LG launches new VRF system

air conditioning, LG, VRF

Just how far is it possible to further the performance of VRF air conditioning? Ken Sharpe has been finding out about LG’s latest range — Multi V 5.

It is only 10 years since LG developed its first Multi V VRF system. That was back in 2006, and already Multi V has reached its fifth generation, with the launch of Multi V 5. Every new generation ha brought in new features and high levels of efficiency, and this latest generation is no exception. Depending on the features, there are two levels of efficiency, the most efficient having an ESEER (European Seasonal Energy Efficiency Rating) of 9.15, 21% better than the 7.54 of the previous model. The new standard unit has an ESEER of 8.13, an 8% improvement.

But before looking at how these efficiency improvements have been achieved, it is notable that Multi V 5 is capable of heat-recovery using a 3-pipe system but that this capability can be over-ridden by setting a DIP switch and restored later if required. This feature avoids having to decide at Cat A fit-out stage whether heat recovery will be required later.

Many of the design features that improve efficiency also help to reduce the size and weight of the outdoor units so that it is possible, for example, for a single outdoor unit to deliver nearly 73 kW of cooling. Just 10 Multi V 5 units have the same capability as 13 previous-generation units, with a 23% reduction in installation space and a 15% reduction in weight.

The main contributors to improving performance and capabilities are:

• dual sensing control;

• inverter compressor;

• heat-rejection fan on the outdoor units;

• split heat exchanger;

• oil management;

• anti-corrosion coating on coil fins.

Dual sensing control involves monitoring temperature and relative humidity to control the evaporating temperature at the indoor unties, increasing the ESEER by 14% to 21%, depending on the outdoor units. The proportion of latent and sensible cooling can be varied, rather than kept in a constant proportion. The benefit will be very significant during a hot, dry summer.

Dual sensing control can also be used to vary the temperature of the air delivered for cooling by the indoor units, rather than on/off operation. A ∆T of 10 K might be comfortable if the return air temperature from the room is at 30°C and the air off the indoor unit is at 20°C. However, return air at 25°C and air off at 15°C would not be comfortable, so the ∆T can be reduced to improve comfort, increase efficiency and avoid on/off operation.

Moving on to the compressor, the scroll impeller and bearing are made of an engineering plastic Polyether ether ketone (PEEK) which reduces wear by permitting a 13% increase in oil-less compression time compared to previous models. The operating range of the compressor is a wide 10 to 165 Hz — increasing partial efficiency, extending capacity and increasing reliability.

LG, VRF, air conditioning
This wire-frame impression of an outdoor unit of LG’s Multi V 5 VRF system shows the new design of heat-rejection fan, new compressor and refrigerant receiver — and also hints at the connections that make it possible to use the dual-section coil in series or parallel to optimise heating and cooling operation.

Refrigerant vapour is injected into the high-sided shell using a 2-stage compression effect that provides powerful heating at low ambient temperature to improve energy efficiency and heating performance.

High-pressure oil return (HiPOR) reduces energy consumption by enabling oil to be returned direct to the sump of the high-sided compressor instead of via suction. This keeps viscosity low and increases volumetric efficiency to increase compressor efficiency by up to 10%.

Another significant improvement to performance is made by active refrigeration. Depending on the mode of operation and load, refrigerant is drawn off into a receiver. There will be more refrigerant in circulation in heating mode and less in cooling mode. Even less refrigerant will be in circulation at partial load.

Similarly, the heat-exchange coil in the outdoor unit is designed to optimise efficiency in both heating and cooling mode.

The heat-exchange coil wraps round four sides of the outdoor unit to increase capacity, with the only gap being for the control panel and to provide access to the compressor and other equipment within the unit. The coil is split into two sections, which are used in series for cooling operation and in parallel for heating operation so as to optimise heat-exchange efficiency.

Controlling the evaporating temperature of the outdoor unit in heating mode in response to relative humidity reduces the build-up of frost — the higher the evaporating temperature, the less frost is formed. Because the coil has two circuits, partial defrosting can be carried out, with the other half of the coil continuing to provide heating.

The various features of Multi V 5 enable 100% heating capacity to be maintained down to -7°C ambient and guaranteed heating performance at -25°C ambient.

But it is the fans in the outdoor units that, perhaps, represent the most novel new technology. Working with the department of mechanical and aerospace engineering of Seoul University in South Korea, researchers drew inspiration from the humpback whale’s functional morphology of flipper structures to give naturally evolved passive flow control. By adopting a biomechanical approach, airflow through a unit has been increased by 10% and power consumption reduced by up to 20%, negating most of the associated negatives. With a wider air guide, discharge air is stabilised and noise levels are also reduced.

The life of the coil is assured by a corrosion-resistant black epoxy-resin coating and a hydrophilic coating to prevent the accumulation of water. The coil has been certified by the Underwriters Laboratories 1500 h salt-spray test. Further internal testing of 3000 h salt spray was carried out with no significant areas of corrosion visible; this test simulated the corrosive load for 27 years.

Andrew Slater, air-conditioning and energy-solutions technical and research manager, says, ‘Building on the continued successes of the past, with its application of unique technologies and components designed and developed by LG’s engineering teams, Multi V 5 will offer the industry unparalleled design and efficiency opportunities.

‘Multi V 5 carries the factors considered at design stage through to real-life system regulation, through humidity monitoring — part of our dual-sensing control.’

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