Inputs
Enter your room and load assumptions. For critical rooms, verify with commissioning data and manufacturer selections.
Example data
Sample assumptions for a small equipment room. Replace with measured values for a real project.
| Item | Example input | Example output |
|---|---|---|
| Room size | 8 m × 5 m × 3 m | Area 40 m² |
| IT load | 18 kW | 18.00 kW |
| UPS losses | 8% | 1.44 kW |
| Lighting | 12 W/m² | 0.48 kW |
| People | 2 × 120 W | 0.24 kW |
| Misc | 1.5 kW | 1.50 kW |
| Safety factor | 15% | Total ≈ 24.40 kW |
| Unit plan | N=2, N+1 | ≈ 12.20 kW each, 3 units |
| Airflow | ΔT = 10 °C | ≈ 4,600 CFM (approx.) |
Formula used
Tons = BTU/hr ÷ 12000
How to use this calculator
- Select Metric or Imperial units for your project.
- Enter room dimensions to compute area and volume.
- Add IT load and a realistic UPS loss percentage.
- Set lighting density, people count, and people sensible load.
- Include miscellaneous loads and choose a safety factor.
- Choose running units (N) and select redundancy if needed.
- Enter your expected supply/return ΔT to estimate airflow.
- Press Calculate to see results above the form.
Sizing scope and assumptions
CRAC sizing starts with sensible heat released inside the room. It supports early budgeting, equipment schedules, and coordination with electrical and structural teams today. This calculator targets equipment rooms where server power, UPS losses, lighting, occupants, and small auxiliary loads dominate. It assumes most electrical input becomes heat within the space, which is a practical approximation for IT racks and power electronics. If humidification, latent loads, or significant outdoor air are used, treat the result as a sensible baseline and validate with a full psychrometric selection.
IT load quality and measurement
Use metered kW at the room distribution level when available. Nameplate ratings often overstate true demand, while virtualized or bursty loads can create short peaks. For design, combine recent peak demand with expected growth and apply a disciplined safety factor. Separating critical from noncritical loads improves accuracy and helps define how many units must remain online during maintenance.
Airflow, ΔT, and containment
Airflow is estimated from sensible heat and a chosen supply-to-return temperature rise. A small ΔT drives higher airflow and can require larger fans, duct paths, and floor openings. Hot-aisle or cold-aisle containment typically increases effective ΔT and stabilizes return temperatures, improving capacity utilization. Verify that rack inlet temperatures remain within your operating envelope under worst-case distribution.
Redundancy planning for reliability
Many critical rooms are designed around N+1 redundancy, meaning one additional unit is installed beyond the number required for the design load. This calculator reports both per-running-unit capacity and total units to procure. Confirm that each unit can operate at your target setpoints and that controls can stage units smoothly to avoid short-cycling at low loads.
Commissioning and final selection
Use the results to shortlist CRAC capacities in kW, BTU/hr, and tons, then validate with manufacturer performance tables. Account for coil conditions, filter loading, fan curves, and altitude effects. During commissioning, trend return temperatures, airflow, and rack inlets to confirm assumptions. Update inputs with measured data to refine capacity and optimize energy use.
FAQs
1) What does the safety factor represent?
It adds margin for uncertainty, future growth, and measurement error. Typical values are 10–25%. Use lower values with strong metering and stable loads, and higher values when growth or assumptions are unclear.
2) Does this include latent load and humidity control?
No. The output is a sensible-load estimate. If your strategy includes humidification, dehumidification, or outside air, complete a psychrometric design and confirm the unit’s total capacity at your operating conditions.
3) How should I choose the ΔT input?
Use the expected supply-to-return rise for your airflow path. Containment often allows higher ΔT than open mixing. If you are unsure, start with 10°C (18°F) and compare against measured return temperatures.
4) Why is altitude included?
Higher altitude reduces air density, so more airflow is needed for the same sensible heat transfer. The calculator applies an approximate density ratio to adjust the airflow estimate, which helps with fan and duct planning.
5) How do I interpret N and N+1 results?
N is the number of units sharing the design load during normal operation. N+1 adds one spare unit for reliability. The per-unit capacity is based on N running units, while procurement count includes the spare.
6) Is the tons value enough to pick a specific model?
Use it as a shortlist indicator. Final selection should be based on manufacturer performance data at your setpoints, coil conditions, filtration, and fan configuration. Always confirm controls, staging, and part-load behavior.