Variable refrigerant low (VRF) systems offer the ideal solution for environmentally focused refurbishment projects, says John Durbin.
VRF (variable refrigerant flow) technology - called VRV (variable refrigerant volume) by Daikin - has won widespread acclaim as being a highly efficient solution for integrating a building's heating, ventilation, air conditioning and even refrigeration requirements.

However, there is a tacit understanding that VRV systems are only appropriate for small to medium buildings and they do not offer the same level of design flexibility as a chilled water system. This is no longer the case.

In fact, VRV and VRF systems offer much greater flexibility than some engineers realise and can be specified successfully for buildings of up to 10,000 sq m, offering precise control of multiple zones. They also take up as little as a third of the central plant space required by traditional air conditioning systems, so they are an attractive solution for major refurbishment projects in which the aim is to maximise the rentable floor space of a building.

Another great advantage is that VRV systems are modular and are therefore ideal for phased refurbishment projects, as the system can be retrofitted floor by floor.

The renowned benefit of VRV, of course, is that the heat pump varies the refrigerant volume within the air conditioning system to precisely match the building's requirements at any moment. This means that each area is able to continually maintain its desired temperature, thus avoiding fluctuations in the internal climate while minimising energy consumption.

As a result, the efficiencies VRV delivers - typically COPs of 3 to 5 - are among the highest currently achieved in the industry. However, these are not the maximum levels of efficiency that can be gained from the very latest systems when employing heat recovery in balanced mode.

For even greater energy savings, VRV systems can incorporate heat recovery, in which waste heat is reclaimed from areas such as plant rooms, IT suites, or indoor units in cooling mode and diverted to areas that require heat. This holistic approach to system design can deliver efficiencies of up to 9 or even 10. In fact a heat recovery system in balanced mode has been proven to deliver a COP as high as 10.07 - a previously unheard-of level of efficiency.

This free heat can be used to produce hot water or warm air at entrances requiring air curtains. Heat recovery air curtains can deliver energy consumption savings of up to 67 per cent compared with a typical electrically heated air curtain. This highly energy efficient solution has been estimated to reduce CO₂ emissions by more than six tonnes and achieve cost savings of £1,500 per annum, offering a payback period of just three years.

Heat reclamation units can also be used in the ventilation process. By extracting waste air from a room via the heat exchange process, the recovered heat energy can then be transferred to the fresh air supply being delivered to that room. The net result is a further reduction in the cooling/heating load on the air conditioning system.

Whatever the proven benefits of VRV and heat recovery systems, the environmental rating systems designed to judge the impact of such systems no doubt have an influence on the decision making process. Obviously there is a cost/benefit analysis to be done, but by-and-large scoring highly under measurement systems such as BREEAM means that end users will benefit from lower fuel bills as a result of having a more energy efficient building.

However, although using the latest heat pump technology with integrated heat recovery equipment increases the number of BREEAM credits received, heat pumps also lose some credits under the pollution section of BREEAM because they use refrigerant. This is something of an anomaly, because many systems that use R410A can be shown to generate far fewer greenhouse gas emissions over their lifetime than less efficient systems that use refrigerants with an apparently lower global warming potential (GWP).

This assessment procedure totally ignores the TEWI (total equivalent warming impact) equation which looks at all the factors involved with an installation and works out the total quantity of greenhouse gasses, or their equivalents, that are released over a period of time. By using such an equation, it can be seen that the lifetime carbon emissions of using a VRV or VRF system may well be significantly less than a system that uses an apparently lower GWP refrigerant such as CO₂.

The decision whether to opt for a chilled water or a refrigerant-based system will be based on many factors, including the size of the building and the refurbishment objectives. However it is important that engineers look beyond the headlines, to consider the TEWI of a system over its entire lifespan.

Even making small adjustments to existing systems can have a major effect. For example, energy savings of 40 per cent can be achieved simply by retrofitting controls. Remote monitoring can also help to optimise the efficiency of a hvac system by analysing data from the equipment to flag up blocked or contaminated air filters and heat exchangers.

• John Durbin is engineering department manager at Daikin UK