Indoor Relative Humidity vs. Outdoor Relative Humidity and Temperature
Recommended indoor relative humidity vs. outdoor relative humidity and temperature.
When cold humid outdoor air is supplied and heated in a building - the relative humidity of the air is decreased.
This heating process can be visualized in a psychrometric chart or in a Mollier diagram - as below:
Example - Indoor Relative Humidity of Heated Outdoor Air
Outdoor air with dry bulb temperature 0 oC and relative humidity 90% is heated to an indoor temperature 20 oC.
The process is visualized in the Mollier diagram above with the process from A to B along the constant specific humidity - x - line. From the diagram we can estimate the indoor relative humidity to approximately 23%.
Note! - indoor supplies of vapor to the moist air - like latent heat from humans, animals or production processes - is not counted for. Latent heat supplied to the indoor air will move point B in the diagram to the right - to higher relative humidity. Sensible heat supplied to the room will move point B further up in the diagram.
Example - Indoor Relative Humidities for a given Outdoor Temperature and Relative Humidities
The table below illustrates the change in indoor relative humidity for a given outdoor temperature and relative humidities.
| Outdoor Temperature | Outdoor Relative Humidity (%) | Indoor Temperature | Indoor Relative Humidity (%) |
|---|---|---|---|
| -7 (oC) 20 (oF) |
0 | 21 (oC) 70 (oF) |
0 |
| 20 | 3 | ||
| 40 | 6 | ||
| 60 | 8 | ||
| 80 | 11 |
Related Topics
-
Air Psychrometrics
Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air. -
Heating Systems
Design of heating systems - capacities and design of boilers, pipelines, heat exchangers, expansion systems and more.
Related Documents
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Health and Relative Humidity of Air
The optimum relative humidity ranges for bacteria, viruses, fungi, mites, asthma. -
Indoor Comfort Temperatures vs. Outdoor Temperatures
Recommended indoor comfort temperatures vs. outdoor temperatures. -
Moist Air - Relative Humidity
Relative humidity in moist air is the ratio of partial vapor pressure to air pressure. -
Outdoor Temperatures and Relative Humidity - U.S. Winter and Summer Conditions
Outdoor summer and winter design temperatures and relative humidity for U.S. states and cities. -
Recommended Relative Humidity
Recommended relative humidity level. -
Relative Humidity in Production and Process Environments
Recommended relative humidity in production and process environments - like libraries, breweries, storages and more. -
Room Sensible Heat Factor - RSHF
Room Sensible Heat Factor - RSHF - is defined as the sensible heat load divided by the total heat load in a room -
Sensible Heat Ratio - SHR
The ratio Sensible Heat (or Cooling) Load to the Total Heat (or Cooling) Load.
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