fluid mixture is available in the literature (Hasan et al., 2002 and Vidal et al., 2006).

4.1 Goswami and SSCA cycles performance and modelling

We calculated the energy balances and performance parameters for the Goswami NH3/H2O

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cycle and for the NH3/H2O, NH3/LiNO3 and NH3/NaSCN SSCA cycles operating in a wide range of temperatures (ths,in, tcw,in and tchw,in). To perform these calculations we used the EES software (EES, 2012). Figs. 5 to 7 show the variation of the power output and effective first

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law efficiency (ηAPC) for the Goswami and SSCA cycles with the heat source, cooling water and chilled water temperatures, respectively. For the SSCA cycles we could observe also the

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effect of the variation of SR on power output and ηAPC. Since the amount of vapour generated in the desorber increases as the heat source temperature rises, the dual output (mechanical power shown in Fig. 5 (a) and cooling) of the cycles also increases. Consequently, as illustrated in Fig. 5 (b), the ηAPC of the cycle increases as the heat source temperature increases. It also shows clearly that when tcw,in = 29 ºC and tchw,in = 12 ºC, the Goswami cycle presents a better energy performance and only when ths,in ranges between 85-90 ºC, the SSCA cycle with NH3/NaSCN and NH3/H2O at SR=0.8 have a similar effective first law efficiency.

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The efficiency rises to more than 9.5% for the Goswami cycle and to around 7.5% for the SSCA cycles at high values of SR and ths,in. Comparing the different SSCA cycles we could see that from 90 ºC to 120 ºC the NH3/H2O pair is the best option followed closely by

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NH3/NaSCN. However, NH3/LiNO3 and NH3/NaSCN cycles are able to operate at relatively low temperatures (70-80 ºC) with a better efficiency than NH3/H2O. Therefore it makes sense

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to use these working fluid pairs at lower temperatures.

Similarly, we analysed the effect of the cooling water temperature on Fig. 6. When tcw,in

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increases from 20 to 40 ºC , at constant ths,in and tchw,in, the power output (shown in Fig. 6 (a)), the heat consumption (in the desorber) and cooling capacity of the SSCA cycles decrease at all split ratios considered (0.2, 0.5 and 0.8). The combined effect on the effective first law efficiencies of the cycles is illustrated in Fig. 6 (b). SSCA cycles present the same trend at SR between 0.2 and 0.8 with efficiencies in the range of 4-7%. Nevertheless, when SR=0.5 the

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efficiency only drops slightly and even at SR=0.8 it increases gently and peaks at 35ºC. In the case of the Goswami cycle, ηAPC declines steadily from a 10.4% to 7.6% operating between 20 and 40 ºC. This is mainly due to the fact that when tcw,in increases, the power output

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(shown in Fig. 6 (a)) of the cycle decreases at a faster rate than the heat consumption in the desorber. It should be noticed that, at a heat source temperature of 120 ºC and a chilled water

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temperature of 12 ºC, the NH3/NaSCN SSCA cycle could not operate at cooling tower temperatures lower than 29 ºC to avoid risk of crystallization of the working pair.

Fig. 7 shows the evolution of power output and ηAPC with the chilled water temperature tchw,in. As tchw,in increases (at constant ths,in and tcw,in) the heat consumption in the desorber of the SSCA cycles increases but the power output, shown in Fig. 7 (a), is almost constant. Even though the cooling capacity of the cycles increases with the tchw,in, its contribution ( Excold

ηII,ref

) to

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the effective first law efficiency (in Eq. 7) is decreasing since it accounts both the quality and quantity of the cooling output of the cycles. Consequently, the effect of the variation of tchw,in on ηAPC is decreasing as illustrated in Fig. 7 (b) except for the Goswami cycle where it is

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almost constant. For a Goswami cycle, the heat consumption and power output is independent of the tchw,in except the sensible (mainly) cooling output which has a lower contribution on the

ηAPC of the cycle. Therefore, the ηAPC of the Goswami cycle remains practically constant at

