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ABSTRACT
A solar thermal energy storage system using phase change material (Paraffin Wax) has been proposed that can overcome the time mismatch between solar availability and demand. The proposed system is a combi-system, which is able to make a contribution to the space heating load and hot water demands of a residential Building .The panels are connected together using push fit connectors for easy assembly which melts the Paraffin Wax in the panels thus storing this thermal energy as both latent and sensible heat. When the heat is drawn from the panels by forced convection of air over the panels, the Paraffin Wax will begin to solidify thus releasing its stored sensible and latent energy which provides space heating. six solar panels are required to meet the space heating load. When air with forced convection is passed over the panels, the air gets heated and is then supplied to the space to be heated.
Key words: phase change material, paraffin wax, thermal energy storage, water heating
INTRODUCTION
The continuous increase in the level of greenhouse gas emissions and the climb in fuel prices are the main driving forces behind efforts to more efficiently utilize various sources of renewable energy. In many parts of the world, direct solar radiation is considered to be one of the most prospective sources of energy. The scientists all over the world are in search of new and renewable energy sources. One of the options is to develop energy storage devices, which are as important as developing new sources of energy. The storage of energy in suitable forms, which can conventionally be converted into the required form, is a present day challenge to the technologists. Energy storage not only reduces the mismatch between supply and demand but also improves the performance and reliability of energy systems and plays an important role in conserving the energy. It leads to saving of premium fuels and makes the system more cost effective by reducing the wastage of energy and capital cost.Over the last two decades a wide variety of solar energy technologies have been developed through research and development, demonstration and large-scale promotion during the eighties and nineties. As a result, some of these technologies have reached maturity and a user-friendly status and are suitable for decentralized applications.
ENERGY STORAGE METHODS
The different forms of energy that can be stored include Mechanical, Electrical and Thermal energy.
MECHANICAL ENERGY STORAGE
Mechanical energy storage systems include Gravitational Energy Storage Or Pumped Hydro Power Plant (PHPS), Compressed Air Storage (CAES) and Flywheels.
ELECTRICAL STORAGE
Energy storage through batteries is an option for storing the electrical energy. A battery is charged, by connecting it to a source of direct electric current and when it is discharged, the stored chemical energy is converted into electrical energy.
THERMAL ENERGY STORAGE
Thermal energy storage can be stored as a change in internal energy of a material as Sensible Heat, Latent Heat and Thermo-Chemical or combination of these.
SENSIBLE HEAT STORAGE
In a Sensible Heat Storage (SHS), thermal energy is stored by raising the temperature of a solid or liquid. The amount of heat stored depends on the specific heat of the medium, the temperature change and the amount of storage material.
LATENT HEAT STORAGE
Latent Heat Storage (LHS) is based on the heat absorption or release when a storage material undergoes a phase change from Solid to Liquid or Liquid to gas or vice versa.
THERMO CHEMICAL ENERGY STORAGE
Thermo-chemical system relay on the energy absorbed and released in breaking and reforming molecular bonds in a completely reversible chemical reaction.
Amongst above thermal heat storage techniques, latent heat thermal energy storage is particularly attractive due to its ability to provide high-energy storage density and its characteristics to store heat at constant temperature corresponding to the phase-transition temperature of Phase Change Material (PCM). Phase change can be in the following form: solid-solid, solid-liquid, solid-gas, Liquid-gas and vice versa. Solid-liquid transformations have comparatively smaller latent heat than liquid-gas. However, these transformations involve only a small change (of order of 10% or less) in volume. Solid-liquid transitions have proved to be economically attractive for use in thermal energy storage systems. PCM absorbs and releases heat at a nearly constant temperature it store 5-14 times heat per unit volume than sensible storage materials such as water, masonry, or rock. A large number of PCMs are known to melt with a heat of fusion in any required range.
SYSTEM OPERATION
Water heated by the solar collector is circulated through the copper tubes that run through the panel. The heat conducted through the walls of the copper tube will melt the Paraffin wax and so store solar thermal energy as both latent and sensible heat. When heat is drawn from the Paraffin wax filled aluminum panels for space heating the paraffin wax will begin to solidify when it reaches its melting point and in doing so releases its stored sensible and latent heat. Water heated by the solar collector can also be used to provide hot water for bathing or washing.
