Biomimetic Building Facades To Reduce HVAC Loads

A human hand holds a stack of several plexiglass sheets with needles glued into the ends. Very faint lines can be seen in the transparent stackup.

Buildings currently consume about 50% of the world’s electricity, so finding ways to reduce the loads they place on the grid can save money and reduce carbon emissions. Scientists at the University of Toronto have developed an “optofluidic” system for tuning light coming into a building.

The researchers devised a biomimetic system inspired by the multi-layered skins of squid and chameleons for active camouflage to be able to actively control light intensity, spectrum, and scattering independently. While there are plenty of technologies that can regulate these properties, doing so independently has been too complicated a task for current window shades or electrochromic devices.

To make the prototype devices (15 × 15 × 2 cm), 3 mm PMMA sheets were stacked after millifluidic channels (1.5 mm deep and 6.35 mm wide) were CNC milled into the sheets. Fluids could be injected and removed by needles glued into the ends of the channels. By using different fluids in the channels, researchers were able to tune various aspects of the incoming light. Scaled up, one application of the system could be to keep buildings cooler on hot days without keeping out IR on colder days which is one disadvantage of static window coatings currently in use.

If you want to control some of the light going OUT of your windows, maybe you should try building this smart LED curtain instead?

21 thoughts on “Biomimetic Building Facades To Reduce HVAC Loads

  1. Just curious. Isn’t the majority of electricity consumption in the future linked to heating and air conditioning? I see two themes for the future – 1) construction of buildings with natural “air conditioning”, 2) limit the cooling of buildings in warm seasons / climates – it is ridiculous to turn a building into a fridge in the summer just so that people can follow the dress code and wear warmer clothes inside.

    1. That is starting to happen now. Passive air conditioning is becoming more common, I had a lecturer at University who owned a company that designed passive air conditioning systems.

      As for your second point, I think that is changing now as the dress code relaxes. At least where I live you wont see people wearing suits all that often.

      1. I worked in a school like that. Built in 2011, it recieved some kind of “green award” for passive heating/cooling. Had a big underground labirynth that was supposed to pool cool air at night then it would be drawn up by convection during the day, with the hot air exhausted by thermal chimneys at the top of the bulding.

        It was fucking awful. One february (southern hemisphere) they had to send all the students home because the building was hazardously hot.

        In winter it was even worse, because the inly heaters were on the top floor. Of an open-plan building. Apparently in architecture school they don’t teach people that heat rises. The ground floor was freezing!

        Right next door was the municipal library, built at the same time. This had a giant 400kW natural gas powered chiller driving a proper HVAC system. The key difference between the two building was the “passive” building was no good in summer or winter.

        When i left, the school was in the process of retrofitting air conditioning at enormous expense, and also enclosing some of the open-plan areas.

        I am all for sensible passive design, I have a degree in sustainability and have employed plenty of passive techniques to heat/cool my own home. But it’s worth pointing out that millions of dollars and a “green building” award don’t necessarily lead to a green building. Not sure if the architect was stupid, the builders were lazy/cheap or both.

        1. The planet has become inhospitable, and without adequate dynamic insulation, vehicles are unsafe for surface travel. The invention of blanket fluid allows vehicles to respond quickly to the fast changing conditions. By modulating the cars thermal insulation and conductivity properties, the blanket fluid regulates the interior climate with much greater efficiency than traditional AC or heat transfer systems.

      1. Hackaday (IIRC) had an article about cooling/refrigeration buildings in Iran (Persia) that cooled by evaporation (made of clay and straw?).
        But I couldn’t find it just now with a site search.

  2. Doesn’t efficiency and conservation lead to inflation? I mean, the utility companies are going to whine about lost revenue and then the regulatory agencies will feel sorry for their loss and grant them more and more rate increases. That’s not irony or sarcasm, that’s the simple truth!

    1. So we should just keep burning up the planets resources until we run out, and/or accelerate climate change to the point where we need more of those resources to remain comfortable (never mind everything we’d have to change/rebuild to adjust to where things grow well, etc.). What a short-sighted & self-centered point of view!

      1. So, when one speaks the truth, it’s “bad”? Grow up. I never said there wasn’t any good to it, I just said there will always be those who profit from anything — and now I realize there will always be someone that fails to analyze a statement before assigning fault that isn’t there.

  3. I’m a little lost.

    Sure – you can pump a fluid in there. Take something that let’s all light pass for winter, something for scattering for privacy, colorful for a party.

    But energy conservation? How exactly?
    If you try to scatter the light, you still absorb some of it – so it is worse for indoor lighting than without.
    If you intentionally absorb IR, you heat up your fluid and still need to cool it down! Once you have the heat inside the window, you still need to get rid of it.
    Is there a liquid that is IR reflective but let’s light pass?
    Reflecting everything might work with liquid metals.

    The next study should compare to external blinds (they can do open, darker and privacy with some light!) and roll-down reflective coated films. Single motor, not chance of leaks

  4. There is a scene in one of the Dune novels where a meeting room has outside-facing windows which can be ‘tuned’ to restrict the amount of inbound light, without affecting the spectrum.

  5. I once saw on someone’s personal webpage the idea of making windows out of two sheets of corner-cube retroreflective plastic or glass with a gap in between. With the gap empty, sunlight would be reflected away, keeping heat out on summer days. Filling the gap with a fluid of the same index of refraction as the window would make it transparent, letting heat out on summer nights. In the winter, the opposite would be done, allowing warmth in during the day and keeping it in at night. It could also be used as a simple transparency control, albeit much slower than electrochromic or liquid crystal windows.
    This was years ago, and I still don’t know why it hasn’t been commercialized. He didn’t even patent it! I wish I could remember his name or the name of his site.

  6. Pleotint’s thermochromic interlayer (marketed as Suntuitive) has been out for years and does this better/cheaper. That said, even they struggle to sell the technology, not because of the tech but rather because there is no value proposition. Who is the buyer? With the exception of occupant owned commercial buildings (a minority of commercial buildings) the people who see the benefit of the technology are not the people who have to pay for the technology so the ROI is zero. Add to that the fact that the HVAC companies have “never had someone tell me I put in too much A/C” so they are all for installing the windows that reduce HVAC load but that won’t stop them from putting in just as much HVAC capacity.

  7. I experimented with a simpler version of this idea more than a decade ago.
    Pump the space between two panes of glass with different density/opaque fluids.
    I used a dark fluid pumped into the bottom, which pushed the clear fluid up into a tank above. To make the window clear, let the lower fluid drain.

    The problem I couldn’t overcome with “garage tinker” materials was keeping the fluids from mixing, or the dye from leeching into the clear fluid.

    You run into all sorts of probms when you need to make a system that needs large amounts of cheap, readily available, nontoxic, environmentally friendly working fluids.

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