The applicability of ISO household refrigerator–freezer energy test specifications in Malaysia

Energy 26 (2001) 723–737 www.elsevier.com/locate/energy

The applicability of ISO household refrigerator–freezer energy test specifications in Malaysia H.H. Masjuki a, R. Saidur a

a,*

, I.A. Choudhury b, T.M.I. Mahlia a, A.K. Ghani b, M.A. Maleque a

Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia b CAD/CAM Unit, University of Malaya, 50603 Kuala Lumpur, Malaysia

Abstract ISO 8187, ISO 8561, and ISO 7371 are the relevant test standards for household refrigerating appliances. This paper presents the possibility of introducing ISO household refrigerator–freezer test standards in Malaysia. An experiment was conducted to investigate the effect of room temperature, door opening, thermostat setting position, relative humidity, and loading on energy consumption of a household refrigerator– freezer. With the experimental data, a multiple regression equation is developed to investigate their combined effect. Finally, energy consumption according to the regression equation with optimum setting conditions is compared with ISO standard test conditions. Our comparison reveals that ISO refrigerator–freezer test standards are applicable with respect to Malaysian climatic conditions and usage patterns.  2001 Elsevier Science Ltd. All rights reserved.

1. Introduction Malaysia, like other developing countries, has experienced dramatic growth in the use of household refrigerator–freezers. Over the last 12 years (1984–1996), the Malaysian economy grew more than 7% per annum. At the same time, Gross Domestic Product (GDP) increased from RM 79,330 million in 1990 to RM 140,600 million in 1997. The per capita income increased from RM 6230 in 1990 to RM 12,050 in 1997 prior to the economic downtrend, which began in July 1997 [1]. Economic growth is the main driving factor for greater use of refrigerator–freezers which, in turn, leads to an increasing need for comfort and a high style of living that has consequently caused a substantial increase in household energy consumption. Household refrigerator–freezer ownership

* Corresponding author. Tel.: +603-79675283; fax: +603-79675317. E-mail address: [email protected] (R. Saidur).

0360-5442/01/$ - see front matter  2001 Elsevier Science Ltd. All rights reserved. PII: S 0 3 6 0 - 5 4 4 2 ( 0 1 ) 0 0 0 2 8 - 7

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Nomenclature b0 Constant used in Eq. (6) bi Regression co-efficient used in Eq. (6) c1 Specific heat of product above freezing point (kJ/kg.K) c2 Specific heat of product below freezing point (kJ/kg.K) DO Door opening E Energy (kWh/day) hif Latent heat of fusion of the product below freezing point (kJ/kg.K) L Load (kg) m Mass of the products (kg) n Allotted time period (hour) Q1, Q2, Q3 and Q4 Heat removal (kj) q Product cooling load (kW) RH Relative humidity (%) t1 Initial temperature of product above freezing point (°C) t2 Lower temperature of product above freezing point (°C) t3 Final temperature of product below freezing point (°C) tf Freezing temperature of product (°C) Tfw Fresh water temperature (°C) Tfz Freezer temperature (°C) Tr Room temperature (°C) TS Thermostat setting position increased for several reasons: (i) increase in household income, (ii) more readily available electricity, and (iii) refrigerator–freezers are more available and less expensive. Refrigeration industries have also expanded to a great extent to meet the country’s demand. Fig. 1 shows the refrigerator–freezer sales structure in Malaysia [2]. Due to the lack of government

Fig. 1. Yearly household refrigerator–freezer sales in Malaysia [2].

