UNANSWERABLE QUESTIONS: VOLUME TWO

Thanks so much to Rachel for asking our newest unanswerable question:

HOW DOES A DE-HUMIDIFIER WORK?

As it turns out, my original thoughts on this question were mostly correct, but there is still one element I don't understand. But we'll get to that a bit later on in this post.

First, a brief refresher on the water cycle, to give us a foundation for our understanding of this process:

This shows the very basics of the water cycle:

1. Water evaporates as it warms, turning from a liquid form into water vapor , which is its gas form (remember the "vapor" root in "evaporation," meaning "the process of turning to gas").

2. Water vapor cools as it travels higher into the atmosphere, causing it to turn back into liquid droplets (condensation).

3. Eventually those liquid droplets get too heavy, and they fall back to earth as precipitation.

4. Finally, those droplets collect or accumulate back on the ground. 

Of course, that's really not final - the process begins all over again. It's a cycle!!

Truthfully, it's more complicated than that, and these images all demonstrate variations on that basic cycle. As you can see, it's a little like the difference between a food chain and a food web. There are many, many things going on at once!

I've arranged these images in order from most basic to most complex. 

We'll come back to all this again, but now back to the de-humidifier question.

As we've discussed before, humidity is the measure of how much moisture is in the air. Very high humidity (or a "humid" day) means the air is holding lots of water vapor. Some very humid days, the air may actually even feel "wet." Low humidity means that there is very little moisture in the air. Warmer air holds more moisture than cooler air. 

So, how does this relate to the de-humidifier?

First, let's break down that word into its parts:

humid+fi (fy) + er = essentially, "humid - maker," then adding the prefix "de-" turns it into the opposite - SO, a dehumidifier makes air less humid. 

HOW?

Well, after some discussion with Mr. Taylor, some observation of our own personal de-humidifier at work in the basement, and some help from the Siri feature on Mr. Taylor's phone, I learned that I was correct in my original thinking, but that there was one thing I did not consider.

The de-humidifier has a fan that pulls in air from the room and cools it. This cooling process causes the water vapor to turn back to droplets and condense. The condensation collects on the dehumidifier's cooling coils, and it eventually drips off and accumulates in a pan or bucket inside the humidifier. Some fancy dehumidifiers have drain pipes and whatnot; we have to empty ours out every now and again. We use the accumulated water to water our plants.

I was a little bit baffled by one thing, though: it blows out hot air.

Why would it blow out hot air if the air is cooled during this process?

I started out trying to over-science it:

Me: "Well, warm air holds more moisture than cold air, so the air around the de-humidifier would be really warm and humid, and if the colder, drier air gets pumped back out of the de-humidifier into the warm, humid room, it could cause..."

Mr. Taylor, looking at me funny: "...a thunderstorm? In the basement?"

Me: "Well, it's like two different air masses, and in nature, that would cause..."

Mr. Taylor: "A thunderstorm?"

So, I suppose we determined that the de-humidifier doesn't heat the air at the end of the process to avoid indoor thunderstorms. Drat! How interesting would that be?

It turns out that this is just a by-product of how the machine works. This means that parts of the de-humidifier heat up during the cooling process. This is random and not something the machine does "on purpose." It just kind of happens, and I couldn't find a very good explanation of WHY it happens. 

This is because the de-humidifier requires a lot of energy usage to do its job properly, and sometimes electrical energy creates heat energy as a by-product of its main function. This can happen in a lot of unexpected places, and it is noticeable on a lot of older appliances (many, but not all, newer appliances solve this problem in becoming more "energy efficient" - less wasted energy means less heat given off). If you have an older refrigerator or freezer in your house, you may be able to feel the heat energy being given off the top or side - weird, right, since its job is to cool things? That is heat being given off as a by-product. Essentially, heat in these circumstances is "extra" energy, at least how I understand it. Maybe we should come back to this part of the question later on in fifth grade when we study energy, force and motion! 

Here are some articles that explain a little more:

http://www.brainpop.com/science/weatherandclimate/humidity/preview.weml

http://www.hometips.com/how-it-works/dehumidifiers-2.html

http://home.howstuffworks.com/dehumidifier.htm

http://www.kidsgeo.com/geography-for-kids/0106-humidity.php

**I've also added a few more links on our weather resources entry from last week that may be helpful to you, as well!

This week's blog assignment:

1. Complete the "blog questions" sheet that will be coming home on Monday, December 10. There is not much homework this week because we have several PTA restaurant nights this week, but you definitely need to do your blog work! It is due next Monday, December 17.

2. Post a comment with a question or observation related to weather. It can be anything, and you can "stretch" it a bit if you want - for example, I would consider this post about de-humidifiers to be related to weather.

Happy blogging! Be sure to ask me questions about this assignment sooner rather than later!

Mrs. Taylor