Experimental Results of a Solar Powered Cooling System

International Journal of Refrigeration 30 (2007) 1050e1058www.elsevier.com/locate/ijrefrig

Experimental results of a solar powered cooling systemat low temperature

Nolwenn Le Pierres*, Nathalie Mazet, Driss Stitou

Laboratory Processes, Materials and Solar Energy (PROMES) e CNRS, Rambla de la Thermodynamique,

Tecnosud, 66100 Perpignan, France

Received 4 September 2006; received in revised form 9 November 2006; accepted 4 January 2007

Available online 13 January 2007

Abstract

A solar thermochemical prototype producing low-temperature cold has been built and tested during the summer and autumn2005 in Perpignan, France. It cools a 560 L cold box down to about �25 �C using only low-grade heat produced by two simpleflat plate solar collectors. The process involves two cascaded thermochemical systems using BaCl2 salt reacting with ammonia.Its working mode is discontinuous, as it alternates between one decomposition mode at high pressure (daytime) and one coldproduction mode at low pressure (nighttime). Experimental results prove the feasibility of this new concept of solar cold pro-duction, with temperatures as low as �30 �C, demonstrate its potential use in housing, by the acceptable size and weight of thesystem and show the system performances during the sunniest months of the year, with a rough solar coefficient of performance(COP) of about 0.031 over the test period. The major meteorological parameters influencing the process efficiency are the solarirradiation and the outside temperature.� 2007 Elsevier Ltd and IIR. All rights reserved.

Keywords: Absorption system; Ammonia; Solution; Barium chloride; Solar energy; Experiment; Performance

Resultats experimentaux d’un systeme de refroidissementsolaire a basse temperature

Mots cles : Systeme a absorption ; Ammoniac ; Solution ; Chlorure de baryum ; Energie solaire ; Experimentation ; Performance

* Corresponding author. Tel.: þ33 4 79 44 45 58; fax: þ33 4 79

68 80 49.

E-mail address: [email protected] (N. Le Pierres).

0140-7007/$35.00 � 2007 Elsevier Ltd and IIR. All rights reserved.

doi:10.1016/j.ijrefrig.2007.01.002

1. Introduction

Solar coolers and refrigerators have been developed formore than 40 years using solid adsorption [1e3], liquid ab-sorption [4,5] or thermochemical reaction processes [6,7].These cold production systems require only heat as input en-ergy, thus they can be used in hot regions with no electricitysupply, for air conditioning or to store food or vaccines. Sim-ple flat plate solar collectors, single- or double-glazed, are

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1051N. Le Pierres et al. / International Journal of Refrigeration 30 (2007) 1050e1058

Nomenclature

A area (m2)C condenserCp specific heat (J kg�1 K�1)E evaporatorDH enthalpy variation (J mol�1)Isun solar irradiation (J m�2)kcin reaction kinetic coefficient (s�1)Dm mass variation (kg)M molar mass (kg mol�1)P pressure (Pa)R reactorR perfect gas constant (J mol�1 K�1)

DS entropy variation (J mol�1 K�1)T temperature (K)X advancement of the reaction

Subscriptsi reaction, evaporation or condensationcoll1/coll2 collector 1 or 2eq equilibriumevap evaporationout outsideop operatingr reaction

usually used to provide the heat at about 70 to 90 �C [8].However, the temperature of the heat source needed to sup-ply simple sorption systems increases when the cold tempera-ture decreases. Thus, to cool a cold box at deep-freezingtemperatures (lower than �18 �C), a heat source at morethan 120 �C is required [9]. Up to now, no solar deep-freezing device has been developed. Erhard et al. [4,10]reached temperatures as low as�10 �C with the NH3eSrCl2couple and a COP of 0.045e0.082 from a solar heat sourceat 100e120 �C. Best and Pilatowsky [11] present an absorp-tion NH3eH2O experiment in Mexico that allowed to reachtemperature as low as�40 �C with a COP between 0.15 and0.5 but from solar parabolic trough concentrating collectorsoperating at 180 �C. Complex and costly solar collectors arenecessary to produce heat at these temperatures. Then, thisproject aims at designing a sorption process producingcold for deep-freezing, and using only low grade solarheat from simple flat plate solar collectors (below 70 �C).This system has to be as cheap and easy to use as possible.The scope of this process would not include the cooling ofproducts introduced into the cold chamber at ambient tem-perature, but only the storage at deep-freezing temperatureover a long period of pre-cooled food or medicine products.The power delivered by the process should then be sufficientto cover the heat transfer through the walls of the chamber.

