Application of Soy Wax Phase Change Material as Thermal Energy Storage in Wall Building

High solar radiation in the tropics area buildings and inappropriate selection of building materials cause an increase in room temperature which interferes with thermal comfort. This study aims to reduce the absorption of heat received in the building with the modification of building walls by adding Phase Change Material (PCM) as Thermal Energy Storage (TES). Soy wax is an organic PCM that is abundant in Indonesia, cheap, and has a melting point of 43.92°C and a freezing point of 38.49°C, which are the range of solar heat radiation in buildings. The application of soy wax on the walls of the building is carried out using a prototype room 80x105x60 cm made of Plywood with a 1 cm thickness of soy wax in the middle of the wall. The test was carried out by comparing the prototype without and with a layer of soy wax pack on the wall. Based on the tests carried out for 24 hours, it was found that the addition of soy wax on the prototype wall can decrease the room temperature to 37°C from 41°C during the day. The use of soy wax can absorb the heat received by the building by 10% at peak load and has a small heat transfer rate of 15.56 W so the heat transferred into the room is small. Soy wax walls function as insulators on the walls and can withstand heat absorbed from outside the building so that it is not completely transferred into the room.


Introduction
The building sector is one of the high-energy users of the air conditioning process, especially in tropical areas that receive high solar heat intensity.Solar radiation is the main contributor to heat gain in buildings, especially residential buildings [1].The effect of the high intensity of solar heat received by the building is the temperature in the room increases and also increases the performance of the air conditioning system to maintain thermal comfort in the room [2].Apart from the use of the HVAC system, the material used in the building is also an important factor so that the heat received by the building is not fully transferred into the room.Error selection of building materials, especially nonappropriate walls, can cause the condition of the room to get hotter because most of the heat is transferred and increase the use of HVAC.Hebel is currently widely used as a building wall in Indonesia which has a mismatch when viewed from its constituent materials designed for buildings in the European region.Due to its cheap and ease of installation, many contractors choose Hebel for the construction of buildings.However, it is not realized that the material mismatch will have a long-term impact after the building is completed, namely an increase in room temperature.Therefore, apart from managing the HVAC system, the determination of building materials is important for energy efficiency systems in buildings [3].
Phase Change Material (PCM) as Thermal Energy Storage (TES) is one solution that is widely studied for reducing heat adsorption in buildings [4].The use of PCM can minimize peak cooling loads, allow the use of smaller Heating, Ventilation, and Air Conditioning (HVAC) technical equipment for cooling, and can keep indoor temperatures within a comfortable range due to smaller indoor temperature fluctuations [5].Design development and technical improvement are needed in PCM technology and application systems.The important parameter of PCM before it will be applied is the thermo-physical nature, which has a direct impact on the thermal test dynamics and has an impact on the temperature profile and space condition.Identification of PCM application design parameters is the main key to applying tests efficiently [6][7][8].Until now many researchers are interested in doing PCM applications in buildings to store excessive thermal energy received by buildings and to reduce the use of HVAC.Laaouatni et al. 2016 also used PCM material to achieve optimal walls made of concrete blocks filled with PCM and ventilated tubes.The experimental results showed that paraffin insertion was able to maintain the thermal increase [9].Sakia et al. 2018 use PCM incorporation on concrete walls can reduce the increase in heat and temperature fluctuations in buildings [10].Thaib et al. 2018 used PCM on BIPV systems in buildings with paraffin and beeswax.Panels without PCM have work efficiency ranges between 6.1% and 6.5% while PV panels with PCM range from 7.0-7.8%.These results prove that the water cooling process can increase the efficiency of PV panels [11].
Determining the type of PCM and placing the PCM in the building is an important factor that must be considered.The selection of a PCM that is suitable for the application temperature will optimize the performance of the PCM as a latent heat absorber.Several studies that have integrated PCM in buildings positioned PCM in various parts of the building such as that conducted by Lee, Kyoung Ok, et al, 2015 [12] making a PCM layer that was encapsulated using aluminum foil bags inserted inside the walls.Silva, Tiago, et al, 2012 [13] inserting PCM into brick cracks used as walls.Al-Absi, Zeyad Amin, et al, 2022 [14] made a PCM composite in the form of gypsum which was used as a coating on walls.Based on several studies that have been carried out the application of PCM to the wall is the most interesting because the wall has the largest cross-sectional area in the building.
In this study, PCM applications were tested on building walls using organic-based PCM materials, which have melting points close to the working temperature or heat received in the building.The test was carried out by comparing prototype rooms with PCM and without PCM composite.The test was carried out under direct solar radiation and then compared the temperature values produced in the building.The use of PCM as an insulator in buildings is expected to reduce the heat absorbed into the building.

Methodology
The PCM material used in this study was organic soy wax with the characteristics in Table 1.Soy wax was wrapped in an aluminum bag with a size of 20 x 30 x 1 cm and then it was sealed as shown in Figure .1. (a).The prototype design of the PCM application room that was made refers to the building standards of the Indonesian Ministry of Public Works and Public Housing with a size of 21 m2 which is the size of a simple house.The prototype size scale is 1:5, with size specifications shown in Table 2 and Fig. 2. PCM packs are arranged in a sandwiching with walls made of Plywood as shown in Figure.

