Nathan Orr is back. In this podcast, we discuss suction pressure in market refrigeration and how rack techs think about it differently than HVAC.

On parallel rack systems, suction temperature helps technicians determine the cooling load and how to get that to temperature. You run your discharge air temperature a bit lower than the product temperature. Your suction pressure also lets you know if your coil is reaching the correct temperature. Coil temp, also called suction saturation temperature (SST), is a vital metric for rack system operation. Lower suction pressure indicates a lower coil temperature or SST.

The evaporator pressure regulating valves help control the evaporator pressure to manipulate the evaporator temperature. Compressors also help drive suction pressure, which is critical because racks may have several of them.

When you walk into a rack room, you may see around five compressors. All suction lines tie into a single suction header (same goes for discharge and liquid lines and headers). Typically, the rack is constructed to maintain the SST even if a compressor goes down. When the SST no longer maintains, there will be a "rack down" call.

If a case is not keeping temperature without an apparent rack issue, you want to take your superheat at the case to get an idea of the suction. The superheat, SST, and suction pressure will be your key indicators of problems, including defrost issues, clogged TXV strainers, and airflow problems. Overall, rack refrigeration systems work best with high suction pressure and low liquid pressure.

Nathan and Bryan also discuss:

• TD in rack refrigeration
• Setting EPR valves
• Rack sizing
• "Rack down" calls
• Troubleshooting produce cases
• Holdback valves
• Frozen cases
• Using dry steam

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