CRAC Sensible Capacity and Return-Air Derate
Computes sensible CRAC capacity from airflow and supply-to-return temperature rise.
Example
You enter
- Unit airflow (cfm) 12000
- Supply air temperature (deg F) 55
- Rated return air temperature (deg F) 75
- Contained return air temperature (deg F) 85
- Bypassed return air temperature (deg F) 68
You get
- Rated-condition sensible capacity 259200 Btu/h
- Rated-condition tons / kW 21.6 tons / 76.0 kW
- Contained capacity btu h 388800
- Contained change (%) 50
- Bypass change (%) -35
Details, formula, and sources
Computes sensible CRAC capacity from airflow and supply-to-return temperature rise, then quantifies containment gain and bypass-air derate. Airflow measurement, fan heat, coil data, and manufacturer ratings govern.
sensible capacity = 1.08 x airflow x (return temperature - supply temperature); tons = Btu/hr/12,000.
The ASHRAE air-side sensible-heat relation and computer-room cooling rating practice. Manufacturer performance data and ASHRAE TC 9.9 govern.
A public sensible-heat balance and unit conversions.
Estimate. AHJ and licensed professional govern.
Field names used by the API: airflow_cfm, supply_temp_f, return_temp_f, contained_return_temp_f, bypass_return_temp_f, capacity_btu_h, capacity_tons, contained_capacity_btu_h, contained_change_pct, bypass_change_pct
- Air constant 1.08 at ordinary standard-air conditionsASHRAE Fundamentals
- Sensible-only model latent load and manufacturer operating-envelope limits excludedcooling-unit performance data