Essential Guide

Shading Control and SMI Tutorial

We have recently installed motorised blinds at Ivory Egg HQ, primarily for security at night, but also for shading from glare during the day. After some extensive research into the best products and suppliers to use for our automated shading control system, we are pleased to have found a solution that shows the full potential of KNX and we hope will inform and educate our customers with future installations. 


Umbra – The Solution Provider


Whilst we knew that SMI (Standard Motor Interface) was the simplest way to provide cost effective, accurate positional control of multiple blinds, finding a UK supplier that would be able to provide these motors seemed a bigger challenge. However, a quick call to Vestamatic, a key supplier of SMI motors and KNX interfaces, and we were speaking to Umbra (https://www.umbrashading.co.uk/), a UK based manufacturer that not only specialise in roller blinds but have a controls first attitude that ensures they offer the best solution for the customer, instead of just focussing on off-the-shelf solutions.

Within a few weeks we had the blinds manufactured, installed and wired to the Vestamatic SMI-KNX interface which allows us to control each blind individually or group them together on each facade. It also has lot of additional features like feedback on the motor states, scene integration and multiple security functions.



The Benefits of Our Automated Blinds Solution


It’s great to have this function of the building automated as it makes the opening and closing procedure so much easier. The next step is to automate the blinds based on the sun position to prevent glare on computers. This can seem complicated but with so much intelligence in individual KNX devices it’s more a case of understanding the principles and making sure you have the right product. It would be much better with venetian blinds as we could tilt them to still allow light into the building, but we can still use the roller shutters to track the sun based on brightness.

We already have a Gira Weather station installed (you can read more about this in an article in KNX Today here  http://knxtoday.com/2017/09/10067/tips-making-the-most-of-weather-stations.html), so along with the positional control function of the blinds we have everything we need for sun tracking.


How it works


There are two key measurements when calculating the position of the sun, azimuth and elevation.  The azimuth specifies the angle between geographic north and a vertical circle through the centre of the sun. The elevation (sun height) is the angle between the horizon and the centre of the sun from the point of view of the human observer. Thankfully we don’t need to calculate these, we just need to tell the weather station where it is in the world and what time it is. Or even easier, as most weather stations have an integrated GPS receiver these will be actually be calculated internally.


Figure 2 Facade settings for sun shading on the Gira Weather Station 2074 00


The rest of the settings relate to the position of the façade you wish to control and the response times. The exact direction the façade faces needs to be calculated either with a compass or using the architect's plans if they have positioned them geographically. The shading area then needs to be set. There are different ways to approach this with some controllers splitting the area into multiple sectors so you can fine tune the control around objects. In the case of the Gira it is just a simple opening angle centred on a perpendicular line to the façade. So, 180° means control will happen over the entire façade whereas 1° means the control will only happen when the sun is directly facing the façade.

Once the decision is made on the area to control it is just a case of setting the brightness threshold that shading control should start from, the time delays between steps which helps to prevent sudden changes based on cloud cover, and the starting minimum and maximum positions of the shutter and slats. Of course, there will need to be some fine tuning of the control, but it is surprisingly easy to implement this advanced functionality.


Figure 3 Facade settings for sun shading on the Gira Weather Station 2074 00



The importance of shading control in your KNX projects


Shading control is one of the key benefits of using a KNX based system as it allows you to reduce solar gain and glare in a building whilst still allowing as much ambient light into the property as possible. If it is considered at the conception of the building it can also free the architect to design the building for maximum light and views, knowing that the comfort of the occupants and the efficiency of the building will still be to the highest standard. Working closely with a shading manufacturer and controls distributor that understands this is key as they can provide the best solution to achieve the most functionality.