Journal of Stored Products Research 89 (2020) 101720
Contents lists available at ScienceDirect
Journal of Stored Products Research
journal homepage: www.elsevier.com/locate/jspr
Design of a low cost, smart and stand-alone PV cold storage system
using a domestic split air conditioner
R. Mishra, S.K. Chaulya*, G.M. Prasad, S.K. Mandal, G. Banerjee
Mine Mechanisation, Automation and Technology Development Group, CSIR-Central Institute of Mining and Fuel Research, Barwa Road, Dhanbad, 826 001,
India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 June 2020
Received in revised form
11 September 2020
Accepted 12 September 2020
Available online xxx
To reduce post-harvest losses of food produce and ensure a better return to marginal farmers, a small
cold storage has been developed using a domestic split air conditioner. The developed solar-powered
cold storage is a low cost, simple and energy-efficient unit. Installation, operation and maintenance
costs of the cold storage are also less. The cold storage is integrated with IoT-based sensors for remote
monitoring and controlling of temperature and humidity as well as tracking of the stored items. It uses
multiple sensors and a microcontroller to maintain and monitor the desired temperature and relative
humidity. Average recorded temperature and relative humidity of the cold storage chamber is found to
be 6.88 (±0.7) C and 95 (±1) % respectively. Total cost of the designed 10 t capacity cold storage is around
$ 15710 in India including installation charges. This low-cost cold storage can be owned by a group of
farmers in the same locality for using it on a sharing basis or it can be owned by a produce trader to store
a variety of fruits and vegetables. Using the developed cold storage, total savings to farmers is calculated
to be $ 7449 per year. Farmers or traders can save around $ 20.46 in storage rent per tonne per week
considering an average 70% utilization of 10 t capacity of the cold storage throughout the year. Further,
the cost of cold storage can be recouped from the rent benefits within the first 2.1 year period.
© 2020 Elsevier Ltd. All rights reserved.
Keywords:
Cold storage
Air conditioner
Internet of things
Sensors
Solar panel
Insulation
1. Introduction
Increasing demand for fresh food has led to the inevitable need
for cold storage chains. Actual quality of food items starts deteriorating with time due to their perishable nature before they reach
customers. This perishable nature of fresh fruits and vegetables can
be appreciably reduced by storing them at low temperature
(Canovas et al., 2007). Generally, for fresh produce items, exposure
of 1 h at 35 C field temperature in between harvesting and precooling can deteriorate their quality equivalent to 20 h in cold
storage under suitable conditions. Loss of moisture can occur due to
delay in pre-cooling which results in weight loss of the produce
(Kumar et al., 2010). It is desirable to store fresh fruits and vegetables for duration of 2e4 weeks excluding potatoes, cabbages,
oranges, etc. However, long term storage degrades actual quality of
produce.
Cold storage improves the efficiency of cooling inside the room
to a great extent. The post-harvest cooling is required to quickly
* Corresponding author.
E-mail address: chaulyask@gmail.com (S.K. Chaulya).
https://doi.org/10.1016/j.jspr.2020.101720
0022-474X/© 2020 Elsevier Ltd. All rights reserved.
remove field heat, decrease the growth of micro-organism and the
production of ethylene (Sunmonu et al., 2014). It gives marketing
flexibility to farmers by allowing them to sell produce at the most
appropriate time. To provide high quality produce to customers, the
provision of post-harvest cooling should be made available to
farmers. Most of the cold storages in India and other developing
countries are based on refrigeration technique, which is expensive
and farmers cannot afford to own such huge cold storage. Further,
to reduce post-harvest losses of food produce and ensure a better
return to farmers, small cold storage facilities are essentially
needed.
In India, nearly 80% of the farmers are small and marginal who
are not even able to recover the cost of production by selling crops.
To prevent wastage of harvested crops, generally, all crops are sold
within a single day regardless of the current market price due to
lack of cold storage facilities in such locality. Most cold storages are
located in big cities, owned by big traders and farmers who charge
around $ 27.81 per tonne per week for storing produce. It has
become an urge to establish a customized, standalone and low cost
cold storage solution for such farmers in the vicinity of their farm
land to earn significant profit. Such units should be made equipped
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
incompatible mixing of products (Patil and Kolur, 2018). Fig. 1
represents the block diagram of the overall system operation.
The cold storage chamber mainly includes an AC unit, temperature sensor, humidity sensor, door sensor, LED tube lights, fan and
an alarm system. For power generation, a number of solar panels
are connected to operate the cold storage. Batteries are provided to
store energy for later use. LED tube light switches on, when the
door is opened and switches off when it is closed through a pushbutton switch which is mounted on the door of the chamber.
