OBJECTIVES
IIn this
thi chapter,
h t student
t d t can :
- How to calculatate and know installation
criterion
it i forf refrigerant
fi t piping
i i
- Understand the function of some vessels and
other
th accessories i such h as : sight
i ht glass,
l solenoid
l id
valve….
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 2
REFERENCES
[1].
[1] R fi
Refrigerant
t I d ti l
Industrial H db k Th
Handbook-The
McGraw-Hill Companies.
[2] Trane,
[2]. T D f
Danfoss t h i l document
technical d t
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 3
REFRIGERANT PIPING
1. Design principles:
- Must
M t supply l sufficient
ffi i t liquid
li id flowrate
fl t t
to
evaporator
- Pressure drop must be low
- Have enough velocity to draw oil back to
compressor
g
- Don’t let refrigerant come back to compressor
p
- Piping must be dry and clean
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 5
REFRIGERANT PIPING
2. Suction pipe:
- Undersizing the suction line reduces
compressor capacity by forcing it to operate at a
lower suction pressure to maintain the desired
evaporator temperature.
- Oversizing the suction line increases initial
project costs and may result in insufficient
refrigerant gas velocity to move oil from the
evaporator to the compressor
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 7
REFRIGERANT PIPING
Pressure drop arcording to saturate
temperature reduction by ASHRAE standard:
Refrigerant velocity in suction pipe should be
7~12m/s. Refrigerant velocity should higher 3m/s
for horizontal pipe and higher than 7m/s in
vertical pipe
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 8
REFRIGERANT PIPING
- While operating, the suction line is filled with
superheated refrigerant vapor and oil. The oil flows
on the bottom of the pipe and is moved along by the
refrigerant gas flowing above it.
- When the system stops, the refrigerant may
condense in the pipe depending on the ambient
conditions. This may result in slugging if the liquid
refrigerant is drawn into the compressor when the
system restarts.
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 9
REFRIGERANT PIPING
- To promote good oil return, suction lines
should be pitched 1/8 inch per foot (10.4 mm/m) in
the direction of refrigerant flow.
- Evaporator connections require special care
because the evaporator has the potential to contain
a large volume of condensed refrigerant during off
cycles.
- To minimize slugging of condensed refrigerant,
the evaporators should be isolated from the suction
line with an inverted trap as shown
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 10
REFRIGERANT PIPING
The trap should extend above the top of the
evaporator before leading to the compressor.
- With multiple evaporators, the suction piping
should be designed so that the pressure drops are
equal and the refrigerant and oil from one coil
cannot flow into another coil.
- Traps may be used at the bottom of risers to
catch condensed refrigerant before it flows to the
compressor. Intermediate traps are unnecessary in
a properly sized riser as they contribute to pressure
drop.
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 11
REFRIGERANT PIPING
- Usually with commercially produced air
conditioning equipment, the compressors are
“prepiped” to a common connection on the side of
the unit.
- Suction line filter driers are available to help
clean the refrigerant before it enters the
compressor. Because they represent a significant
pressure drop -> be added in some circumstances
such as after compressor burnout.
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 12
REFRIGERANT PIPING
+ Double suction riser:
- In a double suction riser at full capacity, the
refrigerant flow passes through both risers with
enough velocity to move the oil.
- At minimum capacity, oil in the riser flows
backward and fills the trap at the bottom. Once the
trap is full of oil, refrigerant flow through the large
diameter riser is cut off and only refrigerant gas
flows through the smaller diameter riser.
- The sum of the two risers is sized for full
capacity. The smaller diameter riser is sized for
minimum capacity.
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ
15
REFRIGERANT PIPING
3. Discharge pipe:
- Undersizing discharge lines will reduce
compressor capacity and increase compressor
work. Over sizing discharge lines increases the
initial cost of the project and may result in
insufficient refrigerant gas velocity to carry oil back
to the compressor.
- Discharge lines should be sized for no more
than 2 to 3°F (1.1 to 1.7°C) pressure loss. The
actual pressure drop in PSI will depend upon the
refrigerant.
12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 18
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