Example

11.4.6.1 Building

A factory building (Fig. 11.43) consists of two spaces: a hall with mechan­ical extract ventilation for combined abrasive and chemical treatment and subsequent bonding and a naturally ventilated assembly hall.

VOCs are released during chemical cleaning of bonding surfaces. The ex­tract system is designed on the basis of the steady-state concentration determined for maximum source strength and considering the mechanical extract ventilation only and no air-exchange with the assembly hall. This concentration must be kept below the threshold concentration (TVL) which is set to 300 mg/kg in this example.

I 1.4.6.2 Problem

The problem is to evaluate cross-contamination of the assembly hal! by VOCs from the chemical cleaning and bonding process in the treatment hall.

11.4.6.3 Approach

Simulation Code Used

The simulations were made using COM1S 3.0.s

Example

Mode/

The factory is modeled as a two-zone network with door, horizontally pivoted windows, and roof shed windows as airflow elements. The extract fan and the duct and hood are modeled as additional airflow elements. Wind pres­sure coefficient data are taken from literature for a simple rectangular build­ing shape surrounded by buildings of equal height.

Schedules

The simulation is made for one month (720 h) with a weather file for moderate climate conditions (April in Zurich, Switzerland), using a 1-h time step. Working hours are from 7 a. m. to 6 p. m. The fan is running during these working hours. Values for air temperatures are taken from simple thermal modeling estimates. Window opening and contaminant source strength sched­ules are fixed according to usual working operation, adapted to the 1-h simu­lation time step. See Figs. 11.44 and 11.45.

Results

Primary results of the simulation are air change rates and concentrations in the two zones per time step (Figs. 11.46 and 11.47). From this, a concentration histogram is derived for the two halls (Fig. 11.48). The results show that the TLV is never reached in the analyzed time period.

Temperature schedule

25 —

G 20-

Treatment hall Assembly hall

 

•5 10­E B

А 5 —

 

Time (h)

Example

Hall door H = 0 to 5 m Pivoted window A = 0“ to 15" Roof shed ,1 = 0" to 30"

Opening schedules

Time (h)

I FIGURE I 1.44 Schedule values for a 24 h time period for room air temperature and opening per­centage of windows and roof sheds.

Example

Example

VOC concentration (mg/kg)

FIGURE 11.48 Concentration histogram for assembly and bonding hall for a one-month period. The figure shows the number of hours during which the concentration exceeds a certain level. Only working hours are considered.

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