The correct capacity and rating of AC suited for a room are
identified based on size and its total storage capacity as well as heat
load calculation. There is no requirement of 3 phase high voltage
power supply (Shende, 2018). It can be well operated through solar
power with backup batteries even in remote areas where there is
no source of power (Kitinoja, 2013). The total capacity of the
designed cold storage chamber is 10 t with a room size of 39.64 m3
as shown in Fig. 2. The power conditioning unit/inverter of solar
power system converts direct current power obtained from solar
panel into 3-phase alternating current for running the cold storage
and different electrical appliances (Sharma and Kalita, 2018;
Shende, 2018).
To operate this cold storage in the best possible way, there
should be proper monitoring of the temperature levels of the room,
the temperature near AC vent, the relative humidity levels of the
room, air circulation, proper space between storage boxes and racks
holding containers, and efficient management of product based on
‘First in First Out Principle’ (Krishnakumar and Dayanandakumar,
2002).
Using a wireless sensor network, automatic monitoring facilities
can be implemented to manage different areas of the cold storage
chamber (Junxiang and Jingtao, 2011). Fig. 3 shows the block diagram for controlling various parameters like temperature, humidity, door movement and alarm system using a microcontroller and
relay module. This is implemented using different sensors for
monitoring cold storage system parameters. Using a microcontroller and a relay module, the desired temperature and humidity
levels of the cold storage chamber has been adjusted. When the
temperature of the room goes above the desired set level, the relay
connected to the AC unit turns on and the compressor of the AC unit
starts working. To control the relative humidity levels of the room,
one relay is connected to automatically turn on the humidifier
when its levels fall below the set point. All these relays are
controlled through a web interface using an ESP8266 Wi-Fi module
and IoT. In this way, using the Internet and mobile phone, one can
communicate with a microcontroller to perform the task. Different
roles of sensors attached to a microcontroller are described
herewith.
Temperature sensor:
with control modules which can be programmed and monitored
using an android phone (Padre, 2019). Due to lack of electrical
power infrastructure in many rural areas, solar power can be used
as an alternative source. For running solar-powered cold storage,
battery backup units are provided to store solar power generated
during day time and supply it during night time and cloudy
weather (Muneer et al., 2005). To meet the challenges of maintaining the desired low temperature and accurate humidity in an
ordinary room, cooling should be done with proper insulation to
store fruits and vegetables in fresh state (Priyan et al., 2016). For
maintaining high relative humidity levels in cold rooms, an effective humidifier must be installed to add moisture inside the room.
Further, it is required to keep darkness inside the cold storage room
for maintaining the quality and colour of produces (Zappia et al.,
2018). The price of solar PV panels is dropping on a yearly basis
due to continuous improvement in PV conversion efficiency. The
substantial growth of the PV based production industry has made
them a significant component of renewable energy-driven AC units.
The stand-alone PV based AC system could store the surplus electricity produced by the PV unit in the batteries throughout the day
time and power the AC unit during night or in cloudy and rainy days
(Chen et al., 2020). The inadequate solar PV generation often leads
to power loss in the running of AC unit. A proper system designing
is needed to fulfill the power consumption of an AC unit with a
correct PV size (Huang et al., 2016). The power consumption need of
the AC unit depends on the weather conditions at the location of its
installation (Opoku et al., 2018). The AC is designed to regulate and
run at a temperature range of 5e10 C, depending on the temperature requirement of different fruits and vegetables (Sharma and
Kumar 2018; Thompson et al., 1996; http://postharvest.ucdavis.
edu). To prevent heat entering through walls of the cold storage
chamber, thermal coating on the inner plastered wall is provided to
save electricity. AC cooling, temperature, humidity, gas proportion,
and LED tube lights are controlled effortlessly using a microcontroller and Internet of Things (IoT)-based sensors (Kitinoja, 2013;
Namdev et al., 2017).
The main objective of this study is to develop a low cost, smart
and energy-efficient solar-powered cold storage using a domestic
split air conditioner (AC) for maximizing the profit of farmers from
their produces. An IoT-based sensor network for remote monitoring
and controlling of temperature and humidity as well as tracking of
the stored items and providing emergency alerts through a mobileapp has been provided. Cost of the cold storage and its economic
benefit for the farmers has been assessed based on the current price
of the required items and resources available in India. This solarpowered cold storage has been designed for the area where solar
light is available for at least 6 h in a day. In the area where prolonged cloudy weather conditions exist, one standby generator
shall be provided to operate the cold storage as well as mitigate
temperature swings inside the cold storage. The capacity of the
designed cold storage is small and initially it is designed for 10 t
capacity. The paper includes design aspects of the developed smart
solar-powered cold storage as well as its installation and operation
procedures, heat load calculation for optimum system, performance assessment and cost-benefit analysis.
