Analysis Performance of Full Direct Current (DC) Refrigerator

Medium Temperature

I Dewa Made Cipta Santosa

, I Nyoman Gede Suta Waisnawa, Putu Wijaya Sunu,

I Wayan Suarsana and I Wayan Andika Adi Wiguna

Mechanical Engineering Department, Politeknik Negeri Bali, Jalan Kampus Bukit Jimbaran, Kuta Selatan, Kabupaten

Badung, Bali 80364, Indonesia

Keywords: DC Refrigerator, Performance, Medium Temperature, Cold Chain.

Abstract: The development of solar power systems in the tropics is very important as a good alternative energy of

conventional fuels (fossil). In addition, the rapid development of batteries become a good new to improve the

performance of solar energy storage. Thus, the refrigeration system with a direct current (DC) system is very

well developed. This study aims to obtain the optimum performance of the medium temperature refrigerator

DC system with solar energy sources using batteries directly without an inverter. With this method, it is

expected that the system can be more efficient from energy loss of DC current to AC current conversion. This

research is an experimental research which was conducted by built a test rig consisting of two main equipment,

namely a DC current refrigerator system and a solar power system. The test was carried out in the Bali-

Indonesia region according to the conditions of the intensity of sunlight and the refrigerator system was tested

with a load of fresh vegetable products. The results of this study found that the DC refrigeration system was

able to work well with COP of 3,6. From these results it can be concluded that this system is very feasible to

be developed along with the development of electrical energy from solar power. This system is also very

feasible to be developed to support the cold chain system in Indonesia to improve the quality of fresh vegetable

and fruit distribution.

1 INTRODUCTION

Refrigeration system is very important to be

developed in order to get health and fresh food

preservation, especially fresh fruits and vegetables.

However, investment cost of refrigeration systems in

developing countries are still relatively expensive

(Santosa, et al., 2020a). One of the best solution is

develop a renewable energy system, especially solar

energy to drive the refrigeration system. This is

because of during the day refrigeration system need

high energy consumption and at the same time the

energy output from the sun also reaches its peak

(Santosa, et al., 2021). As a tropical region, Indonesia

is very suitable to develop and innovate solar energy

systems. From various previous developments, it was

found that a solar power system to drive the

refrigeration system is very compatible with an

integrated energy source system with conventional

electrical energy sources. Innovations for the

https://orcid.org/0000-0002-9912-629X

efficiency of the refrigerator system have also been

developed, such as with a natural humidifier in

combination with a solar energy source. As well as

with the efficiency of heat transfer in the main

components of the refrigeration and air conditioning

system (Santosa, et al., 2020b, 2020c).

Conventional refrigerator systems which driven

by solar power systems has been studied for Gupta et

al., (2014), Bilgili, (2011) and Modi, (2009). The

research was conducted by developing off grid

(stand-alone) solar panels for conventional

refrigerator systems. The solar power system was

analysed according to the capacity of the refrigerator

system and it was found that solar power is very

suitable for the refrigerator system. The system was

further redesigned with a battery and inverter system.

From the test results, the average coefficient of

performance of the refrigerator system is quite good,

which is around 2.1. However, there are still

economic constraints which still require relatively

Santosa, I., Waisnawa, I., Sunu, P., Suarsana, I. and Wiguna, I.

Analysis Performance of Full Direct Current (DC) Refrigerator Medium Temperature.

DOI: 10.5220/0010939600003260

In Proceedings of the 4th International Conference on Applied Science and Technology on Engineering Science (iCAST-ES 2021), pages 41-46

ISBN: 978-989-758-615-6; ISSN: 2975-8246

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

expensive investment costs, because the price of

batteries is still relatively expensive. Furthermore, it

is recommended to emphasize as a follow-up for

urgent matters from the government, that the system

cannot survive economically if it is not given

appropriate incentives which are calculated around

15% of investment costs (Opoku et al., 2016).

One of the most important things to do is how to

optimize the solar power system and the energy

efficiency of the cooling system applied. One of the

variables that has been studied is the comparison of

system efficiency between 12 V and 24 V DC systems

which are operated at temperatures of 25 ° C and 35°

C. From the results of this study, it is found that the

comparison of operating a DC 12 V refrigerator is

much more efficient than the operation of a 24 V

refrigerator. V (Daffallah, 2018). Another thing that

has been studied is from an economic point of view,

which compares the solar power supply system used

for an AC refrigerator operating system with an

inverter and a DC refrigerator without an inverter.

