Energy Saving Cooling Technologies

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Wednesday, September 18 11:00 AM - 11:30 AM

Location: General Session


Event Information

Title: Energy Saving Cooling Technologies

Description:

Discussion of new technologies and system designs that provide Extruders with operating cost savings through lower energy use. In addition to reduced energy use, this discussion will also present ways to reduce water use that is typical of conventional process cooling systems using evaporative cooling towers.

Type: General Session

Abstract:

Energy Saving Cooling Technologies

Plastic processing has seen many changes over the years. We have seen significant advanced in process throughput and increased quality control as well as automatic and controls, but one thing has remained surprisingly the same – the cooling systems.

Often overlooked or considered not as important as other parts of a plastic processing plant, process water cooling systems are gaining more attention as energy costs continue to increase and concerns over water-use increase. There have been a number of advances in technology that provide increased efficiency to reduce production costs as well as global demand for power and fresh water.

Adiabatic Fluid Coolers

Most plastic processing facilities have a cooling tower to provide cooling to hydraulics, chiller condensers, and other process equipment. These systems typically provide 85 to 95°F water using a conventional evaporative cooling tower. Evaporative cooling towers have been around since the early 19th century and were a practical solution to provide cooling of steam powered equipment. They operate on the principle of evaporation and have seen little change over the year. While very effective at providing cooling, they consume a lot of water and require careful monitoring of the water quality to ensure no biological growth or scale can occur.

In the United States, water is generally plentiful and inexpensive, so there has been little drive to develop cooling technologies that use less water. In Europe and other places in the world where fresh water sources are more scares this is not the case. With limited resources and a heightened awareness of the need to reduce energy and water consumption, the use of fluid coolers has become a popular alternative to conventional evaporative cooling towers.

A dry cooler uses dry air to cool the process water. This is effective but is limited by the temperature of the air. In most cases, the practical limit is a process water temperature leaving the dry fluid cooler about 10°F warmer than the entering air temperature. While very useful in moderate climates, this method is not as practical in many areas where summertime temperature routinely exceed 90°F and the lowest temperature achievable is 100°F or warmer.

To expand the usefulness of fluid coolers as a replacement for evaporative cooling towers manufacturers have added evaporative pads to their fluid coolers to pre-cool the warm summertime air through a process called adiabatic cooling. Adiabatic cooling occurs by evaporating water into the hot dry air entering the fluid cooler. As the air absorbs water it is cools and the cooler air is able to provide the desired leaving water temperature. Although this technology used some water, the system is extremely water-efficient and only needed during peak summertime conditions. The result is as much as a 90% reduction in water use versus a conventional evaporative cooling tower. In addition, the water is fully evaporated and not recirculated, as is the case with a conventional cooling tower, so there is no need for water treatment.

Variable-Speed Compressors

When manufacturing processes require water cooler than 85°F, a chiller is used. A chiller uses a refrigerant to remove heat from the process water. The process water passed through part of the chiller called an evaporator. In this part of the chiller, the warm process fluid passes through one side of a vessel and on the other side of the vessel, liquid refrigerant is present. Due to the properties and pressures of the refrigerant, the process water actually boils or evaporates the refrigerant and the process fluid cools to 50°F or so. The refrigerant gas leaves the evaporator and enters the compressor. The compressor compresses the case and the high-pressure, hot refrigerant case goes to another part of the compressor called the condenser. In the condenser, either air or water passed through one side of the condenser to cool the refrigerant and condense it pack into a liquid. Due to the properties and pressures of the refrigerant, condensation occurs at temperatures typically 120°F or warmer. Due to the higher condensing temperature, a cooling tower is often times used to provide cooling of chiller condensers.

Compressor and the use of refrigerant have been around since the 19th century as well and many different types of compressors are used by until recently they all operated at one fixed-speed. A relatively new technology is variable-speed compressors. With this technology, energy use reduction happens by slowing the speed of the compressor. When the compressor slows down there is a reduction of cooling capacity. Most chiller systems designs use the maximum possible heat load at 100% production capacity of the process equipment to ensure there is always enough cooling capacity. In most cases, the production equipment is operating at much less than maximum capacity so the chiller is ‘over-sized’ so a variable speed compressor is a great way to salve energy.

Power use is a square relationship meaning as the speed changes the power use changes as a square of the speed change. For instance, if a compressor operates at 80% of its maximum speed, it will use 64% of its full-speed power. This technology is available in a wide-range of compressor sizes and the initial equipment cost premium for this technology, depending on the hours of operating and load profile, can pay for itself in 12 to 18 months.

Free-Cooling Systems

Considering the ever-increasing need for more efficient systems, the newest trend in central chiller system design is to combine the benefits of a variable-speed compressor with that of an adiabatic fluid cooler. These hybrid system use an adiabatic fluid cooler to cool the condenser of the chiller during the summertime, but when the outside is cooler enough, the adiabatic fluid cooler directly cools the process water, which means the chiller is turns off completely. This saves 100% of the electrical cost of operating the chiller, which is the most significant power consumption of any process cooling system.

The number of hours of Free-Cooling increases when the process fluid temperature is warmer. In many extrusion applications, the chilled water set point temperature is such that the chiller may only need to run 50% of the year.

Conclusion

Energy costs continue to increase, as does the awareness of and desire to reduce the demand for power and fresh water resources. These factors require a continuous drive to look for ways to improve the sustainability of our operations through a careful look at innovative technologies such as adiabatic fluid coolers, variable-speed compressors, and free-cooling systems.


Speakers