report refrigeration

8/3/2019 Report Refrigeration

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INDEX

INTRODUCTION

REFRIGERATIONSOLAR REFRIGERATION CUM

WATER HEATER

Design And Construction

A solar ammonia absorption ICEMAKER

INTRODUCTIONWhile fossil fuels will be the main flues for thermal power,

there is a fear that will get exhausted eventually in thenext century. Therefore other system based on non-conventional and many countries are trying renewable


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source. These are solar, wind, sea, geothermal andbiomass.Solar energy can be major source of power; its potential is178 billion MW, which is about 20,000 times the worldsdemand. But so far it could not be developed on a large

scale. Suns energy can be utilized as thermal andphotovoltaic. The former is currently being used for steamand hot water production.Solar energy has the greatest potential of all the source ofrenewable energy and if only a small amount of this form ofenergy could be used, it will be one of the most importantsupplies of energy specially when other source in thecountry have depleted.The surface of the earth receives from the sun about 1014

kWof the

solar energy

, whichis approximately five orders ofmagnitude greater than currently being consumed from all

resources. It is evident that sun will last for 1011 years.Even though the sunlight is filtered by the atmosphere onesquare meter of there land exposed to direct sun light-receives the energy equivalent of about 1HP or 1kW. Thetechnical utilization of solar energy can prove very useful.Utilization of solar energy is great important to India sinceit lies in a temperature climate of the region of world wheresunlight is abundant for a major part of the year.The basic research in solar energy is being carried inuniversities and educational and research institutions,public sector institutions, Bharat Heavy Electrical Limitedand Central Electric Limited are carrying out a co-ordinatedprogramme of research in solar energy.The applications of the solar energy which are enjoyingmost success to-day are:

Heating and cooling of residential building.

Solar water heating.

Solar drying of agricultural and animal products.

Solar distillations on a small community scale.

Salt production by evaporation of seawater orinland brines.

Solar cookers.

Solar engine for water pumping.

Food refrigeration.

Bioconversion and wind energy, which areindirect, source of solar energy.

Solar furnaces.


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Solar electric power generation by-I. Solar ponds.

II. Steam generators heated by rotatingreflectors (heliostat mirror), or by towerconcept.

III. Reflectors with lenses and pipes for fluidcirculation(Cylindrical parabolic reflectors)

REFRIGERATION

Refrigeration is the cooling of a system below thetemperature if its surroundings.The melting of ice or snow was one of the earliest methodsof refrigeration and is still employed. Ice melts at 0 C. sowhen ice is placed in a given space warmer than 0 C, heatflows into the ice and the space is cooled or refrigerated.

The latent heat of fusion of ice is supplied from thesurroundings, and the ice changes its state from solid toliquid.The refrigeration done with the help of solar energy iscalled SOLAR REFRIGERATION. It is intended for foodpreservation and deserves top-priority in country like India.Solar air conditioning can be utilized for space cooling.Solar assisted heat pumps would provide both cooling andheating.

Cold storage is very important for preservation andconservation of food articles.There are two method of solar refrigeration.


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a. Vapour absorption refrigeration system thatutilizes low grade thermal energy obtained fromflat plate collectors with a little modification.

b. Concentrating collectors to supply heat at ahigher temperature to a heat engine

which then drive the compressor of aconventional refrigerator.Solar refrigeration with an absorption system is a better way of direct

utilization of energy. The vapour absorption system is a better

replacing the compressor by a generator absorber assembly system

can work with wide range of absorbents and refrigerants. In

absorption system motive power required is very small, but still

C.O.P. of the system is low.

SOLAR REFRIGERATION CUM WATERHEATER

SIMPLE SOLAR A DSORPTION REFRIGERATOR

Absorption systems give better C.O.P.

Adsorption system better for small capacity, less

control, easy

Fabrication.

Main components of solar Adsorption system

Solar collector, adsorrber/generator module/s, condenser and evaporator

Commercial units of solar Adsorption system

Activated carbon/methanol system manufactured by BLM Co France

The unit price of the 5.5 kg ice maker is US $ 1500, 30% more thanthe conventional vapour compression system

Zeolite/water system manufactured by Zeopower Co. of USA


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Advantage of Solar Adsorption Refrigerators

Energy saving using solar energy

Environmental Friendly: based on natural

Refrigerants: H2O,NH3, Methanol, CO2

Low maintenance cost

Simple to fabricate and operate

Drawback of Solar Adsorption Refrigerators

Low COP: high thermal mass, poor Thermal conductivity of the

Adsorbent

Smaller Specific Cooling Power: larger cycle time

Intermitted Cycle: cooling effect occurs only during

adsorption process

SOLAR ADSORPTION REFRIGERATORWith Heat Recovery

Performance Is Improved Using

Suitable adsorbent/adsorbate pairs

Optimum cycle with respect to operating conditions

Enhancing mass and heat transfer

Reducing cycle time

Mass Recovery with Pressure Equalization

Increases the cooling COP mostly by 10%


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Regeneration

COP 1.2 and SCP 300 W/kg of AC

COP 0.4 and SCP 290 W/kg of ACfor mobile air conditioningsystem

COP 1.35 and SCP 380 W/kg of ACfor gas fired heat pump

Convective Thermal Wave

Features and Design Parameters

Features

Solar Energy Heated Activated Carbon Bed Up to 180 C

Tap Water Preheating using Condenser Heat 36 C

Hot Water heating using Hot Module Heat Average 50 C

Zero Operating Cost

Environment Friendly

Design Parameters

Refrigeration Capacity, Qe160 W

Evaporator Temperature, Te-10 C

Condenser Water Inlet Temperature, Tcw.i28 C

Concentration Ration, CR 2.1

Solar Irradiation, It750 W/m2


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Temperature at Generator Outlet, Tg.o180 C

