The present operating state of the HVAC plant in a room depends on room operating mode, central supply signals, and local influences. Local influences here include window contact or presence detector. In addition to room operating modes Comfort, Pre-Comfort, Economy, and Protection, there is states Night cooling, boost heating, and rapid cooling for the plant operating mode. The three additional operating modes are controlled from the central functions and are used to optimize energy and comfort.

Night cooling

The plant operating mode cools a room using cooling outside air. The central function sends a "Night cooling request" to the group member rooms. The decision as to whether night cooling makes sense and is energy efficient is made at the central function. Various coordination signals between the primary plant and room automation do the following via central functions:

  • Switch on the fans
  • Set the mixed air dampers to 100% outside air
  • Lock all other equipment including heating coils, cooling coils, humidifier
  • and set the VAV boxes in the room to a defined value

Night cooling only occurs under the following conditions:

  • The room is vacant (Economy or Protection).
  • The outside temperature is above an adjustable setpoint of 9 °C.
  • The temperature difference is sufficiently large for cooling,
    i.e. room temperature – outside temperature > 7 K.
  • The temperature deviation from room temperature and temperature setpoint is sufficiently large, i.e. room temperature > room setpoint + 2 K.

Free cooling

The function free cooling takes advantage of cooling generated without effort to cool the rooms to a room temperature setpoint. Dew point compensation is still available for the chilled water temperature setpoint dependent from the active dew point detector via the grouping function.

This supply chain is continued accordingly, in other words chilled water generation (chillers, refrigeration machines, etc.) are also controlled based on demand.

Preheating

The central functions can trigger the preheating function to heat up a room at end of the night setback period as quickly as possible to the Pre-Comfort setpoint.

Precooling

To prepare an unoccupied room in Economy or Pre-Comfort for occupancy as quickly as possible or take optimum advantage of available cooling energy from the primary plant, can be resolved by the central functions, function precooling.

Start optimization

Start optimization means that the room is heated in advance, so that the desired Comfort conditions are met at the start of occupancy.

One or more rooms are defined as a reference room in the configurable Desigo system. The room temperature and operating mode for the reference room is then distributed via a central function to all assigned rooms.

Control using window contact

Heating and cooling output is reduced to a minimum when a window is opened. The DXR2 automation station always switches to Protection operating mode. The window contact is connected directly to the DXR2 digital input.

The table below displays the actual operating mode based on window contact:

Window contact state

Plant operating mode

Window closed

No effect

Window open

Protection

Control using a presence detector

A presence detector detects the presence of people in a room. It controls the operating mode of a DXR2 during occupancy. Outside building occupancy, it is locked for HVAC and blinds functions. Light always reacts to the presence detector. The settings can be configured individually for each room.

The presence detector has two states:

State

Description

Occupied

Room is occupied, DXR2 switches room operating mode to Comfort.

Unoccupied

Room is occupied, DXR2 switches plant operating mode to Pre-Comfort.

Together with supply signals night cooling, precooling, and preheating, result in the following plant operating mode.

Room operating mode

Presence

Window contact

Night cooling
signal from supply

Precooling from supply

Preheating from supply

Resulting plant
operating mode

-

-

Open

-

-

-

Protection

Protection

-

Closed

-

-

-

Protection

Economy

-

Closed

False

False

False

Economy

 

-

Closed

True

False

False

Night cooling

 

-

Closed

-

-

True

Heat up

 

-

Closed

-

True

False

Cool down

Pre-Comfort

-

Closed

-

True

-

Cool down

 

-

Closed

-

False

-

Pre-Comfort

 

Present

Closed

-

-

-

Comfort

 

Absent

Closed

-

False

-

Pre-Comfort

 

Absent

Closed

-

True

-

Cool down

Comfort

-

Closed

-

-

-

Comfort

 

Present

Closed

-

-

-

Comfort

 

Absent

Closed

-

False

-

Pre-Comfort

 

Absent

Closed

-

True

-

Cool down