1) What this calculator does

• Segments your building (open office, conference, lobby, wards, classrooms, etc.).
• Applies heating densities (W/m²) or your direct overrides (kW/MBH).
• Computes ventilation heating from ACH × volume with user-set indoor/outdoor design temperatures.
• Rolls in diversity, distribution losses, and safety to find a robust peak kW.
• Derives hot-water flow from ΔT; recommends boiler count & size (N or N+1).
• Estimates budget cost (equipment → installed → with markup) and annual fuel usage.
• Outputs a clean HTML report with KPIs, tables, and change log (print-ready).

2) How the math works (short version)

1. Segment loads Qi = Ai × qW/m² / 1000 kW, or enter overrides in kW/MBH. Sum: Qint = ΣQi.
2. Ventilation heating (ACH) Qvent,i ≈ ρ × (A × H) × ACH / 3600 × cp × ΔTair kW, with ρ≈1.2 kg/m³, c_p≈1.005 kJ/kg·K, and ΔT_air=T_indoor−T_outdoor.
3. Allowances Qbase = Qint + Qvent + Qproc → Diversity → Distribution losses → Safety → Qpeak.
4. Hot-water flow SI: L/s = Q(kW) / (4.186 × ΔT[K]); IP: gpm = 2 × MBH / ΔT[°F].
5. Selection If N+1: (n−1) × size ≥ Qpeak.
6. Fuel & cost Fuel power at average: Qpeak/η × loadFactor → kWh/year → tariff; Cost = installed kW × unit rate × install factor × (1+markup).

3) How to use it (step-by-step)

Related tools: You might also like Cooling Load Calculator, Duct Sizing Calculator, Pipe Design Calculator, and Psychrometrics – Moist Air Guide.

4) Worked example — Office floor (full calculation)

Goal: Size a hot-water boiler plant for an office floor with open office, conference room and lobby. SI math shown with key IP equivalents.

Inputs & assumptions

• Indoor/Outdoor: 21 °C inside, 0 °C outside (ΔT_air = 21 K)
• Hydronic temps: 80 → 60 °C (ΔT = 20 K)
• Allowances: Diversity 0.90; Distribution losses 5%; Safety 10%
• Process/DHW: 10 kW
• Ventilation basis: ACH per segment; ρ=1.2 kg/m³, c_p=1.005 kJ/kg·K; ceiling height 3.2 m
• Costing (India): Unit rate ₹3,000/kW; install ×1.5; markup 10%
• Fuel & use: Condensing gas η=0.95; 2,500 h/year; avg load factor 0.55; tariff ₹8/kWh
• Selection: N+1 redundancy

Step-by-step math

1. Segment heating (W/m² → kW)
   Open Office: 600×60/1000 = 36.00 kW
   Conference: 200×90/1000 = 18.00 kW
   Lobby: 100×120/1000 = 12.00 kW
   Internal sub-total = 66.00 kW
2. Ventilation heating (ACH per segment) with ρ=1.2, c_p=1.005, ΔT_air=21 K, height 3.2 m.
   Formula: kW = ρ × (A×H) × ACH / 3600 × cp × ΔTair
   • Open Office: V=600×3.2=1,920 m³ → ṁ=1.2×1920×1/3600=0.64 kg/s → 0.64×1.005×21 = 13.51 kW
   • Conference: V=200×3.2=640 m³ → ṁ=1.2×640×1.5/3600=0.32 kg/s → 0.32×1.005×21 = 6.75 kW
   • Lobby: V=100×3.2=320 m³ → ṁ=1.2×320×2/3600≈0.213 kg/s → 0.213×1.005×21 ≈ 4.50 kW
   Ventilation total = 24.76 kW
3. Allowances → Peak
   Qbase = 66.00 + 24.76 + 10.00 = 100.76 kW
   Diversity: Q′ = 100.76 × 0.90 = 90.684 kW
   Distribution: Q″ = 90.684 × 1.05 = 95.218 kW
   Safety: Qpeak = 95.218 × 1.10 = 104.74 kW
4. Convert & flow
   MBH: 104.74 × 3.412 = 357.39 MBH
   Flow (SI): L/s = 104.74 / (4.186×20) = 1.251 L/s
   Flow (IP): ΔT=36 °F → gpm = 2 × 357.39 / 36 = 19.86 gpm
5. Boiler selection (N+1)
   Choose 3 × 60 kW. Check: (3−1) × 60 = 120 kW ≥ 104.74 kW ✓
   Installed nameplate = 180 kW.
6. Budget cost
   Equipment = 180 × ₹3,000 = ₹540,000
   Installed = ×1.5 = ₹810,000
   With markup (10%) = ₹810,000 × 1.10 = ₹891,000
7. Annual fuel (condensing η=0.95, 2,500 h/yr, load 0.55, tariff ₹8/kWh)
   Fuel kW at average = (104.74/0.95) × 0.55 = 60.64 kW
   Annual kWh = 60.64 × 2,500 = 151,597 kWh
   Fuel cost ≈ ₹1,212,779 / year

Use in the calculator: Enter the same segments, set ACH-based ventilation, allowances, 80/60 °C water, choose N+1 and India pricing. Click Calculate → the KPIs will match these numbers. Then Generate Report for a print-ready sheet.

5) Notes, tips & references

• Validation: Always sanity-check W/m² seeds against envelope U-values, infiltration, occupancy and internal gains. Presets are starting points.
• Ventilation: If your jurisdiction mandates L/s·person or L/s·m² (e.g., CIBSE/ASHRAE/ISHRAE), convert to ACH or compute heating kW directly and enter as a manual ventilation value.
• Hydronic ΔT: 20 K is common for radiators/fan-coils; radiant floors often run lower supply temps—check emitter selection.
• N+1 choices: Three smaller modular boilers often improve turndown and serviceability versus two larger units.
• Budgeting: Unit rate and efficiency are planning values—verify against vendor submittals and seasonal performance.