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Guide to variable refrigerant flow air conditioning (2017)
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Guide to variable refrigerant flow air conditioning (2017)

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Over the last thirty or so years, variable refrigerant systems have become increasingly popular; they are usually referred to as either ‘variable refrigerant flow’ (VRF) or ‘variable refrigerant volume’ (VRV). VRV refers to a specific manufacturer, who patented the use of that name, whereas VRF has been adopted as the generic term for systems of this type.

VRF heating and cooling systems are deceptively simple as manufacturers appear to have almost eliminated the need for any design by a building services or refrigeration (design) engineer by providing simple step-bystep guides and, in most cases, software to select the components and pipe sizes. If properly designed, integrated and applied, VRF systems can produce large scale energy and carbon savings. However, to achieve the most energy efficient design solutions, the skills of such design engineers are essential.

Manufacturers provide great assistance by publishing comprehensive engineering documents and software for their products and systems but design engineers selecting the components and designing the systems need to understand the principles of how they work, how to select the best match of indoor and outdoor units, how to size and design refrigerant distribution systems and how the systems can be best commissioned, operated and maintained.

The main purpose of this publication is to provide an independent source of information to assist designers in selecting and configuring VRF systems to realise their optimum environmental and economic potential. Specifically, it aims to provide:

  • an understanding of the technology and its applications
  • explanations of the differences between VRF and alternative technologies
  • information on the availability and comparability of systems
  • information on the calculation of heating and cooling loads and effects on component selection
  • an understanding and recognition of the importance of diversity and capacity ratios in VRF applications
  • guidance on how to achieve energy efficient systems
  • information on how best to specify VRF systems
  • advice on commissioning procedures
  • information on maintenance, training and resources.
This Guide is a co-production between The Chartered Institution of Building Services Engineers (CIBSE) and The Institute of Refrigeration (IoR).


1 Introduction
1.1 Purpose of this publication
1.2 Objectives and scope
1.3 The role of the system designer

2 Concepts
2.1 What are variable refrigerant flow air conditioning systems?
2.2 Is mechanical cooling really necessary?
2.3 Pros and cons of VRF and water-based heating and cooling fan coil units
2.4 Main types of VRF systems
2.5 Diversity of operation and capacity ratio

3 Design
3.1 Energy efficient design of VRF system
3.2 Calculation of heating and cooling loads
3.3 Capacity ratio
3.4 Defrost
3.5 Operating range
3.6 Equipment selection procedure
3.7 Pipe layouts and effects on system efficiency and performance
3.8 System and multi-system controls
3.9 Compliance with F-Gas regulations, leak detection and BS EN 378
3.10 Oil control and recovery
3.11 Unit location and access for servicing and maintenance
3.12 Pipework distribution and design
3.13 Guidance for preparing specification of VRF systems
3.14 Capacity, efficiency, noise and control

4 Applications
4.1 Applications by type of technology (with watch points)
4.2 Generic buildings, e.g. offices, hotels, schools, healthcare, retail etc
4.3 New-build and refurbishment projects
4.4 Deep plan and shallow plan, high rise and low rise and other building forms

5 Installation
5.1 Pipework
5.2 Commissioning and start-up

6 Operation and maintenance
6.1 Overview
6.2 Air conditioning inspections
6.3 Controls
6.5 Monitoring and assessing year-round performance

References and bibliography


Authors and contributors: David Arnold (Troup Bywaters + Anders); Graeme Maidment (Institute of Refrigeration); Mike Nankivell; Graham Wright (Daikin)
Other acknowledgements: Miriam Rodway (Institute of Refrigeration); Mike Smith (BSRIA)

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