Required Input

11.4.3.1 Parameters

The following input parameters may be defined as time dependent in schedules:

• Outdoor climate and outdoor contaminant concentrations

• Zone temperature

• Zone humidity (if humidity is not considered as species in the contaminant transport calculation)

• Link operating factor (fan operation, window opening)

• Contaminant and humidity source and sink strengths

• Occupants: presence in each zone

11.4.3.2 Difficulties

Quite often it is difficult to define the input data needed for a multizone airflow simulation, especially for the following two input parameters.

Building

Location

Altitude, orientation

Wind pressure distribution

Set of wind pressure coefficient data for each external node

Network

Zones

Height of zone reference level Volume

Air temperature

L. inks

Conductance type Zone connection (from/to)

Height in relation to zone reference level Link factor (e. g., opening factor) Associated link schedules

Conductances (link types)

Crack

Flow coefficient, flow exponent

Large opening

Type of opening (rectangular, horizontally pivoted) Width, height (position of hinge axis)

Discharge coefficient

Opening geometry as a function of opening factor

Ducts and fittings

Diameter length, specific data for pressure-loss calculation

Fan

Fan characteristics (flow as a function of pressure!

Outdoor climate

Wind

Wind speed and direction

Air

Outdoor air temperature and humidity

Contaminants

Outdoor air contaminant concentrations

Contaminants

Characterization

Molar mass

Source and sink models

Time-dependent

Values

Source and sink strengths per zone Initial concentration per zone

Occupants

Characterization

Characteristics of smoking or other contaminant-releasing activities

Leakage Distribution of the Building

In some texts10 guidance is given to estimate and evaluate the leakage of buildings and building components. The multizone airflow model can also be used to adjust the assumed conductances to an overall building leakage, mea­sured by blower door technique, for example.

Wind Pressure Distribution on the BuHdktg Envelope

Data are available only for simple building geometries.10 In Allard,11 a tool for the calculation of wind pressure coefficients for simple geometries is made available, and another tool is described in Knoll et al.12 Existing wind pressure data have to be examined carefully, because many data represent peak pressure values needed for static building analysis. Real cases with ob­structions and buildings in the close surroundings are difficult to handle. Wind-tunnel tests on scale models or CFD analysis will be required.

Nevertheless, in many cases, mean wind velocities can be assumed^ In ven­tilation-system reliability studies, e. g., where minimum ventilation rates are to be determined, a calm situation with little wind must be assumed anyhow, and the need for accurate wind pressure coefficient data is not so obvious.

Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK