PCM integrated cooling systems can make room air drier without elaborate cooling, compression, or other complex systems or controls. After the drying task is complete, the desiccant is dried using hot air in a process called regeneration and is ready to dry more air. Obtained dry process air sent to conditioning by prior mild cooling. The desiccant dehumidification is the most accepted method of dehumidification across industries as desiccant dehumidifier is the most energy-efficient and may make use of renewable energy or industrial waste heat for reactivation.
The reduction in use of electricity is a key requirement in today’s world. Constant amelioration in ambient temperature requires that the air conditioners have become increasingly necessary, upon raising their performance coefficient resulted to utilising less electricity, and so air conditioners must function better. The difficulty in utilising renewable energy sources in systems derives from their temporal volatility when there is a discrepancy between supply and demand. Such an imbalance can be corrected by incorporating thermal storages into systems (Fig. 1) that depend on renewable energy sources. Because of their significant latent heat that is produced or accumulated during the phase-change process, Phase-Change Materials (PCMs) have a theoretical advantage over sensible thermal storage. As a result, the current research offers an analysis of latent thermal storages in hydronic systems for residential hot water, cooling, and heating in buildings. PCMs offer substantially better energy storage densities than current sensible thermal storage techniques, and the heat is stored and released at nearly constant temperatures. Both active and passive space heating and cooling systems can make use of PCMs.
To boost their thermal storage capacity in passive systems, PCMs can be encased in building materials like concrete, gypsum wallboard, the ceiling, or the floor. They have the ability to immediately absorb solar energy or thermal energy via natural convection. By reducing the size of internal air temperature swings so that the indoor air temperature is closer to the ideal temperature over a longer length of time, increasing a building’s thermal storage capacity can improve human comfort. Alternately, to increase overall thermal efficiency and lower peak heating and cooling electrical load, a thermal storage unit using PCMs can be combined with traditional active space heating and cooling systems. Additionally, PCMs can be added to conventional heating and cooling systems to decrease their capacity. Although extensive research has been done on the use of PCMs for space heating and cooling, there are currently just a few systems in use.
Types of PCM
According to their phase shift, PCMs can be divided into solid-liquid, solid-gas, liquid-gas, and solid-solid categories. Given the enormous volumes or high pressures needed to store thermal energy, the phase shift, including the gas phase, is not appropriate. In contrast, solid-solid PCMs often have a very slow phase change and low heat of transition. Because of this, solid–liquid PCMs are thought to be the best materials for storing thermal energy in structures. These PCMs can be divided into eutectic PCMs, inorganic PCMs, such as salt hydrates, and organic PCMs, such as paraffins and fatty acids (a combination of at least two other types of PCMs).
Properties of PCM
Due to their large latent heat capacities, acceptable phase change temperatures, and stable physical and chemical characteristics, organic PCMs have garnered a lot of research interest. Additionally nontoxic, noncorrosive, and with minimal super cooling and segregation qualities are organic PCMs. These PCMs do, however, exhibit low enthalpy, low flammability, and low thermal conductivity. The presence of a super cooling phenomenon suggests that even below the phase transition temperature, latent heat cannot be recovered during the heat recovery stage. Over a series of freeze/melt cycles, the materials of the components separate, and a segregation process also takes place. The high latent heat, non-flammability, high thermal conductivity, and low vapour pressure of inorganic PCMs, in contrast, make them desirable. These materials do, however, also possess some unfavourable characteristics, such as corrosivity, instability, and super cooling. Eutectic PCMs, on the other hand, have a high volumetric energy storage density and can melt or freeze without segregation. These PCMs, however, are not widely available.
Use of PCM in building cooling
Storage with Venting should be considered, since it can result in lighter and/or more compact systems. Single Use Vapour Venting Systems for Thermal Storage (One to a Few Cycles). When heated, liquid held in a porous structure boils, vaporizes, and then the vapour is vented. Hydride Thermal Storage Systems use metal hydrides, which desorb hydrogen when heated. Single Use Hydride Venting Systems for Thermal Storage (One to a Few Cycles) offer a potential volume reduction of 90% or more, when compared with PCM systems. At 240C temperature PCM enclosed in aluminium pouches is used in the PCM cooler. These are used inside a heat exchanger for the air. When cool outside air is allowed to enter the building at night and contact the PCM, the PCM becomes frozen. Throughout the day, the facility is filled with the cool air.
