Solar Water Heating System FULL - basic project

8/3/2019 Solar Water Heating System FULL - basic project

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NEAR EAST UNIVERSITY

Department of Mechanical Engineering

SOLAR WATER HEATING SYSTEM

Submitted By : HAFIZ ADIL RASOOL


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TABLEOFCONTENTS

ABSTRACT ----------------------------------------------------------------------------- I

I INTRODUCTION ---------------------------------------------------------------------- 1

II WATER HEATING SUPPORT SYSTEMS ----------------------------------------- 2

III SOLAR HOT WATER SY STEM COMPONENTS -------------------------------- 4

IV WHAT IS SOLAR COLLECTOR? --------------------------------------------------- 4

V ECONOMICS, ENERGY, ENVIRONMENT, AND SYSTEM COSTS --------- 5

VI TYPES OF SOLAR WATER HEATING SYSTEM -------------------------------- 7

VI.1 PASSIVE SYSTEM ------------------------------------------------------------- 7

VI.2 ACTIVE SYSTEMS------------------------------------------------------------- 8

VII DIFFERENTIAL CONTROLLER OPERATED SYSTEM-------------------------- 9

VIII ACTIVE SYSTEM OPERATIONAL CARBON FOOTPRINT -------------------- 10

IX TYPES OF THERMAL COLLECTOR ----------------------------------------------- 11

IX.1 FORMED PLASTIC COLLECTORS ----------------------------------------- 11

IX.2 FLAT PLATE COLLECTORS ------------------------------------------------- 12

IX.3 EVACUATED TUBE COLLECTORS----------------------------------------- 13

X ALUMINI UM SELECTIVE SURFACED COLLECTOR --------------------------- 15

X.1 Table1. SPECIFICATION OF ALUMINIUM COLLECTOR----------------- 16


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ABSTRACT

The prices of energy resources used for grain drying are increasing year by year. In

order to reduce costs, research into methods of saving energy in grain drying is in

progress.

Equipment for experimental research into the materials of solar collectors are used

for simultaneous comparative studies of two materials. The experimental data are

metered and recorded in the electronic equipment REG. Cell polycarbonate PC (bronze,

hence forth referred to as polycarbonate) with absorbers steel-tinplate and black-

coloured wood was researched in comparison to the polyvinylchloride film (henceforth

referred to as a film). The researches were made with different air velocities. The air

heating degree T in the solar collector is dependent on solar radiatio n I and air velocity v

in the solar collector. In the experimental equipment, which is 1.5 meters in length, the air

was heated to T = 6 C at the velocity v = 0.5 m s-1.

For theoretical investigation of the air heating power in solar systems the

mathematical model is applied; the solution can be used for estimation of different

materials /absorbents/ and their heat source.


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I. INTRODUCTION

Solar energy is radiant energy that is produced by the sun. Every day the sun radiates, or

sends out, an enormous amount of energy. The sun radiates more energy in one second

than people have used since the beginning of time!

Where does the energy come from that constantly radiate from the sun? It comes from

within the sun itself. Like other stars, the sun is a big ball of gases mostly hydrogen and

helium atoms. The hydrogen atoms in the suns core combine to form helium and

generate energy in a process called nuclear fusion. During nuclear fusion, the suns

extremely high pressure and temperature cause hydrogen atoms to come apart and their

nuclei (the central cores of the atoms) to fuse of combine. Four hydrogen nuclei fuse to

become one helium atom. But the helium atom contains less mass than the four hydrogen

atoms that fused. Some matter is lost during nuclear fusion. The lost matter is emitted

into space as radiant energy.

It takes millions of years for the energy in the suns core to make its way to the solar

surface, and then just a little over eight minutes to travel the 93 million miles to earth.

The solar energy travels to the earth at a speed of 186,000 miles per second, the speed of

light. Only a small portion of the energy radiated by the sun into space strikes the earth,

one part in two billion. Yet this amount of energy is enormous.

Where does all this energy go? About 15 percent of the suns energy that hits the earth is

reflected back into space. Another 30 percent is used to evaporate water, which lifted into

the atmosphere, produces rainfall. Solar energy also is absorbed by plats, the land, and

the oceans. The rest could be used to supply our energy needs.

