The following list includes all data points that can be read and written from a BACnet primary plant. The items ensure coordination between primary plant and the room. In addition, appropriate Desigo primary application for the given room function is mentioned.
Data point name | Description | Desigo primary application |
|---|---|---|
CReq | The central function prepares one chilled water demand acquisition and evaluation to the connected rooms for the primary plant. The enumerated result can include: 1:Off Values 3 and 4 set cooling generation to free cooling on primary chilled water generation. | PXC {CGrp65} |
SpCReq | Setpoint for cooling request | PXC {CGrp65} |
FreeCAvl | Free cooling available 0:No | PXC {CGen10} |
FreeCTChw | Free cooling temperature chilled water | PXC {CGen10} |
ChwTOa | BACnet reference for primary plant: Outside temperature of the chilled water supply chain | Data point outside temperature of chilled water supply chain |
Setpoint for cooling request.
Setpoint for cooling request influenced by:
- Base setpoint for cooling
- Valve position(s) of cooling valve in the group
- Number of active condensation monitor in the group
- Dew points
The cooling request setpoint is influenced by the evaluation of valve positions.
| |
ChwVlvPosEvl | Supply chain chilled water valve position evaluation ▶Average of the largest valve position |
ChwSpCorrTFlHi | Supply chain chilled water setpoint correction for higher flow temperature |
ChwSpCorrTFlLo | Supply chain chilled water setpoint correction for lower flow temperature |
Figure: Setpoint cooling request
Free cooling
Under favorable condition (chilled water temperature = FreeCTChw), the central plant can output the signal that free cooling is available (FreeCAvl) via grouping to the rooms. The rooms take the offer and go to comfort condition to use free energy for cooling with comfort setpoints. Free cooling demand is returned via the enumerated chilled water demand signal.
Cooled water
Deactivate sequences
The central function can disable the chilled water equipment in the rooms based on outside temperature. The cooling sequences in the group are locked as soon as the configured value for the outside temperature is reached. Back and forth switching can be prevented using a time constant and hysteresis.
Description | Name | Default value |
|---|---|---|
Cooling limit | CLm | 14 [°C] |
Time constant for cooling limit | TiConCLm | 2 [h] |
Hysteresis for cooling limit | HysCLm | 1 [K] |
Condensation
prevention
Condensation in rooms can be prevented by shifting the chilled water temperature setpoint. Grouping records all active condensation monitors. The resulting adjustment is based on the percentage of active condensation alarms.
| ||
SpTChwShftMax | Maximum shift of setpoint chilled water temperature | 10 K |
SttActvCdnMon | Setpoint shift starts at this percentage of active condensation monitors | 10 [%] |
EndActvCdnMon | The setpoint shift is set to the maximum value at this percentage of active condensation monitors. | 50 [%] |
Figure: Condensation prevention characteristic curve
Valve protection
The valve actuator is operated from time to time to prevent it from blocking after longer periods of inactivity (cooling in the winter). The valve actuator is controlled to lose as little heating energy as possible.
The central function for chilled water supply chain runs the valve kick function; the configuration can be adapted as needed.
Description | Name | Default value |
|---|---|---|
Kick value | KickVal | 50 [%] |
Kick time | TiKick | 2 [Min] |
Kick cycle | KickCyc | 500 [h] |
Centrally override valves
Central functions permit the central override of all valves in the supply group. The following parameters can be used.
Description | Name | Default value |
|---|---|---|
Enable valve position overridden value 0:No | EnVlvPosOvrr | 0:No |
Enable valve position overridden value | VlvPosOvrr | 100 [%] |