Each building was given one of three thermal inertia weights: light, medium, or heavy. In low weight buildings as opposed to heavier buildings, the effects are more noticeable. In a structure with limited thermal mass, summertime temperatures will climb more quickly. The findings demonstrate that it is possible to alter the building’s thermal inertia by adding the PCM. Concrete would require around ten times more mass to achieve the same result. The impact of the PCM cooler is comparable to that of a building with high thermal inertia in a light-weight structure. With the PCM cooler installed, fewer hours during which the temperatures surpass a desired threshold occur.
Use of PCM in thermal energy storage
Applications requiring thermal storage can use PCM heat sinks for a wide range of reasons. Because latent heat from melting and freezing can store far more heat than sensible thermal storage alone, PCMs are perfect for this purpose. The PCM will keep the heat-generating component at a specific temperature while passively storing the heat when it is turned on. The PCM will start to solidify after the heat-generating component is turned off by releasing the stored energy.
Those applications with predictable duty cycles are the most frequent ones that benefit from PCM. Other uses include those where delaying the heat’s dissipation to a period when the sink is cooler (at night) or more accessible is useful.
PCM for Pulsed Power on-chip (Smoothing)
On high power pulsed GaN chips, placing the PCM close to the gates can lower temperatures and/or enhance maximum power without overheating. Electronics heat sinks are utilised for cooling electronics during pulsed power operations and when the current heat sink is insufficient. Vapour Chamber PCM (Increase in Cooling Capacity) by enabling the system to be designed for average power rather than peak power, PCM Heat Exchangers for Pulsed Power (Dampening) can enhance the Size, Weight, and Power (SWaP) for Directed Energy Weapons (DEW). Energy Savings in HVAC (Increase in Cooling Capacity). Cooling in Power Plants (Increase in Cooling Capacity) Megawatts of heat are rejected by dry cooling power plants in order to condense low temperature, low pressure steam without using fresh water. However, when the ambient air temperature is high, dry cooling systems’ ability to produce electricity must be limited since less steam can condense. PCM and thermo syphons are used in ACT’s Cool Storage System to boost cooling capacity during the day by melting the PCM. Thermostatic Ventilation Storage is the majority of thermal storage systems can run for a very long time and are made to store heat by melting a Phase Change Material (PCM). The Storage with Venting should be taken into consideration when only a few cycles need to be handled because it can lead to lighter and/or more compact systems.
Vapour Venting Systems for Thermal Storage with Single Use (One to a Few Cycles) Heating causes liquid contained in a porous structure to boil, evaporate, and then expel the vapour. Metal hydrides are used in hydride thermal storage systems, which when heated desorb hydrogen. When compared to PCM systems, single use hydride venting systems for thermal storage (one to a few cycles) have a potential volume savings of 90% or more.
By utilising all of the on-site energy resources available, air conditioning systems integrated with PCMs can achieve a suitable thermal comfort band, pleasant interior temperature variation, acceptable energy redistribution in buildings, and optimised energy efficiency. Along with lowering the environmental impact of air conditioning systems in terms of their potential to cause global warming, acidification, eutrophication, ecotoxicity, risks to human health, and fossil fuel depletion, PCMs can also offer longer payback periods, higher rates of energy savings, and lower return costs.
Dr. (Prof.) D.B. Jani received Ph.D. in Thermal Science (Mechanical Engineering) from Indian Institute of Technology (IIT) Roorkee. Currently he is a recognized Ph.D. Supervisor at Gujarat Technological University (GTU). He has published more than 180 Research Articles in reputed International Conferences and Journals. He has also published 5 reputed books in the area of thermal engineering. Presently, he is an Associate Professor at GEC, Dahod, Gujarat Technological University, GTU, Ahmedabad (Education Department, State of Gujarat, India). His area of research is Desiccant cooling, ANN, TRNSYS, and Exergy.