Refriger Ac i on Solar

8/13/2019 Refriger Ac i on Solar

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REFRIGERACIN SOLAR EN LA INDUSTRIA DE ALIMENTOS EN MEXICO, UNAESTRATEGA PARA LA MITIGACIN DE GASES DE EFECTO INVERNADERO.

SOLAR COOLING IN THE FOOD INDUSTRY IN MEXICO, A STRATEGY FOR MITIGATION OFGREENHOUSE GASES EFFECT

Dr. Juan M. ACEVES H1., I.A. Alfredo ALVAREZ C.1, Dr. Roberto BEST B.2,Dr. Jorge M.ISLAS S.2, Dr. Fabio L. MANZINI P.2, Dr. Isaac PILATOWSKY F.2, Dr. Genice K. GRANDE A.2

Ing. Yessica P. TREJO D.1, Ing. Jos N. ACEVES G.,1Dr. Mario MOTTA3, Dr. RossanoSCOCCIA.3

(1)Facultad de Estudios Superiores Cuautitln-UNAM, Km 2.5 Carretera CuautitlnTeoloyucan, San Sebastin Xhala, 54714, Cuautitln Izcalli, Estado de Mxico, Mxico.

[email protected],Tel. 56231999 ext. 39431(2)

Centro de Investigacin en Energa-UNAM.Privada Xochicalco S/N, 62580, Temixco,Morelos, [email protected],Tel. 5629736(3)Department of Energy, Politecnico di Milano, Miln ITALIA.
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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RESUMEN

Existe una gran preocupacin a nivel mundial por el incremento en la demanda de energa a nivelmundial y la correspondiente emisin de gases de efecto invernadero, adems del calentamientoglobal y sus efectos devastadores. El protocolo de Kioto y las reuniones entre mandatarios de lospases desarrollados son una consecuencia de esta preocupacin. En Mxico, igual que en otras

partes del mundo, se estn haciendo esfuerzos para promover el uso de la energa solar paraproducir frio y satisfacer las demandas de fro en el sector alimentario, tales como las de crnicos,vegetales y frutas. En el 2008 se inici un proyecto llamado MEXISCO (MEXIcan Solar CoolingProject) financiado por el gobierno Italiano y que fue realizado por el CIE y La FESC, dosinstituciones de la UNAM. En este proyecto se realizaron encuestas a 120 empresas y seseleccionaron dos casos de estudio, esto en base a la informacin disponible, al gran tamao delas empresas y a su deseo expreso de participacin, en el presente trabajo solo se presenta uncaso de estudio por cuestiones de espacio y de tiempo. Los datos proporcionados se usaron paraseleccionar el colector solar ms adecuado y el sistema de absorcin apropiado, adems desimular el tamao de los modulas para el colector. Se propuso el sistema de refrigeracin solar,compuesto por un campo de concentradores solares tipo Fresnel, para activar el sistema derefrigeracin que est compuesto por agua- amoniaco, como refrigerante en un solo paso. La

simulacin se llev a cabo en un programa TRNSYS, que permite modular el sistema decolectores para as tener la carga de refrigeracin requerida por las empresas seleccionadas. Elahorro de electricidad estimado es de alrededor de 20 % del total, sin considerar el aireacondicionado. Esta pequea fraccin se debe al hecho de que la empresa trabaja 24 horas al dacon capacidades de congelacin y refrigeracin muy grandes, y a temperaturas cernas a - 20 C.que no es posible alcanzar con un sistema de refrigeracin solar de una etapa. Finalmente, sepresentan las especificaciones del sistema simulado para la refrigeracin solar. Es importantedestacar que con estas acciones e posible alcanzar las metas de NET ZERO y su filosofa, que esel uso cada vez menor de energas que contaminen el medio ambiente.

Abstract

The increase in energy demand and the correspondent Greenhouse Gases Emissions and GlobalWarming are of big concern for the world countries. In Mexico efforts are being made to promotethe use of solar energy for cooling in the food industries, such as that in the frozen meat,vegetables and fruits sectors. One study case was selected among 120 industries visited; the mainreason for this case was the size of the facility, the information available and their willingness tocollaborate in the present project. Data from the industry was used to select the appropriate solarcollector and absorption cooling system, and to simulate the operation and size of the collectorfield required. The proposed cooling system was composed by a Fresnel concentrating collectorfield to activate a series of air cooled single stage ammonia-water absorption cooling system. Thecooling system simulation was carried out with TRNSYS which allows us to modulate the collectorsystem to cover the required load. The calculated saved electricity was around 19 % of the total,this small fraction is due to the fact that the facilities selected are operating continuously 24 hours

a day with very large refrigeration capacities. Also large fraction of their cooling requirements isbelow the working temperatures of the absorption cooling system selected. The specifications ofthe simulated solar cooling system are presented. With his actions it is possible to get the objectiveof NET ZERO, and its philosophical goals of zero emissions of contaminants in the industry byusing alternative energies.