To sense room temperature and display it; and
To switch on/off AC unit.
Humidity sensor:
To sense relative humidity inside the room and display it; and
To switch on/off humidifier.
2. Design and working of cold storage of food items
One door alarm sensor is connected to door of cold storage
chamber to serve following purposes:
In order to convert an ordinary room, made up of bricks or
concrete walls into a cold storage room, one has to properly
maintain the required low temperature and provide effective
insulation to sustain coolness inside the room. To efficiently store
produce, it is mandatory to monitor different parameters like
temperature, humidity, circulation of air and space maintenance
between containers to allow for sufficient ventilation, and avoiding
To switch on/off lights inside cold storage;
To count the number of times the gate is opened; and
To trigger alarm, in case, the door remained open beyond a
specified period of time.
2
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
Fig. 1. Block diagram of the designed cold storage.
Fig. 2. Cold storage: (a) Layout diagram of cold storage chamber, and (b) View of the cold storage.
However, the evaporator coil of an AC is around 4.44 C cold. The
temperature at which the air comes out of the vents of an AC depends on how warm the air is present near its intake. The
The AC unit for cold storage is designed to maintain a lower
temperature below 10 C. The conventional household AC units can
go as low as 16 C due to the cut-off relay circuit present in them.
3
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
Fig. 3. Block diagram of sensors and devices connected with microcontroller for cold storage.
estimated based on heat load calculation as well as by taking into
account the overall climatic conditions of the place where the cold
storage room will be deployed. The average annual sunlight
received in East India is around 2200 h (Wikipedia contributors,
2019). Hence, daily sunlight availability to run a cold storage
chamber is [2200 h/365] 6 h. So, on a daily basis, there is a
requirement of 18 h power backup.
The energy to be consumed by the AC during the 18 h backup
period (with 0.6 duty cycle) is 21978 Wh. A 215 W industrial humidifier having 180 m3/h air volume has been chosen for this cold
storage in order to provide the desired humidity level for fresh
fruits and vegetables. An air circulating fan with specifications of
22 W, 150 mm blade sweep and 240 m3/h air deliveries is connected inside the cold room to circulate air uniformly. Four LED
tube lights of 20 W each are also fitted to work inside the room.
Now, the total energy to be consumed during the 18 h backup
period is 23978 Wh (Table 1).
thermostat of an AC unit is like an on/off switch that turns on and
off according to the set temperature. The cut-off circuit of the AC
unit has been removed to achieve the desired low temperature. A
new temperature sensor and microcontroller based circuit have
been fitted in a domestic split AC which controls the minimum
working temperature up to 5.0 C. The cooling function stops once
it senses air temperature lesser than the set temperature for the
respective cold storage.
Calculation of total energy requirement and total number of AC
units, batteries, solar panels and other electrical appliances needed
to operate the cold storage is given in Table 1. To design a 10 t
storage capacity solar PV panel powered cold storage, estimation of
different units required have been described.
2.1. Energy requirement
For a cold storage room of 39.64 m3 size, there is a need of an AC
unit with 2 refrigeration ton (7.03 kW) cooling capacity which is
Table 1
Power requirement of 10 t solar-powered cold storage.
Sl. No.
Parameter
Value
A
A1
A2
A3
A4
A5
A6
A7
A8
B
B1
B2
B3
B4
B5
B6
C
C1
C2
C3
C4
C5
C6
C7
Energy requirement
AC tonnage
Rated power
Duty cycle of AC (assumed)
Energy backup required for, hours
Energy consumed by AC during backup [A2 A3 A4]
Energy to be consumed by humidifier, fan, lights and control system
Total energy required for backup [A5þA6]
Energy required per hour [A7/A4]
Battery calculation
Capacity
Rated voltage
Rated energy stored
Battery capacity utilization
Net available energy from a 200 Ah battery
No. of batteries required for 18 h backup [A5/B5]
Solar panel
Sunlight availability per day
Battery power required to be charged per hour of sunlight [A5/C1]
Power required to run AC directly on solar power
Total [C2þC3]
Solar power required (considering 85% efficiency of inverter) (rounding up to next thousand)
Off-grid solar system required
Number of 325 W solar panel required [C6/325]
4
2 ton (7.03 kW)
1665 W
0.6
22 h
21978 Wh
2000 Wh
23978 Wh
1089.9 Wh
200 Ah
12 V
2400 Wh
50%
1200 Wh
20
6h
3997 W
1665 W
5662 W
7000 W
7 kW
22
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
addition to this, the water level inside the battery should be
checked every 2 weeks for getting the optimum performance.
