Author: Mr. Samit Jain, Director, Pluss Polymers | Co- author is Mr. Vishnu Sashidharan (Manager – Business Development (PCM) ).
There is an ever increasing need for refrigeration for chilling, cooling and freezing of food at large due to the increase in food production, need for reduction in food spoilage and a large demand for frozen foods. These applications due to their high criticality need continuous un-interrupted operation. If you are a CEO of business or enterprise in the refrigeration industry you are faced with the challenges of offering an innovative product that differentiates and offers a first mover advantage. This stems the need for technologies that make the system more reliable, efficient and sustainable. By the end of this paper you will know the steps to identify where PCM could fit in your application.
High Energy Consumption:
Refrigeration systems typically consume 65% to 85% of the energy usage whether it’s for cold storage facility or for cooling application in industrial facilities. In temperature controlled transport application energy forms 30% of the expenses. (Logistics week, 2012)
Research by Energy Star shows the cooling capacity in most applications are oversized owing to the losses due to improper refrigerant level, improper air-flow, improper sizing of equipment and loses due to leakages. This loses sums up to a substantial 27% of unused energy that is produced. (Energystar)
The unreliable energy situation in most parts of India is a major problem which affects spoilage of the products. To reduce the spoilage of the products, industries are heavily dependent on diesel generators to meet the demand. The cost of running refrigeration unit using diesel is almost three times that of the cost of electric refrigeration unit. The challenge is utilizing energy when it is available but not required for use. In many parts of India time of the day (TOD) Tariff is effective to encourage consumers to utilize the off-peak electricity to increase the electric load factor of the facility. An improvement in load factor benefits the electric utility as it would be able to cater to a larger number of consumers with power generation capacity and reduce the power outages.
Wide Range of temperature application:
The industrial refrigeration operates within a very wide range of temperatures broadly classified as Chilling (2º – 8º C), cooling (22º – 25º C) and freezing (- 33º – 23º C). Hence, one of the challenges is to custom design refrigeration system as the design varies significantly. Also, in multi – temperature transport it becomes very complex to design a reliable refrigeration system
Products such as fruit, vegetable and other perishables go through a temperature controlled supply chain which is a series of storage and transport. The challenge is to maintain the products temperature uninterrupted throughout this chain in spite of the continuous movement and transition from one mode to another.
A sustainable Solution
Phase change materials can help reduce or eliminate most of the problems of industrial refrigeration discussed above. The concept of phase change material is simple. Phase Change Materials (PCM) fall under the sub category of energy exchanging smart materials. Energy exchanging smart materials is defined as those materials that are able to store latent and sensible energy in the form of light, heat, electricity or hydrogen and exhibit reversibility. A PCM has the ability to store and release large amounts of heat/cold energy while maintaining a constant temperature. PCM’s have tremendous potential to fulfill the growing need of energy for cooling and heating applications across various industries.
Phase change materials are passive cooling materials which can store and release energy at desired temperature. We can broadly discuss two strategies of PCM usage.
1.As a dynamic thermal Insulation:
Unlike conventional (sensible) storage materials, PCM absorbs and release heat at a nearly constant temperature. They store 5–14 times more heat per unit volume than sensible storage materials such as masonry, or rock. A large number of PCMs are known to melt with a heat of fusion in any required range (Atul Sharma, 2009). Phase change materials possess the ability to change their state with a certain temperature range. These materials absorb energy during the heating process as phase change takes place, otherwise this energy can be transferred to the environment in the phase change range during a reverse cooling process. The insulation effect reached by the PCM depends on temperature and time; it takes place only during the phase change (in the temperature range of the phase change) and terminates when the phase change in all of the PCMs would complete. Since, this type of thermal insulation is temporary; therefore, it can be referred to as dynamic thermal insulation.
2.As a back-up for cooling application:
PCM can be used as a thermal battery which will offer un-interrupted cooling. For these applications, the PCM has to be integrated with the existing refrigeration system to ensure PCMs are fully charged by the refrigeration unit and is available instantaneously when there is a power outage. PCMs are widely used for building air-conditioning systems and for mission critical applications. Using PCMs are much lesser in cost as compared to diesel generators as PCMs get charged during off-peak hours when power is available. Another disadvantage of using diesel generators is the time lag to start the system which can be disastrous for mission critical applications.
In the retail or industrial freezers and coolers PCMs are integrated within the body of the machine such that the evaporator coil is in constant contact with the PCM. While the machine is plugged to the power, the refrigeration unit simultaneously charges the PCM and also keeps the cabin cool. The figure below illustrates the application of PCM in deep freezer. PCMs offer a backup of more than 16 hours protecting the product during power shutdowns.
In the cold chain application the reefer trucks consume a large amount of diesel for running the refrigeration unit and in many trucks there are also constraints in mounting a refrigeration unit. PCM integrated trucks offer the benefit of utilizing cheaper electric energy to store the thermal energy which will be sufficient to maintain the temperature for over 12 hours of transportation. This translates in to huge saving in the operational cost with a negligible impact on the capital cost.
Applications with PCMs have endless possibilities and are gaining a large momentum in organizations to integrate it into their products. It has got a large potential to overcome the existing challenges offering new products for known application and new applications for known products. Industry has to step up and find innovative ways of using PCM!