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TECHNICAL PERSPECTIVES OF AND INNOVATION

APPLIED TO CO2REFRIGERATION IN AUSTRALIA K. VISSER

Principal KAV Consulting Pty Ltd,

P O Box 1146, Kangaroo Flat, Vic, 3555, Australia Tel: (03) 5447 9436 Fax: (03) 5447 9805

email: kavconsult@bigpond.com INTRODUCTION

It was none other than his late dear friend Prof. Dr. Gustav Lorentzen who revived the writer‟s interest in

CO2 refrigeration in the mid 1980‟s when the Ozone Depletion potential of CFC‟s and HCFC‟s became

evident. This resulted in the unique International Agreement called the Montreal Protocol to phase out the

use of CFC‟s and HCFC‟s and to prohibit their production and use after certain dates.

Figure 1: The rise, fall and revival of CO2 refrigeration in 130 years|1|

We celebrate Gustav Lorentzen‟s 1993 public call for the revival of the use of CO2 every two years with the

IIR Gustav Lorentzen Natural Refrigerants Conference (IIRGLNRC). The first of these was held in

Hanover, Germany, in May 1994. The 9th

IIRGLNRC was conducted in Sydney, Australia, in April last year

and the 10th

IIRGLNRC will be held in Delft, the Netherlands, in June 2012.

The eminent refrigeration scientist Dr S. Forbes Pearson designed the first application of CO2 in the

modern era in 1992. The system comprised two flooded CO2 evaporators in which the CO2 vapour is

condensed in an ammonia cooled plate heat exchanger. A small demonstration unit was installed in a

small -23o C cold store at Marks and Spencer p.l.c., Kilmarnock, Scotland. CO2 hot gas for defrost was

generated in a CO2 boiler heated by ammonia from the discharge of ammonia compressor. l2l None

other than Gustav Lorentzen called Ref. 2 “A remarkable paper.”

1. THE REVIVAL OF CO2

The term Revival of CO2 is correct. As

Professor RistoCiconkov shows so eloquently

in Figure 2 |3|, CO2 and ammonia were

commonly used in all manner of cooling and

freezing applications from the 1870‟s to the

1940‟s, including cooling for human comfort,

e.g. the cooling in some cinemas in Sydney

until about 1966! But after the advent of

CFC‟s (R12 etc.) in the 1930‟s, the use of

CO2 rapidly declined. Luckily ammonia

(NH3) survived as a Natural Refrigerant for

industrial applications.

The writer has personal experience with CO2

refrigeration on board a ship, which took

frozen meat east bound from Buenos Aires,

Argentina to Yokohama, Japan. Refrigeration

was provided by a CO2 plant. Gustav

Lorentzen told the writer he had the same

The peak of utilizing CO2 as refrigerant Re-activation of CO2 refrigeration

technology (G. Lorentzen)

Proposal to use CO2 as a refrigerant

(Alexander Twining, British patent)

CO2 Compressor

1897

1850 1993 1960 1920 ----------1930 1866

Thaddeus S. C. Lowe, USA Invents CO2 Compressor

Prof. Dr. Gustav Lorentzen

All Natural

NH3 CO2

HCs 1834

ethyl-ether

(R610)

methyl-chloride

SO2

1930

CFC

NH3 CO2

HCs

1950

HCFC

CFC

NH3

1990

HFC

(CFC) HCFC

NH3

2008

HFC

NH3 CO2

HCs Future?

Montreal Protocol 1987

Kyoto Protocol 1997

Risto Ciconkov

Figure 2: A brief history of refrigerants

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experience as a young man before the 2nd

World War sailing between Norway and China.

The first CO2/NH3 cascade plant was installed at a Qantas prepared meals plant in Brisbane, Queensland, in

2001. Since then there have been a number of installations ranging from small CO2/HFC and medium size

CO2/NH3 cascade systems to two transcriticalCO2plants in applications ranging from supermarkets to small

food processing plants.

2. THE SUPERMARKET SCENE IN AUSTRALIA

The supermarket scene in Australia is dominated by the two major operators Woolworths (WW) and Coles

who between them have at least 75% of

the market with WW about 40% and

Coles 35%.

In Figure 3 the total Greenhouse Gas

Emissions (GGEs) in Coles supermarkets

in Australia are shown for a full

operating year |4|. Please note the 14%

of emissions due to direct refrigerant gas

leakage. The figures for WW

supermarkets in Australia are not a lot

different for calendar year 2009. But in

WW‟s New Zealand stores the direct

emissions from refrigerants were 45% of

total emissions, compared to 42% of

indirect emissions due to purchased

electricity. The average leakage rate of

refrigerant gases from most supermarket refrigeration systems is 23%, according to the Australian National

Greenhouse and Energy Reporting Guidelines.

At 30 June 2010, WW had more than 30 carbon dioxide low carbon impact systems – both direct and

indirect – throughout their fleet of supermarkets |6|. We do not know the number of Coles installations.

Both the major operators have plans to reduce GGEs due to refrigeration by reductions in both direct and

indirect emissions, which are linked to each other. CO2/HFC reduce both direct emissions due to reduced

HFC charge in a less leak prone situation and indirect emissions because of an improvement in COP of the

refrigeration system due to improved energy efficiency of cascade systems.

There is an element of enlightened self-interest in the desire of the two Australian supermarket giants

because of the increasing cost of HFC refrigerants. By significantly reducing the HFC charge in a

supermarket cascade refrigeration system both the cost and environmental impact of HFC leaks are sharply

reduced. Furthermore, by restricting the HFC in a less leak prone installation, the chances of leaks are

substantially reduced. The CO2 is distributed to the field and a leak is neither very costly due to the low cost

of CO2 nor devastating for the environment, as CO2 has a Global Warming of 1 versus 1,000 – 3,000 for

commonly used HFC‟s.

