Contemporary Urban Affairs 2017, Volume 1, Number 3, pages 7– 12 Experimental analysis of a flat plate solar collector with integrated latent heat thermal storage * Mauricio, Carmona1, Mario Palacio2, Arnold Martínez3 1 Mechanical Engineering Department, Universidad del Norte, Colombia 2 Faculty of Mechanical and Industrial Engineering, Universidad Pontificia Bolivariana, Colombia 3 Mechanical Engineering Department, Universidad de Córdoba, Colombia 1E mail: [email protected] , 2E mail: [email protected] A R T I C L E I N F O: A B S T R A C T Article history: In the present paper, an experimental analysis of a solar water heating collector with Received 2 August 2017 an integrated latent heat storage unit is presented. With the purpose to determine the Accepted 10 August 2017 performance of a device on a lab scale, but with commercial features, a flat plate Available online 12 October solar collector with phase change material (PCM) containers under the absorber 2017 plate was constructed and tested. PCM used was a commercial semi-refined light paraffin with a melting point of 60°C. Tests were carried out in outdoor conditions Keywords: from October 2016 to March 2017 starting at 7:00 AM until the collector does not Solar collector; transfer heat to the water after sunset. Performance variables as water inlet Thermal storage; temperature, outlet temperature, mass flow and solar radiation were measured in Latent heat storage. order to determine a useful heat and the collector efficiency. Furthermore, operating temperatures of the glass cover, air gap, absorber plate, and PCM containers are presented. Other external variables as ambient temperature, humidity and wind speed were measured with a weather station located next to the collector. The developed prototype reached an average thermal efficiency of 24.11% and a maximum outlet temperature of 50°C. Results indicate that the absorber plate reached the PCM This work is licensed under a melting point in few cases, this suggests that the use of a PCM with a lower melting Creative Commons Attribution - point could be a potential strategy to increase thermal storage. A thermal analysis NonCommercial - NoDerivs 4.0. and conclusions of the device performance are discussed. "CC-BY-NC-ND" CONTEMPORARY URBAN AFFAIRS (2017) 1(3), 7-12. https://doi.org/10.25034/ijcua.2018.36zd72 www.ijcua.com Copyright © 2017 Contemporary Urban Affairs. All rights reserved. 1. Introduction practical applications, latent heat storage Solar energy is the most widely available energy provides higher storage density, with narrow source in the world. However, it presents some temperature variation. (Abhat, 1983) reported obstacles to its implementation such as sensitivity one of the earliest reviews on latent heat thermal to climatic conditions and intermittency. storage. (Zalba et al., 2003) reviewed thermal Therefore, it is necessary to develop *Corresponding Author: technologies that allow storing solar energy for Mechanical Engineering Department, Universidad del Norte, the periods in which it is not available, or its Colombia power is low. Two common methods of storing E-mail address: [email protected] solar thermal energy are sensible and latent heat storage. While sensible heat is more common in JOURNAL OF CONTEMPORARY URBAN AFFAIRS, 1(3), 7-12 / 2017 energy storage with PCM and its heat transfer performed parametric studies of different analysis and applications. (Farid et al., 2004; operating conditions, concluding that as the Kenisarin and Mahkamov, 2007; Nkwetta and material melts, the heat transfer by convection Haghighat, 2014; Sharma et al., 2009) reviewed increases the speed of the accumulation solar energy storage using phase change process. (Koca et al., 2008) performed an materials. (Chandel and Agarwal, 2017) analysis of energy and exergy a latent heat Reviewed the current state of research on storage system with phase change material energy storage, toxicity, health hazards and (PCM) for a flat-plate solar collector. The commercialization of phase changing materials. obtained experimental data showed that exergy (Pandey and Chaurasiya, 2017) reviewed the efficiencies of latent heat storage systems with analysis and development of solar flat plate PCM are very low. However, the area of collectors. collector surface was smaller than that of the Although numerous works on latent heat PCM surface area. As a result of this, the cost of storage, no commercial solar heaters with built- the latent heat storage system was high and in PCM storage have been reported. However, outlet temperature obtained was low. (Bouadila preliminary studies in laboratory prototypes have et al., 2014) have developed an experimental shown considerable increases in efficiency and study on a solar flat plate water heater with an supply capacity. (Kürklü et al., 2002) found a accumulation of thermal energy in the collector large difference between ambient temperature using a PCM. Experimental measurements and water temperature