Window Blind With Forced Ventilation




Especially during the summer it gets quite toasty in my bedroom. The room features some large windows, so I figured that some airflow during the night could really improve things. Therefore, I decided to built myself a window blind that fits into frame of a smaller sash. Some cooling fans force air trough this contraption to support air circulation during the night. Some fixed deflector fins keep out any rain that may come along with the eventual thunderstorm. So you can have this window blind installed all summer long without worries.

If you decide that you want to build such a contraption you need the following materials and tools:


• A sheet of plywood that fits into the window frame in question, 5mm thick works good for me.
• A sheet of plywood that is about 1.5 times as long as the frame to cut the fins, I've used 3mm thick material.
• Some 20mm x 30mm scrap wood. (The actual dimensions are not very critical, however, they need to be at least 4 times the length of the window to from the rails for the fins.)
• A bunch of PC cooling fans, the bigger the better. I've chosen 100mm ones.
• A DC supply that is capable to drive the fans.
• Wood glue
• Weatherproof paint
• Wood screws (25mm).
• 4 machine screws (about 6x50mm)
• 4 thumb nuts matching the machine screws
• Sandpaper


• The only no so common tool required for this built is a hole saw that matches the fans.
• Power drill
• Table saw or some other kind of miter-saw

Step 1: Layout the Window Insert and Cut the Holes for the Fans.

This first step is crucial, so I would recommend to spend some time on this step.

Fist of all measure the window frame to determine the required size of the insert. This part should fit into the window frame with about 2mm gap all around the edges. When inserted, this part should rest securely against the window frame's foremost rim. I would suggest to cut the plywood to size and then try to insert it before proceeding.

When the insert is cut to size, layout the fans evenly across and mark the cutouts with a compass. Keep in mind that the screws that hold the fans in place are also used to attach the strips that hold the fins on the other side. It us a good idea to try that layout with the window in question before cutting out the holes for the fans. Some element may conflict with elements form the window frame.

The fiddly part is over now, so cut out the holes using a hole saw. If you don't have one also a jig saw would do.

Step 2: Pepairing the Insert

Deburr all the edges and prepare the surface of the ply to take on the finish you have chosen. I would recommend to sand it to 180 grit or so.

Step 3: Preparing the Strips and Cutting the Fins

In the next step the thinner ply is cut up into strips for the fins that will protect the fans and the interior from rain. If you want them to cover the openings perfectly, make them 1.41 times longer than their spacing (assuming installing them at a 45° angle). Don't forget to cut a longer one for the very top, the size of this one depends on the hight of the stips you use. This one needs to be (1,41 * hight of the strip) - (depth of the mounting cut in the stips) longer than the other ones. Then cut slots in the strips at the chosen spacing and a 45° angle. This slots need to be as wide as the ply and are perfectly consistent if you clamp all the strips together while doing so. Don't forget to miter also the ends of the strips at a 45° angle.

After cutting all this up, sand all the parts to the desired finish and glue up the strips to line up with the mounting holes of the fans.

Step 4: The Mouning Brackets

In order to attach the insert to the window, we need some kind of retaining device. I went for simple blocks with cutouts that grab the window frame's outside and clamp the insert to it. This may sound a bit sketchy but have a look at picture one that should make it clearer. Picture 3 gives you an idea of the final bracket seen from the outside.

In order to build such brackets we need to cut up some scraps to get some blocks of about 70x20x30mm. The absolute dimensions are not critical, use whatever you have. I used some leftovers from cutting up the strips.

Step 5: Forming the Clamping Face

This step depends on your actual window frame. Cut out a notch that mimics the form of the window frame's foremost rim, so that the bracket is flush with the insert when installed. This is again a bit fiddly.

After you are done with that, drill a hole through the center of the bracket with an appropriate diameter to take whatever machine screw you have chosen to use.

Step 6:

Step 7: Cutting Slots for the Clamping Brackets

In this step drill two holes in the insert for every bracket you wish to install. The outmost hole should allow the bracket to grab the window frame. The inner hole should allow the bracket to retract that much so that it does not interfere with the frame. This position will later be used for installing it. After that use a jigsaw and a file to form a slot from this two holes.

Step 8: Put on the Finish

This thing will get to experience some nasty weather, so better put on a weatherproof paint. You will earn some additional stile points if the color matches the windows.

Use the slots for the fins as a stand when painting them but do not install them at this point. They may interfere with the next step.

Step 9: Install the Fans

Now just install all the fans and wire them up in parallel. At this point you have to decide whether you want to force air inwards or outwards.

I went with having all fans installed so that they force air out of the window. Considering that this insert is intended for a window close to the ceiling (where hot air gets trapped) and I don't want to suck in bugs and dust from outside.

Keep in mind that your DC supply must be able to deliver the cumulative current of all fans. In my setup I run the fans only at about 70% of their nominal voltage in order to get quieter operation. Having a bench power supply at hand is very neat to find the sweet spot between having not too much noise from the fans and still getting satisfactory airflow.

Step 10: Installing the Fins and Brackets

In this step you want to install the fins using short nails, a nailgun or/and epoxy glue. Start from the top and work your way down till all fins are in.

After that add the brackets and add the thumb screws. Fix that brackets in the installation position and you are set.

Step 11: Admiring Your Work

Now is the time to admire your work and have one of your favorite beverages ;-)

Step 12: Installation

Depending on your stile of window frame you want to remove or simple open the window. Since the brackets are retracted, nothing should interfere with the window frame when installing it.

After everything is in place, loosen up the thumbscrews and slide the brackets outwards. As you tighten them again, they should grab the window frame and hold everything in place.