The advent of CO2/NH3 cascades further reduces the potential Global Warming impact due to further

reduced energy consumption – if sound ammonia design practices are followed – and the need to reduce

ammonia leaks to virtually zero due the toxicity of ammonia. Luckily ammonia is a well known refrigerant

and sound application practices are well established and understood by many in contrast to CO2.

Refrigeration uses about 55% of a supermarket‟s electrical energy with lighting and AC consuming about

20% each.

Coles has been the pioneer in implementing CO2 cascade systems for supermarkets in partnership with the

Energy Efficiency Best Practice Program of the Australian Federal Government Department of Industry,

Tourism and Resources.

Coles established an innovative “Greening of Coles” initiative project and the first of its type was installed in

a new Coles supermarket in Gisborne, a commuter town 50km North West of Melbourne. In Coles

internally, the project was driven hard by our late esteemed colleague Don Griffiths, who had the courage of

his convictions and the vision to make a difference. He was fortunate to see his dream come true before he

retired and during his all too brief a retirement. The Gisborne store was commissioned in late 2004/early

2005. A detailed case study has been published on the project |7|.

Electricity

81%

Refrigerant

Leakage 14%

Waste 3%

Other 2%

Figure 3: Coles supermarkets total Greenhouse Gas Emission Sources

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Coles continued its pioneering role with the installation of Australia‟s first CO2/NH3 cascade system at its

new Ropes Crossing, a Western Sydney suburb supermarket, Coles‟ fifth Environmental Concept Store |6|.

These stores are used as Coles‟ testing grounds for environmental initiatives whilst looking like conventional

stores. Environmentally Sustainable Design (ESD) initiatives are installed, tested and evaluated.

Coles‟ Ropes Crossing facility will provide a much needed training ground for a new generation of

refrigeration technicians in an evolving training course being developed in cooperation with the State of

NSW Education Department‟s TAFE (Technical And Further Education) division. Coles‟ community spirit

deserves applause from all.

The Ropes Crossing store includes other environmental improvements such as low energy LED lighting in

freezer cases and freezer aisle motion sensors to turn lights off when there are no shoppers around, and night

blinds on refrigeration cases to reduce energy use during non-trading periods amongst other things.

Since 1985 Coles has made many improvements to its stores, resulting in 40% and 30% reduced energy

consumption by refrigeration and lighting respectively.

Ammonia is lighter than air and for that reason the ammonia part of the CO2/NH3 cascade is built in a

container like structure on top of the supermarket building with a leak detection and water scrubbing system

to absorb any ammonia should there be a leak.

Both Coles and WW have a policy to retrofit natural refrigerant refrigeration plants into stores with

conventional HFC refrigeration systems, which Coles sees as a next crucial step.

Aldi, which now has more than 200 stores in Australia and is steadily growing organically, has recently

installed a small CO2/HFC cascade system in one of their stores for testing and evaluation purposes.

Having regard to the approximately 75% proportion of energy consumption in a supermarket that is due to

refrigeration and air conditioning there must be considerable scope to integrate these functions into one

central plant. This requires a change in the relationship between the supermarket operator who usually leases

a building equipped with sometimes inadequate air conditioning without humidity control.This leads to the

anomaly that freezer glass doors are fitted with electric heating to reduce fogging in the freezer doors |8|.

Such heat increases the heat load to be handled by the refrigeration system. In the case of freezers this

refrigeration duty adds about 1 kW refrigeration plant energy demand for every 2 kW of heat added.

3. FOOD PROCESSING PLANTS WITH CASCADE SYSTEMS

There are three noteworthy small to medium capacity CO2/ammonia cascade refrigeration systems in

operation in Australia. Below are brief descriptions of the three systems provided in the following sections.

3.1 SNAP Fresh Pty Ltd, Queensland. Prepared meals plant.|9|

This was the first CO2/ammonia cascade plant installed in Australia about ten years ago by Scantec

Refrigeration Technologies out of Brisbane, Queensland.

The system consisted of four independent single stage CO2 vapour compression systems each with a

capacity of 14 kW at −28°C evaporating temperature and 0°C condensing temperature. Two cold

stores are each served by two of these independent systems, providing each with a capacity of 28 kW to

maintain the cold storage temperature at −20°C. Each independent system consisted of one 14 kW DX

evaporator, one suction accumulator, one compressor, one oil separator with automatic oil return to the

compressor crank case via a manually set needle valve and a propylene glycol brine cooled CO2 cascade

condenser with brine entering at −8°C after being cooled by the central ammonia plant. From the CO2

receiver, which is located in the cold store, liquid CO2 flows to the TX valves via a filter drier and a

solenoid valve. The CO2 evaporator and its drip tray are electrically defrosted as required.

Although it was the first one of its type in Australia, its start up was relatively trouble free after initial

problems with oil return to the compressor crank case and mechanical TX valve superheat settings. One

compressor failed due to an electrical fault about one month after the plant was commissioned. The

compressor manufacturer replaced the unit under warranty and the system has performed satisfactorily

ever since. A very good result for the first installation in this country.

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3.2 CRF (Colac Otway) Pty Ltd CO2/ammonia cascade freezing and cold storage plant.|10|

.1 Introduction

Lamb processing company CRF (Colac Otway) Pty Ltd in the Western Victorian district town of

Colac processes on average 6,000 lambs per day, and bones out on average 3,000 lambs per day.

The plant is a service provider for supermarket giant Coles (see Supermarkets).