both at day and at ascertain that the outlet temperature was not night. With the experimental techniques used, it affected by the severe global solar radiation was not possible to determine the phase change fluctuations. The solar collector remains a uniform point at least in a general approach. No useful heat around 400W during 5 h after sunset. performance comparison is made against (Serale et al., 2014) present an approach to traditional devices. However they showed that its increase the performance of flat collectors prototype has advantages in manufacturing based on the exploitation of the latent heat of cost and total weight for commercial devices, the heat carrier fluid. The aim of this paper is to although it does not include an energy analysis. analyze experimentally the performance of a In countries with tropical climates, no scientific lab-scale solar collector built with commercial references have been found in studies of this kind features and a latent heat storage unit inside it. of technology, in spite of the great capacity of available solar energy, quite possibly due to the 2. Method and materials lack of suitable commercial PCMs for this It was designed and constructed a flat plate application. (Mehling et al., 2003) presented solar collector prototype with a cavity to place experimental results and numerical simulation of macro-encapsulated PCM under the absorber a water tank with a PCM module using an explicit plate. A schematic representation of the finite-difference method. Experiments and prototype is shown in Fig. 1. Further details of the simulations indicated an increase in energy collector are presented in Fig. 2 and described in density of the tank of 20% to 45%. (Canbazoglu Table 1. et al., 2005) Analyzed experimentally the time The PCM was microencapsulated in 4 variations of the water temperatures at the rectangular steel containers of 4000 X 4000 X 30 midpoint of the heat storage tank of a solar mm. Each container was filled with 3.35 kg of heating system with sodium thiosulfate semi refined paraffin wax with a nominal melting pentahydrate as PCM. It was obtained an point between 58-60 °C. increase in the produced hot water mass and total heat accumulated approximately 2.59– 3.45 times of the conventional solar water- heating system. (Cabeza et al., 2006) constructed an experimental solar pilot plant to test the PCM behavior in real conditions. It was obtained a discharge temperature stabilization near to 54 1C for a period of time between 10 and 12 h. (Mettawee and Assassa, 2006) Figure 1. Schematic representation of the Solar Collector. Mauricio Carmona, Mario Palacio, Arnold Martínez 8 JOURNAL OF CONTEMPORARY URBAN AFFAIRS, 1(3), 7-12 / 2017 Figure. 1. Detailed view of the Solar Collector. Table 1. Detailed component description of the collector Item Description Specifications A Glass cover Thickness: 4 mm B Gasket -- C Air cavity case Thickness: 4 mm Aluminum D Absorber plate Thickness: 1 mm Copper E Inlet line pipe Diameter: 25.4 mm Copper F Plate Case Thickness: 4 mm Aluminum G Lockers -- H PCM Cavity Internal polyurethane insolation I Outlet line Diameter: 25.4 mm Copper J Absorber pipes Diameter: 12.7 mm Copper Separation: 100 mm The experimental set-up is shown in Error! every 5 minutes until the collector did not Reference source not found.. The water was increase water temperature after sunset. supplied by an Aqua Pak LOOP 3V32-9/1115 pump with a fixed volumetric flow rate of 0.2 L/min and monitored by a rotameter Dwyer of 1.2 L/min. A weather station Davis Vantage Pro 2 Plus measured ambient temperature, wind speed, humidity and global solar radiation. Temperatures of the glass cover, confined air, absorber plate, water inlet, water outlet and PCM containers were measured with type-K thermocouples connected to a data acquisition unit Applent AT4532. 8 temperature channels were located on the absorber plate, 2 on the Figure 3. Experimental bank: 1. Water reservoir, 2. Pump, 3. Rotameter, 4. Solar collector, 5. Data acquisition unit, 6. water inlet, 2 on the water outlet, 2 on the glass Water reception tank, 7. Weather station. cover, 2 measured the confined air temperature, 4 on the top of the PCM containers and 4 at the 3. Results & Discussion bottom. Results of accumulated radiation, useful heat The experimental tests were carried out in 3 and efficiency during the 60 days of experimental campaigns with 20 days each one. experimentation are presented in Figure 2 and The first campaign was performed in October summarized in Table 2. The highest efficiency of 2016, the second in December 2016 and the third the collector was obtained in tests carried out in in February 2017. All at the test took place in December while the lowest value during tests Universidad del Norte campus, in Barranquilla executed in October. As can be observed in Colombia (11°1'12.17"N,74°51'5.44"O). The test Table 2, while low efficiencies are found both in started at 7:00 AM monitoring all the variables rainy season with low radiation and clear season Mauricio Carmona, Mario Palacio, Arnold Martínez 9 JOURNAL OF CONTEMPORARY URBAN AFFAIRS, 1(3), 7-12 / 2017 with high radiation the highest efficiency values were obtained during medium radiation values. 