We’ve all heard the stories … a producer ends up dumping a tank of milk because the “hot milk” was refused. No one likes to think about milk cooling until they have a problem and, let’s face it, the equipment necessary for good milk cooling isn’t cheap. Ignoring your milk cooling equipment, thereby risking milk quality, can be a producer’s downfall. As the average dairy size continues to grow, much of today’s milk cooling remains outdated and inefficient. With increasing restrictions on energy consumption nationwide, as well as the rebates available for refrigeration system replacements or retrofits in some areas, it’s an issue every producer and service professional should educate themselves on.
There are a myriad of new technologies available in the refrigeration industry. A few are beginning to make their way into dairy refrigeration. Utilizing these advancements can help a dairy’s bottom line. Some of these new technologies seem scary, but let’s unpack a few of the basics together.
Energy efficiency features available in chillers
• Variable capacity compressors – Advances in variable speed drives and constant speed-variable capacity compressors have allowed dairy producers to have cost-effective, close control refrigeration systems.
These systems can allow for precise milk cooling at wide range of milk flows. The variable capacity system can provide a narrow range of glycol temperatures to a plate cooler, allowing for a more constant milk temperature leaving the plate cooler.
Beware of the hype, however; this is one of the most oversold technologies currently marketed in terms of promised energy savings. These systems by default do not save energy; they allow for precise cooling without sacrificing energy efficiency as has been done in the past with older technologies. This concept is generally misunderstood in all refrigeration applications.
Additionally, erratic milk flows will result in erratic milk temps regardless of how constant the glycol temperature stays. Solving erratic milk flows can often be simpler and less expensive than a complex refrigeration system.
Digital scroll compressor technology is one of the most energy-efficient options available. Digital scrolls are more efficient than hot-gas bypass, more precise than cylinder unloading and simpler than variable frequency drives. Digital scrolls are hermetic scroll compressors that can rapidly load and unload at a constant speed.
They are able to run down to 10 percent of full capacity. This allows a chiller to precisely maintain glycol and milk temperatures without short-cycling compressors.
These systems create an increased level of complexity that must be balanced by a reliability benefit. In this case, variable capacity compressors increase reliability by “cycling” or stopping and starting less. This reduces the mechanical load on the compressor and start components.
• Electronic expansion valves – EEVs are able to control refrigerant superheat more precisely than standard thermostatic expansion valves. The better control helps protect the compressor from liquid flooding, which increases the compressor reliability and longevity.
In cool weather, the electronic expansion valve can operate reliably with lower head pressures, reducing overall compressor power consumption.
These devices have the greatest potential to save the producer energy, far above any other available technology. They also can be retrofitted to existing bulk tank and chiller systems.
Even with their increased complexity, EEVs can actually increase the reliability of the refrigeration system. The controller for the EEV, generally called the “driver,” has a microprocessor on board that is reading superheat, suction temperature and suction pressure.
If any of these go out of range, an alarm can be generated. This alarm signal can be sent to something as simple as a red light on a control panel or to a central programmable logic controller (PLC).
The EEV driver can also detect a failure of the stepper motor, which would prevent the valve from moving. On a traditional thermostatic expansion valve (TEV), we usually find these problems months or longer after they occur. In the meantime, we have been running inefficiently and may have burned up a compressor or two.
• EC motor-driven fans – Electrically commutated (EC) motors are premium efficiency motors with built-in variable speed control. These fan motors will deliver the precise amount of power required for the ambient conditions. In addition to their efficiency, EC fan motors exceed the quality and durability of standard motor-driven fans.
Like EEVs, EC motors are controlled by a small microprocessor. These small controllers embedded in the fan are full of motor protection features that monitor the incoming voltage, the temperature of the windings and the temperature of the control board itself.
The internal controller will shut down the motor if any of these conditions are out of range. The controller also starts the fan slowly, which reduces the required starting torque.
• New refrigerants – R-410a is the refrigerant of choice to replace R-22 in the air conditioning industry. It is slowly being accepted by the dairy industry. The slow acceptance is due to the bad “rap” it gets from its higher operating pressures, causing safety and reliability concerns.
No refrigerant runs at what anyone would call a low pressure. Normal high-side pressures for R-22 are around 250 psi; for R-410a it is around 350 psi. A leak at either pressure is still a leak.
Additionally, R-410a scroll compressors allow the oft-quoted myth that scroll compressors are more efficient than reciprocating compressors to finally be true. For years, producers have been replacing their reciprocating compressors with less-efficient scrolls at the advice of energy utilities.
A new scroll using R-404a/R-507 is less efficient than a new reciprocating compressor using R-404a/R-507. However, a new R-410a scroll is generally more efficient than a reciprocating R-404/R-507 compressor.
• Aluminum micro-channel condenser coils – The aluminum micro-channel condenser coils used in many packaged air-cooled chillers provide many benefits over standard condenser coils. Their all-aluminum construction heads off corrosion; they allow lower refrigerant charges (therefore saving operational costs) and they are easier to clean.
Low tech – high payback
A lot of “old” technologies are so simple, yet still very effective, so they must be mentioned even while discussing new technologies.
• Well water pre-cooling – While not without its drawbacks, this is the king of energy savings; cooling your milk down to 70 degrees with well water cuts your cooling load roughly in half. The cost to pump water through a plate cooler is much less than the cost of a higher-capacity refrigeration system and the energy required to operate it.
Well water pre-cooling is commonly used on instant cooling systems, but not as often on bulk tank applications. Pre-cooling can ease the load on the bulk tank refrigeration system, provide more constant milk temperatures and cut energy consumption.
• Heat recovery – In most refrigeration systems, the heat removed from the milk winds up in the air, in a drinker or in a lagoon. Heat recovery utilizes the waste heat to pre-heat wash water, reducing utility bills. New heat recovery systems pump water through heat exchangers within a refrigeration system or recirculate it through a storage tank.
Incorporating new technologies
Incorporating new technologies in your milk cooling equipment can improve equipment reliability as well as saving operational costs. However, the most important factor in your milk cooling is to utilize trusted service professionals and equipment dealers that are knowledgeable.
Working with professionals who have experience with these technologies, or are willing to learn them, will ensure you receive the highest benefit from your milk cooling equipment. PD
Jeff Johnson
P.E., V.P., Sales and Engineering
Johnson Thermal Systems Inc.
JeffJ@johnsonthermal.com
