Design and Fabrication of Solar
Powered Mobile Cold Room
Group Members
Shikongo JT
Haraseb
Benade
Pinzi F.L
Student No
218037228
NOVEMBER 18, 2022
Table of Contents
ABSTRACT................................................................................................................................................ 2
EXECUTIVE SUMMARY ............................................................................................................................ 3
INTRODUCTION ....................................................................................................................................... 3
AIM AND OBJECTIVE ............................................................................................................................... 3
METHODOLOGY ...................................................................................................................................... 4
Selection of charge controller ................................................................................................................. 4
Design Flow Chart ................................................................................................................................... 5
Block Diagram ......................................................................................................................................... 6
Design Procedures .................................................................................................................................. 6
DESIGN .................................................................................................................................................... 6
Determination of Project Values ............................................................................................................ 7
Load requirement ................................................................................................................................... 8
Sizing of the main control switch ............................................................................................................ 8
Selection of charge controller ................................................................................................................. 9
CONSTRUCTION ...................................................................................................................................... 9
RESULTS ................................................................................................................................................ 11
CONCLUSION......................................................................................................................................... 15
PROBLEMS JUSTIFICATION.................................................................................................................... 16
REFERENCES .......................................................................................................................................... 16
FIGURE 1: CONDENSER AND EVAPORATOR ASSEMBLY......................................................................................................... 2
FIGURE 2: 3 DOOR UNDER DOOR FRIDGE .......................................................................................................................... 3
FIGURE 3: DESIGN FLOWCHART...................................................................................................................................... 5
FIGURE 4: BLOCK DIAGRAM OF THE SOLAR POWERED COLD ROOM ...................................................................................... 6
FIGURE 5: SCHEMATIC DIAGRAM OF ALL COMPONENTS ...................................................................................................... 7
FIGURE 6: DIRECT COMPRESSOR VALUES ......................................................................................................................... 7
FIGURE 7: CHARGE CONTROLLER .................................................................................................................................... 9
FIGURE 8: COLD ROOM PUT TO THE TEST ....................................................................................................................... 10
ABSTRACT
A refrigeration system that makes use of solar power is The Design and Fabrication of Solar Powered
Mobile Cold Room. It was started due to the country's rural areas' erratic power supply and the lack
of a grid supply in some places where it was required.
The following parts make up the mobile cold:





D.C. compressor (Danfoss BD92K),
solar battery (12V, 200AH),
solar panel (12V, 600W),
charge controller (40A, 12V),
500L compartment.
The solar panel supplies the energy instead of the national grid or a generator system. The solar panel
that gathers sun energy is part of the solar-powered mobile cold room. Solar energy from the panels
is transformed into electrical energy and stored in the battery. The power for the cold room is normally
provided by the solar panel, but when the output power of the solar panel is lower, the battery
provides the extra power. The battery is recharged when excess amount of power is produced by the
solar panels. The output supply of the batteries and the solar panel is DC with voltage of about 12V.
A microcontroller was used to show the freezer's internal temperature and protect the compressor
by turning it off for 60 seconds whenever the door is opened. The battery and solar panel are
connected by a charge controller, which controls the voltage from the solar panel for charging the
battery. When there is no sunshine or just weak sunlight, the battery supply is used to power the D.C
compressor of the cool chamber. When the battery is fully charged, the device can operate for 18
hours without sunshine; it also has a large storage capacity of 1926 litters and a longer operating
period than earlier solar refrigerators.
Figure 1: Condenser and Evaporator Assembly
EXECUTIVE SUMMARY
This fabrication was carried out to further enhance the global knowledge of using renewable energy
resources which in turn reduce the challenges faced in the preservation of perishable food items,
drinks, harvest, and beverages for a long period before they are finally consumed by the end users.
However, the cold room will be built on a (cart) and will be accommodated with the batteries and
every other accessory needed.
INTRODUCTION
To close the gap in the availability of perishable food products, cold drinks, and beverages in rural
areas, a shift toward the utilization of renewable energy resources became imperative. Given that
food and other perishable things decay at room temperature, this design and manufacture were
intended to close the gap between socioeconomic circumstances and unreliable supplies of perishable
food items, drinks, and beverages in remote areas. The tools of daily life include refrigerators.
Uninterrupted power should be supplied to refrigerators to maintain cooling service.
