SOL_CNV: Solar radiation conversion

The block SOL_CNV (FB556) calculates a global radiation value measures on a horizontal plant into a global radiation value on any plane (e.g. vertical or tilted facades). The calculation depends on the solar position (solar elevation angle and solar azimuth angle) as calculated by block SOL_POS as well as the average horizontal angle as well as reflective properties of the ground. SOL_CNV_SiUn (FB556), SOL_CNV_UsUn (FB796)

Application

• Converting the global radiation measurement to the horizontal plane into global radiation values on any oriented surfaces reduces the number of individual sensors.
• Estimate of present diffuse light ratio (e.g. for anti-glare functions).

Functionality

Calculates global radiation value to any oriented surface:

The input [SolRdHor] is a measured value of solar radiation on a horizontal plane. A pyranometer is used for a more precise measurement. For the solar protection applications normally implemented using the block, one sensor based on a solar cell should suffice, e.g. Siemens solar impact Sensor QLS60 (mounted horizontally!) or similar sensor. A self-heating sensor/housing is advantageous, since this avoids incorrect measured values in winter (snow on the device) as well.

The solar position (solar elevation and azimuth) as calculated by block SOL_POS is required to convert radiation value measured on the horizontal plane. The inputs are typically interconnect with this block!

Definition of facade angle (facade orientation: azimuth and incline) corresponds to the angle at block SOL_FCD.

The horizontal angle [HorAgl] determines how the facade is shaded from surrounding buildings, terrain and trees.

• A building on flat ground and not shaded by surrounding buildings or trees, [HorAgl] = 0°.
• The typical building value is > 0°. For solar protection applications implemented using the block, it is generally sufficient to use a constant horizontal angle for a specific facade.

Comment:

The horizontal angle dependent on the azimuth (e.g. for horizontal limitation function) can be considered here (SOL_CNV) as well if available. Of course, this requires modifying the input interface for the function block.

Surface reflective properties:

Albedo is a measurement for surface reflective properties of diffusely reflecting, i.e. non-self lighting surfaces. It is determined by the quotients of reflected incoming light and is between 0 and 1.

Setting recommendations for various surfaces:

• 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.

Inputs

Outputs

Input values

Output values

Example

Example: Vertical, southern-facing facade.

Constant input variable:

FcdAzmth = 180°, FcdIncl = 90° (South-facing), HorAgl = 3°, Albedo = 90°.

Input variables varying by time:

Measured data SolRdnH for Zurich from January 1, 2006 through January 7, 2006: SolEtHor and SolAzmth as calculated for Zurich (geographical longitude 8.57° and latitude 47.38°) for January 1, 2006 (local time).

Diagrams:

[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.

Time line for SolRdHor (input variable), SolRdFcd, SolRdDir, SolRdDfs (output variables) for the example above.

The variable SolRdFcdref is entered on the second axis as a supplement.

Process response

Standard (see General rules and information).

Troubleshooting

Standard (see General rules and information).