Calculator inputs
Example data table
| Example | Area (m²) | Occupancy | UA (W/K) | Vent (L/s·person) | Peak (kW) | TR | Flow (m³/h) |
|---|---|---|---|---|---|---|---|
| Office mid-rise | 1,500 | 120 | 4,500 | 10 | ~560 | ~160 | ~80 |
| Retail podium | 2,200 | 250 | 5,800 | 12 | ~980 | ~279 | ~140 |
| Hotel block | 3,600 | 180 | 7,200 | 8 | ~1,150 | ~327 | ~165 |
Formula used
- Envelope sensible: Qenv (kW) = UA (W/K) × ΔT (°C) ÷ 1000
- Internal sensible: Qint = (Area×LPD + Area×EPD + People×Wsens) ÷ 1000 × Diversity
- Ventilation sensible: Qvent,s (kW) = 1.206 × V̇vent(m³/s) × ΔT
- Infiltration flow: V̇inf (m³/s) = ACH × Volume ÷ 3600
- Latent from outdoor air: Qlat (kW) = 3.0 × V̇(m³/s) × ΔW(g/kg)
- Peak with margin: Qpeak = (Qsensible + Qlatent) × (1 + Safety%)
- Chilled water flow: ṁ (kg/s) = Qpeak(kW) ÷ (4.186 × ΔTchw)
- Pipe ID (indicative): D = √(4×(Q̇/Velocity)/π)
How to use this calculator
- Enter conditioned area, ceiling height, and an overall UA estimate.
- Set outdoor and indoor design conditions for peak cooling.
- Add occupancy, ventilation rate, and infiltration (ACH).
- Enter humidity ratios to capture latent loads from air.
- Fill lighting and equipment densities and choose a diversity factor.
- Set chilled water supply/return temperatures and design velocity.
- Press Calculate load to view results above the form.
- Download CSV or PDF for reports and coordination.
District cooling load planning notes
1) Start with peak design conditions
District cooling networks are sized around a peak hour, not seasonal averages. Use the local outdoor design dry-bulb and a realistic indoor setpoint, then confirm the resulting ΔT matches your project basis of design. For early studies, envelope UA can be approximate, but it should trend upward as glazing ratios rise or insulation levels fall.
2) Convert peak kW into connection requirements
The calculator reports peak load in kW and refrigeration tons (1 TR ≈ 3.517 kW). Connection sizing typically starts with chilled-water flow: ṁ = Q/(4.186×ΔTchw). With a 6 °C water temperature rise, every 100 kW needs about 4.0 kg/s (≈14.4 m³/h) of flow, before applying project margins.
3) Treat ventilation and humidity as first-class inputs
Outdoor air can dominate latent load in hot-humid climates. The latent term here uses Qlat ≈ 3.0×V̇×ΔW, where ΔW is the humidity ratio difference in g/kg. A small increase in ventilation or infiltration can materially raise peak demand, so align ventilation rates with code and confirm pressurization and door usage for the construction stage.
4) Apply diversity and safety factors with intent
Diversity reduces internal gains to reflect non-coincident peaks across zones; common preliminary ranges are 0.75–0.95 depending on building use and controls. Safety factor (often 5–15%) should cover uncertainties without double-counting conservatism already embedded in UA, loads, or weather. Track assumptions so later detailed models can replace them cleanly.
5) Build a budget view from energy and demand charges
Monthly cooling energy is estimated as peak kW times operating hours, producing kWh-cooling for tariff comparison. If your provider uses a demand component, the peak kW materially affects cost even when hours are low. Use the COP output only for benchmarking electric equivalence; district billing is usually based on delivered cooling, not plant electricity.
FAQs
1. What does UA mean, and how should I estimate it?
UA is the overall heat transfer coefficient times area for the envelope (W/K). Early estimates can be derived from typical U-values and areas for walls, roof, and glazing. Refine UA as façade details and window-to-wall ratios are confirmed.
2. Why is there a diversity factor for internal loads?
Lighting, plug loads, and people rarely peak everywhere at the same moment. Diversity reduces internal gains to represent coincident demand across zones. Use higher diversity for single-tenant or tightly scheduled spaces, and lower values for mixed-use buildings.
3. How do I choose infiltration (ACH) for construction-stage checks?
ACH depends on façade tightness, door frequency, and pressurization. Early-stage values commonly range from 0.3 to 1.0 for conditioned spaces. If entrances are frequently open or the building is not yet sealed, use a higher ACH and revisit later.
4. What should I enter for humidity ratios (g/kg)?
Use design outdoor humidity ratio from local weather design data and an indoor target consistent with comfort and moisture control. If you only have relative humidity, convert it to humidity ratio using a psychrometric tool or standard HVAC tables.
5. How do chilled-water supply and return temperatures affect results?
The temperature difference (ΔTchw) sets required flow. A larger ΔT reduces flow and often pipe size, while a smaller ΔT increases both. Use the district provider’s stated supply/return targets and confirm allowable return temperature limits.
6. Is the pipe diameter output a final selection?
No. The pipe ID is indicative, based on flow and a chosen velocity. Final pipe sizing must consider pressure drop, available differential pressure, fittings, control valves, and allowable noise/erosion limits. Use it for early coordination only.
7. How should I interpret the monthly bill estimate?
It multiplies your monthly kWh-cooling by the energy tariff and optionally adds a demand charge based on peak kW. Provider billing may include fixed fees, seasonal rates, or minimum charges. Replace tariffs with contract values for accurate budgeting.