Make-Up Air Unit Moisture Loads Tool
This tool demonstrates the effects of moisture capacitance on the latent
sizing calculations for a makeup air unit (MAU). For peak humidity periods,
the latent load in the space can be much larger than the dehumidification
capacity but reasonable space conditions can still be maintained. The reason is
moisture capacitance. The moisture capacitance is estimated by taking the space volume and
multiplying by the moisture capacitance factor (typical values range from 1 to 20).
By selecting different inputs below, the effects of moisture capacitance on space humidity
levels can be demonstrated.
Slides from a recent ASHRAE Seminar on this topic are available
Shirey et al (2001) prepared a Reference Manual for the EPA's
IHAT simulation tool. Section 10 and 14 of that manual provide background and guidance on
selecting Moisture Capacitance Factors for various building applications.