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LoadCairn / Cooling load

Cooling load calculator

Explore a transparent first-pass estimate from IT power, lighting, occupants, and your envelope heat-gain estimate. Values are calculated in this browser and are not saved; no account is required.

Inputs

Illustrative example · editable

Starting values: 8 kW IT load, 1,200 W lighting, 6 people, and 5,000 BTU/hr envelope heat gain. These are examples, not building facts or recommended design values.

Use IT equipment input power in the conditioned space.

The estimate treats all entered lighting power as heat in the space.

A whole-number count using an illustrative office activity rate.

Enter your own estimate for net heat gain through the building envelope.

Live estimate

Rounded for display; calculations retain full precision.

Total cooling load
39,092BTU/hr
Refrigeration capacity
3.26tons
Thermal cooling load
11.46kW thermal

Component breakdown

IT electrical power as heat
27,297.13 BTU/hr
Lighting power as heat
4,094.57 BTU/hr
People (450 BTU/hr each)
2,700.00 BTU/hr
Envelope estimate
5,000.00 BTU/hr

Formula and worked calculation

Formula

Total BTU/hr = (IT kW × 1,000 + lighting W) ÷ 0.2930711
             + people × 450 + envelope BTU/hr
Refrigeration tons = total BTU/hr ÷ 12,000
Thermal cooling kW = total BTU/hr × 0.0002930711

NIST gives 0.2930711 W per Btu_IT/hr, so electrical watts are divided by that factor to convert to BTU/hr. The kW output is thermal cooling load, not electrical demand.

Worked calculation · current inputs

(8 × 1,000 + 1200) ÷ 0.2930711 + 6 × 450 + 5000 = 39,091.6998 BTU/hr

39,091.6998 ÷ 12,000 = 3.26 tons · 39,091.6998 × 0.0002930711 = 11.46 thermal kW

Assumptions and limits

Assumptions

  • All IT electrical input power is assumed to become heat in the conditioned space.
  • All entered lighting power is treated as heat released into the conditioned space.
  • Each person contributes an illustrative 250 BTU/hr sensible plus 200 BTU/hr latent (450 BTU/hr total) for moderately active office work at 75°F.
  • Envelope heat gain is the value you supply; it is not estimated from building details.

What this estimate does not model

  • Design weather, solar gain, envelope construction, or thermal storage and time delay.
  • Ventilation, infiltration, airflow, or cooling distribution.
  • Schedules, load diversity, simultaneous peaks, or HVAC fan and system effects.
  • Cooling redundancy or heat rejected outside the room by liquid-cooled equipment.
  • Changes in occupant activity or room conditions that alter people heat gain.

This arithmetic sum is a first-pass estimate, not a peak design-load calculation, compliant design, or equipment recommendation. For real equipment sizing, use model-specific manufacturer performance data at its stated rating conditions.

Further reading

References

ASHRAE Handbook—Fundamentals, Chapter 18: Nonresidential Cooling and Heating Load Calculations

Reference for internal gains, occupant assumptions, and why a full cooling-load calculation depends on time and building-specific inputs.

ANSI/ASHRAE Standard 183-2024

Professional peak cooling and heating load calculation reference. This simplified calculator does not claim compliance with the standard.

NIST Guide to the SI, Appendix B.9

Published heat-flow conversion: 1 Btu_IT/hr = 0.2930711 W; a refrigeration ton is 12,000 Btu_IT/hr.

Vertiv, Small Cooling Systems

Manufacturer context for small IT-room and server-room cooling. For equipment sizing, use model-specific performance data at the stated rating conditions.