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9.1%. For SSCA cycles, the ηAPC decreases gradually at SR of 0.2 from 6 to 2%. At higher SR values the trend is similar with higher efficiencies and a lower slope. Unlike Fig. 5 (b) and

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Fig. 6 (b), in Fig. 7 (b) is shown that NH3/H2O pair has the higher efficiency in almost all the analysed cooling tower and chilled water temperatures followed closely by the NH3/NaSCN. In order to perform the TRNSYS simulations we estimated the parameters of Eq. 1 and 2 for the Goswami and SSCA cycles. Table 2 shows the parameter values for the different correlations as well as the value of the adjusted coefficient of determination R2. As the

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obtained values of this coefficient are relatively high, we could say that data fit well in a linear model with the three external temperatures. It's important to remark that a, b and c

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correlation parameters of the SSCA cycles depend linearly on the split ratio (SR).

4.2 Simulation of SAPCS

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We developed TRNSYS models for the Goswami and SSCA cycles and combined them with ETC, LFC and PTC solar thermal models to build different SAPCS (Fig. 4). Once these models were assembled (Fig. 4), we carried out annual simulations considering the location of Sevilla city (coordinates 37°22′38″N 5°59′13″W) and assuming that the SAPCS operates 24h per day. Sevilla is selected because it is representative of the most suitable locations for these types of solar power and cooling plants.

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For the exergy balances we considered a constant reference temperature of 290 K. One important issue to mention is that, as ths,in increases the effective first law efficiency of the power-cooling cycles rises, the solar collector efficiency drops, thus it exists an optimum

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value for this temperature for each SAPCS. Additionally, for the specific case of SAPCS with SSCA cycles, the optimum temperature also depends on the value of SR. Consequently we calculated the optimum heat source temperature performing several simulations for each

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particular model using the TRNOPT application, which links TRNSYS (2004) with the

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optimisation software GenOpt (2011).

Table 3 presents some optimal heat source temperatures values for the Goswami cycle for all the solar technologies and SSCA cycles with the ETC solar collector. For SSCA cycles Table 3 only shows the ETC cases because the optimum heat source temperature for these cycles is always below 100 ºC for all the solar collectors considered in this study. At these

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temperatures ETC collectors present by far the best energy performance and besides are more economical than LFC and PTC alternatives. As a consequence the ETC solar technology is the best option for SSCA cycles. On the other hand, regarding to Goswami cycle, we found

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optimum temperatures of 138 ºC for ETC and LFC and 150 ºC for PTC collectors. The main reason that explains these results is the relatively high effective first law (energy) efficiency

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of this cycle at high temperatures as could be seen in Fig. 5 (b).

Apart from the optimum temperatures, Table 3 also shows the total annual values of the heat consumption, solar heat, heat rejection, cooling and power production as well as some energy performance rates as solar efficiency and effective first law efficiency of the APC cycles and SAPCS systems. Furthermore, Fig. 8 offers monthly results for three of the more significant

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cases or the best possible combination of solar thermal collectors and combined absorption cycles: (a) Goswami – PTC.

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(b) NH3/H2O SSCA – ETC with SR = 0.2. (c) NH3/NaSCN SSCA – ETC with SR = 0.8.

According to these results it's evident that Goswami cycle systems produce more power with

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an ηAPC that duplicates the values obtained for the SSCA cycles and with εAPC that is between a 30 and a 45% higher. Nevertheless, when considering the different solar thermal technologies, it could be seen that, despite that Goswami-PTC and Goswami-ETC systems

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present higher values of ηSAPC and εSAPC, SSCA cycles operating at SR of 0.8 reach effective first law efficiencies in the same order of magnitude and even NH3/H2O-ETC and NH3/NaSCN-ETC systems exceed the Goswami-LFC system. These results could be explained by the better performance of ETC solar collectors when coupled with the SSCA

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cycles. On the other hand, if the main interest is the cold production, SSCA cycles at lower SR are the best option because they produce more cooling in spite of the lower values of ηAPC,

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ηSAPC, εAPC and εSAPC.