Keywords

Greenhouse gas emissions, Food Industries, solar cooling system, solar refrigeration systemsimulation.


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Introduction

Energy consumption systems based on fossil fuels are responsible for two thirds of anthropogenicGreenhouse Gases (GHG) emissions, now widely recognized as the major environmental globalcrisis. Global energy demand and GHG emissions are estimated to increase by 60% by 2030 with

respect to 2000 The continued rise in the living standards and demand for service to satisfy humanneeds with the associated impact on electricity demand and global warming drives the search forother alternatives, such as the use of solar energy and other renewable sources for coolingapplications [1].

The Food Industry and specifically the meat, fruit and vegetables sectors in Mexico havepresented a continuous expansion with the subsequent increase of cooling/freezing demand andthe use of electricity [2-5].

The main objective of the present work is to analyze the technical and economic feasibility of solarabsorption technology to satisfy cooling/freezing services in the food industry in Mexico, takingadvantage that the highest cooling demand generally occurs at the same time of maximum solar

irradiation.

1. Case Study

In order to obtain reliable data about electricity used by food industries to satisfy cooling needs in arecent project called MEXISCO [6], a survey among the main food industries in Mexico was carriedout. From the analysis of the 120 agro food industries visited one study case was selected, takenin account the technical information available, the size of the company and its location. This caseof study was called C1 and it is food industry in the meat sector.

1.1 C1 Case study

The case study is a food company that has a global process ranging from producing livestock feedto the elaboration of pork derivatives. For this reason the C1 company has three different plants,the balanced food plant (BFP), the slaughter and cutting plant (SCP) that processes 660,000 pigsper year, it has a daily capacity of 2,300 pigs by shift and a modern courtroom where the cuts areproduced, packed and frozen and the added value plant (AVP) where cuts are produced andindividually frozen, ready for cooking or eating. Only the two last plants are our interest because inthose plants refrigeration cooling and freezing are required.

Figure 1. Geographical locat ion of the food c omp any

The two process plants were analyzed for the integration of the new solar cooling system, basedon the needs of the process. It also had two refrigeration subsystems: a low temperaturesubsystem with operation temperature around -35C to -20C and a medium temperaturesubsystem at 2C to -2C.

HHeerrmmoossiilllloo MMeexxiiccoo

UnitedStatesofAmerica


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Figure 2. Processes in a polyv alent s acri f ice plant

The final choice was the medium temperature processes of the AVP which will be called C1, it wasselected for its simplicity and versatility, foresees the direct connection of the new system by aheat exchanger, while the existing cooling system, fed by the compression chiller, will act as a

backup circuit. Also it does not have a limited available surface area for collector field as in SCP.For the C1 plant, the hourly value of the refrigeration cooling load was not directly available, asenergy bills usually included all the different loads, for this reason, estimations of the loads mediumtemperature cooling subsystems loads were required, based on the available aggregatedinformation such as the total monthly electric consumption and the electric and chilling power ofthe compressors.


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Figure 3. Medium and very low temperature sect ions in the added value plant

The electric power of the compressors working at medium temperature has been compared to thetotal electric power. The same ratio has been applied to the total monthly electric consumption ofthe above mentioned process, thus estimating the electric consumption of the medium temperatureload (figure 4).

Electricity consumption 2008

0

200000

400000

600000

800000

1000000

1200000

1400000

Enero

Marzo

Ma

yo

Ju

lio

Sebtiem

bre

Noviem

bre

Month

Kw/h

Figure 4. Electr ic i ty cons umption in 2008

Figure 5 shows the values that have been multiplied by the nominal Energy Efficiency Ratio (EER,which is the nominal cooling power divided by nominal electric power) in order to quantify therefrigeration load. The peak cooling load is 659 kW in July while the minimum value was 515 kW inJanuary; on the other hand the total annual consumption of the medium temperature coolingsystem was 5,191 MWh.


