ARBS awards Refrigeration Project Excellence Award 2018
Entrant Strathbrook Industrial Services / Danfoss Australia
Project F Mayer Vic
Location 28 Salta Drive
Altona Melbourne Vic
Entrant contact Mr Ian Wilson
Site contract Mr Stephen Goode
Project type Refrigerated cold storage / distribution centre
Trans critical / sub critical CO2 cascade cooling system with high demand secondary
Ammonia micro charged chiller system
System capacity low temp 120kw Q @-27 SST / -5 SCT
Medium temp 280 kw Q @ -5 & -9 SST / 25 SCT (split suction groups)
Chiller room 242kw Q @ -5 SST /25SCT
High demand unit 2 x 200kw Q @ +10 SST / 45 SCT Ammonia water chillers
F Mayer Imports
Food importer and distributor
Located at Altona in Melbourne
Nature of business – Importer and distributor of multiple food goods product lines mostly from Europe.
Design brief
Strathbrook Industrial Services undertook a design and construct project, to install a freezer room, chiller room and loading dock/ staging room and chocolate room, with a Carbon dioxide only, cascade system requested by the F Mayer management team.
System description
Freezer room & Low stage package
The site has a -20 deg C Freezer room, 59m x 21.5m x 10m high (1268m2) of 120 kw capacity, using R744 (CO2 ) in four direct expansion evaporators, with Danfoss electronic TX valves. The defrost system uses warm glycol, recovering heat, generated from the waste heat, rejected by the freezer room refrigeration package.
The package was designed and built by Strathbrook Industrial Services, and features four Bitzer piston compressors, in a single refrigeration circuit, with the lead compressor speed controlled to provide increased load matching ability. The package also has an open flash intercooler / liquid receiver, which stores cold liquid CO2 at -5 deg C . The discharge gas from the oil separator is injected directly into the liquid in the receiver vessel, where it is condensed into liquid. Vapor rising from the vessel is directed into the two high pressure plate heat exchangers where it is re condensed into liquid CO2 before it is gravity fed back to the receiver vessel.
The two inter-stage PHX units, are fed with direct expansion CO2 from the high stage (medium temp) package, forming a Cascade cooling system with CO2 on both stages. The glycol defrost system requires a constant heat source, to maintain the required 45 deg C glycol temperature, and this heat is extracted from the low stage discharge gas, in a discharge gas to glycol PHX unit. Further heat is removed from the discharge gas, and added to the suction vapor, in a second pair of Plate heat exchangers, which are installed to warm the suction gas returning to the compressors. The compressors are then fed with vapor in the +1 to +10 deg C range. This temperature range provides optimal conditions, and ensures that the compressor oil systems are fed with warm oil, free of liquid droplets, which will be present if the compressor sumps are allowed to cool below -10 deg C.
A suction gas temperature sensor, controls the operation of a discharge gas heating solenoid, to provide control over the process. The warming of the suction vapor also increases the compressor discharge gas temperature, which allows more heat to be extracted from the discharge to ensure the Glycol temperature is maintained. The discharge gas temperature is optimized to provide the both maximum heat recovery, and best possible compressor operating conditions.
Chocolate room / staging & dock / high stage package.
The site has a chocolate room of 59m x 22m x 10 m high (1300m2) and is maintained at 16 deg C by three direct expansion air defrost evaporators with electronic TX valves. The cool room capacity is 52kw at -4 deg C The large evaporator TD helps to maintain the dryer environment, required by the products in storage.
The Staging & dock area has six direct expansion CO2 evaporators, maintaining the dock and product staging areas, and has a further 134kw capacity, sharing the same suction group as the chocolate room system.
The rack package has six Bitzer piston compressor machines, designed and built by Strathbrook Industrial Services. The system is a split suction design, with three compressors acting at high stage to the Cascade freezer system, and the remaining three compressors, cooling the chocolate room and dock areas.
The design utilizes a completely transcritical CO2 system, and has a maximum operating pressure of 130 bar.