Sun, is a mid-size star that is composed from high density gasses under very high

temperatures. It is 150 million km away from the earth and its diameter is 1.39 million km

(i.e. 110 times bigger than the diameter of the earth). The temperature which is

determined to be 5777 K at its surface is estimated to be 8 million K in its core. Under

this very high temperature values, electrons are separated from the nucleus of atoms and

are unattached. This mixture is called plasma; under very high temperature values, the

atomic nucleuses of lighter elements gather together to form the nucleuses of heavier

elements. Within this fusion reaction which is called as Thermo nuclear reaction, 564

million tones of hydrogen transfer into 560 million tones of helium in just one second. The

mass difference between these two elements which is 4 million tones, spread into deep

space in the form of thermal and light energy that is known as the solar energy. The

intensity value of the solar energy within the outer bounds of the earths atmosphere is

1367 W/m on average, and this figure is known as the Solar Constant. Sunlight beams

are reflected, deflected and absorbed by dust particles and gas molecules as they pass

through the earths atmosphere. This causes the sunlight beams to weaken. The part of

sunlight beams which pass through the atmosphere without running into any obstacles


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like dust particles and gas molecules and reach the surface of the earth, are called the

direct radiation. The part that is reflected deflected and absorbed by dust particles and

gas molecules and reach the surface of the earth directionless is called the diffuse

radiation.

The total amounts of direct and diffuse radiation indicate the total radiation value that

fall onto the surface of the earth (onto the horizontal surface). Under optimal conditions(cloudless and clear skies, noon time) the total radiation value reaches up to 1000 W/m.

Depending on the type of the collectors, it is still possible to make use of 75 % of the total

radiation [1,3].

II . WATER HEATING SUP PORT SYSTEMS

Figure1: Simple Home water heating system [ 13]

Within these systems which are installed for providing hot water and general heating (like

radiators or floor heating systems), special boilers are used; these boilers are known as

chamber or combi boiler (natural gas central heating boilers) models and have a water

capacity changing between 500 to 2000 litres. The hot water storage capacity of these

systems changes between 160 and 400 litres; within the rest of the storage capacity, thewater of the heating system is stored. As well as it is dependent on the heating potential

of the sun, solar collectors which has a total surface area that changes between 10 to 40

m and operating with selective surface technology, are used in order to feed these

boilers.

First, the water in the boiler is heated by a differential thermostat electronic panel which

has multi circuit control feature. The temperature of the water in the return line of


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radiators or floor heating system and the temperature of the water that is in the boiler are

continuously measured by the panel and compared with each other.

According to the pre-adjusted differential temperature differences, either the water

coming from the plumbing system or the heated water in the boiler is delivered to the

tank by means of three way motor valve that is on the return line. As long as the

temperature of the water in the boiler is higher than the temperature of the water in thereturn line, the heating system is supported by solar energy and as a result, fuel is saved.

In terms of solar energy usage, the floor heating systems are more advantageous when

compared to radiator heating systems, because the temperature of the water circulating

within the system is much lower.

Especially during the winter, fulfilling the heating needs completely by using these

systems only, is out of question. When taking the heat loss of the building, the state of

the isolation systems, the solar heating intensity and the geographic and climatic

characteristics into consideration, the effect of the solar energy system on the annual fuel

savings, will be between 10 % and 45 % (hot water supply + heating). When determining

the quantity of collectors and the capacities of the equipment that forms the system

during the project designing phase, the safety measures related to the redundant energy

that will be produced in summer should be taken into consideration. [3]

Figure 1: ACTIVE, DIRECT SYSTEM [13]

III. SOLAR HOT WATER SYSTEM COMPONENTS


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Understanding the basic components of an RE system and how they function is not an

overwhelming task. Here are some brief descriptions of the common equipment used in

solar hot water systems.

Solar Collectors

Collector Mounting System

Solar Storage Tank

Water Pump

Heat Exchanger

Expansion Tank

Controls

Isolation Valve

Backup Water Heater

Tempering Valve

IV. WHAT IS SOLAR COLLECTOR?

In order to heat water using solar energy, a collector is fastened to the roof of a building,

or on a wall facing the sun. In some cases, the collector may be free-standing. The

working fluid is either pumped (active system) or driven by natural convection (passive

system) through it.

