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Collector Comparison

Part 1 - Performance Basics  |  Part 2 - Understanding IAM  |  Part 3 - IAM Adjustment

When comparing collectors, it is better to use efficiency values from the normal
operating range rather than peak efficiency levels, as this will better represent average annual performance. The "normal operating range" refers to the normal delta-t range
(Tm - Ta) that the collector is exposed to. For domestic water heating an average value
of 30-40oC is common.

Every region has different ambient temperatures and different insolation levels, but for
the purpose of a comparison we can use a "standard" set of environmental conditions.

In a moderate climate, an "average" intermittently clouded day in Spring can provide an insolation level of 3.5kWh/m2/day. The solar radiation distribution throughout the day
from sunrise to sunset is displayed in the following graph.

It can be seen that 90% of the radiation falls between 9:00am and 4:00pm with an
average insolation level during this period of 400W/m2.

We now have a full set of factors in order to do a comparison:

1. Insolation Level = 400Watts/m2 (G)

2. (Tm-Ta) = 35K

3. (Tm-Ta)/G = 0.0875 (x)

4. Tri Solar:

- Performance variables: h0 = 0.717, a1 = 1.52, a2 = 0.0085 (SPF)

- IAM adjustment = 1.2(K)

5. Leading Flat Plate:

- Performance variables: h0 = 0.8, a1 = 2.99, a2 = 0.023 (SPF)

- IAM adjustment = 0.97(K)

The calculations for the two collectors are therefore as follows.

Tri Solar: Performance = 1.2 * 0.717 - (1.52 * 0.0875) - (0.0085 * 400 * 0.08752)

= 1.2*0.717-0.133-0.026 = 70%

Flat Plate: Performance = 0.97 * 0.8 - (2.99 *0.0875) - (0.023 * 400 * 0.08752)

= 0.97*0.8-0.26-0.07 = 44.6%

Given the set of variables used, the Tri Solar solar collector would provide approximately
57% greater heat output throughout the day for a given absorber area.

The same calculation can be completed with other collectors using performance variables
and IAM values. Please note this is just a rough estimation based on average variables
only. For a complete comparison a modeling software package such as FCHART, or TRNSYS should be used.

Please note: Tri Solar does not guarantee the accuracy of these calculations and will not
be held liable or responsible for any activities relating to their use. Tri Solar does not
permit the use of these graphs or data for commercial use of any kind.


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