As the Environmental Protection Agency continues to phase out the use of hydrofluorocarbons such as R22 or R134A, the food processing industry is turning to packaged refrigeration equipment. Why? These low-charge chillers use ammonia or CO2 and a secondary refrigerant to provide a safer method for refrigeration.
In last week’s post, I outlined the benefits of using low-charge packaged refrigeration equipment. However, there are many different types of these systems. The system best fit for your facility is dependant on how many tons of refrigeration you need and at what temperature. (If you’re unsure, reach out to your packaged refrigeration equipment provider for clarification).
Below are five types of refrigeration systems that can be incorporated into low-charge packaged refrigeration equipment:
1. Recirculation system — A recirculated system utilizes a centralized refrigeration machine room where pumps recirculate expanded, cooled liquid from a vessel. Typically, excess liquid refrigerant is provided to the evaporators (cooling coils) to increase heat transfer in the evaporators. If there is excess liquid fed to the evaporators (known as overfeed) it is carried back to the vessel in the suction line (known as wet suction).
2. Direct expansion (DX) system — A DX system uses the pressure differential provided by the refrigerant compressors to move room-temperature, high-pressure liquid from the centralized refrigeration machine room to the evaporators. The refrigerant is expanded, and therefore cooled, directly at the unit. Typically, the liquid is fed to the evaporator at a rate that allows the refrigerant to evaporate so there is typically no liquid found in the suction line (known as dry suction).
3. Cascade system — A cascade system uses a combination of two centralized refrigeration systems (secondary refrigerant) to work in unison to provide cooling to evaporators. The high-temperature refrigeration system (usually ammonia) pulls heat away from the lower-temperature refrigeration system. The lower-temperature refrigeration system (usually CO2) typically uses recirculated liquid to provide cooling to the evaporators.
4. Distributed system — A distributed refrigeration system uses localized refrigeration systems located near the evaporator to keep the refrigerant charge lower. Each evaporator has its own compressors and condensers.
5. Secondary system — A secondary refrigerant system uses a centralized refrigeration system to chill large amounts of a secondary coolant (also known as secondary brine or glycol). The secondary coolant is then pumped out to each air handling unit. Primary refrigerant does not leave the machine room, so the refrigerant charge is minimized and the risk of exposure to plant personnel is greatly reduced.
To learn more about low-charge packaged refrigeration equipment, download our Packaged Refrigeration Equipment Buyer’s Guide.
Stellar is a fully integrated firm focused on planning, design, pre-construction, construction, refrigeration, mechanical & utility, building envelope, and total operations & maintenance services worldwide. Visit the company's blog at www.stellarfoodforthought.net