The collector could be made of a simple glass topped insulated box with a flat solar

absorber made of sheet metal attached to copper pipes and painted black, or a set of

metal tubes surrounded by an evacuated (near vacuum) glass cylinder. In some cases,

before the solar energy is absorbed, a parabolic mirror is used to concentrate sunlight on

the tube.

A simple water heating system would pump cold water out to a collector to be heated, the

heated water flows back to a collection tank. This type of collector can provide enough

hot water for an entire family.


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Heat is stored in a hot water tank. The volume of this tank will be larger with solar heating

systems in order to allow for bad weather, and because the optimum final temperature for

the absorber is lower than a typical immersion or combustion heater. The working fluid

for the absorber may be the hot water from the tank, but more commonly (at least in

active systems) is a separate loop of fluid containing anti-freeze and a corrosion inhibitor

which delivers heat to the tank through a heat exchanger (commonly a coil of copper

tubing within the tank). Another lower-maintenance concept is the 'drain-back': no anti-

freeze is required; instead all the piping is sloped to cause water to drain back to the tank.

The tank is not pressurized and is open to atmospheric pressure. As soon as the pump

shuts off, f low reverses and the pipes empty by the time wh en freezing could occur.

When a solar water heating and hot-water central heating system are used in conjunction,

solar heat will either be concentrated in a pre-heating tank that feeds into the tank

heated by the central heating, or the solar heat exchanger will be lower in the tank than

the hotter one. However, the main need for central heating is at night when there is no

sunlight and in winter when solar gain is lower. Therefore, solar water heating for washing

and bathing is often a better application than central heating because supply and demand

are better matched.

The water from the collector can reach very high temperatures in good sunshine, or if the

pump fails. Designs should allow for relief of pressure and excess heat through a heat

dump. [11,12,05]

V. ECONOMICS, ENERGY, ENVIRONMENT AND COSTS

The typical 50 gallon electric water heater uses 11.1 barrels of oil a year, which translates

into the same amount oil used by a typical 4 door sedan driven by the average consumer.

Electric utility companies often provide electricity by burning and releasing energy from

fuels such as oil, coal and nuclear energy. An electrical home hot water heater sits on an

electrical grid and may be driving the use of unclean fuels on the other end of the grid.

Solar water heating systems can significantly reduce such electricity consumption.

In sunny, warm locations, where freeze protection is not necessary, a batch type solar

water heater can be extremely cost effective. In higher latitudes, there are often

additional design requirements for cold weather, which add to system complexity. Thishas the effect of increasing the initial cost (but not the life-cycle cost) of a solar water

heating system, to a level much higher than a comparable hot water heater of the

conventional type. When calculating the total cost to own and operate, a proper analysis

will consider that solar energy is free, thus greatly reducing the operating costs, whereas

other energy sources, such as gas and electricity, can be quite expensive over time. Thus,

when the initial costs of a solar system are properly financed and compared with energy

costs, then in many cases the total monthly cost of solar heat can be less than other more


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conventional types of hot water heaters (and also in conjunction with an existing hot

water heater). At higher latitudes, solar heaters may be less effective due to lower solar

energy, possibly requiring dual-heating systems. In addition, federal and local incentives

can be significant.

As an example, a 56 ft. solar water heater can cost US $7,500, but that initial cost is

reduced to just $3,300. The system will save approximately US $230 per year, with apayback of 14 years. Lower payback periods are possible based on maximizing sun

exposure. As energy prices rise, payback periods decrease. In cooler locations, solar

heating used to be less efficient. Usable amounts of domestic hot water were only

available in the summer months, on cloudless days, between April and October. During

the winter and on cloudy days, the output was poor. Independent surveys have shown

that modern systems do not suffer these limitations. There are cases of households in

cool climates getting all of their domestic hot water year round from solar alone.

According to ANRE a complete, commercial (active) solar water heating system

composed of a solar collector (3-4 m; this is large enough for 4 people), pipes and tank

(again large enough for 4 people) costs around 4000 euro. The installation by a

recognized worker costs another 800 euro. Electrabels home magazine Eandismagazine

stated in 2008 that a complete system (including 4m2 of solar collectors and a supply

barrel of 200-240 liters) to cost 4500 euro. The system would then pay back itself in 11

years, when the returns are weighed off against a regular electric boiler. Calculation was

as follows: a saving of 1875 kWh (which is 50% of the energy requirements in domestic hot

water production) x 0.10 euro/kWh = 187, 5 euro. This multiplied by 11.6 years made 2175

euro (or the cost of the system with deducted regional tax benefits).