2.2. Battery requirement
Table 2 provides all the necessary details regarding battery selection of tubular type, rated voltage of 12 V and rated capacity of
200 Ah, which can provide rated energy stored in the battery as
2400 Wh. Assuming a battery capacity utilization of 50% (to increase the battery life), the net available energy from a battery is
1200 Wh. Therefore, the required charging current to completely
charge the battery to full sunlight of 6 h duration is [1200 Wh/
(6 12 V)] 17 A. The number of batteries required for the desired
backup is 20. Hence, the required charging current is 340 A. The
batteries having 80% depth of discharge have been installed for the
cold storage, but only 50% of total capacity has been utilized. Thus,
there is buffer capacity of 30%. This buffer capacity is utilized during
low light conditions in the rainy season. Hence, reserve power
backup is available for 14 h (Table 2).
2.5. Inverter
Inverter converts direct current output obtained from photovoltaic solar panels into alternating current which is then fed to
operate cold storage and other electrical appliances present in the
chamber. An inverter of capacity 5.2 kVA of rated power 4420 W is
provided to perform the above mentioned task in operating this
storage chamber.
2.6. Insulation
The correct choice of insulation can be done on the basis of Rvalue, which defines its capability to resist heat (Krishnakumar and
Dayanandakumar, 2002). Higher R-value is preferred to get more
effective insulation.
2.3. Solar panel calculation
Floor insulation: Floor is insulated using 0.1 m thickness polyurethane foam (PUF) based slab over Portland cement concrete
(PCC) as it can support the load imposed on it and maintains the
performance of insulation. This slab has high compressive
strength, good thermal insulation, high resistance for water
absorption, low density, and low moisture-vapour permeability.
It can be used safely even at 50 C temperature level without
any adverse effects.
Wall insulation: Walls are insulated by providing thermal
insulation, which maintains temperature inside the cold
chamber effectively. Insulation of PUF can be jointly used with
cold rolled close annealed (CRCA) sheets for better results (Patel
and Patel, 2012).
Door insulation: A superior quality of PUF insulation is provided
to the hinge base with smooth metal surface for automatic
closing of the cold storage door.
Table 1 summarizes calculation for selection of number of solar
panels required for operation of a cold storage. A single solar panel
installed for a cold storage has the rated power of 325 W.
The required charging capacity per hour is calculated by
dividing the total energy to be consumed by the AC unit during
backup to daily sunlight availability in hours. Hence, value of
charging capacity per hour is 3997 W.
The power required for running a 2 refrigeration ton (7.03 kW)
cooling capacity AC directly on solar power during the day (i.e.
rated power of AC at full load) is 1665 W, which can be utilized for
changing batteries to charge and simultaneously running AC on
solar panel directly. Now, total solar power required per hour is
5662 W. Rounding off solar panel capacity to 7 kW, the number of
solar panels required to fulfill the demand of power is 22.
This solar-powered cold storage system involves 22 solar panels
of 325 W each, a 5.2 KVA inverter of 85% efficiency and a battery
bank of 22 batteries to supply power to the AC unit of cold storage,
so that it can operate uninterruptedly. In rural areas due to longer
time power cut and scarcity of maintenance facilities, this solar
energy source can be proved most effective for operation of cold
storage (Patel and Patel, 2012). Polycrystalline Cells type solar
panels of 325 W, 24 V rating are installed on the rooftop.
3. Storage of food items
Improper storage like overloading of storage chambers and poor
arrangement of the stacked boxes leads to wastage of food items.
All boxes or containers should be placed in an orderly manner
depending on their stacking strength to allow uniform air flow. In
general, metal racks or the use of returnable plastic crates are
preferred for storage since they allow adequate movement of air.
The well-ventilated boxes placed in proper alignment can enhance
performance of cold storage (Krishnakumar and Dayanandakumar,
2002). To remove the field heat from produce, pre-cooling operation should be carried out as it improves shelf-life of fresh produce,
hence decreasing rate of respiration and biochemical reactions
taking place within all new post-harvest produce (Chaudhary and
Sharma, 2015).
System parameters are continuously monitored through sensors
placed at different locations to set a temperature of around 5e18 C
and relative humidity of 90e95%. An alarm is provided in case of
unusual rise or fall in temperature and relative humidity levels.
