Two distinct constraints, one room
A UPS room has to satisfy two unrelated thermal-management constraints. Heat extraction means removing the kW of waste heat that the UPS and battery charger put into the room every second; failing means the room temperature climbs until something shuts down on over-temp. Hydrogen ventilation applies only to lead-acid (VRLA and flooded) batteries, which evolve hydrogen during charging; failing means a potentially explosive atmosphere develops in the worst case. Sealed lithium chemistries don't need the second check.
Where the heat comes from
UPS heat is its electrical loss: P_loss = P_load × (1/η − 1). A 94%-efficient UPS at 20 kW load dissipates ~1.3 kW continuously. Battery float charging adds another few hundred watts to a few kW depending on capacity and chemistry. Total heat scales with UPS loading, not nameplate — under-loaded UPS rooms often surprise dealers with how cool they stay.
IEC 62485-2 ventilation formula
For lead-acid batteries, IEC 62485-2 specifies a minimum air-flow rate of Q = 0.05 × n × I_gas (m³/h) where n is the total cell count andI_gas is the per-cell charge current that contributes to gassing. For VRLA in float, I_gas is about 20% of the nominal current; for equalisation, much higher. We expose the conservative full-current form so the user picks the worst-case airflow. The standard also requires a minimum of 1 air change per hour for the room volume — we surface that as a separate pass/fail check.
Sizing the cooling unit
Cooling capacity is usually expressed in kW (SI), BTU/hr (US), or refrigeration tons (HVAC convention: 1 ton = 3.5168 kW). For small UPS rooms (under 5 kW heat load), a domestic split AC is usually adequate. Above that, look at dedicated computer-room AC (CRAC) units with N+1 redundancy. Always add a design margin of 15–25% for duct losses, future expansion, and worst-case ambient days.