Regarding the solar energy contribution, it ranges between 200 and 300 MWh for Goswami

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and is around 500 MWh for SSCA systems. The higher contribution in the SSCA cases could be explained by three reasons. First of all, Goswami cycle operate at higher optimum temperatures resulting in an important reduction of the energy conversion efficiency of the solar collectors. Secondly, ETC solar collectors capture the diffuse solar irradiation whereas concentrating collectors as LFC and PTC are unable to do it. Thirdly, ETC solar collectors also present a higher optic factor (Table 1) and also higher incidence angle modifier factors. The differences in the energy performance between the three solar technologies analysed in

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this work are more evident if we look at the monthly charts of Fig. 8 in which we can observe that the ETC efficiency ranges from a 30% in the winter months to a almost 50% in summer with NH3/NaSCN SSCA cycle. By contrast, PTC efficiency with the Goswami cycle is less

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than a 10% in the colder months and only is about a 30% in the hotter period of the year. This better performance of the ETC collector leads to higher values of ηSAPCS when compared to the PTC collector despite the fact that the Goswami cycle presents higher effective first law

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efficiency. Even so, we must think that some manufactures limit the operation temperatures of ETC collectors to 120–130 ºC in order to protect some components from high temperatures.

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Therefore, from the point of view of SAPCS effective first law and exergy efficiencies, the best option is Goswami – ETC followed by Goswami – PTC. However, when working at temperatures above 120–130 ºC practical issues of some ETC manufactures have to be considered which means that PTC could be the best alternative. Alternatively, for SSCA solar cycles, as the optimum temperature is always below 100 ºC, the solar ETC collectors are more

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suitable. Table 3 shows that NH3/H2O-SSCA case has a lower solar contribution due to its better thermal efficiency that leads to a lower heat consumption and as a consequence to a higher average temperature on the solar collectors. This is also the explanation of the change

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in the solar efficiency of the solar collectors when changing the SR factor.

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The proposed absorption power and cooling systems are flexible enough to produce only power, only cooling (in case of the single-stage combined power-cooling cycle) or power and cooling simultaneously. However, the mode of operation considered in this paper is the simultaneous mode: for single-stage combined absorption cycle with split ratios of 0.2, 0.5 and 0.8 and for Goswami cycle based on the operating conditions considered (no superheating in order to produce sensible cooling output). Therefore, the suitable performance parameter to assess the energetic performance of the system is the first law efficiency instead of the COP.

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Consequently, the effective first law efficiency (which accounts the thermodynamic quality of the dual outputs) is used to evaluate the energetic performance of the system. The variation of the power output of the proposed systems with the heat source, cooling water and chilled

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water inlet temperatures are presented in Fig. 5 (a), Fig 6 (a) and Fig 7 (a), respectively. In addition to this, we would like to comment that the best configuration cannot be decided just using a given set of operating conditions and run the three working fluids because the effect

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of the solar collectors' efficiency and the partial load behaviour is also very important.

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5. Conclusions

The aim of the current work was to present some SAPCSs based on some novel Single-Stage Combined Absorption (SSCA) Cycles and compare them to the well-known Goswami cycle. We studied SSCA cycles that work with the working pairs NH3/H2O, NH3/NaSCN and NH3/LiNO3. The cycles are partly activated by ETC, LFC and PTC solar thermal collectors.

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To perform the comparison we modelled the SSCA and Goswami cycles with linear correlations based on the thermodynamic models as a function of the heat source, cooling water and chilled water temperatures. These models were implemented in TRNSYS software

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to simulate SAPCS systems for a whole year. Results show that it exist an optimum heat source temperature for each SAPCS depending on the cycle and solar thermal collectors. As

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this temperature is always below 100 ºC for systems with SSCA cycles, we concluded that ETC is the solar technology more suitable for systems with these cycles. On the other hand, although the Goswami-ETC also leads to the best efficiency at 138 ºC, some ETC collectors may not work at these temperature levels and then the PTC collector could be a good option. Finally, we can say that if the main interest of the SAPCS is the power production, then the Goswami-ETC or Goswami-PTC combinations offer the best effective first law and exergy efficiencies. On the other hand, if we are interested in the chilled water production, SSCA

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cycles at lower SR are the best option in spite of the relatively lower values of ηAPC , ηSAPC,

εAPC and εSAPC.

