471-2004-1solargreenhousessoydanceran

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SOLAR GREENHOUSES

DEPARTMENT OF PHYSICS

PHYS 471

SOLAR ENERGY-1PREPARED BY : SOYDAN CERAN

INSTRUCTOR : PROF. DR. AHMET ECEVT

2004-1


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Table of Content

1. Introduction

2. History of greenhouses

3. Basic plant growth

4. Greenhouse design

5. Styles of greenhouses

6. Active and passive greenhouses

7. Insulation of greenhouses

8. Ventilation of greenhouses

9. Greenhouses in our country

10. Cost of greenhouses and

11. Conclusion

References


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1.Introduction

At first, lets start with greenhouse effect on fig. 1 [1].

Heat from the sun passes through the atmosphere, warming itup, and most of it warms the surface of the planet. As the

Earth warms up, it emits heat in the form of infra-red radiation -much like a hot pan emits heat even after it's taken away fromthe cooker. Some of this heat is trapped by the atmosphere,but the rest escapes into space. The so-called "greenhousegases" make the atmosphere trap more of this radiation, so itgradually warms up more than it should [1].


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Figure 1. Greenhouse effect.


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Solar greenhouses are the enclosures where crops,vegetables or flowers are provided proper environmentunder adverse climatic conditions for plant growth andproduction. Certainly all greenhouses receive necessary

sunlight from the sun required for photosynthesis andalso supplementary heat during cold months from sun. Intropical countries ambient temperature is quite high sosummer geenhouses can be designed for reducing theinside temperature and the plants receive sufficient of

sunlight required for photosynthesis [2]. As an example,a greenhouse is shown in fig. 2 [3].


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Figure 2. A greenhouse for flowers.


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1.History of greenhouses

Greenhouse industry was first developed in Hollandduring the 17th century. They grow vegetables, grapesand flowers.

During the years 1800-1900 several enviromental controltecniques were developed in Europe and North America.

After the years 1900 large area greenhousesconstruction was started [2].

In 1940 the greenhouses were used in Antalya [4].


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3.Basic plant growth

There are many parameters affecting the plant growth.

Light intensity for photosynthesis

Temperature for enzymes

Humidity

The amount of CO2

Air movement

Water and nutriens [2].


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4.Greenhouse design

Many parameters are to be considered the

design of a greenhouses. We can manipulate

this parameters for our purposes and with respect to

outer conditions. Now, we will discuss a few importantparameters.

Orientation and tilt

Modes of heat transfer

Glass or plastic glazing materials

Heat storage in greenhouse [2].


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4.1.Orientation and tilt

For optimum temperature and light the orientation and

tilt are important.

ORIENTATION

Actually, a north-south oriented greenhouse will provide

more sunlight over the complete year compared to east-

west oriented greenhouse.

For receiving maximum radiation in winter, the

greenhouse should face east-west direction.If due to local

conditions,it is not possible to orient greenhouse in the

east-west direction we can change direction up to 20o

[2].


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TILT

From solar radiation receipt point of view,the angle of the

roof of greenhouse is important. The slope of the

greenhouse roof should be so selected that the angle ofincidence of sun rays remains within 30o. For winter use,

optimum angle of tilt is equal to latitude of place plus 15o.

The impotance of latitude is shown in fig. 3 [5].


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Figure 3. Solar path at 40 north latitude.


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Also, it is necessary to be carefull about around ofgreenhouse since the high buildings may prevent thesunlight as shown in fig. 4 [6].


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Figure 4. Select location carefully.


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4.2.Modes of heat transfer

The greenhouse should be designed to maximize the

input of solar radiation which will require large glazing

area. Increasing the glazing area means increasing heat

loss from greenhouse to outside.In order to optimumsunlight and temperature glazing area must be optimum.

The energy flow diagram of a greenhouse is shown

fig. 5 [2].


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Figure 5. Energy flow in a solar greenhouse.


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4.3.Glass or plastic greenhouses

Both the glass and plastic greenhouses are made but

plastic greenhouses are prefered because of their low

initial capital cost.

Also, glass is heavy material with respect

to plastic. So the structure of glass made up greenhouses

is different from plastic made up greenhouses.

Morever, glass can hold more long wave radiation inside

greenhouses than plastic as shown in table 1 [2].


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Table 1. Transmittance of glazing materials.


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The flexibility of plastic is an advantage.

Apperance of glass made up greenhouse is better asshown in fig. 6 [3] and fig. 7 [3].


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Figure 6. A glass greenhouse.


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Figure 7. A plastic greenhouse.


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4.4.Heat storage in the greenhouse

The temperature, in the greenhouse can be maintained

and the energy can be conserved by using a suitable

thermal energy device, as shown in fig. 8 [5]. A few

parameters of heat storage materials are given below. The different heat storage materials proposed for use in

the greenhouse are sensible heat storage materials like

water, oil, rock, adobe, masonary wall, soil, etc [2].

The position of thermal storage mass in the greenhouse

is very important in efficient storing and distrubiting the

heat [5].


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Figure 8. Heat storage by storage materials.


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The size of storage materials is also important. The large

size means, it can store more heat with more time but if it is

small, it store less heat with small time interval.

Actually, the ground in the greenhouse when exposed tothe sun also stores the heat and the amount of heat

storage depends on the moisture content of the soil [1].


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5.Styles of greenhouses

With respect to their apearance, two main styles

greenhouses exist. They are lean-to (attached) and

freestanding greenhouses.

LEAN-TO DESIGN

In the lean-to design as shown in fig. 9 and fig. 10, the

greenhouse is put against the wall of building and thus

makes use of maximum sun light and minimum roof

support sutructure. Usually,this style is not for commercial

purpose. The heat loss in this type is very low.


