A New Concept In Domestic Use Of Solar Heating

Ata Atun

 

Near East University, Faculty of Maritime Studies

Nicosia, North Cyprus

 


ABSTRACT  -  The efficiency of the existing domestic solar water heating systems, widely in use in the houses, apartments and condominiums of Turkish Republic of North Cyprus could be dramatically increased and the maintenance costs can be lowered by implementing the usage of  the heat absorbing ability of tar in to the solar heating part of the whole system.

 

Replacing the solar heat collecting panels with an isolated mass of concrete, faced directly to the sun rays on the direction of East-West with an inclination of 1210  degrees, with a facility to allow the water to be heated to circulate with in the mass, will increase the efficiency of the system up to 25%.

 

INTRODUCTION

 

Existing domestic solar water heating systems[1] consists of ;

 

a)       Cold water tank

b)       Hot water tank

c)       Heat collecting panels

d)       Pipes

e)       Main structure

 

The heat collector panels[2] of the existing domestic solar water heating systems, is of flat type, sized  1940 x 940 x 100 mm , nine copper pipes for water circulation , isolated and covered with glass of 4mm in thickness.  

 

Usually they are installed in pairs and  inclined 1450 taking into consideration the position of Cyprus based on Polar coordinates of Earth, vertical axis passing through North Pole.

 

They work quite well during spring and summer,  show moderate performance at autumn and the non-satisfactory performance at winter time.

 

THEORY AND ASSUMPTIONS

 

Actually the plane of the orbit of the earth where the sun is located on centers of the ellipse, makes an angle of 230 27’ with the vertical axis of earth passing through North pole[3].  

 

Sun rays, when hit the earth vertically heats a 1 sq meter area in equivalence of 1360 Watts of power[4] 

 

Since the performance of the existing domestic solar water heating systems do not perform as expected during winter time, a new concept and a new design should be introduced  to lift up the performance, taking into consideration;

 

a)        Recalculation of the angle of panels to receive rays of sun vertically.

b)       Recalculation of the season zone for a maximum performance in winter time.

c)        Usage of more heat absorbing and less dissipating materials.

d)       Finding the best shape of panels to receive sun rays for longer periods during day time.

e)        Simplifying the main structure to reduce the heat loss.

 

CALCULATIONS AND ANALYSIS

 

The equatorial radius of earth is 6378 km and polar radius is 6357 km.

The mean of the global positions of Nicosia and Famagusta is 350 10’ 00’’

 

The formulae of the shape of earth as a circle can be expressed as ;

                               where r = 6357 km.

                              [1]

 

length of arc a = length of unit degree x latitude 

length of arc a = 1.85 x (60 x 35 + 10) = 3903.50 km

 

qc = arc / radius = a / r

qc = 3903.50 / 6357 = 0.614 c     [2]

 

From the drawing ;

Sin qc = y / r                

y = Sin qc x r

                y = 0.57738 x 6357

            y = 3670 km  

 

Cos qc = x / r

x = Cos qc x r

x = 0.81647 x 6357            

x = 5190  km

 

The slope of earth at North Cyprus can be obtained from the derivative of the formulae [1]

               

                y = (r2 – x2)

                y = (63572 - x2)

 

let u = 63572 – x2

 

 

 

at the location of KKTC where x = 5290 km

 

 

  Decreasing slope or anticlockwise slope at KKTC            [2]

 

When calculations are made based on  the sun rays arriving to KKTC vertically, taking into consideration the angle between the orbit plane and polar axis of the earth this slope will yield the best angle of the panels to receive sun rays vertically.

 

From formulae [2]

q = 0.614 c = 350 16’

a = 230 27’

 

b = 90 – (a + q)

b = 310 17’

 

Panel Angle, respect to the slope of earth at KKTC; 

w = 90 + b

w = 1210 17’

For maximum collection of sun rays at winter time, the panels should make 1210 17’ counterclockwise with the slope of earth at KKTC.

 

w = 1210 17’

 

g = 580 43'

 

Tan g = 1,6458

 

The ratio of height (y)  to length (x);

 y = 1,6458 x

 

PANEL DESIGN

 

A) Shape to receive maximum sun rays.

 

In addition to the slope of panel, the panel design itself should also increase the solar absorbtivity and decrease the emissivity of the system.

 

To increase the efficiency of the panel,  the sun rays must hit the collector close to normal during the period from November 1st till  March 21st where it is the Winter period in North Cyprus and the temperature goes down below the summer average.  During the summer time there is no need of sun rays to hit the panel normal to it’s surface as the surrounding heat even is enough to rise the temperature of the water circulating to a satisfactory level for the supply of a hot water when needed for domestic use.   

 

To find the most suitable shape of the panel to receive sun rays close to normal to it’s surface during the North Cyprus winter time, the sun rising hours and sun down times are needed.

 

The following data obtained from ALMANAK 2000 for the territories of North Cyprus.

 

                      Sun Rise      Sun set                                     

Day              (hr-min)       (hr-min)      

Oct      1       05:55           18:38          

Nov     1       06:20           17:07          

Dec      1       06:49           16:48          

Dec 2  1       07:04           16:53          

Jan      1       07:08           17:00          

Feb      1       06:59           17:28          

Mar     1       06:28           17:57          

Mar 21         06:03           18:12          

 

The calculations and findings of the Table-1[5]are made based on the earth’s trajectory and completing one full turn around her axis with in 24 hours.

 

Table-1 shows clearly that a traditional flat panel receives sun rays normal to it’s surface only during the noon time, when it’s position is a tangent to the trajectory.