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Acknowledgment

This research project was financially supported by the Spanish Ministry of Science and Innovation (ENE2009-14177). Dereje S. Ayou thanks to the AGAUR (Catalan Government)

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for the fellowship.

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References

Abed, H., Atashkari, K., Niazmehr, A., Jamali, A., 2013. Thermodynamic optimization of combined power and refrigeration cycle using binary organic working fluid. Int. J. Refrigeration., in press.

Angelotti, A., Caputo, P., 2007. The exergy approach for the evaluation of heating and

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cooling technologies; first results comparing steady-state and dynamic simulations. In: Proceedings of 2nd PALENC and 28th AIVC Conference, Crete Island, Greece, Vol. I, pp. 5964.

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Ayou, D.S., Bruno, J.C., Saravanan, R., Coronas, A., 2013a. An overview of combined absorption power and cooling cycles. Renewable Sustainable Energy Rev. 21, 728 – 748.

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Ayou, D.S., Saravanan, R., Bruno, J.C., Coronas, A., 2013b. Analysis and simulation of modified ammonia/water absorption cycle for power and cooling applications. Int. J. LowCarbon Technol 8, 19 – 26. Baghernejad, A., Yaghoubi, M., 2010. Exergy analysis of an integrated solar combined cycle system. Renewable Energy 35(10), 2157 – 2164.

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Chaudhari, S.K., Salavera, D., Coronas, A., 2011. Densities, viscosities, heat capacities, and vapour – liquid equilibria of ammonia + sodium thiocyanate solutions at several temperatures. J. Chem. Eng. Data 56(6), 2861 – 2869.

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Demirkaya, G., Padilla, R.V., Goswami, D.Y., Stefanakos, E., Rahman, M.M., 2011a.. Int. J. Energy Res. 35(13), 1145 – 1157.

Demirkaya, G., 2011b. Theoretical and experimental analysis of power and cooling

Department, University of South Florida, USA.

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cogeneration utilizing low temperature heat sources. Ph.D Thesis, Mechanical Engineering

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EES, Engineering Equation Solver, 1992 – 2012. F - chart software, www.fchart.com. Erickson, D., Anand, G., Kyung, I., 2004. Heat activated dual function absorption cycle. ASHRAE Trans. 110, 515 − 524.

GenOpt, Generic Optimization Program, User Manual, Version 3.1.0, 2011. Lawrence Berkeley National Laboratory, Berkeley, http://simulationresearch.lbl.gov/GO/index.html.

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Goswami, D.Y., 1995. Solar Thermal Power-Status and Future Directions. In: Proceedings of 2nd ISHMT-ASME Heat and Mass Transfer Conf., Murthy, S., and Jaluria, Y., Eds., Tata McGraw Hill, New Delhi, India, pp. 57 − 60.

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Hasan, A.A., Goswami, D.Y., Vijayaraghavan, S., 2002. First and second law analysis of a new power and refrigeration thermodynamic cycle using a solar heat source. Sol. Energy

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73(5), 385 – 393.

Ibrahim, O.M., Klein, S.A., 1993. Thermodynamic properties of ammonia-water mixtures. ASHRAE Trans. 99(1), 1495 – 1502. Jawahar, C.P., Saravanan, R., Bruno, J.C., Coronas, A., 2013. Simulation studies on gax based Kalina cycle for both power and cooling applications. Appl. Therm. Eng. 50(2), 1522 – 1529, Combined Special Issues: ECP 2011 and IMPRES 2010.