The results showed that the DC refrigerator has the

potential to reduce the overall system installation cost

by 18% compared to the AC refrigerator. And it is

also recommended that for an off grid solar power

system it is more economical to use a DC refrigerator

than an AC refrigerator (Saliliha and Birhane, 2019).

Reducing energy consumption in the refrigerator

system is also carried out with good control of the

load from the system. refrigerator energy

consumption is affected by room temperature, door

opening and thermostat setting. Another thing is that

it is necessary to reduce energy consumption by

reducing the capacity of PV generators and batteries.

This optimization reduces the cost of autonomous PV

installations and helps generalize renewable energy in

the domestic refrigeration sector (Ouali et al., 2016).

Research to perform optimization with the

variable speed method has been investigated by (Su,

et al, 2020; Xua, 2017). The method used is to model

variations in the performance of the refrigeration

system by determining the compressor speed

variation. The analysis and simulation results show

that the refrigeration cycle COP for is around 2.25

when the compressor is running at low speed, and the

COP drops to the lowest value of 1.85 when the

compressor is operating at the highest speed (Su,

2020). Furthermore, because the system directly uses

the solar power system, the radiation intensity has a

significant effect on system performance. With the

increase in radiation intensity, this is certainly very

beneficial for system operations in the tropics (Xua,

et al, 2017).

Based on the above literature review, it can be

summarized that solar energy sources are very

eligible for the operation of the refrigeration system.

However, the conventional refrigeration system (with

AC current) is still constrained by the relatively

expensive investment costs associated with the cost

of batteries and inverters. While the innovations that

have been made to overcome this and at the same time

to improve the performance of the refrigeration

system are by developing a system based on full

direct current (DC), innovating for load and

infiltration efficiency, and investigating compressor

rotational speed. Thus, this research aims to obtain a

DC refrigerator system that is directly supplied with

energy from photovoltaic so that it can be more

efficient in terms of operational costs and investment

costs.

2 METHODOLOGY

This research is an experimental research, where the

method is divided into two parts including the

experimental rig and the measurement method as well

as data analysis.

2.1 Experimental Rigs

In general, experimental rig is explained with a

schematic diagram shown in Figure 1 as follow.

Figure 1: Diagram schematic of experimental rig.

This research is an experimental study with two

main types of equipment, namely: a solar power

Array

Batterie

Condenser

Evaporator

Expansion

Device

coil

Filter

Compressor

Control

Panel

iCAST-ES 2021 - International Conference on Applied Science and Technology on Engineering Science

generation system (Photovoltaic) and a medium

temperature refrigeration system with direct current

(DC).

Photovoltaic is assembled with an "off-grid" or

stand-alone system equipped with an energy storage

system with a battery. This system was chosen

because to get a complete test to drive the direct

current (DC) refrigeration system directly. DC

refrigeration system is a medium temperature system

with cooling capacity up to -5

C. The overall

experimental rig system design is shown in Figure 2

as follow.

(a)

(b)

Figure 2: Test rig: (a) Photovoltaic array, (b) Full DC

refrigeration system.

The photovoltaic circuit uses a series and parallel

circuit system with a slope of 15

north. For the

battery/ battery charging control system using a

system with Solar Charge Control (SCC). This SCC

controls the battery charge and can control the supply

of DC current directly from the photovoltaic system.

While the refrigerator system is a system with a

direct current (DC) system as a whole. The

refrigerator prototype was built with an experimental

rig to facilitate testing and improvement. For the

design of the DC refrigeration system, the main

components have been designed consisting of a DC

compressor, condenser, evaporator, capillary tube,

cooling room box which is made with a special frame

to be tested continuously with the AC refrigerator

system. The system is also equipped with a natural

humidifier system with a monitored hygrostat system.

This system is used for storage at medium

temperature conditions with temperatures up to -5

and 95% humidity. This humidifier system is

operated on and off with a timer control and an

automatic opening and closing mechanism for the

duct.

2.2 Data Acquisition and Analysis

Data collections are shown in Figure 3 and Figure 4.

In Figure 3 show the measurements state from point

1 to point 6 in the refrigeration system. While in

Figure 4 show the positions of cabin room

temperature (T7 and T11), and product temperature

(T8, T9, T10). The instrumentation and measurement

devices were already calibrated very well.

Meanwhile, secondary data were obtained from other

previously published journals and references.

Figure 3: Temperature and pressure measurement on

refrigeration system.

