co booster systems from a...non-residential refrigeration 150 2020 ac (non-residential and...
TRANSCRIPT
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CO2 Booster Systems From a
Service Mechanic’s Perspective
E360 Forum • Raleigh, N.C. • March 1, 2017
Andre PatenaudeDirector — CO2 Business Development
Emerson
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Agenda
Global Regulations
CO2 System Architecture
CO2 as a Refrigerant
Seven Keys to Servicing a CO2 Refrigeration System
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Global Regulations Confusing Time for End Users
• Rule-making process begins in 2017 with possible final rule late 2018
CARB: Short-lived climate pollutant
reduction strategy – proposal April 2016
Commercial application GWP limit Date
All refrigerant sales* 2,500 2020
Non-residential refrigeration 150 2020
AC (non-residential and residential) 750 2021
*Exception for recycled or reclaimed refrigerant
Environmental Canada (EC)
proposal November 26, 2016
Commercial application GWP limit Date
Refrigeration – centralized
systems (MT/LT racks)1,500 2020
Refrigeration – condensing units 2200 2020
Refrigeration – LT stand-alone 1,500 2020
Refrigeration – MT stand-alone 700 2020
Foams 150 2021
Mobile refrigeration 2,200 2025
AC – chillers 700 2025
Domestic refrigeration 150 2025
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CO2 aka Refrigerant R-744
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CO2 DX
CO2 DX
TRANSCRITICAL
BOOSTER
CO2 DX
CASCADESECONDARY
Selecting the Best System Booster vs. Cascade vs. Secondary
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R-744 vs. HCFC/HFC
R-744 HFC / HCFC Impact on R-744 Systems
Global Warming Potential
Ozone Depleting Potential
1
0
1,300 to 4,000
0 for HFC / High for HCFC
Future Proof
Future Proof
Saturation Pressures
Operating Pressures
Standstill Pressures
(Power Outages)
Higher
Higher
Higher
Rapid Pressure Rise
Lower
Lower
Lower
Lower
Additional Safety Design
Specialized Components
Relief Valves/Tanks/ etc.
Pressure Relief Venting
Inert Gas
Flammability
Toxicity
Odor
Yes
A1
No
None
Yes
A1
No
None
Copper May Be Used
Not Flammable
Asphyxiate in High Concentrations
Leak Detection Required
Volumetric Mass Flow
Heat Transfer
High Ambient Performance
Low Ambient Performance
Higher
Higher
Lower
Good
Lower
Lower
Higher
Good
Smaller Tubes and Compressors
Better Thermal Efficiency
System Design to Compensate
Subcritical Cascade Favorable
Cost per Pound
Complexity of Systems
Adoption
Legislation/Regulations
Low
Higher
Low
Low
Higher
Lower
Higher
Higher
Economical
Higher First Cost, Training and Experience
Higher First Cost
Long-term Viability
R-744 Provides Many Benefits Over HFC Options.6
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Refer to MSDS sheets.
Toxicity Levels
• 5,000 ppm (0.5 vol. % in air)
• 10,000 ppm is 1 vol. % in air
• Main alarm 15,000 ppm
• Levels from 0.04% to 20%
• TLV for CO2 = 5,000 PPM
• TLV for R-404A = 1,000 ppm
Max. workplace concentration initial alarm
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Sublimation of Dry Ice
Dry Ice
Sublimation of Dry Ice
• CO2 expands 845 times going from solid to gas
• 1 liter of dry ice will produce 845 liters of gas at 15 °C at 14.7 psi
• Relative vapor density vs. air is 1.52
– It collects low areas
• Leak devices; locate approx. 18” off ground
• When CO2 turns to dry ice in the system, as it warms up, pressure
will build very quickly; must be aware of this.
• If an ice plug forms in a charging line set, flow will stop.
– Extreme care must be taken when this happens.
– The blockage will cause the CO2 trapped between the source
and the “plug” to rise very quickly.
– As soon as the plug melts
– If high-pressure source is not closed off, high pressure will force
the ice plug out the hose with a tremendous force.
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Refrigerant R-744 (CO2) R-404A R-134a R-407A R-407F
Temperature at
atmospheric pressure
-109.3 °F
(-78.5 °C)
Temp. of
dry ice
-50.8 °F
(-46°C)
(Saturation
temp.)
-14.8 °F
(-26 °C)
(Saturation
temp.)
-41.8 °F
(-41 °C )
(Mid-point
saturation temp.)
-45. 5 °F
(-43 °C )
(Mid-point
saturation temp.)
Critical temperature 87.8 °F
(31 °C)
161.6 °F
(72 °C)
213.8 °F
(101 °C)
179.6 °F
(82 °C)
181.4 °F
(83 °C)
Critical pressure 1,056 psig 503 psig 590 psig 641 psig 674 psig
Triple-point pressure 61 psig 0.44 psia 0.734 psia 0.18 psia TBC
Pressure at a saturated
temperature of 20 °C815 psig 144 psig 68 psig 133 psig 139 psig
Global warming potential 1 3,922 1,430 1,990 1,824
Basic Properties of R-744 With R-404A and R-134a Refrigerants Commonly Used in the Retail Sector
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Basic Properties of R-744 With R-404A and R-134a Refrigerants Commonly Used in the Retail Sector (continued)
Refrigerant R-744 (CO2) R-404A
Temperature at
atmospheric pressure
-109.3 °F
(-78.5 °C)
Temp. of
dry ice
-50.8 °F
(-46 °C)
(Saturation
temp.)