A Guntner Gas cooler of 440 kw capacity, is located on the external condenser deck, and features 6 x 900mm EC fans, with a stainless steel coil block and epoxy coated aluminum fin stock. The fan speed is controlled by the Danfoss control system on gas cooler exit temperature. This allows the fan speed to be reduced in cooler weather, to reduce the power consumption of the fans. The gas coolers are also fitted with a high demand water spray system, that further reduces the leaving CO2 refrigerant temperature in hot ambient conditions. This is limited to 400 hours per year of operation to protect the gas cooler from excessive corrosion.
The liquid receiver is a vertical design, with Danfoss electronic control valves maintaining the correct system pressures in the gas cooler and receiver vessel. A suction header / shell and tube heat exchanger, warms the returning suction vapor and sub cools the liquid CO2, which increases the system efficiency and provides improved compressor operating conditions. The lead compressors on each suction group are speed controlled to provide improved load matching.
Chiller room system
The chiller room is also cooled with a transcritical CO2 system, with its own gas cooler and eight Guntner direct expansion evaporators. The chiller room has been built so that it can be converted to freezer duty, in the future, and is equipped with underfloor heating and warm glycol defrost evaporators designed for freezer operation.
The chiller is independent of the other systems, but is similar in design and operation.
Staging room with dock area
The staging area provides working space for date stamping and the assembly of orders, plus an area for unloading containers and road freight. The area is maintained at +10 deg C, and is connected to the same rack package as the freezer high stage and the chocolate room.
High demand unit / Australian design patent
The nature of Transcritical CO2 systems, is that they are more energy efficient than conventional systems during lower ambient temperatures, and less efficient during high ambient conditions. The point where they are equal is around 24 deg. C condenser exit temperature.
When the ambient temperature is significantly higher than 24 deg C, the compressor capacity is greatly reduced (can be as much as 50%) so a conventional transcritical system would normally require considerable additional compressor capacity, which is only required for a few hundred hours per year .
The system patented by Strathbrook Industrial Services, uses a separate refrigeration system, or high demand unit, to cool the refrigerant leaving the CO2 gas cooler. This allows the CO2 system to operate in the same way that it would during cool weather conditions. When the lower ambient temperatures are available, this high demand unit cycles off and uses no power. This allows the CO2 system to operate in sub critical mode at all times, which greatly reduces both the system operating pressure, and the motor input power, required to drive the high stage compressors.
In this case the high demand unit is a pair of 200 kw water chiller with Bitzer direct drive piston compressors on R717 (ammonia), in a direct expansion water cooled water chiller.
The water chiller supplies water at 17 deg C, to a pair of high pressure plate heat exchangers, which are located at the outlet of the gas cooler.
The water passes through the PHX units, and then into an insulated 9000 L storage tank, before returning to the chiller. The storage tank allows the chiller to operate for longer periods of time, when the demand is
low and then cycle off allowing the thermal storage in the tank to maintain conditions.
As the chiller suction temperature is quite high in comparison to the CO2 system, the operating COP is much higher, allowing the total system efficiency to be raised during high ambient conditions.
Please find a copy of the “Carbon dioxide refrigeration high demand system” Patent attached.
The ammonia chillers operate at +12.5deg C sst and 35deg C sct, and can provide 200kw of cooling each, with a COP of 9:1. The ammonia operating charge is 5kg. A large air cooled dry cooler, cools water that is used to provide condenser water cooling for the ammonia chillers. Water sprays provide additional cooling to the dry cooler in high ambient conditions, so that the low ammonia condensing temperature can be maintained.
The ammonia chillers where designed and built by Strathbrook Industrial Services.
The ammonia chillers provide 40kw of cooling per kg of Ammonia refrigerant in circulation.
Control system
The system is controlled by a Danfoss 850 System controller. This system uses electronic input/output cards to feed information to and from the systems microprocessor, which is monitoring and controlling all aspects of the systems operation.
Specialized computer cards also control dedicated devices, such as the liquid receiver electronic motor control valves and the electronic expansion valves. Gas detectors, variable speed drives, room temperature sensors, system pressures and temperatures, are all connected to the controller, so an overall picture of the systems performance can be maintained in real time both on site and remotely via an internet connection. A UPS (uninterrupted power supply ) is provided to ensure the control system remains on line during power outages , and also provides power to the emergency cooling system.
Electrical system
The electrical panel was designed and built by Strathbrook Electrical Services and includes the Danfoss control system and the various power and safety circuits.