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intervention in implementing energy efficiency standards and standardized testing programs, manufacturers do not pay heed to the improvement of their products. Thus, assessing refrigerator– freezer energy efficiency is very difficult. Consequently, inefficient, worn-out equipment contributes to the rapid depletion of the country’s energy resources. Refrigerator–freezers are the major energy consuming electric appliances in the household environment. A survey was conducted by Razali et al. [3] to investigate household energy patterns. Their study revealed that about 76% of total residential homes are equipped with one refrigerator– freezer. In some cases, they showed a multiple number of refrigerator–freezers owned by a single house owner. Introducing standards and labeling for refrigerator–freezers can offer great benefits for both the consumer, and government. Since energy efficiency standards and test procedures are interrelated, an energy test procedure for these appliances is urgently needed to mitigate future demand for energy, as well as to mitigate the environmental degradation. For rating and testing of household refrigerator–freezers, the Standard and Industrial Research Institute of Malaysia (SIRIM), which is the governing body for developing Malaysian standards, has not yet set any standards. Recently, the Department of Mechanical Engineering, University of Malaya, initiated a project to develop minimum energy efficiency standards for household appliances in co-operation with the Ministry of Science and Technology in Malaysia. As a part of the project, the ISO refrigerator–freezer test standard has been analyzed for the testing and rating of household refrigerator–freezers. So, the objective of this study is to develop an energy test procedure that is most suited for household refrigerator–freezers in Malaysia. The experiment was conducted on one 150 L household refrigerator–freezer. The specification of the unit is shown in Table 1. 2. Experimental set-up 2.1. Test conditions The objectives of this experiment were to determine the effect of room temperature, thermostat setting position, door opening, relative humidity, and loading on the energy consumption of a household refrigerator–freezer. The tests were conducted by varying the room temperature, therTable 1 Technical specifications of the test unit Specifications Freezer capacity Fresh food compartment capacity Power rating Current rating Voltage Frequency No. of doors Refrigerant type Defrost system

40 L 110 L 115 W 0.67 A 240 V 50 Hz 1 134a (CF3CH2F) Partial auto

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mostat setting position, door opening, relative humidity, and load independently. During the experiment, while one variable was changed, the other variables were kept constant. The room temperature was varied from 16°C to 31°C in an environmentally controlled chamber located in our laboratory to investigate its effect on the energy consumption. The thermostat setting position was fixed at the medium setting (position 4) and relative humidity was maintained at 60%±5%. The tests were conducted without any load in the refrigerator–freezer and without opening the door. In a 24 h period of operation time, the door was opened for the first 10 h of the experiment. The door opening controls were set in such a way that the door remained open for 12 s at an angle of 90°. In order to maintain 20–75 door openings over 10 h of operation, door closing time was not fixed. Table 2 shows the door opening and closing schedule over these 10 h. Room temperature and relative humidity were maintained 24°C and 60%±5% respectively for all door opening tests and the thermostat setting position was kept at the medium position (position 4). There were seven thermostat setting positions ranging from 1 to 7 for this test unit. Thermostat setting was varied by turning the knob to the desired setting position from 1 to 7 in order to investigate the effect of thermostat setting position on the energy consumption. Room temperature and relative humidity were maintained at 24°C and 60%±5%, respectively, under a no load condition. The door was not opened during this test. To investigate the effect of relative humidity on the energy consumption of the test unit, relative humidity was varied from 60% to 90%. The thermostat was set at position 4, room temperature was maintained at 24°C, with the unit empty with no door openings. The effect of loading on energy consumption was investigated by placing fresh water into the unit. The fresh water temperature was within 24–25°C. The load was varied from 7.5 kg to 18.0 kg in this test. The thermostat was set at position 4, room temperature was maintained at 24°C, relative humidity was kept at 60%±5%, with no door openings. 2.2. Measurement technique After the freezer temperature had reached a steady state, the test was started for a period of 24 h. The steady state was deemed to be achieved when the variation in temperature inside the freezer did not exceed 0.5 K during a period of 18 h. The experiment was conducted as per

Table 2 Door opening schedule No. of openings

Total run time (min)

Closing time (min)

Door remains open (s)

