The Solar Envelope: How to Heat and Cool Cities Without Fossil Fuels

The Oil Drum considers how to use The Solar Envelope: How to Heat and Cool Cities Without Fossil Fuels. The problem is to make cities livable once cheap fossil fuels go away.

The current architectural knowledge is quite advanced for solar heating and cooling of individual buildings. The next stage is to design cities with the same attributes:

Designing a single, often free-standing, passive solar house is quite different from planning a densely populated city where each building is heated and cooled using only natural energy sources. And yet, if we want passive solar design to be more than just a curiosity, this is exactly what we need. Modern research, which combines ancient knowledge with fast computing techniques, shows that passive solar cities are a realistic option, allowing for surprisingly high population densities.

The key to designing such low-energy use cities is the concept of the “Solar Envelope”:

[Ralph] Knowles developed and refined a method that strikes an optimal balance between population density and solar access: the "Solar Envelope". It is a set of imaginary boundaries, enclosing a building site, that regulate development in relation to the sun's motion — which is predictable throughout the seasons for any place on Earth.

Buildings within this imaginary container do not overshadow neighbouring buildings during critical energy-receiving periods of the day and the season, and assure solar access for both passive and active solar systems. On the one hand, the solar envelope allows architects to design with sunlight without fear that their ideas will be cancelled out by future buildings. On the other hand, the solar envelope recognizes the need for development and high population densities, by defining the largest container of space that would not cast shadows off-site at specified times of the day.

Anyone who lives in Sydney knows about how inhabitable the CBD is in Winter with the parks always in shadow and therefore cold. And the buildings built right up to teh boundaries so that the streets become wind tunnels in moderate breezes. I suppose it is one way to get the homeless out of the CBD during Winter!

The article concludes with:

Density is a pet subject of environmentalists, who argue that densely populated cities are the solution to lower the energy requirements for transportation. On the other hand, the solar envelope shows that above a certain treshold, density can also raise energy requirements, in particular those of heating, cooling and daylighting buildings.

This means that it would probably be wise to aim for a compromise. If we would take the highest densities reached under the solar envelope as an upper limit, we could create cities where the critical functions of buildings can be met without fossil fuels, while still retaining (more than) high enough densities to make public transportation, bicycling and walking attractive.