This is one of the more speculative ideas since 3D printing of an entire home is at least a decade away, but here's the idea.
Right now, passive solar buildings are buildings designed to minimize heating and cooling costs by using strategies to take advantage of the natural environment. It's a collection of techniques like southward facing windows, ultra insulating materials, angled overhanging roofs to shade during the summer when the sun is high but let in light in the winter when the sun is low, and putting thermal mass where it will radiate heat when it's cold and take in heat when it's warm.
There are companies that do this right now and it tends to cut about 80% of household energy consumption for heating and cooling when done right. A problem with the process is that sometimes the aesthetics of the house and the demands of the physics don't coincide. Furthermore, the process is done using straight lines and sharp angles while the sun moves in curves. Also, the entire wall has to be built the same way even though the part of the wall two feet off the ground receives a differing amount of sunlight then the part 5 feet off the ground. Finally, the building has to be very meticulously planned to make sure that the sun is hitting the right materials at the right time of year.
My idea is using a program to automatically vary the internal structure of the walls, floor, and roof of a 3d printed house to make it maximally thermally efficient. It uses two unique properties of 3d printing to make this process a lot more precise and, at the same time, a lot less complex to plan.
It relies on two aspects of 3d printing.
1) 3d printers can vary the internal structure of a material while keeping the external appearance constant. This means that It could make a straight or curved wall that from the outside looked to be a single uniform material, but would be able to vary the internal structure to make it a better or worse insulator.
2) 3d printers are computer based and directly computer controlled so what would be very complex calculation and fabrication task if set up by a person can be handled automatically by a program.
Here's how it would work. The architect would design the house in a normal CAD program. Once that was done, the architect would put the CAD file into the 3D printing software. The architect would then add some basic information, like the exact location of the house, locations of adjacent buildings, the kind of ground it will be on, what the desired internal temperature is, what color it will be, data on local weather etc. The 3d printing program would then use that information and the CAD blueprints to make instructions for the 3d printer that's going to build the house.
The 3d printer software would automatically vary the internal structure of the housing materials as it was making the house with the resulting house being thermally optimal for its location. Parts of the walls and floor that would need to absorb, store, and radiate heat would be far denser (and thus have more thermal mass) than parts that didn't. The important innovation here is that, while the external building would look as square or symmetrical as any previous house, an x ray of the walls would show that they varied in density in irregular shapes designed to absorb or repel heat based on where the sun is.
(This is a house built the current way, every flat surface has the same thermal conductivity across its entire face.)
The architect could rotate the building or place it another place, and the program would automatically make a new unique internal structure to that would be thermally optimized for the new location.
The program would also automatically put in things like thermal vents and build around windows, doors, pipes, and electrical outlets and such. The program could even be designed to to place these automatically based on simple parameters (3 outlets in each room, two windows in the living room etc.)
Also, 3d printed houses are built so that they don't have the same amount of joins which allow heat to escape that normal houses do.
So I did some more work on this using Sketchup and I hope I can use this to explain the idea more and show that it's very close to doable with existing materials/techniques/software.
Take for example this "house" I made in Sketchup.
One of the cool things that Sketchup already allows me to do is put in my location, which in my case is Taipei, Taiwan.
Ok, now the program knows exactly where my house is and it can thus give me accurate shadows.
This is how the shading would be on the Winter Solstice at 11 AM.
The program can show which parts of the house receive sunlight at any time on any day of the year. Now, my idea would be to get another program which could then calculate which parts of the house are getting the most sunlight and when for the entire year and then alter the density accordingly. Taking a cue from what people said in this thread about calculating it modularly, I numbered the individual bricks from 1 - 18 on each side and took snapshots every hour on the solstices and compared when different parts got sunlight.
This process took a long time and was very inefficient for me to do by hand, but a computer could do it for all 365 days of the year for every minute that the sun was up, as well as include things like windows, the likely average ambient temperature for that day, likelihood of clouds, etc.
Now, let's say I had several of these houses on a curvy street, like this.
It's apparent that corresponding bricks in each house gets different amounts of sunlight at different times and it would be a nightmare to optimize each house individually by hand. However, in this simplified example, a 3d printer attached to a program to calculate the sun's position and the optimal internal structure, could print out 4 bags of 72 bricks each. Each component would look identical from the outside and be numbered. It then could be assembled without any specialist training in eco home construction. Though it's built in straight lines and right angles, the 3d printer would vary the internal structure of the each block in such a way that a density map of of the building after it's finished would show something like this.
There would curved density gradients to match the path of the sun at different times of year. The only thing that someone would need to know how to build it is putting brick As1 next to As2 etc. I did this with 72 bricks because it was simpler to work with, but there's no reason why something similar couldn't be done with thousands of bricks using existing 3d printers printing with concrete, wood fibers, plastic etc.
I want to say a big thank you to everyone who took an interest in this idea!
The new images below look great and add significantly to the idea. There are two additional areas that could be explored to develop it further.
The first is to respond to Ralph's post on June 3. I think he makes a good point that you might always want to be going for maximum insulation and thermal mass. If this is the case, then it is difficult to see the value of a variable internal structure.
The other question is how one could cost-effectively "print" using low-cost building materials (as per the technical question posed above).