20 30 40 50 60 75

600 600 600 600 600 600

30 20 15 12 10 8

12 12 12 12 12 12

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requirements specified in section 15 of ISO 8187 [4] and in [5] which presents an excellent overview of measurement techniques. 3. Instrumentation A heat pump was used to maintain the required temperature in the environmentally controlled chamber in order to investigate the effect of room temperature. The various modes of operation of heat pump were (i) heating, (ii) cooling, and (iii) soft dry. The unit can maintain the controlled chamber temperature within 13°C to 35°C. The temperature fluctuations were controlled by using an Omega type temperature controller with an accuracy of ±1°C. The controller was interfaced with the heat pump so that the desired temperature could be maintained within the chamber. Daily energy consumption was measured by the YOKOGAWA WT-130 digital power meter, which was interfaced with a PC through RS-232. Lab view software was installed into the PC for data storage and analysis. The accuracy of this power meter is ±0.2% of rdg. T-type thermocouples were used to measure the temperature inside as well as outside the test unit. An Omega HX-92 humidity transmitter was used to measure the relative humidity of the controlled chamber. Thermocouples and humidity transmitter were interfaced with a 20 channel HP data logger (Model 34970A) via a PC for data storage and analysis. Relative humidity was varied from 60% to 90% by using a RECUSORB DR-010 dehumidifier with an accuracy of ±5% to investigate the effect of relative humidity on energy consumption. For the other tests, the relative humidity was maintained at 60±5%. Instead of opening and closing the refrigerator–freezer manually, an automated door-opening and closing mechanism was designed and fabricated. A steel frame containing an AC motor and a gearbox were mounted on the top of the refrigerator–freezer. The door opening and closing arrangements are shown in Fig. 2. The door-opening process is controlled using the Programmable

Fig. 2.

Door opening and closing mechanism.

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Logic Controller (PLC). The operating switch, which is an input device, sends signals to the motor to open and close the door. Total run time, opening time, and closing time is inserted into the operating switch and it runs as per the experimental requirement.

4. Energy test procedure An energy test procedure is the basis of, and represents the technical foundation for, all energy efficiency standards, labels and other related programs. Energy labels could not be created without an energy test procedure. The function of test standards is to establish a uniform and repeatable procedure or standard method for measuring specific appliance characteristics. Meier and Hill [6] have suggested the following criteria for a good test procedure: 앫 앫 앫 앫 앫 앫

accurately reflect the relative performance of different design options for a given appliance; reflect actual usage condition, and yield repeatable, accurate results; cover a wide range of models within that category of appliance; be inexpensive to perform; be easy to modify to accommodate new technologies or features; and produce results that can be easily compared with results from other test procedures.

Unfortunately, these goals are very difficult to achieve. For example, a test procedure for refrigerator–freezers that attempts to closely mimic the actual kitchen environment/conditions and human behavior by which a refrigerator is used is very complicated. It is also expensive to perform the test under such exact conditions. Meier [7] states that an independent testing laboratory charges about US$2000 to perform a Department of Energy (DOE) test on a single refrigerator–freezer. In order to reflect the actual kitchen environment and usage conditions in a household, Japan began its test procedure using two kitchen temperatures (15°C and 30°C) with a complex schedule of door openings. They selected 15°C and 30°C to reflect the energy consumption of the winter and summer seasons [8]. But it was so complicated and expensive that recently Japan abandoned this test procedure in favor of the ISO test procedure. A simple test procedure may be inexpensive but is liable to ignore features that affect the actual energy use, thus causing an inaccurate and unfair ranking of models. Therefore, every test procedure is a compromise. Many countries and regions utilize different test protocols to measure energy consumption of different products. This prevents comparison of energy efficiency for such products across the borders where the test protocols differ. For products whose efficiency is dependent upon climate, like refrigerator–freezers and air conditioners, local climatic conditions are another factor affecting energy efficiency. There have been a number of conferences and workshops that have tried to harmonize regional test protocols, but it is impossible to do this at the global level because each country has its own (i) climate; (ii) characteristic and usage differences for some products; (iii) electricity or fuel prices; (iv) cultural attitudes with respect to voluntary or mandatory specifications; and (v) state of art manufacturing companies for that region.

