VRF air conditioning

What VRF is

VRF stands for variable refrigerant flow. A VRF system connects many indoor units, often across several floors, to one or more outdoor units through a shared refrigerant pipe network. The outdoor plant varies its compressor speed and the flow of refrigerant to each indoor unit to match what each room needs at that moment. Daikin calls its version VRV, for variable refrigerant volume. The principle is the same.

Each room or zone has its own indoor unit and control, and the whole system can be run from a central controller or linked to a building management system. Indoor units can be cassettes, ducted units, wall-mounted units or floor consoles, mixed to suit each space.

Heat pump and heat recovery systems

There are two main types. A heat pump VRF system runs all its indoor units in the same mode at the same time: all cooling or all heating. That suits buildings where the whole floor tends to need the same thing.

A heat recovery VRF system can cool some zones and heat others at the same time. Heat taken out of the rooms being cooled is moved to the rooms that need heating, rather than being thrown away outside. That suits buildings with mixed needs: hotels where one side gets the sun and the other doesn’t, offices with a cold north side and a hot south side, or meeting rooms that heat up while the corridors stay cool. The right choice depends on how the building is used, and we explain the trade-offs in the design.

Where VRF suits

• Offices across one or several floors, with individual control for each area.
• Hotels, where every bedroom needs its own control and guests want quiet.
• Schools and colleges with many classrooms on one system.
• Retail and leisure buildings with a mix of shop floor, offices and stores.
• Surgeries, clinics and public buildings with many small rooms.

For a handful of rooms, a multi-split or individual splits are usually simpler and cheaper. VRF comes into its own when there are many zones and the building needs to be managed as a whole.

Design comes first

A VRF system is only as good as its design. We start with a survey of the building and how each space is used, then work out the heating and cooling loads, choose the indoor units, size the outdoor plant and lay out the pipe network to the manufacturer’s limits. We also plan where the outdoor plant will go, which on many commercial buildings means a roof or plant area, and check access, structure and noise.

Because the refrigerant network serves many rooms, the design has to think about the amount of refrigerant that could reach a small room if a leak happened, and keep within the safety limits for that refrigerant. We take that into account in the layout and, where needed, in leak detection. The controls are designed with the people who will use them, so the system is easy to run day to day.

Refrigerant, leak checks and TM44

VRF systems hold a larger charge of refrigerant than domestic systems, so the F-gas rules apply in full. Equipment containing 5 to less than 50 tonnes CO2 equivalent needs a leak check at least every 12 months, 50 to less than 500 tonnes every 6 months, and 500 tonnes or more needs automatic leak detection. Fitting leak detection lets you double the interval (GOV.UK: leak checks). Only certified companies and qualified engineers may work on the refrigerant circuit (GOV.UK: company certification).

A VRF system will almost always be over the 12 kW threshold for a TM44 inspection, which must be carried out by an accredited energy assessor at least every five years. We build these into the handover and the maintenance plan.

Installation and commissioning

VRF installations are usually phased so the building can stay in use. We agree the programme with you, install the pipe network, indoor units, drains, controls and power, then pressure test the whole network, evacuate it and add the refrigerant charge calculated for the pipe lengths. Commissioning sets up every indoor unit and the controls, and you get the commissioning records, F-Gas records, control settings and the manufacturer’s warranty information at handover. Clients we have worked with on commercial projects include Hilton Hotels, Holiday Inn, Rolls-Royce, McDonald’s and the BBC.

Maintenance, upgrades and price

VRF systems need planned maintenance: filters, coils and drains on every indoor unit, the outdoor plant, the controls and the leak checks the rules require. A maintenance contract keeps all of that on schedule. We also assess older VRF systems, including those on R410A, and give you a costed choice between repair, partial upgrade and replacement. VRF is priced after survey, and you get a fixed price with your quote. VAT on business premises is at the standard rate.