2. Description of the process

For simplicity and reliability, the refrigerant chosen wasammonia, as it allows operating over atmospheric pressureand is neutral with respect to the ozone-layer depletionand to the greenhouse effect. The solidegas reaction wasthe process chosen, as the solid sorbent bed can be locateddirectly inside the solar collectors. Moreover, such systemworks without any moving component (as a pump ora valve). Ammonia can react with various chloride salts[12]. The chosen salt was Barium Chloride (BaCl2), whichreacts following the reversible reaction:

BaCl2ðsÞ þ 8NH3ðgÞ241BaCl2ðNH3Þ8ðsÞ þ 8DHr ð1Þ

In direction 1, called synthesis, gaseous ammonia is fixedon BaCl2 salt. This chemical reaction is exothermic andreleases DHr. In direction 2, called decomposition, the saltreleases ammonia. This endothermic reaction needs the heatquantity DHr. The reaction advancement, X, represents thesalt percentage that has reacted with NH3.

The thermochemical cold production system associatesa solid/gas reaction (1) with a liquidegas phase change ofammonia. These two processes are monovariant. Their ther-modynamic equilibrium conditions follow the ClausiuseClapeyron equation (2) and are plotted in Fig. 1:

lnðPÞ ¼ �DHi

RTþ DSi

R ð2Þ

From an exergetic analysis of ideal cycles [13], the ther-modynamic process described in Fig. 1 was found to suit thesolar cold production application. It associates two ther-mally linked thermochemical systems. The two systems(primary (1) and secondary (2)) contain a reactor R, an evap-orator E and a condenser C. During daytime, the two reac-tors R1 and R2 are heated and decomposition can occur.Ammonia desorbed by the salt can condense in condensersC1 and C2, respectively, both at ambient temperature(w25 �C).

During night time, reactor R2 is cooled down to ambi-ent temperature. Synthesis happens in R2. Ammonia thenevaporates in evaporator E2, which is thermally linkedwith R1. E2 and R1 temperatures then decrease to about5 �C and �5 �C, respectively and R1 is then in synthesisconditions. Ammonia thus evaporates in E1 at very lowtemperatures, down to �33 �C. Evaporation of ammoniain E2 goes on during the whole night period. This evapo-ration maintains R1 temperature low enough for an effi-cient synthesis reaction and thus an efficient evaporationof ammonia in E1.

1052 N. Le Pierres et al. / International Journal of Refrigeration 30 (2007) 1050e1058

60°C

14 bar

BaCl2/ NH3NH3L/G

Ln(P)

-1/T 25°C

A) Day phase

Solar heat

Condensation at Tout

-33°C 5°C

1 bar

14 barBaCl2/ NH3

Ln(P)

-1/T -5°C 25°C

B) Night phase

Evaporation in E1

Reaction at Tout

Heat transfer

from R1 to E2

1 bar

NH3L/G

R1R2C2

C1

R2

E1 R1

E23.5 bar

NH3

NH3 NH3

NH3

equilibrium lineheat transfermass transfer

Fig. 1. The cascaded cycle during (A) the day and (B) the night phases in the ClausiuseClapeyron diagram.