Random opening and closing of the cold storage door for product
loading and unloading causes rise in temperature and fall in relative humidity. Different varieties of fruits and vegetables are categorized on the basis of their requirements in temperature and
humidity levels. It is important that the quality of one produce does
not hamper the quality of another produce while in storage. Fruits
and vegetables are stored depending on their compatibility and
needs. Table 3 shows representation of various fruits and vegetables that can be stored in the categorized groups depending upon
their compatibility with each other (Fellows, 2008; Kumar et al.,
2.4. Miscellaneous items calculation
The total installation cost required for setting-up of the designed
cold storage is $ 210 per KW including solar panel stand, cables cost
required for solar panel, and different electrical appliances like
humidifier, fans, lights and other utilities present inside the cold
storage room, excluding cost of insulating materials and inverter. It
also includes maintenance cost of the whole system. For maintenance purposes, there is a need for a person who can weekly clean
all PV solar panels to get the maximum power and efficiency. In
Table 2
Calculation for battery power and backup availability.
Sl. No.
Parameter
Value
A1
A2
A3
A4
A5
A6
A7
A8
Depth of discharge
Discharge level taken for calculation as per Table 1
Buffer battery capacity percentage [ A1eA2]
Rated energy stored in a battery (Table 1)
Numbers of battery required (Table 1)
Net buffer battery capacity [A3 A4 A5]
Energy required per hour (Table 1)
Number of hours of backup in reserve [A6/A7]
80%
50%
30%
2400 Wh
22
15840 Wh
1089.9 Wh
14 h
5
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
2010).
Further, cold storage should be free from dirt and doors should
be opened for the minimum possible duration to avoid temperature
fluctuations. To prevent fast deterioration of fresh vegetables and
fruits, overstocking should be avoided as it increases the internal
temperature. A compatibility chart is prepared for short-term
storage of fruits and vegetables in cold chamber. Ethylene level in
the cold storage should be kept in low level by:
Table 4
Parameters for heat load calculation.
Separating cold storage rooms from ethylene source;
Ventilating the storage room with fresh outside air; and
Application of an ethylene scrubber.
Parameter
Value
Optimal storage temperature
Optimum relative humidity
Specific heat
Rates of Ethylene production
Ambient temperature
Bulk density of okra
Heat of respiration
10 C
95%
0.00385 kcal/kg C
Low
45 C
398 kg/m3
6669 W/t/day
Total volume of boxes and produce ¼ (Total volume of okra þ box
volume)
¼ 25.13 m3 þ 2.048 m3 ¼ 27.17 m3
4. Heat load calculation
Free volume available inside the cold storage ¼ (Product volume e
Internal volume)
The temperature level should be monitored continuously for
efficient working of cold storage. To calculate the required cooling
capacity, the most severe conditions have been taken into consideration for operating cold storage, such as the maximum outdoor
temperature, the maximum quantity of produce cooled per day,
and the maximum temperature of the produce to be cooled. The
heat load is defined as the total amount of heat that the cooling
system should remove from the cold storage room. The heat load
for the cold storage has been calculated for storage of 10 t of okra
(lady’s fingers). Various parameters considered for head load
calculation are given in Table 4 (Krishnakumar and
Dayanandakumar, 2002).
Capacity utilization of cold storage has been calculated as
follows:
¼ 39.64 m3e27.17 m3 ¼ 12.58 m3
Percentage utilization of cold storage volume ¼ 68.55%
Properties of building and insulating materials are given in
Table 5 and dimensions of the cold storage are mentioned in
Table 6.
Total internal volume of the cold storage is 39.64 m3 and total
external volume is 57.97 m3. External thickness of walls includes
0.015 m plaster, 0.23 m brick, 0.015 m plaster and 0.1 m PUF, from
outer to inner surfaces respectively. External thickness of ceiling
includes 0.3 m concrete and 0.1 m PUF, from outer to inner surfaces
respectively. If the steady state flow is considered than, the heat
flow is calculated as:
Volume of the produce ¼ (Weight of the produce) / (Bulk density of
the produce)
Q ¼ u A (To e Ti) W
¼ 10,000 kg/ 398 kg/m3 ¼ 25.13 m3
Where, u ¼ Over all heat transfer coefficient (W/m2 C)
Size of each box (internal
dimension) ¼ 0.550 m 0.300 m 0.220 m
A ¼ Surface area through which heat is transferred (m2)
To ¼ Temperature of outside air ( C)
Ti ¼ Temperature of inside storage space ( C)
The overall heat transfer coefficient is given by:
Hence, volume of each box ¼ 0.0363 m3
Number of boxes required ¼ (Weight of the produce) / (Weight of
the produce in each box) ¼ 693
Thickness of each box ¼ 0.004 m 0.004 m 0.004 m
Table 5
Properties of building and insulating materials.
