Embed Size (px)
Citation preview
Energy Performance of
Low Charge NH3 Systems
in Practice
Stefan S. Jensen
Introduction
Central type, dual compression stage, ammonia
vapour compression systems.
Main Design Features:
• Reciprocating Compressors (One Screw Plant)
• VFD’s on Everything
• Combination of Superheat and Quality Control (DX)
• Evaporative Condensers (No Receiver)
• Hot Gas Defrost
Global Events and Their
Significance for NH3
Why Are COP 21 (Paris) and The Montreal
Protocol Amendment (Kigali) Important for the
Global NH3 Industry?
They Are Potentially Very Good For Business:
• NH3 Has No Direct Global Warming Effect
• Used Correctly NH3 Can Minimize Indirect Emissions
• NH3 is in the 2L Flammability Category Like R32 and a
Range of Synthetic Low GWP Refrigerants
• NH3 is Cheap and Technically/Environmentally Mature
The Refrigeration Plants
Locations Perth Tamworth Lismore Melbourne Townsville
Refriger-
ated vol.,
m³
43,000 10,000 10,000 43,000 31,000
Cool
room,
16°C
Yes No No No Yes
Cool
room, 4°C
Yes Yes Yes Yes Yes
Freezer,
-25°C
Yes Yes Yes Yes Yes
The Refrigeration Plants
Locations Perth Tamworth Lismore Melbourne Townsville
Annex, 4-
8°C
Yes Yes Yes Yes Yes
No. of comp.
stages
2 2 1 2 2
No. of 1st
stage
comps.
2 2 2 2 2
No. of 2nd
stage
comps.
2 2 N/A 2 2
Comp. type Recip. Recip. Screw Recip. Recip.
The Refrigeration Plants
Locations Perth Tamworth Lismore Melbourne Townsville
VFD’s (all) Yes Yes No Yes Yes
Evap. Cond. Yes Yes Yes Yes Yes
Cond. fan
VFD’s
Yes Yes Yes Yes Yes
Evaporator
enhancement
Yes Yes No Yes Yes
Evaporator
fan VFD’s
Yes Yes Yes Yes Yes
NH3 feed DX DX Flooded DX DX
The Refrigeration Plants
Locations Perth Tamworth Lismore Melbourne Townsville
Injection
Control
SH SH Level SH/X SH/X
Defrost Hot Gas Hot Gas Hot Gas Hot Gas Hot Gas
Pipe
Material
Fe Fe Fe 304SS 304SS
Legend:
DX: Dry Expansion
SH: Superheat
SH/X: Superheat + Quality
Fe: Carbon Steel
Energy Consumption
Locations Perth Tamworth Lismore Melbourne Townsville
SEC,
kWh/m³*a
28.3 43.2 105.6 25.8 22.2
SEC = Specific Energy Consumption
Excepting Townsville SEC is for entire facility
Auxiliaries (IT, Light & Power, split A/C systems, fork lift
charging etc.) ~20%
Feasibility of office A/C with NH3 and chilled water/glycol
in lieu of HFC?
The Lismore problem? More about that later
Energy ConsumptionTownsville
PV Panel Contribution
Location Total Annual
Energy
Consumption,
MWh
Record
Period
Refrigerated
Volume, m³
SEC,
kWh/m³*a
Perth (700+219)/9*12
=1,226
1.7.14-
31.3.15
43,000 28.3
219 MWh supplied by PV panels from 1.7.14 to 31.3.15
700 MWh supplied by the grid from 1.7.14 to 31.3.15
Allowance of ~20% for auxiliaries SEC
= 22.7 kWh/m³*a
Perth
PV Panel Contribution
The Lismore Problem
Floating head pressure reduced SEC to 65-85 kWh/m³*a
This remains almost twice as high as Tamworth. Why?
