J5D4(1) is about the control requirements for mechanical ventilation systems so that the consumption of energy is limited. As outlined in J5D4(1)(a) the mechanical ventilation system may be part of an air-conditioning system described in J5D3 or may be a separate mechanical ventilation system such as a carpark mechanical ventilation system. The requirements do not apply to a mechanical ventilation system that serves only one sole-occupancy unit of a Class 2 building or Class 4 part of a building.

J5D4(1)(a) is intended to only apply when the building or part of a building served by the mechanical ventilation system is unoccupied. For example, if a mechanical ventilation system serves a whole building it is only required to be capable of being deactivated when the whole building is unoccupied. Similarly, if a mechanical ventilation system only serves a single floor of a building, the system must be capable of being deactivated when that part of the building is unoccupied.

J5D4(1)(b) contains specific requirements for when a mechanical ventilation system serves a conditioned space.

J5D4(1)(b)(i) nominates that where the airflow of a ventilation system exceeds the outdoor airflow referenced in Table J5D4, a modulating control or energy reclaiming system must be installed in accordance with the table.

J5D4(1)(b)(ii) requires that the outdoor air requirement of Part F4 not be exceeded by more than 20% when serving a conditioned space.

A number of exemptions from these requirements are provided:

• The first exemption in J5D4(1)(b)(ii)(A) is for free cooling provided as part of an outside air economy cycle.
• J5D4(1)(b)(ii)(B) exempts situations where additional outdoor air to balance exhaust ventilation is required by Part F4. This may occur in areas such as toilets or bathrooms which have high exhaust rates to remove contaminated air or to balance process exhausts such as those used in a health-care building or a laboratory. In such situations, an equivalent level of supply air may be required to balance the system.
• The final exemption in J5D4(1)(b)(ii)(C) is for situations where an energy reclaiming system that preconditions all the outside air is used.

J5D4(1)(c) requires that, where possible, larger mechanical ventilation systems have a variable speed fan.

J5D4(2) contains requirements for miscellaneous exhaust systems. Examples of these types of systems include kitchen hoods, laundry hoods and fume hoods. Consideration should also be given to situations where safety is an issue, such as the exhaust from a chemical storage cabinet. Likewise, it may be more appropriate that fume hoods in some situations operate on a reduced flow while in other situations operate at full flow. A Performance Solution may be considered more appropriate in such situations.

A miscellaneous exhaust system with an air-flow rate of more than 1000 L/s that is associated with equipment with a variable demand, must be capable of stopping the motor when not needed to reduce energy consumption.

The requirements do not apply to a miscellaneous exhaust system serving a sole-occupancy unit in a Class 2, 3 or 9c building.

There is an exemption for situations where the exhaust system must balance the intake of outside air required for ventilation. The exemption recognises that the required minimum ventilation rates take precedence over energy efficiency measures.

J5D4(3) requires that carpark exhaust systems have a carbon monoxide monitoring system in accordance with AS 1668.2.

J5D4(4) specifies the requirements for time switch controlling of power supply to mechanical ventilation systems. The intent is to reduce unnecessary energy consumption attributable to the system when it is not being used.

Mechanical ventilation systems with an air flow rate of more than 1000 L/s are to be provided with time switches in accordance with Specification J6 that can activate and de-activate the respective system.

J5D4(4)(b) contains the required capability of the time switch.

J5D4(4)(c)(i) grants exemptions for time switches for a mechanical ventilation system serving a single sole-occupancy unit of a Class 2, 3 or 9c building or a Class 4 part of a building.

There is also an exemption in J5D4(4)(c)(ii) for a building where mechanical ventilation is needed for 24 hour occupancy such as a hospital emergency room or factory.