Perhaps the most practical attribute of Cube-based Shelter is its optimal orientation for the utilization and management of solar energy – regardless of latitude. Passive solar energy - a major chunk of the solar energy picture - generally pertains to natural lighting, space (and sometimes water) heating, and cooling schemes that in the purest sense require no technologic input or effort from occupants once constructed.
Naturally, much of the details of such schemes are ruled by home site specifics and materials, but the prime geometric criteria met by CBS are: an equator-facing wall (north in the southern hemisphere, and south in the northern hemisphere); and an east-west roof ridgeline conducive to elongation of the equator facing wall.
Because this wall - independent of location - receives the maximum share of sunlight everyday throughout the seasons, this is where most of the home’s glass should be placed in order for entering light to both directly illuminate and heat the interior during the colder months and to indirectly illuminate during the warmer months when that light is barred from direct access. To effect such control, the universal variance of the solstice altitudes ( 23.5* above and below the equinox solar noon altitude) is taken into consideration.
Strategic shading can be effected with the characteristic CBS roof geometry, or flat roofs of minimum width (above left). In that case, “flatness” should determined with geocentric latitude using the latitude correction formula for water drainage purposes. While taking a solar home design course in the 80′s, one option was to move boards over projecting beams to extend the width of a porch roof according to local circumstances and personal preferences. I still like the idea even if it means a chore requiring some exertion for less than 10 minutes every month or so, and even if it breaks from the passive ideal. Of course, a combination of all of the above is also an option.
With incoming sunlight shaded during the warmer months, abundant indirect lighting can potentially fill the abode, a prime reason for favoring proportionally less width in the north/south dimension. Well-placed mirrors can enhance the effect by reflecting more light to back of the house, an approach that can also make a small space feel much bigger.
A factor of considerable importance in the colder months is storing the heat from admitted sunlight for night use by having light fall directly on thermal mass materials. Masonry floors (from concrete slab to spanish tile) in the path is a virtual must while masonry walls or constructs like hearths are options worth considering. Finding the proper balance of such materials to match glazing area can be approached very technically, in which case the orientation of CBS geometry affords an optimal reference point to design from.
Edward Mazria’s Passive Solar Home Design - one of the first in the field and still widely referred to today, includes tables that aid selection of the right material for the right situation and charts referring to solar insolation for various locations. The sun path charts referred to in the 3 most recent posts both inspired me to derive equations and helped confirm I was on the right track.
As stated at the end of the last post on constructing your own chart, the chart I came up with equated vertical degree marks in the vertical dimension to those of the horizontal dimension. The reason for this - beyond better reflecting reality - is that the chart is meant to be partitioned into 4 overlapping 180* quadrants, each representing the prospective home’s 4 basic wall planes precisely oriented east, west, north. and south.
For example, the chart section facing the west is centered precisely there and extends 90* to either side. The reason I wanted the summer solstice altitude when directly above east and west was to emphasize a (vertical) centerline on the chart for these regions. Many texts seem to suggest using these charts and related devices at some ideal spot, but in reality the chart should be moved to various spots along a prospective wall to get different perspectives of obstacles close by or that could change.
Although the equator-facing wall is of paramount importance, the other 3 sides – especially east and west – are given the respect they deserve on the chart so that design features can take advantage of the sunlight (or lack of) appearing there.
In solar design there are competing needs for which designers must seek the best balance. Although the CBS style presents the best orientation for physical solar utilization and the easiest planning orientation from which to strategically balance solar modes, this in itself does not guarantee a good result.
This post doesn’t address passive cooling options (aside from strategically blocking summer sunlight), but will in upcoming posts focusing on the CBS rooftop, CBS breathability, and ground design.
Regarding the latter, when passive solar home design first became a hot item in the 70s, the ideal was to burrow one’s house into the (sunny) south side of a hill. Although such may make the owners look green, the limited applicability of that approach does precious little to solve problems of resource scarcity, pollution, and global entropy. In part, this inspired the search for a universally applicable design method that makes the ideal possible at nearly any location, even on the polar side of a hill.