Surface Condensation Risk and Dew-Point Margin
The failure mode a psychrometric read never screens.
Example
You enter
- Chamber air temp (°F) 80
- Chamber relative humidity (%) 50
- Coldest surface temp (°F, IR read) 50
You get
- Dew point 59.7 degF
- Surface margin -9.7 degF
- Condensation Condensing -- surface at/below dew point
Details, formula, and sources
Warm, humid drying air meeting a cold single-pane window, uninsulated wall, or slab edge and condensing there - secondary water in the worst place for mold. Computes the Magnus dew point from the chamber air temperature and RH, compares it to the coldest surface (IR-read), and flags whether the surface sits at or below the dew point and by what margin. Lower the humidity or warm the surface to clear the risk. A screen; the IR-read surface temperature governs (ANSI/IICRC S500).
T_c = (air_temp_f - 32) x 5/9; g = ln(air_rh_pct/100) + 17.625 x T_c / (243.04 + T_c); dew_pt_c = 243.04 x g / (17.625 - g); dew_point_f = dew_pt_c x 9/5 + 32; margin_f = surface_temp_f - dew_point_f; condensing when margin_f <= 0.
Magnus-Tetens dew-point relation (17.625 / 243.04 degC coefficients) and the keep-surfaces-above-the-dew-point rule of ANSI/IICRC S500, by name. Not edition-bound.
The Magnus dew-point relation is public psychrometrics; the surface-above-dew-point practice is named in the published ANSI/IICRC S500.
Estimate. AHJ and licensed professional govern.
Field names used by the API: air_temp_f, air_rh_pct, surface_temp_f, dew_point_f, margin_f, condensing
- Magnus coefficients 17.625 and 243.04 degC are the standard Magnus-Tetens constants for dew point over waterpsychrometric convention
- Surface temperature the coldest surface is read with an IR thermometer and governs; a single value screens one surface at a timeANSI/IICRC S500