What a room screen actually does, and where it belongs

A room screen looks like the showpiece of an automated villa, but the most important thing it does is also the plainest: it is the thermostat. Once you see it that way, nearly every rule about where a screen goes, how it is powered and which rooms get one follows naturally. Here are those rules as we design them, with the reasoning behind each, so that you can tell a screen that earns its place from an expensive ornament.

It is the thermostat before it is anything else

Every conditioned room needs a way for the people in it to set the temperature, and in the villas we design, that way is the room screen. On some brands the same job falls to a display keypad, but the principle is identical: each conditioned zone gets exactly one climate control surface. A conditioned room with no way to set its temperature is a design failure, however handsome the rest of it may be. A room with two is hardly better, because nobody can be sure which of them is in charge, so we never design a room that way.

Everything else the screen offers is built on that job. It carries the room's lighting scenes as well, so the person standing in front of it can set the light and the temperature in one place. On the main living floors, the larger hub screens also answer the intercom, letting whoever is at the gate be seen and answered from where the family actually spends its time.

The air conditioning has to be listening

A screen can ask for any temperature it likes, but it is the AC unit that has to deliver it. The brand and model of every unit come from the villa's MEP design, and the link between each unit and the KNX system is a gateway chosen for that particular model. That is why the unit's model number matters as much as the screen on the wall.

When a model has no verified gateway, we do not substitute one that is probably fine. The gateway goes on the bill as an open question, and if the total leaves it out, the bill says so beside the total. An open question is less comfortable to read than a confident guess, but it will not turn into a surprise on the day the system is commissioned.

Where a screen belongs, and where it never goes

A screen mounts at about 1.4 m in the room's primary location, which in practice means close to the entrance, where you walk in and decide what the room should be doing. That is a comfortable height to read and touch while standing, and we never mount one higher than 1.6 m.

The places a screen must never go each have a reason, and the most important is about temperature. Because the screen is the thermostat, it is also where the room's temperature is read, so it never sits within 1 m of an AC vent. Air from the vent gives false readings; the screen ends up measuring the vent rather than the room, and the room settles at a temperature nobody chose.

It never sits in sun glare either, because a screen you cannot read in the afternoon is failing at the simplest part of its job. Nor does it ever go at the bedside. The bedside is where you lie down rather than stand, and what it needs is a small secondary point for the lights, not a lit panel at pillow height. The screen stays by the door, where it serves the whole room.

Large screens need a power supply of their own

Many KNX devices draw their power from the bus itself, the pair of wires that carries the system's messages, and part of designing a villa is budgeting that power in milliamps against the supply, with margin in hand. Screens of 7 inches and larger are different. They are not powered by the bus, so each one needs its own 24 V power supply in the distribution board, with a cable run from the board to the screen.

A screen without its supply is as much a defect as a missing actuator, and it is an easy one to miss, because much of the system draws its power quietly from the bus and it is natural to assume the screen does too. If the supply is forgotten at the design stage, it is discovered only when the screen is fixed to a finished wall and stays dark. So every large screen on our bills has its supply listed alongside it, and the contractor page gives the cable for every device, the screen included, so that the run is in place before the walls close. A bill without power supplies is incomplete, whatever its total says.

One screen, and only where someone will use it

Screens are the part of an automation bill that people can see from across the room, which makes it tempting to add more of them than anyone needs. The test we apply is simple: will someone actually stand in front of it and use it? If so, it goes in at the room's primary location and does a real job every day. If not, it is a lit rectangle on the wall and a line on the bill whose only reason is how it looks, and a bill with no reasons behind its lines is a guess with a total.

So a conditioned room gets its one screen by the entrance, not a second on the far wall for symmetry and not another beside the bed. Where a room needs only its lights, the client's own switches, connected to the system through a binary input behind the plate, do that job without a screen at all. The service rooms stay outside the automation entirely. We would rather sell you fewer parts than a competitor would and tell you why each one is there.

What you will see on your bill

On a Homestat bill, each screen appears in the room it serves, with its power supply where it needs one and the gateway for the AC unit it controls, or an open question where no gateway is verified yet. Beside every line is the rule that placed it, written in a sentence you can read. To see that reasoning applied to your own villa, send us your plans and we will design two rooms at full depth before you commit to anything.