Energy Use In Post-harvest
Technology
By:
Dr Mahesh Kumar
Punjab Horticultural Postharvest Technology Centre
P u n ja b A g r ic u lt u r a l U n iv e r s it y
L u d h ia n a

Reasons
1 Post harvest behaviour of perishables
 Respiration & transpiration
- Temperature
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Reasons
• Infrastructure for marketing of perishables
 Primary grading/ collection centers - non existent
 Warehousing and cold storage - inadequate
 Cold chain - non existent
 Quality certification system - non existent
 Transportation for perishables - non existent
 Rural markets - complete lack of infrastructure
 Wholesale markets - in government control, lack modern facilities
 Private / direct markets - limited

What is cold chain
It starts from farm level and cover up to consumer level
Cold chain infrastructure consists of
1. Pre-cooling facilities 2. Cold store
3. Refrigerated carriers 4. Retail outlets
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The energy conservation opportunities
can be explored in the followings
 Field heat
 Respiration of stored product (vital heat)
 Transmission through roof and walls
 Evaporator coil fans, Lights, air leakage

Effect of Colour and Shade on the Temperature of Perishables
Crop Temperature drop by Shading Ambient
(oC) Temp(oC)
Pulp Skin
Brinjal (w) 8.1 12.3 30.5
8.1 12.3
Galgal 9.8 18.7 30.5
Banana 11.1 20.9 27.5
Guava 11.6 16.5 20.8
Mossami 9.2 18.5 20.8
10.4 18.7
Kinnow 8.4 16.0 20.8
8.4 16.0
Brinjal(S) 9.2 20.4 30.5
Brinjal(b) 10.6 20.6 30.5
Brinjal(L) 10.8 17.8 30.5
10.2 19.6

Tomato R 12.7 17.5 30.5
S-beet 13.0 23.3 30.5
Apple 10.7 17.5 20.8
Carrot 5.1 7.0 20.8
Onion 11.8 17.5 20.8
12.1 19.0
ClocasiaL 13.9 23.2 30.5
R 11.7 22.6 30.5
Chikoo S 9.7 16.5 20.8
L 6.2 15.0 20.8
11.8 20.8
Ghia R 9.6 17.5 30.5
L 11.4 19.5 30.5
Cabbage 8.5 17.8 30.5
Guava S 10.6 16.5 20.8
G 8.1 15.5 20.8
Lemon 9.4 15.0 20.8
9.6 17.0
Mango 12 31.5 33.9
Tomato G 13.6 20.5 30.5
Cucumber 11.4 18.5 30.5
Bitter Guard 10.1 17.5 30.5
Banana G 12.7 21.5 27.5
Mossami G 12.2 20.5 20.8
Capsicum 12.2 23.0 20.8
12.0 21.9

Summary : Colour effect
Group Colour Average temp. drop (oC)
No.
Pulp Skin Pulp Skin
I White 8.1 12.3
8.7 15.1
Orange 8.4 16.0
Light green 9.6 17.0
II Yellow 10.4 18.7
10.3 19.2
Violet 10.2 19.6
III Red 12.1 19.0
Blackish 11.8 20.8 12.0 20.6
Dark green 12.0 21.9

Effect of size within same crop
Crop Size Temp. drop(oC) Degree change(oC)
Pulp Skin Pulp Skin
Ghia 97.13 9.6 17.5
1.8 2.0
65.65 11.4 19.5
Clocasia 68.86 11.7 22.6
2.2 0.6
37.93 13.9 23.2
Guava 66.64 8.1 15.5
3.5 1.0
56.04 11.6 16.5
Chikoo 58.04 6.2 15.0
3.5 1.5
48.58 9.7 16.5
Note: Among different crops – erratic trend

Ambient temperature effect
Avg. ambient temp. Avg. temp. drop(oC)
(oC)
Pulp Skin
30.4 11.2 20.1
20.8 9.6 16.5
* Shaded produce w 100C low field tem
ith er perature would save 17% - 28% refrigeration costs