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Libotean, S., Salavera, D., Valles, M., Esteve, X., Coronas A., 2007. Vapour-liquid equilibrium of ammonia + lithium nitrate + water and ammonia + lithium nitrate solutions from (293.15 to 353.15) K. J. Chem. Eng. Data 52(3), 1050 – 1055.

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Libotean, S., Martin, A., Salavera, D., Valles, M., Esteve, X., Coronas A., 2008. Densities, viscosities, and heat capacities of ammonia + lithium nitrate and ammonia + lithium nitrate + water solutions between (293.15 and 353.15) K. J. Chem. Eng. Data 53(10), 2383 – 2388.

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Pons, M., 2009. On the reference state for exergy when ambient temperature fluctuates. Int. J. Thermodyn. 12(3), 113 – 121.

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Baehr, H.D., Tillner-Roth, R., 1994. Thermodynamic properties of environmentally acceptable refrigerants: equations of state and tables for ammonia, R22, R134a, R152a, and R123, Springer-Verlag, Berlin, Germany.

TRNSYS, Transient System Simulation Tool, Program Manual, 2004. Solar Energy Laboratory, University of Wisconsin, Madison, USA.

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Venegas, M., Rodriguez, P., Lecuona, A., Izquierdo, M., 2005. Spray absorbers in absorption systems using lithium nitrate-ammonia solution. Int. J. Refrigeration 28(4), 554 – 564. Vidal, A., Best, R., Rivero, R., Cervantes, J., 2006. Analysis of a combined power and

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refrigeration cycle by the exergy method. Energy 31(15), 3401– 3414. Vijayaraghavan, S., Goswami, D.Y., 2003. On evaluating efficiency of a combined power and

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cooling cycle. Trans. ASME: J. Energy Resour. Technol. 125(3), 221 – 227. Vijayaraghavan, S., Goswami, D.Y., 2005. Organic working fluids for a combined power and cooling cycle. Trans. ASME: J. Energy Resour. Technol. 127(2), 125 – 130. Wagner, W., Pruss, A., 1993. International equations for the saturation properties of ordinary water substance. Revised according to the international temperature scale of 1990. Addendum to J. Phys. Chem. Ref. Data 16, 893 (1987). J. Phys. Chem. Ref. Data 22, 783 – 787.

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Zhang, N., Lior, N., 2007. Methodology for thermal design of novel combined refrigeration/power binary fluid systems. Int. J. Refrigeration 30, 1072 – 1085. Zhu, L., Gu, J., 2010. Second law-based thermodynamic analysis of ammonia/sodium

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thiocyanate absorption system. Renewable Energy 35(9), 1940 – 1946. Ziegler, F., 2007. Novel cycles for power and refrigeration. In: Proceedings of 1st European

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Conference on Polygeneration, Tarragona, Spain, pp. 169 − 181.

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Table 1: Main parameters of the solar collectors for the quasi-dynamic model according to the European standard EN-12975. Solar thermal collector technology

Parameter

PTC collector

ETC collector

Chromasun MCT

SopoNova 4.1

Vario 2400-30

0.565

0.5897

0.12

0

-2 -1 c1 [ W·m ·K ]

0.54

0.9317

-2 -2 c2 [ W·m ·K ]

0.0032

0

7800

2459

-1 c6 [ s·m ]

0

0.01248

2 Aap [ m ]

3.39 0

Tilt angle [ ° ]

20

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Azimuth (S=0°)

1.015

1.936 0.006

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-2 -1 c5 [ J·m ·K ]

0.774

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Model

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LFC collector

12870 n.a.

