Solar Water Heating

Solar Water Heating

aruliya keerthi s gokulnath p karthikeyan g sneha r

by (pe006) (pe015) (pe023) (pe035)

Introduction  

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All forms of energy are from Sun. Common forms of energy (fossil fuels) – used in rapid rate – depleted not too distant future. To supply a large portion of our energy needs – only possibility is incoming Solar energy from sun.

Introduction (cont…) 

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This report describes Solar Water Heating Systems. Its types, specifications, pros and cons etc. Compares Solar water heating system with Standard water heating System.

Historical Perspective 

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The first person known to have used the sun’s energy on a large scale is Archimedes. Serious studies - seventeenth century - Galileo and Lavoisier. Robert Goddard – 1930 - had five patents to send a rocket to the moon.

Historical Perspective (cont…) 

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Practical uses of solar service hot water heaters - 1920s and 1930s - in California. The first building to be practically heated with converted solar service hot-water heaters was constructed at the Massachusetts Institute of Technology in 1938.

Working of Solar Water Heating System 

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Solar energy transmitted as electromagnetic radiations. Solar energy Collectors convert the sun’s radiation to heat. Raise the temperature of the absorbing material. Energy is removed by means of a heat transfer fluid, which may be either liquid or gaseous.

Working of Solar Water Heating System (cont…) 

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The water is heated directly – water itself acts as heat transfer agent. Or heated indirectly – glycol or water – heat transfer agent. The absorbed heat is later transmitted to stored water. Solar heated water is then stored for use as needed. A conventional water heater provides any additional heating that might be necessary.

Solar Collectors 

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The device used for extracting sun’s energy in more useable and storable form. Types of Solar Collectors Flat-plate Collectors Evaculated tube Collectors Concentrating Collectors

Flat-plate Collectors 

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Intercept solar radiation on a metal or glass absorber plate - Heat transfer. The temperature of the absorber plate is greater than that of the environment - heat losses occur. 100 % collector efficiency cannot be realized in practice. Inferior to evacuated tube collectors - still used in many countries.

Evacuated Tube Collectors 

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Made up of rows of parallel, glass tubes – Solar tubes. Type – 1: Glass-Glass - tubes - two glass tubes - fused together at one end. Inner tube - selective surface coated - absorbs solar energy - inhibits radiative heat loss. Air is evacuated b/w two glass tubes vacuum eliminates conductive and convective heat loss. Performs well in low temperature areas.

Evacuated Tube Collectors (cont…) 

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Type – 2: Glass-Metal - tubes - single glass tube. Inside tube - flat or curved aluminium plate attached to a copper heat pipe or water flow pipe. Reliable and cheaper than glassglass. Type – 3: Glass-Glass - water flow path - tubes - water flows into the tube itself.

Concentrating Collectors 

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Parabolic troughs - Mirrored surfaces - concentrate the sun's energy on an absorber tube (receiver) containing a heat transfer fluid or water itself. Commercial power production applications - because very high temperatures can be achieved.

Solar Water Heating System Types 

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Active Systems Open-Loop Active Systems or Direct Systems Closed-Loop Active Systems or Indirect Systems Passive Systems Thermosiphon Systems Batch Heaters

Direct Systems 

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Pumps circulate water through the collectors. Efficient and low operating cost. Not appropriate if water is hard or acidic Scale and corrosion - disables the system. Popular in regions - do not experience subzero temperatures. Flat plate open-loop systems should never be installed in climates that experience sustained periods of subzero temperatures.

Indirect Systems 

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Pumps heat-transfer fluids (glycol-water antifreeze mixture) through the solar water heater. Heat exchangers - transfers heat to the water. Double-walled heat exchangers - prevents contamination of water. Popular - extended subzero temperature areas because they offer good freeze protection. Glycol antifreeze systems are more expensive – must be checked each year changed every few years.

Thermosiphon Systems    

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Natural Convection takes place. The tank must be located above the absorber tubes/panel. As water in the absorber heats - becomes lighter - rises into the tank above. Meanwhile cooler water in the tank flows downwards into the absorber - circulation throughout the system. Widely used - flat plate - evacuated tubes. Proper measures to be taken for having a large tank on the roof.

Batch Heaters 

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Simple - one or more storage tanks placed in an insulated box - glazed side facing the sun. Inexpensive – performs well only in summer when the weather is warm. Evacuated tubes - affordable and efficient than the flat-plate collectors.

Active Systems vs Passive Systems 

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Active Systems – Electrical Components, Heat transfer fluids, More expensive, More efficient, Easy installations. Passive Systems – No electrical components, More reliable, Easier to maintain, Last longer than active systems. Less expensive, Less efficient due to slower water flow rates through the system.

Which type of Solar Water Heaters are being used in our campus and why???

Thermosiphon Systems 

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No Electrical Components requirements like pumps, valves etc. Less expensive. More reliable. Easy maintenance. Sufficient space to install storage tanks above Solar Collectors, so easier to install. Less efficient.

Pros   

Non polluting. Saves energy. Saves money.

Cons  

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Depends on location. Unshaded south facing location is necessary. Hard and Acidic water corrodes the system. Not able to use Direct systems in freezing temperature areas. Because they run on electricity – will not function during power outages.

Cons (cont…) 

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Structure roof should be strong enough to support the storage tanks. Special regulations on roof structure and strength should be taken in earthquake and hurricane danger areas. Initial installation cost is very expensive than conventional electric or gas heaters.

Water Heating Loads 

The amount of energy needed to heat water is the product of the volume of water, its density, its specific heat, and the required temperature increase. Qhw = V (ρc) (Tset – Tsource)

Qhw = energy requirement per day. V = volume of water required per day. ρ = density. c = specific heat. Tset = thermostat set point and desired delivery temp. Tsource = temp of the inlet water.

Water Heating Loads (cont…) 

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Here the amount of heat lost in water heating system and recirculation system should be taken in account. This heat loss consume 20 to 25 % of the fuel used in a hot water installation over the course of a year. The tank and piping loss - thermal conductance of the insulation Uhw multiplied by its surface area Ahw and by the temperature difference the water and the surroundings.

Water Heating Loads (cont…) Qstandby = Uhw Ahw (Tset – Ta) Nh Ta = ambient temperature. Nh = number of hours of use per day, usually 24. 

The total water heating demand is expressed by the sum of two eq.

Solar Water Heater vs Standard Water Heater. SOLAR WATER HEATER

STANDARD WATER HEATER

FREE energy from sun

COSTLY gas or electric

Annual operating cost: $50

Annual operating cost: $500+

Storage Capacity: 80-120 gal

Storage Capacity: 40-50 gal

Life expectancy: 15-30 years

Life expectancy: 8-12 years

Lifetime operating cost: $1,000

Lifetime operating cost: $10,000

Does NOT pollute environment

Depletes fossil fuels

Increases equity in your home

No added value to your home

25% return on your investment

No return on utility payments

Protection from future increases

At mercy of utilities/government

BONUS: Hot water during blackout!

COLD showers, laundry, dishes?

Conclusion     

Solar Water Heating Techniques. Mechanism. Types. Specifications, Requirements. Pros and Cons.

Conclusion (cont…) 

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Thermosiphon Water Heating Systems are being used in our college because of its high efficiency, less expensive, no electrical power requirement. Very much suitable for large populated areas like hospitals, prisons, hostels, hotels etc.

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