Figure 2: 3 door under door fridge retrieved from https://www.bar-fridges-australia.com.au/
Photovoltaic (PV) systems are especially well suited for distant sites since they offer a reliable,
independent electrical power source right at the point of usage. Because of this, rural areas are
increasingly using PV solar energy for refrigeration (Mehmet, 2011). Due to its smaller compressor, a
refrigerator or freezer powered by photovoltaic (PV) technology has a lower cooling capacity than a
standard machine. Due to limited resources and expensive storage costs, using energy efficiently in
solar or other renewable energy-powered systems is more important than in other systems (Ekren,
2011).
AIM AND OBJECTIVE
The aim of this project is to design and fabricate a Solar Powered Mobile Cold Room
The following are the objectives of this fabrication;



To use renewable energy sources to eliminate the use of fossil fuel and electricity to power
the cold room
To Bridge the gap of non-availability of cold drinks in Rural Areas.
To extend the shelf life of perishable food items and post-harvest in off-grid areas.
METHODOLOGY
In designing and fabricating a micro-controller-based solar mobile cold room, there are many guides
involved in the design. This guide provides the information to correctly select the compressor, batteries,
solar array, wiring, blower (cooling fan), limiting resistors, metal sheet, aluminium sheet, and many
others. The method adopted in this study is purely experimental. The device was designed using
mathematical analysis and was converted into an experiment by following the design results obtained
in procuring the needed materials for the design.
Principle Applied
Procedures used in this project work and they are:
1. Freezer volume (constructed i.e., 1.926L)
2. Load requirement
Determination of backup size Batteries stores direct current electrical energy for later use
(Washington State University Extension, 2009). The stored energy is later used at night in the absence
of sunlight.
The formula below was used to calculate the backup size
𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑠𝑖𝑧𝑒
(𝑇𝑜𝑡𝑎𝑙 𝑊𝑎𝑡𝑡 − ℎ𝑜𝑢𝑟𝑠 𝑝𝑒𝑟 𝑑𝑎𝑦 𝑢𝑠𝑒𝑑 𝑏𝑦 𝑎𝑝𝑝𝑙𝑖𝑎𝑛𝑐𝑒𝑠 × 𝐷𝑎𝑦𝑠 𝑜𝑓 𝑎𝑢𝑡𝑜𝑛𝑜𝑚𝑦)
=
(𝐿𝐸𝑂𝑁𝐼𝐶𝑆, 2013)
(0.8 × 𝑛𝑜𝑚𝑖𝑛𝑎𝑙 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑣𝑜𝑙𝑡𝑎𝑔𝑒)
Note that; days of autonomy are the number of days that you need the system to operate when there is no power
produced by PV panels to get the required Ampere-hour capacity of a deep-cycle battery. Similarly, 0.8 is for the
depth of the battery discharge (compressors.danfoss.com).
Determination of PV size a photovoltaic system is an array of components designed to supply usable
electric power for a variety of purposes. When light shines on the cell it creates an electric field across
the layers. The stronger the sunshine, the more electricity is produced (Al Qdah, 2015).
This is used to charge the battery. Stated in equation 5, is the formula used to calculate the Total Wp
of PV panel capacity;
Total Wp of PV panel capacity = Total PV energy needed / 3.43 (Wp) (5)
So that;
Number of PV panel needed = Total Wp of PV panel capacity/selected rating (measured in modules)
(LEONICS, 2013) (6)
Where: WP = watt peak of the panel
Selection of charge controller
The Solar Charge Controller or solar charge regulator is basically a voltage and/or current regulator to
keep batteries from overcharging (Akinola, 2010). It basically regulates the output voltage and outputs
current coming from the solar panels before going directly to the battery assembly. The solar charge
controller regulates this 21-volt output of the panel down to what the battery needs at the time, also
as per the requirement of the mobile cold room compressor at that period of time.
This voltage varies from about 10.5 volts to 14.6 volts, depending on the state of charge of the battery
and the surrounding temperature at that given point of time. Secondarily, it also provides protection
against Overvoltage surges which would enhance the project’s controllability. It also prevents
complete draining (deep discharging) by discharging only to 70-80% of its total capacity, thus
enhancing the operating life of the batteries and providing a good payback option (Akinola, 2010). The
size of the charge controller used in this project was calculated using the formula
Solar controller rating = No of strings x Isc of the panel x 1.3 (7)
Where: Isc = short circuit current of PV array
Design Flow Chart
This section shows the sequence of operation of the flow chat in figure 1
START
INITIALIZING
DISPLAY ON LCD
WANT TO ENTER A
NEW TEMPERATURE
YES
DOES BUTTON
PRESS BEFORE 10
SECONDS
NO
DO FINAL SETTING
CONFIGURATION
YES
IF SET
TEMPERATURE
VALUE IS REACH
ENTER NEW
TEMPERATURE
OFF THE COLD
ROOM
NO
COLD ROOM
IS OPEN
Figure 3: Design Flowchart
Block Diagram
The microcontroller based solar powered freezer consist of eight stages and these stages are shown
in figure 4.
