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Variations on a theme

Since their introduction 30 years ago, variable refrigerant volume (VRV) solutions that accurately match the volume or flow rate to heating or cooling load have proven to be a highly energy efficient way to control a building’s climate system, says Martin Passingham

However, until now there has been an assumption that they are only suitable for certain types of applications, such as small to medium sized office buildings. Recent technological advances mean these assumptions are simply no longer true.

Perhaps because of VRV’s modularity, it is often perceived as one step up from a split or multi-split system and therefore most suitable for buildings of up to 5,000 sq m. In reality, the latest VRV systems can be applied on a much greater scale, to create fully integrated systems for buildings up to three times that size.

In fact, when VRV systems are designed as a whole building solution they can offer the very highest energy efficiencies of all.

Because VRV varies the refrigerant volume within the system to match the building’s precise requirements at any moment, only the minimum of energy is required to ensure that each area maintains its set temperature. The latest VRV system incorporates variable refrigerant temperature control, which automatically adapts the system to the individual building and climate requirements for even greater energy efficiencies.

A genuinely versatile VRV heat recovery system operating in balanced mode to manage climate control over an entire building can increase energy efficiency levels massively.

For example, a typical office building may require cooling down to 16 deg C, heating up to 21 deg C, with 200 litres of water storage required for washrooms and 150 litres of water storage for kitchens. By recovering the heat from indoor units in cooling mode, a COP (coefficient of performance) of 3.97 can be achieved. In milder conditions, when 75 per cent of the indoor units are in cooling mode with 25 per cent heating, the efficiencies rise to COPs of 5.57. But when the system is fully balanced between heating and cooling, the COP can be as high as 10.07.

However, to achieve such high COPs (which we believe are market-leading) it’s vital to analyse right from the start a building’s multiple requirements, usage patterns and varying occupancy levels, in order to design an intelligent solution that optimises energy efficiency and heat recovery.

This may mean specifying the system so it is capable of cooling one area of the building that is experiencing the highest heat gains and transferring that reclaimed heat to other areas of the building that require heating or hot water. By doing so, recovered heat can be diverted to heat water, or to additional applications such as over-door air curtains, and we have found this can save up to 67 per cent in running costs compared to electrically heated models.

The integration of a VRV system with the latest intelligent control systems can increase energy efficiency further. For example, the latest innovations in intelligent controls are capable of allowing users to set system schedules on a weekly, monthly and annual basis. These can take into account holidays and seasonal variations in demand throughout the year, ensuring the system is being operated in the most energy-efficient way.

Additionally, smart controls can monitor energy consumption across a range of equipment, including air conditioning, to pinpoint areas of a building where the greatest energy savings can be made.

According to construction economist Franklin + Andrews, running costs for VRV heat recovery systems are up to £6.25/sq m of gross floor area. This compares favourably with a two- or four-pipe fan coil system, which can cost as much as £8.75/sq m and £10.75/sq m of gross floor area respectively – a 40-72 per cent increase on running costs over a typical heat recovery system.

A VRV system is more space efficient than a chiller too, because it requires much less plant space. For example, Franklin + Andrews estimates that a two- or four-pipe fan coil system could take up around 7 per cent  of the overall lettable floor area of the building, while a comparable VRV building would take up between 3 and 5 per cent.

VRV also provides greater flexibility, because the system can be designed, built and commissioned floor by floor. It can be introduced zone by zone and tailored to the needs of each building tenant throughout a phased refurbishment programme. Because each floor – even each room – can be individually controlled to maximise energy efficiency and prevent energy waste, VRV is ideal for buildings with multiple tenants, which may have vacant areas and variable periods of high and low usage.

Of course, cost savings must be matched by savings in CO2 emissions. A framework of continuous improvements has been set with a new version of the Building Regulations due out in October 2013, followed by an expected change in 2016 and a final revision in 2019. This means that by 2019, all new buildings must deliver zero carbon emissions from the energy required for heating, cooling, hot water and lighting. These challenging targets will require considerable innovations to improve on current practices.

Many organisations and local authorities use BREEAM as a mandatory design standard to ensure that both new build and existing premises meet the exacting requirements for CO2 emission reductions. For example, the healthcare sector has designated that all new buildings must meet a BREEAM Excellent rating and existing building stock must achieve a Very Good rating.

Heat pump technology can assist building designers in meeting the requirements of BREEAM by delivering heat into a building in an energy-efficient, controlled way. Additionally, specific credits can be given for integrated services and building management systems. Further awards for innovation are also possible depending on the system design.

To achieve the highest level of credits for integrated system design, Integrated Environmental Solutions offers a new Daikin Dynamic VRV Systems Sizing Tool within the IES Virtual Environment. This new software tool enables architects and engineers to easily evaluate the best option to lower building energy use, by accurately simulating annual loads, power input and efficiencies delivered by such systems.

So before VRV heat pumps are dismissed as a modular system for small to medium buildings, it is worth taking a look at the bigger picture – and see how they can offer a highly versatile and flexible solution to meet today’s energy efficiency requirements.

Martin Passingham is product manager, DX, at Daikin UK

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