(b).
This test was carried out for 24 hours by comparing the prototype box without a soy wax pack and with a soy wax pack.The change of temperatures in the prototypes was recorded by using a type K thermocouples sensor with the number of thermocouples installed on the prototype without soy wax packs and with soy wax packs of 15 and 19 thermocouples, respectively.The calibration of the measuring instrument carried out in this study was a type K thermocouple connected to the NI cDAQ-9174 data acquisition.Thermocouple calibration is carried out at a temperature of 20°C to 50°C with a periodic temperature increase every 5°C and the calibration standard used is a mercury thermometer as shown in Fig. 3. Based on the graph, it can be seen that the readings of all thermocouples are uniform until they are on the same line at each temperature with an error value of ±0.3°C.Two kinds of prototypes were made, one prototype was made of full Plywood Fig. 5 (a) and the other contained a gap for inserting a soy wax pack Fig. 5 (b).This test is carried out directly in the real environment by providing heating from solar radiation and cooling at night.This prototype was allowed to stand for 24 hours in an open space and the results were compared referring to the temperature values.The disadvantage of this application method is that the solar radiation is not evenly distributed and it is very dependent on the weather at the time of testing so it is necessary to do repeated tests to obtain a result that can represent the actual application conditions.
The steps for testing the application of soy wax packs on building wall prototypes begin with installing soy wax packs throughout the prototype wall area and attaching thermocouples to the building prototype.After the prototype setup is complete, it is continued by connecting it to the NI module and setting up the Lab view to be used.Before starting to record the data, all thermocouple connections were checked and the data results were read on Lab view.After all the settings are complete, then the data collection begins by recording the temperature changes that occur for 24 hours on the prototype.This graph shows all temperature data readings generated on all sides of the walls, glass, roof, and floor of the building.This graph shows the conditions at peak load where the building receives the highest heat during the day and at night when the outdoor conditions are lower than indoors.Fig. 6. shows the temperature generated on all sides of the wall on the prototype with and without a layer of soy wax pack.The line graph for the position outside the prototype gives an unstable reading because the recorded temperature changes are environmental conditions where the solar's heat can change every second.Fig. 7 (a) shows the temperature ratio at the midpoint of the building room.This graph shows the temperature read from the prototype without soy wax pack resulting in a higher temperature than the prototype with soy wax pack at peak load/day.These results indicate that the addition of a soy wax pack on the prototype wall influences room temperature.The soy wax pack can manage the room during the day by lowering the temperature to 37°C from 41°C in a room without a soy wax pack.The use of a soy wax pack can absorb the heat received by the building by 10%.In addition to the decrease in temperature in the middle of the room, a decrease in temperature also occurred on the roof and floor of the prototype even though the roof and floor, are shown in Fig. 7 (b).At peak load, the roof position without soy wax pack produces a temperature of 44°C while the prototype roof with soy wax pack walls produces a temperature of 41°C.There was a decrease of 3°C with a percentage of heat absorption of 7%.Then the floor without a soy wax pack produces a temperature of 38oC while the prototype with a soy wax pack produces a temperature of 34°C.These results indicate a decrease in temperature that occurs in the prototype with soy wax pack by 10%.Temperature readings on the outside of both the prototype wall with glass and door produce similar data which corresponds to the heat radiation received from the outside of the prototype.The effect of applying a soy wax pack layer was seen on the inside of the wall containing the soy wax pack.The entire side of the wall containing the soy wax pack layer results in a lower temperature compared to the prototype without the soy wax pack.Based on all the test data in the form of this temperature comparison, it shows that the addition of a soy wax pack on the prototype wall influences the heat absorption by the PCM.
Based on the test results obtained on the application of pure soy wax packs on the walls of the building prototype, data were obtained to calculate the calorific value absorbed by the walls.Referring to the test results, it is known that both building conditions without and with soy wax packs produced the same trend of solar radiation, which increases during the day, which is the peak load and decreases at night.The visible difference is that the building with the soy wax pack shows the graph below the graph of the building without the soy wax pack.At night the trend of the graph shown by the room with the soy wax pack is slightly above the graph line of the building without the soy wax pack.This happens because at night the PCM releases heat which is absorbed during the day.In addition, the calculation of the total thermal resistance generated from the prototype wall with the soy wax pack shows that the soy wax wall has a large thermal resistance with a total thermal resistance value of 0.257.The heat transfer rate value obtained is 15.56 W, which means the ability of PCM walls to transfer heat into a small room.The PCM wall functions as an insulator on the wall that can withstand the heat absorbed from the outside of the building so that it is not completely transferred into the room.

Conclusion
Integrating PCM in buildings is one solution to the problem of high heat absorption in buildings.The application of the soy wax pack which was carried out on the prototype of a simple house room resulted in a 10% decrease in indoor temperature compared to the prototype of a building without a soy wax pack at peak load.In addition, measurements on the roof showed a temperature drop of 7%, and 10% on the floor of the room.The soy wax pack on the wall can function as an insulator with a total thermal resistance value of 0.257 K/W and the heat transfer rate value of 15.56 W. Placement of a soy wax pack on the wall is the best position because the wall has the highest proportion in the building, so the heat absorption process will be more effective.The heat absorption with soy wax pack on this building prototype is a discovery that can inhibit heat entering the room, especially in the tropics, namely Indonesia.

Figure 1 . 2 .Figure 2 .
Figure 1.(a) Soy wax pack (b) Soy wax pack placement on prototype Table 2. Size of prototype building Part of building Size of the building (m) Size of the prototype (m) Area 4 x 5.25 x 3 0.8 x 1.05 x 0.6 Wall thickness 0.1-0.150.03 (plywood) Percentage of glass in 1 wall 30% : 1 x 1,3 0.2 x 0.26

Figure 4 .Figure 5 .
Figure 4. Setup testing soy wax pack application on the prototype

Figure 6 .
Figure 6.Graph of soy wax pack application test results on prototype

Figure 7 .
Figure 7.Comparison of temperature (a) in the middle of the room, (b) roof and walls on the prototype without and with soy wax pack