[SOL_CNV] Solar radiation conversion
Function block SOL_CNV converts a global radiation value measured on a horizontal plane into a global radiation value on an arbitrarily oriented plane (e.g., vertical or tilted facades).
SOL_CNV converts a global radiation value measured on a horizontal plane into a global radiation value on an arbitrarily oriented plane (e.g., vertical or tilted facades). The conversion depends on the solar position (solar elevation angle and solar azimuth angle) usually calculated by SOL_POS as well as on the average horizontal angle and reflective properties of the ground.
Calculates global radiation value on an arbitrarily oriented surface
The input [SolRdHor] is a measured value of solar radiation on a horizontal plane. For a more precise measurement, a pyranometer can be used.
For the solar protection applications which are normally implemented using SOL_CNV, one sensor based on a solar cell should suffice (e.g., Siemens solar impact Sensor QLS60 that is mounted horizontally, or a similar sensor). A self-heating sensor/housing is beneficial since this avoids incorrect measured values in winter due to snow on the device.
The solar position (solar elevation and azimuth) usually calculated by SOL_POS is required to convert the radiation value measured on a horizontal plane.
Configuration for facade orientation (facade azimuth and facade inclination) is also required for the conversion.
The horizontal angle [HorAgl] determines how the facade is shaded from surrounding buildings, terrain, and trees:
- A building on flat ground that is not shaded by surrounding buildings or trees has [HorAgl] = 0°.
- For typical buildings, [HorAgl] is usually larger than 0°. For solar protection applications using SOL_CNV, it is generally sufficient to use a constant horizontal angle for a specific facade.
Surface reflective properties
Albedo is a measurement for reflective properties of diffusely reflecting surfaces (i.e., non-self-lighting). It is determined by the amount of reflected light and is between 0 and 1.
Recommended configuration for various surfaces:
Surface | Configuration |
|---|---|
Fresh snow | 0.80 - 0.90 |
Old snow | 0.45 - 0.90 |
Clouds | 0.60 - 0.90 |
Desert | 0.30 |
Savannah | 0.20 - 0.25 |
Fields (uncultivated) | 0.26 |
Grass | 0.18 - 0.23 |
Forrest | 0.05 - 0.18 |
Input | Description | Data type | Default value |
|---|---|---|---|
|
SolRdHor | Solar radiation on horizontal plane Measured solar radiation on the horizontal plane (global radiation) | Real | 0.0 [W/m2] 0.0...1500.0 [W/m2] |
SolAzmth | Solar azimuth angle Solar azimuth angle, calculated in SOL_POS | Real | 180.0 -360.0…360.0 |
0°: North | |||
|
SolEtHor | Solar elevation angle from horizon Solar elevation angle from horizon, calculated in SOL_POS | Real | 0.0 -90.0…90.0 |
0°: Sun on the horizontal plane | |||
|
FcdAzmth | Facade orientation: Facade azimuth angle Note | Real | 180.0 -360.0…360.0 |
0°: North-facing facade. | |||
|
FcdIncl | Facade orientation: Facade angle of inclination Note | Real | 90.0 -180...180 [°] |
0°: Horizontal facade facing up (zenith). | |||
HorAgl | Average horizon angle Indicates how the facade is shaded from surrounding buildings, terrain, and trees.
| Real | 5.0 [°] -5.0...90.0 [°] |
Albedo | Albedo Albedo is a measurement for reflective properties of diffusely reflecting (i.e., non-self-lighting) surfaces. It is determined by the amount of reflected light. | Real | 0.2 0.0... 1.0 |
Output | Description | Data type | Default value |
|---|---|---|---|
SolRdFcd | Solar radiation on facade | Real | 0.0 [W/m2] |
SolRdDir | Direct solar radiation on facade | Real | 0.0 [W/m2] |
SolRdDfs | Diffuse solar radiation on facade | Real | 0.0 [W/m2] |
|
SysUnits | System of units Indicates the system of units used by the block. | Integer | 1: International system of units (SI) (fallback) 1...5 |
1: International system of units (SI) (fallback) | |||
ErrCode | Error code indication | Integer | 0: No error |
= 0 - No error | |||
Conversion of the global radiation measurement on the horizontal plane into global radiation values on arbitrarily oriented surfaces (e.g., to reduce the number of individual sensors).
Estimation of the present diffuse light ratio (e.g., for anti-glare functions).
Vertical, southern-facing facade
Constant input values:
[FcdAzmth] = 180°, [FcdIncl] = 90° (South-facing), [HorAgl] = 3°, [Albedo] =0.2
Input values varying in time:
Measured data [SolRdHor] for Zurich from January 1, 2006 through January 7, 2006: [SolEtHor] and [SolAzmth] calculated for Zurich (geographical longitude 8.57° and latitude 47.38°) for January 1, 2006 (local time)
Diagrams
The following example shows the timeline for [SolRdHor] (input variable), [SolRdFcd], [SolRdDir], [SolRdDfs] (output variables)
Key
[SolRdFcd] | Solar radiation on the facade |
[SolRdDir] | Direct solar radiation facade |
[SolRdDfs] | Diffuse solar radiation facade |
[SolRdHor] | Solar radiation on a horizontal plane as input value |