A lot of motorised blind systems are intended for retrofit installations and employ various combinations of low-voltage motors, battery-based power supplies and hand-held radio remote controls. For a new-build I prefer the old-school simplicity of hard-wired cabling and KNX control relays, and because some of the windows are quite wide it makes sense to use 230V motors (rather than 24V). The motors are fitted with 4-core cable: Earth, Neutral, one Switched Live for Up and another Switched Live for Down and so the control aspect boils down to having some relays to control the switching of the Up / Down live connections.
I chose the JAL (short for Jalousieaktor) controllers from MDT. The 8-channel versions are about £200, roughly £25 per blind. Electrically these devices are fairly simple and just control the switching of the Up / Down live feeds to the blind motors but the control logic is surprisingly configurable. Part of this is due the use-case options: roller blinds (or shutters – which tend to be external), venetian blinds (which have the extra complexity of adjusting the slat angle) or electric windows. There’s also the option to react to bad weather, closing shutters and windows (or stowing external venetian blinds) or to help control the internal environment by closing blinds / shutters for shade control or opening windows for ventilation.
Even for roller blinds (referred to as Shutters in the ETS configuration screens, to distinguish them from Venetian Blinds), there are surprisingly many configuration options:
- It’s possible to open a partially open a blind, to 20%, 50% or whatever, and this is accomplished by driving the motor for a fraction of the time required to fully open the blind – so the controller needs to know how long it takes to fully open (and to fully close, in case that is different).
- The opening / closing time cannot be set lower than 10 seconds and on very shallow windows the movement time can be less than this, which means the “partially open” logic won’t work correctly
- By default, the various KNX parameters for Status are not presented, so those need to be enabled
Here is the configuration “recipe” I am using (bold items are changes from defaults):
- Channel Selection: Shutter rather than (venetian) Blind
- Channel X: Shutter
- Time for Up/Down movement: same
- Movement time: (as timed for each specific blind)
- Extension of movement time: 5%
- Short term operation: not active
- Up/Down movement can stop: not active
- Pause on reverse: 500ms
- Switch-on delay motor: 200ms
- Switch-off delay motor: 200ms
- Interchange connections for motor Up/Down: normal (for a blind with a motor on the left); Up/Down inverted (for a blind with a motor on the right)
- Object for reference drive: not active
- Objects for absolute position: active
- 1Bit object for “move to position”: not active
- Status current position: active
- Object for movement status: not active
- Status current direction / position up/down: active
- Status for current blocking/alarms: not active
- Diagnosis as character: send at request
Then, the available Device Parameters are linked to Group Objects as follows:
- “Shutter up/down” is linked to (what I call) SetStatus, the first half of the OpenHab UpDownType command type
- “Stop” is linked to (what I call) Stop, the OpenHab StopMoveType command type
- “Status current direction” is linked to (what I call) GetStatus, the second half of the OpenHab UpDownType command type
- “Absolute position” is linked to (what I call) SetValue, the first half of the OpenHab PercentType command type
- “Status current position” is linked to (what I call) GetValue, the second half of the OpenHab PercentType command type
The exact same logic applies to the control of the electric clerestory windows on the second floor (too high to reach for manual operation and these will also be opened automatically overnight in the summer, to help with temperature regulation). These are actually connected to a slightly different controller (the MDT AKU “Universal Actuator”) which gives the option of linking pairs of channels together for blind / shutter / window control or using them separately as simple relays; this allows for more flexibility in using the spare channels on the controller (since there are only 5 windows).