The control system is programed so that in the event of abnormal operating conditions such as a high pressure event, the controller will progressively shut down devices until the situation is returned to normal, and then gradually return the plant to normal operation , so that events such as a power failure can be handled by the Danfoss controller without intervention by an operator.
The Warm Glycol system
The freezer room sub floor heating and the freezer room defrosting, are both maintained by warm glycol, which is circulated around the system by pumps located in the plant room and above the freezer room.
The main glycol tank is an insulated 4000L stainless steel vat, which is heated by the low stage rack discharge gas.
The heat is maintained in the tank in a food grade glycol solution, and is delivered to the evaporators during defrost events by a small pump. One evaporator is defrosted every 2 hours, so each evaporator has three defrosts per 24 hours. The evaporators are circuited with dedicated glycol tubes, in place of electric heaters, and have glycol headers, which collect the tubes together, so that the drip tray and coil block have enough heat delivered to them to effect a defrost in about 15 min. As the defrost temperature is only 45 deg C, the coil block is not heated to a point where the air within the coil block achieves a chimney effect, which is always present in electric defrost evaporators, and is responsible for large amounts of heat rising up, out of the normal evaporator during defrosts . As the heat tends to stay in the coil block when the glycol system is employed, there is less heat passed into the room during defrost, so less after defrost load is created. The lower defrost temperature, also prevents the vaporization of drip down, water due to high defrost temperatures, which makes the environment inside the freezer room very dry.
As the site has a post tensioned concrete slab floor, we had to prevent any penetrations that could damage the cables within the slab. For this reason the sub floor heating had to be located above the existing slab floor.
The freezer room floor is heated by a second glycol system, which is a separate circuit to the defrost system, it is heated to 14 deg C, by the heat in the CO2 liquid refrigerant line. A small plate heat exchanger passes heat from the water that cools the liquid refrigerant high demand cooling system, to the floor heat glycol on demand, and is controlled by cycling the small water pump, which passes the water between the floor heat system, and the condensed CO2 pipe work.
A glycol pumping station circulates the cool glycol, through an insulated expansion tank, and then directs it into one of three floor heater manifolds, which each has nine nylon heater tubes connected to it. The 27 nylon tubes are each 120m long, making over 3km of heating tube which is laid out in a grid pattern, so that the entire freezer floor has an equal spread of low intensity heat, which prevents frost heave in the sub floor under the freezer. A concrete slurry encases the heater tubes, then Insulation was laid over the area, and a top slab provides a trafficable surface for the forklifts.
Plant room and pipe work
Pipework is run in copper tube, and K65 high pressure copper iron alloy tube, inside a hard PVC outer casing, The gap between the two being flooded with expanding foam. Pipes are bracketed every 2m and color coded.
The plant room floor has three coats of epoxy and the machines has stainless steel drip trays fitted to prevent condensate water from collecting on the floor. Spare CO2 refrigerant is stored in a bottle rack inside the plant room.
Operating cost comparison
The system was evaluated against a conventional R134a/CO2 system, as the client had previously installed a plant of this type. The client requested that we provide a quotation and estimated operating costs for both options. The preference was to install the transcritical / sub critical cascade system, as the client believed that it was a marketing tool that could be used in their dealings with the major supermarket chains, which are major customers of his company.
Some estimates where made, that attempted to predict the power consumption of the different plant configurations, but it is not possible to do an exact comparison as only one style of plant was installed.
These spread sheets are attached and detail the equipment installed and the manufactures computer model for the power consumption, for each compressor considered. We also compared the defrosting and floor heating system with a conventional system.
The Glycol floor heating system has a very positive operating cost benefit, compared to electric element sub floor heating. The freezer room would require 33kw of electric heating, with run and standby heater element sets required ( @ 25 watts per m2 ). At 15 cents per kw hour the running cost would be $43300.00 per year if they ran at maximum, but realistically they would run at 50%, this gives a cost of $20,000.00 per year. The cool glycol system runs one ½ HP glycol pump to distribute the glycol through the pipe network at very low velocity. The operating cost of this pump is $394.00 per year The heat removed from the high stage package by the glycol, actually sub cools the liquid CO2 leaving the gas cooler, and is therefore a benefit to the compressors operating conditions and is delivering a 1- 2% gain in system COP as a result.