In Australia, the cost for an average solar water heating system fully installed is between

$1,800 and $2,800. This is after tax rebates (there is a federal rebate, some state rebates

and Renewable Energy Certificates). According to the Department of Environment and

Water Resources, the yearly electricity savings are between $300 and $700. This brings

the payback period to under 2 years in the best case and under 10 years in the worst case.

Easy Being Green has a program available where consumers can acquire a system for free

(with government rebates) excluding the cost of installation. [07]

VI.

TYPES OF SOLAR WATER HEATING SYSTEM

There are two main categories of solar water heating systems:

Active systems

Passive systems


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In addition, there are a number of other system characteristics that distinguish different

designs:

The type of collector used

The location of the collector - roof mount, ground mount, wall mount

The location of the storage tank in relation to th e collector

The method ofheat transfer - open-loop or closed-loop (via heat exchanger)

Photovoltaic thermal hybrid solar collectors can be designed to produce both hot water

and electricity.

VI.1 PASSIVE SYSTEM

A passive system also known as a compact system or monobloc has a tank for the heated

water and a solar collector mounted on the same chassis. Typically these systems will

function by natural convection (thermo siphon) or heat pipes to transfer the heat energy

from the collector to the tank. It is usually based on the architectural design in order to

heat up any building.

A special type of passive system is the Integrated Collector Storage (ICS or Batch Heater)

where the tank acts as both storage and solar collector. Batch heaters are basically thin

rectilinear tanks with glass in front of it generally in or on house wall or roof. They are

seldom pressurized and usually depend on gravity flow to deliver their water. They are

simple, efficient and less costly than intense plate and tube collectors but only suitable in

moderate climates with good sunshine. A step up from the ICS is the Convection Heat

Storage Unit. These are plate type intense collectors with built-in insulated tanks. The

unit uses convection (movement of hot water upward) to move the water from heater to

tank. Neither pumps nor electricity are used. It is more efficient than an ICS as the intense

collector heats a small(ER) amount of water that is constantly rising to the tank.

Direct ('open loop') passive systems, if made of metals are not suitable for cold climates.

At night the remaining water can freeze and damage the panels, and the storage tank is

exposed to the outdoor temperatures that will cause excessive heat losses on cold days.

Some passive systems have a primary circuit. The primary circuit includes the collectors

and the external part of the tank. Instead of water, non-toxic antifreeze is used. When this

liquid is heated up, it flows to the external part of the tank and transfers the heat to the

water placed inside. (Closed loop'). Open loop (direct) systems have the disadvantage

that during the night-time, where the temperature of the solar panel starts to drop below

that of the water tank, the system starts working in reverse heating the water in the p anel

and cooling the water inside the tank. This problem is least noticeable in closed loop


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system using a heat exchanger as only the water in the heat exchanger and not the whole

tank is affected by it. Zhuhai Tianke Energy Saving Equipment Manufacture Co., Ltd.

managed to solve this problem using a patented design in their solar water heating

systems heat exchanger which forces the flow of the water in the heat exchangers inlet

pipe in an upward flow, thus re stricting cold water flowing down to the panel. The f orce of

the flow is made through a driver inside the heat exchanger (jacket). The jacket and the

driver part is made of the same heat conducting material therefore sharing the same

temperature on same levels of the heat exchanger.

A passive system can save up to 4.5 tons annually of greenhouse gas emissions. In order

to achieve the aims of the Kyoto Protocol, several countries are offering subsidies to the

end user. Some systems can work for up to 25 years with minimum maintenance. These

kinds of systems can be redeemed in six years, and achieve a positive balance of energy

(energy they save minus energy used to build them) of 1.5 years. Most part of the year,

when the electric heating element is not working, these systems do not use any external

source for power (as water fl ows due to thermo siphon principle).

