Air conditioning Direct relaxation Energy recovery systems Heating MiniVRF Reversible Thermal transfer Thermodynamic apparatus VRF (Variable Refrigerant Flow)

3-tube VRF systems: performance and energy savings

Pro May 4, 2020 winter-picto

Summary

3-tube VRF systems, often known as Heat recovery VRF systems or 3-pipe VRF systems, can provide simultaneous heating and cooling in different building zones. By transferring heat from areas requiring cooling to areas requiring heating, they can improve seasonal efficiency and comfort, particularly in mixed-use buildings during mid-season operation. Current project design must also take account of refrigerant safety, EN 378 requirements, lower-GWP refrigerant trends and the evolving European F-Gas regulatory framework.

What is a 3-tube VRF system?

3-tube VRF systems provide both heating and cooling according to the needs of different areas. Particularly suited to mixed thermal demands in mid-season operation, they can help improve energy efficiency by recovering and reusing heat within the building.

VRF systems are direct expansion thermodynamic systems. Instead of air or water circulating through the distribution network, refrigerant is transported to indoor heat exchangers, which operate as evaporators or condensers depending on the selected mode. The refrigerant flow varies according to the demand from the indoor units. While 2-pipe systems are reversible, 3-pipe VRF systems can produce heating and cooling at the same time. This makes them particularly relevant in mid-season, when shaded areas of a building may require heating while sun-exposed areas require cooling.

While VRF remains primarily used in the service and commercial sector, compact and mini-VRF solutions have expanded the range of applications for smaller buildings and light commercial projects. 3-tube VRF systems remain a higher-end solution because of the additional components, controls, distribution boxes and careful design required to deliver simultaneous heating and cooling.

How does a VRF system simultaneously heat and cool?

In a heat recovery VRF solution, the indoor units operate independently, which can increase performance and energy savings where heating and cooling needs occur at the same time. The system can transfer heat from a zone requiring cooling to another zone requiring heating, reducing the amount of energy that needs to be rejected outdoors or generated by the outdoor unit.

Where most indoor units are in cooling mode, energy recovered from zones in cooling mode can help supply areas requiring heat. Where most indoor units are in heating mode, the outdoor unit provides the main heating input, while recovered energy can satisfy cooling demand elsewhere.

Depending on the manufacturer and system design, several indoor units can be connected within the same zone. Indoor units may be wall-mounted, console, ceiling-mounted or connected to a ventilation network. Refrigerant is distributed via branch or distribution boxes, which direct vapour or liquid refrigerant according to the thermal needs and set temperatures of each indoor unit.

What are the refrigerant charge limits and safety requirements?

Because refrigerant circulates directly inside the building in VRF systems, compliance with applicable safety standards and regulations is essential. EN 378 remains a key reference for refrigeration systems and heat pumps, but refrigerant charge limits should not be treated as a single fixed value. They depend on factors such as the refrigerant safety classification, occupancy category, room volume, installation location, system design and manufacturer instructions. The calculation must be checked by the project designer/installer using manufacturer instructions.

Designers should consider dividing installations into several circuits where appropriate, as this can help limit the refrigerant quantity in a single circuit and reduce pipe lengths and pressure losses. Compared with chilled water systems, VRF pipework usually uses smaller sections, which can make routing easier in renovation projects where space is limited.

Refrigerant choice has also become a more important design consideration. The revised European F-Gas framework increases pressure on high-GWP refrigerants through phasedown measures and equipment-specific restrictions, encouraging the move towards lower-GWP alternatives. Depending on the application and refrigerant used, additional safety measures may be required, particularly for mildly flammable A2L refrigerants. Project teams should therefore review refrigerant selection, leak detection, ventilation, access for maintenance and end-of-life considerations at the earliest design stage.

To guarantee and maintain proper operation, it is recommended to establish a maintenance contract with a qualified specialist. Maintenance should cover controls, electronics, indoor unit cleaning, condensate removal, filters, refrigerant charge, leak checks and regulatory inspection requirements where applicable. Condensate should preferably be removed by gravity, without a pump where possible, to reduce additional failure risks. Regular maintenance helps preserve comfort, efficiency and compliance throughout the system’s life.

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Frequently Asked Questions

What is the main advantage of a 3-tube VRF system?

Its main advantage is the ability to provide simultaneous heating and cooling in different zones, while recovering heat from areas that need cooling and using it in areas that need heating.

Are refrigerant regulations important when specifying VRF systems?

Yes. VRF systems use refrigerant directly inside the building, so designers must consider EN 378 safety requirements, refrigerant charge limits, leak management and the impact of the European F-Gas Regulation on refrigerant choice and long-term serviceability.

Why choose a Eurovent Certified VRF system?

Choosing a Eurovent Certified VRF system gives specifiers, installers and building owners access to independently verified performance data. This supports more reliable product comparison, better energy performance assessment and greater confidence that declared values reflect real-world performance.