SOLAR PANEL
CHARGE CONTROLLER
BATTERY
MICROCONTROLLER
CONTROL UNIT
COLD ROOM
FAN
Figure 4: Block Diagram of the Solar Powered Cold Room
Design Procedures
The design procedures were broken down into the following steps:
1.
2.
3.
4.
5.
6.
7.
Selection of Compressor
Metal sheet
Aluminium sheet
Determination of total load
Duration of Operation (Battery Selection)
Selection of Panel
Programming of the microcontroller
The above-listed parameters were used to determine the efficiency of the refrigerator required and
consequently the amount of energy needed to power the system.
DESIGN
The adopted design principle for this project is that of a systematic approach to the design; it entails
the selection of appropriate components workable circuit biasing, the selection of components to be
used based on their operational characteristics, and the utilization of the right materials for the
construction and perfect finishing.
Schematic Diagram of the work Figure 5 shows the schematic diagram of the project which entails the
layout of each component.
Figure 5: Schematic Diagram of all Components
Listed (figure. 5) are the components from the schematic diagram as used in this work.
1.
2.
3.
4.
5.
6.
7.
8.
Solar Panel (12V/600W)
Charge controller(12V/40A)
Solar Battery(12V/200AH)
Fuse
Main switch
Light emitting diode (LED)
12VDC fan
DC Compressor (BD92K)
Determination of Project Values
Using Schematic Diagram 1.
Selection of direct current compressor Table .1 Direct Current compressors with their input and output
power (compressors.danfoss.com).
Figure 6: Direct Compressor Values
From Figure 6, the power of the selected compressor is found to be 100W, as seen in the shaded
portion. P=100W
Load requirement
In calculating the total load in this project work, equation 1 was adopted.
PT = PC + PF + PMCP (equation1)
Recall that Pc = 100W PF = 4.8W in that case,
PT = 100 + 4.8 + 6 = 110.8W
Or by using equation 2;
Total load = total load required x period of usage (Wh/day) (equation 2) 110.8W x 12 = 1329.6Wh/day
So that, the total PV energy needed = total load x 1.3 (Wh/day) (equation 3) 1329.6Wh/day x 1.3 =
1728.48Wh/day
Sizing of the main control switch
Since the total load power has been calculated using equation 3.1 and the result obtained is found to
be 110.8W, joules’ law can be applied and that is,
P = IV P = 110.8, V =12,
Therefore I
Switch = 110.8/12 = 9.23A.
In this project, the switch used was that of 15A, which is capable of handling the required load current.
Determination of backup size Recall that equation 4 is suitable for the battery selection
𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑠𝑖𝑧𝑒 =
(𝑇𝑜𝑡𝑎𝑙 𝑊𝑎𝑡𝑡 − ℎ𝑜𝑢𝑟𝑠 𝑝𝑒𝑟 𝑑𝑎𝑦 𝑢𝑠𝑒𝑑 𝑏𝑦 𝑎𝑝𝑝𝑙𝑖𝑎𝑛𝑐𝑒𝑠 × 𝐷𝑎𝑦𝑠 𝑜𝑓 𝑎𝑢𝑡𝑜𝑛𝑜𝑚𝑦)
(0.8 × 𝑛𝑜𝑚𝑖𝑛𝑎𝑙 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑣𝑜𝑙𝑡𝑎𝑔𝑒)
𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑠𝑖𝑧𝑒 =
(110.8 × 18ℎ𝑜𝑢𝑟𝑠 × 1)
= 208𝐴𝐻
(0.8 × 12)
The nearest available battery in the market is 200AH, therefore, a 2 x 100AH battery was used
Determination of PV size Recall that equation 5 is appropriate for PV selection
Total Wp of PV panel capacity = Total PV energy needed / 3.43 (Wp) (equation 5)
But in equation 3,
Total PV energy needed = 1728.48Wh/day
Therefore, Total Wp of PV panel capacity = 1728.48Wh/3.43 = 503.93Wp,
Similarly,
Number of PV panel needed will be calculated thus;
Number of PV panel needed = Total Wp of PV panel capacity/selected rating (equation 6) = 503.93/150
= 3.359 modules
Actual requirement = 4 modules
Here, charging time is assumed to be 8hrs = 200 8 = 25:
Therefore, a 4 X 150W/6.5A solar panel was used to charge the battery effectively for the chosen time
Selection of charge controller
Recall that in selecting the charge controller rating, the number of strings and the panel short-circuit
current must be known; as such equation 7 was used Solar controller rating = No of strings x Isc of the
panel x 1.3 = 4x6.5x1.3 = 33.8A
Therefore, a 12/40A charge controller was selected for this project work.
