Application

Room Segment Functions
Device Control Functions HVAC
67
Siemens Industry, Inc.
Application Note
A6V11692055
Smart Infrastructure – Building Products
2019-04-01
Basic function: Accept the request signal from its associated room controller and
pass it through a device mode logic switch in the room segment; output the result
as a command to the BACnet object that controls the output device. Specifically,
the Radiant ceiling cooling request (RcgCReq) is received from the room and
processed in the room segment into an analog output signal for the radiant ceiling
(chilled beam) cooling valve position (RcgVlvPosC).
Radiant ceiling (Chilled beam) cooling valve modulation: In response to a
radiant ceiling cooling request from the room, the chilled beam valve is modulated
to control the room temperature at setpoint. The valve can also be 2-positioned in
response to external trigger(s) for special modes such as cool down or safety
conditions.
Multiple panel control: The radiant ceiling valve position collection object
(RcgVlvPosCol) can reference and control multiple ceiling/passive chilled beam
valve actuators. Radiant ceiling valve position objects (RcgVlvPos) are referenced
by the radiant ceiling valve position collection object (RcgVlvPosCol); this collection
object is a common node for any / all RcgVlvPos object(s). The value for RcgVlvPos
comes from RcgVlvPosVal.
Condensation monitoring: To reduce the risk of condensation on the chilled beam,
the modulating water valve can be forced closed at equipment protection priority by
a condensation monitor sensor and/or logic that compares the room’s dew point
temperature to the chilled water temperature. See details in the Safeties section.
Safeties
This AF has two methods to reduce the probability of condensation forming on the
chilled beam: a binary input for a physical condensation monitor switch and a room
dewpoint monitoring cut-off function.
The Condensation monitor detection input (CdnMon) is for a physical
condensation cut-out switch mounted within proximity to the chilled beam. When
the switch activates due to sensing condensation, the chilled beam valve is
commanded off at equipment protection priority (priority 4). (This also drives the
"Available" signal.)
Parameter EnCdnMonIn must be set to 1 (Yes) for the Condensation monitoring to
function (see Configuration below).
Room dewpoint monitoring cut-off: The primary chilled water temperature
(TChwPm) is compared to the room dewpoint temperature (TDwp). The room
dewpoint is calculated from the room unit temperature sensor and relative humidity
sensor values. (See upper drawing in box below ; it is a section of a psychrometric
chart.)
When the primary chilled water temperature is less than the dew point temperature
of the room plus the minimum temperature difference between the room dew point
and the chilled water temperature, then the Device mode (RcgDevMod) is set to
Off at equipment protection priority (priority 4). (This also drives the "Available"
signal.) When the primary chilled water temperature becomes greater than the
above-described equipment cut-off temperature by a configured dead band
(HysTDiffDwpChw), the Off command to the device mode is disabled.
Parameter EnTDwp must be set to 1:Yes for the cut-off to function (see
Configuration).
The primary chilled water temperature is measured at the chiller and
communicated to the room controller dewpoint logic using the supply chain
function.