Thursday, 02 March 2017 14:55

Will your milk cooler meet the new rules?

Written by 
DairyNZ urges farmers to evaluate all options before deciding on a new milk cooling system. DairyNZ urges farmers to evaluate all options before deciding on a new milk cooling system.

A plate heat exchanger (PHE) is the most effective means of cooling milk, says DairyNZ.

But if your current plate heat exchanger and refrigeration unit combination are not capable of meeting the new milk cooling regulations you may need to consider a secondary cooling option.

A PHE consists of a series of very thin stainless steel plates. Water flows along one side of each plate while milk flows along the other. Heat is transferred from the milk to the water via the plate. The capacity of a plate cooler is adjusted by adding or subtracting plates.

The easiest way to check the effectiveness of the plate cooler is to compare the difference between the incoming temperature of the cooling water and the outgoing temperature of the milk leaving the plate cooler.

DairyNZ says an efficient PHE should cool milk to within 2°C of the water temperature before it enters the PHE. For example, if the temperature of the incoming cooling water is 14°C, the temperature of the milk exiting the plate cooler should be about 16°C.

Vat refrigeration is another option. In refrigerated/direct expansion tanks the refrigerant is pumped into the jackets (evaporators commonly referred to as ‘dimple plates’) on the internal surfaces of the bulk milk tank.

Here the refrigerant expands as it takes heat from the milk, is pumped out of the jackets, compressed then pushed into the condenser. The hot refrigerant is cooled by air (or water) flowing through the condenser fins. The cooled gas condenses into a liquid and is pumped back into the jackets around the bulk milk tank to start the cycle again.

Direct expansion has the disadvantage of maximum power draw during and after milking, which is generally peak rate. If large electric motors are used there can be problems in areas of poor power supply.

Direct expansion refrigeration systems are pressurised, which means they require a skilled technician for maintenance.

A secondary cooling option – necessary if your current plate heat exchanger and refrigeration unit combination are not capable of meeting the new milk cooling regulations -- may be costly and require a long payback period. But it may yield the benefit of heat recovery, enabling you to save on hot water costs.

DairyNZ advises farmers to carefully evaluate all options to ensure the system is fit for purpose without over capitalising.

Other options suggested by DairyNZ are;

Cooling towers

Cooling towers can very effectively cool water especially when humidity is low. Water can be cooled to within 5°C of the wet bulb temperature in a properly designed plant.

The most effective plants are fan forced and turn over a large store of water every hour. They operate overnight to cool a large water volume, usually 4½ times the volume of the daily milk yield.

Ice banks

Ice banks generate ice along evaporator coils using night rate power. The ice is used to chill water for the pre-cooler. The warm water is then returned from the pre-cooler to the top of the ice bank and cooled again as it runs down the ice.

Snap chillers

These use a refrigeration system to cool water or a food grade glycol/water mixture. Glycol systems tend to use a very small volume of fluid and create the chilled fluid on demand (at milking time).

Thermal stores

Thermal storage systems chill water using off peak power and require an insulated storage tank to hold a large (one day’s milking) volume of chilled water. Using more energy than a direct expansion tank, they have advantages in installation and maintenance.

Vat wraps

Vat wraps are only utilised by 20% of dairy farms in New Zealand but can save about 15-25% of milk cooling costs.  They insulate milk from outside temperatures, preventing it from heating up and reducing energy used by the refrigeration unit.

More like this

Strong uptake of good wintering practices

DairyNZ has seen a significant increase in the number of farmers improving their wintering practices, which results in a higher standard of animal care and environmental protection.

Better animal genetic gain system

A governance group has been formed, following extensive sector consultation, to implement the recommendations from the Industry Working Group's (IWG) final report and is said to be forming a 'road map' for improving New Zealand's animal genetic gain system.

OSPRI's costly software upgrade

Animal disease management agency OSPRI has announced sweeping governance changes as it seeks to recover from the expensive failure of a major software project.

Musical chairs

OPINION: DairyNZ's director elections has seen scientist Jacqueline Rowarth re-elected for another three-year term.

Featured

Massey Research Field Day attracts huge interest

More than 200 people turned out on Thursday, November 21 to see what progress has been made on one of NZ's biggest and most comprehensive agriculture research programmes on regenerative agriculture.

Expo set to wow again

Stellar speakers, top-notch trade sites, innovation, technology and connections are all on offer at the 2025 East Coast Farming Expo being once again hosted in Wairoa in February.

A year of global challenges

As a guest of the Italian Trade Association, Rural News Group Machinery Editor Mark Daniel took the opportunity to make an early November dash to Bologna to the 46th EIMA exhibition.

National

OSPRI's costly software upgrade

Animal disease management agency OSPRI has announced sweeping governance changes as it seeks to recover from the expensive failure of…

Machinery & Products

BA Pumps expand

Cambridge based BA Pumps & Sprayers, specialists in New Zealand-made spraying equipment, has acquired Tokoroa Engineering’s product range, including the…

Entries open for innovation award

Fieldays and its renowned Innovation Awards are celebrating their 57th year, marking a longstanding tradition in the agricultural calendar, with…

» Latest Print Issues Online

Milking It

Chinese strategy

OPINION: Fonterra may have sold its dairy farms in China but the appetite for collaboration with the country remains strong.

Not fair

OPINION: The Listener's latest piece on winter grazing among Southland dairy farmers leaves much to be desired.

» Connect with Dairy News

» eNewsletter

Subscribe to our weekly newsletter