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Figure 5: Monthly d istr ibut ion o f cold demand for A dded Value Plant

The minimum monthly average ambient temperature in Hermosillo is approximately 15.5 C inDecember and the maximum temperature is 33.6 C on July, with a global radiation on horizontalsurface is 2,101 kWh/m2, a direct normal radiation of 1,536 kWh/m2 [7]. Hermosillo is on thecoordinates 29 06 N and 11057W (figure 1).

2. The Solar Absorption Cooling Plant

Due to the high cooling energy needs required in C1 in relation to the capacity of the chosen solar

cooling machine (nominal cooling capacity 35.4 kW), the following procedure was adopted: toidentify the modular unit (with an adequate dimensioning of collector field, absorption chiller andcold storage) and the number of modular units according to the climatic conditions and to the enduser energy request.

Fig. 6 Compressor s pecif icat ions for case 1 company.

2.1 Preliminary schemes and operation strategies.

The system shown schematically in Figure 2 was developed for a refrigeration load of around 0C

in hot climates and is composed of medium temperature concentrating solar collectors and an air-cooled single effect water ammonia absorption chiller.


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Table 1. Operat ions: slaughter plant

Operat ions Machinery Energy Load

1 Reception of pigs.The animalsare transported by trailers and

the reception is made at the

backyard.

Transporting band. Mechanical. Conditioned

air.

2 Stabilization.The pigs remainwithout food and water for 24

hours.

Room with ventilation. Mechanical. Conditioned

air.

3 Killing the pigs. The pigs aretransported by mechanical band,

for technical needs as to avoid

suffering, electroshock is applied.

Electric shock on the

brain and heart of the

pig.

Electrical. Conditioned

air.

4 Hanging and bleeding.In order

to use the blood as a by-product,the pigs blood are collected and

the pork is cutting by halves and

hag in a hooks for transportation.

Transportation band Mechanical. Temperature

4 C.

5 Scalding-pilling.Since the porkis sold with skin the folicules in

hair are removed with the hot

water and flames in few minutes,

the remainder hair is burned with

fire for few minutes

Band Transportation,

and hot water pools

and small fire room.

Mechanical. Conditioned

air.

6 Deboning.The bones of the pigare removed and the guts, hart,

and all visceras are send for

cooking in other room.

Cutting machinery. Mechanical. Temperature

5 C.

7 Fine cuttings. Special part ofthe pork is cutting for

delicatessen and other big parts

are send to cooling and freezing.

Cutting specialized

machinery


air.

8 Washing and Preparation.

Before sending the cuts to thefreezer and cooling, package with

appropriated weight are

prepared.

Pools with water and

transportation bands.


air.

9 Cooling. (Tempering). When thepork has to be cut the pieces are

heated up to high temperature

because a low temperature is not

possible to cut it.

Specialized

machinery.

Mechanical. Temperature

-5.

10 Freezing and Refrigerating.Quick freezing is necessary in

order to keep the quality of the

Racks in the facilitiesto storage the boxes

with the product.

Electrical. Cooling roomtemperature -5 C.

Freezer room


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meat and also by federal policy

and also for storage.

temperature -35 C.

Table 2.- Operation s: added valu e plant

Operat ions Machinery Energy Load

1 Reception of the pork parts. Transportation band. Mechanical. Temperature

-5 C.

2 Special preparation andCooking. Preparation of ham,

smoked meat, sausages, etc. is

carried out in this section.

Marmites. Heated by

vapor.

Natural gas. Temperature

95 C.

3 Packing and Storage. In thisroom selected cuts and prepared

meals are prepared in specialboxes.

Transportation band. Mechanical. Temperature

-5 C.

4 Cooling. (Tempering). When thepork has to be cut the pieces are

heated up to high temperature

because a low temperature is not

possible to cut it.

Specialized

machinery.

Mechanical. Temperature

-5.

5 Freezing and Refrigerating.Quick freezing is necessary in

order to keep the quality of themeat and also by federal policy

and also for storage.

Racks in the facilities

to storage the boxes

with the product.

Electrical. Cooling room

temperature -5 C.

Freezer roomtemperature -35 C.

This configuration is justified by the high temperature difference between the required refrigeranttemperature of 2C and the ambient temperature which could exceed 30C. In these conditionsthe absorption chiller must be driven by a medium temperature collector.

The chosen absorption cooling system chiller was a single stage cooling unit (35,4 kW nominalcooling power), supplied by ROBUR S.P.A. The chiller operates with water-ammonia and it is air-

cooled, thus not making use of any bulky and expensive heat rejection system. Linear Fresnel(LFC) concentrators were selected as the optimum collector type, following aspects such asworking temperatures, performance, cost and problems in operating conditions.

