Power, Cooling, and Environmental Management
This domain tests the physical plant. Know the power path: utility feed → transformer → switchgear → UPS → PDU/ busway → rack PDU → server PSU. Understand UPS types (online/double-conversion versus line-interactive) and that generators carry long outages while UPS bridges the gap until generators start. Know the difference between kW (real power) and kVA (apparent power), and power factor.
Cooling concepts: CRAC/CRAH units, chilled water versus direct expansion, hot/cold aisle containment, and the ASHRAE recommended versus allowable environmental envelopes. Know that humidity too low risks ESD and too high risks condensation; temperature too high shortens hardware life and triggers thermal throttling. Airflow management - blanking panels, sealing gaps, containment - is often cheaper than adding cooling capacity.
Traps: assuming a UPS is sized in kW when it is often rated in kVA; forgetting that cooling failures can cause outages as fast as power failures; and confusing setpoints with actual rack inlet temperatures.
Worked example / rule of thumb: a 100 kVA UPS at 0.9 power factor supports about 90 kW of real load. Rule of thumb: measure at the rack inlet, not at the CRAC return; and remember PUE = total facility power ÷ IT power, where a lower number is better.