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5. An overview of International Standards ISO 8187, ISO 8561, and ISO 7371 for energy measurement The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies. ISO 8187 [4], ISO 8561 [9], and ISO 7371 [10] are the relevant standards for testing the energy consumption of household refrigerator–freezers having two or more compartments. At least one compartment (the fresh food storage compartment) is suitable for storing unfrozen food, and at least one compartment (the food freezer compartment) is suitable for freezing fresh food and for the storage of frozen food at ⫺18°C or lower. ISO specifies the following four climatic zones and their ambient temperatures as: 1. Extended temperature zone: 25±0.5°C 2. Temperate zone: 25±0.5°C 3. Subtropical zone: 25±0.5°C 4. Tropical zone: 32±0.5°C According to the ISO standard, the test period shall be at least 24 h long with no door openings. Relative humidity should be kept within 45%–75% inside the chamber. 6. An overview of Malaysian climatic conditions To develop the test standards for refrigerator–freezers, climatic conditions for a particular country or region are an important factor. For example, in comparison to a hotter climatic region, in a colder climatic region, there is no need to put some foods into the refrigerator–freezer. Climate affects the refrigerator–freezer’s energy consumption in several ways. ISO has also emphasized the climatic conditions and, as such, it has developed its test standards for a (i) extended temperature zone, (ii) temperate zone, (iii) subtropical zone, and (iv) tropical zone. Malaysia, being an equatorial country, has a uniform temperature throughout the year. A large variation in temperature throughout the country is rare. Table 3 shows the daily average temperature and relative humidity of Malaysia [11]. Table 3 Records of daily average temperature and relative humidity of Malaysia [11] City

Temperature (°C)

RH (%)

Kuala Lumpur Kota Kinabalu Senai Subang Ipoh Bayan Lepas Kota Bharu Kuantan Kuching

26.5 27.0 25.9 26.7 26.9 27.2 26.8 26.1 26.2

85.3 81.5 86.9 82.7 81.4 82.2 82.2 85.4 85.4

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7. Factors contributing to a refrigerator–freezer’s energy consumption The following factors should be considered in order to develop refrigerator–freezer test standards: (i) ambient temperature, (ii) door openings, (iii) control/thermostat settings or compartment temperature, (iv) relative humidity, and (v) food loading. 7.1. Ambient temperature Most of the thermal load on a refrigerator–freezer is by conduction through the refrigerator– freezer wall. ASHRAE [12] shows that about 60%–70% of the total refrigerator–freezer load comes through conduction of the cabinet walls. This conduction load is proportional to the difference between ambient temperature and internal compartment/freezer temperature. The higher the difference, the higher the load imposed on a refrigerator–freezer. For this reason, the temperature of the air around a refrigerator–freezer is a significant determinant of energy consumption. Since compressor efficiency also declines as the ambient temperature rises, a refrigerator–freezer’s electricity use is very sensitive to the ambient temperature. Meier [7] stated that energy consumption varies from 1.25 kWh/day to 2.6 kWh/day for an 11°C increase in temperature. He conducted the experiment for a US style refrigerator. In our experiment, energy consumption increased 560 Wh/day to 1120 Wh/day when the temperature increased from 16°C to 31°C in a Malaysian produced model. Energy consumption increases around 40 Wh for a 1°C increase in temperature. Fig. 3 shows the trend in energy consumption with change in ambient temperature. From Fig. 3, it can be stated that there is a strong influence of ambient temperature on the refrigerator–freezer’s energy consumption. 7.2. Door openings When the refrigerator–freezer door is opened, warm and moist air mixes with the cool air inside the refrigerator–freezer cabinet. When the door is closed, a mass of air at ambient temperature

Fig. 3.

Variation of energy consumption with room temperature.

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is trapped in the compartment. Heat gain during door openings are due to (i) heat/vapor transfer on the interior surfaces of refrigerator–freezer, and (ii) bulk air exchange. The following five categories of loads are associated with the door openings [13]. These are: 1. convective heat transfer from the warm ambient air flowing across the cooler refrigerator surfaces; 2. latent heat transfer with condensation of water vapor from the moist air flowing across the cooler refrigerator surfaces; 3. radiative heat transfer from surroundings to the interior surfaces; 4. sensible heat transfer from the warm air mass within the cooled space after the door is closed; and 5. latent heat transfer due to dehumidification of the air after the door is closed. Alissi [13] showed about a 32% increase in refrigerator–freezer energy consumption for 100 door openings. Gimes et al. [14] found a 6–8% higher energy consumption for 24 door openings. Parker and Stedman [15] estimated that each door opening causes 9 Wh of increased energy consumption. This experiment has been carried out with multiple door openings, beginning with 20 and reaching 75 during the first 10 h of commencement of operation. Our analysis shows about a 10 Wh increase in energy consumption for each door opening. Fig. 4 shows the trend in energy consumption with door openings. 7.3. Effect of thermostat setting A refrigerator–freezer will consume less electricity if its thermostat is re-set to a higher (warmer) temperature. Owing to the single-evaporator design of most refrigerator–freezers, a change of temperature in the freezer compartment generally results in a temperature change in the fresh-food compartment. Grimes et al. [14] examined the impact of compartment temperature on energy use on a 1977-vintage automatic defrost refrigerator. Energy consumption rose 26% from the warmest acceptable to the coldest possible settings. A more recent study of nine large,

