Whether to Paint depends on the Weather | International
At % relative humidity, the dew point temperature and the air temperature are the same, and clouds or fog can . Very useful advice in this particular article!. The temperature usually decreases as the altitude increases. This is called the lapse rate. In general, the closer the dew point is to the ground. relationship between td, t, and RH based on Eq. (8) is shown in Fig. 1, with Dewpoint temperatures (°C) and absolute differences for moist air with a dry-bulb tempera- ture of t = 15°C. .. (any tips from readers would be appreciated). Von.
News 8 Weather Blog: DEW POINT - THE BEST INDICATOR OF COMFORT
Illustration of condensation process. Figure 30 is an illustration explaining some of the interactions between air, vapour, temperature and liquid water.
It is based on the idea that air is like a container that changes size with temperature, representing air's ability to hold moisture. This is also called the dew point temperature.
If further cooling occurs, the container shrinks and some water spills over the top. This is the same as moisture condensing from the air as a liquid.
If the air is now warmed without adding back the condensed moisture the RH would go down, and when it reaches the same starting temperature, the air would be of a lower RH than at the beginning of the exercise. All these relationships can be calculated using psychrometric charts and tables, but the important thing is to understand the relationships between cold surfaces, humidity and condensation: Air that has water vapour in it has a Dew Point Temperature: Condensation will form on a surface that is below the Dew Point Temperature of the air to which it is exposed.
The more vapour in the indoor air, the higher its RH and dew point temperature. Contact Us Whether to paint depends on the Weather Weather plays an important part of our lives and even more so when it comes to painting.
When to paint and when not to is an important choice if perfect finishes are required. But how many of us really understand exactly what this all means, and if we do, how do we actually measure them? This article will try to explain in simplistic terminology what humidity and dew point is and how they inter-relate. What is water vapour? The first question we must ask ourselves is what is water vapour.
What is the relationship between temperature and dew point?
For the purpose of this exercise we should consider that water exists in various forms. As a solid mass it exists as liquid water, ice, and droplets such as rain, mist, steam and clouds. It can then exist in vapour form where it cannot be visibly seen.
What is Relative Humidity?
Relative Humidity RH for brevity is a ratio of how much water vapour is in the air compared to the maximum it could hold at any specific temperature. RH is a measure of water vapour and does not take into account any discreet form of water present such as rain.
How do we measure RH? There are electronic instruments available and these vary in accuracy and reliability. A standard piece of equipment called a Whirling Pschycrometer is one of the most reliable instruments, not requiring any batteries, and only taking around seconds to obtain a reading.
It is like a football rattle and is simply a holder with two thermometers, one of which has its bulb end exposed to the air and the other end covered with gauze which is kept wet via a small inbuilt container topped up with water prior to use.
The unit is spun around for 15 - 20 seconds and the two thermometer readings are taken. Both thermometers will read differently with the wet one reading lower by just a few degrees.
The wet thermometer gives a lower reading because when it is spun around some of the water on the gauze evaporates which cools the thermometer down. Just how much water evaporates depends on the RH at the time. If the RH is high then less water will evaporate and if it is low, then more will evaporate.