Relative Air Humidity Calculation Formula Chart

What is the equation for the relationship between wind speed, relative humidity and the temperature difference between the dry and wet bulb in meteorology? (Along the humidity checklist 1974, 6 compiled by the Central Weather Bureau)

A.1 The formula for relative humidity U:

U=(E/Ew)×100% ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙( A.1)

The formula U is the relative humidity, E is the water pressure (hPa), Ew is the dry bulb temperature t (℃) corresponding to the pure horizontal liquid surface (or ice) saturated water pressure (hPa).

A.2 Calculation formula for water barometric pressure E

E=Etw-APh (t-tw) ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ ( A.2)

The formula Etw (hPa) for the wet bulb temperature tw (℃) corresponds to the pure horizontal liquid surface of the saturated water pressure, wet bulb icing and wet bulb temperature is below 0 ℃, for the saturated water pressure of the pure horizontal ice surface; A is the dry and wet table coefficients, wet bulb is not iced when the ventilation of the wet and dry tables (ventilation speed ≥ 2.5m/s) coefficients is 0.662 × 10-3 ℃ -1, wet bulb icing The ventilation dry and wet table (ventilation speed ≥ 2.5m / s) coefficient is 0.584 × 10-3 ℃ -1; Ph for the station air pressure (hPa); other symbols have the same meaning.

A.3 saturated water air pressure Ew formula:

A.3.1 pure horizontal liquid surface saturated water air pressure formula

∙∙∙∙ (A.3)

The formula Tl = 273.16 (the three-phase point of the absolute temperature of the water, in units of: K) T = 273.15 + ℃ (absolute temperature, in units of: K).

A.3.2 Calculation formula for the saturated water air pressure on the pure horizontal ice surface

∙∙∙∙ (A.4)

The significance of the symbols in the formula is the same as above [1].

X2 represents the air moisture content after dehumidification (0.009kg/kg dry air at 70% RH temperature 18℃)

Expanded Information

Example Analysis:

(1) Place of Use: Finished Goods Warehouse

(2) Overall Space: 1200 square meters * 4.8m = 5760m³; confinement: the door is open without closing

(4) dehumidification before the environmental conditions: indoor temperature: 23 ℃ humidity: about RH72%

(5) dehumidification requirements: the relative humidity of the indoor air will be controlled at RH60%.

(6) with or without air conditioning / exhaust fan: no

Warehouse volume: 5760m³ ;

Required humidity: 60%;

Substitute the formula for the dehumidification volume: E = 1.2 × 5760 * 1.1 × (0.01703-0.01065) × 1.2 = 58.2kg/h

What is the dew point temperature at atmospheric pressure? Atmospheric pressure indoor air temperature and humidity table?

In the air water vapor content remains unchanged, to maintain a certain air pressure, so that the air is cooled to saturation temperature is called the dew point temperature, referred to as the dew point, and its unit and the same as the air temperature. Generally referred to as 0 ℃ above the “dew point”, the 0 ℃ below the “frost point”.

Because there is no direct formula for the dew point temperature, the dew point temperature is obtained by direct inversion of the saturated water vapor pressure formula. The Magrath formula is an approximate solution to the Goff-Gratch formula, which is also an empirical formula. Only one formula for calculating saturated water vapor pressure is listed here.

World Meteorological Organization (WMO) recommended Goff-Gratch (Goff-Gratch) formula:

In the formula:T is the absolute temperature (unit: K); Ew is pure horizontal liquid saturated water vapor pressure (unit: hPa).

Measurement method: generally available dew point hygrometer to measure the dew point.

Air temperature and humidity comparison table:

Extended information:

According to research, the optimal indoor temperature should be maintained in the room temperature up to 18 ℃, the relative humidity should be maintained at 30-40%, the room temperature up to 25 ℃, the relative humidity should be maintained at 40-50% for the most appropriate. The most suitable.

Families with babies, in general, the indoor temperature of about 20 ℃ is appropriate, the humidity should be maintained at 50% to 60%. Can be adjusted appropriately according to the pediatric fear of cold, fear of heat characteristics.

There is a humidity meter at home, today’s relative humidity is more than 90%, how to understand?

Relative humidity

The percentage of the absolute humidity of the air at a certain temperature and the saturation vapor pressure of water at the same temperature is called the relative humidity of the air at that time.

If p is used to denote the absolute humidity of the air at a certain temperature, P is used to denote the saturated vapor pressure of water at the same temperature, and B is used to denote the relative humidity, then

The saturated vapor pressure of water at a certain temperature can be found in the table below. Therefore, knowing the absolute humidity can be calculated relative humidity; in turn, knowing the relative humidity can be calculated absolute humidity.

If the absolute humidity of the air p = 800Pa, when the temperature is 20 ° C, the relative humidity of the air is

When the temperature is 10 ° C, the relative humidity of the air

In the living room, the appropriate relative humidity is about 60%. In rice, the optimum relative humidity is 70% to 80% during the period of tasseling and flowering.

Temperature (°C) Saturated vapor pressure (kPa)












Relative humidityrelativehumidityAn expression of humidity. The percentage value of the density of water vapor actually contained in the air and the density of saturated water vapor at the same temperature. Since the same under the steam density and vapor partial pressure is proportional to the relative humidity is also equal to the actual partial pressure of water vapor and the percentage of saturated water vapor pressure at the same temperature.