Personal air-conditioning system using evapolar as heat waste management

Nor Azazi Ngatiman, Abdul Qaiyum Mohd Shariff , Tole Sutikno, Suparje Wardiyono, Mustafa Manap, Mohd Hatta Jopri Department of Mechanical Engineering Technology, Faculty of Mechanical & Manufacturing Engineering Technology, Universiti Teknikal Malaysia Melaka, Malaysia Department of Electrical Engineering, Universitas Ahmad Dahlan, Yogyakarta, Indonesia State-Owned Enterprise Power Company (PLN), North Kalimantan Province, Indonesia Faculty of Electrical and Electronic Engineering Technology, Universiti Teknikal Malaysia Melaka, Malaysia


INTRODUCTION
The cooling unit to cool a room usually uses a split unit which has a larger amount of cool air to distribute. For example, a standard office with an area 12'x12' will be a waste to cool the whole room since the space needed is a small area. In-office buildings, occupants will have a restricted space to move and have to control their movements. It will give an uncomfortable zone due to unbalanced comfort ventilation [1]- [5]. This proves that a portable air conditioner can cool with a range of 1 meter around a person will be more suitable than split units since it conserves less energy. Hot temperatures in a space must be removed to achieve a thermal comfort zone [6]- [9]. The previous researcher found that the Peltier module can cool down temperature and develop it as a portable air conditioner [10]- [13]. It is proven to overcome waste energy consumption in portable air conditioning, Peltier module was used. Hot effects on the hot side of the Peltier module cannot fully be utilized while vice versa on the cold sides [14], [15]. The problem with the hot sides that not be used in Peltier module must be utilized because portable air conditioning using Peltier module have a great achievement in transferring cool air to surroundings [16], [17]. Peltier module will be affected due to a lot of heat waste in the surroundings. The latest researchers [18]- [20] found that heat waste from portable air conditioning using a Peltier module can be used as heat energy. This study also showed that thermal efficiency in the heat recovery process proves that higher thermal conductivity produces higher heat transfer to the surface. Less amount of heat loss occurred during the study [11], [21]- [23].
From the latest product of portable air conditioning system design [16], [24]- [26], the heat waste is released to the surrounding in large amounts due to unorganized energy [27]- [32]. The thermal comfort zone standardized by The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) is around 22 to 24 o C for most buildings in Malaysia [33]- [35]. Heat waste from the Peltier module spread to the air and cause uncomfortable to users. Due to limited space in a room, users feel hotter because of Peltier module generates the same capacity of hot and cold energy. Adding external energy such as electrical equipment and body, the temperature increase and hot temperature will overwhelm cold temperature [36]- [40] So in favour of producing thermal comfort zones, this research will design new ways on how to recover the heat waste from release to surroundings [41]- [43]. In terms of ergonomics to users, this product needs to be upgraded for a better purpose. The heat waste from the product needs to be recovered to ensure the product will be convenient and increase efficiency [44]- [46]. This method also is a new idea in managing heat waste using evapolar and finding ways to increase the effectiveness of the system.

METHOD
A strategy to develop a portable air conditioning system using evapolar from several previous research is discussed. Different criteria and mechanical engineering concepts are used as a significant strategy [47]- [50]. This section includes the examination, evaluation, preparation, production, improvement, and testing [51], [52]. Figure 1 depicts the process of developing portable air conditioning and also identifies the performance of the product. It starts from defining the standard condition until analysis of the developed product. Design is a process of designing a system to fulfil the outcome for this study, which provides a thermal comfort zone with the help of an evapolar. A good design is defined to achieve the objective by the product's engineering characteristics. The great design of this device can be created by following a standard conventional method which is the Morphological method and Pugh method.

Morphological chart
The morphological technique is the study of shape as well as forms before the product is being developed [53]- [56]. The basic idea of the morphological technique is to elaborate the overall design issue into few variables to generate a solution for each criterion. It also systematically mixes up criteria solutions into multiple effective solutions and evaluate all combinations. It is a visual aid that comes with several ideas for selecting the suitable element throughout the design technique. Table 1 shows the morphological chart attributes for portable air conditioning system.

Pugh method
The Pugh method was introduced by Stuart Pugh, a plan division head at the University of Strathclyde in Glasgow [57]. Pugh is used to assess different alternatives by calculating the overall score between the choices [58]- [60]. The selections derive from the morphological method in which three concepts have produced the character of the product. Pugh method evaluates three concepts in terms of choosing a good concept based on the total raw score. The weightage describes the crucial feature, which should be carefully measured before selecting the best idea as shown in Table 2. Table 2 shows option 1 is the best concept among other concepts due to the highest total raw score. Option 1 from the morphological method applies an electrical power supply, medium device, draw through fan, Arduino controller, thermocouple sensing element, metal sheet casing, finned heat sink, and connect directly. By using these methods, the design of the product is made and the results are shown as in Figure 2.