The warm glycol defrost system, is also using substantially less energy than an electric defrost system, as the total heat used to drive the glycol heating for both the floor heat and defrosting system is less than the motor input power of the low stage rack. The power required to defrost the same evaporator model as those used with electric elements is 18kw ( 3 defrosts of say 30 min each of the four evaporators or 6 hours per day. This equates to $6,241.00 in power consumption, at 15 cents per kw hour. The glycol system uses about $1,000.00 less in power costs to operate the pumps.
The 20kw continuous power saving achieved by the glycol system, would equate to a $26,000.00 saving at 15cents /kw hour. As this heat is recovered from the low stage and is not being transferred to the high stage, the real saving is significantly more than that. We estimate 20 kw THR continuous power is not
transferred to the high stage rack, which reduces the three high stage compressors run time by 20% each.
The choice of Carbon Dioxide as the refrigerant in both stages of the system, provides a significant reduction in the purchase and replacement cost of the gas charge, plus a significant saving in the global warming impact of the system. Typically a plant of this size would require 250kg in each stage . If we assume R134a in the high stage and R404A in the low stage, the total global warming impact potential in the event of a refrigerant leak is equivalent to 1,140,000 kg of CO2 . The system installed has a global warming potential of 350 kg of CO2, (1.5 kg R134a and 10 KG R717) a reduction of 1,139,650 kg, in real terms, this represents .003 % of the global impact of R404A.
When this data is compared to the R134a / CO2 system that was installed at the companies Sydney site, and is conveniently the same size and temperatures, the power consumption is better overall, due mainly to the more efficient high demand ammonia chillers, and the addition of water sprays to the air cooled heat exchangers. This is particularly encouraging as the transcritical system installed should use more power than a conventional cascade system in summer, and less in winter. The fact that the power usage across the summer months is less than the stage 1 plant, makes it very likely that the new CO2 / CO2 system will outperform the Stage 1 system by a considerable amount. The stage 1 system that was considered to be state of the art, when it was installed in 2011. The stage two plant, built 2014, is a plant of similar design to the lastest Melbourne plant , and it is currently outperforming stage 1 by 40%. The stage 3 or Salta drive site, covered in this overview, is out performing stage 2 BY A FUTHER 10%. The owners of the site made the observation, that the new site is 15 times larger in floor area, and double the height of their previous site. This equates to a 30 time larger storage volume, being refrigerated. With 12 months power consumption now on file, the client has advised advised us, that the power consumption of the plant has risen in comparison to the old site by only 80%. (so it is less than double the power usage of their previous site which was 30 times smaller )
They are very Happy !
The ammonia chillers offer the best possible COP due to the high suction temperature, low condensing temperature, and generously sized heat transfer equipment. The COP is more than double that of a standard R134a screw chiller, with an air cooled condenser.
Their very low refrigerant charge allows the system to be used in applications that would not have previously been considered possible.
The compressor is both speed controlled with a VSD, and unloaded with a
Suction unloader, superheat is controlled by a Danfoss motorized expansion valve with digital logic control, and the machine has an automated oil return system, to ensure oil level control is maintained throughout the system.
Each ammonia chiller has a gas charge of 4.9kg of ammonia and 6 litres of 4SA refrigeration oil, with a cooling capacity of 200kw each.
Ammonia chiller with weather panels removed
The ammonia chillers were designed and built by Strathbrook Industrial Service, and have been developed to take ammonia cooling systems into a new age, of extreme low volume gas charges.
The chillers are capable of 200kw cooling with a gas charge of 4.9kg. this equates to 48.97 kw of cooling per kg of refrigerant. These chillers can be used for multiple applications, with this efficiency being achieved for 15 degree water delivery.
summary
The system has been designed and installed to a very high standard and is operating with a high degree of energy efficiency and reliability.
The equipment operates with very stable pressures and temperatures, and receiving high praise from everyone who visits the site. The plant room equipment is very quiet in its operation and has very low vibration levels.
Given that this is the second full scale plant, built to reflect the design detailed in our newly registered Patent, Strathbrooks are extremely confident, that the system will offer long term possibilities, for our future clients projects, and expect to do many more similar systems in the future.
Ian Wilson
Project engineer / Director
