Compute the total, sensible, and latent capacity of an air-handling-unit (AHU) coil from the entering/leaving air state and the dry-air mass flow ṁ_da. Total capacity Qt = ṁ_da·(h1 − h2); sensible capacity Qs = ṁ_da·cp_ma·(T1 − T2) with cp_ma ≈ 1.006 + 1.86·W [kJ/(kg da·K)]; latent capacity Ql = Qt − Qs; Sensible Heat Ratio SHR = Qs / Qt. Each state is described by dry-bulb T plus one humidity input (relative humidity φ, or humidity ratio W); W is derived from the Magnus saturation fit when RH is supplied, and enthalpy h = 1.006·T + W·(2501 + 1.86·T) [kJ/kg da]. Signed result — works for cooling or heating coils.
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Key facts
Category
Math & Numbers
Input types
number, select
Output type
json
Sample coverage
4
API ready
Yes
Overview
The AHU Coil Capacity Calculator computes total, sensible, and latent coil capacity plus the sensible heat ratio (SHR) from dry-air mass flow and entering and leaving air conditions. Enter dry-bulb temperatures with relative humidity or humidity ratio for each state, then choose the output units.
When to use
Estimate cooling coil capacity from entering and leaving air temperatures and relative humidity.
Calculate heating coil capacity using humidity-ratio inputs for the entering and leaving air.
Separate total capacity into sensible and latent components and review the resulting SHR.
How it works
1Enter the dry-air mass flow and select kg/s or kg/h.
2Provide entering and leaving dry-bulb temperatures in °C.
3For each air state, enter either relative humidity in percent or humidity ratio in g/kg or kg/kg.
4The calculator derives humidity ratio and enthalpy as needed, then returns total, sensible, and latent capacity, SHR, and formatted results in kW, W, or BTU/h.
Use cases
HVAC engineers can estimate AHU cooling coil loads and identify the sensible and latent portions of the duty.
Building-services designers can check heating coil capacity from dry-air flow and air-state measurements.
Commissioning teams can compare entering and leaving air conditions using enthalpy, humidity ratio, and SHR results.
Examples
1. Cooling coil capacity from relative humidity
HVAC engineer
Background
An engineer is checking an AHU cooling coil with 2.5 kg/s of dry-air flow. The entering air is 27 °C and 50% RH, while the leaving air is 14 °C and 90% RH.
Problem
Determine the coil's total, sensible, and latent capacity and calculate its SHR.
How to use
Enter 2.5 kg/s, select relative humidity for both states, enter 27 °C and 50% for the entering air, then 14 °C and 90% for the leaving air. Select kW as the capacity unit.
Enter 3 kg/s, select humidity ratio for both states, choose g/kg dry air, enter 5 °C and 3 g/kg for the entering air, then 30 °C and 3 g/kg for the leaving air.