Thanks folks. These are not our domes, but some we've built with a friend in the area, on his land. The round openings are not fan units, but windows. :) The are some fantastic books and resources about the benefits of building superadobe domes and the dome shape generally. As a shape the, the 'catenary curve' has tremendous integrity and strength. The idea of this type of construction, which Nader Kahlili revived as superadobe, is that it is meant to be accessible to most/all people, being inexpensive and somewhat simple. This particular construction is somewhat complex and maybe even a bit fancy, but perhaps you can imagine a simple, single, dome, composed mainly of material from the ground on site..... The windows do not have to be made from concrete rings, but are often left as openings by using removable wooden forms..
https://www.google.com.uy/url?sa=t&source=web&rct=j&url=https://en.m.wikipedia.org/wiki/Nader_Khalili&ved=0ahUKEwjByfTSrdPbAhUIWpAKHWHEDqEQmhMIWzAM&usg=AOvVaw0x0VHiwH2yIT8myqJ_ateC
What is SuperAdobe? — CalEarth
www.calearth.org › intro-superadobe