Actual volume of corrugated 3 ply used per box ¼ 0.0029545 m3/
box
Total volume of boxes ¼ (Volume of each box) (Total number of
boxes) ¼ 2.048 m3
Material
Thickness (m)
Thermal conductivity (kcal/m/h C)
Bricks
Plaster
PUF
Concrete
0.23
0.03
0.1
0.3
0.84
0.796
0.024
0.88
Table 3
List of fruits and vegetables that can be stored together (http://postharvest.ucdavis.edu).
Group Temperature and RH Crops
range
A
B
C
57 C and 90e95% Cabbages, Green beans, Long bean, Broccoli, Fresh Olives, pear, Pomegranate, lychee
RH
710 C and 80e95% Basil, Green beans, Wax, Cucumber*, Peas, Eggplant*, Long Bean, Squash
RH
Pepper: Bell, Chili, Tomatillo, Olive, Winged Bean, Avocado, Grapefruit*
Guava, Lemon*, Orange, Pineapple, Tamarind, Tangerine, Watermelon
1318 C and 85
Bitter Melon, Cassava, Dry Onion, Ginger, Potato, Pumpkin, Squash, Sweet Potato*, Tomato: Ripe, Partially Ripe and Mature Green, Yam*,
e95% RH
Banana, Crenshaw Melon, Jackfruit, Mango, Papaya
Key: * Fruits and vegetables are sensitive to ethylene damage (Thompson et al., 1996).
6
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
¼ 10*6669 W/ metric ton/ day ¼ 66690 W/ 24 h
Table 6
Dimensions of cold storage.
Dimension
Internal (m)
External (m)
Adding values of (1), (2), (3), (4) and (5), we get
Length
Breadth
Height
4.267
3.048
3.048
4.642
3.423
3.648
(f) Total heat load:
¼ 81477 W/ 24 h
1:163
u¼
1
ho
þ
x1
k1
(6)
þ kx2 þ …h1
2
(5)
(g) Miscellaneous load calculation @ 2%:
i
¼ 1630 W/ 24 h
Where, ho ¼ 4, heat transfer coefficient on the outer surface.
(7)
Now, adding (6) and (7), we have
(h) Overall heat load per day:
hi ¼ 15, heat transfer coefficient on the inner surface
x1, x2 … ¼ Thickness of wall, ceiling and insulating material
respectively (m).
k1, k2 … ¼ Thermal conductivity of wall and insulating materials
(W/m h C)
(a) Heat transfer through the walls:
¼ 83,107 W/ 24 h
(8)
Assuming refrigeration operates for about 12 h/day, the refrigeration capacity required [(8)/12]
Overall heat transfer coefficient, u ¼ 1.163/ ((1/4) þ (0.23/
0.84) þ (0.03/0.796) þ (0.1/0.024))
¼ 6926 W
¼ 0.2459710 W/m2 C
1 ton of refrigeration ¼ 3516.9 W
Surface area of all walls ¼ 44.59224 m2
So, refrigeration tonnage required [(9)/(10)] ¼ 6926/
3516.9 ¼ 1.969 ¼ 2.0 ton ¼ 7034 W.
Similarly, heat load of other fruits and vegetables have been
calculated using this approach.
Heat transfer through walls and insulation
¼ 0.2459710*44.59224*(45-10) *24 ¼ 9214 W/24 h
(9)
(10)
(1)
5. Cost analysis of cold storage
The cost estimation of different components utilized for developing this system has been made considering their rate in India
with the dollar conversion factor of 1 USD ¼ 71.963 INR (as on
November 14, 2019). Cost of a single battery costs is $ 247 and cost
of a 325 W solar panel costs is $ 140. A solar charger is also provided
with solar panel.
Cost of the designed cold storage is around $ 15710 in India
including total installation cost for solar panel, AC unit, battery
bank, inverter, room insulation and labour cost. Installation cost
also includes cost of cables, wiring, switches, fan, lights and one
emergency alarm system. Make and model of different components
and overall cost estimation for designing the cold storage is
mentioned in Table 7.
Table 8 represents the calculation of annual recurring cost of the
cold storage chamber, considering straight-line depreciation,
inflation (@ 5% per year), life expectancy of different items
depending on their type and annual maintenance. Overall benefits
from this cold storage are as follows:
(b) Heat transfer through the ceiling:
Overall heat transfer coefficient, u ¼ 1.163/ ((1/4) þ(0.3/0.88) þ(0.1/
0.024)) ¼ 0.2444522 W/ m2 C
Surface area of all walls ¼ 13.005816 m2
Heat transfer through walls and insulation
¼ 0.2444522*13.005816*(45-10) *24 ¼ 2671 W/ 24 h
(2)
(c) Heat transfer through floor:
¼ Half of that from ceiling ¼ 1335.5 W/ 24 h
(3)
The designed cold storage can provide large savings in initial
establishment cost including investment in installation and
equipment cost.