The absorption chiller selected requires minimum firing temperature values as high as 180C,using pressurized water between 140C and 170C corresponds to absolute pressure levelsbetween 3.6 bars and 8 bars.


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Figure 7. Solar Ab sorp t ion cool in g conceptu al scheme

2.2 Solar Absorption Cooling Simulation

The sizing of the solar cooling plant for the study case was bounded by the absorption chiller

capacity, the load profile and the climatic conditions, whereas collector size, cold storage size anddesign load for the absorption chiller were degrees of freedom. It has to be emphasized that cleardesign guidelines do not exist for solar refrigeration applications: their performance is stronglydependant on the external conditions and is dynamic, in the sense that it varies continuouslyduring the day as a consequence of external changing conditions.

The radiation (both intensity and angle of incidence) and the ambient temperature affect the solarcollector heat gain and their outlet temperature. Furthermore, the absorption chillers Coefficient ofPerformance, (COP) and its capacity are depending on ambient temperature, driving temperature,and chilled water temperature. In order to predict the overall system performance during the wholeyear a simulation program using TRNSYS 16 [8] was developed; For the Linear Fresnel reflectorand the absorption chiller, mathematical models were developed by Politecnico di Milano, basedon measured data and these were implemented in TRNSYS.

2.2.1 Identification of the C1 solar cooling base module

The system concept was selected through a simulation campaign which highlighted the optimumconfiguration for the given boundary conditions: the industrial processes selected and the climateconditions. The optimum ratio between the chosen thermal chiller size (nominal cooling power 35,4kW) and the area of one row of the solar field was investigated. Depending on the ratio of coolingload to be covered by the solar system, the base module can be simply replicated n times. Oncethe interface with the existing system was identified and as the load profile and climatic data wereknown, the optimum size of the solar collector area and cold tank storage were calculated by

means of a parametric dynamic simulation.

The cold tank size was not a degree of freedom because cold demand of C1 is continuous (24hours a day) and C1 has very high cold demand. The cold tank was consequently dimensionedonly to smooth the function of each absorption cooler during daylight hours.

It is possible to see, in Figure 8, the different influences of useful heat from the solar system andthe specific useful heat about the solar collector size on system performance: larger surfacesobviously produce more useful heat in absolute values, but the specific useful heat decreases.

Primary circuit Secondary circuit

ROBUR


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Figure 8. Useful solar system heat as funct ion of the Fresnel col lector

This is due to the fact that larger surfaces lead to higher average fluid temperatures, reducing theaverage collector efficiency (higher temperatures lead to higher thermal losses towards theambient).

However large collector sizes enable the chiller to work at higher COP values, the reason is againlinked to higher fluid temperatures which have positive influence on the absorption chiller. Figure 9shows the relationship between the amount of cold produced by the thermal chiller and the specificuseful heat from the collector field. The above mentioned effects lead to an optimal collector area,which corresponds to the intersection of the cold generation and specific useful heat curves: thebetter sizing of solar field for the chosen absorption chiller (nominal cooling capacity 35,4 kW) is asingle row of Fresnel collector for a total gross area of 330 m2 (4 m x 11 x 7,5 m) and a mirror area

of 242 m2

(4 m x 11 x 5,5 m).The optimal values for a module resulted as follows: FresnelCollector Area: 330 m2gross area, 220 m2mirror area and a cold storage tank with a volume of 9m3.

Figure 9. Relat ionship between the amou nts of cold prod uced by the thermal chi l ler and

the specif ic us eful heat from the col lector f ield

2.3 Basic Project data


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The solar cooling plant configuration, shown in Figure 7, was composed of the followingcomponents: solar Fresnel collectors, absorption chiller, cold water storage tank and thepreliminary hydraulic circuit. The solar pump and the two secondary circuit pumps (absorptionchiller driving pump and distribution circuit pump) are set on when the solar conditions areappropriate, in order to keep the cold water storage always at the lower possible temperature andto guarantee cold water circulation in the heat exchanger of the load side, if requested. The chiller,

the solar pump and the absorption chiller driving pump are turned on when the temperature in thehot circuit is above 120 C and are turned off when the same temperature rises to 180 Ccombined with unfocused mirrors. The distribution circuit pump is turned off if the lowesttemperature in the cold tank is higher than the set-point temperature of the medium temperaturecooling sub-system.

