Diffuse radiation formula (Heat Overlay): Difference between revisions

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The diffuse radiation is an input parameter for the [[PET_formulas_(Heat_Overlay)|PET-formula]]
The diffuse radiation is an input parameter for the [[PET_formulas_(Heat_Overlay)|PET-formula]].


The diffuse radation Q<sub>d</sub> at time t is calculated using the following formula:
The diffuse radation Q<sub>d</sub> at time t is calculated using the following formula:


Q<sub>d,t</sub> = Q<sub>gl,t</sub> * f<sub>transmission,t</sub><br>
<math>Q_{d,t} = Q_{gl,t} \cdot f_{transmission,t}</math>
 
where,
where,
* Q<sub>gl,t</sub> is the amount of [[Hourly_radiation_(Heat_Overlay)|sun radiation]] at time t, measured at a weather station.
* <math>Q_{gl,t}</math> is the amount of [[Hourly_radiation_(Heat_Overlay)|sun radiation]] at time t, measured at a weather station.
* f<sub>transmission,t</sub> is the Atmospheric transmission factor at time t.  
* <math>f_{transmission,t}</math> is the [[#Atmospheric transmission factor|atmospheric transmission factor]] at time t.  


==Atmospheric transmission factor==
==Atmospheric transmission factor==
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!Condition
!Condition
|-
|-
|1
|<math>1</math>
|τ<sub>a</sub> <= 0.3
|<math>\tau_a < 0.3</math>
|-
|-
|1.6-2* τ<sub>a</sub>
|<math>1.6 - 2 \cdot \tau_a</math>
|0.3 < τ<sub>a</sub> < 0.7
|<math>0.3 < \tau_a  < 0.7</math>
|-
|-
|0.2
|<math>0.2</math>
| τ<sub>a</sub> >=0.7  
|<math>\tau_a >= 0.7</math>
|}
|}
where τ<sub>a</sub> is the atmospheric transmissivity. This is calculated as:<br>
where <math>\tau_a</math> is the atmospheric transmissivity. This is calculated as:
τ<sub>a</sub>  = Q<sub>gl,t</sub> / (1367 * sin (φ<sub>t</sub>)) <br>
 
<math>\tau_{a} = \frac{Q_{gl,t}}{1367 \cdot \sin(\phi_t)}</math>
 
where,
where,
* Q<sub>gl,t</sub> is the amount of [[Hourly_radiation_(Heat_Overlay)|sun radiation]] at time t, measured at a weather station.  
* <math>Q_{gl,t}</math> 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.
* <math>\phi_{t}</math> is the [[Sun_altitude_(Heat_Overlay)|sun altitude angle]] in ° at time t.
* <math>1367</math> is sourced from the {{Heat DPRA Report}}.
 
{{Template:HeatOverlay_formula_nav}}

Latest revision as of 11:52, 13 September 2021

The diffuse radiation is an input parameter for the PET-formula.

The diffuse radation Qd at time t is calculated using the following formula:

where,

  • is the amount of sun radiation at time t, measured at a weather station.
  • is the atmospheric transmission factor at time t.

Atmospheric transmission factor

The atmospheric transmission factor ftransmission,t is calculated as followed:

ftransmission,t Condition

where is the atmospheric transmissivity. This is calculated as:

where,

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