A refrigeration system with an R-410A condensing unit is located on a rooftop 15 metres above the evaporator, which is rated for 30,000 BTU/hr (8.79 kW). The manufacturer specifies a maximum suction line pressure drop equivalent to 2 K (2°C) temperature glid. Using a reputable piping design chart for R-410A, which of the following nominal copper tube sizes for the suction line (OD indicated) would most likely meet the pressure drop requirements without excessive oil return issues?

Question: A refrigeration system with an R-410A condensing unit is located on a rooftop 15 metres above the evaporator, which is rated for 30,000 BTU/hr (8.79 kW). The manufacturer specifies a maximum suction line pressure drop equivalent to 2 K (2°C) temperature glid. Using a reputable piping design chart for R-410A, which of the following nominal copper tube sizes for the suction line (OD indicated) would most likely meet the pressure drop requirements without excessive oil return issues?

Answer options: ✅ 1 1/8 inch (28.58 mm)

• 7/8 inch (22.23 mm)
• 5/8 inch (15.88 mm)
• 1 3/8 inch (34.93 mm)

Correct answer: 1 1/8 inch (28.58 mm)

Explanation: For a 30,000 BTU/hr R-410A system with a 15-meter vertical lift, a 1 1/8 inch (28.58 mm) suction line offers an appropriate balance between minimizing pressure drop (crucial for capacity and efficiency) and maintaining sufficient gas velocity for oil return, as determined by piping design charts. A smaller line would lead to excessive pressure drop, while a larger line could compromise oil return on the vertical lift.