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ORIGINAL ARTICLE Design and performance analysis of a small solar evaporative cooler Hossein Lotfizadeh it is clean silent renewable and climate friendly Solar systems pro vide a groundbreaking vision of a sun powered world Leggett 2009 Therefore solar energy can be harnessed in various levels around the world The development of solar cell technology begins with the research of French physicist Antoine Cesar Becquerel in 1839 According to Encyclopedia Britannica the first solar cell was built around 1883 by Charles Fritts who used junctions formed by coat ing selenium with an extremely thin layer of gold In 1941 the silicon solar cell was invented by Russell Ohl In 1954 three American researchers Gerald Pearson Calvin Fuller and Daryl Chapin designed a silicon cell that increased 6 energy conversion efficiency with direct sunlight and created the first solar panels Perlin 2004 The other scientists and engineers have subsequently followed previous methods of solar cells to improve them The evaporative cooling is a simple least energy intensive and environmentally benign technique of air conditioning ASHRAE 2003 An earlier form of air cooling was invented in Iran thousands of years ago in the forms of wind shafts on the roof Kheirabadi 1991 Before the advent of residential air condition ing it was the only mechanical means available to make home interiors livable in hot and dry summers Karpiscak and Marion 1991 With the advancement of technology different aspects of evaporative coolers have been studied and a lot of research articles are available which cover a number of significant features of these coolers Maclaine cross and Banks 1989 developed a comprehensive model for the wet surface heat exchanger which could be applied for a variety of evaporative coolers Dai and Sumathy 2002 investi gated a cross flow direct evaporative cooler in which the wet honeycomb paper constituted the packing material and the results revealed that there was an optimum length of the air channel and the perfor mance could represent an improvement on optimizing some operation features There are a lot of research works on applications of evaporative cooling in buildings Belarbi et al 2006 presented a model used for sizing passive evaporative cooling systems and towers for buildings utilizing the passive evaporative downdraught effect Bowman et al 1997 studied passive downdraught evaporative cooling PDEC for reducing energy consumption in hot dry climates A new EC Joule project explaining the application of PDEC in non domestic buildings was described Khandelwal et al 2011 investigated the potential of reducing the annual energy consump tion of a central air conditioned building through ad vanced evaporative cooling systems The building considered was a typical three floor library building of a university The well known building simulation software TRNSYS was used to carry out the heat load calculations and the dynamic simulations of the building HerreroMart n 2009 presented the experi mental study of a semi indirect evaporative cooler which acts as an energy recovery device in air condi tioning systems used for buildings Al Turki and Zaki 1991 studied the effect of intermittent spraying of a building s roof on the cooling load of the building The thermal response of the roof with intermittent stepwise spraying variation was modeled by introduc ing an equivalent fictitious temperature that accounts for meteorological conditions roof to sky radiation and evaporative effects during roof wetted period Costelloe and Finn 2007 presented the results of experimental research into the thermal effectiveness of a water side open indirect evaporative cooling test to achieve low 1 4 K approach conditions in the temperate maritime climate of northern Europe Jaber and Ajib 2011 designed indirect evaporative air con ditioning in order to reduce energy consumption with out negatively affecting the thermal comfort and in order to lower the imported oil bill on the national level and reducing the emission of harmful gases to the environment on the international level Many cooling systems have high electrical energy consumption and cause peak electricity loads This creates demands to build more power plants so they are responsible for increasing the average cost of elec tricity Santamouris and Asimakopoulos 2001 Schulz 2000 invented a new solar evaporative cooler retrofit kit to decrease the amount of electrical power supplied and the cost of operating such a common evaporative cooler Therefore the cooler utilizes the energy from sunlight which reduced the use of com mercially supplied energy In this paper the process of design manufacturing and performance analysis of a simple innovative direct current DC powered solar evaporative cooler is de scribed This cooler is proposed with the underlying aim of being solar compatible and environmentally friendly The cooler can be used for air cooling of a 56Energy Efficiency 2014 7 55 64 small room in a house or an office The cooler was tested in a specified room in order to evaluate its performance The air temperatures at different loca tions in the room was measured and compared during sequential days in the summer The results showed that performance of the cooler is relatively reasonable during the summer The proposed solar evaporative cooler Figure 1 shows the configuration of the solar evapo rative cooler It consists of eight parts aquarium pump 6 V DC water reservoir 40 40 cm2 conventional pads water distribution line computer fan 8 8 cm2 battery solar panel 10 W and solar control charger The main body of the cooler is made out of galvanized iron and has the volume 42 42 50 cm3 It is gener ally accepted that a beautiful design is one of the most important factors of manufacturing base so a wooden inlay covers the external area of the cooler s body to make it more preferable As shown in Fig 1 the cooler is located on a stool in order