Circuit Diagram the circuit diagram for micro controller based solar based cold room system is shown
in figure 4.
Figure 7: Charge Controller
CONSTRUCTION
The building of the microcontroller-based solar-powered mobile cool room began with the creation
of a 500-liter cold chamber (figures 5–13) made of mild steel and aluminum, with an approximate
volume of 498750cm3 (V = w x b x h cm3). A 12V D.C compressor, model number BD92K, was chosen,
and R600a was pumped into it. The cold room was powered by a 12V/200AH solar battery, and each
piece of the building was put together to create an unified unit. Using bolts and nuts, the chosen DC
compressor was attached and securely tightened. The compressor's discharge low suction line (pipe)
and the condenser pipe coils positioned at the back of the cold air intake were joined by welding.
Figure 8: Cold Room put to the test
RESULTS
At the end of the fabrication, a functional mobile Solar Cold Room having the wall capacity of 1926L with about
17.3 hours of cooling when fully loaded was fabricated.
Project name:
3 Door Under bar Fridge
Coolselector2
version:
Printed:
5.1.2. Database: 91
Preferences
used:
All applications
Sunday, 20 November 2022
Refrigerant:
R134a
Evaporating dew point
temperature:
-5.0
°C
Ambient
temperature:
33.0
°C
Evaporating pressure:
243400
Pa
Sub cooling:
3.0
°C
Useful superheat:
6.5
°C
0
°C
Additional superheat:
0
°C
Additional
sub cooling:
Altitude:
0
m
Return
temperature:
Rating conditions:
1.5
°C
Required
capacity:
gas
cooling
Custom
268 W
Match percentage (127.9%) is higher than maximum
110%).
Model
OP-MCGC006FRA04G
Code number
114X0203
Compressor
model
FR6GX
Product range
Optima™
Product version
A04
Refrigerant
R134a
Cooling [W]
343
COP
[W/W]
1.67
cooling
Total power [W]
205
Total current [A]
1.241
Frequency [Hz]
50
Power supply
220 - 240 V 1 ph.
Tc [°C]
43.5
Figure 9: Refrigerant R134a properties
Cold room 1 - Liquid line
Operating conditions (synchronized across application)
Refrigerant:
R134a
Mass flow in
0.002391
kg/s
line:
Evaporating
temperature:
-5.0
°C
Evaporating
pressure:
243400
Pa
Useful
superheat:
6.5
°C
Additional
0
°C
superheat:
Discharge
temperature:
65.6
°C
System and
line:
Dry - Liquid line
Line total
Pressure drop
Saturation
temperature
drop
870400
Pa
48.5
°C
Cooling capacity:
343
W
Heating capacity:
451
W
Condensing temperature:
43.5
°C
Condensing pressure:
1114000
Pa
Sub-cooling:
3.0
°C
Additional sub-cooling:
0
°C
Pipe. Piping: Copper pipe DIN-EN 6
Length
Angle
1.00
0
m
Deg
Pressure drop
Saturation
temperature
drop
Velocity, in
Connection
151.6
Pa
0.0
0.17
OK
°C
m/s
95.78
Pa
0.0
°C
0.17
Open
Ok
m/s
EVR. Solenoid valve: EVR 3 v2
Pressure drop
Saturation
drop
Velocity, in
Valve state
Connection
Figure 10: Liquid Line
temperature
Figure 11: Suction Line
Cold room 1 - Suction line
Operating conditions (synchronized across application)
Refrigerant:
R134a
Cooling capacity:
343
W
Mass flow in line:
0.002391
kg/s
Heating capacity:
451
W
Evaporating
temperature:
-5.0
°C
Condensing
temperature:
43.5
°C
Evaporating pressure:
243400
Pa
Condensing
pressure:
1114000
Pa
Useful superheat:
6.5
°C
Sub cooling:
3.0
°C
Additional superheat:
0
°C
Additional
cooling:
0
°C
Discharge
temperature:
65.6
°C
System
line:
and
Dry - Suction line
Line total
Pressure drop
95.92
Pa
Saturation temperature drop
0.0
°C
Pipe. Piping: Copper pipe DIN-EN 12
Length
1.00
m
Angle
0
deg
Pressure drop
95.92
Pa
Saturation temperature drop
