By KLAAS VISSER Dip.Mar.Eng.
Hon M.IIR, M. Inst. R, M.IIAR, M.ARA, M.KNVvK, Meurammon
PRINCIPAL - KAV CONSULTING Pty. Ltd
P.O. BOX 1146, KANGAROO FLAT, Vic 3555 AUSTRALIA
Tel:- +61 3 54 479 436 Fax:- +61 3 54 474 896
Email: - [email protected]
INTRODUCTION
Slide 2
•
CO2 evaporative condensers and gas coolers enable the efficient
application of CO2 refrigeration anywhere in the world
•
At 28°C ambient Wet Bulb Temperature (WBT) 31°C CO2 gas cooler exit
temperature, i.e. the critical temperature, is easily achievable
•
Ambient design WBTs above 28°C are experienced in very few locations in
the world like The Gulf and Vietnam
•
Suction Heat Exchangers are obviated in virtually all applications
•
Energy recovery from expanding transcritical fluid no longer has much
merit with the high COPs resulting from evaporative condensers and gas
coolers.
•
Suitable for conversion of existing HFC/CO2 cascade systems and
expensive CO2 cascade condensers are no longer required.
•
Large scale application of CO2 to all refrigeration and AC duties awaits the
availability of larger compressors
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
Performance of a Bock HGX 46/345-4SCO2T
CO2 Compressor at 50HZ.
18
+10°C SST, 5K SSH, 3K Liq. Subc.
+5°C SST, 5K SSH, 3K Liq. Subc.
−5°C SST, 5K SSH, +5°C gc out
−5°C SST, 5K SSH +10°C gc out
17
16
15
−5°C SST, 5K SSH, 5K Liq. Subc.
14
→ Raw COP = Q ÷ BkW
13
12
11
10
2
9
3
8
7
6
5
4
4
3
5
2
16
18
20
22
24
26
28
30
→ Saturated Condensing Temp.,°C
Figure 1. CO2 Compressor COP variation with
subcritical saturated condensing temperature.
Slide 3
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
Compressor Make & Model for R717, R22, R507A, R290 &
R134a: Mycom 8 WB, 1,000 rpm
8
7
Compressor Make & Model for CO2: Bock HGX 46/345 - 4S CO2 T @ 50 Hz
6
→ COP
R717
R22
R507A
R290
R134a
Saturated Suction Temp: ‒8°C
Suction Superheat: 5 K
Liquid Subcooling: 3 K
−5°C SST, 5K SSH, +5°C gc out
−5°C SST, 5K SSH +10°C gc out
−5°C SST, 5K SSH, 5K Liq. Subc.
5
4
3
2
16
18
20
22
24
26
28
30
→ Saturated Condensing Temp., °C
32
34
36
38
40
Figure 2: The variation in COPs of R717, R22, R507A, R290 and R134a with
Saturated Condensing Temperature compared to subcritical CO2 from 16 to
30°C Saturated Condensing Temperature
Source: Bock VAP10 Software
Slide 4
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
CO2 compressor performance for chilled water AC & retrofit.
Transcritical Compressor: BOCK, 50 Hz
MODEL: HGX 46/345-4SHCO2T; 30.2m3/h, 37 kW
Sat. Suction Temp.: +5C
Suction Superheat: 5K
6.66
7
6.5
COP @ 75 bar discharge pressure
COP @ 80 bar discharge pressure
COP @ 90 bar discharge pressure
6.31
6.05
6
5.92
5.73
→ COP
5.5
5.5
5.39
5.11
5
5.02
5
4.85
4.5
4.6
4.58
4.43
4.28
4.21
4
3.98
4.24
4.04
3.96
3.73
3.5
3.58
3.47
3.18
3
5
10
15
20
25
30
35
→ Gas Cooler CO2 Exit Temperature, °C
-4
2
8
14
20
26
→ Approximate Ambient Wet Bulb Temperature, °C
32
Figure 3: COP variation with gas cooler CO2 leaving
temperature at 75-100 bar discharge pressure, +5°C SST, 5K SSH
Source: Bock VAP10 Software
Slide 5
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
Figure 4. USA climate zones with approximate percentage
incidence of subcritical CO2 condensing annually
Slide 6
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
Figure 6. Virtually all of Continental Europe can enjoy
subcritical CO2 condensing 100% of the time
Slide 7
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
ADVANTAGES OF CO2 EVAPORATIVE CONDENSERS AND GAS
COOLERS
•
Lower discharge pressures mostly below critical point
•
Lower CO2 exit temperature from gas cooler
•
A high cost CO2 cascade condenser is no longer required
•
Above three factors increase capacity and reduce energy consumption –
High COP
•
Compressors have easier operating conditions both lower pressures and
temperatures – reduced maintenance, higher reliability, lower oil
consumption
•
High pressure of CO2 allows much lower discharge pressures down to
15°C condensing and even lower
•
Evaporative CO2 condensing outperforms all other refrigerants, including
ammonia, over a whole year running with surprisingly high COPs
DISADVANTAGES
Slide 8
•
Higher capital cost but offset by elimination of a cascade condenser
•
Consumes water
•
Poses a minor potential legionella threat if not maintained properly
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
ADVANTAGES OF HYBRID CO2 EVAPORATIVE CONDENSERS AND GAS
COOLERS
•
Less air circulated
•
Less water consumption
•
Less energy consumption
•
Air cooled section more effective with adiabatically precooled air
•
Smaller footprint
•
High discharge air temperatures reduce legionella threat
•
No plume formation – much less if any free water in the air discharge
•
Allows 100% air cooled operation in winter in cool climates
DISADVANTAGES
•
Slide 9
More expensive than evaporative condensers
ATMOsphere 2014, San Francisco USA, 18-19 June 2014
Slide 10
ATMOsphere 2014, San Francisco USA, 18-19 June 2014

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