Respiration rate at different temperatures (mg/Kg/hr)
Crop Temperatures Respiration Increase
0 5 10 15 20 25 for 10oC rise in temp.
Apples 3 6 9 15 20 - 2.22
Banana - 18 30 50 88 148 2.96
Cabbage 5 11 18 26 39 56 2.15
Cauliflower 18 21 34 46 81 112 2.43
Orange 4 6 8 19 28 33 1.74
Mangoes - 16 - 45 113 120 2.66
Mushroom 36 36 50 - 290 - 5.8
Onion 3 4 8 11 17 28 2.55
Okra - 56 91 146 261 345 2.36
Peach 5 8 16 38 81 102 2.68
Pear 5 8 15 38 50 - 3.33
Peas 39 66 93 191 303 360 1.88
Plum 3 7 9 12 22 50 2.44
Potatoes - 6 9 9 12 18 1.33
Tomatoes - 7 15 22 35 43 1.95

Heat of respiration aat different temperatires (KJ/ ton/ day)
Crop Temperatures (oC)
5 10 15 20 25
Okra 14349 23318 37411 66879 88403
Peas 16912 23830 48942 77641 92246
Banana 4612 7687 12812 22549 37924
Cauliflower 5381 8712 11787 20755 28699
Mango 4100 7943 11531 28955 30749
Peach 2050 4100 9737 20755 26136
Potato 1537 2306 3075 3844 4612
Tomato 1794 3844 5637 8968 11018
Onion 1025 2050 2819 4356 7175

Refrigeration load in a cold store
Crop Total heat load (KJ/day) Tons of refrigeration Saving in
Refrigeration
35 25 Storage 35 25 Storage
Okra 24346262 18328017 5429113 107 80 24 27
Peas 24781762 19455491 6198013 109 85 27 24
Banana 17735262 12331991 2508013 78 54 11 24
Cauliflower 16915262 12255091 2738713 74 54 12 20
Mango 17043362 12998191 2354413 75 57 10 18
Peach 16197762 9923891 1739413 71 44 8 27
Potato 13865962 9923391 1585513 61 44 7 17
Tomato 14660362 10589591 1662613 64 46 7 18
Onion 14096662 9948991 1431913 62 44 6 18

Share of heat of respiration to total heat load
Crop Share of heat of respiration to total
refrigeration load (%)
35 25 Storage
Okra 46 49 79
Peas 47 52 82
Banana 25 26 55
Cauliflower 22 24 59
Mango 23 28 52
Peach 19 25 35
Potato 5 6 29
Tomato 10 12 32
Onion 7 6 21

Energy used in room cooling
Heat Load at different temperatures
Crop Saving
(%)
25 35
Okra 9316 10953 14.9
Peas 9957 11551 13.8
Banana 7950 8491 6.4
Cauliflower 7893 8391 5.9
Mango 7879 8847 10.9
Peach 7779 8391 7.3
Potato 7409 7452 0.6
Tomato 7551 7736 2.4
Onion 7395 7480 1.1

Energy used in package icing
Quantity of ice needed for Saving in quantity
Crop pre-cooling (lbs) of ice (lbs)
35 25
Banana 943 1007 64
Cauliflower 936 995 59
Mango 934 1049 115
Okra 1105 1299 194
Peach 923 995 73
Peas 1181 1370 189
Potato 879 884 5
Tomato 896 917 22
Onion 877 887 10

Heat transmission and leakage
 Insulation to walls & roofs
70% of total heat entering a cold store
room comes through roof & 25% from walls
 Painting the exterior walls and roofs
painting light colour on walls can reduce
wall temp. by 110C

ACU
Fin Evaporator v/s Old System

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Evaporator system
 Discard bunker/ diffuser air-cooling unit
 Large length of pipe required for cooling.
 Saving in space (2-3%) compared to bunker/
diffuser (15-20%, Approx. 8 feet height)
 Fin evaporators save 30% energy in cooling.
 Uneven distribution of air
 Bunker/ diffuser has less suction pressure (25-
27PSIG) to ammonia compressor compared to fin
evaporator (35-37 PSIG)

ACU Selection
 For cooler 8’ width; shallow coil (1-2) ceiling/ wall mounted.
 Storage installation (±1OC): 2-3 FPI
 Higher temperature: 14 FPI
 Optimum flow rate for efficient cooling
 Coil should be 3“ away from ceiling
 Use insulated coil decks

Refrigerant fluid
 Prefer ammonia based system over HCFC-22
 Lower mass of ammonia
 Lower pipe size and length
 More tolerance of ammonia to water
 Better thermal and transport properties
 Higher refrigeration capacity – 2.5 times.

