The fan-powered box (a fan-supported VAV box) with two controlled air flows. The primary air is controlled with an air damper; the fan is speed controlled. The fan can be physically installed at two different locations: As the serial fan and the parallel fan.
- The serial fan-powered box transports the overall volume flow.
- The parallel fan-powered box transports only the recirculating portion.
The fan-powered box application can be configured using a FPB (Fan-Powered Box) application type. Each FPB application type can also combine a radiant/chilled ceiling (beam) or radiator application. The image below provides an overview of the FPB application type with all possible HVAC components that can be configured for a FPB application. The configuration enables the applicable (required) aggregate on the DXR2.
Plant diagram
Figure: Application types for FPB applications
Key:
DXR2… | Automation station |
| B4 | Primary air temperature |
B1 | Return air temperature sensor |
| R1 | Room operator unit |
B3 | Supply air sensor |
| D1 | Presence |
B6 | Differential pressure sensor (supply air) |
| B7 | Mixed air temperature sensor |
YC | Chilled water cooling coils |
| D2 | Window contact |
YHC | Heating/cooling coils |
| YS | VAV supply air |
YH | Hot water heating coils or electric heating coils |
| Q1 | Serial or parallel fan |
Change from parallel to serial fan-powered box
The fan position must be configured in the application. The monitoring signal of the fan in the VAV is switched on and off:
Description | Name | Default value |
|---|---|---|
Enable monitoring for fan state 0 : No (parallel mode) | EnMonFanSta | 0:No |
The serial fan-powered box transports the overall volume flow
In a serial FPB application, the supply air can be mixed from return and primary air (cooling).
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YS | VAV supply air |
| P | Primary volume flow |
Q | Serial fan |
| R | Return air volume flow |
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| F | Fan volume flow |
Figure: Serial fan for a FPB application
An application with serial fan must transfer the fan state to the VAV controller so that the VAV supplies only fresh air if the fan is also operating. This ensures that no fresh air enters the room via the return air duct. The following image is a diagram of the various locking and monitoring signals of a serial fan-powered box applications.
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P | Primary volume flow |
| AirFlSu | Supply air volume flow sensor |
R | Return air volume flow |
| AirFlMx | Mixed air flow sensor |
F | Fan volume flow |
| TSu | Supply air temperature sensor |
AirFlSt | Air flow state |
| AirFlVavReq | VAV request signal to fan |
FanSt | Fan state |
| AirFlHReq | Request signal from heating register to fan |
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| AirFlHldH | Switch-off delay signal from heating register to fan |
Figure: Serial FPB application
Serial fan-powered box control sequences
The serial fan-powered box control sequences are explained using the example with an auxiliary heating register. The associated setting parameters are explained in the following table that lists the preset values.
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VlVPos | Valve position heating register |
| Hcl | Heating register |
VavSu | Supply air VAV |
| AirFl | Supply air flow VAV |
FanVarSpd | Supply air fan |
| FanSpd | Fan air flow |
P | Primary volume flow |
| AirFlVavReq | VAV request signal to fan |
R | Return air volume flow |
| AirFlHReq | Request signal from heating register to fan |
F | Fan volume flow |
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Figure x: Serial FPB application sequence
Parameter settings
Description | Name | Default value |
|---|---|---|
Supply air VAV maximum air volume flow for cooling | VavSuAirFlMaxC | 100 [m3/h] |
Supply air VAV minimum air volume flow for cooling | VavSuAirFlMinC | 50 [m3/h] |
Supply air VAV minimum air volume flow for ventilation | VavSuAflMinVnt | 0 [m3/h] |
Fan start speed by fan-powered box | FanSttSpdFpb | 50 [%] |
Fan end speed by fan-powered box | FanEndSpdFpb | 100 [%] |
Maximum fan speed for heating | FanSpdMaxH | 100 [%] |
Minimum fan speed for heating | FanSpdMinH | 50 [%] |
The parallel fan-powered box transports the recirculating air portion
Supply air is typically not mixed in a parallel fan-powered box application. There is either a primary (cooling) air flow by the central air flow system via the supply air damper or return air for general cooling and/or heating.
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YS | VAV supply air |
| SA | Supply air volume flow |
Q | Serial fan |
| P | Primary volume flow |
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| F | Fan volume flow |
Figure: Parallel fan of a FPB application
The non-return damper ensures on an application with parallel fans, that no fresh air can enter the room via the return air duct.
The fan receives demand signals from the VAV box and the auxiliary heating register. The following image is a diagram of various locking and monitoring signals of a serial fan-powered box application.
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P | Primary volume flow |
| AirFlSu | Supply air volume flow sensor |
R | Return air volume flow |
| AirFlMx | Mixed air flow sensor |
F | Fan volume flow |
| TSu | Supply air temperature sensor |
AirFlSt | Air flow state |
| AirFlVavReq | VAV request signal to fan |
ReDmp | Return damper |
| AirFlHReq | Request signal from heating register to fan |
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| AirFlHldH | Switch-off delay signal from heating register to fan |
Figure: Parallel FPB application
Serial fan-powered box control sequences
The serial fan-powered box control sequences are explained using the example with an auxiliary heating register. The associated setting parameters are explained in the following table that lists the preset values.
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VlVPos | Valve position heating register |
| Hcl | Heating register |
VavSu | Supply air VAV |
| AirFl | Supply air flow VAV |
FanPrl | Parallel fan |
| FanSpd | Fan air flow |
P | Primary volume flow |
| AirFlVavReq | VAV request signal to fan |
R | Return air volume flow |
| AirFlHReq | Request signal from heating register to fan |
F | Fan volume flow |
| ReDmp | Return damper |
Figure x: Serial FPB application sequence
Parameter settings
Description | Name | Default value |
|---|---|---|
Supply air VAV maximum air volume flow for cooling | VavSuAirFlMaxC | 100 [m3/h] |
Supply air VAV minimum air volume flow for cooling | VavSuAirFlMinC | 50 [m3/h] |
Supply air VAV minimum air volume flow for ventilation | VavSuAflMinVnt | 0 [m3/h] |
Fan start speed by fan-powered box | FanSttSpdFpb | 50 [%] |
Fan end speed by fan-powered box | FanEndSpdFpb | 100 [%] |
Maximum fan speed for heating | FanSpdMaxH | 100 [%] |
Minimum fan speed for heating | FanSpdMinH | 50 [%] |