3. Description of the prototype

3.1. Prototype components

The two collectors (respectively of 2 and 4 m2) are sim-ple flat plate solar collectors, single glazed (Figs. 2 and 3A).The glazing is an extra-clear 6-mm thick glass, with a trans-mission factor of 90%. The collectors contain the 89-mmdiameter and 1-m long reactor tubes (respectively, 8 and16 tubes for reactors 1 and 2), which are covered by anabsorbent coated copper Sunselect, with a solar absorbanceof 95% (Figs. 2B, C and 3A). These tubes are separated bya distance of 180 mm. The inter-tube space is also coveredby selective copper, linked to the tubes as presented inFig. 2B and C. The 89 mm tube diameter was the bestcompromise to enhance both heat and mass transfer in thereactor material, following previous research [14].

The sorbent salt BaCl2 (respectively, 41 and 82 moles forthe two reactors) is located in the reactor tubes. It is insertedin consolidated reactive blocks using expanded naturalgraphite as binder. This manufacturing mode was developedto improve heat and mass transfers in the thermochemicalreactors [15]. Three gas diffusers (diameter 8 mm) are addedin each reactor tube, to improve the gas transfer along thewhole length of the reactors [16].

Evaporator E2 is a smaller coaxial tube in reactor R1(Fig. 2C). Both collectors are insulated on the back side,as well as the lateral faces of collector 1. Collector 2 walls(top and bottom faces) can be opened during the night (hin Figs. 2A and 3A) to enhance the natural convection ofR2 in ambient air. These walls are closed during daytime,to block that convection. Moreover, R2 has fins on theback side, to improve the heat transfers when the walls areopen. The opening of the collector walls is insured by twosmall motors (Fig. 3A) which could be easily driven bya small photovoltaic module. For our prototype, the

irradiance threshold for the automatic opening of the wallsis 20 W/m2.

The condensers C1 and C2 are parallel fined tubes of,respectively, 9 and 24 m2, cooled by natural convection inambient air (Figs. 2A and 3B). They are situated in the shadeof the collectors. Evaporator E1 (5 m2 finned tubes) is locatedinside the cold box (CB). This 560 L box is insulated bya 15 cm thick high performance insulation (0.022 W/(m K)at 10 �C) and loses 1.4 W/K. When the cold box at �20 �Cis located in a room at 20 �C, its cold loss is thus 60 W.

This process does not involve any rotating piece or anyvalve. The system operating mode is thus autonomous, ro-bust and silent. The only moving components are four checkvalves in the secondary system (a, b and c Fig. 2A), that con-trol the ammonia flow inside that system [17]. Check valvesa and b open when the pressure difference between the twosides is higher than 0.3 bar. Check valve c opens when thepressure difference is higher than 0.05 bar.

3.2. Measurements

The prototype is instrumented with 57 thermocouples.Results given in the following are mean temperatures ofthe components (three thermocouples for E1, one for E2,four for R1, eight for R2, six for the fins and eight forCB). Thermocouples are placed on the wall of each compo-nent. Different probes are positioned on both sides of the re-actor tubes (front and back sides of the collectors) as shownin Fig. 2B and C. The thermocouples in the cold box are sit-uated in the cold box air, at various heights and distancesfrom the evaporator. Temperature measurements were testedand are accurate �1.5 K for each thermocouple.

A pyranometer (Fig. 3A) measures the global solarirradiation received in the plane of the solar collectors�10 W/m2. Three pressure transducers (Bourdon Haenni0e25 bar� 0.3%) are distributed between the two systems


Tank 2C2

R1

C1

Cold box

E1

Tank 1

R2

E2

ba

cg

f hd

Room in whichthe cold box isplaced

Roof

d

R2

fg

e

A

B

d

R1

g

e

C

E2

thermocouple level detectorPressure transducer

Fig. 2. (A) Schematic representation of the solar cooling prototype. (B) Details of collector 2. (C) Details of collector 1. (a, b and c, check

valves; d, collector glass; e, selective copper; f, fins; g, insulation; h, openable collector walls).

and two level detectors are located in the storage tank 1 andin E2 (Fig. 2A). Reactor 1 advancement X1 was calculatedthrough the ammonia level in storage tank 1. X1 relative errorwas estimated at 13.5%. Due to a positioning problem of thelevel detector in E2, accuracy of X2 was very low, with arelative error over 60%. X2 value was thus not used and isnot presented in this paper.

