Air Flow

Used to calculate the total air flow to all rooms included, assuming either a constant volume or VAV system.

Ribbon: Energy Simulator > Calculations > Steady State Calculations > Air Flow

Setting

Description

Select Rooms

Click to select and deselect the rooms displayed in the report. Clicking the icon changes the layout of the dialog. Rooms can be selected/deselected individually by clicking on them, or select/deselect all by clicking the two buttons provided.

Select all — Used to select all rooms with a single click.
Deselect all — Used to deselect all rooms with a single click.
OK — Applies all changes and closes the Room selection view.
Cancel — Cancels all changes, and closes the Room selection view.

Design Data

A set of default data must be set up to define the heat gain and air flow basis for rooms. All rooms are subjected to the default data, unless you define some data variations and set some rooms up as different from the default.

Room design temperatures — Room design temperatures may be design Air or design Resultant temperatures. This affects the heat gain calculations for rooms.
Supply air temperature - The value entered here is used to compute the required air flow rate to the room from a heat flow viewpoint.
Temperature rise - An allowable temperature rise for rooms may be defined. Reduces heat gains if specified.
Include external shading - When on, the calculation checks if each window is shaded by external obstructions at each hour of the day.
Include window fins - When on, shaded windows receive diffuse solar radiation only.
Minimum air change rate - This must be defined for rooms, and may, depending on the value specified, increase the calculated air flow to rooms.
Recirculation at the central plant is specified - Specified as a recirculation percentage. When on, the computed fresh air requirement is computed from the recirculation percentage, rather than from the specified fresh air data.
System is VAV - When on, the system is defined as VAV (variable air volume). When off, a constant volume system is assumed.

Setting

Description

Fresh air loads

A fresh air load can optionally be included in the load calculation. Contains controls to define one.

No additional fresh air - When on, no additional fresh air is included in the calculation.
Fresh air introduced locally to rooms - Affects the room load when on.
Conditioned primary air - When on, conditioned air is supplied at the defined supply temperature, with an optional supply humidity control. Conditioned primary air affects both room loads and central plant loads.
Note: If Conditioned primary air is specified, and this fresh air requires heating at the central plant, when the building requires cooling (or vice versa), then the fresh air heat load is excluded from the central plant loads.
Fresh air from the central plant with conditioned air - When on, forms part of the supply air and becomes a load on the central plant.
Fresh air type - Fresh air is supplied to all included rooms using one of the following criteria:
- Air change rate
- Fresh air requirement per person
- Fresh air requirement per square meter

Fixed temperature air

A fixed temperature air supply to rooms can be specified. This could be a fixed air flow from another space, or a tempered air supply to rooms.

Each room included in the calculation is subject to the specified fixed temperature air supply, which is assumed to occur throughout the day and night.

Include a fixed temperature air supply to rooms - When on, you can select from one of the following criteria.
- Air change rate
- Fresh air requirement per person
- Fresh air requirement per square meter
Air temperature and % saturation of the fixed air supply must also be specified.

Outside conditions

Design day/month - Sets the month and day for the calculation.
Temperatures - Max and Min design Dry bulb and Wet bulb temperatures are computed from the Meteorological Office data on the weather data base, using a method described in Section A2 of CIBSE Guide. This defines the design temperatures for the peak month (usually July) and the minimum month (usually January).
Re-calculate - Design temperatures for the day of the calculation are computed by assuming sinusoidal temperature variation through the year, with a peak at July and minimum in January. The actual design day for the calculation determines the position on the sine wave and hence the maximum and minimum outside dry bulb temperatures. Hourly values of dry bulb temperature for the design day are obtained by assuming sinusoidal temperature variation through the design day with a maximum at 15.00 hours and a minimum at 3.00 hours.
Wet bulb temperatures are computed hourly, using a similar technique to dry bulb.

Results

Contains controls used to view reports detailing the CIBSE Air Flow calculation results.

Setting	Description
Toolbar	Located along the top of each of the dialog tabs, the toolbar provides controls for viewing, navigating, printing and exporting reports. The controls from left to right are: Navigate back/forward in history - Disabled Stop - Click to stop regeneration of the reports. Refresh - Click to refresh the results being displayed. First page - Click to jump to the first page of the report. Enabled when "Switch to print preview" is selected. Previous page - Click to jump to the previous page in the report. Enabled when "Switch to print preview" is selected. Next page - Click to jump to the next page in the report. Enabled when "Switch to print preview" is selected. Last page - Click to jump to the last page of the report. Enabled when "Switch to print preview" is selected. Page setup - Opens the Page Setup dialog. Switch to print preview / interactive view - Click to change the layout of the report. The print preview allows you to view each printed page. It activates the navigation buttons (first, previous, next, last page). The interactive view (default) displays the reports in a single scrollable page. Print report - Prints the report. Zoom - Selects a zoom factor from the available drop down menu. Close document map - Click to hide/unhide the table of contents (left panel). Save - Used to save as/export the report to the following formats: Acrobat (PDF) file CSV (comma delimited) Excel 97-2003 Rich Text Format TIFF file Web Archive
Design basis	Used to display key design parameters considered for the calculation. Selecting Design basis in the selector panel (left) updates the reports display panel (right), scrolling to the Design basis display.
Results	Displays results for each room: Sensible and latent gains are shown, together with the computed supply air temperature for each room. The total air flow (m³/s) and air change rate is given. If a constant volume system has been specified, then the actual fresh air flow to each room is shown.
Plant results	For the central plant, the peak coincident building load is shown (hour by hour simultaneous peak for all rooms), together with the peak time. The fresh air is also shown and the total plant load includes the building load and the fresh air load. The time of the peak may differ from the building peak, as the fresh air load may move the total peak. The fresh air load is computed using the actual fresh air load at the central plant and takes into account the mean return air temperature for the system.

Tip: You can open the Results Viewer utility to step through the calculations for displayed results by selecting the result value and clicking for more information (as prompted).

Key-in: BBSENERGYANALYSIS CALCULATE cibseairflow