Environmental Sustainability, Energy Efficiency and Greening of Cold Stores
By
Deepa Sathiaram, Executive Director En3 Sustainability Solutions Pvt. Ltd.
Sustainability is having a growing influence on every type of industry and construction. The cold chain industry is
no longer left behind and energy efficiency and sustainability of the entire cold chains are increasingly becoming
an important issue, largely driven by buyers and consumers. Best practices led by increasing energy prices, climate
change issues and increasing pressure from buyer groups are looking at issues ranging from basic reinventing of
cold store designs and operations to transport, environment, waste and pollution, and operator health, safety and
welfare issues throughout the supply chain. World-over there is substantial movement towards adopting green
practices in cold chains and it is suggested that over time suppliers of products will need to demonstrate that their
cold stores and chain logistics partners, not just the producer or exporter, are environmentally and socially
responsible. We may well see the buyer preferring suppliers that are more environmentally conscious and even
use sea or rail transport over road or air because of the modes’ relative impact on the environment. Transport
companies that do not pay an acceptable wage to their staff or lack sound health and safety arrangements may be
precluded in the future. Equally it is important to assess the ‘green’ or sustainability performance of a business and
a cold storage facility. More importantly energy efficiency and greening of cold stores is not just to help the
environment but more so to help the owners themselves reduce their operating costs and make their business
more profitable.
It is now widely accepted that we need to be proactive in our efforts to reduce our impact on the planet and the
depletion of its limited resources: turning off lights and electronic equipment, walking more etc. But cold stores
cannot be turned off overnight. Also, these units must provide consistently accurate and stable temperatures to
ensure proper preservation, requirements that have traditionally necessitated higher energy consumption. This
note addresses some of the aspects of energy efficiency in cold storage facilities.
Factors influencing Environment and Energy consumption in Cold Storages:
There are several factors influencing energy consumption and many ways to conserve energy but largely they can
be classified into four different categories
-
Design – the manner in which the cold store itself is designed
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Equipment – the selection of refrigeration equipment to reduce energy consumption
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Refrigerant – the use of environmentally friendly and better performance refrigerants
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Controls – the provision of better and accurate control systems that can further help reduce energy use
Design
Energy use in a cold storage facility is affected by the amount of heat the refrigeration equipment must remove
and the efficiency of the equipment. The sources of heat in a storage facility include:
-
Thermal transmission through walls, roof, floor and openings
Evaporator coil fans
Lights
Air leakage, and
Respiration of the stored commodity
Thermal ingress in a cold storage facility through walls can be minimized by increasing the insulation. Painting the
exterior a light color will help. Doubling the insulation (as evaluated by its R value) reduces transmitted heat by
half. These days, it is not uncommon to see insulation levels as high as R40 in walls and R60 in ceilings.
In general, it is advisable to build with more insulation than the current utility costs may justify today, because
energy costs are difficult to predict and it is much cheaper to install insulation during construction than after
construction is completed.
Direct radiation such as the sun shining on walls and roof dramatically increases the effective outside temperature,
increasing heat flow into a storage facility. A dark, flat roof can be upto 75°F (42°C) warmer than the outside air
temperature. Painting a south-facing wall a light color can reduce the effective wall temperature by upto 20°F
(11°C) compared with a dark wall. Walls and roof of a cold storage facility should be painted a light color or shaded
from the direct sun.
Fans are used in cold storage facilities to move air through the evaporator coils and to uniformly circulate cooled
air around stored commodities. During the initial filling of a storage facility, 100 cfm per ton of product (0.3 m3.m1 per tonne) stored is needed to remove the residual field heat of the product. However, after the commodity has
reached the desired temperature, air movement can be reduced by 60 to 80%. Also during the winter months, the
outside air temperature drops and less heat enters through the walls compared to summer conditions. Also
introduction of variable speed drives can help considerably reduce the energy consumption of these fans especially
in part load operations.
Lights in the cold storage room should be turned off when not needed. Use plastic flap doors to reduce infiltration
of warm outside air during loading and unloading. Seal around openings for pipes and electrical conduits. Heat
produced by respiration of the stored commodity can be minimized by keeping the commodity minimum
recommended storage temperatures.
Refrigeration system design has a great effect on energy use. The temperature of the refrigerant fluid after it is
cooled in the condenser should be as low as possible. For example, a facility maintaining 32°F (0°C) and a
condensing temperature of 125°F (52°C) requires 50 percent more power than one that operates at a condensing
temperature of 95°F (35°C). In warm areas, evaporative condensers should be selected over aircooled units.
Utilities often offer rebates to install extra heat exchange surface for the condenser in order to further reduce
refrigerant condensing temperature. Maintaining highest possible suction pressure also reduces compressor
energy use. Use large evaporator coils and a control system that increases suction pressure as demand on the
refrigeration system is reduced. Use a compressor system that operates efficiently over the required range of
refrigerant flows. Screw compressors operate efficiently only at flow rates near their maximum capacity. Use
several in parallel, shutting down those that are not needed, or consider using reciprocating compressors for peak
loads. They operate efficiently over a large range of refrigerant flows.
The design of the cold storage especially deciding on the inside temperature conditions has a huge impact on the
energy consumption. In many cases it is found that most cold stores can be maintained at higher temperatures
than they are actually maintained and this can help in energy conservation considerably. For example a 1 Deg C
reduction in temperature lift can save 2-3% energy. Moreover reduction of the temperature difference of air and
the refrigerant can also conserve energy. Another key factor to be considered in the design of cold stores is to
ensure that we avoid temperature fluctuations as much as possible. Recommended temperature fluctuation is +/0.5 Deg C variations but in reality most cold stores maintain +/- 3 Deg C thereby consuming more energy.
Further detailing during design of cold stores need to be done to ensure energy efficiency. For example, having the
same suction lines for blast freezers and cold stores will lead to more energy use since blast freezers require close
to –40 Deg C while most cold stores are fine with -30 Deg C.
Another key design feature to reduce energy use is to ensure that the cold store design takes into account
seasonal adjustments to evaporating temperature settings. This is a missed opportunity as the cooling load on a
cold store is lower in winter than in summer. A 1 or 2 deg C increase in suction temperature may be easily
achievable, especially if combined with use of variable speed drive fans and a flexible defrost regime and can lead
to considerable energy savings.
Further energy use reduction can be achieved in cold stores by ensuring a flexible and effective defrost system.
Many stores do not have a flexible defrost regime, in terms of frequency and length of defrost. In winter time air
holds about 30% of the moisture that it holds on a warm summer’s day. Also, the rate of air flow through an open
doorway is slower in winter, as it is proportional to the temperature difference between the air inside the store
and the air outside. Taking these 2 effects into account it is likely that the rate of frost formation in winter time is
less than a quarter of the rate that occurs in summer. Many defrost control regimes are based on “worst case
scenario”, which is the summer time requirement. In winter a different regime can be adopted. This will reduce
the heat entering the store during a defrost cycle and avoid such large temperature variations thereby leading to
further energy savings.
Equipment
While the design of cold stores is critical the selection of the right equipment is equally critical to ensure better
energy performance. Owners and designers will have to start seriously looking at the coefficient of performance
(COP) of various refrigeration systems and select the best performance systems. Today, in-efficient equipment
accounts for over 80% of the contribution of refrigeration to global warming and it is becoming imperative that we
utilize newer systems that can operate at lower temperatures reducing evaporation and increasing energy
efficiency.
Also today there are completely newer types of systems that are becoming available such as the “cold tubes”
where air blows longitudinally through the products and helps in conserving energy rather than the traditional
cold stores and more and more of the upcoming cold stores world-wide are adopting such high COP systems and
newer equipment for better energy performance.