In an effort to reduce high freezing costs incurred from a third party in Melbourne, 150 km away,

and increase efficiency it was decided that Otway Fresh Pty Ltd (OF), a separate entity but related

company, would build a $7 million cold storage facility to provide this service in house.

OF appointed a design team comprising meat processing specialist Meateng Consultants, RealCold

Milmech Pty Ltd, the successful tenderer for the refrigeration plant including an Automatic Air

Blast Freezer (AABF). KAV Consulting was invited to become involved in the development of the

detail design of the refrigeration system.The team tapped into the Victorian State Government‟s

Commercial Office Building Energy Innovation Initiative (COBEII), which provided a $110,000

grant and support for the project.

The facility freezes, chills, and stores meat products and by-products such as offal which are

produced at the CRF plant next door. The facility opened in November 2005 and has performed

very well since.

.2 System overview

Pumped CO2 is used for both low and high stage loads. The chosen CO2 liquid recirculation rate is

2.5:1. The installed CO2 capacity is 350 kW low stage plus 200 kW high stage. Reciprocating

compressors were used for both the CO2 low stage and ammonia high stage. The plant is built for

future expansion. The central piece of equipment in the project is an automatic air blast-freezing

tunnel (AABF) developed by RealCold.

The facility also includes two forklift-loaded carton blast freezing cells, palletising areas, chilled

product storage and frozen product storage.

.3 Use of natural refrigerants

CRF was keen from the outset to use natural refrigerants for the project. The use of ammonia in

cold storage and freezing applications is common in Australia. A CO2/ammonia cascade system

was chosen as it offered the following benefits.

.1 CO2 is non-toxic, non-flammable and has good thermal properties at the required subcritical

operating conditions.

.2 At the required operating temperature a CO2/ammonia cascade system is more energy efficient

than a two stage ammonia system.

.3 The meat in storage would not be adversely effected should there be a CO2 leak.

.4 CO2 has a low Global Warming Potential of 1 and is environmentally sustainable.

.5 By using CO2 in all product storage and work areas, the ammonia was restricted to the plant

room, thus enhancing Occupational Health and Safety for personnel.

.6 At the required temperatures of −40°C and lower, CO2 operates under a positive pressure,

thereby avoiding the risk of air entering the system, which is sometimes a problem with

ammonia operating at a vacuum at temperatures below −33°C.

.7 With CO2 in all evaporators and piping outside the engine room the required ammonia charge

in a CO2/ammonia system is only about 10% of the charge required for a two stage ammonia

system.

.8 CO2 has better heat transfer properties than ammonia at low temperature.

.9 Pressure vessel diameters are about half the diameter of ammoniapressure vessels, although

the CO2 vapour volumes are only about 12 to 16% of ammonia vapour volumes. However,

vapour velocities for effective liquid separation are only about one third of ammonia vapour

velocities due to the high density of CO2 vapour.

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.4 Disadvantages of CO2

.1 CO2 pressure vessels operate at much higher pressures than NH3 vessels. This requires Low

Temperature steel to be used in pressure vessel construction.

.2 In confined spaces CO2 can be fatal at concentrations exceeding 8%. There is sufficient CO2

in the system to fill any of the refrigerated chambers with more than 8%. CO2 detectors were

installed in all refrigerated chambers close to floor level, because CO2 is considerably heavier

than air and settles at lower levels, in case of a leak.

.3 The ammonia cooled CO2 cascade condenser is an expensive piece of equipment. Should CO2

leak into the ammonia side of the heat exchanger ammonium carbonate will be formed, which

is a highly abrasive substance which would quickly damage rotating machines like

compressors very substantially.

.5 Supplier issues

.1 All evaporators proposed by suppliers were overrated, particularly those proposed by Chinese

suppliers.

.2 The contractor used ammonia separation velocities on the −40°C pump accumulator and this

required the vessel diameters to be increased by at least 75%.

3.3 A CO2/NH3 cascade refrigeration system with the refrigerants separated by a propylene

glycol loop.|11|

This system is installed at a South East Queensland, Australia, food processing plant.

The 100 kW CO2 loop serves a 6,783 m3 cold store equipped with two DX CO2 penthouse evaporators

and induced draught fans.

After the CO2 is compressed it is condensed by a propylene glycol cooled condenser. The propylene

glycol is cooled in a Plate Heat Exchanger which is a flooded ammonia unit. This is an elegant and

simple way to keep the CO2 and ammonia separated in the cascade condenser. When CO2 and ammonia

mix, such as they would in an ammonia cooled CO2 cascade condenser developing a leak, ammonium

carbonate would be formed. This is a white powder, which would have a devastating impact on the

ammonia compressors in a system and force a shutdown of a plant. The down side of the arrangement

is an energy consumption penalty as the temperature difference between ammonia and CO2 is increased

from a nominal 5K to at least 10K.

There are three reciprocating ammonia compressors handling the heat load from the flooded 500 kW

ammonia glycol cooler. Glycol is also used to cool air coolers in processing areas and chilled water for

office Air Conditioning duties. Ammonia condensing is achieved in adiabatically assisted air cooled

ammonia condensers.

The combination of CO2 for low temperature duties and glycol brine for CO2 condensing, process area

cooling and chilled water generation for a 115 kW office AC load ensures that a limited charge of

ammonia is present in the plant room only.

After nearly two years of troublesome operation due to frequent failure of the copper discharge piping,

difficulty with reliable superheat control and difficulty with reliable electric defrosting of the

evaporators the plant has been running reliably for nearly three years now.

The CO2 compressor discharge piping was replaced with high pressure hydraulic steel tubing, a new

evaporator superheat algorithm was developed and the defrost times were altered.

All in all a successful plant, notwithstanding problems in its early life.Full marks to the persistence and

competence of Scantec. See also the first study in this report.

