Air control

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Blue Star’s vrf systems include outdoor units that can be operated in ambient temperatures of up to 52°C.

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Daikin offers outdoor unitsrated at 6.5-24TR for its trademarked variable refrigerant volume (vrv) systems.

In an environment that uses air conditioning to such an extent, it is little surprise that technical innovation is constantly strived for. The system chosen to provide cool air to a building can have a significant effect on the overall energy consumption and the sector's manufacturers are continuously developing and improving products in the quest to meet greater demands for energy efficiency.

One technology that is beginning to gain in popularity due to its relatively low energy use is variable refrigerant flow (vrf) air conditioning systems. Recent research from the UK-based Building Services Research and Information Association (BSRIA) found that vrf systems are the fastest growing product type in the air conditioning sector. Its World Air Conditioning Market Review 2007 reports that the vrf market value is growing at double-figure percentage rates in all major countries worldwide and this trend is expected to continue. In the UK alone the market rose 40% in volume and 42% in value during 2006 and their use in the Middle East is beginning to rise. "They provide space saving and energy benefits - two factors which are being taken very seriously in this market, so they are an attractive option," explains Doug Hahn, general manager of the LG Electronics training academy.

Introduced in Japan over 20 years ago and already popular in European markets, the systems' outdoor units were previously unsuitable for use in the region due to the climatic conditions. However, product developments mean that is no longer the case and a number of manufacturers are now offering vrf systems specifically intended for use in such climates, with more set to be introduced later in 2007. But what is a vrf system?

System design

VRF systems typically comprise of an outdoor unit with multiple compressors that serves a number of individual indoor units to provide air conditioning for different zones in a building. The indoor units can simultaneously condition each area to establish individual setpoints.

The systems are ductless and transfer heat to or from a space by circulating refrigerant to evaporators located near or within the individual zones. In contrast, conventional systems transfer heat from the space to the refrigerant by circulating air or water throughout the building. An inbuilt controller regulates the amount of refrigerant flowing to the indoor units to enable temperatures to be met. "Every zone within a building requires a precise amount of cooling," explains Saidja Geirnaert general manager, Daikin Middle East. "This individual cooling capacity is achieved by matching the requirement with the exact amount of refrigerant volume needed to transport the required energy."

A direct digital control (DCC) system provides a network link between the controller and outdoor compressor unit to operate the entire system. This means that fan speeds can be operated to maintain heat, while the evaporator fans can be controlled to maintain precise temperature setpoints.

"An electronic expansion valve continually adjusts the flow of refrigerant to respond to the load requirements of the indoor units," adds Geirnaert. "This enables the system to maintain temperatures at a virtually constant and comfortable level without the fluctuations typical of conventional on/off control systems, meaning that less energy is wasted." Local, individual control of the indoor units is usually also possible.

The technology boasts a number of benefits over other types of air conditioning systems. VRF units are modular and lightweight making installation fast, simple and suitable for phased projects. "The small-bore piping system used can be installed quickly on a floor-by-floor basis so that sections of a building can be put into use quickly," explains Geirnaert. "This means that the air conditioning system can be commissioned and operated in stages rather than on final completion." The primary components of vrf systems also make them suitable for retrofitting into existing buildings as no structural changes are needed.

"The units are small and because [the main unit] is placed outside you have space saving, allowing for more rentable space," explains Basil Al Khayat, air conditioning divisional manager of United Electronics Company, the distributor of Mitsubishi VRF systems. "There is also flexibility over where you install the room units. Mitsubishi Electric's City Multi brand comes in exposed and concealed floor-mounted, ceiling suspended and wall-mounted versions, which can be positioned virtually anywhere within a room.

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