Humidification
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Absolute humidity is the mass of water vapour in a volume of air divided by the mass of dry air. Relative humidity (RH) is a measure of the water vapour density of air compared to the water vapour density for saturated air at the same temperature and pressure (that is, the maximum amount of moisture that air can 'hold' at that temperature and pressure). | Absolute humidity is the mass of water vapour in a volume of air divided by the mass of dry air. Relative humidity (RH) is a measure of the water vapour density of air compared to the water vapour density for saturated air at the same temperature and pressure (that is, the maximum amount of moisture that air can 'hold' at that temperature and pressure). | ||
| − | Humidity in buildings is regulated by Approved Document C (Site preparation and resistance to contaminates and moisture) and Approved Document F (Ventilation) and further guidance is available in BS 5250 Code of practice for the control of condensation in buildings. | + | Humidity in buildings is regulated by Approved Document C (Site preparation and resistance to contaminates and moisture) and Approved Document F (Ventilation), and further guidance is available in BS 5250 Code of practice for the control of condensation in buildings. |
= Adjusting levels of humidity = | = Adjusting levels of humidity = | ||
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Humidity can influence thermal comfort. Air that is too dry can cause problems such as dry eyes, nose, ears and throat. It can also make some natural materials (such as wood) shrink and crack, and it can cause wall coverings to peel at the edges. | Humidity can influence thermal comfort. Air that is too dry can cause problems such as dry eyes, nose, ears and throat. It can also make some natural materials (such as wood) shrink and crack, and it can cause wall coverings to peel at the edges. | ||
| − | Low humidity levels can be controlled by making dry air wetter. When moisture, water vapour or humidity are added to the air without changing its dry bulb (DB) temperature (a measure of air temperature taken when the thermometer bulb is dry), this | + | Low humidity levels can be controlled by making dry air wetter. When moisture, water vapour or humidity are added to the air without changing its dry bulb (DB) temperature (a measure of air temperature taken when the thermometer bulb is dry), this procedure is referred to as humidification. |
| + | |||
| + | While temperature modifications are not an essential part of humidification, the process frequently takes place in conjunction with temperature control systems associated with air conditioning and heating equipment. Other types of humidifiers use different methods to introduce moisture into the air - including ultrasonic, high frequency vibrations that create a type of cold mist. | ||
= Cooling and humidification = | = Cooling and humidification = | ||
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Through this technique, moisture is added to the air by releasing a spray or stream of water that is kept at a temperature that is lower than the DB temperature of the surrounding air. When that air comes into contact with the cooler stream of moisture, small droplets of water in the stream evaporate as they adjust to the warmer temperature of the surrounding air. | Through this technique, moisture is added to the air by releasing a spray or stream of water that is kept at a temperature that is lower than the DB temperature of the surrounding air. When that air comes into contact with the cooler stream of moisture, small droplets of water in the stream evaporate as they adjust to the warmer temperature of the surrounding air. | ||
| − | The water from the evaporated stream is absorbed along with its moisture content into the air to increase humidity levels. The cooler temperature from the evaporated stream is also incorporated into the air, which decreases | + | The water from the evaporated stream is absorbed along with its moisture content into the air to increase humidity levels. The cooler temperature from the evaporated stream is also incorporated into the air, which decreases the temperature of the air. |
Cooling and humidification techniques do not work in hot, humid conditions. They can only be used in places with very hot, dry climates, such as deserts. | Cooling and humidification techniques do not work in hot, humid conditions. They can only be used in places with very hot, dry climates, such as deserts. | ||
| − | An evaporative cooler (also known as a desert cooler) is a | + | An evaporative cooler (also known as a desert cooler) is a type of cooling and humidification device. It operates on the same general principle as a conventional air conditioning and humidification system, but it is simpler and less expensive. |
For more information, see Evaporative cooling. | For more information, see Evaporative cooling. | ||
| − | Cooling and humidification is frequently used in textile manufacturing and other industries where temperature and humidity levels must | + | Cooling and humidification is frequently used in textile manufacturing and other industries where temperature must remain cool and humidity levels must be kept constant. |
= Heating and humidification = | = Heating and humidification = | ||
| − | The process of humidification can be incorporated into heating systems and then activated while this equipment is being used to | + | The process of humidification can be incorporated into heating systems and then activated while this equipment is being used to make the air warmer. This form of humidification increases the DB temperature of the air as well as the humidity. |
| − | Through this technique, moisture is added to the air by releasing steam kept at a temperature that is higher than the DB temperature of the surrounding air. When | + | Through this technique, moisture is added to the air by releasing steam kept at a temperature that is higher than the DB temperature of the surrounding air. When the surrounding air mixes with the warm steam, the moisture droplets in the steam evaporate as they adjust to the temperature of the surrounding air. |
This process causes the relative humidity level and the DB temperature level of the air to increase. The wet bulb temperature and dew point temperature increase as well. | This process causes the relative humidity level and the DB temperature level of the air to increase. The wet bulb temperature and dew point temperature increase as well. | ||
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= Humidification in homes = | = Humidification in homes = | ||
| − | In a typical house with modern standards of insulation and heating, the average level of humidity in the winter months can be as low as 15% (as opposed to 40% to 60%). | + | In a typical house with modern standards of insulation and heating, the average level of humidity in the winter months can be as low as 15% (as opposed to the recommended level range from 40% to 60%). This is why it is not uncommon for residents to increase the level of humidification in the home by using a humidifier. |
One common type of home appliance is a cool air humidifier. This device incorporates a fan that blows air through a wet permeable membrane. It incorporates a reservoir for water and an electric motor that drives a fan. In addition, there’s usually a speed selector switch, a timer, an air filter and a broad belt of permeable material to soak up the water. A separate motor moves the moist permeable belt through the airflow from the fan. | One common type of home appliance is a cool air humidifier. This device incorporates a fan that blows air through a wet permeable membrane. It incorporates a reservoir for water and an electric motor that drives a fan. In addition, there’s usually a speed selector switch, a timer, an air filter and a broad belt of permeable material to soak up the water. A separate motor moves the moist permeable belt through the airflow from the fan. | ||
Revision as of 13:47, 3 February 2022
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Contents |
Introduction
Absolute humidity is the mass of water vapour in a volume of air divided by the mass of dry air. Relative humidity (RH) is a measure of the water vapour density of air compared to the water vapour density for saturated air at the same temperature and pressure (that is, the maximum amount of moisture that air can 'hold' at that temperature and pressure).