The measurement time step was 5 min from 24th May to28th July 2005, and 10 min from 9th September to 10thOctober. Fig. 4 shows the meteorological conditions, withmeasurement lacks in 20e22 July and 26e27 September dueto acquisition problems. This graph shows three differentperiods: before 17th June, relatively low ambient temperatures(w20 �C); then high temperatures until the end of July(w25 to 30 �C); the autumn measurements show low tem-peratures (w15 to 20 �C) and lower irradiations.

4. System operating mode

Experimental results for 3rd and 4th July are presented inFig. 5. The corresponding meteorological conditions arehighlighted in Fig. 4. The first day was warm and sunnyand the second cloudy and milder.

The evolution begins at sunrise. During the first hours(between 0 and 3 h), the advancement X1 increases, showingthe synthesis process happening in R1, while the two reactortemperatures increase due to solar irradiation. This paradox-ical behaviour is due to the positioning of the thermocouplesof the reactors, not inside the salt beds but on the reactorwalls. Hence, at the beginning of the heating up of the re-actors, the recorded temperatures increase faster than theaverage bed temperature.

Once the R1 and R2 temperatures reach about 50 �C,decomposition reactions begin. There is a plateau in thetemperature evolution, as the heat absorbed by the solarcollectors is mainly used by the endothermic decompositionprocess. The reaction in R1 is very fast, and once the ad-vancement reach about 0.2, the reaction rate decreases andR1 temperature rises again to over 130 �C. This slow-down in the reaction rate as X decreases is consistent withthe kinetic expression for decomposition processes [18]:

dX

dt¼ kcinX

Pop �Peq

Pop

ð3Þ

The temperature plateau is longer for reactor R2, due tothe lower efficiency of this collector, because of its poorer

Fig. 3. Photographs of the solar cooling prototype. (A) Front side. (B) Back side (h, openable collector walls).


thermal insulation: the closing of the collector walls duringdaytime blocks the main part of the convection between thereactor and the ambient air, but this closing is not completelyleak proof. Indeed, the fins temperature in collector 2 re-mains about 5 �C lower than the reactor temperature(0e8 h). R2 temperature plateau stops at about 8 h, showingthat the endothermic decomposition process is completed,on that day. The following irradiation induces a temperaturepeak of R2 (10 h).

During daytime (0e15 h), evaporator E2 is empty andheats up, as it is thermally linked to R1. E1 heats slowlyup from �23 to þ5 �C: this is the natural temperature evo-lution of the empty box with no cold production.

After about 8 h, the solar radiations decrease and afterabout 11 h, they become too low to counteract the collectors’heat losses. Thus, the reactors cool down progressively. Thiscooling changes the pressure conditions in the different parts

of system 2 and ammonia contained in tank 2 at ambienttemperature flows toward E2. Thus, E2 temperature de-creases strongly at 14 h, making the synthesis reaction beginin R1 (increase of X1), as the reaction heat can be transferredfrom R1 to E2.

The night phase begins at sunset (15 h) with the openingof the side walls of the secondary solar collector in order toenhance R2 cooling. Thus, there is an abrupt decrease of thefins temperature at 15 h, toward the ambient temperature.The salt in R2 begins to react with gaseous ammonia andthe reaction heat is rejected to the environment. Pressurethen decreases in system 2 and the evaporation rate of am-monia in E2 is enhanced. Consequently, reactor R1 iscooled, and the reaction heat of the exothermic synthesisin R1 is transferred to E2. R1 is thus cooled down belowthe ambient temperature, down to 10 �C (24 h). The synthe-sis reaction goes on in R1 (14e27 h) and X1 increases