Flat solar thermal collectors are usually used, but passive systems using vacuum tube

collectors are available on the market. These generally give a higher heat yield per square

meter in colder climates but cost more than f lat plate collector systems. [08,09]

VI.2 ACTIVE SYSTEMS

Active solar hot water systems employ a pump to circulate the water or heat transfer fluid

and a controller to turn the pump on and off depending on the temperature of the tankand collectors. Active systems are usually significantly more efficient that passive

systems but are more complex, more expensive, more difficult to install and rely on

electricity to run the pump and controller. During active heating, solar energy is stored,

collected, and distributed in buildings, providing hot water or space heating. When

sunlight falls on a building's collector, it is transformed into heat and conveyed into a

carrier fluid. It is then pumped into a conversion, later into a storage, and finally into the

distribution system.

Newer electronic controllers permit a wide range of functionality such as measurement of

the energy produced, more sophisticated safety functions, thermostatic and time-clockcontrol of auxiliary heat, hot water circulation loops, others display and transfer of error

messages or alarms, remote display panels, and remote or local data logging.

The most commonly used solar collector is the insulated glazed flat panel. Less expensive

panels like polypropylene panels (for swimming pools) or higher-performing ones like

evacuated tube collectors, are sometimes used. [08,09]


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VII. DIFFERENTIAL CONTROLLER OPERATED SYSTEM

The direct active system has one or more solar energy collectors installed on the roof and

a storage tank somewhere below, usually in a garage or utility room. A pump circulates

the water from the tank up to the collector and back again. This is called a direct (or open

loop) system because the sun's heat is transferred directly to the potable water circulatingthrough the collector tubing and storage tank; no anti-freeze solution or heat exchanger

is involved.

This system has a differential controller that senses temperature differences between

water leaving the solar collector and the coldest water in the storage tank. When the

water in the collector is about 15-20F warmer than the water in the tank, the pump is

turned on by the controller. When the temperature difference drops to about 3-5F, the

pump is turned off.

In this way, the water always gains heat f rom the collector when the pump operates.

A flush-type freeze protection valve installed near the collector provides freeze

protection. Whenever temperatures approach freezing, the valve opens to let warm water

flow through the collector.

The collector should also allow for manual draining by closing the isolation valves (located

above the storage tank) and opening the drain valves.

Automatic recirculation is another means of freeze protection. When the water in the

collector reaches a temperature near freezing, the controller turns the pump on for a few

minutes to warm the collector with water from the tank.

Photovoltaic operated system. The photovoltaic system differs from other direct active

systems in that the energy to power the pump is provided by a photovoltaic (PV) panel.

The PV panel converts sunlight into electricity, which in turn drives the direct current (dc)

pump. In this way, water flows through the collector only when the sun is shining.

The DC-pump and PV panel must be suitably matched to ensure proper performance. The

pump starts when there is sufficient solar radiation available to heat the solar collector. It

shuts off later in the day when the available solar energy diminishes. As in the previous

systems, a thermally operated valve provides freeze protection.

The main advantage of this system is that hot water is always available during a power

outage. The pump is operated by the sun and is completely independent from the FPL

utility. [08,09]


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VIII. ACTIVE SYSTEM OPERATIONAL CARBON

FOOTPRINT

The source of electricity in an active system determines the extent to which a system

contributes to atmospheric carbon during operation. The type of active solar thermal

systems which use mains electricity to pump the fluid through the panels are called low

carbon solar because the pumping negates the carbon savings of the solar by about 20%,

according to data in a report called "Side by side testing of eight solar water heating" by

DTI UK. However, zero-carbon active solar thermal systems typically use a 5-20W PV

panel which faces in the same direction as the main solar heating panel and a small, low

power diaphragm pump or centrifugal pump to circulate the water. This represents a zero

operational carbon footprint and is becoming an important design goal for innovative

solar thermal systems. [09]

IX. TYPES OF THERMAL COLLECTOR

There are three main kinds of solar thermal collectors in common use. In order of

increasing cost they are:

Formed Plastic Collectors

Flat Plate Collectors

Evacuated Tube Collectors

The efficiency of the system is directly related to heat losses from the collector surface

(efficiency being defined as the proportion of heating energy that can be usefully


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obtained from insulation). Heat losses are predominantly governed by the thermal

gradient between the temperature of the collector surface and the ambient temperature.

Efficiency decreases when either the ambient temperature falls or as the collector

temperature increases. This decrease in efficiency can be mitigated by increasing the

insulation of the unit by sealing the unit in glass e.g. flat collectors or providing a vacuum

seal e.g. evacuated tube collector. The choice of collector is determined by the heating

requirements and environmental conditions in which it is employed. [11,08]

IX.1 FORMED PLASTIC COLLECTOR

Formed plastic collectors (such as polypropylene, EPDM or PE T plastics) consist of tubes

or formed panels through which water is circulated and heated by the sun's radiation.

