Diffuse radiation formula (Heat Overlay)
Revision as of 12:07, 12 September 2019 by Frank@tygron.nl (talk | contribs)
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.