Critical temperature 87.8 °F
(31 °C)
161.6 °F
(72 °C)
Critical pressure 1,056 psig 503 psig
Triple-point pressure 61 psig 0.28.9 Hg
Pressure at a saturated
temperature of 20 °C815 psig 144 psig
Global warming potential 1 3,922
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P. 7
Liquid and gas density
are the same only at
critical point.
https://www.youtube.com/watch?v=-gCTKteN5Y4
Pressure-Enthalpy Diagram of CO2
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Pressure-Enthalpy Diagram, CO2
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Transcritical Systems Can “Transition” From Subcritical to Supercritical
p. 17
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Climatic Impact of CO2 System Architectures
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European CO2 Market
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More Than 10,900 CO2 Transcritical Stores Worldwide
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Medium-
Temperature
R-404A
Low-
Temperature
R-404A
162 °F
Critical Point
R-404A
162 °F
Critical Point
R-404A
-20 °F Low
Temp.
+25 °F
Med.
Temp.
Products
• Mechanical TXV
• Mechanical EPR
• Mechanical CPR
and differential
valves
• Mechanical
pressure controls
• Typically, on/off
compressor
control
Traditional Supermarket System
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CO2 Transcritical Booster Operation
Must Use
• Facility management system
• Electronic expansion valves
• High-pressure gas cooler
controls
• High-pressure and bypass
valves
• Superheat/de-superheating
valves
• Pressure transducers/temp.
sensors
• Electronic oil controls
• VFD condenser fans
• Digital or VFD compressor
suction group
700 -
1600
psig
580
psig
580
psig200
psig
450
psig
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Transcritical CO2 Booster System — Animation
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Seven Keys to Servicing a CO2 Refrigeration System
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Accelerate America Article
2015 Natural
Refrigerant Guide21
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Seven Keys to Servicing a CO2 Refrigeration System
• Three Main Differences Between HFC and R-744 Systems
1. High pressure
2. Low critical point
3. High triple point
• Dealing With Standstill Pressures
4. Managing power outages
5. Managing pressure reliefs
6. How to mitigate risk
• Peculiarities of R-744
7. Managing superheat
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Refrigerant R-744 (CO2) R-404A
Critical pressure 1,056 psig 503 psig
Triple-point pressure 75 psia 0.44 psia
Pressure at a saturated
temperature of 20 °C815 psig 144 psig
Understanding the Differences: R-744 vs. HFC
1. High Operating Pressures
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Understanding the Differences: R-744 vs. HFC (continued)
Where they occur
1. High Operating Pressures
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The coefficient of expansion for R-744 is significantly higher than for
other refrigerants.
• The effect of a 36 °F (20 °C) temperature rise (from 14 °F to 50 °F)
• The pressure will increase from 638 psig (44 bar) to 3,481 psig to (240 bar).
Relationship between temperature and pressure of trapped liquid R-744
Pre
ssu
re (
psig
)
14,503
145
14.5
1,450
36°F
2843 psig
Trapped liquid
Understanding the Differences: R-744 vs. HFC (continued)
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Understanding the Differences: R-744 vs. HFC (continued)
2. Low Critical Pressure (1,055 psig; 87.8 °F)
R-744 transcritical
booster system
https://www.youtube.com/watch?v=GEr3NxsPTOA Video of phase change of CO2
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Efficiencies Great for Cold Climate
1020Hrs/yr
W/Std Gas Cooler
9 Hrs/yr
W/Adiabatic
Gas Cooler
202 Hrs/yr
W/Std Gas Cooler
Atlanta, Ga. Toronto, Ont.
2. Low Critical Pressure
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Understanding the Differences: R-744 vs. HFC
3. High Triple Point (60.4 psig; -69.8 °F)
-109.3 °F
surface temp. of dry ice
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I Fell Victim of Dry Ice During a Training Session
Originally drawn from
top to flash tank —
caused dry ice issue Correctly drawn off
of liquid line FD 29
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Seven Keys to Servicing a CO2 Refrigeration System
• Three Main Differences Between HFC and R-744 Systems
1. High pressure
2. Low critical point
3. High triple point
• Dealing With Standstill Pressures
4. Managing pressure reliefs
5. Managing power outages
6. How to mitigate risk
• Peculiarities of R-744
7. Managing superheat
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What’s a Standstill Pressure?
Standstill Pressure Occurs When System Is not Operating.
Effect on Standstill Pressures
• Ambient when below critical point; 68 °F (20 °C) = 812 psig
• Ratio of refrigerant charge to system volume
• For most systems, the standstill pressure is greater than the maximum operating pressure.
