When calculating the heat output
of a collector, the cosine adjusted IAM value should be
included in the efficiency formula.
The key
difference to that formula presented on the
first page of this
section is the inclusion of the factor K in front of the
peak efficiency value. K represents the cosine adjusted IAM
value.
The IAM
adjusted efficiency value can then be put into the following
formula:
Heat Output =
Performance x Insolation x Absorber Surface Area
Example:
Performance @ 30o
angle= 66.3%
Insolation = 800 Watts/m2
Absorber Surface Area = 2.4m2
Heat Output = 0.663 x 800 x 2.4 = 1298.4Watts
So the collector will provide 1298.4 Watts of heat output.
Simplifying IAM Adjustment Calculations
The calculation completed
above is only for a specific point in time, and does not
give an indication of the the actual performance over an
entire day. Using performance modeling software, hour by
hour calculations can be made taking into consideration
average daily temperature changes, cold water temperatures,
hours of sunlight, solar insolation levels in addition to
collector performance variables and cosine adjusted IAM
values. Monthly and annual average performance values may
therefore be estimated.
To complete a simple single day calculation for the purpose
of comparing collector performance, an average IAM value can
be use, along with an average Watt/m2
value. Although this won't give a completely accurate
indication of the heat output for the day, it allows a
comparison between the two collector to be made.
As the majority of useful solar radiation falls during the
middle 6-7 hours of the day, an average of the IAM values
during this period can be used. If 1 hour corresponds to 15o
then 7 hours corresponds to 50o either side of
midday. The average cosine adjusted IAM for the AP solar
collector for this period is 1, and a flat plate collector
is 0.83 (see
table here). These factors can therefore be used in the
performance formula. See the following section for more
details.
|
|
AP Efficiency -
Part 3 IAM Adjustment
