Module 59: Ensuring best performance in variable refrigerant volume/flow systems

This module looks at the development of VRV/VRF systems and how legislation and environmental assessment are shaping their implementation

Variable refrigerant volume/flow (VRV/ VRF) systems have grown in popularity since their first introduction in the 1980s. Early systems had one outdoor unit connected to a maximum of eight indoor units, with relatively short interconnecting pipe runs. Today, this has expanded to installations that are far more extensive, typically offering the possibility of 64 indoor units being connected to three outdoor grouped units, with the freedom of up to 1,000 metres of interconnecting pipework.

This CPD will consider the current state of the UK marketplace and explore how legislation and the prevalent UK environmental assessment technique are influencing VRV/VRF implementation to ensure best performance.

Table 1: HEVAC sales statistics of VRF units1

Although new VRV/VRF systems are potentially extensive, currently installed systems are still often much less ambitious, typically with six indoor units for each outdoor one, as shown in the sales data in Table 1. These sales statistics indicate that there were likely to be approximately 16,000 outdoor units sold in the UK in 2012 and that this number is increasing year on year.

Figure 1: An example of a contemporary installation2

A variety of indoor units may be connected, ranging from water heat exchangers and thermal stores through to ducted or ‘cassette’ (ceiling mounted modular) units. An example of a typical system with an outdoor unit connected to DX fan coils and a heat recovery, low temperature water store is shown in Figure 1.

The fast rate of adoption of these units has meant that building designers, installers and end users have to catch-up on how these complex DX systems meet the changing requirements of both new legislation and environmental assessment methods. In the UK, the considerations that affect these systems may be broadly divided into four elements – and, of course, each one of these may interact with the others.

  1. UK Building Regulations and associated supporting documents
  2. EU legislation on the handling of F-gases and ozone depleting substances
  3. The EU Energy-Related Products Directive (ErP)
  4. Environmental assessment methods.

UK Building Regulations

Approved document Part L, Conservation of Fuel and Power, is the key element of the UK government’s legislation leading compliance with the Energy Performance of Buildings Directive (EPBD) requirement to reduce carbon emissions by 20% by 2020. There have been several iterations of Part L published since 2006, the most recent being in 2013. Amongst other things, it sets a requirement ‘to analyse and take into account the technical, environmental and economic feasibility of using high-efficiency alternative systems’, which can include heat pump systems featuring VRV/VRF installations.

Part L sets aspects determining the thermal performance of the building design. However, considerations that affect complex DX equipment are detailed in the separate supporting document, the Building Services Non Domestic Compliance Guide (amended 2011), which schedules minimum performance requirements for specific equipment. The guidance provided in this publication may be used in full or in part or potentially even ignored, providing the building meets the requirements of the National Calculation Method3 (NCM)ascalculated,forexample, by using SBEM3 (Simplified Building Energy Model) software. Using the compliance guide is relatively straightforward but is dependent on specific test requirements for each product grouping – VRV/VRF systems are currently testedtoEN14511.4 Thisspecifiesthatthe system data should be presented with the appropriate combined outdoor and indoor units. This is different to more traditional centralised water chillers with distributed fan coils, which are presented as separate systems – the chillers being tested against the same standard as VRF but the fan coils requiring a separate specific fan power (SFP) rating.

Actual performance will be subject to operating conditions. Both cooling and heating operation can be presented in the form of the energy efficiency ratio (EER) and coefficient of performance (COP). However, the compliance guide offers the opportunity to present a seasonally-adjusted EER (SEER). SEER attempts to take account of the operation of the system throughout the whole operating season by applying weighting factors to simulate the actual energy consumption. The weighting factors may be based on fully modelled data for the application or by using ‘typical’ values for the building type, or using other derived factors – providing they are as rigorous as the prescribed method.

EU F-gas regulation and regulation on substances that deplete the ozone layer

The F-gas regulation first came into operation in 2006, with requirements that affect the work of designers, installers and end users, particularly when dealing with equipment containing more than 3 kg of F-gas (hydrofluorocarbon, or HFC) refrigerants. The regulation focuses on the records and maintenance of refrigeration equipment to ensure leaks are swiftly dealt with and refrigerant is properly recovered when removed from systems. It requires that any service personnel who install or maintain complex DX systems should be properly trained and registered with one of the government-recognised bodies, such as Refcom. Responsibility for enforcement of the F-gas regulation has recently moved to the Environment Agency,5 which will raise awareness and use risk-based targeting to check that individual companies are operating within the law. (The website also provides some useful resources.)

Figure 2: Example unit energy label showing SCOP and SEER as well as sound power levels

Some manufacturers have embedded operational routines for their products that monitor, alert and recover refrigerant to the outdoor unit in the case of a suspected leak from a system.

As a result of the EU regulation on substances that deplete the ozone layer, new R22 systems have been outlawed since 2004. There is a final ban on R22 that comes into effect on 31 December 2014, when it will become illegal to repair a R22 refrigerant circuit; if a fault is detected, the equipment should be taken out of service and the refrigerant must be handled as a hazardous waste. There are several ways of replacing existing R22 systems that can reuse existing system pipework so that compliant HFC systems may be applied with limited disruption to the building. The F-gas regulation will continue to evolve, so the way that HFC refrigerants are handled will also change over the next 15 to 20 years. However, a complete ban on HFC is unlikely, as replacements currently cannot meet the energy efficiency requirements of the EU Energy Related Products Directive.