5.38

3.05

0

0

0

20

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Table 2: Correlation parameters for the driving heat, dissipated heat, cooling capacity and power output of the SAPCS according to the Eq. 1 and 2. Goswami cycle

Qɺ in

Qɺ cw

Qɺ cold

a

1.586

1.581

0.376

b

-3.447

-3.372

-0.656

c

0

0

0.438

154.362

146.572

-16.600

0.9667

0.9711

0.9938

2

Adjusted R

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d

Wɺ e 0.382

-0.730 0

-2.385

0.9910

SC

Parameter

NH3 / H2O Single-stage combined absorption cycle (a = a1 + a2·SR, b = b1 + b2·SR, c = c1 + c2·SR)

a

Qɺ cw

1

2

1

3.717

0.968

6.412

Qɺ cold 2

1

-2.076

2.702

Wɺ e

2

1

-2.647

4.765·10-3

0.398

-2

0.754

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Qɺ in

Parameter

2

b

-9.704

-3.899

-18.355

5.168

-8.693

8.318

-3.675·10

c

6.895

4.252

14.896

-2.972

7.985

-7.284

-1.539·10-2

d 2

Adjusted R

0

0

0.9963

0.9956

-6.059·10-2

0

0

0.9932

0.9937

NH3 / NaSCN Single-stage combined absorption cycle (a = a1 + a2·SR, b = b1 + b2·SR, c = c1 + c2·SR)

Qɺ cw

2

a

6.356

1.601

b

-16.928

-5.996

c

8.579

5.999

d

0 2

Adjusted R

Wɺ e

2

1

2

1

2

10.752

-3.233

4.378

-4.217

-2.078·10-2

0.621

-30.329

8.182

-13.409

12.743

7.765·10-3

-1.454

18.170

-3.163

9.578

-8.823

2.000

0.346

0.9986

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Qɺ cold

1

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1

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Qɺ in

Parameter

0

0

0

0.9981

0.9955

0.9943

NH3 / LiNO3 Single-stage combined absorption cycle (a = a1 + a2·SR, b = b1 + b2·SR, c = c1 + c2·SR) Parameter a b c

Qɺ in

Qɺ cw

Qɺ cold

Wɺ e

1

2

1

2

1

2

1

2

6.234

0.968

10.027

-3.240

3.796

-3.699

1.335·10-3

0.511

-15.902

-2.946

-26.706

8.557

-10.873

10.523

-6.250·10-2

-0.989

-7.181

-2

8.234

2.720

15.768

-4.420

7.565

2.671·10

3.579·10-2

d

0

0

0

0

Adjusted R2

0.9980

0.9975

0.9945

0.9942

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Table 3: Annual energy values and energy efficiency rates for the SAPCS. In all cases we assumed a solar collector field facing to the South (azimuth angle 0 º) with an aperture area of 600 m2 and a tilt angle of 20º. For the Single-Stage Absorption Cycles we considered several split-ratios (SR) to change the power/cooling production ratio. Single-Stage Absorption Cycles with ETC solar collectors

Solar Technology ETC LFC PTC 0.2

NH3/H2O

NH3/NaSCN

SR

SR

0.5

0.8

0.2

0.5

0.8

90.3

90.5

78.7 90.3 94.9

Annual energy (MW·h)

0.8

90.0

90.0

99.4

469

480

492

502

513

493

Qheat

2448 2448 2594

1531

1683

1853 1517 2032 2423 1900

2076

2600

Qcold

199

199

234

797

530

235

782

624

310

875

585

302

Power

267

267

302

23

70

118

12

71

139

19

68

142

2305

2143

2593

2760

2392 2392 2538

525

0.5

245

Qcw

201

508

506

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Solar heat 303

0.2

SC

90.0

NH3/LiNO3 SR

Optimal annual heat source temperature (ºC) 138.2 138.2 150.0

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Goswami Cycle

1970 2287 2586 2594 2756

Annual energy efficiency factors (%) 12.4

8.2

9.4

30.6

28.5

26.5

34.6 25.0 20.9

26.4

24.7

18.9

ηsolar

26.1

17.3

21.1

40.3

41.2

42.2

45.1 43.6 43.5

43.1

44.1

42.3

ηAPC

14.9

14.9

16.3

5.3

6.3

7.2

4.5

5.6

6.6

4.4

5.2

6.2

ηSAPCS

4.1

2.8

3.4

2.1

2.6

3.0

2.0

2.4

3.0

1.9

2.3

2.6

εAPC

51.8

51.8

52.9

26.6

31.7

36.6

26.1 29.0 32.9

22.8

27.1

29.8

εSAPCS

4.1

2.8

3.6

2.2

2.7

3.2

2.2

2.0

2.4

2.8

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SF

2.6

3.0

SC

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Solar buffer tank 36 m3

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Solar Thermal Collectors Aperture area = 600 m2

Recooling subsystem Heat rejected

Boiler

Heat input

Conventional heating subsystem

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Solar thermal subsystem

Absorption power-cooling subsystem

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Figure 1: Block diagram illustrating the main components of the SAPCS.

