PPT – "Dew Point and Relative Humidity PowerPoint presentation | free to view

PPT – "Dew Point and Relative Humidity PowerPoint presentation | free to view

Weather and Humidity

Here's what happens in winter to make it feel so dry in our houses. Let's say that the outdoor temperature is 0 degrees C, or 32 degrees F. The maximum amount of water that a cubic meter of air can hold at this temperature is 5 grams. Now you bring this cubic meter of air inside and heat it to 25 degrees C or 77 degrees F. The relative humidity is only 23 percent:

5 grams of water in the air / 22 grams possible
= 23 percent relative humidity

It gets worse as the temperature outside falls lower. This is why the air inside any heated building in the winter feels so dry. Any time the temperature outside is below freezing, relative humidity inside will be below 20 percent unless you do something to increase the humidity.

The outside air might have a comfortable level of humidity, but when that air is heated, the relative humidity drops, causing the air to be very dry inside the house.

During the dry months, a humidifier can help maintain a comfortable level of humidity.

As the winter air enters, the humidity drops slightly within the crawlspace.  Notice relative humidity is 62%, beyond what the EPA considers acceptable.  As the air migrates upward, it warms greatly and relative humidity drops drastically.  The house feels dry, but the crawlspace still requires dehumidification.  To control dust mite populations, it is recommended that the crawlspace be kept at 40% R.H. all year long.  Unfortunately, most dehumidifiers will not work at a 45° temperature.  Though, our Dri-CrawlSpace^® dehumidifiers will run just fine all the way down to 33°.

Still winter time, but here we have a cold rainy day.  It will still feel dry indoors, but notice as the outside air enters the crawlspace, relative humidity only drops to 70%.  During this type of weather, your crawlspace dehumidifier should be running.  Be sure to choose a Dri-CrawlSpace^® Dehumidifier because it is one of the few that can operate in temperatures this low.

This is the type of weather where mold really thrives, especially if it were to rain.  It’s too cold to run the air conditioner, so high humidity goes unchecked.  If it were raining, relative humidity outside would be 100%.  This would raise the dew point to 55°.  With the crawlspace at 58°, humidity would rise to a whopping 89%.  All your cold water pipes and exterior walls would be dripping wet.

Here’s a nice warm day with comfortable 50% humidity. But because it is so warm, dew point is also going to be warm.  Any surfaces below 60° will form condensation.  Look how high the relative humidity gets as the air cools to 65° in the crawlspace.  At 83% relative humidity, your crawlspace is sure to grow a good amount of mold, as well as make a fine home for spiders, termites, cockroaches and other pests.

The mild summer night is the worse case scenario for allergies. As temperatures near the dew point, dust mites and mold will multiply and run rampid throughout your home.  Notice how quickly food goes bad in this weather.  Also, if you notice more bugs in your home,  these are indications of high humidity.  A good crawlspace dehumidifer like the Dri-CrawlSpace^® can keep up with these humid conditions and make your home comfortable while taking some strain off your air conditioner.