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Solar Water Heater

SOLAR WATER HEATER

1. Introduction
Solar water heaters capture the solar energy thermal energy to heat up water. Hot water can then be used for domestic purposes (shower, kitchen…etc) space heating, industrial processes or even solar cooling.

A solar water heater is one of the most effective ways of cutting a household’s carbon footprint and electricity bill by reducing reliance on dirty fossil fuel usage or electricity from the grid.

While solar water heater devices have been around for over 100 years, the last 20 years have seen significant advances in absorber coating technologies, resulting in solar collectors that can now reliably convert >50% of available solar radiations.

The average life expectancy of certified solar water heating systems can be 20 years, much longer than standard gas or electric storage water heaters (1).

2. How does it work?
Solar water heaters are operating under the principle of natural convection (thermosiphon) and the effects of optical glass to absorb solar energy, to convert it to heat and simultaneously trapsit.
The major component of SWH is the solar collector. It is generally installed on the roof. This component absorbs the incoming solar radiation, converts it into heat, and transfers this heat to water flowing through the collector.
Cold water from the lower part of the storage tank is going through the solar water heater where solar radiationsare transformed into heat that heat the water up (~600C).
Thereafter, by convection, the warmed water is moving up and then is reentering a the upper part of the storage tank.
This process occurs continuously until the average temperature in the storage tank is the same as the temperature of the water in the collector.

 3. Benefits
•  
Save money: your electricity bill decreases considerably. The application of solar water heaters can save about 944 kWh per household (average household of 4 people)(2).
•  The use of solar water heaters also contributes directly to reduce power consumption during the peak hours.
• Short payback period: from 2 years for residential systems and from 4 years for collective systems(3).
• Reduce carbon footprint

4.Application(3)
Residential buildings
For individual homes (town houses or shop houses, villas), SWH provide hot water for showering and cooking. Thereby the required volume of het water usually does not exceed 500 liters/day. One retail unit is generally enough. This type of SWH usually uses the natural convection principle.

Commercial Buildings
For this type of installation, the required quantity of hot water needs several panels and tanks. The sizes are customized for optimal efficiency and most importantly, a central controller must be set up in order to collect the water temperatures and control operation of the circulation pump of water inside. Besides, a return pump and pressurized pump may be used to meet the required pressure and temperature at the outlet. This installation has become particularly popular among hotels.

5. Hints
•  
You should install the solar collector facing south or south-west, forming an angle from 15 degrees (best configuration), to about 25-30 degree, above the horizontal.
  Select a water capacity in accordance with the quantity of people in the family to use.Systems with a capacity of about 200 litres should sufficient to serve a family of 5 people.
•  Design the output pipe as short as possible as well as insulate it properly in order to limit heat loss.
 Make sure that you will get proper work,  guaranty and regular maintenance from the installation company.
 Contaminated water sources: Consult with your SWH supplier about the required quality of water source before you install the system.
 Shading and sunlight exposure: Make sure that the sun exposition of your home or building aresuffucient and that no shading will prevent the system from collecting heat.
 You may choose solar water heaters compliant with standard ISO 9459-5(orDIN EN 12975)

References|
(1) http://www.energystar.gov/index.cfm?c=solar_wheat.pr_savings_benefits
(2) Handbook for Green Housing – Edit 1, Michael Waibel
(3) Handbook for Green Housing – Edit 2, Michael Waibel

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