to be used in various situations Aquarium pump Water is used to soak the pads in the cooler while circulating It is widely believed that pumps are hearts of cooling systems The function of pumps is to cir culate water continuously To achieve this we needed an appropriate pump There are different sizes of pumps used in different evaporative coolers Since the lowest energy consumption was needed an aquar ium pump was chosen which worked on 6 V DC The aquarium pump was placed at the bottom of the cooler to pump water from the reservoir and circulated water while working To prevent clogging of the air it was put in a way to suck water continuously Thus a box made of rubber and full of water was installed to act as a damper and coped with the vibration of the pump As it can be seen in Fig 1 the pump was easily connected to the lower water reservoir by a hose Subsequently the output of the pump was connected to the distribution line to complete the operation of the pump Water reservoir Two water reservoirs were used in the cooler One was located at the top of the cooler which was responsible for water distribution by the holes that were made in it In order to divide water among pads in a careful and well organized way the holes were created by laser cutting machine Both of the water reservoirs were made out of Plexiglas because it is transparent light and it can be attached with glue immediately The other reservoir was located at the bottom of the cooler to collect the returning water The latter part was equipped with a ruler for measuring the water level and consumption while testing the cooler Since water was circulated during the tests in the reservoirs they were obliged to be hermetically sealed Therefore aquarium glue was used to seal different parts of water reservoirs Conventional pads These days cooler pads come in different shape and material that affect the performance and operation of Fig 1 Solar evaporative cooler Energy Efficiency 2014 7 55 6457 evaporative coolers Conventional pads have been used by different manufacturers since 1945 Essick 1945 The patent has helped designers to make their evaporative coolers more efficient In this research we have done a test on conventional pads in order to indicate how they can be adapted to the solar evapo rative cooler The tests started by a single conventional pad and then by two and three conventional pads that were put inside the cooler with equal distance of about 10 cm As shown in Fig 2 the former contained a single one that was located at the rear of the internal area of the cooler and the latter contained three pads Water distribution line A water line was used to connect the bottom water reservoir to the top water reservoir that was shown in Fig 1 It was a hose pipe which was well suited for completing the water cycle Since the water reservoirs were made of Plexiglas Mitreapel fast glue was cho sen to fasten it to the top water reservoir and the aquarium pump output Computer fan A computer fan is usually used to draw cooler air into the computer case and expels heated air from inside to keep the components within their safe operating tem perature limits Cooling the central processing unit became implemented into computers by 1997 Designers have tried to improve the operation of com puter fans to reduce the noise and energy consump tion Four computer fans 12 V 0 2A DC were installed at the front of the solar evaporative cooler As seen in Fig 1 the fans were placed in the same distance from each other to draw cool uniform air into the room The computer fans assisted us in taking full advantage of them to introduce the unique solar evap orative cooler Solar panel A solar cell directly converts the energy of the light into electrical energy through the process of photovol taic In the course of the years many scientists have tried their best to increase the efficiency of solar cells There are many types of solar cell technologies which are in development but some of them are most com monly used such as crystalline silicon thin films concentrators and thermophotovoltaic solar cell tech nologies AsshowninFig 3 thecrystallinesiliconpanel 10 W was used for the solar evaporative cooler which contained two layers positive layer and negative layer Positive layer exists on the top side whereas nega tive layer exists on the bottom Electric field is made by two layers which are responsible for producing electricity This electricity is transferred as DC in the panel The solar panel was located in front of the room s window to absorb direct sunlight Battery Batteries are the most important factors of solar electric systems that store power when the sun goes down As shown in Fig 4 a LEOCH lead acid battery DJW12 12 12 V 12AH was used for the solar electric system The battery stores energy when it is needed in particu lar on a day that there is no strong sunlight Solar charge controller A solar charge controller is needed in all solar power systemsthatutilizebatteries Theroleofthesolarcharge controller is to control the power going from the solar panels to the batteries The basic job of the solar charge controller is to regulate the battery voltage and to open the circuit stopping the charging when the battery voltage rises to a well defined level It is also used for preventing reverse current flow Thus it is an essential Fig 2 Schematic of the placement of a single b double and c triad pads in the evaporative cooler 58Energy Efficiency 2014 7 55 64 factor that completes a solar electric system Figure 4 shows the solar charge controller used for the cooler to regulate the battery voltage Solar evaporative cooler testing Evaporative coolers are generally classified according to the position of the cooler in relation to the building Typically there are three sorts 1 up draft ground mounted 2 side draft eave or window mounted and 3 downdraft roofmounted Inpresentresearch the second kind side draft was chosen for having a test on three forms of pads which