These are often used for extending the swimming season in swimming pools. In some

countries, heating an open-air swimming pool with non-renewable energy sources is not

allowed, and then these inexpensive systems offer a good solution. This panel is notsuitable for year-round uses like providing hot water for home use, primarily due to its

lack of insulation which reduces its effectiveness greatly when the ambient air

temperature is lower than the temperature of the fluid being heated. [11]

IX.2 FLAT PLATE SOLAR COLLECTOR


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Figure 3: Flat Plate Solar Collector [4]

A solar collector consists of a network of pipes through which water (or in colder climates,

antifreeze) is heated. Collectors come in various sizes, with 4 by 8 feet (1.2 x 2.4 m) the

most common. On a typical summer day (sunny and warm), the fluid in the collectors

reaches 140F to 180F (60C-80C). On a clear winter day (sunny and cold), it can reach120F to 150F (50C-65C). When its cloudy and warm, collectors can reach 70F to 90F

(20C-30C), and when its cloudy and cold, 50F to 60F (10C-15C). As long as the

temperature in the collector is greater than that of your incoming cold water (usually

about 50F; 10C), your solar hot water system is saving you energy. Several types of solar

collectors are on the market. Flat-plate are thin (3-4 in.; 7-10 cm), black, and covered with

glass to hold in the suns energy. In evacuated tube collectors, a glass tube surrounds

each individual pipe in a vacuum. This nearly eliminates the influence of ambient air

temperature. Evacuated tubes perform better than flat plate collectors in cloudy weather,

and can achieve higher temperatures compared to other collector types, but are typically

more expensive. All active systems and some thermo siphon systems may use either flatplate collectors or evacuated tube collectors. A third type, called integrated collector

storage (ICS) or batch, combines the solar collector and storage tank into one unit. An ICS

panel can resemble a flat-plate collector with greater depth (6 in.; 15 cm). A simple batch

heater

A flat plate collector consists of a thin absorber sheet (of thermally stable polymers,

aluminum, steel or copper, to which a black or selective coating is applied) backed by a


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grid or coil of fluid tubing and placed in an insulated casing with a glass or polycarbonate

cover.

Fluid is circulated, using either mains or solar electricity, through the tubing to remove

the heat from the absorber and to transport it to an insulated water tank, sometimes

directly or otherwise to a heat exchanger or to some other device for using the heated

fluid. Some fabricants have a completely flooded absorber consisting of 2 sheets of metalstamped to produce a circulation zone. Because the heat exchange area is greater they

may be marginally more efficient than traditional absorbers.

As an alternative to metal collectors, new polymer flat plate collectors are now being

produced in Europe. These may be wholly polymer, or they may be metal plates behind

which are freeze-tolerant water channels made of silicone rubber instead of metal.

Polymers, being flexible and therefore freeze-tolerant, are able to contain plain water

instead of antifreeze, so that in some cases they are able to plumb directly into existing

water tanks instead of needing the tank to be replaced with one using heat exchangers.

By dispensing with a heat exchanger in these flat plate panel, temperatures need not be

quite so high for the circulation system to be switched on, so such direct circulation

panels, whether polymer or otherwise, can be somewhat more efficient, particularly at

low light levels. As with evacuated tubes, most flat plate collectors have a life expectancy

of over 25 years. [11, 12]

IX.3 EVACUATED TUBE COLLECTOR

Evacuated tube collectors are made of a series of modular tubes, mounted in parallel,

whose number can be added to or reduced as hot water delivery needs change. This type

of collector consists of rows of parallel transparent glass tubes, each of which contains an

absorber tube (in place of the absorber plate to which metal tubes are attached in a flat-

plate collector). In some cases, the tubes are covered with a special light-modulating

coating. In an evacuated tube collector, sunlight passing through an outer glass tube

heats the absorber tube contained within it. The absorber can either consist of copper

(glass-metal) or specially-coated glass tubing (glass-glass). The glass-metal evacuated

tubes are typically sealed at the manifold end, and the absorber is actually sealed in thevacuum, thus the fact that the absorber and heat pipe are dissimilar metals creates no

corrosion problems. Some systems use foam insulation in the manifold. Soda-lime glass is

used in the higher quality evacuated tubes manufacture.

