# How to Calculate Heat Loss Due to Moisture Present in Air?

Calculating % heat loss due to moisture present in air to determine the boiler efficiency.

## % Loss Due to Mositure Present in Air

The percentage heat loss due to moisture present in air is one of the factor to determine the boiler efficiency. The vapour present in the incoming air is in the form of humidity which is super heated when it passes through the boiler. As, the heat passes through the stack it causes a loss. Below given the formula to calculate the % heat loss due to moisture present in air. Formula:
L4 = (AAS x Humidity Factor x Cp (Tf - Ta) / GCV of Fuel) x 100
Where,
AAS = Actual mass of air supplied per kg of fuel
Humidity Factor = Kg of water / kg of dry air
Cp = Specific heat of superheated steam in kCal/kgoC
Tf = Flue gas temperature in oC
Ta = Ambient temperature in oC (dry bulb)
GCV of Fuel = Gross Calorific Value of Fuel Let us consider an example on how to calculate the heat loss due to moisture present in air with the given values.
Step 1: Given that,
Actual mass of air supplied per kg of fuel = 20 kg
Humidity Factor kg of dry air = 0.015
Specific heat of superheated steam = 0.45 kCal/kgoC
Flue gas temperature = 250 oC
Ambient temperature = 30 oC (dry bulb)
GCV of Fuel = 13000 kJ/kg Step 2: Applying the values in the formula
L4 = (AAS x Humidity Factor x Cp (Tf - Ta) / GCV of Fuel) x 100
L4 = (20 x 0.015 x 0.45 (250 - 30) / 13000) x 100
L4 = 0.228 % Result: % Heat Loss Due to Moisture Present in Air = 0.228% 