Tools — TheEngDigest

1) Cooling Load from Flow × ρ × Cp × ΔT

SI units. Result shows power (kW) and refrigeration tons (TR).

Volume flow (m³/h)

Density ρ (kg/m³)

Specific heat Cp (kJ/kg·K)

ΔT (°C)

ṁ = Q_vol·ρ/3600; kW = ṁ·Cp·ΔT (Cp in kJ/kg·K); TR = kW/3.517.

2) Quick Cooling Load Estimator (Area/Occupancy)

Very rough estimate. For accurate results, use Calc #1 or detailed load tools.

Floor area (m²)

People count

Lighting (W/m²)

Equipment (W/m²)

Climate factor (0.8–1.3)

Model: Q = (Area·(Lighting+Equipment) + People·100W sensible + People·75W latent)·Factor. TR = kW/3.517.

3) Chilled Water Flow from Load & ΔT

Load (TR)

ΔT (°C)

Density ρ (kg/m³)

Cp (kJ/kg·K)

From kW = TR·3.517 = ṁ·Cp·ΔT, with ṁ = ρ·Q_vol. Outputs m³/h and L/s.

4) COP & kW/TR

Capacity (TR)

Power (kW)

COP = (Capacity in kW) / kW_in; kW/TR = kW_in / TR.

5) District Cooling Savings Estimator

Annual hours (h/yr)

Average load (TR)

Baseline kW/TR (onsite)

District kW/TR

Tariff (USD/kWh)

Energy saved = (kW/TR_base − kW/TR_DC)·TR·hours. Cost saved = kWh·tariff.

6) Pump Affinity Laws

Given Q₁,H₁,P₁ at N₁ (or D₁). Enter new speed N₂ (or impeller D₂).

Q₁ (m³/h)

H₁ (m)

P₁ (kW)

N₁ (rpm)

N₂ (rpm)

Q ∝ N, H ∝ N², P ∝ N³ (same impeller diameter).

7) Pump Power Requirement

Flow Q (m³/h)

Head H (m)

Density ρ (kg/m³)

Efficiency η (0–1)

P = ρ·g·Q·H / η. (Q in m³/s; g=9.81 m/s²). Output shaft kW.

8) NPSH Check

Atmospheric head (Pa/ρg) or absolute suction head (m)

Static suction head z (m)

Vapor head Pv/ρg (m)

Suction losses h_f (m)

NPSHr from pump curve (m)

NPSHa = (Pa/ρg) + z − (Pv/ρg) − h_f. Check NPSHa ≥ NPSHr.

9) Condensate Recovery Estimator

Based on air mass flow and humidity change across coil.

Airflow (m³/s)

Air density (kg/m³)

Inlet humidity ratio w_in (kg/kg)

Outlet humidity ratio w_out (kg/kg)

Hours per day

ṁ_air = ρ_air·V̇. Condensate kg/s = ṁ_air·(w_in − w_out). Liters/day ≈ kg/day.

10) CO₂ Savings from Energy Reduction

kWh saved / year

Grid factor (kg CO₂/kWh)

tCO₂ = (kWh saved)·(kg/kWh) / 1000.

11) Cooling Tower Heat Rejection Split (Psychrometrics)

Full inputs (DB/RH/Twb optional, air mass or volumetric, water in/out with auto ΔT, exit RH, h_fg model). Two models shown side-by-side: ECM (Energy Conservation) and DEM (Direct Enthalpy/Psychrometric).

Air T_db,in (°C)

Air RH_in (%)

Air T_wb,in (°C) (optional)

Barometric pressure p (kPa)

Air mass flow ṁ_air (kg/s dry)

Or Air volumetric flow at inlet (m³/s)

Water in T_w,in (°C)

Water out T_w,out (°C)

Cooling range ΔT (°C) (auto if Tw,in/Tw,out set)

Water flow ṁ_w (kg/s)

Or Water flow (m³/h)

Water c_p (kJ/kg·K)

Exit RH_out (%)

Latent heat model

Energy Conservation Model (ECM)

Direct Enthalpy Model (DEM)

Path-Integrated Model (PIM)

ECM Split

DEM Split

Cooling Tower FAQ — deep dive →

ECM forces balance: Q_sensible = ṁ_air,dry·c_p,dry·ΔT_air, Q_latent=Q_water−Q_sensible. DEM uses Cp_moist, Δw and h_fg. Residual shows DEM vs water-side difference. Also shows evaporation, exit air state, Approach (T_w,out−T_wb,in), and Merkel KaV/L & KaV/G.