variable refrigerant flow(vrf) ppt
TRANSCRIPT
S.EZHIL RAJ
M.E-THERMAL(R&AC)
1
VARIABLE REFRIGERANT FLOW
(VRF)
OUTLINE
2
INTRODUCTION
HISTORY
HVAC SYSTEMS
WHAT IS VRF ?
TYPES OF VRF
DESIGN FEATURES
BUILDING CHARACTERISTICS
APPLICATION
CONCLUSION
INTRODUCTION
3
Controlled refrigerant is supplied in the evaporator
unit as per load requirement.
No intermediate medium for the heat exchange which
makes it efficient.
In a VRF system, multiple indoor fan coil units may be
connected to one outdoor unit.
HISTORY
4
Variable refrigerant flow (VRF), also known
as variable refrigerant volume (VRV), is invented
in Japan by Daikin company in 1982.
Daikin had registered the VRV term as an official
trademark. All other companies use VRF for their
similar HVAC systems.
Eventually, VRF is the more common term
for these types of systems, and this is the term that will
be used for the rest of the article.
Split Air-conditioning
5
It consists of one indoor unit along with an
outdoor unit constitute a single split AC.
source-carrier
Few advantages and Disadvantages
of Spilt AC’s
6
Advantages:
These AC’s have low initial cost
Ease of installation
No ducting required
Each system have own control.
Disadvantages:
Distance between indoor and outdoor unit should not be greater than 100- 150 ft otherwise the performance will suffer.
Limited air throw.
Multi-Split Systems
7
There are multiple evaporator units connected to
one external condensing unit. These type of
systems were designed mainly for small to
medium commercial applications.
Each indoor unit has its own set of refrigerant
pipe work connecting it to the outdoor unit.
SOURCE-DAIKEN
Multi-Split Systems
8
Advantages of Multi-splits:
No need of duct work installation.
System efficiency improves then individual Split unit.
Multi-splits are suitable for single thermal zone applications i.e. either for cooling mode or heat mode.
Drawbacks:
Main Drawback is that Individual system control not possible.
In this systems whole system will turn OFF or ON completely in response to a single thermostat. These systems are therefore not suitable for areas/rooms with variable heat gain/loss characteristics
Variable Refrigerant Flow
Systems
9
Adjust cooling and heating by adjusting refrigerant
flow and variable speed compressor .
Indoor units can be in different modes .
VRF systems are equipped with enhanced features like
inverter drives, pulse modulating electronic expansion
valves and distributed controls.
Types of VRF systems
10
Cooling only systems – those systems can only cool.
Heating is not available. Fan and Dry modes are
available for each indoor unit independently.
Heat Pump systems – All the indoor units can either
heat or cool . Fan and Dry modes are available for each
indoor unit independently.
Heat Recovery systems – These systems are the most
sophisticated ones, where cooling and heating may be
available by each indoor unit, independently, at the
same time.
VRF heat pump systems
11
VRF heat pump systems permit heating or cooling in
all of the indoor units but not simultaneous heating and
cooling.
When the indoor units are in the cooling mode, they
act as evaporators; when they are in the heating mode,
they act as condensers.
These are also known as two-pipe systems.
VRF heat pump systems
12
SOURCE-DAIKEN
Heat Recovery VRF system (VRF-
HR)
13Source-DAIKEN
2 PIPE WITH BC VRF –HR
SYSTEM
14SOURCE-DAIKEN
VRF-HR
15
Typically, extra heat exchangers in distribution boxes are used to transfer some reject heat from the superheated refrigerant exiting the zone being cooled to the refrigerant that is going to the zone to be heated.
It should be noted that this perfect balance of heating and cooling demand is unlikely to occur for many hours each year, but whenever mixed mode is used energy is saved.
Units are now available to deliver the heat removed from space cooling into hot water for space heating, domestic hot water or leisure applications, so that mixed mode is utilized for more of the year.
DESIGN FEATURES
16
Separation tubes and Header
A separation tube has 2 branches whereas a header has more
than 2 branches. Either of the separation tube or header, or
both, can be used for branches. However, the separation tube
is never provided after the header because of balancing issues
DESIGN FEATURES
17
The compressor unit includes two or more scroll or
rotary compressors which is an inverter-controlled
variable-speed VRF compressor. The variable-
speed compressor units are rated at significantly
higher part-load efficiency than constant-speed
systems.
SOURCE-CARRIER
Compressor Efficiency
18
SOURCE-CARRIER
DESIGN FEATURES
19
Electronic Expansion Valve (EEV) instead of
Thermostatic Expansion Valve (TXV)
TXV valves are spring actuated (mechanical)
Prone to hunting (overfeeding or starvation of
refrigerant)
Source-CARRIER
DESIGN FEATURES
20
Inverter Technology
Converts AC to DC and then modulate to desired
frequency required for the desired motor load.
• Multiple or single inverter driven compressor is
used
SOURCE-SAMSUNG
Pipe Design
21
The long pipe lengths will introduce pressure losses in
the suction line and, unless the 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.
The maximum allowable length varies among different
manufacturers.
Building Characteristics
22
The maximum allowable vertical distance between an
outdoor unit and its farthest indoor unit is 50m
The maximum permissible vertical distance between
two individual indoor units is 15m,
The maximum overall refrigerant piping lengths
between outdoor and the farthest indoor unit is up to
180m. Note: The longer the lengths of refrigerant
pipes, the more expensive the initial and operating
costs.
23SOURCE-CARRIER
ADVANTAGES
24
Energy Saving claimed upto 40 %.
High COP.
Space saving
Lesser Noise
Precise temperature control
Simultaneous heating and cooling (three-pipe
VRF heat recovery system only)
Heat recovery
Zoned comfort
LIMITATIONS
25
Initial cost is High ,since additional backup unit is
needed
Separate Ventilation system
Refrigerant Piping
Environmental Concerns
For high rise building the system cannot be used
Source-DAIKEN
Applications
26
VRF systems may be a particularly good option for
buildings with multiple zones or wide variance
heating/cooling loads across many different internal
zones.
These systems provide individual control and are the
most versatile of the multi-split systems. Hotels,
schools and office buildings are good examples.
CONCLUSION
27
The variable refrigerant flow system is considered
to be one of the most promising energy saving
technologies gaining its momentum in recent years.
A viable energy efficient technology is needed to
conserve energy as well as to achieve better
human comfort. So this is been relatively new and
efficient way to design HVAC system with VRF
technology.
References
28
Goetzler, W. (2007). Variable refrigerant flow
systems. ASHRAE Journal.
VARIABLE REFRIGERANT FLOW SYSTEMS
Technology Overview ASHRAE
NB/PEI,SEPTEMBER 2011 Roger Nasrallah, ing.
Enertrak in
http://www.ashrae.in
http://totalclimatecontrol.com.au/heat-recovery-
vrf-system-vrf-hr/