Automation in Refrigeration Cycle (2)

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REFRGERATION ENGINEERING
AUTOMATION
IN REFRIGERATION CYCLE
Võ Lưu Lan Vi – 1552428
Lại Đỗ Tuấn Hùng – 1552153
Nguyễn Minh Anh – 1552023
Huỳnh Huy Phương Tường – 1552421
CONTENT
1. Fundamentals of Automation in Refrigeration cycle
• 1.1. Introduction
• 1.2. Classification
• 1.3. Introduction to a Typical Automation System for
Refrigeration Cycle
2. Automation in Refrigeration cycle
• 2.1. Automation in Compressor
• 2.2. Automation in Condenser
• 2.3. Automation in Evaporator
1. Fundamentals of Automation in Refrigeration cycle
1.1. Introduction
FUNDAMENTALS
1.1. Introduction
Using additional equipment
What is
Automation in
Refrigeration
system??
Programmed settings
Safely & Automatically
 Optimized working condition
1.1. Introduction
FUNDAMENTALS
Maintain operating parameters within an acceptable limit
Protect operators from risks during operation
Advantage
s
Keep the system working stable
•
•
•
•
•
More reliable than manual operation
Increase system efficiency
Product quality 
Equipment lifespan
Accuracy 
Energy loss 
Operating cost 
1.1. Introduction
FUNDAMENTALS
Hardware components
 “Control loops”
Software components
Adjust & Measure
process variables:
temp.,pressure...
FUNDAMENTALS
1.1. Introduction
 “Open-loop
control system”
• Non-feedback system
• Continuous control system: output has no influence on control action of input
• Disadvantage: Poor to handle with disturbances
Example:
FUNDAMENTALS
1.1. Introduction
 “Closed-loop
control system”
• Feedback control system
• An error signal = reference input – actual output is generated to achieve
desired output condition
• Advantage: Sensitive to disturbance  reduce error
Example:
error signal = required dryness – actual dryness
1. Fundamentals of Automation in Refrigeration cycle
1.2. Classification
FUNDAMENTALS
1.2. Classification
Operating
parameters
Principle
• Mechanical
• Electrical
• Mechanical
& Electrical
combined
•
•
•
•
Pressure
Temperature
Humidity
Liquid level
Adjustment
techniques
• Continuous
control: P, PI, PID
P:Proportional
I: Intergrative
D: Derivative
• 2-point control
(ON-OFF)
Drive
mechanism
• Direct:
mechanical
(valve...)
• Indirect:
energy
(electrical,
electronic,
compressed
air...)
Objective
• Systematic:
refrigerator,
heat pump,
air con.
• Equipment:
compressor,
condenser,
evaporator,..
.
1. Fundamentals of Automation in Refrigeration cycle
1.3. Introduction to a Typical Automation System for
Refrigeration Cycle
FUNDAMENTALS
1.3. Introduction to
a Typical Automation System for Refrigeration Cycle
Compressor controls: Oil
temp; Suction press; Discharge
press; Oil mass flowrate...
Condenser controls:
- Water cooled condenser
controls: condensing pressure,
cooling water flowrate.
- Air cooled condenser
controls: air flowrate,
minimum condensing
pressure.
- Liquid level inside condenser.
Evaporator controls:
evaporating temperature,
evaporating pressure,
2. Automation in Refrigeration cycle
2.1. Automation in Compressor
AUTOMATION IN REF. CYCLE
2.1. Automation in Compressor
Compressor Controls
1. Compressor Capacity Controls
2. Discharge Temperature Control with Liquid Injection
3. Suction Pressure Control
4. Reverse Flow Control
2.1. Automation in Compressor
2.1.1. Compressor Capacity Controls
• Step Control
 to unload cylinders in a
multi-cylinder compressor
 to open and close the
suction ports of a screw
compressor
 to start and stop some
compressors in a multicompressor system.
2.1. Automation in Compressor
2.1.1. Compressor Capacity Controls
• Variable Speed Control
 A two-speed electric motor
or a frequency converter can
be used to vary the speed of
the compressor.