Temperature at Adsorber Outlet, Ta.o52 C

CONCLUSION

Solar Refrigerator cum Water Heater

Designing and Testing of 160 W Cooling Capacity Solar Refrigerator cum WaterHeater

Designed with evacuated glass tube of size 70 mm outer glass tube outer

diameter

Tested with evacuated glass tube of size 57 mm outer glass tube outer

diameter

Experimental Results for Data Dated on 27/05/2007, between 6:00 am and 4:30pm

Cycle time / number of cycle6:00 amto 4:30 pm/ 70 to 75 min

Evaporator temperature-7 C

Cycle COP, solar COP and0.11 to 0.15/ 0.054 to 0.072

SCP 8.5 to 28.5 W/kg of activated carbon


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Hot water capacity / bulk temperature over 120 l per day / 50 to 55 C

The Unit is Economically Viable

Generating two utilities together, reducing the pay back period by half

Environmental Friendly

Using solar energy, using natural refrigerant

Design and Construction of a Solar Energy RefrigerationSystem

Using Vacuum Concentric Tubes with Adsorption

Abstract

The R&D project that is envisioned here will consist in thephysical construction of a Solar Refrigeration System. The

theory, on which our design will be based, will be that ofusing an adsorption thermodynamic system based on theuse of an Activated Charcoal and Methanol as working fluid.The Solar collector will consist of a Vacuum ConcentricTubes (VCT)(Tubes that are actually in our position in theDom. Rep.) the refrigeration cycle will consist of a de-adsorption of the methanol during the heating period of thesolar radiation of the day. The vapor will condense andaccumulate as a liquid during this period. During the night

the process will invert and methanol will be absorbed bythe Activated Charcoal and evaporate, lowing its pressureand temperature, producing ice in a refrigerated isolated


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box. This box can be used as a refrigerated in remoteplaces. It is our intention to establish an R&D process inorder to fabricated a working commercial model that canproduce refrigeration plus hot water simultaneously.

Keywords: Solar Energy, Refrigeration and A/C, VacuumSolar Tube CollectorIntroductionThe Dominican Republic is at the present stage immersedin a critical situation due to the inability to satisfy theenergy needs of its people. It struggles day to day in orderto make the needed equilibrium between supply and

demand of its electric power in the utility grid. Costs ofproducing electric power from fossil fuels are to big aburden to the nation. Therefore it is our intention with thisR&D project to Adsorption cycles for solar cooling aredescribed and past work reviewed, but is our intention tobuild a refrigeration system that will work with solarenergy. Because of the fact that Vacuum Solar Tubes areavailable at economic values, it is our belief that due totheir high efficiencies we can make a difference fromprevious research work done in this subject. Zeolites havebeen used as adsorbents in many systems but this workconcentrates on activated charcoal adsorption.Refrigeration system that will work with solar energy.Because of the fact that Vacuum Solar Tubes are availableat economic values, it is our belief that due to their highefficiencies we can make a difference from previousresearch work done in this subject. Zeolite have been usedas adsorbents in many systems but this work concentrateson activated charcoal adsorption. of an underdevelopedcountry. Substitution of fossil fuels by solar energy is ourgoal in this segment of energy requirements, whichrepresent more then 60 % of the consumption. (AirConditioning, Refrigeration and water heating.)

RESEARCH AND DEVELOPMENT PROCEDURE

The process that will be executed in this project is dividedin three main sections. First, will be involved in theestablishment of the thermodynamic theory used for the

proper formulations and modeling, plus bibliographicsearch. Second, design of our prototype and selection andprocurement of materials. Third, Construction and


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experimentation of model, with all possible scenarios takeninto consideration. In all sections of this project, studentsof last year of Mechanical Engineering will be involved aspart of they thesis requirements. The University possessesmechanical engineering laboratories that can do all the

necessary works indoors. We have all machine shops andtolls needed in our Campus Oriental in Santo Domingo. Atthe present time, we have all the needed Solar VacuumTubes in our possession. These tubes were bought in China,and specifications are given further in this paper. Thecentral part of this R&D project is the use of the SolarVacuum Tubes. Supplier was: Xu Guangwen, COAST CORPLTD,

Section 1:THERMODYNAMIC CYCLE OF REFRIGERATION PROPOSED.

