When is relative humidity the highest

Zeolite pellets may be of use in climatic areas in which the endemic relative humidity is naturally high Australian Library and Information Association A Japanese researcher has developed a treated natural zeolite pellet capable of absorbing and releasing large amounts of water vapour. The pellets have been combined with Japanese paper with the resultant material being produced as a sheet or a paper-covered honeycomb board filled with pellets.

Incorporating these materials in storage and display cabinets will minimise relative humidity fluctuations. Zeolites have the added advantage of being able to absorb odours and as such, have been manufactured and sold commercially in packet or bag form for use in the home.

They have been used to lower the relative humidity and absorb odours in refrigerators. If contemplating the use of these products always check their effect in the space in which they are to be used. This is important so that the risk of desiccation, or even inadequate dehumidification, is minimised.

An alternative way of controlling relative humidity levels is to incorporate other materials that absorb moisture, such as treated wood, paper and textiles in the cabinet or display case with the moisture-sensitive artefacts. These water-absorbing materials reduce relative humidity fluctuations by taking up or releasing moisture as conditions change. In this way the artefact is subjected to smaller relative humidity variations.

Materials used in this way must be compatible with the moisture-sensitive object. It would not be appropriate for instance, to store a lead object in an oak box or to use alkaline-buffered acid-free tissue paper with leather objects. In Japan this type of approach is used to deal with the naturally high humidity experienced in that country. Objects are stored in wooden chests in wooden buildings to take advantage of the natural moisture-absorbing and releasing properties of wood.

In this way the box contents are buffered against both the naturally high relative humidity and against any changes in external conditions. This approach would not be suitable for all material types however, especially those sensitive to the acidic vapours given off by wood.

With the right choice of wood hoop pine for example and wrapping of artefacts in acid-free tissue, this approach may allow some of the problems associated with endemically high relative humidity conditions to be overcome without the need for more costly and active intervention. Alternatively, if passive methods such as those outlined above are not sufficient, this problem may be tackled by lowering the relative humidity of the storage or display area itself.

This can be achieved by employing a thermostatically controlled refrigerant dehumidifier to remove excess moisture. As mould formation is encouraged by conditions of high relative humidity, warm temperatures and stagnant air, it may be necessary to employ a combination of dehumidification, air circulation and temperature control. Refrigerated air coolers can remove moisture from a building or room by condensing it outside. Water collected by this process is pure enough for use in the sling psychrometer.

Air conditioning systems should not be regarded as the first step in stabilising environmental conditions. While they are very good at maintaining appropriate temperatures, their impact on relative humidity control is highly variable, with higher fluctuations often being recorded following the installation of air conditioning systems. This is particularly the case when air conditioning operates intermittently.

If the aim of air conditioning is to maintain objects in the best possible conditions then the system should run for 24 hours a day. If the air conditioning is turned off overnight the environment inside the building will tend towards external values.

In winter a lowering of temperature in a well-sealed building will result in an increase in relative humidity. When the air conditioning plant is turned on in the morning there will be a rapid increase in temperature accompanied by a rapid decrease in relative humidity.

These rapid changes in relative humidity should be avoided. It is obviously better to use passive controls to minimise fluctuations in environmental conditions. Air conditioning systems which incorporate humidity control are available but these tend to be very expensive to set up, run and maintain. It is important to prevent the development of extreme conditions of temperature and relative humidity. Usually such extremes are localised and often only affect a few objects. For example, localised heating and consequent low relative humidity may be caused by direct sunlight falling on an object, by having spotlights positioned too close or by having radiators or heaters adjacent to an object.

It is also important to position sensitive objects away from the incoming air stream of air conditioning systems. This allows the incoming air to mix and equilibrate with the bulk of the air in the room before reaching a sensitive object, thereby minimising the impact of relative humidity fluctuations. A common cause of high humidity is leakage of rainwater through the roof or walls.

It is wise not to place objects or shelving against external walls as damp and localised extremes of both temperature and relative humidity are likely. Common sense and adequate building maintenance will minimise such problems. Relative Humidity and Temperature These deterioration factors are considered together because of their close inter-relationship.

Principles The relative humidity RH of the air is an indication of how much water vapour is in the air at a particular temperature compared with how much water vapour the air could actually hold at that temperature. Mobile Newsletter chat subscribe. Forces of Nature. Atmospheric Science. The Whole Dew Point of the Matter " ". The higher the dew point, the muggier it will be. Humidity FAQ What is relative humidity? Relative humidity is a percentage that represents the amount of water vapor in the air at a given temperature compared to the max possible water vapor amount at that same temperature.

For instance, relative humidity of 25 percent means that air is at a quarter of its possible water vapor capacity. What is absolute humidity? The higher the air temperature is, the more water vapor it can potentially contain. What's the difference between absolute humidity and relative humidity? Both readings measure water vapor levels in the air.

However, relative humidity measures how much water vapor the air actually holds by comparing it to the maximum achievable amount at a given temperature. In contrast, absolute humidity simply measures the total amount of water vapor air can hold without considering the temperature.

What is an uncomfortable level of humidity? Most people are comfortable with a relative humidity level of percent. Higher levels are uncomfortable because there's too much moisture in the air, making people sweaty and unable to cool down. What causes high levels of humidity? High humidity which is anything over 50 percent or so is caused by high temperatures.

What is it in antiperspirant that stops sweat? Why does your body temperature rise when you have a virus such as the flu? Sources Environmental Protection Agency. Humidity is a measure of the amount of water vapor in the air. Relative humidity measures the amount of water in the air in relation to the maximum amount of water vapor moisture. The higher the temperature, the more water vapor the air can hold.

Relative humidity is what your morning weather reporter would refer to. Humidity is a natural part of our atmosphere, it comes from the amount of water vapor in the air. It is an integral part of the water cycle, as water vapor is continuously generated by evaporation and removed by condensation. When the temperature is higher, the air can hold more water vapor, meaning that the warmer the climate, the higher the humidity level can be.

For example, a densely saturated amount of air may contain 0. Colder air cannot handle as much moisture as warmer air. Consider for example a winters day. On the other hand, warm air can handle more moisture than cooler air.

If you cool it down to below That is why air conditioning systems often have a dehumidifier built-in. Without them, your walls in the home would be soaking wet during the summer. Unable to hold any more, it would rain. Colder climates often have lower humidity levels than warmer climates as colder air holds less moisture than warm air. In winter, humidity levels tend to be typically lower.