KNX Occupancy-Based Office Automation
Design KNX occupancy-based office automation with sensible zones, separate lighting and HVAC timers, daylight control, overrides, privacy, and measurable results.
Occupancy-based office automation should answer a modest question: what can the building safely reduce when a space is not being used, and how quickly should it recover when someone returns?
KNX is well suited to coordinating presence sensors, lighting actuators, room controllers, blinds, meters, and BMS gateways. The difficult part is not sending the telegram. It is agreeing on what “occupied” means for each service and avoiding a building that saves energy by irritating everyone in it.
Presence, occupancy, and people count are different data
Use precise terms in the point schedule.
| Signal | Meaning | Appropriate use |
|---|---|---|
| Raw presence | Recent movement detected in a sensor zone | Local lighting retrigger or input to room logic |
| Qualified occupancy | Room considered in use after timing/logic | HVAC comfort mode, room status, schedules |
| Vacancy | No qualifying presence after defined delay | Lighting OFF, HVAC setback, non-critical load release |
| People count | Estimated or measured number of occupants | Ventilation demand, space analytics, booking validation |
| Booking state | Calendar says room is reserved | Preconditioning or availability indication—not proof of presence |
A PIR sensor normally tells you that movement occurred, not how many people are present. Do not label a 1-bit KNX object “occupant count” because a dashboard designer asked for a heat map.
Zone the office by controllable outcome
The sensor grid, lighting circuits, HVAC zones, and tenancy boundaries rarely line up automatically. Overlay them before selecting devices.
For each area, mark:
- seated work positions and circulation;
- window and internal daylight bands;
- lighting control groups;
- VAV, fan-coil, radiator, or chilled-ceiling zones;
- blind facade orientation;
- meeting-room boundaries and movable partitions;
- cleaning and after-hours routes;
- separately metered or tenanted areas.
The right occupancy zone is the smallest useful area that the controlled services can respond to. Detecting each desk brings little value if one air-handling zone serves the whole floor and the lighting cannot be subdivided.
| Space | Sensible starting zone | Why |
|---|---|---|
| Cellular office | One room | Clear boundary and local override |
| Meeting room | One room; divisible rooms follow partition state | Booking, AV, HVAC, and scenes act together |
| Open office | Lighting/HVAC/furniture module | Balances savings, stability, and maintenance |
| Corridor | Travel segment, not adjacent offices | Avoid false holds through doorways/glazing |
| Break room | Whole room or functional zones | Intermittent use gives useful vacancy periods |
| Reception | Desk plus waiting area as operationally required | Constant circulation should not drive unrelated zones |
Write a sequence for each service
One “occupied” group address should not directly drive everything with the same delay.
Lighting
For daylit offices, manual ON with automatic OFF is often a good starting point. A user who has enough daylight does not need the lights to switch on merely because they entered. Internal zones or dark corridors may use automatic ON.
A practical sequence might be:
- First presence qualifies the zone as occupied.
- Lighting remains OFF until a local command, unless auto-ON is approved.
- Daylight control maintains the commissioned target while occupied.
- A manual dim/scene command suspends or offsets automatic regulation.
- After the lighting absence delay, lights warn/fade and switch off.
- A new presence event during warning restores the previous occupied state.
HVAC
HVAC usually needs slower timing. Moving from comfort to standby after a short coffee break creates poor comfort and unnecessary valve/fan movement.
Use states such as Comfort, Pre-Comfort/Standby, Economy, and Protection where supported. Define who sets each state: schedule, presence, booking, window contact, central BMS, or local override. Keep plant safeties, frost protection, minimum ventilation, and equipment interlocks in their approved control layer.
Shading
Solar protection should not disappear because the office is empty. External blinds may still need automatic sun, wind, rain, and facade-temperature logic. Occupancy can influence glare preference or local override, but weather protection retains priority.
Plug loads
Only control designated non-critical outlets or equipment. Never apply a generic vacancy OFF to PCs, network switches, refrigerators, medical equipment, chargers with operational requirements, or anything not reviewed by the electrical and user teams.
A room control matrix
| Condition | Lighting | HVAC | Blinds | Non-critical plug loads |
|---|---|---|---|---|
| Scheduled occupied, no presence | OFF or background by policy | Standby/pre-comfort | Solar protection active | OFF |
| Presence detected | Manual/auto ON and daylight control | Comfort after qualification | Local glare control available | ON after approved delay |
| Short absence | Hold, then warn/fade | Remain Comfort | Hold last safe automatic state | Hold |
| Long vacancy | OFF | Economy/setback | Weather/solar logic continues | OFF |
| Window open | Lighting unaffected | Heating/cooling inhibited after delay | Local/weather logic | Unaffected |
| Fire/emergency input | Per approved life-safety strategy | Per approved mechanical/fire strategy | Per approved facade strategy | Per approved electrical strategy |
This matrix is where conflicts become visible. It should be approved before ETS programming, not reconstructed from the finished group-address list.
