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HUMIDIFIRST
HUMIDIFIRST
humidifier sizing calculations
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 in outside air 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 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 the
humidification season, then this dehumidification process must be taken 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, a stable relative humidity level
requires that one pound of moisture be added to the air.
Please note that there are other factors that can affect humidification requirements, such
as moisture absorption of items in the space. These factors generally may be ignored
because most often they play only a minor part in the humidification requirements.
Contact Humidifirst for any unique applications.
See the next page for a simple chart that can be filled in and sent to Humidifirst. We are
happy to assist with the sizing of any humidification system.