Fig. 4. Variation of energy consumption with door openings.

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1993-vintage US refrigerator–freezers [16] found a 6.5% increase in energy consumption for a 1°C reduction in freezer temperature. We have conducted experiments from warmest thermostat setting to coldest thermostat setting to investigate its effect on the energy consumption. In our investigation average, warmest, medium, and coldest thermostat setting temperatures were around ⫺4°C (setting position 1), ⫺13.3°C (setting position 4), and ⫺18°C (setting position 7), respectively. Energy consumption increased about 790 Wh from warmest to coldest position. This is about a 10% increase in energy consumption for each degree decrease in temperature. Fig. 5 shows the trend in energy consumption with different thermostat setting position. 7.4. Effect of relative humidity Humidity has little effect on energy consumption. Grimes et al. [14] reported a 5% increase in energy consumption when the relative humidity was increased from 40% to 60%. The greatest energy impact of humidity is probably the operation of the electric resistance anti-condensation heaters. When humidity increases, vapor condenses at the wall of the refrigerator–freezer. An anti-sweat heater turns on to prevent condensation from raising refrigerator–freezer energy consumption. In this experiment, we raised the humidity from 60% to 90% and the corresponding energy consumption increase was 10%. 7.5. Effect of loading on energy consumption One study [17] reported that the heat removed from food loadings accounted for the majority of the refrigeration load. This load is the function of product type, mass, and temperature difference before and after cooling of the product. However, one survey in [18] concluded that loading has very little effect on energy consumption, although the authors could not find a general conclusion. The primary sources of refrigeration load from products brought into and kept in the

Fig. 5.

Variation of energy consumption with thermostat setting position.

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refrigerated spaces are (i) heat removal required to reduce the product temperature from receiving to storage temperature, and (ii) heat generated by products in storage, mainly fruits and vegetables. The quantity of heat to be removed can be calculated from knowledge of the product, including its state upon entering the refrigerating space, final state, mass, specific heat above and below freezing temperature, and latent heat. When cooling a definite mass of product from one state and temperature to another, the following loads are associated in accordance with [19]: (1) Heat removal in cooling from the initial temperature to some lower temperature above freezing: Q⫽mc1(t1⫺t2)

(1)

(2) Heat removal in cooling from the initial temperature to the freezing point of product: Q2⫽mc1(t1⫺tf)

(2)

(3) Heat removal to freeze the product: Q3⫽mhif

(3)

(4) Heat removal in cooling from the freezing point to the final temperature below the freezing point: Q4⫽mc2(tf⫺t3)

(4)

Refrigeration system capacity for products brought into refrigerated spaces is determined from the time allotted for heat removal and assumes that the product is exposed in a manner to remove the heat in that time. The calculation is: Q1+Q2+Q3+Q4 q⫽ 3600n

(5)

Latent heat of fusion of a product is related to its water content and can be estimated by multiplying the percent of water in product by the latent heat of fusion of water. The experiment was conducted by placing fresh water of 24°C–25°C into the fresh food and freezer compartment. Some of the tests were performed with water loaded only in the fresh food compartment while the others were done with water loaded in both compartments. Energy consumption was comparatively higher when water was loaded in both of the compartments. Fig. 6 shows the energy consumption trend when loaded with water. It has been found that energy consumption increases by about 90 Wh per kg of water. Energy consumption increases by 78% from minimum load to maximum load. Although there is a significant increase in energy consumption due to the increase in load, other factors must be taken into consideration. In actual kitchen conditions, a household refrigerator– freezer is usually equipped with vegetables, meat, fruits, and so on, which differently influence the energy consumption. Energy expended in removing heat from those products has been

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Fig. 6.