2.3.1 Base module design data

The solar cooling base modules defined previously was characterized. Generally speaking, asolar cooling plant could be divided in two parts. The first, called Primary circuit, includes thesection of the system between the Fresnel solar collector and the absorption machine and the

second, called Secondary circuit, includes the part of the solar plant from the absorption machineto the heat exchanger of the load side, as shown in Figure 7.

2.3.2 System description

The solar absorption cooling plant is designed for supplying cooling energy to the productionprocess of C1. The proposed solar thermally driven cooling system for this case study wascomposed by a linear concentrating Fresnel collector that supplies heat directly to an air cooledwater/ammonia absorption chiller. The heat transfer medium in the primary circuit is pressurizedwater which is still liquid at temperatures higher than 100C. This chiller feeds the produced coldinto a water/glycol storage tank.

Figure 10. Dif ferent parts and temperatures of an absor pt ion chi l ler

The conventional compression chiller, which was already installed as part of the existing coolingplant, was used as backup; in fact the system was not designed to cover the total cooling load of


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C1, as this would lead to high investment costs and a bad economic efficiency of the system. Thesynergy between the absorption chiller and the conventional chiller of the existing plant is balancedby a three way valve installed after the cold storage: the valve control checks the tank temperatureand compares it to a set-point value. If the tank temperature is below the set-point, water is takenfrom the tank. Otherwise, the conventional chillers circuit must provide the total cooling energyrequest by the load.

2.3.2.1 Solar Collector

During the simulation campaign for base model identification, various sizes of Fresnel solarcollectors were simulated. Each size of solar collector is a multiple of a defined sub-module (grayarea) as it is shown in Figure 10 and the technical data of the chosen collector are: the Sub-module gross collector area (4 x 7,5) is equal to 30 m2, Sub-module aperture (=mirror) collectorarea (4 x 5,5) of 22 m2 and one series collector area of 330 m2.

2.3.2.2 Collector Field

As for the choice of the solar collector size various solar collector fields were simulated. The

collector field size had a huge influence on both, energetic and economic performance of thesystem. Varying this parameter during the simulation campaign allowed performing a detaileddimensioning of the system, searching for the best energetic and economic results. Theparameters were: number of modules for each row of 7-15, number of rows of 1-10, with a width ofcollector rows 28 (7 x 4) 60 (15 x 4) m, collector row height (collector height) 7,5 m, nominalthermal power 771,650 kW and size of total solar field of 2104,500 m2.

Figure 11. Fresnel solar col lector dim ension

2.3.2.3 Solar system control and piping

The solar system control had the following specifications: it wasis of type of independent control ofboth the primary and secondary circuits. The primary circuit has a lower solar radiation level (Tl)of 20 W/m2and upper solar radiation level (Th) of 50 W/m2. And for the secondary circuit, it had alower temperature difference (Tl) of 1C and upper temperature difference (Th) of 3C.

2.3.2.4 Flow rates and electrical power consumption of circulation pumps


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Pumps are one among the basic components of a solar thermal plant: they are responsible for thecorrect fluid circulation in the primary and secondary circuit and they must withstand hightemperatures. For this reason, pumps must be carefully dimensioned, in this way the flows are thenext : flow rate of primary circuit is 8,500 102,000 kg/h and flow rate secondary circuit 64,800(kg/hr, so the total power of the pumps varied from a min of 500 + 100; and a max of 6,000 + 1,200W.

2.3.2.5 Cold Generation

This section was divided in four parts in order to get a better understanding, where it is possible tofind information about operation conditions and characteristics of the equipment.

Thermally driven chiller: The chosen thermal chiller is a single effect ammonia/water absorptionchiller. It is driven by the hot water from the solar circuit and it is air cooled. Chiller technicalspecifications are: Nominal cooling capacity of 1 x 35,4 12 x 35,4 (424.8) kW, Nominal COP0,67; the nominal operations conditions are the followings: External air temperature 35C, inlettemperature to generator of 180 C, outlet temperature from generator of 170C, inlet chilled watertemperature of 1,0C and outlet chilled water temperature -2,0C. During the simulation campaign,one or more absorption chillers of the same size operating in parallel were simulated.

Thermally driven chiller control: The control system activates the absorption chiller wheneverfollowing conditions are fulfilled: a) the temperature in the lower part of the tank is higher than 0Cthat is that the maximum temperature cold storage is 1C because in these moment the chiller ison and b) the working fluid temperature is higher than 130 C that is the minimum temperature ofheat source (water from collector field). The chiller is turned off when the tank temperature is below-2 C that is the minimum temperature of cold storage.

