| 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/m 2
(G)
2. (Tm-Ta) = 35K
3. (Tm-Ta)/G = 0.0875 (x)
4. Apricus:
- 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.
Apricus: 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 AP
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 modelling software
package such as FCHART,
or TRNSYS should be
used.
Please note:
Apricus Solar Co., Ltd does not guarantee the accuracy of
these calculations and will not be held liable or responsible
for any activities relating to their use. Apricus Solar Co.,
Ltd does not permit the use of these graphs or data for commercial
use of any kind.
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