 

To collect the most of the sunrays during the winter time, the panel should be in shape of the trajectory and at least making an obtuse angle of 147.500 ±  10%  at the base.

B) Shape to minimize the emissivity.

 

Placing the hot water tank within the panel will decrease the loss of heat and increase the time period to preserve the hot water. Panel itself will behave like the insulation of  the hot water tank enclosed.

 

C) Heat transfer method

To transfer the possible maximum heat from the media with in the panel to the hot water tank, wings should be installed around the hot water tank, to increase the heat transfer area. Placing wings around the hot water tank will increase the heat transfer surface area and consequently heat gain of hot water tank will increase and the period to keep the water hot with in the hot water tank will elongate.  

 

D) Finalizing the shape

 

The final shape will take place, after installing all the related parts together, shown on the right side.

 

A chamber made of polystyrine, making a semi circle of around 147.500 ±  10%  inner angle, diameter of 95 cm at the base and an ellipse of  60 cm. larger diameter at the top with a height difference of 100 cm. in between, enclosing the hot water tank, hugged by wings of  at least 14 layers around, will form the main structure.

 

E) Sun rays and the media to collect the heat.

 

Spectral examination of the sun’s radiation outside the earth’s atmosphere indicates that its monochromatic intensity distributes among the wavelengths much as blackbody emission.

The sun’s normal irradiation at the earth’s surface is:

 

Gsn = Eb (Ts) rs2/re2

 

Where :

Gsn      : Irradiation of sun                                   

Eb     : Emissive power of

         blackbody

Ts      : Sun’s surface

         temperature

rs       : Radius of sun

re       : Radius of earth’s

         orbit

 

 

The normal intensity received at the earth, just outside the atmosphere, varies with the time of the year since the earth’s orbit is not circular. For the purpose of this research, the yearly average value will be considered as;

 Gsn = 1396.9 W/m2   or    Gsn = 442.8 Btu/h-ft2

 

Using this value, an average value of the earth’s orbit radius of 149 x 106 km, the sun’s radius of 0.70 x 106 km. and Emissive power of blackbody is 5.67 x 10-8 . The Gsn formula yields an equivalent solar temperature of  ;

                  Ts = 57800K @ 58000K

 

Gs = Gsn cosqs (as shown in the above figure)

Where qs = angle of incidence ( 310 17’ in North Cyprus)

 

Under the Solar radiation, Tar shows very high solar absorptivity and radiant exchange character, which lead us to the conclusion and decision of using Tar as the media to collect heat from sun and transfer it to the tank, enclosed.

F) Final water circulation

 

The temperature of the water entering to the hot water tank with the help of the gravity, gradually will rise up to maximum as it reaches to the top. When there is a demand, the hot water will leave the tank from the upper part, with a satisfactory temperature, and by-pass the check valve due to low pressure on the faucet end and will flow out.

 

When there is no demand, due to convection with the help of the one-way check valve the water will circulate with in the hot water tank

 

CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY

 

It was shown that the efficiency of the existing systems can be improved and more efficient designs and methods could be used to increase the  rate of transfer of solar heat to domestic use. However, in the beginning, crude approximations were made for the design. For the Research and Development purposes, after building the prototype of the solar water heating system, more accurate calculations and design is recommended to improve the new concept and the system.  

 

 

 

 

 

References

 

1-    L. S. MARKS : “Mechanical Engineers’ Hand book”, 8th Ed., New York, McGraw Hill, 1978

2-    D: B. MACKAY : “Design of Space Power Plants”, Englewood Cliffs, N.J., Prentice-Hall, 1963

3-    T. P. COTTER : “Theory of Heat Pipes”, Los Alamos Sci. Lab. Rep.LA-3246-MS, Los Alamos, N.M., 1965

4-   J. C. Bartholomew, P. J. M. Geelan, H. A. G. Lewis, P. Middleton, B. Winkleman : “ The Times Atlas of the World “ , Times Books Ltd., London 1967

5-   V. HERDER : “Grosser Weltatlas, Ansiklopedik Büyük Atlas” , R. Oldenbourg Graphische Betriebe, Münih, 1993

6- J. F. LEE, F. W. SEARS : “Thermodynamics”, 2nd Ed., Addison-Wesley  Publishing Co. Tokyo, 1962

 

                 Sun Rise Sun set     Difference Total    Sun rising Angle  Sun down Angle       

Day          (hr-min)    (hr-min)    (hr-min)      Angle       (Deg-min)           (Deg-min)

Oct    1     05:55        18:38        12:43          190.75      950 22’ 30’’          2750 22’ 30’’

Nov   1     06:20        17:07        10:47          161.75      800 52’ 05’’          2600 52’ 05’’

Dec   1     06:49        16:48        09:59          149.75      740 52’ 30’’          2540 52’ 30’’

Dec 2  07:04        16:53          09:49         147.25      730 37’ 30’’          2530 37’ 30’’

Jan    1     07:08        17:00        09:52          148.00      740 00’ 00’’          2540 00’ 00’’

Feb    1     06:59        17:28        10:27          156.75      780 22’ 30’’          2580 22’ 30’’

Mar   1     06:28        17:57        11:29          172.25      860 07’ 30’’          2660 07’ 30’’

Mar 21     06:03        18:12        12:09          182.25      910 07’ 30’’          2710 07’ 30’’

 

 

 
 

 

 

Foot Notes


[1] Details obtained from Turbo Metal Sanayi of Famagusta

[2] Turbo Metal Sanayi introductory leaflet, P. 4

[3] The TIMES ATLAS of the world, P. XV

[4] Grosser Weltatlas, P.48

[5] Table-1  placed on last page. 



Table-1