Refrigeration Systems & Components Flashcards
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According to ASHRAE 15, a refrigerating system machinery room must be equipped with a refrigerant detector that activates at a concentration not exceeding:
Answer: The ASHRAE Standard 34 occupational exposure limit (OEL) for the refrigerant in use
ASHRAE 15 requires refrigerant detectors in machinery rooms to alarm and activate ventilation at concentrations not exceeding the refrigerant's occupational exposure limit (OEL) as defined by ASHRAE 34.
A high-pressure relief valve on a refrigeration system is set to relieve at a pressure that:
Answer: Does not exceed the maximum allowable working pressure (MAWP) of the high-side components
Pressure relief valves must be rated and set to relieve at or below the MAWP of the weakest component on the high-pressure side to prevent equipment failure and ensure personnel safety.
What is the primary function of an electronic expansion valve (EEV) compared to a traditional thermostatic expansion valve?
Answer: The EEV provides faster, more precise superheat control using a stepper motor and electronic controller
EEVs use a stepper or pulse-width modulated motor controlled by an electronic controller reading multiple inputs, enabling faster and more accurate superheat modulation than a mechanical TXV, improving efficiency especially at part-load conditions.
When using a pressure-enthalpy (P-H) diagram to analyze a refrigeration cycle, the refrigeration effect is represented by:
Answer: The horizontal distance (enthalpy difference) across the evaporator on the low-pressure line
On a P-H diagram, the refrigeration effect equals the enthalpy of the refrigerant leaving the evaporator minus the enthalpy entering the expansion device, read as a horizontal span at low-side pressure.
In a hot-gas defrost system, refrigerant used for defrosting is drawn from:
Answer: The high-pressure discharge side of the compressor and directed to the frozen evaporator coil
Hot-gas defrost diverts high-temperature, high-pressure discharge gas directly from the compressor to the evaporator, where it condenses and releases latent heat to melt frost from the coil.
An evaporative pressure regulator (EPR valve) installed in the suction line of a multi-temperature refrigeration system is used to:
Answer: Maintain a minimum evaporator pressure to keep the coil above a target temperature
An EPR valve holds the evaporator pressure at or above its setpoint, preventing the coil from getting too cold (e.g., protecting a medium-temperature display case when connected to a low-temperature suction header).
Which condition would cause a refrigeration system to have higher-than-normal suction pressure AND higher-than-normal discharge pressure simultaneously?
Answer: Leaking or failed compressor discharge valve
Failed or leaking discharge valves allow high-pressure discharge gas to bleed back into the suction side, raising suction pressure while reducing the amount of gas actually pumped to the high side, which simultaneously elevates both pressures and significantly reduces capacity.