Cooling

Power

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6

REC 4

13

5 II

III

Heat Source Fluid

DES

SC

3

SH

2A

14

I

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10

SHX 11

2B 2

SEV 12

1

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Cooling Water

ABS

EP

9

7

8

C

Chilled fluid

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Figure 2: Schematic diagram of the Goswami cycle with NH3/H2O mixture.

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(a) – For NH3/H2O mixture

(b) – For NH3/LiNO3 or NH3/NaSCN mixture

Figure 3 (a, b): Schematic flow diagram of the single-stage combined absorption cycles.

Type 91 HEX Type 110 Pump1

Type 4a Storage 1 Type 110 Type 709 Pump2

Type 510

Type 11f Diverter

Description

Type 709 Pipe

Type 110 Pump4

Type 510 Cooling tower

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ETC, LFC or PTC solar thermal collectors (using new type of model according to the quasi-dynamic model in the standard EN-12975) Connecting pipe Variable speed pump Heat exchanger with constant effectiveness Thermal storage/Stratified storage tank/Fixed inlets/Uniform losses Pipe or duct tee-pieces/mixer/used for fluids except moist air Flow diverter/used for fluids except moist air Auxiliary heater/boiler New type created : Combined absorption power and cooling cycle (Goswami or SSCA cycles) Cooling tower (for heat dissipation)

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Type 709 Type 110 Type 91 Type 4a Type 11h Type 11f Type 6 Power-cooling cycle

Power-cooling cycle

Pipe

TRNSYS Model Type 1288

Type 110 Type 6 Pump3 Type 709 aux. boiler Pipe

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Type 709 Pipe

Type 11h Tee-piece

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Type 709 Pipe

Type 709 Pipe

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Figure 4: General Schematic of the TRNSYS Simulation Studio models for the SAPCS.

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35 Goswami

30 25

SR=0.5 LiNO3 SR=0.8 LiNO3

20

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Power [kW]

SR=0.2 LiNO3

tcw, in = 29 oC tchw, in = 12 oC

SR=0.2 NaSCN SR=0.5 NaSCN

15

SR=0.8 NaSCN

10

SR=0.2 H2O SR=0.5 H2O

SC

5

SR=0.8 H2O

0 70

80

90

100

ths, in

110

120

[oC]

130

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60

(a) – Power output

10

SR=0.2 LiNO3 SR=0.5 LiNO3 SR=0.8 LiNO3

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6 4 2

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0

60

70

80

SR=0.2 NaSCN SR=0.5 NaSCN SR=0.8 NaSCN

tcw, in = 29 oC tchw, in = 12 oC

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ηAPC [%]

8

Goswami

SR=0.2 H2O SR=0.5 H2O SR=0.8 H2O

90

ths, in

100

110

120

130

[oC]

(b) – Effective first law efficiency (ηAPC)

Figure 5 (a, b): Variation of the power output and effective first law efficiency with the heat source temperature for the Goswami and NH3/LiNO3, NH3/NaSCN, NH3/H2O single-stage combined absorption cycles.

