Server Inlet Temperature and Humidity Envelope
Calculates dew point and classifies server inlet air against entered recommended and allowable temperature.
Example
You enter
- Rack inlet dry bulb (deg F) 78
- Rack inlet relative humidity (%) 45
- Recommended minimum (deg F) 64.4
- Recommended maximum (deg F) 80.6
- Allowable minimum (deg F) 59
- Allowable maximum (deg F) 89.6
- Upper dew point limit (deg F; 59 recommended, 62.6 allowable A1) 59
- Upper relative humidity limit (%; 70 recommended, 80 allowable A1) 70
- Alternative dry bulb (deg F) 82
- Alternative relative humidity (%) 50
You get
- Entered dew point 54.9 deg F -- PASS
- Entered dew-point / RH margin 4.1 deg F / 25.0 points
- Alternative temperature at original RH 58.5 deg F dew point; margin 0.5 deg F
- Alternative condition 61.4984
- Alternative dew-point margin -2.5 deg F
Checked against published worked examples from: Vaisala Oyj.
Details, formula, and sources
ScopeRelative-humidity, and dew-point limits. It exposes the hot-and-humid corner where dry bulb passes but dew point fails; the installed equipment class governs.
Formula or tabledew point is calculated from dry bulb and RH with the Tetens correlation, then dry bulb, RH, and dew point are checked independently against entered recommended and allowable limits.
Source and editionASHRAE TC 9.9 thermal guidelines for data-processing environments and the Tetens saturation-vapor-pressure approximation. The current equipment-class limits govern.
Free accessThe dew-point correlation is public; envelope limits are entered rather than reproducing a proprietary table.
What governsEstimate. AHJ and licensed professional govern.
API field namesdry_bulb_f, relative_humidity_pct, recommended_min_f, recommended_max_f, allowable_min_f, allowable_max_f, upper_dew_point_f, upper_rh_pct, alternative_temp_f, alternative_rh_pct, dew_point_f, dew_point_margin_f, warm_same_rh_dew_point_f, alternative_dew_point_f, alternative_dew_point_margin_f
- One humidity limit pair the entered dew point / RH ceiling is checked for both conditions; the worked example uses the RECOMMENDED 59 F / 70% (there is no default; enter the limit), while A1 ALLOWABLE is 17 C (62.6 F) dew point and 80% RH, so enter those to judge an allowable excursion. Lower humidity limits are not checkedASHRAE TC 9.9 Thermal Guidelines, 5th ed. (2021), Table 2.1
- Correlation range ordinary data-center air temperatures within the validated input boundsTetens correlation
- Steady inlet condition rack-level spatial and temporal excursions are not averaged into complianceASHRAE TC 9.9 / site survey