8 40 ]y 7 35 a d /h 6 30 W k[ ygrenE deta 345 122505 ]%[ ycneiciffE lum 2 10 u c c 1 5 A 0 0 0 10 20 30 40 50 60 Day Acumulated radiation Useful Heat Efficiency day Figure 2. Experimental results by day. Table 2. Results of the tests and weather conditions. Days in Average Acc.rad Rad. Std. dev Average Exp. Campaign Weather Figure X [kWh/day] [kWh/day] Efficiency [%] Oct 01 - 20 Rainy 4.45 1.33 20.34 Dec 21 - 40 Scattered 5.22 0.41 27.44 Feb 41- 60 Clear 6.16 0.51 24.57 Total - 5.27 1.10 24.11 The following graphs present the behavior of the shows that the outlet temperature did not collector on March 12, 2017. Figure 3 and Figure decrease too much during the cloudiness events 4 shows respectively the solar radiation and wind of 11:00 and 15:00 which shows that the thermal speed measured by the weather station. This day energy storage system provides stability to the has a high incidence of solar radiation with an water supply. accumulated radiation of 5.27 kWh. Figure 5 1200 5 ]2^m 1000 ]s/m 4 /W[ noitaid 468000000 [ deepS d 23 ar ra 200 niW 1 lo 0 0 S 6 8 10 12 14 16 18 20 22 24 0 2 4 6 8 10 12 14 16 18 20 22 24 Time [H] Time [H] Figure 3. Solar radiation Figure 4. Wind speed Mauricio Carmona, Mario Palacio, Arnold Martínez 10 JOURNAL OF CONTEMPORARY URBAN AFFAIRS, 1(3), 7-12 / 2017 70 70 ]C 60 ]C 60 [ e 50 [ e 50 ru 40 ru 40 ta ta re 30 re 30 pm 20 pm 20 eT 10 eT 10 0 0 6 8 10 12 14 16 18 20 22 24 6 8 10 12 14 16 18 20 22 24 Time [H] Time [H] T.in T.out T.plate T.PCMU T.PCML T.amb Figure 5. Temperatures of absorber plate, water inlet, and Figure 6. PCM Temperature and ambient temperature water outlet 70 250 60 ]C 200 [ e 50 ]W ruta 40 [ xu 150 rep 30 lf ta 100 m 20 e eT 10 H 50 0 0 6 8 10 12 14 16 18 20 22 24 6 8 10 12 14 16 18 20 22 24 Time [H] Time [H] T.air T.glass Figure 7. Temperature of air gap and glass cover Figure 8. Useful Heat. It can be observed in Figure 6 that the PCM containers store heat energy by sensible heat 4. Conclusions until 14:00, from where the temperature at In this paper, an experimental analysis was container’s top (T.PCMU) remains at 60°C until carried out to evaluate the performance of a flat 16:00, indicating storage by latent heat. plate solar collector with integrated However, it should be noted in Figure 5 that the microencapsulated PCM as latent heat storage temperature of the absorber plate reaches the system. The highest efficiency of the prototype melting point of the PCM only for 2 hours, in many was obtained at accumulated radiation of 5.22 experimental tests the phase change kWh/day. Values above or below this amount of temperature is never reached. This gives a short radiation resulted in lower efficiency values. time to the PCM to accumulate energy by latent Asymmetric PCM charge/discharge process was heat resulting in a PCM discharging process at a observed. Therefore, reduce the PCM mass is non-constant temperature. On the other hand, it recommended to avoid upper layers discharge can be seen in Figure 6 an asymmetric thermal energy to lower layers instead of the charge/discharge process. Despite the proper absorber plate. It was obtained that the PCM charging process during the morning the storage modules provided stability to the outlet system was unable to provide thermal energy to temperature against strong fluctuations in solar the working fluid after 18:00 as can be seen in radiation. However, it was unable to supply Figure 8 This may be due to an excess of PCM in thermal energy to the working fluid during the the solar collector. In fact, Figure 6 shows that, night. The short time the absorber plate reached although the upper part of the PCM reaches the the melting point of the PCM may be a cause of phase change temperature, the lower part this. Thus, experimental analysis and simulation never reaches it and even its maximum with PCM with lower phase change temperature temperature is reached about 2 hours later. is recommended. Therefore, it can be inferred that during the night the molten PCM transfers heat to the solid PCM Acknowledgments layers instead of the working fluid. This investigation has been partially funded by the Colombian Administrative Department of Science, Technology, and Innovation- COLCIENCIAS, through the program “es Tiempo Mauricio Carmona, Mario Palacio, Arnold Martínez 11 JOURNAL OF CONTEMPORARY URBAN AFFAIRS, 1(3), 7-12 / 2017 de Volver”. Authors wish to express their storage system with phase change material acknowledgments to COLCIENCIAS and its for a solar collector. Renew. Energy, 33. excellent program. doi:10.1016/j.renene.2007.03.012 Kürklü, A., Özmerzi, A., Bilgin, S. (2002). Thermal References performance of water-phase change Abhat, A. (1983). 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