Diffuse radiation formula (Heat Overlay): Difference between revisions
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* Q<sub>gl,t</sub> is the amount of [[Hourly_radiation_(Heat_Overlay)|sun radiation]] at time t, measured at a weather station. | * Q<sub>gl,t</sub> is the amount of [[Hourly_radiation_(Heat_Overlay)|sun radiation]] at time t, measured at a weather station. | ||
* φ<sub>t</sub> is the sun altitude angle in ° at time t. | * φ<sub>t</sub> is the sun altitude angle in ° at time t. | ||
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Revision as of 12:05, 12 September 2019
The diffuse radiation is an input parameter for the PET-formula
The diffuse radation Qd at time t is calculated using the following formula:
Qd,t = Qgl,t * ftransmission,t
where,
- Qgl,t is the amount of sun radiation at time t, measured at a weather station.
- ftransmission,t is the Atmospheric transmission factor at time t.
Atmospheric transmission factor
The atmospheric transmission factor ftransmission,t is calculated as followed:
| ftransmission,t | Condition |
|---|---|
| 1 | τa <= 0.3 |
| 1.6-2* τa | 0.3 < τa < 0.7 |
| 0.2 | τa >=0.7 |
where τa is the atmospheric transmissivity. This is calculated as:
τa = Qgl,t / (1367 * sin (φt))
where,
- Qgl,t is the amount of sun radiation at time t, measured at a weather station.
- φt is the sun altitude angle in ° at time t.
