VRV/VRF systems provide efficient zone cooling and temperature control, while a properly planned ventilation system introduces outdoor air based on a building's occupancy, use, and project requirements. These are two different functions within an HVAC system — and in Malaysia's hot, humid climate, fresh air also needs to be considered together with cooling load, humidity, filtration, exhaust, and condensation control.
Reviewed by Lim Eng Yew (Ryder Lim), Founder & Managing Director, RY Lim Electrical & Aircond Engineering · Last reviewed: September 2026
A fresh-air (ventilation) system introduces filtered outdoor air into a building and removes stale indoor air, independently of how the space is cooled or heated. Its purpose is air quality and occupant health — diluting CO₂ and indoor pollutants, replenishing oxygen, and controlling odours — rather than temperature control.
In Malaysia, mechanical ventilation for air-conditioned and mechanically ventilated buildings is addressed under the Uniform Building By-Laws 1984 (UBBL), By-Law 42 and its Third Schedule, which set out fresh-air provisions for such buildings. Actual requirements depend on building use and occupancy, and should be confirmed with the project's M&E consultant or the relevant authority.
Not by itself. A VRV/VRF system circulates and conditions refrigerant to cool or heat air already inside the building — it recirculates indoor air rather than introducing outdoor air. Bringing in fresh air requires either a separate ventilation system, or specific equipment integrated with the VRV/VRF system for that purpose.
This is a common misunderstanding: a building can have excellent VRV/VRF cooling and still lack adequate outdoor-air ventilation if fresh air was never designed into the system.
Enclosed, air-conditioned spaces with only recirculated air can build up CO₂, odours, and airborne contaminants as occupants breathe and work in the space. Malaysia's Department of Occupational Safety and Health (DOSH) guidelines on office ventilation recommend a minimum fresh-air rate of around 10 litres per second per person, or 10 litres per second per 10 square metres of floor space, as a general reference point for office environments — actual design rates are set by the project's M&E consultant based on occupancy and use.
A well-designed system balances these three so that fresh air introduced roughly matches air exhausted, keeping the building neither excessively pressurised nor depressurised.
FAHU (Fresh Air Handling Unit) — a dedicated unit that filters and conditions outdoor air before it's introduced into the space, improving air quality without relying on the main cooling system to process raw outdoor air.
AHU (Air Handling Unit) — a larger air-processing unit, often used for bigger spaces, that can circulate and condition air (sometimes including outdoor air) across extensive ductwork runs. AHUs can be integrated with a VRV system via an expansion valve kit, sharing the same refrigerant line as indoor units.
ERV (Energy Recovery Ventilator) — a ventilation unit that recovers energy (heat and/or moisture) from the exhaust air stream to pre-treat incoming fresh air, reducing the extra cooling load that raw, humid outdoor air would otherwise add. According to the 2020 ASHRAE Handbook (HVAC Systems and Equipment, VRF chapter), fresh air can be introduced to a VRF system in three common ways: direct (outdoor air mixed directly with return air at the indoor unit), integrated (outdoor air pre-treated by a dedicated unit such as a FAHU, DOAS, or ERV before reaching the indoor unit), or decoupled (a separate ventilation duct system entirely independent of the cooling ductwork).
Malaysia's outdoor air is both hot and humid, so introducing untreated fresh air directly into a VRV indoor unit adds extra heat and moisture load that the unit must remove. This is why manufacturers such as Daikin often restrict direct fresh-air connections on indoor units to a small percentage of total airflow, and why pre-treating fresh air with a dedicated FAHU or ERV before it reaches the VRV system is generally preferred for larger fresh-air requirements — it reduces the burden on the VRV indoor units and improves comfort and part-load performance.
Malaysia's tropical climate means outdoor air is consistently humid year-round. Introducing humid outdoor air without proper treatment can raise indoor humidity, cause discomfort even when temperature is well controlled, and in poorly ventilated spaces contribute to condensation and mould risk. Some VRF systems can be scheduled into a dry (dehumidification) mode during unoccupied hours to help manage humidity, but where a meaningful volume of fresh air is required, dedicated ventilation equipment with proper humidity control is generally the more reliable approach.
Ideally, at the same time as the air-conditioning layout is being designed — not after ceilings, partitions, and cooling equipment positions are already fixed. Fresh-air ductwork, wall or facade openings, and equipment space requirements are far harder and more expensive to retrofit once a fit-out is complete. For office renovations, raising ventilation requirements early alongside the M&E consultant or interior designer avoids conflicts later in the project.
Fresh-air ductwork needs space above the ceiling alongside refrigerant piping, electrical containment, fire services, and any existing structure — the same coordination challenge that applies to VRV/VRF piping and cassette placement. Duct routes, diffuser positions, and any wall/facade penetrations for outdoor air intake should be planned with the interior designer so they don't conflict with ceiling design or fall in a way that disrupts the space's finished look.
Toilets, pantries, and similar wet areas typically have dedicated exhaust systems extracting stale or odorous air to the outside. These exhaust systems and the building's fresh-air supply are related: air exhausted from these areas is generally replaced by fresh air supplied elsewhere in the building, so the two should be sized and coordinated together rather than designed in isolation.
Fresh-air planning should be coordinated with the overall air-conditioning system, ceiling layout, duct routes, drainage, electrical services and exhaust requirements. For VRV/VRF projects, considering these requirements early can reduce coordination conflicts during installation — the same principle that applies to our commercial air conditioning and office tower projects, where piping, ductwork and cassette placement are already planned around existing building services.