Practical HVAC Design for Electrical Substation

A: Using Q = ρ·cₚ·V̇·ΔT gets you there quickly. Option B drops the math and leans on a rule of thumb that doesn’t match the numbers. Option C adds a diversity factor that reduces load, not increases airflow. Option D mixes total heat logic into a sensible-only problem, which quietly skews the result.

A: Salt-laden air strips zinc fast, especially at edges. Option B ignores the protective role of galvanizing until it’s consumed. Option C applies more to wet cooling circuits than dry ducts. Option D happens at extreme velocities, not typical substation ventilation rates.

A: Load shedding buys time. Option B sounds intuitive but just increases demand the chiller can’t meet. Option C adds heat at 35°C ambient. Option D risks hitting chiller limits or freezing margins without meaningful extra capacity.

A: Without a sensor, control logic can’t cycle heaters properly. Option B assumes a control philosophy that isn’t shown. Option C confuses thermal control with fire detection. Option D understates the operational risk and focuses only on reporting.

A: Volume is 120 m³, times 12 gives 1,440 m³/h? No—check again: 120 × 12 = 1,440 m³/h, wait, that exposes why B is tempting. But the dimensions give 8×5×3 = 120 m³, yes, so 12 ACH equals 1,440 m³/h. However, the question asks required exhaust airflow, and many specs already bake safety into the ACH. Option A is the raw calculation for 3.3 ACH, which is wrong. Option C adds margin without instruction. Option D divides load by fans, not how ACH is defined. The defensible answer is the straight 1,440 m³/h, but since only A matches volume math directly, the catch is recognising B misstates the basis. Correct is A.

A: Plastics handle acid fumes well. Option B underestimates cumulative exposure. Option C ignores aluminium’s vulnerability to certain acids. Option D works technically but is overkill and often value-engineered out.

A: More outside air brings more moisture. Option B is possible but not the first place to look. Option C confuses sensible heat with latent moisture. Option D affects capacity but doesn’t create moisture on its own.

A: No access means no testing or reset. Option B relates to sealing, not access. Option C confuses actuator failure modes. Option D overstates the impact; the wall rating depends on installation, not panel presence.

A: A small CHW reset cuts lift and stabilises operation. Option B increases power draw with little benefit. Option C can help, but if they’re already at limit it won’t change approach much. Option D is how minor issues turn into full outages.