We need to remove condensed water from the inside of a skylight, which is made of two panels of regular glass. The skylight is quite heavy. Disassembly of this skylight does not appear to be easy or practical. We are looking for a simple solution to extract the water condensed between two glass panels over time.
This particular skylight has an aluminum frame (see picture below). Two glass panels are mounted inside it and sealed with mastic. Because the panels are made of glass, the entire unit is quite heavy. Therefore, removing one panel for the purpose of cleaning the glass inside from water and dirt does not seem like a good idea, for a "on top of a roof" project.
Unfortunately, I did not have my camera handy before I started to work on this project, so all pictures below show the skylight with already removed water from the inside.
This was phase 1 of this project. Apparently, the air inside skylight is too humid. The idea is to try to ventilate it by allowing the air to escape outside. We accomplish it by drilling a couple of holes in the bottom of aluminum fame between the glass panels.
In this first phase of the project, we had 2 openings in skylight frame. The picture above shows a PVC tube going through one of them to get you an idea where the holes are. The second hole is 15-20 cm to the left of it. Below is a close-up picture of one of the ventilation holes in skylight frame.
We can drill holes with a cordless drill, something like below.
Ventilation holes did help a bit, meaning that some of condensation disappear during a few days I had them open. Unfortunately, the problem was not solved entirely, as a lot of water was still trapped inside on glass panels.
To summarize, in this phase of the project we attempted passive ventilation through a couple of small openings in aluminum skylight frame. Some water did escape, but the problem was not solved completely.
To improve efficiency in skylight water condensation removal, we next tried forced air pumping into one of the ventilation holes. To accomplish this, we needed a small air pump, a thin PVC tube, and a power supply, mounted together on a small board. Below is a picture of the entire water condensation removal gadget.
The air pump is on the right, and the tube from it goes inside one of the ventilation holes in our skylight. The air pump needs 5-6 volt direct current. To make things quick and easy, I used an Arduino board with a standard connector and jumper wires to the air pump motor. Wiring is extremely simple, we just used 5V and ground connections. In fact, you don't need Arduino for this project at all. We simply piggy-backed on it for a quick 5V power connection.
The picture above show how wires are connected to our dehumidifier air pump. One wire goes to GND, another to +5V pin. This particular air pump has a 4.3 mm opening, and we used a 4 mm PVC hose together with it. We can also try a smaller pump from another kit (shown below). This one runs on 3.3V power and has a smaller, 3 mm hose connected to it.
Below are two air pumps mounted together alongside with Arduino, to get you an idea about dimensions.
Wiring picture for the smaller air pump is below. Notice that instead of 5V pin we use 3.3V pin for this pump.
The plastic pipes that came from my source were bent multiple times over due to tight packaging. Apparently, this creates a problem for air suction. I resolved this by wrapping a small piece of Scotch tape around bent areas.
For better results, you may wish to pump some dryer air inside skylight. You can accomplish this by pumping outside air through a container filled with silica gel. You can by them in bags, similar to shown on the picture below.
Silica gel granules look like transparent balls about 3 mm in diameter.
I did not use silica gel for this project, as the result accomplished with the previous step was "good enough". Some very minor water condensation can still be visible in skylight corners in early mornings, together with dew on outside grass. This very little condensation quickly disappears as outside temperature rises. So, this "dry-up" step does not seem really necessary at this time, but we'll see what happens in winter and perhaps use it if then.
I used silica gel in another project, where it seems necessary. Mentioning it here in case outside air is too humid.
After building this gadget and pumping outside air into skylight for about couple of hours, we accomplished 100% water condensation removal. Next morning, there was some minor residual water condensation on the glass. We repeated forced air pumping during the next day to remove residual moisture.
Now, after we fixed the problem, we need to seal the ventilation holes so that water vapours don't get inside. We can do it with Scotch tape, see the picture below showing a close-up of one sealed ventilation holes.
It the first phase of the project with passive ventilation holes, we observed partial condensation removal. To fix the problem entirely, we then pumped outside air into the space between skylight glass panels, on one sunny day for a couple of hours. This removed all visible water from the inside of skylight. Repeating the process next day helped to remove small traces of residual water condensation.