Components
The main components of space heating are
1) Room
2) Heat Exchanger
3) Phase Change Material
4) Digital Thermo Meter
5) Copper Tubes
Working
In the working process of the space heating water is heated by using the solar panel the hot water is passed through the copper tubes to heat exchanger and heat exchanger is filled with paraffin wax which is use to store the latent heat in this process the heat from the hot water received by paraffin wax by convention process and by using the another copper tube in heat exchanger by passing the cool water to solidify the paraffin wax and then latent heat is released by the paraffin wax the latent heat is received by the room to increase the room temperature than we can calculate the raised temperature by using digital thermometer
PROPOSED SYSTEM
The proposed system is a combi-system which is able to make a contribution to the space heating load and hot water demands as illustrated in Fig.The system consists of flat-plate solar collector and a number of interconnected metal panels filled with paraffin wax as a phase change material(PCM). The panels are manufactured from aluminium sheet and have a coil of copper tubing running through them.
A length of copper tube protrudes from each end of the PCM panel as illustrated in Fig are used to connect the panels together using push fit connectors. The panels can be located on top of a concrete floor. Back up heating can be provided by a gas fired condensing boiler or a wood stove during periods of low solar irradiation and cloudy days, since the solar energy availability is often intermittent, variable and unpredictable.
A temperature differential controller is provided to monitor the condition of inlet and outlet water temperatures in solar flat-plate collector and the temperature inside the storage tank. For every 2 °c rise in the temperature of water can be monitored and the set temperature in the device is 60 °C. Until the set temperature is reached in the storage tank the cycle is repeated. The cold water tank supplies cold water to the storage tank and to the backup system. A mixing valve is provided to bypass the water to the heat exchanger to attain the required temperature and the non condensable gases can be exhausted to the environment by an air vent.
Cooling using PCM:
Due to the increasing use of air conditioning (AC) in residential and office buildings, the Italian daily electrical load curve shows remarkably high peaks during summer months, leading to the shifting of the peak consumption and the consequent pollutants and GHGs emissions, and to protect the electrical grid from overloads. This can be achieved by shifting the power consumption needed by the air conditioning units towards off peak hours, integrating thermal storage systems. At the moment, several solutions are adopted in large industrial applications, but not in residential air conditioning systems.
Operating in off-peak hours, which would certainly provide benefits at the level of national electrical energy distribution, can also increase the performance of air conditioning systems. In fact, during the night, the Chiller’s coefficient of performance (COP) increases due to the lower external temperatures. Moreover thanks to the adoption of a storage system, the chiller can operate mostly at constant and optimal power (peak shaving concept) instead of following the user requirements profile, leading to a strong enhancement of energy efficiency and to a reduction of installed power. All these benefits lead to a potential reduction of electrical consumption of 20% and more.
Among the existing methods to store thermal energy, the ones using phase change materials (PCM) are particularly interesting. These substances store the heat through their latent enthalpy, changing the phase from liquid to solid during charging and from solid to liquid during releasing. Several PCMs for storage applications have been developed and are available on the market at reasonable prices. Moreover,
An innovative solution to store cold energy by means of the solidification latent heat of PCMs is presented. The cold storage system is suitable for domestic application (typically in/out primary circuit temperature =7-12ºc) since it stores cold energy at 55ºc. The innovative heat exchanger system implemented in the storage unit allows the increase of energy charge/release dynamics and, therefore, leads to high power both in charge and release phases.
PHASE CHANGE MATERIALS (PCM):
One of the prospective techniques of storing thermal energy is the application of PCMs. In 1983 Abhatgave a useful classification of the substances used for TES. The use of a latent heat storage system using PCMs is a helpful approach of storing thermal energy and has the advantages of high-energy storage density because of the isothermal nature of the storage process. PCMs were mostly used in latent heat thermal storage systems for heat pumps, solar engineering and space craft thermal control applications. There are large number of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. There are large number of organic and inorganic materials, which can be known as PCM from the point of view of melting temperature and latent of fusion.. In general inorganic compounds have almost double volumetric latent heat storage capacity (250-400 kg/dm3) than the organic compounds (128-200 kg/dm3). Some of the essential properties required for PCMs are
(i) high latent heat of fusion per unit mass, so that a lesser amount of material stores a given amount of energy
(ii) High specific heat that provides additional sensible heat storage and also avoid sub cooling.
RESULT
CONCLUSION
A solar thermal energy storage system using phase change material (Paraffin Wax) has been proposed that can overcome the time mismatch between solar availability and demand. The proposed system is a combi-system, which is able to make a contribution to the space heating load and hot water demands of a residential building of 5mx4mx3m dimensions. Though no experimental data on the system is yet available, the theoretical research on a similar system has indicated that it has the potential to reduce energy use upto 18-32% , and hence CO2 emissions on an all-year round basis