When calculating the humidification loads of a space we will generalize and assume that the majority of the humidification load will come from two areas:
1. Ventilation, Exhaust, or Infiltration of air: Most buildings have air exchanges with the outside because of one or more of these three items.
A. Ventilation is a result of air conditioning systems bringing outside air in to provide fresh air to the inhabitants.
B. Exhaust is the mechanical removal of air from a space when processes inside of the building require the removal of dirty, hot or unwanted air.
C. Infiltration occurs when air comes into a space from outside. Air may come in through small openings around doors, windows, ceilings, etc. Also, infiltration often occurs from frequent opening of doors.
For each Cubic Foot per Minute (CFM) of outside air that is brought into the space, moisture must be added to achieve your relative humidity requirements.
2. Air conditioning: When an air conditioner runs, it removes moisture from the air. This is known as Latent cooling. If the air conditioner will be running during your humidification season, you must take this dehumidification process into account.
The cooling ability of an air conditioner is normally rated by the manufacturer and is stated in Sensible and Total cooling capacity in btu’s per hour. Subtract the Sensible cooling capacity from the Total cooling capacity to get the Latent cooling capacity. For every 1000 btu’s/hour of Latent cooling capacity you will need to add one pound of moisture.
Please note that there are other factors that can add to your humidification requirements, such as moisture absorption of items in your space. We generally ignore them because most often they play only a minor part of your humidification requirements. Contact us if you think you have unique requirements.