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Figure 9. Different types of attached greenhouse [5].


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Figure 10. An attached greenhouse [3].


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FREESTANDING DESIGN

In this design, as shown in fig. 11, greenhouse is not

attached a buildings. Usually, this greenhouses are

constructed for commercial purposes.


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Figure 11. A freestanding greenhouse [3].


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6.Active and passive greenhouses

ACTIVE GREENHOUSES

The greenhouses, in which auxiliary energy is used for

distribution, are called as active type. An active method for

solar heating greenhouses uses subterranean heating.

This method involves forcing solar heated air, water or

phase change materials which moves through the pipes

buried in the floor [5].


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PASIVE GREENHOUSES

In that kind of greenhouses there is no use of auxiliary

energy for disturibution. The energy distiribution is obtained

by convection and heat storage materials.


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7.Insulation

Obviously, one of the most imortant thing aboutperformance of greenhouses is their insulation.

WALL AND FLOOR INSULATION Glazing is what allows light and heat into a solar

greenhouse. It can also be the greatest area for heatloss. As mentioned previously, increasing theinsulating value of glazing often decreases theamount of sunlight entering the greenhouse. Whenselecting glazing for your greenhouse, look formaterials that provide both good light transmission

and insulating value. For example, polyethylene filmsreferred to as "thermal films" have an additive thathelps reduce heat loss. Double or triple glazingprovides better insulationthan single glazing [2].


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Greenhouse curtains limit the amount of heat lost throughgreenhouse glazing during the night and on cloudy days. By

installing greenhouse insulation sheets made from 6 cmthick bats of polystyrene, you can reduce the heat thatwould otherwise be lost through the glazing [2]. The variousconservation techniques and resulting percentage annual

saving are given in table 2 [2].


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Table 2. Annual percercent saving with extra insulator.


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On greenhouse floors, brick, masonry or flagstone servesas a good heat sink. However, they can quickly lose heat tothe ground if there is not an insulating barrier between theflooring and the soil. To protect against heat loss, insulatefootings and the foundation with 3.5 cm to 7cm sheets of

rigid insulation or with a 15 cm wide trench filled withpumice stone [1].


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EXTERNAL INSULATING

You can also insulate your greenhouse by burying part ofthe base in the ground or building it into the side of a south-facing hill. Straw bales or similar insulating material canalso be placed along the unglazed outside walls to reduce

heat loss from the greenhouse. Underground or bermedgreenhouses, as shown in fig. 12, provide excellentinsulation against both cold winter weather and the heat ofsummer. They also provide good protection against windyconditions [5].


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Figure 12. Structure of an underground greenhouse [5].


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8.Ventilation

A building designed to collect heat when temperaturesare cold also needs to be able to vent heat whentemperatures are warm. Air exchange is also critical inproviding plants with adequate levels of carbon dioxide

and controlling humidity. Roof ridge and sidewall ventsprovide natural ventilation. The sidewall vents allow coolair to flow into the sides of the greenhouse, while ridgevents allow the rising hot air to escape. Some wind isnecessary for this type of ventilation system to function

effectively. On still, windless days, fans are necessary tomove air through the greenhouse. The area of theventing should be equal to between 1/5 to 1/6 of thegreenhouse floor area [5].


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Ventilation requirements vary with the weather and season.One must decide how much the greenhouse will be used. Insummer, 1 to 1 air volume changes per minute are needed.Small greenhouses need the larger amount. In winter, 20 to 30percent of one air volume exchange per minute is sufficient formixing in cool air without chilling the plants.

Mechanical ventilation uses an exhaust fan to move air outone end of the greenhouse while outside air enters the other endthrough motorized inlet louvers. Exhaust fans should be sized toexchange the total volume of air in greenhouse each minute.

Small package evaporative coolers have a fan and evaporativepad in one box to evaporate water, which cools air and increaseshumidity. Heat is removed from the air to change water fromliquid to a vapor [4].


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9.The different greenhouses

The other kinds of greenhouses which have different

design and working principles, are shown in fig. 13,14 [2].


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Figure 13. Brace solar greenhouse design


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Figure 14. Ksr solar greenhouse design.


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10.Greenhouses in our country

In our country, greenhouses is common on the

mediterranean region and where there exist geothermalenergy.The total greenhouse area in our country is morethan 40000 hectar. Anamur, Fethiye are the sites wheregreenhouses are the most important source of income.Fig. 15 shows the greenhouses in Anamur [4].


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Figure 13. There are large number of greenhouses in Anamur [4].


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10.Cost

The cost is depend large number of paramaters.The

area, selection of glazing materials and also using extra

insulating materials.Now, in our country avarage cost of a

240 m2

, plastic greenhouse is 1000 YTL [4].


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11.Conclusion

Solar greenhouse technology is one way of the using

solar energy. It provides ideal environment for plants in all

year and helps to obtain maximum efficient from plants. So

for obtaining the vegetables, fruits, and flovers which areout of season or from another climate condition, we have to

use and develop greenhouses[7].


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References

1. http://royal.okanagan.bc.ca/mpidwirn/atmosphereand

climate/greenhouse.html#a

2. H.P. Garg, Advance in Solar Energy Technology,Dordrecht: D. Reidel Publishing Company, 1987.

3. http://www.mvutd.bc.org/solar/pic/greenhouse.html

4. http://www.mu.edu.tr/departments/fethiye/seracilik

5. http://attra.ncat.org/attra-pub/solar-gh.html

6. http://www.wvu.edu/~agexten/hortcult/greenhou/building

7. http://www.hobby-greenhouse.com/UMreport.htm

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