4. TWO STAGE TRANSCRITICAL CO2 SYSTEMS

There are two of these systems in Australia. One of them has been running for a little over three years now

at a supermarket at Angle Vale, an outer Adelaide suburb. The other one has recently been commissioned at

a small food processing factory in Melbourne.

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4.1 Angle Vale Project

The Angle Vale Project was the first and only two stage transcritical CO2 plant in Australia until the

Melbourne project, which has been commissioned recently.

The Angle Vale system started life as a demonstration plant for Australian supermarkets. It attracted

part funding from the Australian Natural Refrigerant Transition Board, which had been funded to the

tune of AU $2 million by the Australian Federal Government‟s Department for the Environment, Water,

Heritage and the Arts (DEWHA) to part fund four or five demonstration projects for the purpose of

technology development and required skills development.

An audit of the NRTB accounts by an independent auditor allegedly found financial irregularities in the

NRTB books and the Minister stopped the flow of funds. This came at a very critical time for the

owners of the brand new Angle Vale supermarket. When the funding stopped about three years ago, the

two stage transcritical CO2 plant at Angle Vale was being commissioned without expert assistance from

the NRTB and the Italian supplier of the CO2 compressor racks. The local contractor was left to its own

devices and had to learn the hard way.

After three years of struggling the plant is now performing to an acceptable standard. Difficulties were

experienced with:

Compressors, but the Italian compressor manufacturer proved a reliable partner.

TX valves. They were changed to Carel electronic TX valves which performed a lot better after

calibration.

The plant is extremely sensitive to weather changes, with erratic feeding of CO2 to TX valves. This

can happen in a short time, e.g.when the temperature drops from 42 to 25°C when a frontal system

moves through or from the heat of the day to the cool of the night.

Oil management is very difficult.

High cost to get the plant to a functional state.

Predicted energy cost savings have not eventuated and energy consumption compares unfavourably

with conventional HFC refrigeration systems.

When performing, the rate of cooling is very good with rapid reduction in temperatures.

4.2 A world first in CO2 cooling and heating for a Melbourne food processing plant.

.1 General description

In September 2009 Exquisine Pty Ltd decided to install a two stage transcritical CO2 refrigeration plant to replace 22 independent systems providing heating and cooling at their Thornbury, Victoria, food processing facility where they manufacture high end frozen dairy desserts. The system is supported by a 50% grant from AusIndustry under the Re-Tooling for Climate Change program. A CO2/ammonia cascade plant was briefly considered but with residential properties bordering the site, it was judged best not to use ammonia. Plant noise was also a potential problem.

The new two stage transcritical CO2 refrigeration plant carries out all the required blast freezing, cold and chilled product and ingredient storage, factory and packing area cooling, office AC cooling and chilled process water cooling. In addition the system heats all potable tap water for sanitary and factory cleaning purposes. Process hot water is also partially generated to provide AC reheat and space heating for the office and factory. A secondary ethylene glycol circuit provides underfloor and door jamb heating for two large cold store and three blast freezer doors.

The new central plant includes nine Bitzer CO2 compressors comprising two AC and three high stage transcritical compressors plus one common standby and three boosters including one standby. All compressors have VSD drives allowing the machines to run between 30 and 60 Hertz speeds delivering 60 to 120 percent capacity of the 50 Hertz ratings. The AC transcritical compressors are used as water heating machines in the first instance because of their high COP at + 5°C Saturated Suction Temperature conditions. The three high stage machines are also able to run in a transcritical condition to heat water when required. The two AC and three high stage compressors can also discharge to an oversized two stage Guentner gas cooler which is adiabatically assisted on the second stage to achieve as low a gas cooler exit temperature when running in transcritical mode during hot weather, which is estimated to occur 6% of the time in the Melbourne metropolitan area. When not heating water, the machines run in subcritical mode at as low a condensing temperature as possible as limited by the compressor manufacturer‟s requirements to achieve high operating efficiency.

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Fig. 4. Subcritical CO2 booster rack.

Photo courtesy Bitzer Australia.

Fig. 5 Transcritical CO2 compressor rack

Photo courtesy Bitzer Australia.

One of the most critical parts of the design was the oil management. To that end each of the six

transcritical compressors was equipped with an oil separator, whilst the three boosters share one

unit. In addition two refrigerant heated oil stills with electrical assistance are employed as no oil

separator is 100% effective. We found this to our great chagrin with oil consumption being 200

times as great as what was specified. This caused a substantial delay but swift, decisive, effective

and cooperative action by Mr Jim Nonnie of Temprite, USA, Mr Mark Kristiansen of HB Products,

Denmark, and Messrs. Reudiger Rudishhauser and Julian Hudson of Bitzer Australia resolved the

problem. The next oil problem carry over occurred during the transcritical water heating cycle and

that has now also been resolved. There are still several areas where oil is causing intermittent

problems. They are in line for rectification.

Troubles were also experienced with the control of flash gas between the +10 and +5 vessels as

well as between the +5 and −5 vessels.

The oil still in the −5°C system is totally ineffective, but the suction trap in the −40°C booster

suction collects oil effectively. A −5°C liquid CO2 coil in the −40°C suction trap acts as a liquid

subcooling coil in the liquid feed to the −40°C evaporator when boiling off liquid carried over.

This is thermo-dynamically neutral and does not increase running costs.

The plant is handling the refrigeration duties comfortably at about 25% of design capacity,

although defrosting with warm glycol circuits in the freezer and cold store evaporators is

unreliable. Glycol defrosting was preferred to electric defrosting which is quite energy intensive.