Auxiliary chiller: due to the uncertain availability of solar radiation, the backup system will cover theload during periods with bad weather. What is more, the solar cooling plant should run as manyhours as possible at maximum power, in order to reach the best economic performance,

minimizing the amount of energy to be purchased from energy suppliers.

The backup system characteristics were as follows: a conventional compression chiller, with amaximum cooling capacity of 650 kW and a COP of 2,8, which is already installed in the mediumtemperature circuit, was selected. Another solution would be to install a so called warm backup,that is a heat generator providing thermal energy to the absorption chiller when no solar radiationis available.

Cold storage and distribution: along each 35,4 kW absorption machine a cold tank is installed. Itspurpose is to regulate the machines operation. Some characteristics are as follows: volume of coldstorage tank for each collector row 9 m3, with a height of 3 m.

2.4 Design Results

The process used to find an optimum solar cooling plant for C1 medium temperature circuit fromthe preliminary results was realized using multiple solar cooling base modules.

The results are presented for the systems with a nominal cooling power limited to the smallestvalue of the monthly cooling power of AVP part cooling circuit (515 kW). This consideration wasestablished in order to limit the maximum size of the solar field and to guarantee that the solarsystem can operate continuously at the design power along the year. In this way shorter pay-backtimes can be reached due to a higher specific useful energy ratio. The simulations showed thatthe 35,4 kW thermal chiller and 330 m2of collector gross area lead to an annual cold generation ofabout 93,500 kWh for the C1 case. In order to reach higher solar fractions, the system was

multiplied in parallel.


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In the C1 case study the basic modular collector area was up scaled by a factor of four (330 x 4m collector size, 35,4 x 4 kW thermal chiller cold generation, 9 m x 4 cold storage tank) andfurther three cases were up scaled by a factor of 6, 8 and 10 as shown in Table 3.

Table 3. Up scaled base mo dule performance

Case n"base

module" in

parallel

Areacollector

[m2

grossarea]

Power chiller[kW cooling]

Useful heatsolar system

[kWh]

ThermalChillerCold

Generation [kWh]

SolarFraction

%

C1

4 1320 141.6 667,399 376,602 7

6 1980 212.4 1,001,098 568,830 11

8 2640 283.2 1,348,013 758,440 14

10 3300 354 1,701,536 954,594 18

For the C1 case study the up scaling results for the base module x 8 (2 640 m collector size) incomparison to the base module (330 m collector size) that it can reach more than 8 times theuseful solar heat from 165 200 kWh to 1 348 000 kWh, and the total net solar fraction increasesfrom 1,5 % to 14 % and cold generation from 93 500 kWh to 758 400 kWh.

The results show an almost linear trend of the cold generation and of the solar fraction over thecollector area and chilling power. This is due to the fact that several base modules are linked inparallel and therefore behave as separated systems except for the piping heat losses.

According to the above mentioned results, the system composed of eight base module referencesystems for C1 were chose, as the collector field of these solutions and are very close to themaximum available area for installing the collector field.

2.5 Detailed simulation results of a specific system for C1

2.5.1 Solar contribution to total cold demand

In Figure 12, the direct solar radiation on a horizontal surface, the contribution of the solar system(useful solar heat) and the auxiliary cold supply, as well as the net solar savings and the solarsystem efficiency are given. The net solar savings are the difference between the total colddelivered to the load and the cold supply by the auxiliary system (compression chiller). The grosssolar fraction shows the percentage of the total cold produced in the system that is covered bysolar energy, whereas the net solar fraction takes into account the proportional reduction due tostorage, distribution and conversion losses in the solar system.


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Figure 12. Summary of solar contr ibut io n to the total demand

2.5.2 Solar thermal subsystem for C1

In Figure 13, the energy flows related with the solar thermal subsystem are presented, indicatingthe conversion efficiency from incident solar radiation to output at the solar field (solar systemefficiency), the losses in the solar field piping, and the resulting net or useful heat delivered by thesolar system. The useful heat compared to the collector output, is an indicator that shows that partof the thermal energy delivered by the collectors is available at temperatures below the minimumrequired by the absorption machine and is therefore not usable.

2.5.3 Cold generation for the C1 case study

The contributions of the thermal chiller to the total cold generation has the maximum percentageon April with the 18.7 % and the minimum on December with 9.4% , with a annual average value of14,4% and a annual average value of COP of 0,57. The parasitic electricity represents theconsumption of pumps, thermal chiller and control equipment that is not directly used forproduction of cold, but it is necessary for system operation, the values are in range and 6,5-7,4%of the total of consumption between solar system and cold supply system and thermal chiller.

