Editing Passive solar building design (section)

===Hybrid direct/indirect solar system===
Kachadorian demonstrated that the drawbacks of thermal storage walls can be overcome by orienting the Trombe wall horizontally instead of vertically.{{Sfn|Kachadorian|2006}} If the thermal storage mass is constructed as a ventilated concrete slab floor instead of as a wall, it does not block sunlight from entering the home (the Trombe wall's most obvious disadvantage) but it can still be exposed to direct sunlight through double-glazed equator-facing windows, which can be further insulated by thermal shutters or shades at night.{{Sfn|Shurcliff|1980}} The Trombe wall's problematic delay in daytime heat capture is eliminated, because heat does not have to be driven through the wall to reach the interior air space: some of it reflects or re-radiates immediately from the floor. Provided the slab has air channels like the Trombe wall, which run through it in the north-south direction and are vented to the interior air space through the concrete slab floor just inside the north and south walls, vigorous air thermosiphoning through the slab still occurs as in the vertical Trombe wall, distributing the impounded heat throughout the house (and cooling the house in summer by the reverse process).

The ventilated horizontal slab is less expensive to construct than vertical Trombe walls, as it forms the foundation of the house which is a necessary expense in any building. Slab-on-grade foundations are a common, well-understood and cost-effective building component (modified only slightly by the inclusion of a layer of concrete-brick air channels), rather than an exotic Trombe wall construct. The only remaining drawback to this kind of thermal mass [[solar architecture]] is the absence of a basement, as in any slab-on grade design.

The '''''Kachadorian floor''''' design is a ''direct-gain'' passive solar system, but its thermal mass also acts as an ''indirect'' heating (or cooling) element, giving up its heat at night. It is an alternating cycle hybrid energy system, like a [[hybrid electric vehicle]].