1. ADSORPTION CYCLES FOR SOLAR COOLING

Adsorption cycles for solar cooling are described andpast work reviewed, but is our intention to built arefrigeration system that will work with solar energy.Because of the fact that Vacuum Solar Tubes are

available at economic values, it is our belief that due totheir high efficiencies we can make a difference fromprevious research work done in this subject. Zeolite havebeen used as adsorbents in many systems, but this workconcentrates on activated charcoal adsorption

A general study of the cycle thermodynamics shows thatprovided the latent heat of the refrigerant exceeds about10(K) kJ/kg and the concentration change exceeds about

l0% then the coefficient of performance (COP) can only beslightly improved by further increase. Looking at activatedcharcoal in particular, the Dubinin- Astakhov (D--A)equation is used to predict cycle COPS based on limiteddata available for chosen refrigerants and carbons. Of therefrigerants that are sub atmospheric at 10C.Methanol, acetonitrile, methylamine, and NO2 are suitable,with methanol giving the best COP. Of the refrigerantsabove atmospheric pressure at l0oC, ammonia,

formaldehyde, and SO2 are suitable. Overall methanolgives the best COP, with 0.5 being achievable in a single-stage cycle. Insolation levels, and no firm electricity supplyto power conventional systems. The most promising Solar


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cooling could be a useful technology in areas of the worldwhere there is a demand for cooling; high applications arevaccine storage and food storage (particularly fish). Solarthermal systems for refrigeration have been studied forsome years, and many refrigerators built and tested.

Earlier work concentrated on intermittent absorption cyclessuch as the ammoniawater machines built Exell [1. 2] andVan Paasen [3]. More recently, solid adsorption cycles havebeen examined. These have the advantage of requiring norectifiers, valves, or liquid seals such as are needed in theammonia water cycle.The adsorption cycle is best understood with reference tothep-T-x(pressure-temperature concentration) diagram of

Fig. 1 and the schematic diagram of Fig. 2. The processesinvolved areas follows:

Figure 1.- p-T-x diagram of a Simple adsorption cycle

1. Starting in the morning with the valve open and atambient temperature of about 30 C (Ta2 the richconcentration adsorbent in the generator/absorber isheated by solar energy until the pressure reaches a levelthat enables refrigerant to desorbed and be condensedin an air or water cooled condenser.

2. Refrigerant is driven off at constant pressure, the

adsorbent becoming more and more dilute until the

maximum cycle temperature of about 100C (Tg2) is

reached. The condensed liquid is collected in a receiver.


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3. The valve is shut, and the adsorbent cools and reduces

its pressure. At some stage of the evening or night its

pressure will be the saturated vapor pressure of refrigerant

at -10C, (Te) which is sufficiently low for ice production.

4. The valve is now opened, and the liquid refrigerant

starts to boil in the evaporator. Initially the refrigerant

within the evaporator and receiver simply cools itself, but

having dropped below 0C it can start to freeze water.

Adsorption is completed by the following morning,

completing the cycle. During this process heat is released

in the absorber and so the generator/absorber must be

cooled be ambient temperature air or water.

This ideal cycle can be used to calculate Cops withreasonable accuracy, but in practice an isolating valve isnot necessary and processes c and dmerge into a smoothcurve and there are no sharp corners on the experimentalp-T-.vdiagram. The diagram used is essentially the samefor all adsorption cycles. Although silica gel has been usedin at least one closed-cycle refrigerating system, the vastmajority of experience is with Zeolite or activated carbons.Critoph and Vogel [8] compared Zeolite and active charcoalwith refrigerants R11. Rl2. R22, and R14 and in all casesfound charcoal a preferable adsorbent for solar cooling.Meunier et al. [7..-...L0] have compared synthetic Zeolite water, synthetic Zeolite methanol and charcoalmethanolCombinations. They find that activated charcoal-methanol gives a better COP

Generally but that when the nighttime ambienttemperature to evaporating temperature difference isparticularly high then a Zeolitewater combination isbetter. However, this will also require a higher generatingtemperature from the solar collector during the day.Meunier, comparing AC35-methanol with Zeolite 13X-water,suggests that the Zeolite combination will only be superiorwhen the temperature lift (adsorption-evaporatingtemperature) exceeds45C.


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Figure 2.- Schematic diagram of the simple adsorption

cycle.

The COP is based on heat input to the adsorbent ratherthan to the solar collector and so the reduced solarcollector efficiency at higher temperatures may actuallymake charcoalmethanol combinations superior at evenhigher temperature lifts.

There are other reasons for preferring charcoals:1. Activated charcoals are cheaper than Zeolite.

2. Activated charcoals can be made with properties to

suit particular applications by Varying the activationtime and temperature etc.

3. Activated charcoals (particular coconut shell charcoal

can be manufactured in the Dominican Republic.)

2. THERMODYNAMICS OF ADSORPTION CYCLES

Consider thep-T-xdiagram of Fig. 1. The varioustemperatures are: Ta1 = temperature at start ofadsorption, Ta2 = temperature at end of adsorption, Te =evaporatingTemperature, Tc = condensing temperature, Tg1 =temperature at start of generation, Tg2 = temperature at


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end of generation. Te depends on the application; airconditioning, ice making, deep freeze, etc. Tc is a heatrejection temperature andShould be as near to ambient as heat transfer andeconomics will allow. Ta2 should be as low as possible so

that the strong concentration is as high as possiblethismaximizes the concentration change in desorption, thusminimizing the quantity of charcoal that must be wastefullyheated and cooled with the adsorbed refrigerant. Ta2 isalso limited by ambient temperature and heat transferconsiderations. Although Ta2 is not necessarily equal to Tc(different heat exchangers may be used and the ambienttemperature may change between adsorption anddesorption) it is useful to consider the simple case where

they are equal.Both the pure refrigerant and the isosteres approximatelyobey Troutons rule, and assuming that the isosteres on theIn pv vs. 1/Tdiagram are indeed linear, it can shown thatTg1 Ta1= Tg2 Ta2.In the case of solar cooling, Ta2 might vary between 25oCand45C depending on ambient conditions, and Te couldvary between 20oC for cold storage to +5oC for airconditioning. A few possible combinations are listed withcalculated value of Tg1 in table 1.

The values ofTg2 are normally within 2 to 5oC of theresults for detailed calculations on specific pairs. Giventhat Tg1 is the temperature at the start of generation andthat in practice Tg2 will be at least 10C Given that Tg1 isthe temperature at the start of generation and that inpractice Tg2 will be at least 10C Given that Tg1 is thetemperature at the start of generation and that in

Application AmbientTemperature

Te oC Ta2 oC

Tg1 oC

Freezing Moderate -20 25 79Hot -20 45 126

Ice Making Moderate -10 25 65Hot -10 45 112

Air

Conditioning

Moderate -5 25 46

Hot -5 45 91


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practice Tg2 will be at least 10C and Adsorber should beas close to ambient as possible to avoid excessively highsolar collection temperatures. The assumption that Ta2 =Tc, is reasonable in many circumstances but may not betrue for a diurnal cycle in a climate with large diurnal

temperature variations. The maximum cycle temperatureTg2 is not fixed by the above relationships but is a designvariable that must be optimized. The higher Tg2., the morerefrigerant is driven off and so the greater the coolingeffect per Unit mass of adsorbent. However, progressivelyless refrigerant is desorbed as the temperature rises, andthe extra heat input is mainly used in sensible heating ofadsorbent and refrigerant, rather than in desorption.Considering the ideal case of an adsorbent with negligible

thermal mass and a refrigerant of negligible specific heatcompared to enthalpy of vaporization, then the COP =Enthalpy of vaporization (at Te) / Mean heat of adsorption.Taking a base ofTe = -10C, Tc = 30C, and Tg = 90C, thenthe ideal COP is 0.83. This may be compared with theCarnot COP of a similar cycle Te = - 10C, TA = 30C. Tg2 =9OoC which is 1.09. The difference is, of course, due to theconstant heat source and sink temperatures assumed inthe Carnot cycle. This is a new and useful limitation oncycle efficiencies specific to adsorption or adsorptioncycles.

When taking account of the sensible heating and cooling ofadsorbent and refrigerant, the COP is further reduced. Forany particular application. Te,, Tc,. And Ta2 are fixed, andTg1 and DH/L can be calculated. It can be seen that therefrigerant needs a high, and if possible a low cpR.Unfortunately. High latent heats tend to be associated withhigh specific heats and so a high specific heat must betolerated. The adsorbent should have as low a specific heatas possible, but its main requirement is that it gives a highconcentration change between Tg1 and Tg2The reasoning presented as a theory and postulate, will

provide a practical cycle COP with limitation lower than

that of pure calculations, but more specific information

must be provided to calculate the COPS. The objective of

our research project will be to construct with the VacuumTubes in our possession a working model and find the

parameters that will fit these equations.


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Section 2:

TUBULAR SOLAR ENERGY COLLECTORS

1.Solar Energy With Vacuum Tubes. Our Method Of

Choice.

Two general methods exist forsignificantly improving theperformance of solar collectors above theMinimum flat-plate collector level. The first methodincreases solar flux incident on the receiver; theSecond method involves the reduction of parasitic heat lossfrom the receiver surface, such as the TubularVacuum Solar Collectors. Tubular collectors, with theirinherently high compressive strength and

Resistance to implosion, afford the only practical means forcompletely eliminating convection losses bySurrounding the receiver with a vacuum on the order of 1O-4 mmHg. The analysis of evacuated tubularCollectors are the principal topic of this section.

3. Evacuated-Tube Collectors.Evacuated-tube devices have been proposed as efficientsolar energy collectors since the early 20th Century. In

1909, Emmett6 proposed several evacuated-tube conceptsfor solar energy collection, two of which are being soldcommercially today. Speyer2 also proposed a tubularevacuated flat-plate design for high-temperatureoperation. With the recent advances in vacuum technology,evacuated-tube collectors can be reliably mass-produced.Their high-temperature effectiveness is essential for theefficient operation of solar air-conditioning systems andprocess heat systems.

The level of evacuation required for suppression ofconvection and conduction can he calculated from basicheat-transfer theory. As the tubular collector is evacuated,reduction of heat loss first occurs because of the reductionof the Rayleigh number. The effect is proportional to thesquare root of density. When, the Rayleigh number isfurther reduced below the lower threshold for convection,the heat transfer mechanism is by conduction only. Formost gases the thermal conductivity is independent ofpressure if the mean free path is less than the heattransfer path length.4. Optical Analysis of the CTC. (Concentric Tube Collector)


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Since close packing of CTC tubes in an array can result inshading losses at any angle other than normal incidence, itis cost-effective to space the tubes apart and to use a backreflector in order to capture any radiation passing betweenthe tubes. Evacuatedtube designs and concentrating

designs should be closely packed to optimize solar energycollection. Beeklcy and Mather (ref) base analyzed the CTCin detail and their analysis is recommended for furtherstudies. CTC arrays can collect both direct and diffuseradiation. Each radiation component must be analyzed inturn.5. Thermal Analysis of the CTC

The heat loss from a CTC occurs primarily through themechanism of radiation from the absorber surface. The rateof heat loss per unit absorber area qL then can heexpressed as gl= uc(tr-tc) Total thermal resistance 1/Uc. isthe sum of three resistances:R1 radiative exchange fromabsorber tube to cover tube R2 conduction through glasstube R3___ convection and radiation to environment.The CTC energy delivery rate qu on an aperture area basiscan be written as whereAt, is the projected area of a tube(its diameter) andAris the receiver or absorber area. Thereceiver-to-collector aperture area ratio is pDr./d.