Refrigerant
One of the key requirements of green cold stores is the use of better and CFC-free refrigerants that have low
ozone depletion and global warming potential. Today, there are several refrigerants that can be used especially
those with a high critical condensation point to optimize energy efficiency and reduce ozone depletion. Selection
of correct refrigerant not only is environmentally-friendly but also can lead to better performance of the
equipment. Recent findings reveal Co2 as a possibly good refrigerant especially in the U.S. for commercial
refrigeration because of increased COP of the equipment with Co2 as refrigerant compared to ammonia or other
traditional refrigerants.
Controls
It has been observed in the past that it is not sufficient to do the right design and select the right equipment.
Energy savings in most cold stores is best achieved by implementing the right controls that ensure that the design
and equipment are operated at the optimum settings to achieve maximum energy savings. Controls can play an
important role; especially:
- To avoid overcooling
- Closely monitor the temperature and humidity levels
- Reduce /avoid large fluctuations in temperature (maintain +/- 0.5 Deg C)
Right design and operation of these controls can help reduce energy consumption in the tune of up to 15 – 20%
thereby leading to huge energy savings and reduced operating costs. Hence it becomes critical that the cold stores
are incorporated with the correct control systems to maximize energy savings.
While energy is a very important aspect even in green cold stores, other areas where substantial greening
opportunities exist in cold stores are water use reduction, reduction of green house gas emissions,
environmentally-friendly transportation and waste management that go a long way in ensuring that the cold stores
are sustainable and reduce their negative impact on the environment.
Water use reductions can be achieved in many ways including on-site treatment of waste water and reuse of the
same for custodial purposes, rain water harvesting throughout the entire site and collection and reuse of rainwater
to reduce the dependence of cold stores on potable water and selection of low-flow toilet fixtures including dual
flush closets, sensor based urinals and hand washes for the staff.
Transportation also plays a key role especially in the environmental aspects of cold chains. Many cold stores are
looking at reducing the green house gas emissions through better transportation options such as rail and sea
transport compared to road transportation, use of better vehicles that are less polluting and also use of solar
powered trucks in the form of renewable energy. There are many solar powered refrigerant units currently under
experimental use in U.S and U.K. These units can produce electricity and store them in batteries to keep
refrigeration units running. While they are yet to come in mainstream practice it is only a question of time before
such environment-friendly practices and options become common and are adopted by the entire industry.
In Conclusion
Is it enough to adopt Best Practice Cold Chain Logistics?
If best practice cold chain logistics management is inclusive, anticipates and responds to change, has a through
chain approach with all its partners and addresses safety, security and sustainability then the answer is Yes. If it
doesn’t then the answer is No.
In closing we need to recognize that keeping up with changes occurring on many fronts, finding like-minded quality
supply chain partners and quality focused customers can be hard. Equally important is integrating environmental
sustainability though it can be complex. But as the saying goes “Life wasn’t meant to be easy”
Is it all too hard?
Yes if you only rely on others and don’t know how each element of the cold chain works and can contribute to
sustainability. The answer is No if we manage the cold chain well and look ahead.
So I’ll leave you with this thought – Early adoption of sustainability leadership might not be natural to everyone but it is an option worth considering, especially if you have a feeling that the present situation can be improved. As
a saying from the great philosopher Aristotle goes “To move the world, we must first move ourselves”; it is not
easy but definitely worth exploring since not only does “going green” benefit the environment but frankly “going
green also makes great business sense”.
About the Author
Deepa Sathiaram is the Executive Director of En3 Sustainability Solutions Pvt. Ltd., one
of the premier energy efficiency, sustainability and green building consulting firms in
India consulting for over 60 million square feet of green space world-wide. She is a
leading international green building, HVAC, refrigeration and building systems design
consultant for several global corporations including The World Bank, The International
Finance Corporation and public benefit authorities like the International Code Council
(ICC), USA. She is also the National Environment Chair for CII Young Indians and
Immediate Past President of the ASHRAE (American Society for Heating, Refrigerating
and Air-conditioning Engineers) South India Chapter. She can be contacted at
[email protected]