Testing condition
A field measurement is carried out in this research to investigate the performance of a product in an office room [61]- [63]. This room size is measured and it is situated in Ayer Keroh, Melaka. It used a VRF (variable refrigerant flow) fan system where it is efficient and reliable. The ceiling measurement height from floor to ceiling is 2.5 meters. The collected data will be summarized. This equipment will be placed on the table at 1-meter height from the ground.

Peltier performance
The efficiency of both generators and coolers conclude the greater the value of this term, the greater the efficiency [64]- [66]. The heat flux gives the value of the thermoelectric of merit between hot and cold sides due to conduction is: Where S is Seeback coefficient=0.053 V/K, K is Lattice thermal conductivity=0.3 w/m.K, R is electrical resistance=0.45 Ω, and I is current. Electrical power consumed by the module is calculated based on the heat flux difference of the two sides of the module as, where I is current, V is voltage, and t is time.

Performance coefficient of device
A previous thermoelectric air-conditioner (heat pump) typically contains a large number of n-type and p-type bulk semiconductor thermoelements linked electrically in series by copper strips and sandwiched between two electrically insulating, but thermally conducting ceramic plates. In the cooling mode, the cooling capacity performance of the cooling effect is expressed as (3).
Where Cr is heat capacity ratio as (4) Cr= ℎ The arithmetical average temperature of the thermocouple is as (4).
V is an electrical voltage as (6).
Hence, the power can be obtained by using the volt calculated, as shown in (6).

RESULTS AND DISCUSSION
The newly developed product is considering design parameters defined from the morphological chart where the combination of specific conditions for the creation of a product is shown in Figure 3. The system features use Peltier as a cooling source, a heat sink with aluminium finned to increase the heat transfer rate of a wood case to guard the internal component, evapolar as a medium to cool down condenser and the fan to blow the cool air.

Thermoelectric performance
This measurement repeated three times to prove whether the product achieve efficiency at different times. Table 3 shows the time taken to the temperature of Peltier becomes hot and cold. The temperature is measured every 5 minutes and COP for Peltier performance is calculated. Figure 4 shows the relationship between the Cop of Peltier performance after several tests. The trend of the chart is almost similar. Based on the previous research, the highest COP for Peltier reach 0.3205, which had different conditions that need to be counted. For this experiment, it shows COP for Peltier can reach 0. 58  2957 that for series connection and condition inside a room can affect the performance of Peltier. Thermal paste was used in this Peltier to lessen heat transfer losses that occur and increase the efficiency of Peltier.  Figure 4. COP against the number of tests compared to the previous researcher [68] From Figure 5, the temperature difference is increasing and the longer time is taken, the higher the temperature difference will occur. The efficiency of the Peltier can be seen due to the series connection to the wiring for all Peltier. When the current is in series connection it increases the voltage to the maximum while parallel connection increases the current to maximum [67]. For this experiment, R 2 values that are near to 1 are shown and R 2 data for each analysis reaches a suitable determinant coefficient. The data obtained is acceptable for the overall result of testing because it is higher than the set value where y=1.4771x + 23.18 can be used to calculate the difference in temperature at any point for this product.   Figure 6 shows the different numbers of tests in the same conditions of the product. All of the temperatures have a minimal difference, which shows that the limit of the product that can be reached. Test 1 shows that for TCout, the temperature that blows to occupants can reach 26.9 o C when ambient temperature which TCin, at 31.8 o C. Next, THin which temperature of the air outside shows 35.7 o C while the temperature inside can reach 48.5 o C. This data showed that with the evapolar mechanism, the amount of heat waste that could be removed is high and more productive. Figure 6. Different in temperature hot and cold with the number of tests Table 4 shows the summarize of data for all three tests. It demonstrates that there are no significant changes for each test since an average of temperature shows a consistency of data.

Tariff of the device
A number of tests with the temperature of Peltier recorded is shown in Table 5. From the table shown, the data for current and voltage are stable and good result is determined with the greater temperature different, ∆ [46], [69]. All three set of collected data shows a stability of the system developed. Referring to Table 6, the estimation of the bill depends on the Malaysian tariff [70]. Compared to the previous researcher [68], 2.88 kWh power per day was used instead of 6.894 kWh. The monthly energy consumed is 137.88 kWh, while this product consumes only 57.74 kWh, which can save almost 58% of its electricity. 26 Figure 7 shows the amount of the bill per day to be paid for this product is RM1.12, which the previous shown RM1. 50, which can save 25% of the bills per day. Besides, the margins are increasing as compared in the month that this new product can save 26 %. Based on the above information, this product provides consumers with fewer electricity bills while providing an individual with comfort.

CONCLUSION
The performance study of an office scale portable Peltier air conditioner is demonstrated. The product can reduce the temperature inside the room. The objective of the study has achieved which design is made based on the Pugh method and Morphological chart. The design process has also been done using Solid Work Software. The performance of the product using evapolar as heat waste management has been discussed. It reaches the purpose to remove heat from the inside of the product to the outside using evapolar as heat removal. The coefficient of performance is similar to the level of the previous product, which means it can provide higher efficiency despite no controller temperature. Tariff for electricity shows this product can save energy approximately by 25% compared to previous one.