0.0
°C
Velocity, in
2.60
m/s
Connection
OK
sub
Cold room 1 - Cold room details
Evaporator conditions
Cooling capacity:
Dew point temperature:
Air inlet temperature:
Mean temperature difference:
Estimated fan power:
Estimated defrost power:
343
-5.0
5.0
10.0
28
215.6
Calculated cold room load:
Transmission:
93 W
Infiltration:
52 W
Ice on evaporator:
2W
Goods total:
59 W
Goods, cooling:
59 W
Goods, respiration:
0W
Light:
5W
People:
28 W
Fans:
28 W
Other:
0W
Defrost:
1W
Total:
268 W
Cold room details:
Room conditions:
Temperature:
5.0 °C
Relative humidity:
80.0 %
Operating hours:
17.3 h
Inner dimensions:
Length:
1.07 m
Width:
1.20 m
Height:
1.51 m
Goods:
Type:
Mixed products
Quantity per day:
217.2 kg
Inlet temperature:
10.0 °C
Air exchange (infiltration):
Figure 12: Evaporator Conditions
W
°C
°C
°C
W
W
Temperature:
32.0 °C
Relative humidity:
32.7 %
Door openings:
Regular
Air exchange rate:
35.9
Heat transfer:
Panel thickness:
0.0750 m
Temperature of surroundings:
32.0 °C
Temperature below floor:
15.0 °C
Floor is insulated:
Yes
Additional loads:
Lights:
40 W
Fans:
28 W
People:
2.0 h/day
Other:
0W
Defrost:
Defrost type:
Natural
Defrosts per day:
4.0
Defrosts time:
30
CONCLUSION
A conventional prototype DC Cold Room was designed,
and mounted in the cart. This project bridged the gaps of
availability of cold drinks and the eradication of
food spoilage as a result of non-constant/inadequate
in rural areas.
Figure 14: Fixing of the Evaporator after first padding
fabricated,
the
nonperishable
power supply
Figure 13: Mounting of the microcontroller and
the charge controller
PROBLEMS JUSTIFICATION
The device can be used for the storage of food items, drinks, beverages, and vaccines. Mobile Solar
Cold Room is ideally suited for countries, places, and remote areas where electrical power is epileptic
or not easily available. It promises to be in high demand by those whose businesses are centred on
perishable food items, beverages and drinks, and primary health centres. It also bridges the gaps of
non-availabilities of perishable food items, drinks, and beverages in rural areas.
References
• Al Qdah, K. (. (2015, October 24). Performance of Solar- Powered Air Conditioning System under
AlMadinah AlMunawwarah Climatic Conditions. Smart Grid and Renewable Energy. Retrieved
from http://dx.doi.org/10.4236/sgre.2015.67018
Ekren O., Y. A. (2011). Experimental Performance Evaluation Of A PvPowered Refrigeration System.
Electronics And Electrical EngineeringIss 1392 , 1215.
Ewert, M. K. (1998). Experimental Evaluation of a Solar PV Refrigerator with Thermoelectric, Stirling
and Vapor Compression Heat Pumps. Proceedings of Solar , 98. Retrieved from
http://solar.nmsu.edu/pub
Mehmet, A. A. (2011). International Journal Of Physical Sciences. Experimental Study Of A
MultiPurpose Pv-Refrigerator System, 6(4), 746-757 .
Refrigeration, F. L. (2017, January 15). Ice Maker Machines, Commercial Refrigeration & HVAC.
Retrieved from Cold Rooms, Freezer Rooms, Blast Freezers, Island Freezers, Under Bar Fridges:
http://freezelogic.co.za/commercial-refrigeration-repairs-installation-service/
Stoecker, W. F. (2010). Refrigeration and Air Conditioning Publisher McGraw . Refrigeration and Air
Conditioning Publisher , 212-216.
UniversityExtension, W. S. (2009). Solar Electric System Design, Operation and Installation. (W. 9. Bldg
3 Olympia, Ed.) An Overview for Builders in the Pacific Northwest, 98.