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About

Utility billing disputes and HVAC system sizing often revolve around the conversion between volumetric flow and actual thermal energy delivery. While meters typically measure volume in cubic meters, billing is frequently based on heat energy in Gigacalories (Gcal). This conversion is not linear; it is thermodynamically dependent on the temperature difference (ΔT) and the specific heat capacity of the fluid.

This utility provides engineering-grade precision by allowing users to define inlet and outlet temperatures or a direct temperature delta. Unlike simple multipliers, this tool accounts for the specific physics of heat transfer, making it indispensable for facility managers auditing district heating bills or engineers designing thermal loops.

HVAC calculator Gcal converter thermal energy heating systems water flow

Formulas

The thermal energy Q is calculated using the specific heat formula adjusted for volume and density:

Q V × ΔT × Cv

Where the volumetric heat coefficient Cv is derived from:

Cv = ρ × cp106

Detailed parameters:

  • V: Volume in m3.
  • ΔT: Temperature difference (Tin Tout) in °C.
  • ρ: Density of water at avg. temp (kg/m3).
  • cp: Specific heat capacity (kcal/kg°C).
  • 106: Conversion from kcal to Gcal (since 1 Gcal = 1,000,000 kcal).

Reference Data

Temp (°C)Density (kg/m3)Spec. Heat (kcal/kg°C)Energy Factor (Gcal/m3°C)
20998.20.9980.000996
40992.20.9980.000990
60983.20.9990.000982
80971.81.0000.000972
90965.31.0010.000966
100958.41.0020.000960
120943.11.0040.000947
140926.11.0070.000933

Frequently Asked Questions

The value 0.001 is a convenient approximation assuming water density is 1000 kg/m³ and specific heat is 1 kcal/kg°C. However, at 90°C, water expands (density drops), making the actual factor closer to 0.00096. This 4% difference is significant in industrial billing.
The default values are for water. Glycol (antifreeze) has a lower specific heat capacity (approx 0.85 depending on concentration) and different density. You must manually adjust the "Specific Heat Coefficient" field if calculating for non-water fluids.
If you have flow rate (e.g., m³/h), the output will be energy rate (Gcal/h). The math remains identical; just treat the time unit as consistent across input and output.
For liquid water in typical district heating systems (under 150°C), pressure has a negligible effect on density and specific heat compared to temperature. For steam, however, pressure is critical, and this calculator is not suitable for steam.