The most cost-effective method of recovering refrigerant from a low-pressure chiller with more than 500 lbs of refrigerant and to meet EPA requirements is to recover the refrigerant using what protocol?

Correct Answer: Option D — liquid recovery using a liquid pump, followed by vapor recovery using a vacuum pump based recovery unit

EPA guidelines and thermodynamic efficiency dictate removing the bulk liquid refrigerant first via a liquid pump, then using a vacuum-based recovery unit to extract remaining low-pressure vapors.