What is VRF?
VRF is short for “Variable Refrigerant Flow”. It is a
type of direct expansion (DX) multi-split system that incorporates a
variable capacity compressor with a network of multiple indoor fan coil
units. A VRF system increases efficiency by providing cooling or heating
only to the individual zones where conditioning is required. Most VRF
systems also employ a stand-alone controls and communications network.
How is a VRF
system different from a conventional system?
A conventional system usually operates at a fixed
speed. On days where the full capacity is not required, the system will
turn off and on to maintain the space temperature. These systems will
also have a single indoor unit connected to a network of ducts. A fan
distributes air through the ducts and brings return air back to the
central system. This is less efficient than a VRF system because it can
only heat or cool the entire system; there can only be one set point.
Also, the fan and duct losses of a conventional system can add an
additional 30% to the total energy consumption.
What is a Heat
Recovery or Simultaneous VRF system?
A heat recovery VRF system has the ability to cool
one room (pull heat from one room) and distribute heat to another room.
By doing this, the efficiency of the system is improved. While this is
effective for some applications, there are also additional material and
installation expenses associated with Heat Recovery. For many
applications, the energy savings does not justify the additional
installation costs. Instead, by using proper zoning and system design, a
Heat Pump VRF system can be designed to provide comfort for all
How is the
efficiency of VRF rated?
Prior to January 1, 2010, VRF systems were rated
using the Integrated Part-Load Value (IPLV). This is the same method
used to calculate part-load efficiency of chillers. However, after
January 1, 2010, ASHRAE 1230 defined IEER as the standard rating for VRF
How is IEER
The IEER rating requires that the unit efficiency be
determined at 100%, 75%, 50% and 25% load (net capacity). These
efficiency values are then weighted based on real world conditions with
each efficiency given a weighted value using the following equation:
IEER = (0.020 · EER@100%) + (0.617 · EER@75%) +
(0.238 · EER@50%) + (0.125 · EER@25%)
Because if improved part-load performance of VRF
systems, IEER values should always be better than full load value of the
How is it
possible for a VRF system to produce better part-load efficiency?
When a VRF system is operating at part-load capacity,
the heat transfer across the indoor and outdoor coil is significantly
improved. For example, if a 20 ton VRF system were operating at 50%, it
would be delivering the performance of a 10 ton system. However, this
“10 Ton System” would have the coil surface area of a 20 ton system.
This drastically improves the efficiency of this system
What is the
Heating Seasonal Performance Factor (HSPF)?
HSPF is the total heating output of a heat pump,
including supplementary electric heat, necessary to achieve building
heating requirements during its normal annual usage period. This is
calculated by dividing heating by the total electric power consumed
during the same period.
Does a VRF system require Traps and Sight Glasses?
Because of efficient oil management, a VRF system
does not require any traps or sight glasses. Instead, most of the oil is
collected in the oil separator, located immediately after the
compressor. For the small amount of oil that makes its way into the
system, a VRF system will go into “oil recovery” mode. During oil
recovery, the compressor ramps up and pushes any lingering oil back to
the accumulator where it can be returned to the compressor.
Can I deliver
greater than 10 tons from a 10 ton system?
This is a common misconception. A VRF system often
allows for a greater connected capacity than the condensing unit. This
is beneficial for applications where there are multiple zones which have
a large total capacity, but where every room will not call for
heating/cooling at the same time. A VRF system can shift the load to the
occupied rooms based on changes in demands. However, this system will
never be able to provide more than the maximum total capacity of the
Do VRF Systems
qualify for LEED points?
Yes! Depending on the features which are installed, a
VRF system can qualify for up to 40 LEED points.
A VRF system uses a
combination of advanced electronics and precision mechanical components
to deliver the highest efficiency possible.
As such, the initial cost for a VRF system
tends to be more than most conventional systems. However, when you take
into consideration the quality of the system, ease of installation and
the reduced energy consumption (which represents 80% of the lifecycle
cost of the equipment), a VRF system is almost always the most