The ABCs of a VRF system (I)

What is the system Variable Refrigerant Flow (VRF)? Why I prefer it? This article will clarify many doubts.
by Lennox
A VRF system comprises an outdoor unit (three units can be combined in a module of larger capacity) connected to various types of indoor units through a single refrigerant line network.
Each indoor unit or area is controlled by the user or by a central controller that can operate multiple zones. The system constantly varies the amount of refrigerant passing each indoor unit to fit the internal load requirement, allowing the compressors to operate only the necessary capacity to meet that burden.
So less energy than systems on / off; even if the execution time is longer VRF system. When designed properly, a VRF system generally operates at a lower capacity to 100%.
A VRF system is a sophisticated heat pump system. At the most basic level, a VRF system (heat pump or heat recovery) is a heat pump. It has one outdoor unit connected to various types of indoor units through a single cooling pipe network. In North America all VRF systems currently used refrigerant R410a. ASHRAE and AHRI (Institute of Air Conditioning, Heating and Refrigeration) have formulated a definition of the VRF. The main criteria are that the system has a network of common refrigeration and three control steps.
ASHRAE defines the VRF as follows: "It is a multi-split system direct expansion (DX) incorporating at least one variable capacity compressor, which distributes coolant through a network of pipes to multiple indoor units of air conditioning, each of which is capable of controlling the temperature of separate zones, through integral control devices zone temperature and common communications network. Variable Refrigerant flow uses three or more steps in the shared control and intercommunicating pipe ".
AHRI defines the VRF as follows: "Multi-split system VRF: A heat pump or air conditioning multi-split incorporates a single refrigerant circuit, with one or more outdoor units, at least one variable speed compressor or a combination of reciprocating compressors for varying the capacity of the system in three or more steps, several inner air-conditioning units units (each of which is measured separately), and are individually controlled by a device integral control and a network common communication. The system is capable of operating either as air conditioning or heat pump.
System VRF Multi-split heat recovery "incorporates a single refrigerant circuit, with one or more outdoor units, at least one variable speed compressor, or a combination of reciprocating compressors for varying the capacity of the system in three or more steps several units Fan coil, each of which is measured separately and individually controlled by are integral control device and a network common communication. The system is capable of operating either as air conditioning or heat pump. The system is also able to provide heating and cooling simultaneously, thanks to which the energy recovered from the indoor units operating in one mode can be transferred to one or more indoor units operating in the other mode.
The VRF systems function as heat pumps and follow the same refrigeration cycle than any other cooling equipment. The evolution of VRF systems dates back to the air conditioning units single speed. These units had a compressor single speed, a capacitor, a measuring device and an evaporator. The system could only cool, not warm.
Figure 1
Air conditioning single speed followed the heat pump system; a reversing valve and a device for measuring both indoor units and outdoor units, which were the main components that allow the system to have the ability to produce heating and cooling without a component of supplementary heating is added.
Figure 2
Then the inverter compressor to vary the speed and electric expansion valves that allowed the capacity modulation system was introduced. This provided a more accurate and higher capacity control.
Figure 3
In order to have zoning functions, additional indoor units to the system were added. This allowed individually control the temperature of each zone. Thanks to a compressor inverter system, the system operates at a capacity that conforms to the internal load, increasing the overall efficiency.
The efficiency is achieved by reducing capacity at part load conditions; Most systems operate 60% to 80% partial load time. As additional areas require cooling, the compressor is accelerated to provide the necessary capacity. When a zone needs are met or the cooling load decreases, the compressor slows down and reduces the capacity to the level needed only. This makes the system highly efficient, since it is only providing the necessary capacity and no wasted energy.
Figure 4
key components
There are two fundamental components in a system VRF: variable speed compressor controlled by an inverter system, digitally switched and the valve electronics, or EXV expansion.
VRF systems use inverter technology with electronic expansion valves to control the flow of refrigerant to vary the capacity. The inverter is an electronic component that varies the compressor speed. By varying the speed, the mass flow rate of the refrigerant increases or decreases to match the required internal load. This allows the system to produce VRF only the necessary capacity required at a particular time. Most manufacturers are using VRF controlled by an inverter compressor in the outdoor unit system.
The electronic expansion valve, EXV, opens and closes in increments which allow the precise amount flowing refrigerant through the evaporator coil. The EXV is also opened to a predetermined position during heating mode operation to allow the refrigerant flow through the condenser, thus making it unnecessary to have a bypass valve type. Each indoor unit has a EXV. EXV has a frequency variable pulse which modulates the flow of refrigerant in the indoor unit. It allows passage to the indoor unit of the required amount of refrigerant to meet the demand in the area.
System Types
VRF come in form of heat pump system and heat recovery system. A system VRF heat pump can heat or cool the space, you can not do both at the same time. A VRF heat recovery system allows simultaneous heating and cooling of individual spaces. The VRF heat recovery system moves the heat recovered from one area to another. This is a controlled total comfort that allows cooling and heating in one area while another system. The ability to use the waste heat created when a space is cooled to a different space heating represents the true value of the heat recovery system. Most recovery systems contain three tubes: tube liquid discharge tube and high pressure gas suction pipe low pressure gas.
Two heat pump systems
A heat recovery system
indoor units
The indoor units come in a wide variety of styles and capacities to suit different applications. VRF interior styles ductless units include units for wall mounting or ceiling. Styles with air conditioning ducts are usually horizontal and vertical medium and high static.
Figure 5
Mode selection box
VRF in heat recovery systems a box selection mode is used, also known as heat recovery box, to enable simultaneous heating and cooling. This box is used to set the mode of the indoor units located down the selection box.
Figure 6
The VRF controls provide feedback to the VRF system on the load requirements of space. Typically this is a communications system which allows serial connection mode control a separate zone (heating or cooling) and temperature control. Through gateways or interfaces, the control system VRF can connect to building management systems BACnet or LonWorks.
Figure 7
Accessories can range from condensate lift pumps to control auxiliary heating options, connections bypass refrigerant pipe and remote sensors for rooms.
The VRF systems have many advantages over conventional systems on and off.
Please note: To read the second part do click here.


pere ricardo pedraza
# pere ricardo pedraza 04-09-2015 02:08
excellent explanation and hope second part
thank you
Hugo Morillo
# Hugo Morillo 09-09-2015 14:59
excellent information, congratulations
Duvan Chaverra
# Duvan Chaverra 15-09-2015 13:29
thanks Hugo
Waiting for the second part of this article.
Duvan Chaverra
# Duvan Chaverra 15-09-2015 13:30
Thanks Ricardo,
Soon we publish the second part of this article.
# Alvaro AGURRE 28-07-2017 16:51
Roberto Rois
# Roberto Rois 26-09-2017 05:19
I would like to install this vrf system in my apt. I would like to know if the advantages to the split split are really significant and I would be interested to know that another brand could recommend unlike Lennox. Also know the risks to health in terms of leakage. Thank you
# alex 22-03-2018 00:00
# Mijail 02-04-2018 22:01
the shunts when they are installed, can they only be placed horizontally or vertically? Thank you...
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