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Solar Hot Water

Forced flow solar hot water systems have better performance than natural circulation systems but require more components and electricity for pumping. Natural circulation systems are simpler with fewer components and do not require active control equipment but are less efficient and have storage tank placement limitations. There are two main types of solar collectors - flat plate and vacuum tube. Closed loop solar hot water systems have better performance than open loop systems but are more complex, require more components and are more expensive to manufacture and install. Open loop systems are simpler with fewer components and cheaper to implement but have limitations in cold climates and water quality issues. Key aspects of solar collector construction include selective absorber coatings, insulation, casing materials and transparent covers.

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Sahil Dua
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48 views6 pages

Solar Hot Water

Forced flow solar hot water systems have better performance than natural circulation systems but require more components and electricity for pumping. Natural circulation systems are simpler with fewer components and do not require active control equipment but are less efficient and have storage tank placement limitations. There are two main types of solar collectors - flat plate and vacuum tube. Closed loop solar hot water systems have better performance than open loop systems but are more complex, require more components and are more expensive to manufacture and install. Open loop systems are simpler with fewer components and cheaper to implement but have limitations in cold climates and water quality issues. Key aspects of solar collector construction include selective absorber coatings, insulation, casing materials and transparent covers.

Uploaded by

Sahil Dua
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOC, PDF, TXT or read online on Scribd
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Forced-flow versus natural circulation SHW systems

forced flow +better performance +can be installed in large systems +allows independent location of collector and hot water tank
requires more components needs electrical energy for pumping and control is more expensive

natural circulation(thermosiphon) +simple and require less components +work without active control equipment +cheaper
not suitable for large systems less efficient storage tank must be located above the collec

Types of collectors and Selective coatings


1. Flat Plate 2. Vacuum tube 3. Concentratic tube

Open- versus closed-loop SHW systems


Closed loop +better performance avoids air bubbles +Prevents siltation of the collectors +allows use of antifreeze
Some temperature loss needs significantly more components more expensive more difficult to manufacture

Open loop +simple and require less components +Requires less tecnical skill +Cheaper and less sensitive to flaws
not suitable for frost area not suitable for poor quality water There are basically two types of coatings black solar paint + easy to handle + absorber can be painted locally + good absorption of solar radiation + low costs

high emission losses selective coatings + high absorption of solar radiation + low emission losses + prefabricated absorber stripes exist on the market higher costs must be handles with care Construction of a solar collector The absorber coating

Construction of a solar collector Casing


Materials - hardwood (resistant painting improves durability) - aluminum profiles - sheet metal casing (aluminum, steel) Features

- protects the collector from the elements (rain, dust)


- must be rigid to avoid the break of the glass cover - all connections to the piping should be kept insulated - must allow room for thermal expansion - must provide adequate ventilation to avoid

condensation

Construction of a solar collector Insulation insulation of the back side is very important to

reduce heat losses and improve the efficiency at least 5cm of a low conductivity insulator is recommended mineral wool and polyurethane foam is the most common material reflective lamination is often included between layers of insulation Construction of a solar collector transparent cover Why is a transparent cover necessary? protection of the absorber from the environment reduction of heat losses special solar glass (4mm) + high mechanical resistance + high transparency for solar radiation high weight and costs normal glass (4mm) lower mechanical resistance lower trasparency high weight + lower costs polycarbonate cover (3mm) + high resistance + less weight

lower transparency co s t s ? plastic foil + light and cheap low resistance short life span

Conclusions Characteristics of a good collector: selective absorber coating low heat capacity, high heat transfer coefficients iron-free glass cover stiff and light casing sufficient insulation of the back side no thermal bridges at the connecting pipes Two options available: flat-plate collectors evacuated tube collectors

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