Relative humidity in air and on the surfaces [water activity: amount of water available for microorganisms on the sampling surface (16)] was calculated based on measured dry-bulb and wet-bulb temperature, and
absolute humidity (grams per kilogram) was estimated using a psychrometric chart.
For a temperature difference between freezer and room [DELTA]T = 47.2 [+ or -] 0.3[degrees]C (85.0 [+ or -] 0.5[degrees]F) and an
absolute humidity difference between the cavity and the environment [DELTA]W = 0.015 [kg.sub.w]/[kg.sub.a] (0.015 [lb.sub.w]/[lb.sub.a]), the gasket total thermal load is [Q.sub.g] = 3.12 [+ or -] 0.05 W (10.65 [+ or -] 0.17 Btu/h); 86% corresponds to the heat transfer load through the freezer gasket and 14% to the gasket infiltration load.
The two cases on the left side of Figure 16 are with the same
absolute humidity. The ratio of current and arc length is the same so we don't see an influence by the humidity level.
Figure 6b shows the variation of
absolute humidity in the passenger area of the coach.
Absolute humidity (or dew-point temperature), which increases in all months, is a better indicator than relative humidity of change in building energy requirements.
While the data at 82% and 92% rh (a3.5 and 3.9
absolute humidity) have a similar frost mass and frosting period, a decrease of only 10% in relative humidity, that is, a decrease of the
absolute humidity from 3.5 to 3 grams of water vapor per one kg of dry air, extended the frosting time to about 120 minutes.
As can be seen in this survey, two problems exist with the controls: the control sensors are inaccurate and unable to precisely control the humidity; and the units are fighting one another due to the inaccuracy of the control sensors and the use of relative humidity for control (the controllers in these older CRACs could not be configured for
absolute humidity control).
The simple spreadsheet model predicts condensate to occur when the outdoor air
absolute humidity levels are above those for the assumed supply air conditions.
To achieve the 55[degrees]F (13[degrees]C) DP
absolute humidity condition in the data center, 26 grains of moisture per pound of air (3.72 g/kg) would be required to be added by a separate humidification system.
where [m.sub.w,inf] is the mass flow rate of moisture from infiltration (lbw/min),[V.sub.inf,air]is the volume flow rate of infiltrating air ([ft.sup.3]/min), [[rho].sub.inf,air] is the density of infiltrating air (lba/[ft.sup.3]),[[omega].sub.inf air] is the
absolute humidity ratio of air infiltrating the freezer (lbw/lba), and [[omega].sub.f] is the
absolute humidity ratio of the freezer air (lbw/lba) based on the actual freezer dry-bulb temperature measured and an assumed freezer relative humidity of 95%.
There is a simple solution to this dilemma, and this involves using
absolute humidity and/or dew-point sensors.
Wood "sees" relative humidity, rather than vapor pressure or
absolute humidity. At night when the wood cools, the relative humidity increases.