The data analysis method is carried out with

statistics that can be shown by pictures, graphs or

tables. The results of the analysis will be used as a

reference for planning the optimization and efficiency

of the use of solar power for the electricity

consumption needs of the refrigerator system. Data

analysis will use the help of several computer

Photovoltaic array:

Two photovoltaic in Seri array and three series array

connected in Parallel

Condenser

Coil extension

(cooler)

Filter drye

Evaporator

Expansion

Device

Coil

super heat

Compressor

=Pressure (Bar) = Temperature (

6 5

Analysis Performance of Full Direct Current (DC) Refrigerator Medium Temperature

programs, namely: cool pack, PVSys, and spread

sheet.

Figure 4: Temperature measurement positions on cabin and

products.

The temperature is measured using a type K

thermocouple, a pressure transducer with a voltage

signal. Environmental conditions are measured using

a special logger which includes air temperature,

humidity and dew point. The thermocouple has an

accuracy of +/- 0.5K, humidity +/- 0.5%, and pressure

(voltage output) 0.08%. The pressure sensors use

pressure transducers that are connected to a data

logger. Voltage, electric current and solar intensity

are measured separately with a digital system.

Data collection is carried out with loggers and by

using high-precision instrumentation and measuring

instruments. The research was carried out at the

Refrigeration Lab, Bali State Polytechnic because

some very necessary facilities are available in this

Lab. The refrigerator testing procedure is carried out

using a cooling load and without a cooling load.

Data is logged every 2 seconds and stored on the

laptop. All experimental data is imported into spread

sheets for easier calculation and analysis using simple

statistical methods. Data is tabulated in tables as well

as in graphs. The coefficient of performance (COP)

of the system was calculated using the @Coolpack

computer program and analysed. The effect of

operating natural humidity is also observed in detail.

3 RESULTS AND DISCUSSIONS

Based on the testing procedure on the refrigeration

cycle system, setting the test temperature is done at a

temperature of 0

C. The results of the data logger are

shown in the following tables and graphs Data is

obtained from a complete data logger and data on the

performance of the refrigeration system is taken

during the most stable test as shown in Figure 5 and

Figure 6 as follows.

Figure 5: Temperature characteristic of refrigeration cycle.

Figure 6: Variation temperature of cabin and products.

In Figure 5 can be seen that the compressor works

very optimally according to the “on and off” control

setting condition. Furthermore, the average operation

temperature on each point or stage is shown in Table

1. In addition, in Figure 6 is shown the temperature

condition in cabin and product (fresh vegetable). It

can be seen that the temperature different between

near evaporator position and near door position is

slightly high at around 3

C, an also temperature

different between upside and downside cabin at

around 6

C. This problem can be solved with better

insulation on the cabin.

In term of the theoretical Coefficient of

Performance (COP) calculation is based on the

average temperature and pressure conditions when

operating (on) excluding when the compressor is off

in each state with the type and specification of

refrigerant using refrigerant-R600a. The conditions

T10

T11

iCAST-ES 2021 - International Conference on Applied Science and Technology on Engineering Science

for each state (temperature and pressure), sub-cooled

and super heat conditions for calculating the average

theoretical COP are shown in Table 1.

Table 1: Average State condition during operation

(compressor on).

Point

Average

value

Point

Average

value

7,4

C P

sat

5,2 Bar, 40

C P

, T

sat

1 Bar, -12

33,0

C RH % 95%

31,0

C T

-5,0

C T

-0,2

From the data and calculations in Table 1, it can

be seen that the condition of the degree of superheat

) is very good and it is very convincing that the

evaporator capacity and compressor performance are

very good and the condition of the refrigerant

entering the compressor is really in a superheated

vapor condition. In terms of the degree of sub-cooled,

it is slightly higher (general standard 3K-2K) this is

because the installed condenser capacity is slightly

larger than the required capacity, considering the

availability in the market for fin and tube type

condensers. Meanwhile, the COP of the refrigeration

system as a whole is 3.63. This COP for the medium

temperature refrigeration system is quite good and

can be improved again by improving the insulation in

the cabin. Calculation of COP with @Coolpack is

shown in the following figure.

Figure 7: The COP analysis using computer program

@coolpack.

4 CONCLUSIONS

Based on the above result and discussion, it can be

concluded that the refrigerator system with total

direct current (DC) has a good performance which

indicated by the COP is 3.63. This COP can be

considerable very good if compare with the

conventional refrigerator system (alternating current-

AC). However, to improve the optimisation of the

system, it needs to be done with better insulation on

cabin this is indicated by the temperature different

between up and down part in cabin is slightly high at

around 5

C. And because of still development, this

refrigerator DC has only been developed for

household capacity.

