What HVAC system is best for an apartment building?

It depends on the building size. For buildings under 10 apartments, individual split systems are typically the most cost-effective. For 10-50 apartments, VRF (Variable Refrigerant Flow) systems offer a good balance of individual control and efficiency. For 50+ apartments, central chilled/hot water plant with fan coil units in each apartment provides the best long-term efficiency and maintainability.

Do apartment common areas need air conditioning?

Not always. NCC Part J6 applies to conditioned spaces, so non-conditioned corridors, lobbies, and carparks are excluded from HVAC energy calculations. However, lobbies and corridors often receive supplementary conditioning for comfort, and carparks require mechanical ventilation for exhaust gas removal per AS 1668.2.

How much does HVAC design cost for a residential apartment building?

A small apartment building (4-10 units, 3-4 storeys) typically costs $8,000-$20,000 for mechanical design. Medium developments (10-50 units, 5-10 storeys) range from $20,000-$50,000. Large developments (50+ units) are $50,000-$100,000+ depending on system complexity and mixed-use requirements.

HVAC Design for Multi-Storey Residential Buildings

Section 1

What You Need to Know

Apartment buildings are classified as Class 2 under the National Construction Code. This covers buildings where people live above and below each other, and includes single-storey attached dwellings built above a common basement or car park. Class 2 buildings have specific HVAC requirements that differ from commercial or single-residential projects.

Every apartment needs its own individually controllable heating and cooling system. The building also needs mechanical ventilation for internal bathrooms and kitchens without openable windows, car park exhaust ventilation, and smoke control systems for common corridors. All of this must comply with NCC Part J6 for energy efficiency and BASIX in NSW for residential sustainability targets covering thermal comfort, energy, and water.

The mechanical design must coordinate with the building fabric, glazing performance, acoustic separation requirements, fire safety systems, and riser distribution through the building. Getting these right at the design stage prevents costly rework during construction.

Section 2

System Options by Building Size

1

Split Systems (Under 10 Apartments)

Individual split systems or multi-split systems for each apartment. Each unit has its own outdoor condenser, typically on a balcony or roof. This is the most cost-effective approach for small buildings with straightforward layouts.

Tradeoff: Simple and cheap to install, but outdoor unit placement becomes a coordination challenge. Balcony-mounted condensers create noise issues. Roof mounting requires long refrigerant pipe runs and structural provisions.

2

VRF Systems (10 to 50 Apartments)

Variable Refrigerant Flow systems connect multiple indoor units to shared outdoor units via a refrigerant riser. Each apartment retains individual temperature control. Outdoor units are consolidated on the roof or a plant deck, reducing the number of condensers and simplifying facade design.

Tradeoff: Higher capital cost than split systems, but better efficiency and less visual clutter. Refrigerant piping through risers requires compliance with AS 5149 safety requirements for occupied spaces. Maximum pipe run lengths limit building height for some manufacturers.

3

Central Plant with Fan Coil Units (50+ Apartments)

A central chilled water and hot water plant (typically on the roof or basement) distributes water through risers to fan coil units in each apartment. Each fan coil provides individual control. This is the standard approach for large residential developments and mixed-use towers.

Tradeoff: Highest capital cost and requires dedicated plant room space. However, it provides the best long-term energy efficiency, the lowest maintenance burden per apartment, and the simplest path to NCC Section J compliance. Central plant also allows heat recovery between apartments in heating and cooling simultaneously.

Section 3

Key Design Requirements

BASIX compliance (NSW) – All residential apartments must meet BASIX thermal comfort and energy targets. The HVAC system type and efficiency directly affect the BASIX energy score. BASIX SEPP
NCC Section J energy efficiency – Part J6 sets requirements for HVAC system efficiency, including minimum equipment performance and controls. Building fabric, glazing, and HVAC must be coordinated to meet the overall energy budget. NCC 2025 Part J6
Car park ventilation – Enclosed car parks require mechanical exhaust ventilation for removal of vehicle emissions. Ventilation rates must comply with AS 1668.2, which was updated in 2024 with revised rates reflecting modern vehicle emission profiles. AS 1668.2:2024
Mechanical exhaust for internal rooms – Bathrooms and kitchens without openable windows require mechanical exhaust ventilation. The NCC requires either an energy reclaiming system with minimum 60% sensible heat effectiveness, or demand-controlled ventilation, for these mechanical ventilation systems. NCC 2025
Fire sprinklers – Mandatory for Class 2 buildings of four or more storeys since NCC 2019. The sprinkler system affects ceiling void coordination and clearances for HVAC ductwork and piping. NCC Specification 17
Smoke control and exhaust – Common corridors require smoke exhaust or smoke control systems. This interacts with the HVAC design for corridor conditioning and pressurisation. NCC 2025
Acoustic separation – NCC Part F5 sets sound transmission requirements between apartments. HVAC ductwork, piping, and equipment routing must avoid creating flanking paths for noise between units. Equipment vibration isolation and duct lining are standard requirements. NCC 2025 Part F5
Riser design – Vertical distribution of refrigerant piping, chilled water, or ductwork through the building requires dedicated risers. These need to be sized, fire-rated, and coordinated with hydraulic and electrical risers from the outset. NCC 2025
Condensate drainage – Every indoor HVAC unit produces condensate that must be drained. On upper floors, this requires coordinated drainage routes to a suitable discharge point, typically via the hydraulic drainage system. AS 3500

Section 4

Common Design Decisions

1

Outdoor Unit Placement

Condensing units or outdoor plant can be located on the roof, a podium level, or individual balconies. Each option has different acoustic, structural, and architectural implications. Roof mounting consolidates equipment but requires longer pipe runs and structural loading provisions. Balcony mounting keeps runs short but creates noise for residents and affects facade appearance. Podium levels offer a middle ground but consume lettable or communal space.

2

Air-Cooled vs Condenser Water Systems

Small to mid-size buildings typically use air-cooled condensers (simpler, lower maintenance). Large developments may justify water-cooled plant with cooling towers, which is more efficient but requires water treatment, legionella management, and additional plant room space. The decision usually comes down to building scale and the developer's preference for capital cost versus operating cost.

3

Common Area Conditioning

Lobbies, corridors, and car parks are not required to be air conditioned. NCC Part J6 applies only to conditioned spaces, so leaving common areas unconditioned simplifies compliance. However, lobbies and ground floor foyers often receive supplementary heating and cooling for occupant comfort. Car parks always require mechanical ventilation for exhaust gas removal regardless of conditioning.

4

Mixed-Use Separation

Buildings with Class 2 apartments above retail or commercial (Class 5, 6, or 7) require different HVAC treatment for each classification. The residential and commercial portions may use separate systems entirely, or share central plant with separate metering and controls. Separate outdoor air requirements, operating hours, and energy compliance paths apply to each building class. The interface between classifications needs careful coordination at the design stage.

Section 5

Who Needs to Know What

Section 6

References

National Construction Code 2022, Part J6 – Air-conditioning and ventilation energy efficiency
AS 1668.2:2024, The use of ventilation and airconditioning in buildings – Ventilation design for indoor air contaminant control
BASIX (Building Sustainability Index), NSW Department of Planning and Environment
NCC 2025, Specification 17 – Fire sprinkler systems