Milk cooler a clever on-farm solution

Current regulations require that milk is no warmer than 18˚C at the completion of milking, and is cooled to 7˚C or below, within three hours of completion.

The new regulations, largely based on the US Food and Drug Administration grade A pasteurised milk ordinance, has several requirements:

Within four hours from the start of milking the milk must be cooled to 10˚C or below

Within six hours from the start and two hours of completion, the target temperature is 6˚C

Once cooled, the milk must be held at 6˚C or below until collection or the next milking cycle

Once cooled, stored milk temperature must not exceed 10˚C as the product of subsequent milkings is added.

Currently most systems rely on the tried and tested method of cold water plate coolers and simple refrigeration plant to achieve required temperatures. And therein lies a potential problem.

With median temperatures of NZ bore water around 19-20˚C, it is only feasible to get milk temperatures down to around 16-18˚C, which obviously meets current, but not future, requirements. So to achieve the 10˚C threshold a secondary cooling element must be introduced. In its simplest form this is likely to be a body of cold water chilled by a refrigeration plant, probably using off-peak electricity and held in an insulated vessel. The temperature will need to be sub 7˚C to allow it to be passed through a second plate cooler and bring into the vat at the 10˚C threshold. This type of system will require large volumes of water, possibly problematic for future installations, and from a thermodynamic perspective very inefficient.

The alternative to plate cooling based systems is to go the route of secondary or ‘snap chill’ layouts that use modern refrigeration systems to get milk to the required temperature quickly, and hold it there for the duration. These could achieve economies by saving power and large quantities of hot water via their heat exchanger properties.

One such system was showcased at the recent South Island Agricultural Fieldays at Kirwee, and indeed it won the premier prize for NZ innovation and manufacture.

The Coolsense VariCool features a standalone unit built onto a substantial chassis, and containing all the system components. This lends itself to easy installation, usually less than one day.

The heart of the unit uses a variable output compressor supplied by Danfoss that can change the flow of the glycol based chilling unit from 3800 to 13,000L/hour to meet demand. This ability to increase or decrease flow rates results in significant energy savings over 30% when compared to fixed speed compressor systems. The ability to adjust the compressor load to the system requirements results in temperatures being held to target more precisely, and increasing the energy saving efficiency of the plant.

Also, the system is highly automated, allowing it to look after a number of tanks at one time, and keep them all at the required temperature. After installation the company takes control of monitoring remotely, and alerts the operator to any anomalies, so protecting a valuable asset – the vat of milk.

While initial installation costs may look a little high, the peace of mind achieved by opting for a one-step system must have its benefits. Considering the potential for energy savings up to $14,000 per annum over conventional systems, plus the ability to generate up to 500L/hour of water at 70˚C, it might be worth looking at.

www.coolsense.co.nz