- Single Stage Compression
- No Compressor Speed Control
- Poor Compressor Part Load Efficiency
- Poor Compressor Combination
Locations Perth Tamworth Lismore Melbourne Townsville
SEC,
kWh/m³*a
28.3 43.2 105.6 25.8 22.2
The Lismore Problem
Ener
gy c
on
sum
pti
on
[kW
h/m
on
th]
Month
Monthly Energy Consumption Comparison
The Lismore ProblemCompressor Combination
Combination #1: Single Stage Screw Compressor
Combination #2: Single Stage Screw Compressor with Economizer (e)
Combination #3: Single Stage Screw and Dual Stage Reciprocating Compressor
Combination #4: Single Stage Screw (e) and Dual Stage Reciprocating
Compressor
Combination #5: Dual Stage Screw Compressor
Combination #6: Dual Stage Screw and Dual Stage Reciprocating Compressor
Combination #7: Dual Stage Reciprocating Compressors
Pattern I: Combination of Plates and Freezer Stores, Load Variation 10-100%
Pattern II: Combination of Blasts and Freezer Stores, Load Variation 40-100%
The Lismore Problem
Compressor
combination
1 2 3 4 5 6 7
Screw [kW]
Recip. [kW]
1x500
-
1x500
-
1x452
1x48
1x452
1x48
1x500
-
1x452
1x48
-
3x150
1x50
Pattern I,
[MWh/a]
1,845 1,812 740 725 898 665 675
Pattern II,
[MWh/a]
1,890 1,825 1,440 1.370 1,250 1,150 1,075
Compressor Combination
No VFD’s and No Medium Temperature Loads
Source: Lorentzen, Gustav, Energiøkonomisering i Kjøleteknikken, Scandinavian Refrigeration 4/1981
= Dual Stage Compression
= Economizer
Low Charge NH3 vs. HFCLow Charge NH3
Heat Loads LT HT
Flour Room, 16°C 11.1
Cool Room, 4°C 51.2
Freezer, -25°C 173.7
Annex, 4°C 166.4
Total, 43,000 m³ 173.7 228.7
Monthly kWh Cost A$13,752
(04/2015)
Monthly Supply (04/2015) 81.2 MWh
Heat Loads LT HT
Freezer 1, -25°C 88.8
Freezer 2, -25°C 94.8
Cool Room 1, 4°C 46.0
Cooler Corridor, 4°C 6.0
Cool Room 2, 4°C 17.6
Dock, 4°C 41.1
Annex, 4°C 82.1
Total, 22,000 m³ 183.6 192.8
Monthly kWh Cost A$ 42,000 (avg.)
All Heat Loads in [kW]
Air Cooled HFC
Low Charge NH3 vs. HFC
Monthly Supply of ~80
MWh is not unusual
Monthly kWh Consumption
Is It the NH3 That Does It…Or Are Other Factors Affecting Energy Performance?
Item Energy Conservation Factor Percentage
Impact, [%]
1 Selection of Compressor Type 15-25
2 Evaporator Fan Speed Control 15-25
3 Evaporator Design 5-25
4 Compressor Capacity Control 10-20
5 Compressor Turn-Down versus Load Variation 0-15
6 Condenser Size, Fan Speed Control and Efficiency 5-10
7 Liquid Injection Control into The Evaporators 5-10
8 Elimination of Liquid within Suction Lines 2-15
9 Low Friction Schedule 10 304SS in lieu of Carbon Steel
Piping
1-2
Is It the NH3 That Does It…Or Are Other Factors Affecting Energy Performance?
Item Factor Reference
1 Compressors Practical comparison between two systems
2 Evaporator VFD Practical comparison between two systems
3 Evaporator
Design
Practical experience from several systems
4 Capacity Control Retrofitting of VFD’s to dual stage screw system
(Sydney)
5 Turn-Down See Tamworth and Gustav Lorentzen Table
6 Condenser See Tamworth example
7 Injection Practical measurements of differences
8 Dry Suction Theoretical estimate
9 304SS Measurement at Truganina
Plant Images
Perth
Lismore
TownsvilleTamworth
Melbourne
Latest Jobs Not DiscussedWith Higher Mobility and Lower NH3 Charges
Medium Temperature Secondary Refrigerant Loop and Horizontal Vessels
~0.7 kg/kW or
~5 lbs/TR
Latest Jobs Not DiscussedWith Higher Mobility and Lower NH3 Charges
Ambient Air Defrost i.e. No Need to
Accommodate Defrost Condensate
~1 kg/kW – Capacity 197 kW
Operating NH3 Inventory ~2 kg
Discussion….or Why Bother With Synthetic Refrigerants?
- The Energy Performance of Low Charge NH3 is Up To 2/3 Better than HFC
- NH3 Belongs to the 2L Flammability Category Like R32 and Many HFO’s
-Additional Capital Cost of Central Low Charge NH3 Usually Returned in 3 Years
- Loss of NH3 Charge in One of Three Freezer Coils Usually Yields <200 ppm
NH3 concentration in the refrigerated space
- Use of Low Friction 304SS Piping Extends Plant Durability Significantly
- Central Type Low Charge NH3 Plants Are Extendable Like Liquid Overfeed
Plants
- Exceptionally Low Indirect Emissions IF DESIGNED & CONTROLLED
CORRECTLY
- No Direct Refrigerant Emissions
- Completely Future Proof
- High Degree of Operator Safety
