Sustainability Hacks: Automatic window control

Sometimes, changing one little bit of a green hack turns it into a build that wastes as much energy as our gaming rig. [Dr. West]’s automatic window controller is one of these builds. The good news is the window controller can be easily modified to cut energy costs in the fall and spring.

[Dr. West] doesn’t have any control over the heat in his apartment and for the entire Canadian winter, his apartment gets really hot. He doesn’t pay for his heat, so he does what any of us would do – crack a window. Inspired by this post, he put a linear actuator in the frame of his kitchen window. [Dr. West] didn’t want to damage the window frame, so he attached the actuator to a piece of square aluminum tubing that mounts to the existing screw holes.

The electronics, [Dr. West] used a Rabbit 2000 dev board, LCD display and keypad, and built an H-bridge circuit on a bit of breadboard. Because of a port conflict and admitted laziness, an Arduino is used to read the thermistor. The display shows the current and desired temperature, and the Rabbit opens and closes the window accordingly. All the source code is posted in the forum post.

While it’s not the most ‘green’ idea to dump heat from a building’s HVAC system out into a frozen tundra, this would be a great build to automatically open and close windows in the more temperate seasons. Open windows during the day, close them at night and you’ll have no more problems coming home to a house that’s either too hot or too cold. Check out a video of the automatic window after the break.

42 thoughts on “Sustainability Hacks: Automatic window control

  1. That is insane.

    As someone who have to pay to keep a reasonable temperature in winter such kind of waste is something that I don’t understand.

    Updating the heating system of the building is such a difficult thing that don’t pay for itself in some years?

    Or there is a magical heat source in Canada that I never heard of?

    1. It might not make sense if the building is old. Some of those buildings have incredibly old heating systems such as oil fired hot water. They were put in when such heating was cheap.

      To replace them can be ridiculously expensive. Not only do you have to replace the heating unit, you often have to bring things up to code, particularly if you’re a landlord and not just a homeowner doing it yourself. That means new radiators. That means labor to rip out old systems and run new piping. It means replacing the exhaust stack for the heater. It means new wiring. It means possibly having to relocate things because of code changes. And let’s not forget the downtime to do all this when your residents are screaming that it’s too cold or hot.

      Yeah, it’s stupid to just turn the whole building on “heat” or “cool”, but sometimes it actually is cheaper to just do it that way.

      I’d suggest code changes to permit cheaper replacement, but you have to be careful with that. People complain, but building codes are why entire city blocks don’t burn down every month.

      1. Sometimes renovating old houses up to code can also cause them to develop moisture problems, because you have to add insulation to a wall that was never designed for it. End result is that the outer parts of the wall go cold and the dew point shifts to inside the wall, and it rots. To prevent that, you then have to seal the whole thing with plastic on the outside, and you get a house that doesn’t breathe at all, and then you have to deal with moisture coming from the inside of the house condensing on the inside of that plastic etc. etc.

        Old buildings are usually built to leak a bit from here and there, and that keeps the structures ventilated and dry, and healthy for hundreds of years as long as you keep them warm. If you try to apply new codes to the old desing, you start to develop problems the moment you turn off the ventilation fan because you’re basically living inside a big vinyl bag with lots of naturally decaying materials.

      2. In NYC most residential buildings are old and have antiquated steam heat systems. Since there are laws dictating at what outside temperatures the heat must be turned on and what the ambient temperature must remain inside, it is difficult to maintain an exact temperature for each room in every apartment. So some apartments get too hot in order to make sure others get sufficient heat. That’s when you may have to open the window or suffocate. I noticed a lot of space taken up on the counter for his electronics. I would not like to have that much equipment taking up horizontal space I like how the window opens, but I would never open a window to a fire escape at night lol.

    1. opening the top sash would be better as hot air is at the ceiling and venting it is a better idea.

      Perfect would be to open the top and bottom at the same time. 3″ open at top and 3″ open at bottom will vent hot air and let in cooler air lower to displace the hot air leaving. Best would be to do this across two rooms to get air transfer for the whole apartment.

  2. Dumping the heat out the window is pretty green compared to the alternative* if your landlord refuses to install thermostatic controls.

    * The alternative: At an old apartment, where there were no thermostats and the valves in the radiators were corroded and stuck in the open position, I called up the landlord company and asked them if there was anything I could do other than open my windows. They replied, and this is a direct quote, “Well, you could run your air conditioner.” (Bear in mind they paid for the heat and the electricity.)

    Many landlords are extremely economically short-sighted, either they don’t have the funds floating around for investments with long-term payoffs, or they’re public companies who only care about next quarter’s profits, even at the expense of next year’s.

    1. Where I live in the In Canada we have huge temperature swings and low humidity. This would be a perfect application.

      It work extremely well in the summer helping a house cool off. No one in Calgary has air conditioning because goes from 35C during the day down to below 20C at night. Letting the house warm up in the morning would be great too.

      He have used systems like this to automatically control natural ventilation as well.

  3. Come to think of it, what about some automatic covers for the heaters?

    We’re talking about water based heating(not electricity) and there shouldn’t be any problem if you cover the heater.
    So a simple system should just unroll some insulation material on the heater.

    1. That’s a good idea. Build a styrofoam insulating box. Attach that to the actuator and have the actuator move it up/down to cover varying amounts of the radiator.

      Or, if there’s room, build an insulating box with an inlet/outlet for air and a fan. Turn the fan on/off as needed to pull air across the radiator.

      1. The box doesn’t need to be made of insulating materials, because the radiators depend mainly on convection to transfer heat to the room.

        Water filled radiators aren’t hot enough to actually radiate much heat, and air is a pretty good insulator at just 0.024 W/(m*K) which means that a 1 centimeter airgap will pass just 2.4 Watts of heat over a 1 sq-m area per Kelvin if the air stays still. This is why foam insulation works.

