The versatility of ice banks

By Kevin Walter, mechanical engineer at Lutz Refrigeration

Aside from their popularity in the dairy scene, ice banks can be installed Aside from their popularity in the dairy scene, ice banks can be installed in any perishable food application.

Ice banks are a fantastic option where water temperatures needs to be as close to zero as possible without glycol or any other anti-freeze being added.

These kinds of systems are found in facilities where water must be in contact with food products, for example, the snap cooling of cherries, grapes and fruit in general.

Ice banks have been around for as long as most people can remember. They are particularly popular amongst dairies as they give the dairy the ability to generate ice all day long and when bottling or pasteurisation begins, they can rapidly burn the ice off with an effective cooling at the moment of magnitudes higher than their compressor power would normally allow for.

Awarded in February 2019, Lutz Refrigeration installed an ice bank at a meat facility in the east of Johannesburg. The client sought to produce 15000 ℓ/hr of water at as close to 0°C as possible for various meat cooling processes around the factory. This would equate to a water chiller duty of nominally 400kW.

Admittedly, every project comes with its challenges and this one was no different. It was soon discovered that this would be the largest ice bank we’ve ever produced so ensuring a quality installation was top priority. Scheduled to run for five months, the project ran four weeks over schedule and various unforeseen challenges cropped up in the finishing straight, that were of course resolved.

Prior to installation, we bounced ideas around to meet the requirements, and suggested adding salt to the water to try and bring freezing point as low as -2°C. But in the end we erred on the side of safety as the risk of corrosion on the ice coil was too high to justify the extra few degrees of cooling.

System installation

The system comprises of three ice coils each with their own compressor feeding into a split circuit evaporative condenser. Each ice coil is located within a common tank and is monitored for ice thickness individually, controlling the ice thickness between roughly 2mm and 12mm for the melt and build phases.

The benefit to breaking the coil into three sections is that the plant runs in increments of 33/66/100% cooling, depending on client demand. Generally speaking, the plant seldom runs more than two circuits at a time while the other circuits are in melt phase. This keeps peak kVA usage down and ensures that the condenser is well-sized to run the compressors at low condensing temperatures which is similar to a multiplex/rack design philosophy.

As with all installations these days energy saving is critical. For this reason, traditional dry cooled systems were replaced by water cooled condensers which are oversized to be able to run all three compressors at extremely low condensing temperatures. This combined with electronic expansion valves allows for condensing temperatures to be below 35°C even on hot days.

To make a quick and easy comparison between traditional air- and water-cooled plant the difference in Coefficient of Performance (COP) improves from 2.6 to 3.5 (45°C condensing vs 35°C) resulting in 35% more cooling per kW/hr electricity used.

Additionally, the concept of an ice bank gives the flexibility to make ice outside of peak tariff periods and melt ice during the peak periods for your cooling. This takes strain off the electrical grid and moves the client’s energy usage out of the more expensive tariff windows.

Meeting challenges

To elaborate on these challenges, structural requirements on tank design as well as ice build control systems become exponentially more intricate when the tank gets to the scale of this unit so we had headaches finding ways of controlling the ice thickness as the old tried-and-tested approaches could no longer be leant on.

Space became an issue as we had to squeeze an 8000ℓ tank with stainless coils (4km total internal pipe length) as well as an Evapco cooling tower and Plant Skid with all compressors, switchgear and controls onto a site which was basically populated with no space allowed for this unit. We investigated building mezzanines above the electrical DB room which was going to be very difficult with regulations and so on, and eventually had to opt to build a plinth remotely and pipe the chilled water over a bridge over the road.

The final product

This system produces a great mix between traditional ice bank design with a coil in tank while incorporating modern energy saving and control systems to bring this concept into the modern era.

This system will add a major load of electrical power usage to their operation, with a peak kVA draw of as high as 200kVA, however the product that is being chilled is now being chilled far quicker and more directly than the previous cold room air cooling approach, so in this sense the kW cooling will be more efficiently directed to the product saving on energy usage while also increasing production potential at the facility and extending product shelf life too.

Evaporative cooled condensing reduces COP from a traditional air-cooled approach by 35%. Electronic expansion valves ensure that suction pressures are as high as possible without having liquid flood back to the compressor and of course the main trump card to a system like this is the ability to store cooling in the form of ice which can later be used during peak times when the electrical grid is under strain and tariffs are as much as three times higher than standard periods.

Client feedback

As soon as the system went live the client was able to increase production by moving product through the cooling chambers faster and tests began immediately to assess the improvement in shelf by cooling the meat quicker showing results of up to five days more shelf life.

Conclusion

These plants require very little maintenance, however, to be on the safer side this unit will be inspected once a month with a service level agreement being signed to keep it running for decades to come.

Click here to read the issue of Cold Link Africa

 


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