Variable Refrigerant Flow (VRF) Systems: Ir. Dr. Sam C. M. Hui
Variable Refrigerant Flow (VRF) Systems: Ir. Dr. Sam C. M. Hui
Variable Refrigerant Flow (VRF) Systems: Ir. Dr. Sam C. M. Hui
http://ibse.hk/SBS5311/
Oct 2017
Contents
• System Overview
• System Operation
• Design Issues
System Overview
(Source: Fujitsu)
VRF system with simultaneous cooling & heating (by heat recovery)
(Source: Fujitsu)
System Overview
• VRF systems:
• Similar to unitary and other common DX systems,
and share many of the same components (i.e.,
compressor, expansion device, heat exchangers)
• Highly engineered, with single or multiple
compressors, multiple indoor units (ducted and
non-ducted types), and oil and refrigerant
management and control components
• Typical capacities: 5.3 to 223 kW for outdoor
units and 1.5 to 35 kW for indoor units
History of variable refrigerant flow (VRF) system
(Source: Fujitsu)
Variable refrigerant flow (VRF) system with mixed indoor units
(Source: Daikin)
Common
types of VRF
indoor units
(Source: ASHRAE Handbook 2016 HVAC Systems and Equipment, Chapter 18 – Variable Refrigerant Flow)
Variable refrigerant flow (VRF) system ---
refrigerant circuit and control communication devices
(Source: Fujitsu)
Components and Types
Two-pipe heat
recovery VRF
system
(Source: ASHRAE Handbook 2016 HVAC Systems and Equipment, Chapter 18 – Variable Refrigerant Flow)
Heat pump and heat recovery VRF systems
(Source: Carrier)
System Operation
CONVENTIONAL
(Source: John Chavez, Gunder & Associates) LEV = linear expansion valve
System Operation
• Pipe design
• The long pipe lengths will introduce pressure losses in the
suction line and, unless correct diameter of pipe is selected,
the indoor units will be starved of refrigerant resulting in
insufficient cooling to the end user
• So it is very important to make sure that the pipe sizing is
done properly, both for the main header pipe as well as the
feeder pipes that feed each indoor unit
• Maximum allowable vertical distance between an outdoor unit and
its farthest indoor unit; maximum permissible vertical distance
between two individual indoor units
• Maximum overall refrigerant piping lengths between outdoor and
the farthest indoor unit
Pipe length limits of typical VRF systems
(Source: Fujitsu)
Example of VRF piping design
(Source: http://www.stingmarketing.com/multi_flex/appl-hvac.html)
Design Issues
(Source: Fujitsu)
Design Issues