• When the standstill is the same as maximum operating pressure, then relief valves will vent unless there are means in place to reduce it.
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CO2 Booster Refrigeration System
4. Managing Pressure Reliefs
Compressor
discharge
135 bar
1,958 psig
PRV vented
to outdoor
110 bar
1,600 psig
PRV
vented to
outdoor
45 bar
650 psig
PRV
vented to
outdoor
45 bar
650 psig
PRV
vented to
outdoor
35 bar
500 psig
PRV
vented to
outdoor
45 bar
650 psig
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Pressure Relief Valve Installation
Flash tank
650 psig
2 PRV with
three-way valve
Gas cooler
1,600 psig
2 PRV with
three-way valve
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Fresh
Frozen
1
2
R-744
section
to atmosphere
Advantage;
• Less stress on PRV
• Less CO2 discharged vs. PRV
• Lowers overall maintenance costs
Generator/UPS source
Unplanned Outages — “Burp Valve”
5. Managing Power Outages
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Fresh
Frozen
1
2
R-744
section
to atmosphere
• Auxiliary condensing unit starts on power failure, which is
powered by generator
• Recirculates liquid from receiver/flash tank to keep the
saturation temperatures below the pressure relief point
Unplanned Outages — Auxiliary Condensing Unit on Generator
Generator Powers Auxiliary
Condensing Unit
5. Managing Power Outages
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Backup Unit and Generator
Generator to keep
controller
and backup unit running
Auxiliary condensing unit
In case of power outage, keeps CO2 receiver temperature
down to prevent pressure relief from blowing off
5. Managing Power Outages
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Managing Power Outages
• Generator and standby condensing units
• Need a refrigerant plan
– Local codes
– Stock, storage
– Getting it to the machine room
• Concerns with resumption of power Semi-hermetic
broken reed
Scroll thrust
surface galled
6. How to Mitigate Risk
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System Startup Sequence, After Resumption of Power
Circuit Is Stage on to Avoid Overloading the Rack
Recovery Sequence After Failure
TIME INTERVAL LT RACK MT RACK
0–3 Minutes Pump down Pump down
3–6 Minutes 25% ON
6–9 Minutes 50% ON
9–12 Minutes 25% ON
12–15 Minutes 75% ON
15–18 Minutes 50% ON
18–21 Minutes 100% ON
21–24 Minutes 75% ON
24–27 Minutes 100% ON
6. How to Mitigate Risk
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Steps to follow:
1. Low-temperature circuit OFF
• Let unit run for 3–5 minutes (minimum)
2. Medium-temperature circuit OFF
• Let gas cooler run for 3–5 minutes (minimum)
3. Turn evaporators OFF
System Shutdown — Planned
Care must be taken when shutting down a CO2 system. Go in stages to prevent
over-pressurization of the system leading to relief valve venting the charge.
6. How to Mitigate Risk
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What Does Your Service Tech Need to Know?
Three Main Differences Between HFC and R-744 Systems
1. High pressure
2. Low critical point
3. High triple point
Dealing With Standstill Pressures
4. Managing pressure reliefs
5. Managing power outages
6. How to mitigate risk
Peculiarities of R-744
7. Managing superheat
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Liquid to Suction Heat Exchanger to Assure Minimum 36 °F SH
7. Managing Suction Superheat
36 °F minimum
superheat
CascadeBooster
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POE Oil Viscosity in CO2 vs. Suction Superheat
Oil temp.
measured
bottom of
sump
36 °F (18 °K SH)Floodback 0 °F (0 °K SH)
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Floodback
Evaporator Cooling With Closed EEV
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Evaporator Cooling With Closed EEV (continued)
• Issue with suction piping free
• Draining down into the case
• Corrected piping
• No free draining
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Charging From a Remote Location
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R-744 CO2 Sensitivity (PPM)
Liquid
Temperature
14 °F
(-10 °C)
32 °F
(-10 °C)
41 °F
(5 °C)
68 °F
(-10 °C)
Very Dry 8 11 13 20
Dry/Caution 14 19 22 34
Caution/Wet 29 39 46 72
Wet 46 63 75 116680 psig MWP
Moisture Indicators and Driers
680 psig MWP
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System Cleanliness/Dryness
System Dryness
Oil Separator
Filter Photo
R744 CO2 Sensitivity (PPM)
Liquid Temperature 14 °F 32 °F 41 °F 68 °F
Very Dry 8 11 13 20
Dry/Caution 14 19 22 34
Caution/Wet 29 39 46 72
Wet 46 63 75 116
Steel Pipe
Special
CO2 Model
System
Cleanliness
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Seven Keys to Servicing CO2 Refrigeration System
• Three Main Differences Between HFC and R-744 Systems
1. High Pressure
2. Low Critical Point
3. High Triple Point
• Dealing With Standstill Pressures
4. Managing Power Outages
5. Managing Pressure Reliefs
6. How to Mitigate Risk
• Peculiarities of R-744
7. Managing Superheat
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Questions?
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