        Simply blocking the airflow with a cardboard box will reduce the heat output dramatically. Conversely, opening the top and bottom of said box will increase heat output because the box then acts as a chimney that increases airflow.

        Therefore, it would be more useful to put a box around the radiator and shutters at the top and the bottom, rather than opening and closing a window.


    That is the dumbest idea ever.

    During summer at night it is the coldest. so you open at night and close during day. but then you need to be able to shield heat gain during the day, I hope you have R36 in the ceiling!

    In winter, you will never have it warm enough to grab heat from outside air so you use solar heat collectors in the windows.

    1. Depends where you live. Here in Melbourne, in late winter/early spring daytime can be a nice ~20°C but night time a chilly ~6°C. Having the windows and doors open during the day can make quite a big difference in internal temperature.

  5. My dorm room sophomore year of college had no thermostat of its own. In fact, to my knowledge the building had no thermostat at all. Someone, presumably the same people who’d fix the hot water heater whenever it broke (often), would turn the AC or heater on or off, and there was nothing any of the residents could do about it aside from call and complain. You bet your butt I opened the window. It was the only way to make the place livable.

    My college had people specifically to recommend ways to save energy (and therefore money) but the admins ignored them at every turn.

    1. Wow, excellent point! I would never get this window open in an emergency without a brick… but luckily I have a secondary escape window in the other room that will suffice in case of a fire :) Thank you for this comment!

  6. I think a number of people are ignoring the fact that this solution works exactly the same as if you were venting excess heat in summer and bringing in warm air in early spring/late fall days.

    I do like the suggestion of venting the radiators to reduce the original purpose of this hack, but it is still useful.

  7. Well yea this is not about sustainability, but I can live with the misnomer. Personally I never come across a sash window that operated that easily as to open from a single pill or lift point. Really can’t blame an apartment dweller for doing what they can to be more comfortable, when they have no control of the real problem.Sad thing is, it IS the apartment dwellers that who are ultimately paying for the wasted energy. Until more sensible housing is available landlord will be able to increase rent to cover their cost, therefor have no incentive to change things. I really doubt highly insulated covers for the radiators will be effective

      1. It will work, even without any special insulation because air is a great insulator. All you need is a box to stop the airflow around the radiator, like I explained above.

        The problem I’m seeing is on the landlord’s end, if the boiler is too old/broken to cope with the hot water returning back unused. They’re probably pushing it at a constant output, which would make the boiler boil over if the tenants tried to throttle their radiators.

  8. My radiators use steam, and they are already turned off (they have manual valves). It STILL gets too hot just from the heat in the apartments/hallway below me. Box covers for the rad’s won’t do anything.

  9. Actually, in some locations the law requires that all apartments be kept at a minimum temperature during the heating season (Mid Sept to mid Jun where I live). If the old buildings are not amenable to well-controlled temperatures for each apartment, then the coldest apartment is heated to the minimum temperature and all the others end up hotter still.

    I have the thermostat off year round and still end up hot – only the coldest winter days result in comfortable temps.

    I’ve considered an automatic window opener. However, I want it to close the window automatically when the a**hole next door smokes his El Stenchoes on the balcony. Anyone know of a reliable smoke sensor?

    1. Wouldn’t a regular fire alarm smoke detector work…? I’m not exactly sure how they work, but maybe you could jack up the sensitivity on it and have it trigger your window to close rather than beeping.


    Sounds like a good way to solve the larger problem then…

    Seriously though, a ducted cover over the radiator to throttle airflow and therefore heat transfer is a marvelous idea. One unit doing it isn’t going to affect the main boiler.

  11. Just came across this and have some questions about the board. Does the Arduino directly run the linear actuator? Or are there relays? I am looking to use an Arduino to run a reversible hydraulic motor and a piston (18amps running, unknown startup), ordered the board, but haven’t got it to play with yet. I lived in an apartment with steam as well and luckily was on the first floor, so turning off the heat turned off the heat. If only you could sell your landlord on thermostatic valves for the apartments below you. No doubt you have a 90 year old lady living under you that would set the thermostat on her rad at boiling anyway and negate the effort. If windows are being opened in the building, these valves pay for themselves very quickly even at $65 a pop. If you have one pipe steam, they are called one pipe steam thermostatic radiator valves. They have them for water and 2 pipe steam as well. In one pipe steam, they replace the air vent.

  12. @dax
    Evidently radiators filled with hot water are capable of radiating plenty of heat, or they wouldn’t be used to heat spaces, and this discussion wouldn’t have occured. Yes air is a good insulator, but in time it’s ability to isulate breaks down like any other iinsulator. No matter the material used to surround theradiator in time it’s room side surfaction will become as hot as the radiator, and it will act as a radiator creating convection air cuurents in the room heating the room. Really unwise to use any combustable materials like cardbord in an attempt to stem the heat coming from the radiator. The flash point of a combustable material that subjected to a heat source for long period of time will lower to the tempurature of the heat source. Really unfortunate that people have to resort to kludge fix like opening a window to prevent becoming over heated by their apartment’s heating system, in time it will be the tenants paying for the wasted energy. Installing electric space heating probaly is the best option for the owners of older apartment buildings. Even if they have to use the fuel oil or gas they are now using to fire a boiler, to operate an on premises electrical power plant.

  13. I think this would work well in particular conditions. But, will not make everyone happy.
    In theory, I would suggest putting a humidity sensor, and temperature sensor in doors and out doors. The window will automatically open to adjust to your suggested temperature. If you want it 72 in room, and it is 74 in room, yet 70 outside. The window could open long long enough to displace the temperature. I also like the idea of opening both top and bottom windows for best venting.
    If it were to get too humid window would shut.

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