In the S2-tank interconnection configuration, the system converted 20 to 41 % of the intercepted solar radiation to useful thermal energy (for wind speed v < 2.6 m s-1) and retained 28.7 to 39.7 % of this energy (Table 3). The average efficiency of heat retention (pr) was 34.7 % which compares well with the findings of Chaurasia and Twidell (2001) who report an average value of 38.9 % for an ICS system with a transparent insulation material (TIM) fitted between the absorber plate and glass cover.

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5. Conclusion

A solar water heater of the integrated variety has been designed, constructed and tested. The system has two horizontal cylindrical tanks: one in the lower part while the other tank is in the upper part of the system. Test results show that the thermal performance of the ICS system is most satisfactory when the two tanks are interconnected with two pipes: one pipe connected from the top part of the lower tank to the top part of the upper tank while the other pipe is connected from the bottom part of the lower tank to the bottom part of the upper tank. In this mode of operation, the heater converted 20.4 to 40.7 % of solar radiation to thermal energy, and stored 28.7 to 39.7 % of the collected heat for use the next morning.

Nomenclature

Aa aperture surface area of the system (m2)

Cpw specific heat capacity of water at constant pressure (J kg-1 oC-1)

Hi total solar radiation received by a unit surface area from sunrise to time t = t| (J m-2)

He total solar radiation received by a unit surface area from sunrise to time t = te (J m-2)

M mass of water (kg)

Qr amount of solar energy intercepted by system (J)

Qw amount of heat absorbed by water (J)

Tb temperature of water at the bottom part of a tank (oC)

Tt temperature of water at the top part of a tank (oC)

T mean temperature of water at the beginning of the solar collection process (oC)

Te mean temperature of water at the end of the solar collection process (oC)

T0 overall mean temperature of water (oC)

^c mean daily solar collection efficiency

^r mean efficiency of heat retention

Subscripts

an ambient air at night

c collection

e end

f final

i initial

L lower tank

u upper tank