Example data table
| Item | Example value | Notes |
|---|---|---|
| Shelter size | 6 m × 3 m × 3 m | Typical small equipment room. |
| Outdoor / Indoor | 40°C, 50% RH / 24°C, 50% RH | Use local design conditions. |
| U-values | Walls 0.50, Roof 0.35 W/m²·K | Adjust for insulation and cladding. |
| Infiltration | 0.5 ACH | Tighter construction reduces load. |
| Equipment heat | 2500 W | Use nameplate plus diversity if needed. |
| Safety factor | 10% | Helps cover uncertainty and cycling losses. |
Formula used
- Transmission: Q = U × A × ΔT
- Infiltration airflow: V̇ = ACH × Volume / 3600
- Humidity ratio: W = 0.62198 × Pv / (P − Pv)
- Enthalpy: h = 1.006T + W(2501 + 1.86T) (kJ/kg dry air)
- Infiltration load: Q = ṁdry × (hout − hin)
- Cooling total: sensible + latent + solar, then apply safety factor
How to use this calculator
- Choose the unit system and enter shelter dimensions.
- Set outdoor design temperature and humidity, then indoor setpoint values.
- Enable auto areas, or enter wall, roof, and floor areas manually.
- Enter realistic U-values for walls, roof, floor, doors, and windows.
- Set infiltration ACH and optional outdoor air ventilation if required.
- Add internal gains from equipment, lighting, and any occupants.
- Apply a safety factor, calculate, then export results to CSV or PDF.
Note: This is a planning-level estimate. Critical shelters should be verified with detailed design methods and local standards.
Professional notes on equipment shelter HVAC loads
1) Why load estimating matters for shelters
Equipment shelters often protect radios, PLCs, batteries, and controls that must stay within tight temperature limits. Even a small enclosure can develop high heat density when electronics run continuously. Many operators aim for 18–27°C and controlled humidity to reduce corrosion and condensation risk. A realistic load estimate helps avoid nuisance alarms, premature component aging, and short compressor cycling.
2) Envelope heat transfer is the base load
Transmission follows Q = U × A × ΔT. For insulated panels, typical U-values may range from about 0.25 to 0.60 W/m²·K, while doors and glazing are usually higher. Roof area often dominates in compact shelters, and thermal bridges at frames can add hidden load. Large temperature differences (for example 40°C outdoors and 24°C indoors) can add several kilowatts in warm climates.
3) Infiltration and humidity create latent load
Air leakage is frequently underestimated. A tight shelter might be near 0.2–0.6 ACH, while poorly sealed penetrations can exceed 1.0 ACH. The calculator separates sensible and latent portions using moist-air enthalpy at a standard pressure assumption. Latent load increases when outdoor humidity is high, driving dehumidification demand and raising coil moisture removal requirements.
4) Internal gains dominate when electronics run 24/7
Electronics heat converts almost entirely to sensible load. For planning, use measured power draw when available, or apply a realistic diversity factor for intermittent devices. Typical small shelters may carry 1–5 kW of equipment heat, plus lighting and minor occupant gains during inspections. Include losses from UPS units, rectifiers, and battery chargers because they can be continuous.
5) Interpreting results for equipment selection
Cooling is reported in kW and refrigeration tons (1 TR ≈ 3.517 kW). Apply a modest safety factor (often 5–20%) to cover unknowns such as solar exposure, fouled filters, and future expansions. Check that selected equipment can handle both sensible and latent capacity at your design conditions. For critical sites, consider redundancy (N+1), monitoring, and verification with detailed design methods.
FAQs
1) Should I use internal or external shelter dimensions?
Use internal clear dimensions when estimating air volume and conditioned space. For envelope areas, either enter measured panel areas or enable auto areas from the internal geometry as a consistent approximation.
2) What ACH value is reasonable for a sealed shelter?
A well-built shelter with sealed cable entries may be around 0.2–0.6 ACH. If doors are frequently opened or penetrations are poorly sealed, values near 1.0 ACH or higher may be more realistic.
3) How do I estimate equipment heat accurately?
Prefer measured electrical power at peak operation. If only nameplate data is available, apply a diversity factor for intermittent loads and include losses from rectifiers, chargers, and power supplies that run continuously.
4) Why is latent cooling shown even without occupants?
Latent cooling can come from outdoor air entering through infiltration or ventilation. High outdoor humidity increases moisture content, and the HVAC system must remove this moisture to maintain the indoor humidity target.
5) Should I include solar gain for metal shelters?
Yes, if the shelter is exposed and has limited shading. Solar gain can be significant for dark surfaces. Use conservative estimates or site measurements, then validate with commissioning data once the shelter is operating.
6) How should I choose a safety factor?
Many teams start with 10%. Increase it when inputs are uncertain, the shelter may expand, or maintenance access is limited. Avoid excessive safety factors that can lead to oversizing and poor humidity control.
7) Does this replace a full HVAC design?
No. It provides a planning-level sizing estimate. Final design should check equipment performance at design conditions, controls strategy, airflow distribution, filtration losses, and any project-specific standards or reliability requirements.