Energy-Related Products Directive

The Eco-design of Energy-Related Products Directive (ErP) and associated directives6 support the aims of the EU by encouraging the use of environmentally-conscious designs in order to reduce greenhouse gas emissions and their environmental impact. Air conditioning technologies, such as VRV/VRF systems, are affected by the directive across a number of the ErP ‘Lots’ including Lot 2, Lot 10, Lot 21 and ENTR Lot 6, in what can present rather a confused picture of domestic and non-domestic applications (for further details of the ErP and its ‘Lots’, see the November 2012, CIBSE Journal CPD article).

EN14511 defines the specific external design conditions that are applied for standard testing of units, and seasonal testing (to determine SEER and SCOP) is undertaken to standard EN14825.7 EC document 2012/C 172/01 provides a useful explanation of the required calculations.

For units up to 12 kW, the output must be shown on a product energy label (in accordance with EU regulation 626/2011, as illustrated in Figure 2) that includes both the design loads and seasonal performances. It shows the SEER value, a measure of cooling performance, and the seasonal coefficient of performance (SCOP), measuring heating performance, for up to three defined climate conditions: ‘average’, corresponding to Strasbourg; ‘warmer’, based on Athens; and ‘colder’, relating to Helsinki (the ‘average’ climate profile is mandatory, whereas the other two are voluntary). Manufacturers must make the labels for their products freely available through the web.

Figure 3: Published criteria changes for Lot 10 equipment split systems under 12 kW

Enhanced requirements are due to come into force in 2015, 2017 and 2019 (as indicated in Figure 3) that, for example, will mean that a G-rated product today will not be allowed to be sold in 2015, and that by 2019 the minimum SEER of 2.60 and SCOP of 1.90 will rise to a minimum SEER of 3.60 and a SCOP of 2.50. The use of a unified labelling system will help inform the selection of units – although the incremental changes may cause some interim confusion in the marketplace.

Environmental assessment methods

The Building Research Establishment Environmental Assessment Method (BREEAM) is often applied as the environmental assessment method and rating system for buildings both in the UK and worldwide.

Table 2: BREEAM calculation of direct effect life cycle CO2 equivalent emissions (DELC)

VRV/VRF systems can help meet the design requirements of BREEAM, but the majority of the available credits require that the air conditioning system is an intrinsic part of the overall system in order to gain credits for free cooling and ventilation. However, there are targets for leak detection and refrigerant recovery, as well as reducing the amount of HFCs that are used within a system, that will provide a positive contribution to the BREEAM score.

For example, under the section that considers the impact of refrigerants that considers aspects of leak detection and refrigerant handling, a factor may be determined, the Direct Effect Life Cycle CO2 Equivalent Emissions (DELC CO2e). This takes a number of parameters including how large the systems are, the refrigerant global warming potential (GWP), how much refrigerant leaks, the purging arrangements and the chances of a catastrophic failure. If the resulting value comes to less than (or equal to) 1,000 kgCO2e ·kW-1, one BREEAM credit is gained. An example of the calculation (employing the BREEAM calculator) is shown in Table 2.

Equipment manufacturers can advise on appropriate values to use in the calculation. To ensure that a given design for a VRV/VRF system meets the DELC calculation conditions, designers should aim to limit the size of system and the length of installed pipe work.

Although less directly linked to VRV/VRF systems, other BREEAM points that may also be gained from the application of VRV/ VRF systems could include Ene 01, ‘Energy Performance Ratio for New Constructions’, a measure of the buildings CO2 emissions; and Hea 03, ‘Thermal comfort’; this is particularly relevant to both the controllability and zoning capabilities of VRV/VRF.

Similarly, in the Leadership in Energy and Environmental Design (LEED) rating system,8 environmentalassessmentsystem points may be achieved particularly in the ‘Energy and Atmosphere (EA)’ and ‘Indoor Environmental Quality (IEQ)’ sections – the latter being strongly dependent on the associated ventilation strategies that work with the VRV/VRF systems.


The application of VRV/VRF systems is continuing to gather pace in the UK. To apply designs successfully, as well as properly operate and maintain the resulting installations, requires an understanding of an increasing range of legislation and guidance. However, developing a working knowledge of the supporting literature will empower the designer/operator to both create compliant innovative systems and reduce energy usage and operational CO2 emissions.

© Tim Dwyer, 2013.


  1. Data supplied by HEVAC based on market intelligence by BSRIA.
  2. Daikin consultant sales brochure, 2013.
  4. BS EN 14511:2013, Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling, BSI 2013.
  6. business/ecodesign/index_en.htm
  7. BS EN 14825:2013, Air conditioners, liquid chilling packages and heat pumps, with electrically driven compressors, for space heating and cooling. Testing and rating at part load conditions and calculation of seasonal performance, BSI 2013