0

5

10

15

20

25

30

35

24th

May

30th

May

5th Ju

ne

11th

June

17th

June

23th

June

29th

June

5th Ju

ly

11th

July

23th

July

17th

July

13th

Septem

ber

19th

Septem

ber

25th

Septem

ber

1st O

ctobe

r

7th O

ctobe

r

T (°C

)

0

5

10

15

20

25

30

Daily irrad

iatio

n (M

J/m

2)

Irradiation Tout night Tout day

July, 3rd/4th

Fig. 4. Meteorological conditions (daily irradiation, mean daily temperature and mean nightly temperature) during the measurement periods.

steeply, up to 0.65. E1 is cooled down to about �22 �C(26 h). Collector 2 fins approach the ambient temperatureduring the night, but remain higher, due to the heat transferfrom R2.

The second day evolutions are similar to the first one.However, that day presents worse weather conditions thanthe previous one. Thus, after about 6 h of decomposition(at 31 h), the reacting process stops, and X1 remains constantuntil the beginning of the following night. R1 and R2 tem-peratures remain between 50 and 60 �C during the wholeday, due to the lack of irradiation.

Then, the opening of the collector side walls at sunset(36 h) decreases steeply the fins’ temperature. As the ampli-tudes of reaction advancement are smaller during that night,a lower reaction heat is released by R2 and the fins and R2quickly reach the ambient temperature. Thus, R1 cooling(thanks to E2) is weaker and its temperature remains overthe ambient one (38 to 48 h). The cold box is cooled downto�10 �C during the night phase (38 h) and then its temper-ature stabilises, due to the low reaction rate in R1. E2 tem-perature seems to decrease more than the previous nightand reaches about �5 �C (40 h). This is due to the

-40

-20

0

20

40

60

80

100

120

140

160

0 10 15 20 25 30 35 40 45time from the sunrise of July 3rd, 2005 (h)

Tem

peratu

re (°C

)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1 Ad

van

cem

en

t X

(-) an

d irrad

iatio

n (kW

/m

2)

E2 R1 R2 E1 fins out X1 solar irradiation

DAY NIGHT DAY NIGHT

5

Fig. 5. Temperature and advancement evolutions of the solar cooling prototype on 3rd and 4th July 2005 and corresponding weather condi-

tions (ambient temperature and solar irradiation).


inadequate location of the thermocouple in the lowest part ofE2, where a small quantity of ammonia was accumulated.

These results thus show the possibility to produce cold atdeep freezing temperature from simple flat plate solar col-lectors. However, the cold box temperature also increasesover �18 �C and up to 5 �C during the day phase, thus theaim of maintaining deep-freezing temperatures in the cham-ber is not attained. Hence, the average temperature of theevaporator is e8.5 �C over these two days. This comesfrom the higher heat losses of the box than expected, dueto the introduction of the evaporator in the chamber and con-densation in the insulation material of the box during thetests. The chamber losses are then as high as 65 W as pre-sented before, whereas the cooling process was designedfor a 40 W heat loss. Consequently, the use of a phasechange material (PCM) to store the cold produced duringthe night could not be experienced. This cold storage willbe an essential component of a thermochemical deep-freezer. A phase change at �22 �C is planned to keep thecold chamber at a temperature lower than �18 �C. In thatcase, evaporation at lower than �25 �C would be neededand the average temperature of the evaporator would bedecreased compared to the presented experimental results.An improved box of lower volume and lower heat losseswill be built in order to improve these experimental results.

5. Performances and influences of the meteorologicalconditions

Fig. 6A shows the maximum temperatures reached by thetwo collectors during the 93 days of the measurement pe-riod. This curve illustrates the lower efficiency of collector2 compared to collector 1. Fig. 6B shows minimum temper-atures reached by E1 and by the air inside the cold box (CB)during the nights. The capability of the process to producedeep-freezing temperatures depends strongly on the solarirradiation. The lowest E1 temperature is �31 �C. E1 tem-peratures lower than �20 �C are obtained mainly when thesolar irradiation is higher than 18 MJ/(m2 day) and, overthe measurement period, during 72% of the nights. CB tem-perature is from 3 to 6 �C higher than E1, as could be ex-pected taking into account the low natural convection heattransfer and the cold box losses. This temperature will notbe further discussed, because of the CB problems expressedin the previous paragraph. The plot also shows average E1temperatures during the days. These average temperaturestake into account also the decomposition phase during whichno cold is produced. They reach e16 �C on some days, butthis is not sufficient for a deep-freezing purpose.