Step 13: Enyoing Cool Air on a Hot Summers Day

After you installed the insert in the window you simply switch on the DC power to ensure air circulation throughout the room. Check the thumbscrews every now and than to be sure nothing gets loose and falls down on you.

Adding some automatic control to this device based on in and outside temperature could be easily achieved using some lines of Arduino code and a suitable transistor.

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    44 Discussions


    3 years ago on Introduction

    Why go through all this rigmarole when one can buy mains operated appliance cooling fans in the market ? Just connect them all in parallel and you are set. Should not pose any problems from insurance point of view either. Just use properly rated fuse / circuit breaker. One can also use BCD type power switch to control the number of fans powered on.

    4 replies

    Reply 3 years ago on Introduction

    Thats true, to be perfectly honest I would have gone for AC fans if I hadn't a bunch of the PC fans at hand. However, in the mean time I've upgraded this setup to be controlled with a µ-controller. Something that would be quite a bit more challenging with AC fans.


    Reply 3 years ago on Introduction

    Not really true. Until quite recently ceiling fan speed regulators used in line resistors to drop the voltage to the fan. Nowadays what is being used is in line capacitor types to control the current. This serves 1 additional purpose, reduce your power bill instead of wasted energy in the resistors. These are available in capacity up to 100 watts of load power. There are usually 3 capacitors to give 5 speed settings, by using BCD mode switch. These are usually "Make before Break" type of switches. I am pretty sure you could use µ-controller with optically coupled triacs to regulate the speed and save money overall.


    Reply 3 years ago on Introduction

    I'd rather say thats a matter of taste. If you have a spare bunch of DC fans around they are obviously the cheapest option. With respect to the driver circuit and its efficiency, having a PWM modulated DC drive using a cheap and highly efficient motor driver is surely as efficient as messing around with opto-triacs. However, when playing around with circuitry on breadboard level I generally avoid to mess with live mains, thats why I called it less challenging.
    Nevertheless If you want to use a AC fan approach, having a PFC drive is surely the simplest feasable way to controll the fans speed.


    Reply 3 years ago on Introduction

    I suggested opto controlled triacs only in the event you WANT to use a micro-controller otherwise 100 watt rated capacitor based fan regulator will directly control 8 fans drawing 12 W each. These cost no more than $ 1.50 No additional circuitry of any kind would be needed. These regulators also have an OFF position.


    3 years ago

    I made one for these awhile back! I used a pic power supply and and basic house hold thermostat. I connected the AC pins of the thermostat to the green and one of the black wires on the power supply. This allowed me to control the temp. At night

    1 reply

    Reply 3 years ago

    Sorry that should have said "PC power supply"


    3 years ago on Step 13

    Cool! (pun intended)

    Also: I would add that you have a very nice view from your window.


    Exceptionally nice! One suggestion: if you use a diode and 16 smaller fans, the diode can directly rectify your A/C rendering about 190 VDC (filtering should be unnecessary), thus eliminating the need for a power supply per se. Wiring the fans in series gives 12 VDC per fan. Caution: you may need to install a resistor in parallel with each fan to minimize current hogging. 10-15% the resistance value of the fan should do.

    3 replies

    This is dangerous and can cause a lot of trouble with insurance companies if your house should have a fire (caused by the device or not).


    Reply 3 years ago on Introduction

    Thats true additionally the AC here is 230V eff, which would result in 330V DC when rectified. Despite being a tempting idea because it is cheap and simplistic, I found out that the commutation electronic inside the fans hates unstable power rails. In fact I had cases where when 3 or more fans where connected in series, their rates would change periodically. That caused funny noises and surely some wear on their internals. Therefore I went for a 15V 2A fixed DC power supply and an cheap adjustable buck converter while having all fans in paralell.


    Reply 3 years ago on Introduction

    230vAC mains, and a single diode, will NOT give 330VDC -- you're thinking of a full bridge. You'd lose half the mains cycle at a stroke, and end up with more like 165V lumpy DC.

    In any case, it's not a safe idea -- putting the fans in series does cause odd behaviour. I've tried it with 2x12v on 24v and found that one can overspeed while the other struggles to start :(

    Stick with the 9-12V DC power supplies.


    3 years ago

    Great work!!! :D

    maybe something to think about... how about adding little sollar panels on your protection fins to drive your fans.

    I think its a great idea man. A perfect solution for more than a few areas of use. quick Q: How many total volts is needed to run it? I'm "pro solar" and envision a little solar panel providing the juice.

    You got a vote from me!

    3 replies

    The question is more about the power needed, not the voltage. Typically all the fan are powered with 12 V. They however need current, let say 0.15 A for each ... which lead to 8 x 0.15 = 1.2 A to supply.

    So you need a solar panel able to provide at least 14.4 W


    Reply 3 years ago on Introduction

    Thats correct, the fans I used are rated 12V 0.2A, however, I'm running them most of the time at 9V where they draw about 0.1A each mostly to reduce noise. So in fact this fan array runs at about 7.5W which should be manageable with a solar module. Nevertheless I have to point out that I'm using it mostly at night to cool down the room as long the air outside the building is cooler than on the inside. Therefore, a storage battery would need to have about 8h*7.5W=60Wh capacity. That results in about 8 18650 cells which is still manageable but asks for a bit more sophisticated battery management.


    It wouldn't take much of a solar panel to put out 15w here's an example from Sunpower: SUN 15 Watt - 12V $22.00 Dimensions: L: 15.19in x W: 14.2in x H: 1.2in.

    The solar cell toy image in my logo thingy in the upper left is the size of a postage stamp (little bit bigger but not much).

    Kudos for a well done project!


    How could I go about powering this without a "bench power supply"? Why are there no stand alone power supplies to power muffin fans?