The AC unit and other equipment installed in the designed cold
storage consume lesser electricity than conventional
refrigeration-based cooling systems.
The maintenance cost for this designed cooling technique is very
less in comparison to conventional cooling units. Any general
technician with less expertise can install the AC unit.
Conventional refrigeration based cooling units require higher
investment because it includes both equipment cost as well as
installation cost. The conventional cooling methods need lots of
coolant, one big size motor, a large surface area, and multiple
(d) Product cooling:
Heat required to cool down the produce to required
temperature ¼ 10000*(45-10) * 0.00385 *1.163
¼ 1567 W/ 24 h
(4)
(e) Respiration load during cold storage:
Net amount of produce (tons)* heat of respiration
7
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
Table 7
Cost of different components of 10 t capacity cold storage with manufacturer details.
Component
Cost
($)
Make and Model
Air conditioner
Battery bank
Solar panel
Inverter
Installation cost of solar
panel
Insulation materials
Contract labour
Cost of construction of cold
storage
Humidifier
700
4940
3080
388
1470
Voltas Ltd., India; 2 refrigeration ton (7.03 kW) 5 Star Split Inverter AC (245 V ZZV)
Exide Industries Ltd., India; Type- IT750, Part No. FEIO-IT750
Luminous Power Technologies Pvt. Ltd., India; 325 W 24 V Polycrystalline Solar PV Module Panel, LUM 24325
Luminous Power Technologies Pvt. Ltd., India; Luminous Cruzeþ 5.2 kVA Sine Wave Inverter
700
1150
3000
Omkar Puf Insulation Pvt. Ltd., India; Puf Insulated Cold Room Panels, flooring and hinged door
250
Hangzhou Senrees Electric Appliance Co. Ltd., China; CJ-30Z
Power: 215 W, Air volume: 180 m3/h, Industrial humidifier
Sonoff India, Model: AM2301, Temperature measuring range: e40 C ~ þ80 C, Humidity measuring range: 0e99.9% RH and Wireless
temperature and humidity monitoring switch, Model: TH16
Temperature and humidity 32
sensor
Total
15710
Table 8
Annual recurring cost of a cold storage of 10 t capacity.
Item
Price in $
(P)
Useful life in years
(UL)
AC
700
10
Battery
4940
6
Solar panel
4550
20
Inverter
420
10
Insulation
700
10
Cold storage structure including labour 4150
15
cost
Sub-total (A)
Maintenance
@ 4% of total installed facilities
cost (B)
Total (AþB) 2679
Total price including inflation in $ {NI/100)þ Annual recurring cost in
Net inflation in %
1}*P
$
(NI)
{(1.05)UL e 1}*100
63
34
165
63
63
107
1141
6620
9419
685
1140
8591
114
1103
603
69
114
573
2576
103
numbers of fans unlike the designed method which mainly
works on AC unit. The AC unit has been controlled by the temperature controller circuit with Wi-Fi switches.
Instead of using refrigeration based commercial cold storage
available in the market by paying rent, farmers can save significantly if a group of farmers of the same locality own this small cold
storage. Total savings to the farmers per year by using this designed
cold storage is $ 7449 considering 70% utilization of cold storage.
Thus, the farmers can save $ 20.46 in storage rent per tonne per
week even if 70% capacity utilization of stored food produce is
considered. Further, payback period will be 2.6, 2.1 and 1.3 year
with the average 60, 70 and 100% capacity utilization of the cold
storage respectively.
6. Results and discussion
The cold storage can provide efficient cooling and reduce quality
losses of produce by increasing their shelf-life. Temperature of the
cold storage room and surrounding ambient environment were
measured for 7 days by continuously monitoring and storing
temperature and humidity data after every 5 min using the
installed sensors inside and outside the cold storage. The average
temperature and relative humidity recorded from this chamber
were 6.88 (±0.7) C (Fig. 4) and 95 (±1) % (Fig. 5) throughout 7 days
monitoring period. Figs. 4 and 5 represents the hourly variation of
temperature and relative humidity inside and outside the cold
storage for 7 days.