 Compressor capacity can be
regulated by running at the
high speed when the heat
load is high (e.g. cooling
down period) and at the low
speed when the heat load is
low (e.g. storage period).
2.1. Automation in Compressor
2.1.1. Compressor Capacity Controls
• Hot Gas Bypass
‐ Is applicable to compressors with
fixed capacities.
‐ Part of the hot gas flow on the
discharge line is bypassed into the
low pressure circuit.
‐ Help decreasing the refrigeration
capacity in two ways: by
diminishing the supply of liquid
refrigerant and releasing some
heat into the low pressure circuit
2.1. Automation in Compressor
2.1.2. Discharge Temperature Control with Liquid Injection
Liquid refrigerant from the outlet of the condenser or receiver is injected into
the suction line, the intermediate cooler, or the side port of the screw
compressor.
2.1. Automation in Compressor
2.1.3. Suction Pressure Control
2 ways to overcome overloading in compressor:
 Start the compressor at part
load. The capacity control
methods can be used to start
compressor at part load
 Install a back pressure controlled
regulating valve in the suction
line.
2.1. Automation in Compressor
2.1.4. Reverse Flow Control
• For piston compressors, reverse
flow can result in liquid
hammering.
• For screw compressors, reverse
flow can cause reversed
rotation and damage to the
compressor bearings.
To avoid this reverse flow, it is necessary to install a check valve on the outlet of
the oil separator.
2. Automation in Refrigeration cycle
2.1. Automation in Condenser
AUTOMATION IN REF. CYCLE
2.2. Automation in Condenser
Why Condenser need
automation control?
• To control the condenser capacity when the ambient
temperature is low  Condensing pressure is maintained
above the minimum acceptable level
• To save cooling water for water cooled condensers
AUTOMATION IN REF. CYCLE
2.2. Automation in Condenser
Air cooled condenser
Water cooled
condenser
Evaporative
condenser
2.2. Automation in Condenser
2.2.1.Air cooled condenser
Refrigerant control
Air control
2.2. Automation in Condenser
2.2.1.Air cooled condenser
Refrigerant control
2.2. Automation in Condenser
2.2.1.Air cooled condenser
Air control
The sensor of
temperature role
If the temperature decrease (lower than setting
value)  First fan will be switched off.
The temperature continue to decrease (lower than
setting value of the second fan)  Second fan will
be switched off.
2.2. Automation in Condenser
2.2.1.Air cooled condenser
Air control
Orientation setting values:
• The last fan has the lowest temperature, and the first one is
the highest.
• Setting temperature range should be divided equally by the
number of fans of the condenser.
• Condensing temperature usually higher than the ambient
temperature about 15oC.
2.2. Automation in Condenser
2.2.2. Water cooled condenser
2.2. Automation in Condenser
2.2.3. Evaporative condensers
2. Automation in Refrigeration cycle
2.3. Automation in Evaporator
2.3. Automation in Evaporator
2.3.1. Direct expansion control
Thermostatic expansion control
2.3. Automation in Evaporator
2.3.1. Direct expansion control
Electronic expansion control
ả
2.3. Automation in Evaporator
2.3.2. Pumped liquid circulation control
2.3. Automation in Evaporator
2.3.3. Defrost
• Hot gas defrost for DX evaporator
2.3. Automation in Evaporator
2.3.3. Defrost
• Hot Gas Defrost for Pumped Liquid Circulation Air Coolers
2.3. Automation in Evaporator
2.3.4. Multi temperature changeover
S2: CVP is preset to 3.6 bar, and
P: CVP is preset to 4.4 bar.
I: EVM pilot opens. Hence the
evaporating pressure is controlled
by S2: CVP.
II: EVM pilot closes. Hence the
evaporating pressure is controlled
by P: CVP
2.3. Automation in Evaporator
2.3.5. Media temperature control
• Media temperature control using pilot operated valve ICS
2.3. Automation in Evaporator
2.3.5. Media temperature control
• Media temperature control using direct operated valve
2.3. Automation in Evaporator
SUMMARY
2.3. Automation in Evaporator
SUMMARY
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