AS 1668.2-2012 CENTRAL AIR CLEANER FILTER EFFICIENCY FOR REDUCED OUTDOOR AIR AND MULTIPLE ENCLOSURE CALCULATIONS

This calculator applies the multiple-enclosure outdoor-air and air-cleaning provisions of AS 1668.2-2012. When several rooms (enclosures) are served by one air-handling unit or fan coil unit that recirculates air, the outdoor air introduced at the system can be less than the simple sum of each room's requirement. This is because air returned from lightly-occupied rooms still carries usable, "residual" outdoor air, which is recycled back into the supply and helps dilute the busier rooms.

The Standard captures this with a multiple-enclosure factor (M) based on the critical enclosure — the room with the highest ratio of required outdoor air to supply air. The calculator computes that factor, the system outdoor-air rate, and — where validated air cleaning is used — the central air-cleaner efficiency needed to support a reduced outdoor-air rate. It is intended for mechanical and building-services engineers, and its results are validated against the worked example in Clause D7 of the Standard.

Step-by-Step

Running a calculation

• Choose the air-cleaning type
  In System Basis, select No air cleaning for a plain outdoor-air-rate result, Particulate filtration only (7.5 L/s/p floor), or Particulate + odour treatment (2.5 L/s/p floor). This sets which method and floor rate apply.

• Set the system basis
  Confirm the Default Table A1 rate (applied to new enclosures). Optionally enter the total floor area to test the 0.35 L/s.m² floor, and the system exhaust so the tool can flag whether the introduced air clears the make-up requirement.

• Add your enclosures
  For each room served by the system, add an enclosure and enter people, supply air and the room's Table A1 rate. Use Add Enclosure / the delete icon to match your zone count, or Load D7 Example to see a worked case. The required outdoor air is qmin = qf × n.

• Run the calculation
  Press Run Calculation. The tool identifies the critical enclosure (highest qmin/qs), computes the multiple-enclosure factor M, the introduced outdoor air Qf, and — in air-cleaning mode — the required efficiency ec.

• Read the headline result
  In No air cleaning mode the headline is the minimum introduced outdoor air Qf (L/s). In an air-cleaning mode it is the required ec (%) with the recommended filter class. The metric tiles and the dark System Parameters strip show M, R, rc′, Qs, N and the effective outdoor air Qeff.

• Review the breakdown and filter selection
  The Per-Enclosure Breakdown lists each room's qmin, ratio r and residual outdoor air, and marks the critical room. In an air-cleaning mode, the Table D1 panel shows each filter class against the required ec and highlights the lowest class that meets it.

• Print or save a record
  Use Print / Save PDF to produce an A4 record of the inputs and results for the project file. The layout reformats automatically for printing.