The rough solar coefficient of performance (COP) of thesolar system is defined as the ratio of the heat extracted byevaporation in the cold chamber (E1) to the solar irradiationreceived by the two solar collectors. It is calculated witha relative accuracy of 22% from the amount of ammoniaevaporated in E1 ðDmNH3

Þ according to the simplifiedformula:

COP¼DmNH3

�DHevap

MNH3

�CpNH3

�Tout� Tevap

��

ðAcoll1þAcoll2ÞIsun

ð4Þ

The average COP (total cold produced during all the ex-perimental periods divided by the corresponding total irradi-ation) is 0.031 over the 93 days of experiments. This is lower(about one-third) than the COP of other solar cold produc-tion systems but working at higher evaporation temperatureof about �10 �C [2e5,7,8,19,20].

For this deep freezing thermochemical system, the idealCOP is 0.23 [21]. It is defined as the ratio of cold produced byammonia evaporation in E1 in the ideal thermodynamic cy-cle to the heat required for salt regeneration (in R1 and R2).The experimental COP of 0.031 takes into account thedynamics of the process and the sensible heats of the salts,ammonia and inert components during the transient phases.The sensible heats of the reactive salt and fluid account foran important part of the COP decrease, as the COP valuetaking into account this parameter is 0.17 [21]. It also takesinto account the solar collector efficiency, that is the ratiobetween the heat transferred to the reactors to the input solarirradiation, and that is about 60% for flat plate solar collec-tors. However, it is likely that the present solar collectorsare less efficient than usual flat plate collectors, due to quitepoor thermal insulation of collector 2 and higher radiativelosses at the high collector temperatures reached.

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30daily irradiation (MJ/(m2.day))

T (°C

)

Tmax collector 1Tmax collector 2

-35

-30

-25

-20

-15

-10

-5

0

5


T (°C

)Tmin E1 nightT E1 averageTmin CB air night

A

B

Fig. 6. (A) Maximum collectors temperatures and (B) minimum

and average E1 and minimum cold box (CB) air daily temperatures

vs. daily irradiation during the 93 days of the measurement periods.


The daily cold quantity produced in E1 and the corre-sponding COP during the measurement periods are shownin Fig. 7. This figure as well as the following one presenta large scatter of data, due to an important number ofinter-related influencing parameters on the prototype func-tioning in real weather conditions. The following discussionwill try to enhance the influence of two of these meteorolog-ical parameters.

The cold production increases with the irradiation(Fig. 7), but in a non-linear way and thus the resultingCOP decreases. Indeed, when the daily solar irradiation islower than about 15 MJ/(m2 day), it is not sufficient to coverboth the heating of the collectors to over the decompositiontemperature and the reaction heat. Most of the irradiation isused to heat up the walls and the inert components of the re-actors. Thus, the cold production during the following nightis low. On the contrary, for high irradiation, once the ad-vancements X reach their minimal values (lower than 0.2),the reaction rates decrease, and the irradiation is then usedto heat up the inert reactor components to over the decompo-sition temperature (see temperature peaks at 10 h in Fig. 5).Moreover, at these high temperatures, the efficiency of thesolar collectors decreases.

Consequently, this process seems best optimised for a so-lar heat quantity of about 18e22 MJ/(m2 day): this quantityis high enough to allow an efficient decomposition and lowenough to avoid a too high temperature peak of the solar col-lectors and too many heat losses of the reactors. This sametype of influence was found by simulations for an experi-mental adsorption refrigerator [22], but the optimum radia-tion quantity was then found at 12 MJ/(m2 day) for thedesigned machine.

