A mechanical drawing shows a chilled water pipe marked '6" CHW S'. What does the 'S' most likely indicate?
Correct Answer
A) Supply line
In HVAC drawings, 'S' following CHW (Chilled Water) typically indicates the supply line, as opposed to 'R' for return line in chilled water systems.
Why This Is the Correct Answer
In HVAC mechanical drawings, 'S' following CHW (Chilled Water) is the standard abbreviation for 'Supply line.' This indicates the pipe carries chilled water from the chiller to the cooling equipment or air handling units. The supply line delivers the cold water at design temperature, typically around 42-45°F, before it absorbs heat and returns through the return line (marked 'CHW R'). This is universal HVAC notation.
Why the Other Options Are Wrong
Option B: Safety line
Suction line terminology is primarily used in refrigeration systems for the low-pressure vapor line from evaporator to compressor. In chilled water systems, pipes carry liquid water, not refrigerant vapor, so suction line designation doesn't apply. Chilled water systems use supply and return terminology instead.
Option C: Suction line
Secondary line is not a standard HVAC piping designation. While secondary systems exist in complex HVAC designs, they would be marked differently, typically with more specific notation like 'SEC' or numbered designations. The single letter 'S' in chilled water systems universally refers to supply, not secondary applications.
Memory Technique
Remember 'CHW S = Supply' and 'CHW R = Return' - think 'S for Sending cold water out, R for Receiving warm water back.' Supply goes TO the equipment, Return comes FROM the equipment.
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