Finally, it can be recommended that the

refrigeration DC system has the advantage of being

more efficient because it does not use an inverter

which has significant electrical power losses in the

solar power system circuit. This system will be very

suitable for use in areas in agricultural centres with

limited access to electricity networks as well as in

hotels with integrated solar energy sources. However,

this system still uses a battery so there is an additional

investment for the battery. However, with future

battery technology that is more sophisticated and

mass production and battery life will be longer, this

expensive investment cost analytically can become

cheaper.

ACKNOWLEDGEMENTS

This research was supported by the Directorate of

Sumber Daya, DIKTI, Ministry of Education, Culture

and Research Technology, Indonesian Government,

Grant No: 180/E4.1/AK.04.PT/2021 and

29/PL8/PG/2021 for the in cash contribution. The

authors wish to acknowledge the contributions of The

Mechanical Engineering Department -Bali State

Polytechnic for the in-kind contributions. Also,

Centre for Research and Community Service (P3M-

PNB) for all administrative support.

REFERENCES

Santosa,I,D,M,C , Waisnawa, I,G,N,S, PW Sunu,P,W IBP

Sukadana, I,B,P. (2020a). Temperature Characteristics

Investigation of Chilled Refrigerator with Humidifier.

Journal of Physics: Conference Series, Vol.1569, issue

3, 032040.

Santosa, I,D,M,C, Waisnawa, I, N,G, S, Sunu, P, W,

Wirajati, I, G, A, B. (2021). Investigation of

optimization of solar energy refrigerator with natural

humidifier. International Journal of Thermofluid

Science and Technology, Volume 8, Issue 2, Paper No.

080201

Santosa, I,D,M,C, Waisnawa, I, G, N, S. (2020b). Analysis

Feasibility of Photovoltaic Array Drive a Medium

Analysis Performance of Full Direct Current (DC) Refrigerator Medium Temperature

Temperature Refrigerator, Logic: Jurnal Rancang

Bangun dan Teknologi, Vol.20, issue 3, 200-204.

Santosa, I,D,M,C, Waisnawa,I,N,G,S, P,W, Sunu, Temaja,

I,W.(2020c). Evaluation of Air Side Characteristics

Performance of Finned Tube Evaporator. Journal of

Physics: Conference Series, Vo.1569, Issue 3, 032039.

Modi, A, Chaudhuri, A, Vijay, B, Mathur. (2009).

Performance analysis of a solar photovoltaic operated

domestic refrigerator. Applied Energy, Vol. 86, Issue

12, pp. 2583-2591.

Bilgili, M. (2011). Hourly simulation and performance of

solar electric-vapor compression refrigeration system.

Solar Energy, Vol.. 85, Issue 11, pp. 2720-2731.

Gupta,B,L, Bhatnagar, M , Mathur, J. (2014). Optimum

sizing of PV panel, battery capacity and insulation

thickness for a photovoltaic operated domestic

refrigerator. Sustainable Energy Technologies and

Assessments. Vol.7, pp. 55-67.

Daffallah, K, O. (2018). Experimental study of 12V and

24V photovoltaic DC refrigerator at different operating

conditions. Physic B: Condensed Matter, Vol. 545,

pp237–244.

Opoku,R, Anane, S, Edwin, I, A, Adaramola, M,S, Seidu,

R. (2016). Comparative techno-economic assessment

of a converted DC Refrigerator and a conventional ac

refrigerator both Powered by solar PV. International

Journal of Refrigeration, Vol.72,1-11.

Ouali, M, Djebiret ,M,A, Ouali, R, Mokrane, M, Merzouk,

N, K, Bouabdallah, A. (2016). Thermal control

influence on energy efficiency in domestic refrigerator

Hydrogen Energy, pp.1 -7.

Saliliha E.M, Birhane, Y,T. (2019). Modelling and

performance analysis of directly coupled vapor

compression solar refrigeration system. Solar Energy,

Vol.190 , pp.228–238.

Su, P, Ji, J, Cai, J, Gao, Y, Han, K. (2020). Dynamic

simulation and experimental study of a variable speed

photovoltaic DC refrigerator. Renewable Energy, Vol.

152, pp, 155-164.

Xua, Y, Ma, X, Hassanien, R, Hassanien, E, Luo, X, Li,

G, Li, M. (2017). Performance analysis of static ice

refrigeration air conditioning system driven by

household distributed photovoltaic energy system.

Solar Energy, Vol. 158, pp. 147–160.

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