The PUF slabs with CRCA sheet used in this cold storage as an
insulating material provided satisfactory result in controlling heat
flow from the outside environment as well as maintaining the
desired level of the temperature and relative humidity. It has been
found that the room temperature and humidity remains almost
constant up to 20 min after switching off the AC and without
opening the cold storage door.
Saving of farmers from the designed cold storage has been
estimated based on its percentage of capacity utilization (Table 9).
The designed storage capacity of cooling chamber is approximately
10 t. The cold storage unit can significantly reduce post-harvest
losses and boost income of marginal farmers.
7. Conclusions
The developed AC based cold storage is better than the conventional refrigeration system in terms of simplicity, energysaving, cost-saving and ease of maintenance. The developed cold
storage is powered by solar PV panels and based on a domestic split
AC unit. Temperature-controlled relay circuit connected to AC unit
proved that it is fully capable of maintaining the lower set temperature below 10 C even in hot weather conditions when the
outside temperature ranges from 39 to 42 C. The average temperature and relative humidity recorded inside the cold storage
chamber were 6.88 (±0.7) C and 95 (±1) %. Different sensors
connected inside the room provide real-time value of important
system parameters like temperature and humidity. These parameters can be monitored even from any outside location of the cold
storage room having internet connectivity. The designed cold
storage is capable to provide savings in initial establishment cost
which includes investment in installation cost and equipment cost.
The AC unit and other equipment installed in the designed cold
8
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
Ambient temperature
Temperature inside cold storage
35
temperature °C)
30
25
20
15
10
5
0
0
6
12
18
24
30
36
42
48
54
60
66
72
78
84
90
96 102 108 114 120 126 132 138 144
time (hrs)
Fig. 4. Measured temperature of the designed cold storage chamber.
Ambient rela ve humidity
Rela ve humidity inside cold storage
100%
90%
relative humidity %)
80%
70%
60%
50%
40%
30%
20%
10%
0%
0
4
8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100104108112116120124128132136140144
time (hrs)
Fig. 5. Measured relative humidity of the designed cold storage chamber.
Table 9
Cost of storage and benefits for farmers in comparison with the refrigeration based cold storage.
Sl. No.
Items
Cost ($) estimate based on
percentage of capacity utilization of
the cold storage
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
Percentage utilization of cold storage
Capacity (t)
Annual recurring expense of farmers in maintaining and running a cold storage
Weekly expense of farmers in maintaining and running cold storage
Weekly expense of farmers in storing a tonne of produce
If farmers keep their produce in a commercial cold storage, they will be charged rent (@ per tonne per week)
Net saving to farmers per tonne per week
Net saving to farmers per week
Net saving to farmers per year
Payback period in year (cost of the cold storage $15710/A9)
60%
6
2674
51.42
8.57
27.81
19.24
115.44
6003
2.6
70%
7
2674
51.42
7.35
27.81
20.46
143.25
7449
2.1
100%
10
2674
51.42
5.14
27.81
22.67
226.68
11,787
1.3
produce when price increases.
A mobile-based or web-based application can be developed in
future to monitor the current rate of produce in the market so that
farmers can sell their produce to the customers at appropriate time
to earn the maximum profit. Further, with the use of IoT one can
control the functionality of cold storage as well as set real-time
temperature and provide emergency alerts through this suggested mobile-app.
storage consume less electricity than conventional refrigerationbased cooling systems. The current cost of the designed 10 t capacity cold storage is around $ 15710 in India. Total savings to a
farmer per year by using this designed cold storage is $ 7449 in
comparison to the conventional refrigeration-based cold storage.
The payback period of the developed cold storage will be 2 year 1
month with its 70% capacity utilization. Thus, the developed AC
based small cold storage will help a group of farmers or a trader to
store produce for longer period and they earn profit by selling the
9
R. Mishra, S.K. Chaulya, G.M. Prasad et al.
Journal of Stored Products Research 89 (2020) 101720
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R. Mishra, S. K. Chaulya, G. M. Prasad, S. K. Mandal and G.
Banerjee.
Richa Mishra: Methodology, formal analysis, original draft
preparation and investigation.
Dr. Swades Kumar Chaulya: Conceptualization, system implementation and technical supervision.
Dr. Girendra Mohan Prasad: Design and reviewing the paper.
Dr. Sujit Kumar Mandal: Revising and editing the article for
intellectual content and validation.
Dr. Gautam Banerjee: Approved the article for publication,
including references and technical advice.
Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgements
Authors are thankful to Dr. P. K. Singh, Director, CSIR-Central
Institute of Mining and Fuel Research, Dhanbad, India for his
valuable guidance and granting permission to publish this paper.
Authors are also grateful to the Ministry of Electronics and Information Technology, Government of India for supporting the project.
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10