HVAC & Thermal Calculators
Refrigeration COP, duct friction, air changes, and R-values.
- Refrigeration Cycle COPCoefficient of performance for a cooling or heating cycle from duty and compressor power, with the Carnot ceiling for comparison.COP_cool = Q_c / W , COP_heat = (Q_c + W) / W = COP_cool + 1 , COP_Carnot = T_c / (T_h − T_c)
- Heat-Pump COP + Reversible LimitGet heating COP from compressor work plus the Carnot ceiling for the same temperature lift.COP_h = Q̇_H / Ẇ , COP_Carnot = T_H / (T_H − T_C) , η₂ = COP_h / COP_Carnot (T in K)
- Duct Static-Pressure LossFriction loss in a round duct run — Swamee-Jain friction factor on standard air, with in. w.g. per 100 ft for the ASHRAE-chart crowd.ΔP = f·(L/D)·½ρV², V = Q / (πD²/4), f = 0.25/[log₁₀(ε/3.7D + 5.74/Re^0.9)]²
- Air Changes Per Hour (ACH ⇄ CFM)Convert between room air changes per hour and supply airflow for any room volume.CFM = ACH · Volume ÷ 60 ACH = CFM · 60 ÷ Volume , Volume = L · W · H
- Cooling Tower Approach & RangeGet range, approach, and cooling effectiveness from hot/cold water temps and the ambient wet-bulb.Range = T_hot − T_cold , Approach = T_cold − T_wb , Effectiveness = Range / (T_hot − T_wb) × 100%
- Pump/Fan Affinity LawsScale flow, head/pressure, and power when a centrifugal pump or fan changes speed or impeller diameter.Q₂/Q₁ = r , H₂/H₁ = r² , P₂/P₁ = r³ where r = N₂/N₁ or D₂/D₁