Processing applications have seen many changes over the years. We have seen significant advancements in process throughput and increased quality control, as well as automation and controls. But one thing has remained surprisingly the same — the cooling systems. What most people do not realize is there are new technologies today that can reduce their industrial cooling system operating costs by more than 40%.
Often overlooked or considered not as important as other parts of a manufacturing plant, process water cooling systems are gaining more attention as energy costs and concerns over water use continue to 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.
Cut water use by 90% with adiabatic fluid coolers
Most processing facilities have a cooling tower to provide cooling to hydraulics, chiller condensers and other process equipment. A cooling tower has a fan and evaporates water to produce 85°F process water. While effective at providing cooling, it uses a lot of water and requires water treatment to control biological growth. Cooling towers also expose the process water to the atmosphere and then require constant filtering.
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.
Similarly, a fluid cooler uses ambient air to cool the process water. However, this is done through a cooling coil and without exposing water to the atmosphere. This method is effective but limited by the temperature of the ambient 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.
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 dry air entering the fluid cooler. As the air absorbs water, it is cooled, and the cooler air is able to provide a consistent and stable output leaving water temperature of 85°F to process.
Although this technology uses some water, they 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.
Reduce energy consumption up to 34% with variable-speed chiller compressors
When manufacturing processes require water cooler than 85°F, a chiller is used. A chiller uses refrigerant, a compressor and an evaporator to remove heat from the process water and cool the process fluid to approximately 50°F.
Compressors and the use of refrigerant have been around since the 19th century, and many different types of compressors are used. But until recently, they all operated at one fixed speed. A relatively new technology is variable-speed compressors. With this technology, energy use is reduced by slowing the speed of the compressor to just what is needed for the conditions.
When the compressor slows down, there is a reduction of cooling capacity. Most chiller system 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.” A variable speed compressor is a great way to save this excess energy.
Power use is a “square relationship,” meaning that as the compressor 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. In addition, this initial equipment cost premium for this technology, depending on the hours of operating and load profile, can pay for itself in 12-18 months.
Dramatically cut chiller energy costs with 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 systems use an adiabatic fluid cooler to cool the condenser of the chiller during the summertime, but when the outside ambient temperature is cool enough, the adiabatic fluid cooler directly cools the process water, which means the chiller 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 applications, the chilled water set point temperature is such that the chiller may only need to run 50% of the year.
Bob Smith has 30 years of experience at Thermal Care and is currently the director of product management for the company.
