When should I use split systems instead of central plant in a commercial building?

Split systems suit commercial buildings under 1,000 m2, such as small offices, retail shops, and medical centres. They cost less upfront ($80-$150/kW installed) and give each room independent temperature control. Above 10,000 m2, central chilled water plant is standard practice.

What does NCC Section J require for HVAC systems?

NCC 2025 Part J6 requires all HVAC equipment to meet MEPS efficiency ratings, variable speed fans on systems exceeding 1,000 L/s where airflow varies, automatic isolation valves on chillers and boilers, insulated ductwork and pipework, and economy cycles where cost-effective (J6D3).

What is the cost difference between split systems and central plant?

Split systems typically cost $80-$150 per kW installed with lower upfront cost. Central chilled water plant typically costs $200-$400 per kW installed but runs 15-20% cheaper on energy each year at scale. Over a 30-year building life, central plant can be 10-20% cheaper overall.

How long do split systems and chillers last?

Split systems last 10-15 years according to ASHRAE guidelines. Water-cooled chillers last 20-25 years. Over a 30-year building life, you replace split systems twice but a chiller only once, which affects lifecycle cost calculations.

What is a VRF system and when should I use it?

VRF (variable refrigerant flow) is a large-scale multi-split system where one or more outdoor units serve up to 64 indoor units. VRF suits mid-range commercial buildings between 1,000 m2 and 10,000 m2, including offices, hotels, and aged care facilities. Piping runs are limited to 75-165 m per indoor unit.

Split System vs Central Plant: HVAC Picking Guide (2026)

Section 1

What You Need to Know

Split systems cool one room at a time. Central plant systems cool an entire building from one place. The right choice depends on building size, budget, and how long you plan to own the asset. Get it wrong and you pay too much upfront, too much each year, or both.

A split system uses refrigerant piped between an outdoor unit and an indoor unit. A central plant uses a chiller to make cold water, then pumps that water to cooling units on each floor. Both must meet NCC 2025 Section J energy rules and MEPS (Minimum Energy Performance Standards).

Section 2

The Rules

All HVAC equipment must meet MEPS efficiency ratings - AEER for cooling, ACOP for heating (GEMS Act 2012)
Split systems under 65 kW must meet minimum AEER and ACOP values that vary by product class and capacity, starting at ACOP 3.1 for smaller single-phase units (GEMS Determination 2019)
Equipment over 65 kW has separate, stricter MEPS requirements (GEMS Determination for air conditioners above 65 kW)
NCC 2025 Part J6 requires variable speed fans on systems with supply air exceeding 1,000 L/s where airflow can vary (J6D3)
Chilled water systems must have automatic isolation valves to stop flow through idle chillers and boilers (NCC 2025, J6D3)
All ductwork and pipework carrying heated or cooled fluids must be insulated (NCC 2025, Part J6)
Economy cycles (free cooling with outdoor air) are required where cost-effective (NCC 2025, J6D3(1)(c))
VRF systems in occupied spaces must comply with refrigerant safety limits (AS/NZS 5149 and ASHRAE Standard 15)

Section 3

What This Means in Practice

Take a 500 m² medical centre with six consulting rooms, a waiting area, and a server room. Each space has different hours and cooling needs. Six split systems (each 5–7 kW) handle this well. Total installed cost: roughly $25,000–$40,000. Each room gets its own thermostat. The server room runs 24/7 while consulting rooms shut off at 6 pm.

Now take a 15-storey office tower with 20,000 m² of floor area. That building needs around 2,000 kW of cooling. Putting split systems on every floor means 80–100 outdoor units on the roof or facade. The refrigerant piping runs become too long for reliable operation (most manufacturers limit individual pipe runs to 75–165 m, depending on the model). A central chiller plant with two or three chillers, a cooling tower, and chilled water piped to fan coil units on each floor is the standard solution. The plant room sits on the roof or in the basement.

The grey zone sits between 1,000 m² and 10,000 m². Buildings in this range can go either way. VRF (variable refrigerant flow) systems bridge the gap. A VRF system works like a large multi-split: one or more outdoor units serve up to 64 indoor units through refrigerant piping. VRF suits multi-storey offices, hotels, and aged care facilities in this mid-range.

Section 4

Key Design Decisions

1

Building Size and Cooling Load

Below 1,000 m², split systems or multi-splits almost always win on cost and simplicity. Above 10,000 m², central chilled water plant is standard practice. Between 1,000 m² and 10,000 m², compare VRF against a small chilled water system.

Trade-off: Split systems typically cost $80–$150/kW installed. Central plant typically costs $200–$400/kW installed but can run 15–20% cheaper each year on energy at scale.

2

Building Height and Piping Distance

VRF refrigerant piping has limits that vary by manufacturer: typically 75–165 m per individual pipe run and around 50 m vertical. Chilled water has no practical distance limit since pumps move the water. For buildings taller than 10 storeys, chilled water avoids the piping constraints of VRF.

Trade-off: VRF saves on plant room space but cannot serve distant zones. Chilled water needs a dedicated plant room (allow around 30–50 m² for a 500 kW system) plus riser space for pipes.

3

Zoning and Operating Hours

Split systems give each room independent control. Central plant systems need a BMS (building management system) to manage zones. If different areas run at very different hours (such as a retail shop plus offices plus a gym in one building), split systems avoid paying to run a central plant for one late-night tenant.

Trade-off: Running a 500 kW chiller for a single 10 kW tenant after hours wastes energy. A split system for that tenant costs $4,000–$6,000 and runs independently.

4

Lifecycle Cost and Asset Life

Split systems last 10–15 years. Chillers last 20–25 years. Over a 30-year building life, you will replace split systems twice but a chiller only once. For a 5,000 m² office, the 30-year lifecycle cost of central plant is typically 10–20% lower than multiple split systems, once energy savings and fewer replacements are counted.

Trade-off: Central plant needs higher upfront capital. Developers selling within 5 years may prefer the lower upfront cost of splits. Owner-occupiers benefit from the lower lifecycle cost of central plant.

Section 5

Who Needs to Know What

Section 6

References

National Construction Code 2022, Volume One, Section J — Energy Efficiency (Part J6: Air-conditioning and ventilation)
GEMS (Greenhouse and Energy Minimum Standards) Determination 2019 - Air conditioners up to 65 kW
GEMS Determination - Air conditioners above 65 kW
AS/NZS 5149:2016, Refrigerating systems and heat pumps — Safety and environmental requirements
AIRAH DA09, HVAC Systems Handbook
ASHRAE Standard 15, Safety Standard for Refrigeration Systems (international reference)

Split System vs Central Plant: HVAC Picking Guide (2026)

What You Need to Know

The Rules

What This Means in Practice

Key Design Decisions

Building Size and Cooling Load

Building Height and Piping Distance

Zoning and Operating Hours

Lifecycle Cost and Asset Life

Who Needs to Know What

Need this engineered for your project?

References

Related design memos

VRF System Design for Multi-Storey Commercial

VRF vs Chilled Water: Which System for Your Building?

VRF vs Ducted Split System for Commercial Buildings