Noise emanating from the plant was a serious consideration and the gas coolers were deliberately

oversized to deliver the required capacity with the fans running at 75% speed maximum. Noise

tests were conducted and noise was found not to exceed legal limits by a substantial safety margin.

The 22 existing systems being replaced by the new system comprise four individual systems for

blast freezing and cold storage – one off each – and two chillers. Then there is one independent

chilled water system, one evaporative cooler used for factory cooling, four reverse cycle office AC

units, six air to water heat pumps, three gas fired mains pressure hot water systems and four electric

underfloor and freezer door circuits.

Calculated savings amount to a 33% reduction in electrical energy consumption, a 60% reduction

in natural gas consumption, a 44% reduction in direct and indirect global warming emissions and a

40% reduction in cooling water consumption.

The big challenge was to achieve high efficiency operation with this relatively large plant at low

production levels and that is the reason for the liberal use of Variable Speed Drives on the

compressors and the fans on the gas coolers, in the blast freezer and in the office and factory

cooling Air Handling Units. The electrical energy savings are understated by 25% for that reason.

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.2 Definition of plant functions|12|

A complete range of high end desserts are manufactured at the factory where the two stage

transcritical CO2 plant needs to be installed.

.1 Refrigeration duties and capacities

.1 Carton blast freezing of 1,500 kg of product/day growing to 7,500 kg/day at an average

air temperature of –33°C. Q = 70kW@To = –40°C

.2 Cold storage with the same plant of about 50 tonnes of frozen products mostly in shipper

cartons, but some unpacked. Q = 20kW@To = –40°C.

.3 Chill storage for ingredients at 0°C. Q = 10kW@To = –5°C.

.4 Packing area cooling to a temperature of +10°C maximum. Q = 25kW @ To = –5°C.

.5 Generate 5,000 litres of 4°C process chilled water/day from a mains water temperature of

+20°C. To = 0.5°C, back pressure controlled.

.6 Factory cooling and AC. Q = 25kW@To = +5°C.

.7 Office cooling and heating. Q = 10kW@To = +5°C.

.2 Heating duties

.1 Underfloor heating of cold store and blast freezer, 2kW.Process hot water to glycol via

PHX.

.2 Factory AC reheat. Max. 15kW direct from process water. This is also required for air

reheat during cleaning with full fresh air exhaust cycle.

.3 Office AC reheat and heating in winter 10kW direct from process hot water.

.4 Potable 65°C hot water for daily cleaning, 5,000 litres, 30-60kW. 12 to 6 hours.

Depends on availability of suitable heat.

.5 Potable domestic hot water.

.6 Process hot water for several production processes like chocolate melting.

.3 Refrigeration capacity summary

.1 90kWR@To = –40°C for blast freezer and cold store.

.2 151kWR@To = –5°C for high stage, packing room, water chilling and chill store.

.3 35kWR@To = +5°C for factory cooling and office AC.

4.3 Description of system. See Fig. 6|12|

Three Bitzer CO2 booster compressors (18), including one standby unit (19) serve the DX

evaporators in the blast freezer (16) and cold store (17). The boosters discharge to a –5°C

intercooler (14), which also serves a suction trap for the evaporators in the ingredient holding

chiller, the packing area and the process water chiller. Four Bitzer high stage compressors

including one standby (3 & 2) discharge either to a two stage gas cooler (4a & 4b) or two PHX

water heaters (5) as required by hot water demand. The PHX water heaters will heat a maximum

of 10,000 litres of water per day from mains water temperature to 65 to 80°C depending on demand

and requirements. Switching from the gas cooler to the PHX water heaters is effected by automatic

three way valves.

Transcritical or subcritical CO2 is expanded via automatic ICMT valves into an expansion vessel

(7) which is maintained at a pressure of 45 bar (+10°C SST). Flash gas is relieved via a back

pressure regulator into the +5°C AC suction accumulator (8).

From the 45 bar vessel liquid is fed to the +5°C DX evaporators for factory cooling (9) and office

AC (10) with the suction returning to the +5°C suction accumulator (8).

The level in the 45 bar vessel is maintained by allowing excess CO2 to flow to the +5°C suction

accumulator by a Differential Pressure (DP) sensor operated modulating valve.

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Two Bitzer AC compressors (1) maintain the pressure in the +5°C vessel at 38.7 bar on demand.

In addition to the AC load these compressors also act as flash gas i.e. economiser compressors for

the rest of the system. This means the rest of the system with the bulk of the capacity is fed with

+5°C liquid, i.e. the bulk of the system runs with a virtual gas cooler exit temperature of +5°C. As

can be seen from Fig. 2 the COP in transcritical operation is highly sensitive to the gas cooler exit

temperature. The two AC compressors may also discharge to the water heaters or two stage gas

cooler as required.

From the +5°C suction accumulator liquid CO2 is fed to the evaporators in the ingredient chiller

(11), the packing area (12) and the water chiller (13). The suction from these is going to the –5°C

suction trap/low pressure receiver (LPR) (14). This vessel is now fed with liquid CO2 from the

+5°C AC suction accumulator/economiser flash off vessel in which a constant level is maintained

by a DP sensor operated modulating valve maintaining a level with excess CO2 flowing to the –5°C

LPR.

Liquid CO2 from the –5°C LPR is fed to the three blast freezer (16) and one cold store TX valves

(17). Three feeds to the BF coil are needed because of the wide fluctuation in refrigeration heat

loads from the start of operation (1,500 kg/day) to ultimate capacity (7,500 kg/day).

