ACTIVE HOME SOLAR SYSTEM
By
SUNIL KUMAR SINGH
B.E.ELECTRICAL
Under the guidance of
Prof. B.V.VIBHUTE
Electrical Engineering Department
Bharati Vidyapeeth (Deemed University)
College of Engineering
Pune
ABSTRACT
No one needs to define for the average citizen the term "energy crunch". Our monthly fuel and utility bills are constant reminders of that.And the "experts" warn that the crisis is here to stay. Of the alternatives to conventional forms of energy, the one receiving most serious consideration--at least for home, farm and small business heating needs--is solar energy. Today, many new homes are being planned and constructed to accommodate solar heating systems. Various types of portable collectors and solar heating conversion packages are readily available on the retail market. Unfortunately, too many perspective users of solar energy have too little information about some of the aspects of building or converting to a solar heating system. One area of inadequate or misinformation in particular (and a costly one it mistakes are made) is the storage of collected energy. Active solar systems consist of collectors that collect solar radiation and electric fans or pumps to distribute heat from the collectors. A liquid or air is used as the heat transfer fluid. Most systems also incorporate storage systems to provide heat when the sun is not shining.
INTRODUCTION
The function of a building or a house is to provide shelter to its occupants from weather. Since the weather conditions vary widely over the year in different places and people feel comfortable within certain range of air temperatures and humidities, the houses are made to provide living comfort everyday. The heating of houses in winter to provide comfort by the use of solar energy is an ancient concept and is in use since man started to build habitations. Basically the solar heating systems are divided into two categories: the passive heating and active heating. Passive systems do not need any mechanical system and are designed such that the glazed area, walls and roofs are used for collecting, storing, and distributing the heat indoors by natural processes of convection, radiation, and conduction. In active heating systems, separate solar collectors are used to heat a fluid; storage devices are used to store heat for use at night and on cloudy days; auxiliary heating systems are used to supply heat when required; and distribution systems along with controls are used to supply heat to required spaces. ,
COMPONENTS OF SOLAR HEATING SYSTEMS
The major components of an active solar heating systems are given below. The five important subsystems are :-
Fig: Simple basic layout of an active solar heating system
1) Solar Collector: It transfers the radiant energy of incident sunlight to working fluid which may be air or water. There is a large variety of solar energy collectors, both of liquid and air heating type that are used for space heating purposes .The liquid collectors range from simple zigzag tube welded on a metal sheet to the more sophisticated evacuated tube collectors, and the other commonly used collectors are: corrugated sheet type flat-plate
collector, roll-bond type of flat-plate collector, tube-in-plate type of flat-plate collector, water trickle type collector.
2) Thermal Storage System:
Thermal storage is an essential part of an active solar space heating system due to anticyclic nature of heat demand and diurnal variation of solar radiation. The size and type of heat storage media depends on the weather conditions and the percentage of total heating load to be supplied. Therefore, the thermal storage can be either a short term storage say from 1 to 8 days or long term storage generally
termed as seasonal storage. The most obvious choice with liquid collectors is water in tank and sometimes with some antifreeze liquid additive. Water has a high specific heat of 4.2 kJ/kg K but a heat exchanger is required to transfer energy from stored water to the point of use. Rock is another choice for use as sensible heat storage medium and has specific heat of 0.8 kJ/kg K. The rock bed system is generally used along with air collectors. Air can be used as a heat transfer media in rock bed system without heat exchanger. This combination has an additional advantage that it can not freeze and a little leakage will not be a problem. Rocks for a storage system should be carefully selected. It should be hard, of optimum size and the storage bin should have proper void spaces.
3) Auxiliary Heat Supply System:
Auxiliary heat supply arrangement is to be provided in all solar active space heating systems. This auxiliary heat can be supplied through a furnace which can be gas or oil fired, or electrically supplied or through a heat pump system in case of air heating systems. In case of liquid heating systems, auxiliary heat is supplied either directly through electric coils or through a boiler which is fired by oil, gas, electricity or any other fuel. Generally, electricity is not preferred due to economical reasons.