Later technology evacuated tube systems use the glass coated absorber. The glass is a

boron silicate material and the aluminum absorber and copper heat pipe are slid down

inside the open top end of the tube. In lower quality systems moisture can enter the


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manifold around the sheet metal casing is eventually absorbed by the glass fiber

insulation and then finds its way down into the tubes. This leads to corrosion at the

absorber/heat pipe interface area, also freeze ruptures of the tube itself if the tube fills

sufficiently with water.

Two types of tube collectors are distinguished by their heat transfer method: the simplest

pumps a heat transfer fluid (water or antifreeze) through a U-shaped copper tube placedin each of the glass collector tubes. The second type uses a sealed heat pipe that contains

a liquid that vaporizes as it is heated. The vapor rises to a heat-transfer bulb that is

positioned outside the collector tube in a pipe through which a second heat transfer liquid

(the water or antifreeze) is pumped. For both types, the heated liquid then circulates

through a heat exchanger and gives off its heat to water that is stored in a storage tank

(which itself may be kept warm partially by sunlight). Evacuated tube collectors heat to

higher temperatures, with some models providing considerably more solar yield per

square meter than flat panels. However, they are more expensive than flat panels, but

generally of a less cost to repair in the event of damage. Evacuated heat tubes perform

better than flat plate collectors in cold climates because they only rely on the light they

receive and not the outside temperature. The high stagnation temperatures can cause

antifreeze to break down, so careful consideration must be used if selecting this type of

system in temperate climates. Tubes come in different levels of quality so the different

kinds have to be examined as well. High quality units can efficiently absorb diffuse solar

radiation present in cloudy conditions and are unaffected by wind. They also have the

same performance in similar light conditions summer and winter.

For a given absorber area, evacuated tubes can maintain their efficiency over a wide

range of ambient temperatures and heating requirements. The absorber area only

occupied about 50% of the collector panel on early designs; however this has changed as

the technology has advanced to maximize the absorption area. In extremely hot climates,

flat-plate collectors will generally be a more cost-effective solution than evacuated tubes.

When employed in arrays of 20 to 30 or more, the efficient but costly evacuated tube

collectors have net benefit in winter and also give real advantage in the summer months.

They are well suited to extremely cold ambient temperatures and work well in situations

of consistently low-light. [11,04]

X. ALUMINIUM SELECTIVE SURFACED COLLECTOR


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Figure 4: Aluminium Selective Surfaced Collector [4]

The selective surface (i.e. the absorber plate) of SOLARTEK solar collector is made of

aluminium. The absorber plate body consists of monolithic aluminium profiles. The body

profiles are fixed to diffuser and collecting pipe profiles by clamping under high pressure;

no welding process is used. As a result, SOLARTEK is freed of all problems that may arise

from welding seams. It is resistant against high temperature. By creating a turbulence

formation within the fluid circulation, every molecule of the fluid is contacted with the

surface and as a result, more efficient energy transfer is acquired. When the fluid is

inactive, i.e. when there is no circulation, the surface temperature increases to 191 C.

The high pressure that is generated during this process is far from creating a problem for

SOLARTEK.

By a special galvanic coating technique, within the range in which the sunlight beams can

emit thermal energy that is between 0.2 m and 2 m wave length, a radiation absorption

rate between 93 % and 97 % is ensured. The nickel pigmented aluminium oxide coating

which is developed to protect its surface characteristics for years, is highly resistant

against atmospheric conditions. The heating canals in the absorbent plate which consistsof profiles that are developed by extrusion technique are monolith with the surface. As a

result the energy gathered on the surf ace, is transferred to the fl uid smoothly.

Regular ferrous glass which has a solar energy conductivity value of 86 % is used within

the STANDARD model collectors. When the corrective factors related to glass and the

beam absorption values of absorbent plate are taken in to consideration, the optical

efficiency value of STANDARD model collector changes between 75.6 % and 78.9 %. [4]


19/19

Figure 5: Detailed Diagram of Aluminium Selective surface collector [4]

X.1 Table1. SPECIFICATION OF ALUMINIUM COLLECTOR

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Solar Water Heating System FULL - basic project