Legend Figure 6

Item Description

No

No. Off

1 AC and economiser compressor 2

2 Standby for 1 and 3 1

3 High stage and chiller comp. 3

4a First stage gas cooler – air cooled 1

4b Second stage gas cooler – air cooled

Adiabatically assisted – 10% of time

1

5 PHX water heaters – SWEP 2

6 CO2 expansion valves – ICMT 2

7 +10°C (44 barg) expansion vessel 1

8 +5°C (39 barg) suction trap 1

9 Factory cooling evaporator 1

10 Office AC evaporator 1

11 Packing area evaporator 1

12 Ingredient chiller evaporator 1

13 Ingredient for process chilled H2O 1

14 –5°C LPR/de-superheater 1

15 –40°C suction trap with boil off coil 1

16 Blast freezer evaporator – ETX 1

17 Cold store evaporator – ETX 1

18 CO2 booster compressors 2

19 Standby CO2 booster compressor 1

20 Super-heat regulator Hi St.

compressor suction

1

21 High side float with DP sensor

maintains level in 7

1

22 High side float with DP sensor

maintains level in 8

1

23 BP regulator for 44 bar in 7 1

24 BR regulator for 39 bar in 8 when

CO2 compressors 1 are stopped at

light load

1

P = Pressure transducer

T = Temperature transducer

M = Valve modulating motor

The pressure in the +5°C vessel will be maintained by capacity controlling the lag AC compressor

down to 60% speed. As the load in the +5°C vessel from AC and flash gas reduces further, the

AC/economiser compressor will be stopped and the pressure maintained by a back pressure

regulator feeding flash gas to the –5°C suction trap (LPR) via (24). The LPR is also used as a de-

superheater for the CO2 booster discharge. The amount of de-superheating in this vessel depends

Figure 6. Schematic of two stage transcritical

CO2 refrigeration system with heat

recovery and AC/economiser

compressors

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on how much booster discharge gas is admitted directly into the high stage compressor suction to

regulate the amount of superheat with respect to the final compressor discharge temperature to

generate a sufficiently high water temperature in water heating mode.

Apart from transcritical running for water heating, the system will run mostly in subcritical mode

given the prevailing ambient temperature conditions in Melbourne through any year.

A strong emphasis has been placed on overall total system efficiency. The oversized two stage gas

cooler is adiabatically assisted on the second stage only in the chase for a low gas cooler exit

temperature – in transcritical mode – or a high degree of liquid subcooling. It is estimated that the

system will run in transcritical mode a maximum of 20% of the total time, whilst the remainder of

the time it will run in subcritical mode.

5. CO2 HEAT PUMP HOT WATER SYSTEMS.

ECOCUTE technology is represented in Australia by MAYEKAWA MYCOM in Sydney, and the

SANDEN distributor EDSON in Melbourne.

At both ends of the scale, Mayekawa has a nominal water heating capacity of 100kW, and the Sanden of

4.5kW

One market where both will be installed this year is Darwin in the Northern Territory. Darwin has a

population 110,000 people with distinct wet and dry seasons.

Commercial water heating in tropical Australia was traditionally solar boosted or LPG gas. In 2004,

commercial application heat pumps were introduced to the Northern Territory. Growing acceptance of this

low energy technology has opened the door to the next level of greenhouse friendly low GWP CO2 water

heating heat pumps. Several notable projects are in train with Smart Hot Water NT, the only business

specialising in this area in the NT.

5.1 First Installation.

On June 14th this year the first 9 SANDEN ECOCUTE CO2 heat-pumps were commissioned at a 102 room

and kitchen guest residential facility in Darwin. This site has 3 separate HW plants, each feeding ring mains

to guest ensuites and to a communal kitchen. Each plant has an EDSON 90 evacuated tube solar array and 3

Sanden heat pumps. The combined heat pump capacity of each plant is13.5kW at 65 C. The hot water

storage is 2000 litres. Permissions are assigned to solar and heat pumps to optimise the solar fraction. Design

parameters are:- HW plant cost per room $700 (AUD); HW electrical demand total on site is only11kW;

amortised demand per room is 74 watts; estimated reduction of HW energy and costs compared to electric is

91% plus or minus 3%. One of the three HW plants is monitored for performance outcomes.

Fig. 7 Three 4.5kW air to water CO2 heat pumps with water storage. Photo courtesy Geoff Little.

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5.2 Second Approved Project

Early 2012, a 750 room guest residential facility and meal capability of 4,500 meals per day will be opened.

The specification is for 4 major hot water plants and 2 smaller plants, plus (unfortunately) several smaller

electric 50 litre water heaters remote from ring mains. Each major plant has an Edson 600 evacuated tube

solar array and a single Mayekawa CO2 100 kW heat pump with a capacity of 100kW at 65 C at this latitude.

Each plant has 10,000 litres of storage. Permissions are assigned to solar and heat pump to optimise solar

fraction. Excluding the electric resistive systems, 99% of site hot water will have an electrical demand of

only 105kW. Amortised demand per room is 107 watts. Delivered hot water energy consumption is expected

to be less than 4.2 kWhrs per 1000 litres compared to a conventional of 39.2 kWhrs per 1000 litres, a

staggering 89% reduction in energy consumption! The two smaller plants each have a solar array and

Sanden heat pump with 315 litres of stored hot water. At the deemed NT power supply emission of 680 gm

per kWh, CO2 emissions are reduced from 26.7 to 2.86kG per 1000 litres of hot water.

5.3 Two additional future Projects.

Two city guest properties have applied for Green Building loans to upgrade HVAC and guest hot water.

The specification submitted at each property utilises a water to water Mayekawa CO2 100 kW heat pump,

with primary water drawn from the HVAC cooling tower returning to the chillers. This will reduce the

energy required to operate the chillers. The output is utilised for guest hot water, in one case displacing LPG

burners operating at less than 65% thermal efficiecy. The balance of the heat is utilised to recondition

desiccant dehumidifiers on the fresh air input. Seasonally adjusted, the modelling indicates a positive

feedback loop for reduction of significant HVAC energy.

