Has Daikin finally cracked CO2 VRF?

BELGIUM: As a possible solution to the viability of VRF air conditioning technology in a low-GWP future, Daikin will preview a CO2 VRF system at the ISH show in March.

Daikin Europe has revealed no further details of its CO2 VRV system, but it is not the first time the air conditioning manufacturer has been linked to the development of VRF systems using CO2. 

VRF (variable refrigerant flow) air conditioning was pioneered by Daikin Industries in Japan in 1982 and introduced by Daikin Europe in 1987. Later trademarked by Daikin as VRV (variable refrigerant volume), these energy efficient and flexible systems have for many years used high GWP refrigerant R410A. 

The European F-gas regulation, a requirement to eliminate high GWP refrigerants which, in line with the Kigali Amendment, is being mirrored worldwide, means R410A is no longer sustainable. 

For large commercial applications, such as Daikin’s VRV systems, the legislation allows for a longer transition time. Increasingly, HVAC manufacturers are launching VRF systems using R32 and providing customers with a solution for new installations at least until 2033. However, the flammability of R32, an A2L refrigerant, continues to restrict its application in larger VRF systems and in applications in some European member states.

Long-term option

During presentations at the recent Chillventa exhibition, Daikin Europe acknowledged that the forthcoming phase-down and quota restrictions required lower GWP solutions to be developed.

The company highlighted CO2 as “a promising long-term option” for medium and large commercial systems and “the next logical step” for VRV systems. “It is a solution that deserves the full attention of all stakeholders in the HVAC market: component and HVAC manufacturers, as well as their engineering and installer partners, with the aim of launching the next generation of direct expansion systems,” Daikin said.

A CO2 VRV system was first previewed at the Chillventa trade fair in Germany way back in 2008 and was subsequently exhibited at a number of exhibitions in early 2009. That unit featured a Daikin swing compressor with dual compression, a two-stage intercooler circuit, three-row heat exchanger and four-way electronic expansion valve. It boasted a nominal cooling capacity of 28kW and heating capacity of 31.5kW. It weighed 330kg.

At the time, Daikin insisted that the new CO2 VRV system was intended more to demonstrate and investigate the new environmental technology but this early design never went into production.

Four-stage compressor

In 2016, Daikin presented a paper at the Purdue Conference in the US referencing its work with a prototype CO2 refrigerant VRF air conditioning system. This 14kW cooling capacity unit used a four-stage compressor and expander and an all-aluminium microchannel heat exchanger.

The size of the heat exchanger was increased by about 150% to match a similar R410A unit. This combined with the necessary extra componentry increased the estimated weight of the outdoor unit by about 250% compared to a unit running on R410A. 

The extra componentry, including the three internal heat exchangers, resulted in a 300mm increase in casing width and a 146% larger internal volume, compared to an R410A unit.  

Daikin recognised that breakthrough technical advances were needed to further reduce product weight and size before CO2 VRF would spread widely into the commercial sector.

The company remains tight-lipped at the moment regarding its latest version, and has not indicated when, or whether, it will find its way to market, but has promised further information in the coming weeks.