shall be recorded at intervals not to exceed ten minutes, and should be in units of Celsius to
the nearest one tenth of a degree.
Solar insolation (Wm
-2
) and ambient temperature (C) shall
be recorded at least as frequently.
Record and report the frequency of attended (manual)
tracking, if any.
Report azimuth angle(s) during the test.
Report the test site latitude and the
date(s) of testing.
7.2
Calculating Cooking Power.
The change in water temperature for each ten-minute
interval shall be multiplied by the mass and specific heat capacity of the water contained in
the cooking vessel(s).
This product shall be divided by the 600 seconds contained in a ten-
minute interval, as:
P = (T
f
- T
i
)MC
v
/600
[1]
Where:
P
=
cooking power (W)
T
f
=
final water temperature
T
i
=
initial water temperature
M
=
water mass (kg)
C
v
=
heat capacity
(4186 Jkg
-1
K
-1
)
7.3
Calculating Interval Averages.
The average insolation, average ambient
temperature, and average cooking vessel contents temperature shall be found for each
interval.
7.4
Standardizing Cooking Power.
Cooking power for each interval shall be corrected
to a standard insolation of 700 Wm
-2
by multiplying the interval observed cooking power by
700 Wm
-2
and dividing by the interval average insolation recorded during the corresponding
interval.
P
s
= P
i
(700/I
i
)
[2]
Where:
P
s
=
standardized cooking power (W)
P
i
=
interval cooking power (W)
I
i
=
interval solar insolation (Wm
-2
)

5
7.5
Temperature Difference.
Ambient temperature for each interval is to be subtracted
from the average cooking vessel contents temperature for each corresponding interval.
T
d
= T
w
– T
a
[3]
Where:
T
d
=
temperature difference (C)
T
w
=
water temperature (C)
T
a
=
ambient air temperature (C)
7.6
Plotting.
The standardized cooking power, P
s,
(W) is to be plotted against the
temperature difference, T
d,
(C) for each time interval.
7.7
Regression.
A linear regression of the plotted points shall be used to find the
relationship between cooking power and temperature difference in terms of intercept (W) and
slope (WC
-1
).
No fewer than 30 total observations from three different days shall be
employed.
The coefficient of determination (r
2
) or proportion of variation in cooking power
that can be attributed to the relationship found by regression should be better than 0.75 or
specially noted.
7.8
Single Measure of Performance.
The value for standardized cooking power, P
s,
(W)
shall be computed for a temperature difference, T
d,
of 50 C using the above determined
relationship.
NOTE: for product labelling and sales literature an independent laboratory using a
statistically adequate number of trials shall determine this number.
While this value, like
the fuel economy rating of an automobile, is not a guarantee of performance, it provides
consumers with a useful tool for comparison and product selection.

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