Case studies will be conducted and made publicly available as soon as they have been concluded.

6. EQUIPMENT AND SYSTEM DEVELOPMENT, AND EDUCATION AND TRAINING

The first subcritical CO2 compressor rack for the Snap Fresh project was imported about ten years ago, as

was the first transcritical system for the Angle Vale project.

6.1 Equipment and System Development

Bitzer Australia Pty Ltd (BA) has pioneered the development of CO2equipment and has built an enviable

record in this area here in Australia. At last count BA had shipped a total of 122 factory assembled CO2

systems in the following broad categories.

69 Direct Expansion (DX) Systems of which 65 went to supermarkets and 4 to food distribution

centres. See Fig. 8 below.

40 Liquid Recirculation/DX cascade systems. In these systems the freezing is accomplished by TX

valves supplying the evaporators being fed under pressure with liquid from the CO2 cascade receiver.

A glandless pump pumps saturated CO2 liquid to the chiller evaporators where 50 to 70% of the

liquid CO2 is evaporated. The wet vapour leaving the evaporator returns to the cascade condenser,

where the vapour is recondensed together with the hot CO2 gases from the discharge of the CO2

compressors. Thirty six of these systems went to supermarkets, 3 to food distribution centres and 1to

a food processing plant.

One transcritical system as described in section 4.2 above and as shown on figures 4,5 and 6. BA is

currently building a transcritical system for a supermarket in New Zealand with 100% heat recovery

for sanitary domestic hot water and for heating of the super market.

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Fig. 8 - A subcritical LR/DX system ready for site

installation. Photo courtesy Bitzer Australia.

Fig. 9 - A Liquid Recirculation/DX Training

Centre. Photo courtesy Bitzer Australia.

6.2 Education and Training. As reported above the prototype system built by BA for demonstration purposes soon became a training tool

for TAFE in NSW. The demand became too great and BA has supplied a total of 13 traning systems to both

private companies and TAFE centres in Australia and overseas.

Three LR/DX systems were sold to three Australian design and construct refrigeration contractors

for in house training of their engineers and technicians. See Fig.9 above.

Two LR/DX systems were supplied into China, one into Indonesia and one went to Bitzer

Headquarters in Germany, i.e. a total of 4 were exported.

The TAFE colleges in Adelaide, SA and Granville, NSW installed one LR/DX unit each.

The TAFE Green Skills development centres in Acacia Ridge, Queensland and Maroubra, NSW

have each installed one LR/DX system plus one transcritical system.

This is all good news as the skills development associated with the early NRTB program came to a

grinding halt when funding stopped. There is a lot more to be done, but a good start is being made

with the establishment of Green Skills Development centres by the TAFE colleges.

7. CONCLUSIONS AND THE FUTURE

From the previous sections it is fair to conclude that most of the projects reviewed above have experienced a

degree of difficulty ranging from minor to severe.

The overall positive conclusion is that all systems have been made to perform their intended function, but not

always at the promised efficiencies and at significant expenditure of time and money.

We have not been able to obtain much information from the major supermarket chains direct. Practically

everything said about supermarket systems has been gleaned from Woolworths‟ and Coles‟ websites.

Australian supermarkets are installing an increasing number of liquid recirculation CO2 systems, which is a

very healthy development and one adaptation of many possibilities from sound industrial ammonia

refrigeration practices and hopefully the first step in integrating all refrigeration and cooling functions for a

supermarket into one plant.

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In the case of the supermarket chains, we believe that enlightened self-interest will induce their

managements to continue with their natural refrigerants program. The self-interest is stimulated by the

exceedingly high cost of HFC refrigerants, the ever escalating cost of electrical energy, the impending

imposition of a carbon tax and increasing pressure from consumers. Notwithstanding that, there is currently

still a degree of lip service being paid in some quarters and the strong, and well funded and resourced pro

HFC lobby is still quite influential behind the scenes.

Supermarkets collectively use about 1% of this nation‟s energy directly on their sites and considerably more

in the energy consumed in their distribution centres and the transport of goods to the individual stores.

Notwithstanding the NRTB failure, Australian governments at both State and Federal level have supported

the projects the writer has been involved in, i.e. the project described in 3.3 earned a $110,000 grant from the

Victorian State Government and the Federal Government contributed nearly $500,000 to the project

described in Section 4.2.

Although transcritical CO2 refrigeration systems do not have a good reputation in this country due to the

Angle Vale project, the total integration of all supermarket refrigeration, AC and heating duties into one two

stage transcritical CO2 system holds a lot of promise to very substantially reduce the total energy

consumption and attendant emissions, plus the entire elimination of direct emissions caused by the escaped

fugitive HFC refrigerant gases.

There is no doubt in the author‟s mind that transcritical CO2 systems offer a great opportunity to reduce the

cooling and heating costs in existing buildings as they are eminently suited to being retrofitted. Purpose

designed and built CO2 systems for the built environment coupled with other strategies have an even greater

potential for energy consumption reductions.

CO2/NH3 cascade systems also have a bright future for both cooling and heating in supermarkets and the

built environment generally.

Ammonia itself has great potential for the heating and cooling of buildings using secondary refrigerants like

water and brine. Ammonia technology is well established. Janos Maté of Greenpeace International and

Claudette Papathanasopoulos of Greenpeace USA list 44 ammonia plant in 10 countries that service office

buildings, hospitals, airports, department stores, trade fair buildings, shopping and convention centres,

museums, supermarkets, universities, district heating and cooling systems, television studios, casinos and

even one parliament building, the Palais Grande Ducal and Parliament in Luxembourg |13|.

