One of the roadblocks to the penetration of perishable and dairy products in the rural segment is unavailability of reliable power. There is a large demand for refrigeration equipment that offer additional features to protect the products during uncertainties such as from mechanical failure and power outages. The second challenge is the total cost of energy and energy consumption of refrigeration equipment. The second challenge is perennial in both rural and urban India. The high operating costs is a cause of discouragement for the last mile operators to do away with refrigeration all together. This article attempts to explain the impact of Phase Change Materials also known as ‘Thermal Battery’ that has the potential to revolutionize the HVAC and refrigeration sector. The focus of this article is on chest freezers or coolers which are commonly referred to as deep freezers or coolers. These are used commonly in convenient stores, hypermarkets, supermarkets with an annual demand of 5,00,000 units worth Rs 1,000 crore with a CAGR of 18 per cent.
Phase Change Materials (PCM)
Phase Change Materials (PCM) fall under the subcategory of energy exchanging smart materials. Energy exchanging smart materials are materials that 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 or energy while maintaining a constant temperature unlike conventional solutions as shown in the figure 1 below.
PCMs have tremendous potential to fulfill the growing need of energy for cooling and heating applications across various industries. It finds its application globally in diverse sectors like cold chain, HVAC, refrigeration, automobile air-conditioning, apparels, waste heat recovery, consumer goods and more; wherever there is a need for thermal energy storage.
Thermal battery as backup
Freezers for ice-creams are designed to maintain a temperature between – 18C to -23C while beverages are maintained between 2C and 8C in a cooler. The PCM chosen for both of these applications are different due to the different temperature requirements. Shown below in figure 2 is an illustration of PCM integration within the walls of the ice-cream freezer. The selected PCM charged passively when the power is available within 9 -10 hours. The selection of the PCM is important as one of the critical factors is the minimum temperature that the refrigeration unit can offer to ensure that the PCM is completely charged. Once fully charged the PCM is in ready state to release the energy in event of a power or equipment failure. The figure 3 shows the graph of the temperature inside an empty freezer compartment monitored by sensors at various locations. This freezer is designed to maintain a temperature of -18C to -19C at an ambient of 40C for a minimum of 16 hours and in spite of several opening and closing of the lid.
Thermal Battery as a power saver up to 25%
The phase change materials in its charged state acts as a concentrated thermal mass which increases the efficiency of the envelope of the freezer. The combined effect of insulation and a lining of PCM causes a significant delay in the change of temperature. For instance, the compressor turns OFF once the temperature in the return line of the refrigerant lowers down below a set threshold eg: -28C for a freezer, similarly it turns ON when the temperature increases above -23C. The temperature bandwidth of 5C between compressor turning ON and OFF are few minutes which increases by 35 per cent. This effect is also known as Thermal Inertia wherein the incorporation of a thermal mass such as PCM, the tendency to resist change in temperature. The below figure 4 illustrates the energy consumption between two chest freezers; one without PCMs and the other with it. The effect of thermal inertia results in a steady divergence of the energy consumption graph.
There are several refrigeration companies in India and outside which have now introduced chest freezers and chest coolers incorporated with these PCMs to cater to the market in low and middle-income countries where power availability is an issue. Now with the added advantage of reduction in power saving, this innovation makes can be implemented across equipment even in urban cities. The variety of PCMs available now allow OEMs to manufacture a range of refrigeration equipment to cater to different temperature requirements. The application could be extended to living spaces, cold storages, household refrigerators, automobiles. The growing demand and addition of over a million refrigeration units added each year the effect of the energy saved per equipment is massive.
Pluss Advanced Technologies Pvt. Ltd (PLUSS) is a venture-funded organisation with equity stake being held by Tata Capitals premium innovation fund promoted by the Tata. Founded in 1994, the company has seen tremendous growth in the recent past. With strong roots, the company is now poised to make a global impact with its innovative products. Pluss is engaged in R&D and manufacturing of specialized polymers and Phase Change Materials (PCMs). PCM technology finds its application globally in diverse sectors like cold supply chain, Building HVAC, refrigeration, automobiles, thermal wear, waste heat recovery, consumer goods and more; wherever there is a need to store thermal energy.
Pluss has pioneered in the PCM technology in India and is presently the only company in India with a wide range of indigenous manufactured PCMs with several patents. With its innovative products, the company is making its presence felt across the globe with representatives in USA, Turkey, South East Asia, Russia, Ukraine and South Africa. Pluss intends to be among the top innovative companies in the world in the near future.