NYSAN DAYLIGHT-ENHANCING VENETIAN BLINDS
External specialty venetian blinds are the most effective shading device in as much as:
- They can be retracted when not required
- They can be lowered when sun comes onto the building elevation
- The slats can be tilted between open and closed to cope with varying sun angles
- The slats can be perforated to provide some outward vision, even when in the closed position, and
- They provide effective control of both daylight/glare and solar gain.
An external specialty venetian blind is similar to the ½” and 1” blinds that are commonly installed internally, with a number of key exceptions:
a) The slats are larger – generally being between 2” (50mm) and 4” (100mm)
b) The blinds are generally motorized for ease of raising / lowering and tilting
c) The main components (headrail, bottom rail and tilt mechanism) are more robust to cope with external weather conditions, and
d) The slats are held on side guide wires or extrusions so that the blinds are not too significantly affected by wind. That said, external venetian blinds are often used with a control system which will automatically raise the blinds if the wind speed exceeds a pre-set level.
The standard method of operation is motorized, although a manual (gearbox and crank handle) version is also available for blinds that are installed internally. A number of standard venetian blind motors, manufactured by Elero are used. Key technical details relating to these are as follows:
| Speed: |
35 rpm |
| Power: |
110 – 120 watts |
| Current draw: |
1.15 – 1.35 amps |
| Voltage: |
110 volts |
| Torque: |
6, 12 Nm |
| Max. lift capacity: |
160 lbs. |
| Max. no. of turns |
85 |
The standard slats that are available comprise:
The slats are manufactured from aluminum with a thickness of 0.4 to 0.5mm and have a double stove enameled finish. They are available in a standard range of colors – both solid and perforated. The standard perforation has an openness of about 9% and slats can be provided fully perforated, half perforated or perforated with a solid strip down the center of the slat. The flexible (FL) slats have been specifically designed to be used externally and wind tunnel tests have demonstrated that they can withstand significant wind speeds / pressures without damage.
The lift tapes and ladders are manufactured from Trevira and have specifically been developed for external use. Additionally, the slats are mechanically fixed to the ladder tape to ensure that they are held securely in strong winds and do not move or vibrate.
For external use, side guides are required to prevent excessive movement of the slats. For flexible slats, perlon or nylon coated stainless steel side guide wires are used; extruded aluminum side guide profiles are used for the 80mm rolled-edge slats. For wider blinds using flexible slats, intermediate cables might also be required
The headrail is manufactured from extruded aluminum and is open on the underside to give access to the motor and the tilt mechanism. This can be closed off with 2” (50mm) slat infill pieces (to match the main blind slats) so that the mechanism is not visible when the blinds are installed.
Section through 4” (100mm) system with ‘saddle’ fixing bracket
A variety of installation methods are available, including saddle brackets and key hole slots in the headrail to allow direct installation to the structure. A range of extruded aluminum bottom rail profiles is also available.
Bottom rail options
In addition to the standard blind systems, daylight blinds are also available. With a daylight venetian blind, the tilt of the slats in the top part of the blind (generally the first 7 no.) is different from the remainder of the blind. This is achieved by modifying the ladder tape. The slats in the upper part of the blind are more open, allowing daylight to enter the building. The lower slats, which close further provide the necessary light control to ensure that glare is not a problem for people working close to the window. Daylight blinds have been designed for internal use only; they should not be used externally.
The key parameters relating to the Venetian blinds are as follows:
| Motorized operation |
2” (50mm)
flexible slats |
3” (80mm)
flexible slats |
3” (80mm)
rolled edge |
4” (100mm)
flexible slats |
| Maximum width |
16’4”
5000mm |
16’4”
5000mm |
13’1”
4000mm |
16’4”
5000mm |
| Maximum drop |
16’4”
5000mm |
19’8”
6000mm |
13’1”
4000mm |
19’8”
6000mm |
| Maximum area |
270 ft²
25 m² |
320 ft²
30 m² |
172 ft²
16 m² |
320 ft²
30 m² |
| Manual operation |
|
|
|
|
| Maximum width |
16’4”
5000mm |
16’4”
5000mm |
13’1”
4000mm |
16’4”
5000mm |
| Maximum drop |
9’10”
3000mm |
9’10”
3000mm |
9’10”
3000mm |
9’10”
3000mm |
| Maximum area |
97 ft²
9 m² |
97 ft²
9 m² |
65 ft²
6 m² |
97 ft²
9 m² |
The maximum parameters, however, will depend upon specific site conditions.
The calculation of stack height when the blind is in the raised position is as follows:
| Headrail |
3 1/16” |
78mm Constant, irrespective of blind drop |
| Slat pack: |
| 2” (50mm) flexible |
13/32” per ft. |
35mm per m |
| 3” (80mm) flexible |
23/64” per ft |
30mm per m |
| 3” (80mm) rolled edge |
21/32” per ft |
55mm per m |
| 4” (100mm) flexible |
19/64” per ft |
25mm per m |
| Bottom rail: |
| 2” (50mm) flexible |
25/32” |
20mm |
| 3” (80mm) flexible |
15/16” |
24mm |
| 3” (80mm) rolled edge |
15/16” |
24mm |
| 4” (100mm) flexible |
15/16” |
24mm |
The following table gives approximate stack heights for a number of blind drops:
| Blind drop |
2” (50mm) flexible |
3” (80mm) flexible |
3” (80mm) rolled edge |
4” (100mm) flexible |
3’0”
915mm |
5 1/8”
130mm |
5 1/8”
129mm |
6”
152mm |
4 5/16”
125mm |
5’0”
1525mm |
6 3/32”
155mm |
1 13/16”
148mm |
2 5/16”
186mm |
5 1/2”
140mm |
8’0”
2440mm |
3 1/4”
183mm |
4 29/32”
175mm |
5 5/16”
236mm |
6 13/32”
163mm |
10’0”
3050mm |
8 1/16”
205mm |
7 5/8”
193mm |
6 5/8”
270mm |
7”
178mm |
12’0”
3660mm |
8 29/32”
226mm |
8 11/32”
212mm |
7 61/64”
303mm |
7 5/8”
193mm |
15’0”
4575mm |
10 1/8”
258mm |
9 13/32”
239mm |
N/A
N/A |
8 1/2”
216mm |
18’0”
5485mm |
N/A
N/A |
10 1/2”
267mm |
N/A
N/A |
9 13/32”
239mm |
For external purposed, it is also recommended that a head box / pelmet is used to protect the slats, tapes and ladders against adverse weather conditions when the blinds are in the raised position. If a pocket has not been incorporated into the window wall design, extruded aluminum pelmets are available. Alternatively they can be manufactured from sheet steel or aluminum. The minimum internal pelmet widths (to ensure that they blind can retract and that ladders will not be damaged over a period of time) are as follows:
| 2” (50mm) flexible |
3 17/32” |
90mm |
| 3” (80mm) flexible |
4 11/32” |
110mm |
| 3” (80mm) rolled edge |
4 11/32” |
110mm |
| 4” (100mm) flexible |
5 1/8” |
130mm |
For an external installation, the approximate maximum wind speed that the different specialty venetian blind systems can withstand is as follows:
| Beaufort |
6 – 7, Strong |
| Mph |
24 – 38 |
| knots |
22 – 34 |
| m/s |
11 – 17 |
At wind speeds in excess of this, it is recommended that the blinds are retracted. The system with 3” (80mm) or 4” (100mm) flexible slats has been tested in a wind tunnel in speeds up to 17 m/s (38 mph) without any damage to the slats or to the mechanism.
For additional information contact Nysan at 403.204.8675