Integration of the refrigeration and AC functions in supermarkets would lead to significant reductions in

electrical energy consumption as some of the heat rejected could be used for reheat to reduce the dewpoint of

the air in the store. Indeed, using part or all of the refrigeration plant as a heat pump would provide hot

water to heat the store during cooler weather and for domestic sanitary and cleaning purposes. These

enhanced ESD features would reduce energy consumption in supermarkets significantly more. This also

opens the prospect to use two stage transcritical CO2 systems to perform all refrigeration, AC and cooling

and heating functions in supermarkets, including domestic hot water, etc.

CO2 as a refrigerant is suitable for use in very small to very large systems in all manner of applications.

However, the large scale development so desirable awaits the development of larger, new high pressure

compressors or the adaptation of existing high pressure compressors with high crank case pressure

capability, such as Compressed Natural Gas compressors.

Accelerated education and training at all levels is a critical requirement and worthy of the attention of

governments the world over. This is now being taken up by the TAFE system in some states in Australia, but

a lot more is needed at an accelerated time scale

Since necessity is the mother of invention, phasing out of HFCs by 2022 would accelerate the development

of CO2 technology further, like what happened in Denmark between 1996 and 2006, when the Danish

government severely limited the use of HFCs by June 2006. This should be an example to all governments

and international government organizations like the United Nations of the possibilities and options available,

particularly after the abject failure of the well-intentioned but much abused CDM programme. The CDM

programme has only served to establish high Global Warming Potential HFCs, analogous to CFCs and

HCFCs without Ozone Depletion Potential, in developing countries, which eventually will need to be phased

out. Indeed, there is now a movement starting to add the HFC phase out to the Montreal Protocol charter.

The sooner the better.

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In respect of low natural refrigerant hot water heater heat pumps, it is a question of maturity of the segment.

There is a significant gap in the Australian market. Between 4.5kW and 100kW nominal models, the bulk of

commercial market potential is located. It may be the case that existing manufacturers will adapt

conventional technology to HC where the standards for class 3 (inflammable refrigerants) permit.

Observations are that most potential purchasers still weight capital cost as a decisive factor at purchase.

Indicators are that a change of attitude regarding longer term ROI and environmental factors will generally

be imposed by regulation or peer pressure rather than altruistic intent.

The now completed CFC phase out and the continuing HCFC phase out are leading to the increased use of

HFCs, which have high to very high Global Warming Potential (GWP) like the CFCs and HCFCs they are

replacing. But HFCs have no Ozone Depletion Potential (ODP) like the CFCs and HCFCs. As Global

Warming continues to increase, there is more and more emphasis being placed on the high GWP of HFCs,

which will, in future, need to be replaced with natural refrigerants like hydrocarbons, CO2 or ammonia. The

development in these technologies is sufficiently advanced to be of immediate use and then we would be

able to leap frog the HFC phase. This is fiercely, and successfully, resisted by the well-resourced HFC

lobby, which will ultimately be to the detriment of humanity at large.

8. ACKNOWLEDGEMENTS

The author acknowledges with thanks the assistance provided by the following colleagues.

Mr Ray Clarke – Managing Director – Iseco Pty Ltd.

Mr Julian Hudson – Senior Engineer – Bitzer Australia Pty Ltd

Mr Stefan Jensen – Managing Director – Scantec Refrigeration Technologies Pty Ltd

Mr Geoff Little –Operations Manager – Smart Hot Water NT

Mr John Mott – General Manager– Gordon Bros. Industries Pty Ltd

Mr Ruediger Rudishhauser – Managing Director – Bitzer Australia Pty Ltd.

Mr Bob Soang – General Manager – Drake Supermarkets Pty Ltd.

Mr Mark Turner – General Manager – Hill Equipment Pty Ltd.

9. REFERENCES

|1| Mr Holm Gebhardt, Vevey Switzerland – Nestle – retired. Figure 1.

|2| Professor RistoCiconkov – University of Saints Cyril and Methodius, Skopje, Republic of

Macedonia.Figure 2.

l3l Pearson, S. Forbes – Star Refrigeration Ltd.. Development of Improved Secondary Refrigerants. Proc.

Inst.R. 1992-93.7-1

|4| Coles supermarket website. http://sustainability2010.coles.com.au

|5| http://www.woolworths.com.au/wps/wcm/connect/Website/Woolworths/About+us/o...

|6| Natural Refrigerant Case Studies, pp. 18-20.Australian Institute of Refrigeration, Air Conditioning and

Heating (AIRAH).

|7| „Australian Supermarket First‟, Ecolibrium, August 2008, pp. 14-16.

|8| http://woolworthscrr09.reportonline.com.au/climate_change.php

|9| Bellstedt, Michael, Ph.D.Eng.; Frank Elefen, Ph.D.Eng.; Stefan S. Jensen, B.Sc.Eng. Application of

CO2 (R744) Refrigerant in Industrial Cold Storage Refrigeration Plant.

|10| Natural Refrigerant Case Studies – See |5| above.

|11| Jensen, S.S. and Skrlin, M. – Scantec Refrigeration Technologies.Cascade Refrigeration Systems

Employing NH3 and CO2 – Operating Experiences from a Food Processing Plant.

|12| Visser, K.An HFC/HCFC Free Food Processing Plant: The Energy and Environmenatal Benefits of a

Two Stage Transcritical CO2 plant. 9th IIR Gustav Lorentzen Conference: Natural Working Fluids,

Sydney, 12-14 April 2010.

|13| Maté, Janos, Greenpeace International and Papathanasopoulos, Claudette, Greenpeace USA.Cool

Technologies: Working Without HFCs – 2010, pp.12.