Methodology
The calculators provide SI-unit preliminary estimates using simplified engineering formulas and published methodology references.
Standards And Assumptions
English pages default to international assumptions such as ASHRAE, EN 442, and ISO-style methodology where implemented. Chinese pages default to China-standard assumptions such as GB 50736-2012, GB/T 13754-2017, and CJJ/T 34-2010.
Limitations
Results are intended for early-stage screening, comparison, and educational use. Final HVAC designs should account for local climate data, building envelope details, equipment manufacturer data, commissioning requirements, and applicable codes.
Units
All calculators use SI metric units. Inputs and results are labeled on each calculator page.
Calculators
- Heating Load — Room-by-room heat loss via Q = U × A × ΔT, with infiltration and orientation corrections per ASHRAE / GB 50736 / SHASE-S 101 standards. Radiator section count uses EN 442 (ΔT=50K) or GB/T 13754 (ΔT=64.5K) reference outputs.
- Cooling Load — Unit index method with orientation, insulation level, and window area corrections. Supports ASHRAE RTS-equivalent default index values and GB 50736 regional climate coefficients.
- Duct Sizing — Continuity equation A = Q / v for rectangular and circular ducts. Recommended velocities per ASHRAE/SMACNA, GB, and SHASE-S 010 standards.
- Pipe Flow — Darcy-Weisbach friction factor calculation with Colebrook equation. Supports water and air as fluid types with standard density/viscosity values.
- Pump Head — Total head = static lift + friction loss (Hazen-Williams or Darcy-Weisbach) + fitting losses. Estimated brake power from head, flow rate, and pump efficiency.
- Radiator Sizing — Sections = heat load ÷ output per section. Column radiators per EN 442 (ΔT=50K) and GB/T 13754 (ΔT=64.5K); panel radiators per area-based method.
- Pipe Insulation — Required thickness per ISO 12241 steady-state heat transfer, balancing allowable heat loss per linear metre against insulation thermal conductivity.
- Boiler Size — Total capacity = heating load + DHW demand + oversizing factor, derated for altitude. Based on standard manufacturer sizing practice for preliminary equipment screening.
- Expansion Tank Size — Tank volume from system water volume, temperature differential (ΔT), and operating pressure range using the thermal expansion method. Accounts for water coefficient of expansion and system pressure limits.
- HVAC Unit Converter — Client-side unit conversion across power, air flow, pressure, temperature, length, area, velocity, volume, energy, and efficiency. Pure arithmetic converter with standard conversion factors.