Condenser System
 Temperature of refrigerant fluid after cooling.
 Economical ACC – 43OC
 Heat exchange surface
 ACC – smaller installation
 Water cooled – large installation
 Economical water flow rate – 2.5-3 gal/min/ton
 Scaling load –inhibited solution of muriatic acid (18%)

Compressor
 Select compressor system that operates efficiently
over required range of refrigerant flow.
 Rotary compressor – less than 2 ton
 Centrifugal compressor/ reciprocating compressors
– 50 ton or above

Quick Selection – Ammonia ACU with various compressors
Frick/ Coil Super/ Sinco Capacity of Cold Estimated
Ammonia Kirloskar Storage Compressor
Compressor Ammonia Capacity
Compressor
80Kg bag MT TR/hr
4x4 4 1/2 x 41/2 7500 600 12
5x5 51/2 x 51/2 12500 1000 20
6x6 6 1/2x 61/2 18750 1500 30
7x7 71/2 x 71/2 25000 2000 40
- 81/2 x 81/2 56250 4500 90
9x9 - 62500 5000 100
Selection: 1 TR/ hr. - 50 MT

Pre-Cooling Units
Selection of pre-cooling methods
 Nature of product
 Sensitivity to chilling and moisture
 Packaging requirements
 Volume of produce handled
 Economic constraints

Distribution of heat input in pre- Cooling
Item Percent of total heat input
Vacuum Hydro Forced air
Product 100 54 47
Fan/ pumps 0 9 37
Leakage/startup, 0 37 7
conduction
Lift tructs 0 0 8
Light/people etc. 0 0 1

Typical Energy efficiency in pre-
cooling operations
Type of cooler Energy coefficients
Vacuum cooler 2.5 – 1.5
Hydro cooling 2.3 – 0.7
Forced air cooling 1.5 – 1.4

Pre-Cooling Times for 7/8th cooling of Pears
Method of Cooling Cooling Time
Room Cooling 16-24 hrs
Forced air cooling 3-6 hrs
Hydro-cooling 40-45 Min

Hydro-cooler
 1/3 heat input
- Due to heat leakage
- Heat conduction and
- Cooling water reservoir start up each day
How to improve energy efficiency
 Minimized distance between shower pan and product top
 Adding insulation, shading or painting light colour reduces heat conduction
 Place hydro-cooler in refrigerated building – 30% energy saving

Forced air cooler
 Fan contributes 33 – 50% to total heat removed in addition
to its own energy consumption
 Use cartons with 5% vent area
 Aligning pallets vents with cooler to reduce air flow
resistance
 Use variable frequency control fans to slow fans at the end
of cooling cycle

Guide table for cold store owners for knowing RH in the chambers
RH at various DBT (%)
1 1.5 2 2.5 3 3.5 4 4.5 5
WBT RH WBT RH WBT RH WBT RH WBT RH WBT RH WBT RH WBT RH WBT RH
0.1 85 0.1 77 0.1 70 0.1 63 0.1 56 0.1 50 0.2 45 0.2 40 0.2 35
0.4 90 0.3 80 0.5 75 0.2 64 0.4 61 0.5 55 0.5 50 0.6 45 0.6 40
0.7 95 0.6 85 0.8 80 0.6 70 0.7 65 0.8 60 0.6 51 1.0 50 1.0 45
1.0 100 0.9 90 1.0 84 0.9 75 1.0 70 1.2 65 0.9 55 1.3 55 1.4 50
1.2 95 1.4 90 1.2 80 1.4 75 1.5 70 1.2 60 1.7 60 1.7 55
1.5 100 1.7 95 1.6 85 1.7 80 1.8 75 1.6 65 2.0 65 2.1 60
2 100 1.9 90 2.0 85 2.2 80 1.9 70 2.4 70 2.5 65
2.2 96 2.4 91 2.5 85 2.0 71 2.7 74 2.8 70
2.5 100 2.7 95 2.8 90 2.3 75 3.1 80 3.2 75
3.0 100 3.2 95 2.6 80 3.4 85 3.6 80
3.2 96 3.0 85 3.8 90 3.9 85
3.5 100 3.3 90 4.1 95 4.3 90
3.7 95 4.5 100 4.6 95
4 100 5 100

onclusions
Harvest crop at night or keep harvested crop in shade during cooling delays.
Save 30% energy by installing hydrocooler in a cold room.
Provide R 60 PUF insulation for roof and R 40 for walls.
Optimum flow rates of fan required are 1 litre/sec/kg of produce.
Always provide vapour barrier coating on the hot side of insulation.
Prefer finned coil evaporators over bunker or diffuser system for more efficiency and
saving in storage space.