Qu =dr\d [earIeff-uc(tr-ta)]

5. Physical and Thermal Characteristics of the Evacuated-Tube Solar CollectorThe tubes that are actually in our possession have thefollowing characteristics: Tube is a new generation of sun-heat collect device withlow cost but high efficiency of solar thermal conversion. Tube is made of all-glass body and has the configurationof two concentric Borosilicate glass tubes, Inner glass tube(Absorber glass tube) and Outer glass tube (Cover glasstube). There is a selective absorbing surface on the outside ofinner glass tube (Absorber glass tube), this selective


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absorbing surface is based as a layer of aluminum-nitrogen,this aluminum-nitrogen layer was manufactured using aspecial coated surface by using the process of magnetronsputtering.

The jacket between cover (outer) and inner glass tubes isevacuated and permanently sealed off. These Tubes are widely utilized due to their highefficiency, low heat losses, long lifetime and low costs.Outside Diameter OD47 mm.

Specifications of Glass Vacuum Tubes:

Tube material: Borosilicate glass, Configuration: Twoconcentric tubes Length: 1.5 meters, Cover tube diameter:47mm Absorber tube diameter: 37mm Net weight of tube:1.4kgs of 1.5 meter. Tube wall thickness: 1.6mmTransmittance of cover tube: 91% Solar absorptance(AM1.5): 93%Emittance (80 c): 6% Pressure of vacuumspace: < 0.005Pa Stagnation temperature (typical): 200 c

degree Heat loss coefficient of tube: < 0.8W/m2.c Impactresistance: withstand 25mm diameter hailstone withoutbreaking glass strength (pressure tested): 1 Mpa Lifetime:15 - 20Years


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SOLAR AMMONIA ABSORPTION ICE MAKER

Everywhere in our world, refrigeration is a major energy user. In poor areas,

off grid

Refrigeration is a critically important need. Both of these considerations

Point the way toward refrigeration using renewable energy, as part of a

Sustainable way of life. Solar-powered refrigeration is a real and exciting

possibility

Working with the S.T.E.V.E.N. Foundation (Solar Technology and Energy for

Vital Economic Needs), we developed a simple ice making system-using

ammonia as a refrigerant. A prototype of this system is currently operating at

SIFAT (Servants in Faith and Technology), a leadership and technology

training center in Lineville, Alabama. An icemaker like this could be used to

refrigerate vaccines, meat, dairy products, or vegetables. We hope this

refrigeration system will be a cost-effective way to address the worldwide needfor refrigeration. This icemaker uses free solar energy, few moving parts, and

no batteries!

Types of Refrigeration

Refrigeration may seem complicated, but it can be reduced to a simple strategy:

By some means, coax a refrigerant, a material that evaporates and boils at a

low temperature, into a pure liquid state. Then, lets say you

Need some cold (thermodynamics would say you need to absorb some heat).Letting the refrigerant evaporate absorbs heat, just as your evaporating sweat

absorbs body heat on a hot summer day. Since refrigerants boil at a low


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temperature, they continue to evaporate profusely thus refrigerating even

when the milk or vaccines or whatever is already cool. Thats all there is

To it. The rest is details. One of these details is how the liquid refrigerant is

Produced. Mechanically driven refrigerators, such as typical electric kitchen

fridges, use a compressor to force the refrigerant Freon into a liquid state.

Heat-driven refrigerators, like propane-fueled units and our icemaker, boil therefrigerant out of an absorbent material and condense the gaseous refrigerant

to a liquid. This is called generation, and its very similar the way grain alcoholis purified through distillation.After the generation process, the liquefiedrefrigerant evaporates as it is re-absorbed by an absorbent material. Absorbentmaterials are materials, which have a strong chemical attraction for therefrigerantthe way grain alcohol is purified through distillation.After the

generation process, the liquefied refrigerant evaporates as it is re-absorbed by anabsorbent material. Absorbent materials are materials, which have a strongchemical attraction for the refrigerant.

This process can be clarified using an analogy: it is like squeezing out a sponge

(the absorbent material) soaked with the refrigerant. Instead of actually

squeezing the sponge, heat is used. Then, when the sponge cools and becomes

thirsty again, it reabsorbs the refrigerant in gas form. As it is absorbed, the

Refrigerant evaporates and absorbs heat: refrigeration!

In an ammonia absorption refrigerator, ammonia is the refrigerant.

Continuously cycling ammonia refrigerators, such as commercial propane-

fueled systems, generally use water as the absorbent, and provide continuouscooling action.

