Laboratory design parameters: laboratory layout as shown below, arranged 1 set of 1524mm bench-mounted fume hoods, laboratory specific parameters are as follows:

Laboratory size = 12’ x 14’ x 10’ (1,680 ft3)=3.658m*4.267m*3.048m=47.57m3

1524mm bench-mounted fumehood(1set)=300CMHmin* 1500 CFM max*

Flow offset = 150-475CMH

Ventilation flow= 475CMH* (ACPH = 10t/h)

Cooling flow = 680CMH*

Design pressure= -0.001 “ H2O*=-0.25Pa

Design temperature= 72F=22.2℃

Room Pressure Control System:

(1) TSI Model 8636 Direct Pressure Control System mounted in the laboratory.

(2) A through-the-wall pressure sensor mounted between the corridor(referenced space) and laboratory (controlled space).

(3) Damper, pressure dependent VAV box or venturi valve with actuator assembly mounted in supply air duct(s).

(4) Damper, pressure dependent VAV box or venturi valve with actuator assembly mounted in exhaust air duct.

(5) Flow station mounted in supply air duct. (Required for non-venturi valve applications only).

Temperature Control System:

(1)Temperature Sensor (1000Platinum RTD) mounted in the laboratory.

(2) Reheat coil mounted in supply air duct(s).

Fume Hood Control System:

(1) Independent VAV Face Velocity Control system.

 0.0929 m2/SUP DCT AREA 1.0 ft2 (12”* 12”) Supply duct area

 VENT MIN SET 475CMH 10 air changes per hour

COOLING FLOW 680CMH Required flow to cool laboratory.

TEMP SETP 72F/22.2℃ Laboratory temperature set point.

-0.001 “ H2O*=-0.25Pa/ SET POINT –0.001 in. H2O Pressure differential set point.

Sequence Of Operation

Beginning scenario: Laboratory is maintaining pressure control; -0.001” H2O, Temperature requirement is satisfied.

Fume hood sashes are down; Total hood exhaust is 300CMH.Supply air is 475CMH (maintain ventilation).

General exhaust flow is not measured. The general exhaust flow is modulated to maintain the pressure differential.

The fume hood is opened so that the chemists can load experiments into the hood. The face velocity (100 ft/min) is maintained by the fume hood face velocity controllers by modulating the fume hood dampers. The total fume hood flow is now 1500CMH.

The general exhaust damper will first be modulated closed in order to maintain the pressure differential. Once the general exhaust damper is fully closed, the supply air volume will then be increased to maintain the pressure differential. The supply air volume will nominally be increased to 1350CMH.

The hood is shut after the experiments are loaded so the fume hood exhaust flow decreases to 300 CMH. The supply flow will first be reduced to its minimum flow (VENT MIN SET). Once the supply flow reaches is minimum, the general exhaust will be modulated to maintain pressure.

An oven is turned on and the laboratory is getting warm. The rise in space temperature is measured by the space temperature sensor. The controller will first close the reheat valve, and begin a 3-minute time period. If, after the 3-minute time period the space temperature is still too warm, the controller will gradually increase the supply flow to the COOLING FLOW set point. This increases the supply air to 680CMH. The general exhaust air must also increase (damper opens) to maintain the pressure differential.

The control loop continuously keeps the room pressure, and temperature control satisfied.