In liquid systems, either hot water from the top of the solar storage system is directly supplied to the radiant panels in the rooms or it transfers heat to air in a liquid to air heat exchanger and the hot air is supplied to the rooms. In both the cases the cooled water or air from the rooms is collected and returned to the bottom of the solar energy storage tank. While in air heating systems hot air from the solar storage tank is directly supplied to the rooms and the cooled air from the rooms is supplied to the bottom of the storage tank. Whatever type of storage system or auxiliary system is used, it is essential that the solar collectors should be supplied with the coolest possible liquid or air so that the collectors operate at maximum efficiency. The hot liquid or air from the top of the solar energy storage tank should be supplied to the load loop and the cooled room liquid or air should be supplied to the bottom of the tank. Stratification in the storage tank helps in the performance of the solar collectors but it is difficult to maintain due to several operational parameters.There are several modes of supplying auxiliary heat to the solar heating system as shown in Fig. Auxiliary heat should be supplied to the load loop and not the collector loop. This will help in augmenting the solar heat or replacing it when required. In collector loop this will unnecessarily raise the fluid inlet temperature to the collector.The conventional way of providing auxiliary heat in the load loop is shown in Fig.a where the auxiliary system is in series. In this system the auxiliary heater works as a booster, adds required amount of heat to the solar heated fluid, supplied to the load and later returned to the solar storage system. In this case, there is a possibility that the fluid returned from the load is at a temperature higher than that at the bottom of the solar storage thus adding heat to the storage resulting in reduced collector efficiency and increase in the use of auxiliary energy.Another auxiliary arrangement in a solar heating system, which is generally preferred over the one shown in Fig.a is shown in Fig. b. Here, the auxiliary arrangement is provided in parallel to the load loop and is used only when the desired temperature in the radiant panel or convector is not met by solar storage. If the solar storage temperature is low then with the help of special automatic valve the auxiliary heat is supplied to the rooms to meet the requirement. In this parallel arrangement solar heat is not wasted, since it goes on adding up in the solar storage and can be used wheneve desired.An auxiliary system with separate auxiliary heat storage and solar storage systems will perform even better since in this the off-peak electricity is used in charging a separate auxiliary storage system. The auxiliary storage will be charged whenever there is a generating capacity and will be used only at the end of the each off-peak period. This arrangement is shown in Fig. c. Alternatively a combined storage for storing solar and auxiliary heat can also be used as shown in Fig.d. Here during off-peak periods, the electric energy is used to charge the storage system and is used for room heating. Whenever, solar. energy is available it is used to charge the storage system. This combined storage system results in lowering the collector performance due to increase in inlet temperature. Mechanically single storage system is simpler compared to the two tanks system, but suffers from poor performance.
Fig: Possible modes of auxiliary heat arrangements in solar active space heating
4)Control Systems:
A control system is a must for any active space heating system whether it is liquid based or air based. A controller consists of three components, the sensors which sense the state of affair and communicate to the control unit, a control unit meant for taking decisions as per preprogramme based on sensor inputs, and actuators which carry out the decisions based on the control unit. The requirement of the controller is that it should be low in cost, dependable, and provide energy at a maximum efficiency. Generally, controllers turn off and on pumps, blowers, dampers, valves, etc. Now-a-days various kinds of control units are available for solar active heating operations but one should be careful in deciding the type of control unit required for the system.The heart of the control system is a differential thermostat, which measures the difference in temperature between the collectors and storage unit. When the collectors are 10°F to 20°F (-12.2°C to -6.7°C) warmer than the storage unit, the thermostat turns on a pump or fan to circulate water or air through the collector to heat the storage medium or the house.
Materials used for storing solar heat :
A number of materials will work as storage media in home, farm or small business solar heating systems; but only three are generally recommended at this time-rock, water (or water-antifreeze mixtures) and a phase-change chemical substance called Glauber's salt. These Fig: Comparative volumes for the same amount of heat storage using 3 different storage materials.
are the materials that most consistently meet the criteria for selecting a storage medium--namely, the ability (1) to deliver heat to its application points at a desirable temperature, and (2) to do it cheaply, based not so much on cost of the material as on cost of the total system and its maintenance.
Cost of Active Space Heating Systems
Active space heating systems cost between $8,000 and $25,000. They offer the greatest return on investment to those who heat with electricity in sunny winter climates.
The Performance and Maintenance of Active Systems
How well an active solar energy system performs depends on its quality, durability, system design, and installation. Active systems are generally more reliable and efficient than they were a decade ago
Most systems require 8 to 16 hours of maintenance annually. Set up a calendar with a list of system maintenance tasks. Different systems require different types of maintenance. Some suggestions include checking pipes and ductwork for leaks and collectors for damage. Clean the filters in the air systems and check the glazing on the collector. Also lubricate pumps and fans.
Comparing Liquid and Air Systems
Air Systems -
Advantages:
1. Air will not freeze or boil.
2. Air will not cause corrosion.
3. Warmed air can circulate directly from the collectors to living areas.
Disadvantages:
1. Ductwork and storage units are bulky.
2. Air leaks in ductwork and storage are difficult to detect and can significantly degrade system performance.
3. Extensive ductwork can be difficult and costly to retrofit.
Liquid Systems -
Advantages:
1. Liquids transfer heat more efficiently than air.
2. Area for storage and piping is smaller than for air systems.
3. Plumbing is usually easier to retrofit than ductwork.
Disadvantages:
1. Freeze and boil-out protection is necessary.
2. Components are subject to corrosion.
3. Leaks can damage other parts of the structure.
PRESENT STATUS:-
1)A work was was supported by Belgian government in 1970’s as a part of Belgian R&D programme on solar heating system using air collector with rock bed storage system.
2)A research work is also funded by heating and cooling division of solar energy of US Energy And Research Development Administration.This work is related to the development of a collector as a roof integrated structure for the National Security and Resources Study center(NSRSC)in Los Alamos.
CONCLUSION:
· Solar heat is environmentally friendly.
· Solar heat does not pollute or produce greenhouse gases.
· Solar heating helps in conservation of earth's energy resources.
· Solar heat is the best choice for people with allergy problems and chemical sensitivities.
REFERENCES:-
1) www.ases.org
2) www.eere.com
3) Solar Energy Fundamental and Applications by H.P.Garg and J.Prakash.
4) Solar Energy International Progress by T.Nejat Veziroglu.
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