❄️ HVAC

Chiller Tonnage Calculator (TR Sizing)

Calculate chiller capacity in TR and kW from building cooling load. Size air-cooled or water-cooled chillers. ASHRAE / AHRI compliant.

📐 Standard: ASHRAE / AHRI
✅ Free to use
📄 PDF export
📱 Mobile friendly

ℹ️ About This Calculator

A chiller is the heart of a central HVAC system — it produces chilled water that is distributed to AHUs and fan coil units throughout the building. Selecting the correct chiller tonnage is critical: undersizing means the building cannot be cooled; oversizing means the chiller cycles on and off, reducing efficiency and increasing maintenance costs. 1 TR (ton of refrigeration) = 3.517 kW of cooling.

AHRI Standard 550/590 governs chiller rating conditions. Air-cooled chillers are rated at 35°C ambient; water-cooled at 29°C entering condenser water. IPLV (Integrated Part Load Value) is the weighted average efficiency over a full operating season — more important than full-load efficiency for Indian buildings where the chiller runs at part load for most of the year. BEE (Bureau of Energy Efficiency) star ratings for chillers are based on IPLV.

📐 Chiller Sizing Formula

ASHRAE / AHRI

Cooling Capacity:
  TR = Total Cooling Load (kW) / 3.517
  or
  TR = Total Cooling Load (BTU/hr) / 12,000

Chiller kW Input:
  kW_input = TR × 3.517 / COP
  Typical COP: Air-cooled: 2.8–3.5 | Water-cooled: 4.5–6.5

Chilled Water Flow:
  Q_chw (L/s) = Cooling (kW) / (ρ × Cp × ΔT)
             = kW / (4.187 × 5)    [for 7/12°C CHW system]

Condenser Water Flow (water-cooled):
  Q_cw = (Cooling kW + Compressor kW) / (4.187 × 5)  [for 29/34°C CW]

❓ Frequently Asked Questions

How many TR is needed per 1000 sq ft of office space? +
A typical commercial office in India requires 0.8–1.2 TR per 100 m² (0.07–0.11 TR per sq ft). For 1000 sq ft ≈ 93 m²: approximately 0.75–1.1 TR. Actual requirement depends on glass area, orientation, occupancy density, lighting load, and outdoor climate. Always perform a full heat load calculation.
Air-cooled vs water-cooled chiller — which should I choose? +
Water-cooled chillers are 40–50% more energy efficient (COP 4.5–6.5 vs 2.8–3.5) but require a cooling tower, condenser water pumps, and chemical treatment — higher first cost and maintenance. Air-cooled chillers are simpler, cheaper to install, and suitable for rooftop installation but consume more electricity. For systems above 200 TR and where year-round operation is required, water-cooled is usually more economical over the lifecycle.
What is a good COP for a chiller in India? +
BEE minimum standards: Air-cooled chillers: COP ≥ 2.80 (IPLV). Water-cooled centrifugal: COP ≥ 5.0 (IPLV). BEE 5-star rated chillers achieve COP 3.3+ (air-cooled) and 6.0+ (water-cooled). Premium inverter-driven variable speed centrifugal chillers achieve IPLV up to 9.0 — these are the benchmark for green building projects.
What is chiller staging and why does it matter? +
Chiller staging means running multiple smaller chillers in parallel rather than one large chiller. A building with 500 TR total load might use two 250 TR chillers. At 40% load, you run one chiller at 80% — close to its peak efficiency. A single 500 TR chiller at 40% load runs very inefficiently. Staging improves part-load efficiency and provides redundancy. Minimum recommended: two chillers for any system above 100 TR.
How do I convert chiller capacity from BTU to TR to kW? +
1 TR = 12,000 BTU/hr = 3.517 kW. So 100 TR = 1,200,000 BTU/hr = 351.7 kW. To convert kW to TR: divide by 3.517. To convert BTU/hr to TR: divide by 12,000. To convert BTU/hr to kW: multiply by 0.000293.

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⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

❄️ Chiller Tonnage Calculator
Reference: ASHRAE / AHRI