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35

Goswami

30 25

SR=0.5 LiNO3 SR=0.8 LiNO3

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Power [kW]

SR=0.2 LiNO3

ths, in = 120 oC tchw, in = 12 oC

20

SR=0.2 NaSCN

SR=0.5 NaSCN

15

SR=0.8 NaSCN

10

SR=0.2 H2O

5

SC

SR=0.5 H2O SR=0.8 H2O

0 20

30

tcw, in

40

50

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10

[oC]

(a) – Power output 12

Goswami

ths, in = 120 oC tchw, in = 12 oC

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SR=0.5 LiNO3

8

SR=0.8 LiNO3 SR=0.2 NaSCN SR=0.5 NaSCN SR=0.8 NaSCN

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ηAPC [%]

10

SR=0.2 LiNO3

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6

SR=0.2 H2O SR=0.5 H2O SR=0.8 H2O

4

10

20

30

40

50

tcw, in [oC] (b) – Effective first law efficiency (ηAPC)

Figure 6 (a, b): Variation of the power output and effective first law efficiency with the cooling tower temperature for the Goswami and NH3/LiNO3, NH3/NaSCN, NH3/H2O single-stage combined absorption cycles.

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35

Goswami

ths, in = 120 oC tcw, in = 29 oC

30

SR=0.2 LiNO3 SR=0.5 LiNO3 SR=0.8 LiNO3

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Power [kW]

25 20

SR=0.2 NaSCN

SR=0.5 NaSCN

15

SR=0.8 NaSCN

10

SR=0.2 H2O

SC

SR=0.5 H2O

5

SR=0.8 H2O

0 10

12

14

16

18

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tchw, in [oC]

20

(a) – Power output 10

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6

SR=0.2 LiNO3 SR=0.5 LiNO3

oC

ths, in = 120 tcw, in = 29 oC

SR=0.8 LiNO3 SR=0.2 NaSCN SR=0.5 NaSCN SR=0.8 NaSCN

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ηAPC [%]

8

Goswami

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4

SR=0.2 H2O SR=0.5 H2O SR=0.8 H2O

2

10

12

14

16

18

20

tchw, in [oC] (b) – Effective first law efficiency (ηAPC)

Figure 7 (a, b): Variation of the power output and effective first law efficiency with the chilled water temperature for the Goswami and NH3/LiNO3, NH3/NaSCN, NH3/H2O single-stage combined absorption cycles.

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0.6 0.5 0.4

150

RI PT

Energy [MWh]

200

0.3

100

0.2

50 0

Qheat

2

3

Solar heat

4

5

6

7

8

9

10

M AN U

1

SC

0.1

Qcold

Power

η_APC

η_solar

Solar fraction / ηx / Ex [ - ]

250

0.0 11

12

η_SAPCS

Ex_APC

(a) – NH3/H2O Goswami Cycle with PTC solar collector.

0.30

1

Qheat

2

Solar heat

3

0.20 0.10

Solar fraction / ηx / Ex [ - ]

100

0

0.40

EP

150

50

0.50

TE D

200

AC C

Energy [MWh]

250

0.00 4 Qcold

5

6

Power

7

8

η_APC

9

10

η_solar

11

12

η_SAPCS

Ex_APC

(b) – NH3/H2O Single-Stage Combined Absorption Cycle with ETC solar collector and SR=0.2.

0.50

200

0.40

150

0.30

100

0.20 0.10

0 Qheat

2

3

Solar heat

4 Qcold

5

6

7

8

9

M AN U

1

SC

50

Power

η_APC

10

η_solar

11

Solar fraction / ηx / Ex [ - ]

250

RI PT

Energy [ MWh ]

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0.00 12

η_SAPCS

Ex_APC

(c) – NH3/NaSCN Single-Stage Combined Absorption Cycle with ETC solar collector and SR=0.8.

AC C

EP

TE D

Figure 8 (a, b and c): Monthly energy values and energy efficiency rates for some SAPCS.

ACCEPTED MANUSCRIPT

Highlights o PTC collector technology is suitable for solar power and cooling Goswami cycle.

RI PT

o ETC technology is more suitable with single-stage combined absorption (SSCA) cycle. o For more chilled water production, SSCA cycles at lower SR are the best option.

AC C

EP

TE D

M AN U

SC

o For power production, Goswami-ETC or PTC combinations offer best efficiencies.