Universal Devices ISY-994i Series, User Manual

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Figure 261: Weather Provider Settings
There are several variables that are adjustable by the user.
•
Calculation Method - The method used to calculate ETo
o
Penman-Monteith: Accurate, but relies on averages of Temperature, Wind
speed, and Dewpoint throughout the day. Some users had reported problems
with communication to the HAM Weather servers which can cause errors in
the averages.
o
Hargreaves-Samani: Less accurate, but relies on Min/Max temperatures
alone. These can be acquired during one snapshot at the end of the day. As a
result, the calculation is far more robust in the presence of HAM Weather
access issues.
•
Irrigation Region - adjusts for the differing ET in inland vs coastal areas.
o
coastal region, interior plains region
•
Absorption Factor/Soil Type - adjusts for the relative efficiency of soil absorption.
o
80% absorption is recommended for level ground. This is a generally
accepted industry % absorption for rainfall. Users with steep slopes can
apply lower percentages to compensate for runoff.
o
Absorption is applied to both rainfall and irrigation:
▪
Rainfall .5 inches: Effective rain = 0.8 * .5 = .4 inches
▪
Irrigation 0.5 inches: Effective irrifation = 0.8 * 0.5 = .4 inches
•
Crop Coefficient/Plant Type - Plant needs are species dependent and defined as ETc
= ETo * Kc (Kc = crop coefficient).
o
Cool season grasses (Bluegrass, Rye, Fescue) use Kc of 0.8
o
Warm season greasses (Bermuda, Saint Augustine, Zoisya, and Centipede)
use a Kc of 0.6.
o
Additional values are provided to encompass a range of
plants/trees/gardens.
o
Note: the current Evapotranspiration variable is actually ETc (=ETo * Kc)