Mechanical ventilation is being laid out for an equipment room that holds a large refrigerant charge. Where should the exhaust pickup be placed, and what is the reason for that placement?
- AHigh at the ceiling, because refrigerant vapor rises through the room the way natural gas does above the machines
Natural gas is lighter than air and rises, which is why fuel gas detection sits high. Carrying that habit to refrigerant puts the pickup in exactly the wrong place and leaves the hazard on the floor.
- Low near the floor, because refrigerant vapor is heavier than air and collects at the lowest level
- CAt the doorway, because that is the path vapor takes when it leaves the room and the corridor
A doorway is a leakage path, not a controlled exhaust point. Ventilation has to capture vapor where it settles rather than waiting for it to drift out into a corridor.
- DDirectly above the compressor, because heat from the machine carries the vapor upward to the roof
Machine heat creates some local air movement but does not lift a dense vapor cloud off the floor and hold it there. The bulk of a release still ends up at the lowest point of the room.
Why B is correct
Because refrigerant vapor is denser than air, it sinks and builds a layer along the floor. Placing the exhaust pickup low puts the ventilation where the hazard actually is, so the system removes the concentrated vapor instead of drawing off the clean air above it.
What this question is testing
The item checks whether a candidate knows the vapor density of refrigerant relative to air and can apply it to ventilation design and sensor placement. It specifically probes whether the candidate wrongly transfers the lighter than air behavior of fuel gas to refrigerant.
On the job
This is why a trench, a sump, or the bottom of a stairwell next to a chiller room is treated as the worst place to be after a release, and why monitor sensor heads are mounted low on the wall rather than at the ceiling. It also explains a grim detail of leak incidents: a worker who becomes disoriented and drops to the floor falls into a higher concentration, which is why rescue means ventilating and using supplied air, not reaching in.
Memory technique
Refrigerant pools like water on the floor. Drain it from the bottom, the same way you would drain a puddle.
Exam tip
Refrigerant sinks, fuel gas rises. Any answer that puts refrigerant exhaust or detection at the ceiling is wrong.
Where to look it up
Refrigerant vapor is heavier than air, so exhaust and sensors go low in the room.