Assortment / System Description

Control function
Plant operating mode determination
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11.3 Plant operating mode determination
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.
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.
The function free cooling to take 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 on 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.
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.
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 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.
Night cooling
Free cooling
Preheating
Precooling
Start optimization