One more consideration for chillers: due to the nature of this application, the coefficient of performance (COP) and therefore the energy efficiency ratio (EER) are much lower than most chilled water systems. This means the horsepower per ton requirements are much higher than typical HVAC or even many other process applications. Compression ratio is significantly higher in this application than in most chiller applications. This increases the lift the compressor must generate, as well as increasing the input and waste energy. Basically, the plasma fractionation process requires bigger and more heavy-duty equipment to do the work because it is all done at significantly lower temperatures.
Because this chiller system needs to be colder than usual (below freezing), you might need a specialty refrigerant because plasma fractionation requires such low temperatures. For example, R-134a, a common refrigerant, is usually not suitable in a chiller supplying fluid temps below -13℃ (8℉).
Refrigerant selection influences the chiller design because it is typically difficult and costly—if not impossible—to convert a chiller to a different refrigerant. Therefore, you need to commit to your refrigerant early in the design process. Consult with the chiller manufacturer before you arbitrarily select a refrigerant, and make sure you consider the equipment already in use, and the serviceability, safety, and projected future availability of additional equipment. Environmental, toxicity, and combustibility (flammability) concerns and legislation may also constrain your refrigerant selection.
One final word of advice: refrigerant leaks can be damaging and costly. Make sure you actively monitor for leaks and make repairs immediately when they happen.
While the chiller controls the temperature, the pump powers the flow. The pump recirculates the liquid, or thermofluid, from the chiller through the whole building using a series of heat exchangers and vessel jackets.
Properly aligning and balancing a pump is critical to achieving reliability and longevity. A pump of this capacity is typically driven by a separate external electric motor, requiring a shaft seal to allow the input power to enter the pump without the glycol leaking out.
The piping forms the delivery system of the cooling system. Piping and manual and automatic valves within the pumps control the rate and direction of the glycol flow.
The combination of the low temperature fluid in the pipe and the dew point of the air outside of the pipe can cause condensation to form on the surface of the pipe, just like a cold glass of water on a hot day. Condensation can lead to dripping, which may create mold, slippery surfaces and ice blocks. To prevent this, insulate all exposed pipes. Select the right insulation with two things in mind: minimizing heat gain into the piping (which is a parasitic heat load) and ensuring the surface temperature of the insulation remains below the dew point of the surrounding air. A vapor barrier and sealed insulation sheathing prevents condensation from forming on the pipe, and the insulation prevents the surface of the insulation sheathing from being cold enough to form condensation. The insulation needs an air-tight seal.
A normal chilled water system uses only water, but in this case, you’ll need to use a heat transfer solution instead of chilled water to achieve heat transfer fluid temperatures low enough for plasma fractionation. The solutions generally include ethylene glycol or propylene glycol (mixed with water) which can bring the freezing point of the mixture to below -10℃ (14℉).
A few thousand gallons of the glycol water mixture run through the entire cooling system. The liquid is recirculated through a closed system and only replaced if it is spilled or in the event of facility construction. These fluids can be oily or toxic, so be aware of spills and make a clear plan to prevent fluids from entering the city sewer.
Additionally, there are complications that come with using glycol: biological growth control, increased corrosion, and lower heat transfer rates. Using glycol requires larger heat exchangers and higher flow rates, therefore requiring bigger pipes, bigger pumps, and higher pumping energy requirements compared to water. Chemical additives packages (i.e. inhibitors and buffers) must be added to the glycol to inhibit biological growth and corrosion. Also, perform scheduled, periodic monitoring and chemical testing on the glycol to ensure it is not degrading.