Variation of energy consumption with loading.

explained in Eqs. (1) through (5). Once the product attains the desired cooling temperature, it does not affect the energy consumption significantly until fresh products are placed in the refrigerator again. If the products remain for several days in the refrigerator–freezer after cooling to the desired temperature, an increase in the energy consumption may be attributed to the loading of fresh food during that period. So, a general conclusion would not be possible. But it can be hypothesized that energy consumption will be significantly lower than the amount we found from our experiment and other relevant studies. 8. Statistical analysis To investigate the combined effect of room temperature, door opening, thermostat setting position, relative humidity, and loading on energy consumption, the experimental data have been analyzed. A multiple linear regression equation was developed by using PC based “Essential regression” software. The equation is given below. E⫽⫺512.8⫹6.5⫻DO⫹34.4⫻Tr⫹129.7⫻TS⫹62.5⫻L⫹0.7⫻RH

(6)

Table 4 shows the predicted daily energy consumption at different test condition and usage patTable 4 Predicted energy consumption DO (No.)

T (°C)

TS

L (kg)

RH (%)

E (kWh/day)

30 40 50 60 60 70

24 25 26 27 27 27

2 3 4 4 4 5

6 7 8 8 9 10

60 70 80 85 90 90

1.19 1.48 1.78 1.88 1.95 2.21

Remarks

Optimum

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terns by using Eq. (6). The reason behind the ‘optimum’ test condition is illustrated in the Conclusions. 9. Standard energy consumption P.K Bangsal et al. [5] carried out tests for four different refrigerator–freezers at different tests standards, namely American National Standard (ANS), Australian New-Zealand Standard (ANZS), International Standard Organization (ISO), Japanese Industrial Standard (JIS), and Chinese National Standard (CNS). They have developed a correlation between these standards. In ISO test conditions, they used 25°C as the ambient temperature. We also measured daily energy consumption of a 150 L household refrigerator–freezer under ISO refrigerator–freezer test specifications. Under tropical test conditions (i.e. ambient temperature 32°C), energy consumption was found to be 1.90 kWh/day. This test condition was chosen, because it is most suitable with respect to Malaysian climatic conditions.

10. Uncertainties Although the predictions in energy consumption by Eq. (6) closely match those of the experimental investigation, the following uncertainties should be considered: In this study, only one household refrigerator–freezer was tested and therefore it may not be appropriate to generalize the results. It would be more appropriate to carry out more extensive experimentation on a number of refrigerator–freezers of similar type to reach a generalized conclusion. To achieve that goal, more units of different brands, capacities, and features are currently under investigations. We do hope that the investigation will help us to reach a generalized conclusion.

11. Conclusions From Table 4, it is clear that, for optimum conditions, the predicted energy consumption was about 1.88 kWh/day. The following points may explain the optimum conditions: 1. In an actual household environment, a refrigerator–freezer door is opened 40–60 times per day. 2. The maximum daily average temperature was found to be about 27°C from Table 3. 3. A thermostat seting position at normal or average (position 4 in this setting) is the one most often used in a kitchen environment. 4. Energy consumption due to loading is a complicated one, so we considered an approximately 8 kg load to predict the energy consumption. 5. A 85% relative humidity with respect to the Malaysian climatic condition is a good estimate. However, experimental energy consumption was found to be 1.90 kWh/day as per ISO test specifications. So, there is a negligible amount of difference between the experimental results and predicted results. Moreover, in the prediction, we have included a 78% increase in energy con-

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sumption due to loading. In actual cases, it would be lower. So, considering all the points that we have discussed above, it is a good estimate to conclude that ISO 8187, ISO 8561, and ISO 7371 test standards can be introduced as a starting point for testing and rating of Malaysian household refrigerator–freezers.

Acknowledgements The authors would like to acknowledge the Ministry of Science, Technology, and Environment, Malaysia for funding the project. The research has been carried out under the IRPA project no: 02-02-03-0471.

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