HVAC Humidification Calculations in Excel

HVAC humidification is the process of adding moisture to the air in a building or a room to improve the comfort and health of the occupants. Humidification can also help prevent damage to wooden furniture and floors, and reduce energy consumption by making the air feel warmer.

There are two main methods of humidification in HVAC: isothermal and adiabatic. Isothermal humidification involves adding steam or hot water to the air, which increases both the humidity and the temperature of the air. Adiabatic humidification involves adding water at a lower temperature than the air, which increases the humidity but lowers the temperature of the air. Both methods have advantages and disadvantages depending on the application and the climate.

Some examples of isothermal humidifiers are steam humidifiers, which use electricity or gas to boil water and inject steam into the air ducts, and hot water humidifiers, which spray hot water into the air stream. Some examples of adiabatic humidifiers are evaporative coolers, which use a fan to blow air over a wet pad or a spray of water, and ultrasonic humidifiers, which use high-frequency vibrations to create a fine mist of water droplets.

The optimal level of humidity for human comfort and health is between 40% and 60%. Too low humidity can cause dry skin, nose, and throat, increase the risk of infections and allergies, and make the air feel colder. Too high humidity can cause mold, mildew, and dust mites, increase the risk of asthma and respiratory problems, and make the air feel hotter. Therefore, it is important to monitor and control the humidity level in HVAC systems using humidistats, sensors, and controllers.

Basic Theory:

Humidification is the process of adding moisture to the air, and it plays a vital role in achieving and maintaining comfortable indoor conditions. The HVAC system is responsible for regulating both temperature and humidity levels. The most common method of humidification involves using devices like humidifiers that introduce water vapor into the air.

Procedures:

1. Determine Desired Humidity Level: Begin by establishing the target humidity level for the indoor environment. This is typically expressed as a percentage, such as 40% relative humidity.
2. Calculate Required Humidity: The next step is to determine how much moisture needs to be added to achieve the desired humidity level. This can be calculated using the formula:

      

3. Select Humidification Equipment: Based on the required humidity, choose the appropriate humidification equipment. The capacity of the humidifier is crucial in this selection process.
4. Calculate Water Evaporation Rate: The water evaporation rate, often measured in gallons per hour (GPH) or liters per hour (LPH), can be calculated using the formula:

      

Excel Formulas:

Let’s use an Excel table to illustrate these calculations:

Scenario:

Suppose the current humidity is 30%, and we aim to achieve 40% humidity with a humidification efficiency of 0.008.

Excel Calculation:

1. Desired Humidity: 40%
2. Current Humidity: 30%
3. Required Humidity:
4. Humidification Efficiency: 0.008
5. Water Evaporation Rate:

MATLAB Comparison:

In MATLAB, you can use a script to perform the same calculations and compare the results with Excel.

            % MATLAB Script
            desiredHumidity = 40;
            currentHumidity = 30;
            requiredHumidity = desiredHumidity - currentHumidity;
            humidificationEfficiency = 0.008;
            waterEvaporationRate = requiredHumidity / humidificationEfficiency;

            fprintf('Water Evaporation Rate (MATLAB): %.2f GPH\n', waterEvaporationRate);