include a single pad a dual pad and a triad pad Fig 2 In order to test the solar evaporative cooler and compare the experimen tal data with each other different temperatures were measured which consisted of T1 T2 T3 T4 Tin Tout and Twb T1 T2 T3 and T4 indicate the air tempera tures near top right bottom right top left and bottom left of every wall respectively Tin Tout and Twbshow the internal external and wet bulb temperatures of the cooler respectively which were used for calculat ing the cooler efficiency As shown in Fig 5 the cooler was put in the room 510 310 320 cm3 and in front of the window 310 335 cm2 Subsequently the walls of the room were numbered from 1 to 4 covered by insulation Every wall was divided into four thermal areas to measure the air tem perature distribution in the areas near the walls Figure 6 shows the schematic picture of the numbered walls of the room Thesolar evaporative coolerwas testedonthe same outside temperature and the same experimental hours when the sun was directly shining through the window It was important to ensure that the experimen tal data are accurate Thus the mentioned temperatures were measured meticulously in order to demonstrate the operation of the cooler properly Results and discussions Temperature changes The solar evaporative cooler was tested for every hour from 12 00 PM to 4 00 PM As mentioned earlier Fig 4 Picture of the charge controller used in the test Fig 3 Picture of the 10 W solar cell used in the solar evapora tive cooler Fig 5 Picture of the evaporative cooler installed in the room in front of the window Energy Efficiency 2014 7 55 6459 Fig 6 shows the numbered walls of the room First the air temperatures T1 T2 T3 and T4 near every wall were measured Digital thermom eters were mounted on the walls in the four men tioned areas The pictorial data below attempt to illustrate the air temperature changes near every wall for three forms of pads in order to show the differences among them Fig 7 The data of ev ery wall are shown separately Figures 8 9 and 10 show the air temperature changes near walls 2 4 during time respectively The same behavior can be seen in all cases As it can be seen in above diagrams the tempera tures increase from 12 00 PM to 3 00 PM After 3 00 PM the temperatures decrease One more point we would like to put forward is that a triad pad which was installed has a distinct effect on decreasing the tem peratures in comparison with a single pad and a dual pad It is easy to notice that the surface evaporation is nearly three times in the case of a triad pad which is responsible for diminishing the temperatures Water consumption In this research water consumption of the solar evapo rative cooler was also measured to compare the results Figure 11 shows water consumption from 12 00 PM to 4 00 PM As it is depicted in the diagram water con sumption rises from 12 00 PM to 3 00 PM and drops from 3 00 PM to 4 00 PM for the same reason discussed earlier Also it shows how much a triad pad increases water consumption in comparison with a sin gle pad and a dual pad It is clear that increased surface evaporation is the main reason behind the ascent Fig 6 Schematic picture of the room and its four numbered walls with respect to the window Fig 7 Air temperature changes near wall 1 60Energy Efficiency 2014 7 55 64 Thermodynamics of the evaporative cooling The experiment was done when the average air tem perature and the relative humidity of air were 37 5 C and 37 45 respectively As it can be seen in the above diagrams the cooler was able to cool air to within 5 4 7 9 C According to the first law of ther modynamics for an adiabatic saturation process Fig 8 Air temperature changes near wall 2 Fig 9 Air temperature changes near wall 3 Energy Efficiency 2014 7 55 6461 Fig 12 Sonntag et al 2003 ha1 w1hv1 w2 w1 hl2 ha2 w2hv2 1 The solar evaporative cooler efficiency The efficiency of an evaporative cooler can be calcu lated using the following equation Koca et al 1991 Al Sulaiman 2002 Gunhan et al 2007 Kittas et al 2001 efficiency Tin Tout Tin Twb 2 Where Tinand Toutdenote the inlet and outlet bulb temperatures of the air at the test section respectively and Twbis the wet bulb temperature The coolers saturation efficiency depends of course on the internal temperature Tin and the exter nal temperature Tout of the cooler As a result the temperatures are measured and put in the above equa tion As it can be seen in Fig 13 the cooler efficiency decreased from 12 00 PM to 4 00 PM due to increased temperature In addition as shown in Fig 13 the solar Fig 10 Air temperature changes near wall 4 12 00PM13 00PM14 00PM15 00PM16 00PM A single pad0 60 80 90 90 65 A dual pad1111 21 1 A triad pad1 21 31 41 51 35 0 0 2 0 4 0 6 0 8 1 1 2 1 4 1 6 Water consumption CC S Comparison of water consumption in the solar evaporative cooler Fig 11 Water consumption of single dual and triad pad solar evaporative coolersFig 12 Schematic of the evaporative cooling 62Energy Efficiency 2014 7 55 64 evaporative cooler has the maximum efficiency while using a triad pad Error analysis In this study error analysis refers to three items including temperatures water consumption and the effectiveness of the cooler To indicate the error analysis a method should be considered The mean of a set of numbers is defined as the sum of all the numbers divided by the number of them In mathe matical language if there are N in this paper N 5 observations and xirepresents any one of the obser vations then the arithmetic mean which we desig nate by the symbol x is given by Bevington and Keith 2003 x x1 x2 xN N 1 N X N i 1 xi 3 Awidely accepted quantitative measure of scatter is the sample standard deviation s For the special case where all data points have equal weight the sample standard deviation is defined by the following equa tion Barford 1967 s ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi PN i 1 x1 x 2 N 1 s 4 The standard deviations defined by the above equa tion provides t