Humidity in buildings is regulated by Approved Document C (Site preparation and resistance to contaminates and moisture) and Approved Document F (Ventilation), and further guidance is available in BS 5250 Code of practice for the control of condensation in buildings.
Adjusting levels of humidity
RH is expressed as a percentage. Typically, a relative humidity of 40% to 60% is appropriate in many buildings.
Humidity can influence thermal comfort. Air that is too dry can cause problems such as dry eyes, nose, ears and throat. It can also make some natural materials (such as wood) shrink and crack, and it can cause wall coverings to peel at the edges.
Low humidity levels can be controlled by making dry air wetter. When moisture, water vapour or humidity are added to the air without changing its dry bulb (DB) temperature (a measure of air temperature taken when the thermometer bulb is dry), this procedure is referred to as humidification.
While temperature modifications are not an essential part of humidification, the process frequently takes place in conjunction with temperature control systems associated with air conditioning and heating equipment. Other types of humidifiers use different methods to introduce moisture into the air - including ultrasonic, high frequency vibrations that create a type of cold mist.
Cooling and humidification
The process of humidification can be incorporated into air conditioning equipment and then activated while these systems are being used for cooling purposes.
Through this technique, moisture is added to the air by releasing a spray or stream of water that is kept at a temperature that is lower than the DB temperature of the surrounding air. When that air comes into contact with the cooler stream of moisture, small droplets of water in the stream evaporate as they adjust to the warmer temperature of the surrounding air.
The water from the evaporated stream is absorbed along with its moisture content into the air to increase humidity levels. The cooler temperature from the evaporated stream is also incorporated into the air, which decreases the temperature of the air.
Cooling and humidification techniques do not work in hot, humid conditions. They can only be used in places with very hot, dry climates, such as deserts.
An evaporative cooler (also known as a desert cooler) is a type of cooling and humidification device. It operates on the same general principle as a conventional air conditioning and humidification system, but it is simpler and less expensive.
For more information, see Evaporative cooling.
Cooling and humidification is frequently used in textile manufacturing and other industries where temperature must remain cool and humidity levels must be kept constant.
Heating and humidification
The process of humidification can be incorporated into heating systems and then activated while this equipment is being used to make the air warmer. This form of humidification increases the DB temperature of the air as well as the humidity.
Through this technique, moisture is added to the air by releasing steam kept at a temperature that is higher than the DB temperature of the surrounding air. When the surrounding air mixes with the warm steam, the moisture droplets in the steam evaporate as they adjust to the temperature of the surrounding air.
This process causes the relative humidity level and the DB temperature level of the air to increase. The wet bulb temperature and dew point temperature increase as well.
Humidification in homes
In a typical house with modern standards of insulation and heating, the average level of humidity in the winter months can be as low as 15% (as opposed to the recommended level range from 40% to 60%). This is why it is not uncommon for residents to increase the level of humidification in the home by using a humidifier.
One common type of home appliance is a cool air humidifier. This device incorporates a fan that blows air through a wet permeable membrane. It incorporates a reservoir for water and an electric motor that drives a fan. In addition, there’s usually a speed selector switch, a timer, an air filter and a broad belt of permeable material to soak up the water. A separate motor moves the moist permeable belt through the airflow from the fan.
When the appliance is working, moisture is absorbed by the air as it passes through the belt and out of the appliance. This increases the humidity of the air in the room and reduces its temperature at the same time.
Related articles on Designing Buildings
- Air conditioning.
- Condensation.
- Cooling systems for buildings.
- Dry-bulb temperature.
- Evaporative cooling.
- Heating ventilation and air conditioning HVAC.
- Humidity.
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