# AHU Coil Capacity Calculator (Cooling / Heating)

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.

> Canonical page: https://elysiatools.com/en/tools/ahu-capacity-calculator

- **Category:** Math & Numbers

- **Keywords:** AHU, air handling unit, coil capacity, cooling coil, heating coil, sensible, latent, SHR, psychrometric, enthalpy, dehumidification, HVAC

## 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.

## Inputs

- **Dry-air Mass Flow ṁ_da** (number): Dry-air mass flow rate ṁ_da, in the selected Flow Unit.
- **Flow Unit** (select)
- **Entering Dry-bulb T1** (number): Entering (coil-on) dry-bulb temperature in °C.
- **Entering Humidity Input** (select)
- **Entering Humidity Value** (number): Entering humidity value. RH in % (0–100); W in the selected Humidity Ratio Unit.
- **Leaving Dry-bulb T2** (number): Leaving (coil-off) dry-bulb temperature in °C.
- **Leaving Humidity Input** (select)
- **Leaving Humidity Value** (number): Leaving humidity value. RH in % (0–100); W in the selected Humidity Ratio Unit.
- **Humidity Ratio Unit** (select)
- **Capacity Unit** (select)
- **Decimal Places** (number)

## 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

- Enter the dry-air mass flow and select kg/s or kg/h.
- Provide entering and leaving dry-bulb temperatures in °C.
- For each air state, enter either relative humidity in percent or humidity ratio in g/kg or kg/kg.
- The 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.

## Frequently asked questions

### What does this AHU coil calculator calculate?

It calculates total capacity, sensible capacity, latent capacity, and sensible heat ratio (SHR).

### Can I calculate both cooling and heating coils?

Yes. The signed result supports both cooling and heating coil calculations.

### What humidity inputs are supported?

Each air state accepts either relative humidity from 0–100% or humidity ratio.

### Which units can I use for humidity ratio?

Humidity ratio can be entered in g/kg dry air or kg/kg dry air.

### Which capacity units are available?

Results can be displayed in kilowatts (kW), watts (W), or BTU per hour (BTU/h).

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