Why slat angle matters

A Raffstore is not a roller shutter — its unique capability is selective solar control. The horizontal aluminium slats can be rotated between fully open (vertical, maximum light) and fully closed (horizontal, maximum shade). The critical insight is that the optimal angle changes continuously as the sun moves across the sky. A fixed angle is correct only at one moment of the day.

Sun tracking math — slat angle formula

The geometrically correct slat angle to block direct sun while admitting indirect daylight is derived from the sun's elevation angle relative to the facade. For a south-facing facade the formula is:

// Slat angle calculation for external venetian blind

// Variables:
//   sun_elevation  — degrees above horizon (0° = sunrise, 90° = zenith)
//   facade_factor  — accounts for facade orientation:
//                    1.0 for south facade (sun hits perpendicular)
//                    cos(facade_offset_from_south) for other orientations
//   slat_angle     — 0% = horizontal (closed), 100% = vertical (open)

slat_angle (%) = 90 - (sun_elevation × facade_factor)

// Examples (south facade, facade_factor = 1.0):
//   sun_elevation = 10°  →  slat_angle = 90 - 10 = 80% (nearly open)
//   sun_elevation = 30°  →  slat_angle = 90 - 30 = 60%
//   sun_elevation = 60°  →  slat_angle = 90 - 60 = 30% (mostly closed)
//   sun_elevation = 90°  →  slat_angle = 90 - 90 =  0% (fully horizontal)

// East facade at solar noon (sun in west, facade_factor ≈ 0.0):
//   slat_angle = 90 - (60 × 0.0) = 90%  →  slats fully open
//   (no sun on east facade at noon — no shading needed)

// Practical implementation: ETS6 lookup table maps elevation
// steps → slat angle percentages rather than computing in real-time

The formula simplifies into a lookup table in ETS6 — the Elsner P04 provides the sun elevation in real time via KNX, and the MDT JAL-04UP slat table maps elevation to slat angle without any intermediate computation. For east and west facades the table values are rotated to account for the different angle of incidence.

Elsner P04-KNX-GPS — sensor telegrams

The Elsner P04-KNX-GPS is the standard weather station for sun tracking in KNX installations. The GPS module provides precise time and location, enabling calculated sun position even when the pyranometer sensor is shaded by clouds — a critical advantage over lux-only sensors that cannot track the theoretical sun position on overcast days.

ETS6 implementation — MDT JAL-04UP slat table

The MDT JAL-04UP.02 sun logic parameter block accepts the Elsner P04 elevation telegram and maps it to a slat angle via a configurable lookup table. This table is set in ETS6 and defines exactly how the slats respond at each elevation step.

Slat table — elevation to slat angle mapping

The following table is the standard slat angle configuration for a south-facing Raffstore in Central Europe (47°N–54°N latitude). It provides direct sun block at all solar elevations while keeping slats as open as possible to admit diffuse daylight.

Slat angle 10% (not 0%) is used at maximum elevation to ensure a small gap between slats for minimal air circulation and emergency fire brigade visibility. Check local fire code — some jurisdictions prohibit fully closed external blinds.

Seasonal adjustment — GPS automatic tracking

The sun's maximum elevation varies dramatically between summer and winter at European latitudes. GPS-equipped sensors track this automatically — the same slat table works year-round because the Elsner P04 reports the actual elevation, which is naturally lower in winter.

Override hierarchy

KNX blinds control uses a strict priority hierarchy so that safety alarms always take precedence over comfort functions, while allowing user manual override to temporarily supersede automation.

EN 15232 compliance — Class B solar shading

EN 15232-1 (Energy performance of buildings — Impact of building automation) classifies solar shading control into four classes. Sun-position-controlled shading qualifies for Class B, which is required for most commercial new-build projects in Germany (GEG), France (RE2020), and across the EU.

For compliance documentation, capture the Elsner P04 group addresses used for azimuth and elevation input, and the ETS6 slat table parameter values. These demonstrate that shading is controlled by calculated sun position rather than a simple timer or lux threshold — the distinguishing criterion for Class B under EN 15232-1.