Figure 13. Solar thermal subs ystem


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3. Economic analysis

The parameters used as main indicators for the environmental impact assessment are totalprimary energy consumption, generation of CO2eq, water consumption and generation of highlyradioactive nuclear waste. Primary energy consumption is the preferred parameter to be used asmain indicator, and should be minimized, as it represents a weighted mean of the different types of

emissions. For example the reference system has a primary energy consumption of 5,025MWh/year is emitted 975t/ CO2eq, with a solar cooling system the consumption will be 4,446MWh/year, it implies 112 t/ CO2eq without emitting, this represents 11,5% in savings.

4. Estimation of potential in Mxico to reduce electricity consumption and GHG of solarcooling technology in the Food Industry

An estimation of the potential of solar cooling technologies in the field of food industry (FI) ofMexico is given in this section. The study is based on forecasted energy consumption profilesworked out from literature data, reasonable assumptions and analyses of the industrial processes.

The parameters considered were: the specific cooling demand profile and the operatingtemperature range. For this study, given the industry characterization carried out and the results ofsimulation campaigns, it has been possible to carry out an estimation of Primary Energy Savings(PES) and CO2emission savings achievable through the application of solar refrigeration in theMexican FI sector. It is based on the industrial refrigeration utilizes 7.8% of the electrical powerconsumed in Mexico.

In the case studies, a single stage (water-ammonia) absorption chiller that can produce water attemperature around 0C has been chosen. For this reason those processes that require coldproduction temperatures, below -10C have not been taken into consideration. A process aimingto proof the technical compatibility of the presented systems with the FI sector characteristics hasbeen developed based on this estimation. The technical analysis has considered a range ofpossible solar fractions from 20 up to 40% as result of previous simulations results. Moreover,starting from the 2010 forecasted electricity consumption; three scenarios of refrigeration energydemand growth have been drawn.

In order to produce a picture as close as possible to the real potential savings achievable, in theanalysis (following the indications given by the Task 33 Solar Heat for Industrial ProcessesIEASHC) only the 10% of the technical potential has been considered as realistic potential for Solarcooling primary energy savings in FI. The reason behind this choice, in accordance with Task 33experts, is to take into account all the not technical barriers which affect the actual potential, as forexample the limited area available for the installation of collectors fields. The results in terms ofprimary energy consumption (PES), CO2emission savings and extra-cost of the plant (calculated

throughout the presented algorithm) are summarized in the Table 2, for the different scenarios(solar fraction, year, savings on CO2 emissions).

Table 4. Solar refr igerat ion potent ial analysis for dif ferent grow th scenarios

SF* =20% SF* =30% SF* =40%Year 2010 2030 2010 2030 2010 2030Growthscenarios

low+5%

med.+10%

high+15%

low+5%

med.+10%

high+15%

low+5%

med.+10%

high+15%

SolarcoolingCO2emission

savingsin AFI [kt]

18.3 19.2 20.1 21.0 27.4 28.8 30.2 31.5 36.6 38.4 40.2 42.1

* The fraction of the total load which is covered by solar energy


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In Mexico, at present conditions, at least 95 GWh primary energy savings could be obtained andan equivalent amount of 18,3 kt CO2emissions to the environment could be avoided every year.On the other hand the annual extra cost would be 86 million dollars (1000 millones de pesos). Theeconomic analysis and the potential analysis show that the estimated reduction in primary energyconsumption, PES and CO2emission has its relative high price. This high price is mainly causedby four reasons: 1) cheap conventional cooling systems, 2) expensive solar cooling systems due tolow diffusion, 3) expensive solar cooling system design due to little experience and 4) cheap

electrical energy from conventional sources.

The first point will most likely not change in the future. Conventional cooling systems have reacheda very low price at the end of the learning curve. This could be different for the second and thirdpoint. By a wider diffusion of solar cooling systems and therefore a larger number of producedsolar cooling equipment (especially absorption chillers and medium temperature collectors) priceswill certainly be lower. Also the last point is expected to change. Primary energy and thuselectricity prices will rise. All of the last three effects will favor the implementation of solar coolingsystems in the food and agro industry. Systems at present prices would have been economicallyfeasible (amortization time minor to 10 years) without subsidies only if the electricity price inMexico was nine to twelve times higher than today.

