Overview Block Ventilation

This block controls a mechanical ventilation system with heat recovery on demand, based on the CO2 level and the humidity. It provides the fan stage both as individual bits and as a value, switches the bypass for summer cooling, releases the pre-heater for frost protection, counts the operating hours and reports when the filter is due for replacement.

Occupancy is taken from the Block Presence block, as with every block element; input AB acts in addition. See also Presence in general.

The matching control element is Block Ventilation. It is used to set the base stage per occupancy state, the switching times and the filter interval; the block must be linked to the control element.

For a single extract fan in a toilet or bathroom, use the block Block Exhaust air.

Demand calculation

The stage that is actually run is always the highest of all demands. This is simple, easy to follow and covers practical requirements. Demand comes from:
  • CO2: The value at input CO is compared with the thresholds of stages 1 to 4. The highest threshold that is exceeded determines the stage.
  • Humidity: The same applies to the indoor humidity at input RF.
  • Base stage: If input BA is linked, its value 0 to 4 selects the stage through the parameters "Base stage operating mode 0" to "Base stage operating mode 4". If BA is not linked, the base stage of the current occupancy state set in the control element applies.
A manual setting at input SV overrides all of this: it fixes the stage and, if desired, switches the system off completely until it is set back to automatic.
  • Boost ventilation: A rising edge at input PA runs the configured stage for the configured run-on time.
The limiters override all of this: SP forces stage 0, FE acts according to the configured behaviour, and AB falls back to the base stage of the state "Absent".

Hysteresis: When stepping up, the threshold itself applies; when stepping down, the threshold minus the hysteresis. Without hysteresis the system would oscillate at every threshold.

Minimum run time: A higher demand takes effect immediately. Stepping down only happens once the current stage has reached its minimum run time. This keeps the system from cycling at the threshold.

Humidity protection

If the indoor humidity rises above the value "Humidity protection from", at least the configured stage is run.

However, this only happens if the outdoor air is absolutely drier than the indoor air. To determine this, the block calculates the absolute humidity in g/m³ from inputs RF/TI and RA/TA. If the outdoor air is more humid, ventilating would raise the humidity in the room instead of lowering it - humidity protection then does not take effect. In summer this is the normal case: 70 % at 28 °C outdoors contains considerably more water than 70 % at 22 °C indoors.

If inputs RA or TA are not linked the comparison cannot be made; humidity protection then always takes effect.

Bypass and pre-heater

The bypass routes the supply air past the heat exchanger and therefore cools in summer. It only opens when all conditions are met at the same time: the outdoor temperature is above the release threshold, the indoor temperature is at least the configured difference above the outdoor temperature, and there is a cooling demand (indoor temperature above the configured threshold). In addition the system must be running, that is, at least stage 1 must be active.

The pre-heater protects the heat exchanger against icing up. It is released as soon as the outdoor temperature falls below the configured limit, and switched off again once the temperature exceeds that limit by the hysteresis.

While frost protection is active the bypass always stays closed.

Operating hours and filter maintenance

The block counts the time during which a stage greater than 0 is run and outputs it at output BT in hours. The counter value is stored on the controller and survives a restart.

The maintenance interval is set in the control element in operating hours, not at the block - this way the user can also change it in the APP. Once it is reached, output FW goes to 1. Acknowledgement is done either with a rising edge at input QU or with the button in the control element; the counter then starts again from zero. The value 0 switches filter maintenance off.

Inputs

CO
 CO2
 CO2 level of the room air in ppm. If the input is not linked or the CO2 evaluation is switched off, this demand does not apply.
RF
 Humidity indoors
 Relative humidity in the room in %. Basis for the humidity stages and for humidity protection.
RA
 Humidity outdoors
 Relative humidity of the outdoor air in %. Needed together with TI and TA to compare the absolute humidity.
TI
 Temperature indoors
 Room temperature in °C. Basis for the cooling demand of the bypass and for the humidity comparison.
TA
 Temperature outdoors
 Outdoor temperature in °C. Basis for the bypass and for frost protection.
SV
 Set stage
 0 = automatic (no manual setting), 1 to 4 = fixed stage, 5 = switched off by hand.

