solar water heater tubes - SHHPC

solar water heater tubes

Collector efficiency:

Solar water heater performance is often presented as a graph, or set of three performance variables. Values may be provided based on gross area, aperture area or absorber area. In Europe, aperture or absorber is often used, in the US, gross area is often used. It doesn't really matter which values is used, as long as you use the correct value. ie. Don't use absorber area when using performance values based on gross area

The three performance variables for the Sunhome collector as follows:

Conversion Factor: η0 = 0.717

Loss Coefficient: a1 = 1.52 W/ (m2K)

Loss Coefficient: a2 = 0.0085 W/(m2K2)

The equation for calculating basic efficiency is:

η(x)=η0-a1*(x)-a2*G(x)² [x=(Tm-Ta)/G]

(Tm=average manifold temperature, Ta=ambient temperature, insulation level (G) in Watts/m )

Eg. At 2:00pm, the ambient temperature is 25o C (77o F), and the average water temp [(Tin +Tex )/2] is 50o C (122o F). The insulation level is 800Watts/m2 (252Btu/ft2).

x = (50-25)/800 = 0.03125

Now enter all the values into the formula:

η(x) = 0.717 - (1.52*0.03125) - (0.0085*800*0.031252 )

=0.717 - 0.0475 - 0.0066

=0.663

The solar conversion efficiency for that specific point in time and set of environmental conditions is 66.3%. That is: 66.3% of the energy provided by the sun is actually used to heat the water.

Based on the assumption that those three environmental factors (G, Tm and Ta) are stable for a period of one hour, then 800 x 0.663 = 530.4 Watts of energy per m2 of absorber area will be used to heat the water (168Btu/ft2)

530.4Watts is equivalent to 456kcal, which could heat 100L of water by 4.56o C (20 Gallons by 10.9o F)

Below is a graph showing the performance curves for the solar collector at three different insulation levels, from 0 to 80o C Delta-T. In most cases the Delta-T values will be in the range of 20-50o C, with higher values present for high temperature heating such a for absorption cooling applications, or during very cold weather. As can be seen conversion efficiency is highly dependent on solar insulation levels, with higher insulation yielding greater levels of solar conversion.

For more information, please contact me.

Ally Qin

Tel: 0086 1340 169 1567

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