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Chapter 3

Direct Solar Energy

Air

Geothermal

Inlet

Pump

BIPV/T Roof

Variable Speed Fan

Passive Slab

Ventilated Slab

External

Rolling

Tilted

Shutter

Slats

Exhaust Fan

q

Solar

Dryer

HRV

DHW

Light Shelf

Side-Fin

Internal Rolling Shutter

Blinds

Figure 3.2 | Left: Schematic of thermal mass placement and passive-active systems in a house; solar-heated air from building-integrated photovoltaic/thermal (BIPV/T) roof heats ventilated slab or domestic hot water (DHW) through heat exchanger; HRV is heat recovery ventilator. Right: Schematic of several daylighting concepts designed to redistribute daylight into the office interior space (Athienitis, 2008).

be concentrated on the equatorial side, as should the main living rooms, with rooms such as bathrooms on the opposite side; they should avoid shading by other buildings to benefit from the essential mid-winter sun; and they should be ‘thermally massive’ to avoid overheating in the sum- mer and on certain sunny days in winter (Everett, 1996).

Clearly, passive technologies cannot be separated from the building itself. Thus, when estimating the contribution of passive solar gains, the follow- ing must be distinguished: 1) buildings specifically designed to harness direct solar gains using passive systems, defined here as solar buildings, and 2) buildings that harness solar gains through near-equatorial facing windows; this orientation is more by chance than by design. Few reliable statistics are available on the adoption of passive design in residential buildings. Furthermore, the contribution of passive solar gains is miss- ing in existing national statistics. Passive solar is reducing the demand and is not part of the supply chain, which is what is considered by the energy statistics.

of existing homes as well. Many homes also add a solarium during retrofit. The new glazing technologies and solar control systems allow the design of a larger window area than in the recent past.

In most climates, unless effective solar gain control is employed, there may be a need to cool the space during the summer. However, the need for mechanical cooling may often be eliminated by designing for pas- sive cooling. Passive cooling techniques are based on the use of heat and solar protection techniques, heat storage in thermal mass and heat dissipation techniques. The specific contribution of passive solar and energy conservation techniques depends strongly on the climate (UNEP, 2007). Solar-gain control is particularly important during the ‘shoul- der’ seasons when some heating may be required. In adopting larger window areas—enabled by their high thermal resistance—active solar- gain control becomes important in solar buildings for both thermal and visual considerations.

The passive solar design process itself is in a period of rapid change, driven by the new technologies becoming affordable, such as the recently available highly efficient fenestration at the same prices as ordinary glaz- ing. For example, in Canada, double-glazed low-emissivity argon-filled windows are presently the main glazing technology used; but until a few years ago, this glazing was about 20 to 40% more expensive than regular double glazing. These windows are now being used in retrofits

The potential of passive solar cooling in reducing CO2 emissions has been shown recently (Cabeza et al., 2010; Castell et al., 2010). Experimental work demonstrates that adequate insulation can reduce by up to 50% the cooling energy demand of a building during the hot season. Moreover, including phase-change materials in the already- insulated building envelope can reduce the cooling energy demand in such buildings further by up to 15%—about 1 to 1.5 kg/yr/m2 of CO2 emissions would be saved in these buildings due to reducing the energy

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