The influence of the outside temperature on the COP andthe cold temperature is shown in Fig. 8. To separate the in-fluence of the irradiation and of the temperature, the daysrepresented here are only the ones during which the irradia-tion was between 22 and 26 MJ/(m2 day). The most favour-able days are the coolest and the day or night temperatureshave the same influence on the COP: a decrease of about0.005 for a temperature increase of 10 �C. However, it is

0

1

2

3

4

5

6


CO

P*100

0

1000

2000

3000

4000

5000

6000 co

ld

p

ro

du

ced

in

E

1 (kJ)

cold producedCOP

Fig. 7. Daily cold production and rough solar COP of the solar

cooling prototype vs. daily irradiation.

difficult to separate the influence of the night temperatureand of the day one, as both are closely related, as shownin Fig. 4.

The increase in outside air temperatures lowers thesystem performances for three reasons:

- at night time, the high air temperature slows down R2cooling. Thus, time available for the synthesis reac-tions and the reaction rates are both reduced and thisprocess can be stopped before completion at sunrise.

- moreover, R2 synthesis temperature is high at night,thus increasing E2 and R1 temperatures. This, inturn, increases the boiling temperature in E1 andthus the cold box one. The minimum evaporatortemperature rises of 6.3 �C for an ambient temperatureincrease of 10 �C.

- during daytime, the high air temperature increases theammonia one in the air-cooled condensers. Thus, thereactor equilibrium temperature must also be higher.The solar collector efficiencies are reduced in theseconditions, thus the rough solar COP is also decreased.

6. Conclusion and outlooks

A new thermochemical process has been built and stud-ied at PROMES laboratory in Perpignan (South of France),to generate cold at low temperature (below �20 �C) fromlow grade heat produced by simple flat plate solar collectors.This process associates two cascaded thermochemical cy-cles working in parallel and using the BaCl2eNH3 reaction.

The experimental prototype reached evaporator tempera-tures as low as �30 �C using low temperature solar heat inthe range of 55e80 �C. Experiments showed the system per-formances during the sunniest months of the year, witha rough solar COP of about 0.031 over the three monthsmeasurement period. The efficiency of the process is mainlyinfluenced by the solar irradiation and the outside tempera-ture. However, the experimental cold box did not show

1,5

2

2,5

3

3,5

4

4,5

12 17 22 27T (°C)

CO

P*100

-35

-30

-25

-20

-15

-10

-5

0

Min

im

um

tem

peratu

re o

f E

1 (°C

)

COP = f(Tout) COP = f(Tout night) T E1 min

Fig. 8. Minimum E1 temperature vs. mean daily temperature (over

24 h) and rough solar COP vs. mean daily and nightly temperature

(measurements for days with an irradiation higher than 22 MJ/m2).


constant temperatures over the day, as this cold box showedhigher heat losses than the average cooling capacity of theprocess. Moreover, the average cold box temperature ishigher than �18 �C over the test period. Thus, this experi-ment is only a first step toward solar-powered deep-freezing.

Further work will be carried out by studying the systemevolution over a longer period and by considering the poten-tial use of other types of low grade heat (such as waste orgeothermal heat) as energy input for this process. Anotherpoint under study is the improvement of the cold box insu-lation and the use of a PCM in this box to ensure a low tem-perature over the whole day from a discontinuous coldproduction. This cold storage will also be necessary consid-ering the fluctuating solar irradiation received depending onthe weather conditions and on the season. A simulation workis also under progress to find the best compromise betweenan acceptable coverage of the chamber needs and an over-dimensioning of the process components.

Acknowledgement

This work was supported by the French governmentalAgency for Energy Management and Environment(ADEME) and the ‘ENERGIE’ program of the CNRSthrough the project PRI ‘Froid Solaire’ 6.1.

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Documents

Experimental Results of a Solar Powered Cooling System