The S.T.E.V.E.N. Solar Icemaker We calls our current design an icemaker. Its

not a true refrigerator because the refrigeration happens in intermittent cycles,

which fit the cycle of available solar energy from day to night. Intermittent

absorption systems can use a salt instead of water as the absorbent material.

This has distinct advantages in that the salt doesnt evaporate with the

Water during heating, a problem encountered with water as the absorber.

Our intermittent absorption solar icemaker uses calcium chloride salt as the

absorber and pure ammonia as the refrigerant. These materials are

comparatively easy to obtain. Ammonia is available on order from gas suppliers

and calcium chloride can be bought in the winter as an ice melter.

The plumbing of the icemaker can be divided into three parts: a generator for

heating the salt-ammonia mixture, a condenser coil, and an evaporator, where

distilled ammonia collects during generation. Ammonia flows back and forth

between the generator and evaporator.

The generator is a three-inch non-galvanized steel pipe positioned at the focus

of a parabolic trough collector. The generator is oriented east-west, so that only


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Seasonal and not daily tracking of the collector is seasonal and not daily

tracking of the collector is required. During construction, calcium chloride is

Placed in the generator, which is then capped closed. Pure (anhydrous)

ammonia obtained in a pressurized tank is allowed to evaporate through a

valve into the generator and is absorbed by the salt molecules, forming a

calcium chloride-ammonia solution (CaCl2 -8NH3).

The generator is connected to a condenser made from a coiled 21-foot length of

non-galvanized, quarter-inch pipe (rated at 2000 psi). The coil is immersed in a

water bath for cooling. The condenser pipe descends to the

evaporator/collecting tank, situated in an insulated box where ice is produced.

Operation

The icemaker operates in a day/night cycle, generating distilled ammonia

during the daytime and reabsorbing it at night. Ammonia boils out of the

generator as a hot gas at about 200-psi pressure. The gas condenses in thecondenser coil and drips down into the storage tank where, ideally, 3/4 of the

absorbed ammonia collects by the end of the day (at 250 degrees Fahrenheit, six

of the eight ammonia molecules bound to each salt molecule are available).

As the generator cools, the night cycle begins. The calcium chloride reabsorbs

ammonia gas, pulling it back through the condenser coil as it evaporates out of

The tank in the insulated box. The evaporation of the ammonia removes large

quantities of heat from the collector tank and the water surrounding it. How

much heat a given refrigerant will absorb depends on its heat ofvaporization, the amount of energy required to evaporate a certain amount

of that refrigerant. Few materials come close to the heat of vaporization of

water. We lucky humans get to use water as our evaporative refrigerant in

sweat. Ammonia comes close with a heat of vaporization 3/5 that of water.

During the night cycle, all of the liquefied ammonia evaporates from the tank.

Water in bags around the tank turns to ice. In the morning the ice is removed

and replaced with new water for the next cycle. The ice harvesting and water

replacement are the only tasks of the operator. The ice can either be sold as aCommercial product, or used in a cooler or old-style icebox refrigerator.

Under good sun, the collector gathers enough energy to complete a generating

cycle in far less than a day, about three hours. This allows the icemaker to work

Well on hazy or partly cloudy days. Once generating has finished, the collector

can be covered from the sun. The generator will cool enough to induce the night

cycle and start the ice making process during the day.

Future Design

A refrigerator, which is able to absorb heat at any time from its contents, is

more convenient than our current intermittent icemaker. To enable constant


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operation, a future design will include several generator pipes in staggered

operation as well as a reservoir for distilled ammonia. Staggered operation will

allow the refrigerator to always have one or more of the generators thirsty

and ready to absorb ammonia, even during the day when generation is

simultaneously happening. Generation will constantly replenish the supply of

ammonia in the storage reservoir. We are currently in the first stages of makingthese modifications to the icemaker.

Solar Ice Maker: Materials and Costs

Quan. Material Cost4 Sheets galvanized metal, 26 ga. $1001 3" Black Iron Pipe, 21' length $75120 Sq. Ft. Mirror Plastic @$0.50/sq. ft. $602 1/4" Stainless Steel Valves $50

Evaporator/Tank (4" pipe) $40Freezer Box (free if scavenged) $40

1 Sheet 3/4" plywood $206 2x4s, 10 ft long $20

Miscellaneous 1/4" plumbing $202 3" caps $151 1/4" Black Iron Pipe, 21' length $154 78" long 1.5" angle iron supports $15

Other hardware $1515 Lbs. Ammonia @ $1/lb $1510 Lbs. Calcium Chloride @ $1/lb $10

Total $510

Caution: Safety First!

Working with pure ammonia can be dangerous if safety precautions are not

taken. Pure ammonia is poisonous if inhaled in high enough concentrations,

causing burning eyes, nose, and throat, blindness, and worse. Since water


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combines readily with ammonia, a supply of water (garden hose or other)

should always be on hand in the event of a large leak. Our current unit is a

Prototype. We will not place it inside a dwelling until certain of its safety.

Unlike some poisonous gases, ammonia has the advantage that the tiniest

amount is readily detectable by its strong odor. It doesnt sneak up on you!

For the longevity of the system, materials in contact with ammonia in the

icemaker must resist corrosion. Our unit is built with non-galvanized steel

plumbing and stainless steel valves, since these two metals are not corroded by

ammonia. In addition, during operation the pressure in the system can go over

200 psi. All the plumbing must be able to withstand these pressures without

leaks or ruptures.