KNX object and ownership example
L04 / Open Office East / Presence Raw
L04 / Open Office East / Lighting Occupied
L04 / Open Office East / HVAC Occupied
L04 / Open Office East / Lighting Auto Enable
L04 / Open Office East / Lighting Level Command
L04 / Open Office East / Lighting Level Status
L04 / Open Office East / HVAC Mode Command
L04 / Open Office East / HVAC Mode Status
L04 / Open Office East / Manual Override Active
L04 / Open Office East / Window State
Assign one authoritative source for every command and state. If the KNX sensor, room controller, BMS, and visualization all calculate their own occupancy timeout, status will drift and fault finding becomes guesswork.
We normally let the room-level KNX logic produce qualified local states, then expose those states to the BMS. The BMS can apply schedules and global modes without reproducing every sensor timer.
Choose sensors for the actual work pattern
Office workers make small movements. Size PIR coverage using the selected product’s seated-person detection area and final mounting height. Account for partitions, acoustic baffles, pendant lights, tall plants, shelving, and supply air.
Test locations on the reflected ceiling plan after furniture coordination. The geometric centre of a ceiling tile grid is not automatically the right sensor position.
For small-motion areas or complex rooms, higher-sensitivity or dual-technology sensing may be justified. For space analytics, use a technology designed and governed for that purpose rather than pretending a lighting detector is a counting system.
See our detailed KNX presence sensor placement guide for detection geometry and site tests.
Manual override is part of automation
Users need to understand when the building will resume automatic control.
Define:
- whether local ON is temporary or remains until vacancy;
- whether manual dimming suspends daylight control;
- how long an after-hours override lasts;
- how an override is indicated at the keypad or UI;
- whether facility staff can force a zone and how it is released;
- what happens after mains, bus, controller, or network recovery.
Avoid invisible permanent holds. A facility manager should be able to find why a zone has stayed in Comfort for three weeks.
Privacy and data minimization
Basic room presence can often be processed locally as a 1-bit state. Detailed desk-level history, camera analytics, device identifiers, or named booking data create a different privacy and cybersecurity scope.
Before exporting occupancy data, document:
| Question | Design answer required |
|---|---|
| What is collected? | Raw events, qualified room state, count, or identifiable data |
| Why is it collected? | Control, maintenance, energy analysis, or workplace analytics |
| Where is it processed? | Sensor, KNX controller, BMS, on-premise server, or cloud |
| How long is it retained? | No history, short diagnostic window, or approved period |
| Who can access it? | Named roles and support paths |
| Can the function work with less data? | Prefer local aggregated state where adequate |
Follow applicable privacy, labour, tenancy, and cybersecurity requirements. “It is only a sensor” is not a data-governance decision.
Measure results without inventing savings
ISO 52120-1 provides a framework for building automation and control functions that contribute to energy performance. It does not mean a specific KNX project automatically saves a fixed percentage.
Build a measurement plan:
- Record baseline lighting and HVAC operating hours or energy where available.
- Note weather, occupancy, floor area, tenant hours, and fit-out changes.
- Trend commanded state and actual feedback separately.
- Compare like periods or use an agreed normalization method.
- Check comfort complaints and manual overrides alongside energy.
A drop in lighting runtime is useful only if it came from true vacancy, not false-offs that drove occupants to tape over sensors.
Commissioning and seasonal tuning
| Test | Pass condition |
|---|---|
| Quiet desk work | Presence holds for typing/reading without exaggerated motion |
| Adjacent-zone movement | Empty zone does not remain occupied |
| Manual ON/auto OFF | User choice and absence timing match the brief |
| Daylight control | Window/internal rows respond smoothly without hunting |
| Short absence | Lighting and HVAC use their separate approved delays |
| Return from setback | Space recovers within the agreed comfort window |
| Window contact | HVAC response occurs only after approved debounce/delay |
| BMS command and release | Priority is visible; local control returns correctly |
| Network/server outage | Local room control continues as documented |
| Power recovery | Modes and outputs return to their approved states |
Revisit the floor after occupants move in and during a different season. Furniture, daylight, hybrid work patterns, and tenant schedules change the tuning. Save every accepted parameter change in the project file.
FAQ
Can one presence sensor control both lighting and HVAC?
Yes, but derive separate qualified states and delays. Lighting may switch off after a short absence; HVAC normally needs slower, stability-oriented logic.
Is automatic ON or manual ON better for office lighting?
Manual ON with automatic OFF works well in many daylit offices. Automatic ON may suit internal areas, corridors, and operational needs. Decide by space, not with one building-wide rule.
Does occupancy-based control require a central server?
No. KNX sensors, actuators, and room controllers can execute local control. A BMS or server is useful for schedules, trends, alarms, and portfolio coordination but should not be an unnecessary dependency for basic room operation.
How much energy will occupancy automation save?
It depends on baseline operation, vacancy periods, zoning, loads, tuning, and user behaviour. Establish a baseline and meter or trend the relevant outputs; do not promise a generic percentage.
Technical references
- ISO, ISO 52120-1 framework for building automation and energy performance
- U.S. Department of Energy FEMP, wireless occupancy sensors for lighting controls
- U.S. Department of Energy, office lighting-control selection guidance
- KNX Association, real office project using occupancy detection and daylight control
- KNXmart, KNX HVAC zoning design
- KNXmart, KNX energy management in smart buildings
Good office automation is quiet. Occupants notice that rooms are comfortable and controls make sense; the facility team sees shorter runtimes, trustworthy status, and fewer manual corrections.