What is 90-Bar?
A bar is a unit of pressure. 90-bar is about 1305 psig (pounds per square inch gauge). In the context of CO2 refrigeration systems, a 90-bar rating signifies the low pressure side of the system can safely operate up to 90 bars of pressure
Why choose 90-bar?
Standard safety relief valves are designed to refrigerant based on the system pressure exceeding its safety limit. With a 90-bar rating, the system can handle higher pressures before the valve activates. This translates to a higher temperature tolerance during downtime events. The system can withstand a greater rise in temperature within the condenser (due to trapped heat) before pressure reaches the relief threshold.
The Benefits of a 90-Bar Rating
In situations where unexpected downtime events are a concern 90-bar refrigeration system offers several advantages:
Stronger components
With a 90-bar rating, the system can handle higher pressures before a safety relief event. This translates to a higher temperature tolerance during downtime events. As the system absorbs heat from the surrounding ambient, it can withstand a greater rise in pressure within the flash tank, liquid and suction lines, and the evaporators.
Improved system uptime
Due to the higher-pressure rating of a 90-bar system, relief events are minimized. Maintaining the refrigerant charge maximizes system uptime and cooling.
Reducing Risks in hotter ambient temperatures
Higher ambient temperatures decrease the amount of time between power loss and a safety relief event, making a relief event/the release of refrigerant more likely to occur. A 90-bar system can allow for system disruptions and increased pressures without having a safety relief event, saving the refrigerant charge. The cost to replace a lost charge includes a service charge for the technician, the cost of replacement refrigerant, and replacing potential product lost during downtime.
For illustration purposes, if a 90-bar and a 45-bar system in the same region were to experience a downtime event on a day with an ambient temperature of 95°F (35°C), the 45-bar system would release refrigerant and the 90-bar system will hold its charge. The 90-bar option offers more assurance that a pressure relief event will not occur.
Pressure Temperature Chart
Frequently Asked Questions
What components does 90-bar affect?
- The display case refrigeration components affected by 90-bar include: refrigerant piping, fittings, valves, and additional components. Systems components affected by 90-bar are compressors, flash gas tank, and associated piping and components.
What is the Pressure-Temperature Relationship in Refrigeration Systems?
- A refrigeration system functions by circulating refrigerant, absorbing heat from the space (evaporator) and rejecting it to the surrounding environment (gas cooler).
- Pressure and temperature are closely linked within the system. As the temperature of the refrigerant increases (during heat absorption), its pressure also rises.
- A properly functioning system maintains a pressure balance within its design limits.
What pressure ratings are display cases typically designed for?
- 45-bar (650psig) has been the standard for display case components.
What is a safety relief event?
- Safety relief events are the release of refrigerant charge through a safety relief valve into the atmosphere when it exceeds the system’s design pressure. Exceeding the system’s design pressure can damage piping and components.
How does a safety relief event occur?
- Initial State: The system is functioning normally. The evaporator coil operates at design operating pressure and temperature, absorbing heat from the cooled space. The compressors act to move the CO2 refrigerant from the evaporator coils to the gas cooler. The gas cooler, at a higher pressure and temperature, rejects that heat into the surrounding ambient air.
- Disruption: An unexpected event, like a power outage, electronic control communication error, or compressor failures due to a lack of oil, disrupts the system’s cycle. The system stops circulating refrigerant, halting the cooling process.
- Temperature Rise & Pressure Buildup: Since the refrigerant isn’t circulating, the flash tank and liquid lines start absorbing heat from the surrounding ambient environment, ultimately causing a rise in pressure within the system.
- Charge Release: The unexpected downtime event disrupts the flow of refrigerant, leading to a rise in pressure within the 45-bar rated segment of the system. This causes the release of CO2 through the safety relief valve in order to protect the system from exceeding pressure limits.
What is the impact of releasing refrigerant?
- Loss of refrigerant leads to the loss of product cooling, necessitates refilling the system, increases operating costs and potentially leads to product spoilage due to system downtime.
- Operating a system without recharging the refrigerant: A system with a less than required refrigerant charge operates less efficiently and will not provide enough cooling to maintain proper temperatures.
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