Would-be solar icemaker builders are cautioned to seek technical assistance

when experimenting with ammonia absorption systems.

Conclusion

The S.T.E.V.E.N. icemaker has both advantages and disadvantages. On the

down side, its somewhat bulky and non-portable, and requires some special

plumbing parts. It requires a poisonous gas, albeit one, which is eco-, and

ozone- friendly in low concentrations, so precautions must be taken. In itsfavor, it has few moving parts to wear out and is simple to operate. It takes

advantage of the natural day/night cycle of solar energy, and eliminates the

need for batteries, storing solar cold in the form of ice.


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Solar Chill - a solar PV refrigerator without battery

Introduction

A solar powered refrigerator (Solar Chill) has been developed in an

international project involving Green peace International, GTZ, UNICEF,

UNEP, WHO, industrial partners and Danish Technological Institute. The

refrigerator is able to operate directly on solar PV panels, without battery or

additional electronics, and is therefore suitable for locations where little

maintenance and reliable operation is mandatory. The main objective of the

Solar Chill Project is to help deliver vaccines and refrigeration to the rural

poor. To achieve this objective, the Solar Chill Project developed and plans

to make freely available a versatile refrigeration technology that is

environmentally sound, technologically reliable, and affordable. Solar Chill

does not use any fluorocarbons in its cooling system or in the insulation.For domestic and small business applications, another type of solar refrigerator

is under development. This is an upright type, suitable for cool storage of food

and beverages in areas where grid power is non-existent or unstable. The

market potential for this type is thus present in industrialized countries as well

as in countries under development.

The unique feature of Solar Chill is that energy is stored in ice instead of in

batteries. An ice compartment keeps the cabinet at desired temperatures

during the night. Solar Chill is made from mass produced standard

components, which results in a favorable cost compared with other vaccinesolar refrigerators.

The Solar Chill has undergone intensive laboratory tests in Denmark, proving

that it fulfils the objectives set for the project. In addition, a field test


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programmed in three different developing countries is ongoing with the aim to

gather practical experience from health clinics.

The paper describes the product development, possible Solar Chill applications

and experience with the two types of solar refrigerators, as well as results from

the laboratory and field test.

Background

A developing project funded by the Danish Energy Agency and conducted by

the Danish Technological Institute started in 1999 in co-operation with Dan

Foss Compressors, Vest frost and other Danish companies. The aim was to

develop a photovoltaic powered vaccine cooler without battery back up. Instead

energy storage of ice should keep the temperature stable during nights and

periods without sunshine.

In parallel to that discussions were held at various times (starting in 1998-99)

between UNEP, WHO, Green peace and GTZ with the objective to promote

environmentally sound refrigerators. The idea to bring all these interested

parties together arose at a refrigeration summit in Chicago in November 2000,

which then led to a common meeting at GTZ headquarters in 2001. This

resulted in an international project with the aim to develop, test, and use

environmental sound, affordable and reliable photovoltaic powered vaccine

cooler.

The Solar Chill project is a unique partnership among key international

agencies, research and industry bodies. The Project Partners and their main

respective roles are:

Green peace International provides project coordination and fundraising;

GTZ Proklima provides technology advice and assessment and fund raising;

United Nations Children's Fund provides need analysis and technology advice

and assessment;

United Nations Environment Programmed provides overall technologyassessment and policy advice;

World Health Organization provides equipment specifications and technology

advice and assessment

Program for Appropriate Technology in Health provides technology advice

and conducts field test

Industry partners: Vest frosts, Vibocold, Dan Foss, Gaia Solar providehardware

Danish Technological Institute coordinates the technology development;


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The basic technology

The main task has been to develop a new cooler, which fulfill the current WHO

requirements for vaccine coolers with battery back up, as no standard exist

for the battery less type. According to these guidelines the design temperatureinterval is 0 C to + 8 C. The vaccine must also be kept cool for four days

without power, and this is the sizing

Fig. 1 Diagram of the first Solar Chill prototype

Criteria for the ice storage in the cooler. Computer simulation was done based

on the most efficient mass-produced cabinets on the market. Those cabinets has

100 mm polyurethane insulation and are of the chest type.

The reason for choosing energy storage in ice was to avoid a lead battery for

energy storage. Lead batteries tend to deteriorate, especially in hot climates, or

they are misused for other purposes. This makes it necessary to install a new

battery after a couple of years, and has in practice been an obstacle for the use

of solar powered refrigerators. In addition to that some pollution of lead might

be expected from the batteries.Instead kerosene or gas powered absorption refrigerated coolers are widely

used in areas with poor or no grid electricity. Absorption coolers are used for


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both vaccine storage and for household applications and obviously needs

regular supply of fuel. Furthermore, they are difficult to adjust, which does

often result in destructive freezing of the medicine.

So far, two generations of prototypes have been build and tested in climate

chamber at the DTI and an advanced control were build with the purpose to

control the temperature in the cooler and the speed of the DC-compressor inorder to exploit maximum power from the solar panels.

Specific energy of ice storage

A simple calculation shows the interesting result, that the cooling capacity in

the ice storage is at similar level as in a lead battery based on both volume and

weight.