Also is important to mention there is much to improve and to learn about air cooled absorptionchillers for solar systems (internal heat exchangers, power of internal circulation pump, and powerof fan), which are still in prototype phase rather than industry production phase. This will lead in thefuture to increase both their electrical and thermal COP and thus improve both the performancethat the economy of the entire system.

5. Conclusions

From the data available from industry, one study case was selected from the meat sectors whichare using cooling traditional systems. It was concluded that it is possible to applied solar energy in

cooling systems using temperatures as low as -2C. It is a conclusion that the more convenientcollector for those applications is the Fresnel type collector. For this purpose the TRNSYS softwareprogram was used and the gross area and the collector modules area of the mirrors were alsocalculated. The potential analysis conducted showed a good saving potential in terms of primaryenergy and GHG emissions. Although the costs for the savings potential seems to be very high,solar cooling systems for industrial processes are expected to be economically feasible in the nearfuture due to rising tariffs for electricity and gas and also due to lower system and planning costs.In fact the diffusion of the highly promising solar cooling technology is a realistic hypothesis.Additional benefits which are not easily quantified in financial terms for the end user of the solarcooling system, but are very important from a regional, national o global point of view, are not yettaken into account, such as the those listed below: Decrease of the peak loads in electricity grid,environmental protection by less CO2emissions, less dependency on primary energy imports by

using a local, abundant and free energy source, new job creation and development of nationalknow-how at various levels, and the accomplish of the zero net objectives and philosophy. Theabove points would certainly justify the mentioned fiscal exemption on this novel technology thatcould offer a substantial contribution to the economic growth and the environmental profile ofMexico.

6. Nomenclature

COP: Coefficient of Performance (adimensional)Acoll: Collector Area (m

2)Tl: Differential of temperature Low (C)

Th: Differential of temperature High (C)


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7. References

Bermejo, P., Rosa, F., Pino, F.J. 2010, Solar absorption cooling plant in Seville. SolarEnergy, (84) 8: 1503-1512.

Prospectiva del sector electrico 200-2024, 2010, Secretaria de Energia,

http://www.energia.gob.mx/res/PE_y_DT/pub/Prospectiva_electricidad_2009-2024.pdf

Sector alimentario en Mexico 2009, 2010, Instituto Nacional de Estadstica y Geografa,http://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2009/sam2009.pdf

Sector alimentario en Mexico 2010, 2011, Instituto Nacional de Estadstica y Geografa,http://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2010/sam2010.pdf

Banco de Informacin Econmica BIE, Instituto Nacional de Estadstica y Geografa (INEGI)web site: http://dgcnesyp.inegi.gob.mx/

Best, B.R., Pilatowsky, F.I., Islas, S.J., Aceves H.J., Motta, M., Scoccia, R., 2010, MEXISCO:

feasibility studies of solar industrial refrigeration in the food and agro industry in

Mexico Politecnico diMilano, Centro de Investigacin en Energa, UNAM, final report.

Surface meteorology and Solar Energy: A renewable energy resource web site (release 6.0)

sponsored by NASA's Earth Science Enterprise Program web site:

http://eosweb.larc.nasa.gov/cgi-bin/sse/sse.cgi?

Trnsys user guide web site:http://www.trnsys.com

8. Acknowledgments

We knowledge the technical information support of: Lic. Ma. de Jess Prez Orozco.
http://www.energia.gob.mx/res/PE_y_DT/pub/Prospectiva_electricidad_2009-2024.pdfhttp://www.energia.gob.mx/res/PE_y_DT/pub/Prospectiva_electricidad_2009-2024.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2009/sam2009.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2009/sam2009.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2010/sam2010.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2010/sam2010.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2010/sam2010.pdfhttp://dgcnesyp.inegi.gob.mx/http://eosweb.larc.nasa.gov/cgi-bin/sse/sse.cgihttp://www.trnsys.com/http://www.trnsys.com/http://www.trnsys.com/http://www.trnsys.com/http://eosweb.larc.nasa.gov/cgi-bin/sse/sse.cgihttp://dgcnesyp.inegi.gob.mx/http://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2010/sam2010.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2010/sam2010.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2009/sam2009.pdfhttp://www.inegi.org.mx/prod_serv/contenidos/espanol/bvinegi/productos/integracion/sociodemografico/SAM/2009/sam2009.pdfhttp://www.energia.gob.mx/res/PE_y_DT/pub/Prospectiva_electricidad_2009-2024.pdf

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