Supply chain relief function (SplyRlfFnct11)

Overview

The application function "Supply chain relief function 11" (SplyRlfFnct11) calculates the demand on the AHU to make sure it is sufficient to ensure operational stability (control of the static pressure) of the primary AHU. If demand is too low, the relief command (RlfCmd) is distributed to the VAV controllers in the segment, which respond by increasing the air flow setpoint.

Function

If the overall demand for central air flow (number of air demands, NumAirDmd) is too low, the relief command (RlfCmd) is set to 1:On and distributed via grouping to the VAVs of the segment(s), to induce more air volume flow at the central AHU.

In the following illustration, the AHU is started at the minimum level of two demands, and relief (RlfCmd) is set to On and will remain on until/unless 10 demands are exceeded.

AirDmdMax

Maximum air demand plant mode, see Configuration

HysAirDmdMax

Hysteresis for maximum air demand plant mode, see Configuration

AirDmdMin

Minimum air demand plant mode. This parameter is contained in SplyAir11. Configurable low end range number of air demands. If the number of air demands present are between AirDmdMin and AirDmdMax, then the relief command (RlfCmd) is distributed to the segments.

HysAirDmdMin

Hysteresis for minimum air demand plant mode. This parameter is contained in SplyAir11.

NumAirDmd

Number of demands. This object is contained in SplyAir11. The calculated value of the present number of active air demands.

RlfCmd

Relief command

EnAhuDmd

Example of an air demand enabling point at the AHU

Configuration

Parameters

Description

Parameter

Default value

Number of maximum air demand plant mode
▶ Configurable minimum number of air demands necessary to ensure operational stability of the central AHU.

1...50

AirDmdMax

10

Hysteresis for number of maximum air demand plant mode

1...5

HysAirDmdMax

2

 

Interface

Interface

Description

Type

Ref.

Owned by

RlfCmd

Relief command
▶ If the number of air demands is between AirDmdMin and AirDmdMax, then the RlfCmd is distributed via SplyAir-grouping to the VAVs at the segment, to enact a predefined flow setpoint.

0:Off
1:On

BPrcVal

●

-

SplyAirMst

Manager for supply chain air

GrpMaster

◉

SplyAir11

Engineering and commissioning

Define the minimum number of air demands necessary to activate the primary AHU.