Demo. Laboratory Space Pressurization---Adaptive Offset Control Supply and Exhaust Valves 

Laboratory design parameters:

Laboratory size(volume) = 5m*4.4m*3m=66m3

1500 bench-mounted fumehoods(2sets)=230CMHmin*-1150CFM max*

Flow offset =230-990CMH

Minimum ventilation flow= 990CMH* (ACPH = 15t/h)

Cooling flow = 792CMH*(ACPH = 12t/h)

Design pressure = -1.0Pa

Design temperature= 25℃

Model selection：

Room Pressure Controller：TSI Sureflow™ Model8682 Adaptive Offset Controller;

Face Velocity Controller for Fumehood：TSI Model FHC50-02 Fume Hood Controller;

Static Pressure Controller for Exhaust Fan and MAU：TSI Sureflow™ Model 8635-ST Static Pressure Controller.

Controlsequence of Face Velocity Controller for Fumehoods:

The Model FHC50-02 fume hood controller uses a sash sensors continuously measure the fume hood sash opening, and through a VAV venturi valve to control the exhaust volume of the fume hood to achieve rapidly-stable face velocity. Meanwhile, the pressure-independent venturi valve itself mechanically compensates static-pressure changes from ductwork system without any action on the valve. If the sash openning become larger, the controller will increase the exhaust volume to maintain the face velocity stable at the pre-set value. If the sash openning become smaller,  the controller will reduce the exhaust volume to maintain the face velocity stable at the pre-set value. When unoccupied,the controller will maintain face velocity in "standby" status setting.

Controlsequence of Static Pressure Controller for Fans and MAUs:

The Model Sureflow 8635-ST Controller use a static-pressure sensor to maintain static pressure of exhaust fans and MAUs stable at a pre-set value. If the measured value is higher than the setpoint, the controller will reduce the exhaust fans or MAUs drive speed back to the set-value. If the measured value is lower than the setpoint, the controller increases the exhaust fans or MAUs drive speed back to the set-value. When unoccupied, the controller will maintain static pressure value in "standby" status setting.

General Sequence of Operation

The room controller simultaneously controls room balance, room pressure, ventilation and temperature in the laboratory. 

Room Balance and Room Pressure Control Sequence of Operation

The room controller continuously measures and maintains a constant flow offset between supply and exhaust volumes. If the offset becomes too large, indicating that the room balance is too negative, the room controller closes the general exhaust and then opens the supply to its maximum setpoint. If the offset becomes too small, indicating that the room balance is not negative enough, the room controller closes the supply to its minimum ventilation or cooling flow and then opens the general exhaust.

The room controller simultaneously measures the differential pressure between Demo. Lab and office  and resets the flow offset to maintain pressure at setpoint. If the room pressure differential is too negative, the room controller decreases the control offset to its minimum setpoint until room pressure setpoint is reached. If the room pressure differential is not negative enough, the room controller increases the control offset to its maximum setpoint until room pressure setpoint is reached. 

Ventilation Control Sequence of Operation

The room controller continuously measures and maintains the supply air volume at or above its minimum setpoint.