Overview Block Exhaust air

This block controls a single extract fan of the kind used in a toilet, bathroom or storeroom. It combines the usual triggers - light, motion, push button and humidity - with run-on times, a minimum run time, a minimum idle time and a night set-back.

What sets it apart from a hand-built solution is the detection of the rise in humidity: in winter the absolute humidity threshold is often never reached, because the cold supply air keeps the room air dry anyway. The rapid rise while showering, however, is always measurable.

Occupancy is taken from the Block Presence block, as with every block element. In the control element you can define per state whether the fan may start at all. See also Presence in general.

The matching control element is Block Ventilation; it operates both the ventilation system and the extract fan.

For a mechanical ventilation system with heat recovery, use the block Block Ventilation.

Sequence

The fan runs as soon as at least one demand is present:
  • Light: If the light is on for longer than the switch-on delay, a demand arises. The delay prevents the fan from starting when somebody only briefly enters the room.
  • Motion: Takes effect immediately, without delay.
  • Push button: Every rising edge restarts the run-on time. The control element also operates through this address.
  • Humidity: Either the absolute threshold is exceeded or a rise in humidity has been detected.
When the demand disappears, the fan keeps running for the run-on time. A separate, usually longer run-on time applies to humidity.

Minimum run time and minimum idle time override everything else. Without them the fan cycles at the humidity threshold - it starts, lowers the humidity by a tenth of a percent, switches off, and starts over. The minimum run time prevents switching off, the minimum idle time prevents restarting immediately.

The maximum run time ends operation when a stuck demand would otherwise keep the fan running indefinitely - a light switch that was forgotten, for example. The fan only starts again once the demand has disappeared in the meantime.

Rise in humidity

The block records the humidity value once a minute. If the current value is higher than the value from ten minutes ago by the configured amount, the rise counts as detected and the fan starts - even if the absolute threshold is still far away.

The detected rise expires as soon as the humidity has fallen below the value at the moment of detection minus the hysteresis. It deliberately does not end at the absolute threshold - that is exactly what is never reached while showering in winter.

After a restart of the controller the series of measurements starts empty. Until enough values have been collected, no rise is reported; a false trigger during start-up is therefore ruled out. The absolute humidity threshold works completely normally during this time.

The value 0 switches rise detection off.

Night set-back

Within the configured time window the fan can either be locked completely or respond to humidity only. The second option is the usual case: at night the fan should not start every time the light is switched on, but it should still start when somebody takes a shower.

If the time window starts later than it ends, it spans midnight.

Inputs

LI
 Light on
 1 = the light in the room is on. After the switch-on delay this becomes a demand.
BE
 Motion
 1 = motion detected. Takes effect without delay.
RF
 Humidity
 Relative humidity in the room in %. Basis for the humidity threshold and for rise detection. If the input is not linked, both are omitted.
TA
 Push button
 The push button toggles: if the fan is running, the rising edge switches it off, otherwise on. An extract fan has to be switchable off by hand as well.

The manual switch-off applies until no demand is present any more - with the light still on the fan therefore does not start again immediately. Switching on and off by hand takes effect immediately, without the minimum run time and without the minimum idle time. The control element also operates through this address.
FR
 Release
 0 = the fan stays off. An input that is not linked counts as released.

Outputs
LU
 Fan
 1 = the fan is running.
NL
 Run-on active
 1 = the fan is only still running because of the run-on time, the actual demand has already disappeared.
BT
 Operating hours
 Operating hours since the last acknowledgement. The counter value is stored on the controller and survives a restart. The maintenance interval is set in the control element.
ST
 Info status
 Status value for the visualisation. The bits are added up:
1 = light on
2 = motion
4 = push button
8 = humidity threshold exceeded
16 = rise in humidity detected
32 = run-on active
64 = maximum run time reached
128 = minimum idle time running
256 = night set-back active
512 = maintenance due

Parameters
Switch-on delay light
 The light has to be on this long before the fan starts. The value 0 lets it start immediately.
Run-on time
 The fan keeps running this long after light, motion or push button have disappeared.
Evaluate humidity
 Switches the humidity threshold and rise detection on or off.
Humidity threshold
 From this relative humidity onwards the fan starts.
Humidity hysteresis
 The humidity has to fall below the threshold by this amount before the demand ends.
Rise in humidity
 If the humidity rises by this amount within ten minutes, the fan starts. The value 0 switches rise detection off.
Run-on time after humidity
 Separate, usually longer run-on time for the humidity demand.
Maximum run time
 After this time the fan is switched off, even if a demand is still present. The value 0 switches the limit off.
Minimum run time
 The fan runs at least this long before it may switch off.
Minimum idle time
 The fan stays off at least this long after switching off.
Night set-back
 Off, humidity only, or lock completely - valid within the configured time window.
Night start / night end
 Time window of the night set-back, each as hour and minute. If the start is after the end, the window spans midnight.

See also general parameters of all function blocks.