Parallel Racksory Name
A centralized supermarket system piping multiple compressors in parallel to shared suction and discharge headers.
What is a multiplex (or parallel compressor rack) system?
A defrost method suitable only for medium-temperature cases operating above 32°F that runs evaporator fans while the compressor is off.
What is an off-cycle (or air) defrost?
The high-side vessel that captures oil mist from discharge gas and sends it to the central oil reservoir.
What is the main discharge oil separator?
A circulating liquid fluid—such as water or glycol—that transfers heat from display cases to a primary refrigeration chiller.
What is a secondary coolant (or secondary loop fluid)?
The minimum full system charge threshold that subjects commercial refrigeration equipment to mandatory EPA leak rate rules.
What is 50 pounds?
The typical saturated evaporating temperature range for a supermarket medium-temperature display case rack.
What is 20°F to 25°F (for 35°F to 40°F case temperatures)?
A rapid commercial defrost strategy that routes high-pressure, high-temperature discharge vapor directly into evaporator coils.
What is hot gas defrost?
The storage vessel on a parallel rack that maintains a reserve of lubricant under intermediate pressure.
What is an oil reservoir?
The primary natural refrigerant increasingly used as a low-temperature secondary or direct expansion fluid in cascade supermarket racks.
What is carbon dioxide (CO2/R-744)?
The maximum allowable annual leak rate threshold for commercial refrigeration appliances containing 50 or more pounds of refrigerant.
What is 20% (under EPA Section 608)?
The two primary methods rack controllers use to modulate compressor capacity to match fluctuating store loads.
What are compressor staging (cycling) and cylinder unloaders (or VFDs)?
The auxiliary valve used in hot gas defrost loops to create a pressure differential that drives hot gas through the evaporator.
What is a differential (or holdback) check valve?
The valve mounted on top of the oil reservoir that vents excess refrigerant vapor back to the suction header.
What is an oil reservoir pressure differential check valve (vent valve)?
The main environmental advantage of converting a supermarket from direct expansion (DX) to a secondary loop design.
What is a major reduction in synthetic refrigerant charge and leak points?
The mandatory timeframe a technician has to repair a commercial system once the leak rate threshold is exceeded.
What is 30 days?
The auxiliary heat exchanger used on supermarket racks to drop liquid line refrigerant temperatures down to 40°F–50°F before reaching display cases.
What is a mechanical subcooler (or liquid subcooling circuit)?
The control device that terminates defrost when a specific coil temperature is reached, regardless of remaining timer schedule.
What is a defrost termination thermostat (or temperature sensor)?
The component mounted on each compressor crankcase sight glass that meters oil into the crankcase on demand.
What is an oil level regulator (mechanical float or optical electronic)?
The type of pump used in secondary coolant loops to continuously circulate chilled glycol across multiple display cases.
What is a centrifugal circulation pump?
The two verification tests required by the EPA: one performed before recharging, and one performed at normal operating pressure.
What are an initial verification test and a follow-up verification test?
The piping problem prevented by mechanical subcooling during long liquid-line runs across supermarket roof trusses.
What is flash gas (premature boiling of liquid refrigerant)?
The defrost method where liquid refrigerant is boiled off inside a warm header before entering the suction line to prevent compressor slugging.
What is reverse-flow hot gas defrost with a suction re-evaporator?
The differential pressure setting typically maintained between the oil reservoir and the suction header to feed oil regulators reliably.
What is 5 to 20 psid (differential)?
A dual-fluid system where the evaporator of a high-temperature circuit condenses the discharge of an ultra-low-temperature circuit.
What is a cascade refrigeration system?
The required record-retention period for commercial refrigeration leak inspections and service logs on 50+ lb systems.
What is 3 years?