The manual setting overrides the demand, it does not merely cap it: only this way can the system be switched off by hand while CO2 or humidity are still requesting. It takes effect immediately, without waiting for the minimum run time. The control element and the switching times both operate through this address - a switching time can therefore force a fixed stage and hand the system back to automatic later.
PA
 Boost ventilation
 A rising edge starts boost ventilation: at least the configured stage is run for the configured run-on time.
AB
 Absent
 1 = nobody at home; the base stage of the state "Absent" applies. The input acts in addition to the central occupancy state and therefore only needs to be linked if absence is to come from a different source.
BA
 Operating mode
 Operating mode 0 to 4. If the input is linked, the corresponding parameter "Base stage operating mode x" sets the base stage and takes precedence over the setting in the control element.
FE
 Window open
 1 = a window is open. What happens then is defined by the parameter "Behaviour with window open".
SP
 Lock
 1 = the system goes to stage 0 and stays there as long as the input is set.
QU
 Acknowledge filter
 A rising edge resets the operating hours counter to zero and thereby clears the filter message.

Outputs
S0
 Stage 0
 1 when the system is stopped.
S1 to S4
 Stage 1 to 4
 Exactly one of these outputs is set. All outputs are always present; stages above the configured number of stages remain permanently 0.
SW
 Stage as value
 The current stage as a value from 0 to 100 %, relative to the configured number of stages. With three stages this gives 0, 33, 67 and 100 %. For ventilation units with a continuous input.
BY
 Bypass
 1 = bypass open (summer cooling).
VH
 Pre-heater
 1 = frost protection active, the pre-heater is released.
FW
 Filter maintenance due
 1 = the configured maintenance interval has been reached.
BT
 Operating hours
 Operating hours since the last acknowledgement.
ST
 Info status
 Status value for the visualisation. The bits are added up:
1 = CO2 is requesting
2 = humidity is requesting
4 = humidity protection active
8 = boost ventilation running
16 = manual setting active
32 = window open
64 = locked
128 = bypass open
256 = frost protection active
512 = filter maintenance due

Parameters
Number of stages
 Number of fan stages, 2 to 4. Outputs S0 to S4 are always present regardless of this setting.
Evaluate CO2
 Switches the demand based on CO2 on or off.
CO2 threshold stage 1 to 4
 CO2 level in ppm at which the respective stage is run. Typical values: 800, 1000, 1200 and 1500 ppm.
CO2 hysteresis
 The value has to fall below the threshold by this amount before the stage is reduced.
Evaluate humidity
 Switches the demand based on the indoor humidity on or off.
Humidity threshold stage 1 to 4
 Relative indoor humidity in % at which the respective stage is run.
Humidity hysteresis
 Like the CO2 hysteresis, applied to the humidity.
Humidity protection from
 From this indoor humidity onwards at least the humidity protection stage is run - but only if the outdoor air is absolutely drier.
Humidity protection minimum stage
 Stage that humidity protection requests as a minimum.
Base stage operating mode 0 to 4
 Base stage per value at input BA. Only evaluated if BA is linked.
Boost ventilation stage
 Stage that is run as a minimum during boost ventilation.
Boost ventilation run-on time
 Duration of boost ventilation in minutes.
Behaviour with window open
 No change, reduce by one stage, fall back to the base stage, or switch off completely.
Minimum run time per stage
 A stage stays active at least this long before it is reduced. A higher demand takes effect immediately.
Bypass active
 Releases the bypass control.
Bypass release from outdoor temperature
 Below this outdoor temperature the bypass stays closed.
Bypass minimum difference indoors-outdoors
 This much cooler it has to be outside for the bypass to achieve anything at all.
Bypass cooling demand from indoor temperature
 Only above this room temperature is there a cooling demand.
Bypass hysteresis
 The conditions have to fall short by this amount before the bypass closes again.
Pre-heater active
 Releases frost protection.
Frost protection from outdoor temperature
 Below this outdoor temperature the pre-heater is released.
Frost protection hysteresis
 The outdoor temperature has to rise by this amount again before the pre-heater is switched off.

See also general parameters of all function blocks.