One supplier of lead battery informs, that a 50 Ah, 12 Volts battery has the

weight of 13,6 kg. The dimensions are 0.24*0.175*0.175 meters. The energy

content of 50 Ah can be calculated as a specific energy content of 0.159 MJ/kg

or 294 MJ/m3.

The cooling system will have a COP-value (coefficient of performance) of about

1.3 (Dan Foss BD35F, CECOMAF-data for 15 C, 2000 RPM). This will result

in a specific cooling capacity of 0.206 MJ/kg or 382 MJ/m3. For the ice storage:

the specific cooling capacity is identical to the melting heat of ice, which is 0.333

MJ/kg or 333 MJ/m3.

The conclusion is, that the specific cooling capacity of ice is 62 % higher

compared to lead battery on basis of weight and 13 % smaller compared withlead battery based on volume. In reality, the ice storage outperforms the lead-

acid battery, because the allowed daily cycling is less than the nominal 50 Ah,

which corresponds to 100% depth of discharge.

Compressor and control

The first prototypes were equipped with a standard Dan Foss BD35F direct

current compressor and an external electronic control. A big electrical

capacitor (60 mF) was used in order to overcome the start torque.During 2003 a quite new compressor BD35K became available. The new

compressor is using R600a (isobutane), which does not contribute to the

greenhouse effect. A new integrated electronic control was also available. This

control has been developed to ensure that photovoltaric solar panels can be

connected directly to the compressor without an external control and/or

capacitor. The compressor is able to do a smooth start at low speed and is

equipped with an adaptive energy optimizer (AEO-control). By using this

control, the compressor will slowly speed up from minimum to maximum speed

(from 2000 to 3500 RPM). If the panels cannot give sufficient power, thecompressor will stop and after a short while it will try to start again. If the start

fails, the compressor will try to start again afteranother one minute. Once the

power from the solar panels is sufficient, the compressor will start at low speed


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and slowly speed up again. The controller accepts a voltage between 10 and 45

Volts. The voltage from solar panels can vary, so this new feature is good for

solar powered refrigerators and freezers. On a 12 V module, the compressor

needs a current of about 4,5 A to start, and it can run continuously at 2 A.

System Storage BOS componentsNormal solar refrigerator Battery Cable, charge regulator,

blocking diode

Solar chill Ice packs Cable(with plugs)

Cabinets

The vaccine cooler cabinet was build by Vest frost, and is based on a highly

insulated standard cabinet. The net volume of the vaccine compartment is

about 50 liters and is separated from the ice storage of about 18 kg, made by a

number of standard plastic containers. The evaporator is integrated into the icestorage end during daytime forced convection is cooling the vaccine. If the

temperature in the vaccine compartment gets to cold during daytime, a small

electrical heating element is keeping the vaccine above freezing temperature. A

thermostat controls the heater. During nighttime the vaccine is kept cool by

natural convection from the ice department.

Photo1: Prototype of vaccine cooler. The vaccine will be placed in three baskets,placed vertical in the left side of the cabinet. The ice storage is placed under the

blue lid in the right side of the photo. The compressor is placed in a room under

the ice.


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Laboratory test results

The vaccine cooler has been tested in climate chamber at DTI. The holdover

time for the vaccine cooler was measured to be about four days at 32 C

ambient temperatures. For the upright version, the holdover time is one day

less due to the geometry and smaller ice volume. The tests have been used to

determine the necessary PV panel size for the selected locations. As the critical

parameter is the minimum current for start of the compressor, it was decided

to use a panel with a short circuit current of 2.5 times the start current. In this

way it is ensured that the compressor will also start at most overcast days, but

the economical optimum may be found at a smaller panel size.

Field trial

In January-February 2004 9 coolers were shipped from Unicef in Copenhagen

(3 to Senegal, 3 to Indonesia and 3 to Cuba) and they are expected to reach

their destinations in March 2004 where after they will be installed and the field

test will begin. One additional cooler has been installed at DTI for field test,

which began in February 2004. Each unit is packed with 3x60 W solar PV

panels and has data loggers integrated for evaluation of the operating

conditions.

For the unit installed at DTI there are now sufficient data to conclude that the

operation under real solar conditions ensures an inside temperature within thedesired range (at an ambient temperature of 20C).There have been sunny and

less sunny periods, but from the figures below it can be seen that the

temperature becomes rather stable after a period of freeze-in.


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Fig.5 After freeze in the temperature inside the vaccine compartment is kept

within the design range 0-8 oC. Tamb = 20oC

Conclusion and perspectives

The Solar Chill has been developed in a fruitful co-operation between leading

appliance manufacturers and international organizations, setting the desired

properties of the product. It has been proven that it is fully possible to run a

solar refrigerator without battery or start capacitor, both elements that would

decrease the reliability. This opens up for a more general acceptance and

dissemination of solar refrigeration, not only in the health sector, but also for

commercial or domestic use. Some obvious future applications for this product

could be milk chilling, vending booths for food and beverages, recreational

purposes or as a grid independent household refrigerator.

Even after an expected WHO approval, there is still basis for optimization, such

as:

- Minimization of the module area for specific climatic regions

- Optimization of the control strategy in order to minimize the needed PV-power

- Further simplification and cost reduction of the construction

The authors sincerely wish to thank the sponsors and project partners for their

very constructive assistance and participation in this project.


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report refrigeration

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