Passive Solar Design Unpacked

by Felton Constructions

Increased awareness of the ways in which a home’s design can enhance energy efficiency is becoming evident in many home designs NSW.

NSW home builders are frequently asked to include solar panels, water conservation measures, easy transitions between indoors and outdoors and even the option to install Tesla batteries to home designs, but one of the most significant steps forward in this area is in passive solar design.

Passive solar design is all about using the sun’s energy for the heating and cooling of a home. A lot of this has to do with building materials, which can reflect, transmit, or absorb the solar radiation. At the same time, the movement of the heat produced by the sun can be manipulated through the clever use of design elements and materials.

A typical passive solar system comprises a number of features. The first of these is referred to as an aperture or collector and usually translates to a large glass area, through which sunlight enters the building. Next, the absorber is storage element featuring a hard, darkened surface that sits in the direct path of sunlight. Another key element is known as thermal mass and this should be made from materials that retain or store the heat produced by sunlight. While the absorber is an exposed surface, the thermal mass is the material below and behind this surface.

Distribution is another key aspect of this kind of system and refers to the means by which solar heat circulates from the collection and storage points to different areas of the house. Another complementary component is the ‘control’ which might take the form of roof overhangs that shade the aperture during summer months. Other controls include electronic sensing devices, such as a thermostat, vents and dampers that allow or restrict heat flow; low-emissivity blinds; and awnings.

Passive solar design

When it comes to keeping your home warm, the goal of passive solar heating systems is to capture the sun’s heat and release it during cool periods

There are a number of ways to capture that heat. For example, have you ever considered that your living room can function as a solar collector, heat absorber and distribution system? The inclusion of north facing glass admits solar energy into the house where it strikes floors and walls, which absorb and store the solar heat, which is radiated back out into the room at night. If these elements are executed in a dark material, they will absorb the optimum heat possible.

In terms of cooling your home, passive solar cooling systems work by reducing unwanted heat gain during the day. So, in summer, all windows should be shaded by a large eve, veranda or similar structure, as well as shading solutions such as awnings, shutters and trellises.

Thermal mass can also be used in a passive cooling design to absorb heat and moderate internal temperature increases on hot days. During the night, thermal mass can be cooled using ventilation, allowing it to be ready the next day to absorb heat again. It is possible to use the same thermal mass for cooling during the hot season and heating during the cold season.

Naturally ventilation is a very important element of any passive cooling system, maintaining an indoor temperature that is close to the outdoor temperature, so it’s only an effective cooling technique when the indoor temperature is equal to or higher than the outdoor one. The climate determines the best natural ventilation strategy.

To make the most of breezes and ventilation during the day, a good Sydney home design should feature openable windows on the side of the building facing the breeze and the opposite one to create cross ventilation – put simply, this involves designing windows into the walls facing the prevailing breeze and opposite walls.

Another form of passive cooling is convective cooling, whose purpose is to bring in cool night air from the outside and push out hot interior air. If there are prevailing night time breezes, then high vent or open on the leeward side (the side away from the wind) will let the hot air near the ceiling escape. Low vents on the opposite side (the side towards the wind) will let cool night air sweep in to replace the hot air.

At sites where there aren’t prevailing breezes, it’s still possible to use convective cooling by creating thermal chimneys. Thermal chimneys are designed around the fact that warm air rises; they create a warm or hot zone of air (often through solar gain) and have a high exterior exhaust outlet. The hot air exits the building at the high vent, and cooler air is drawn in through a low vent.

There are many different approaches to creating the thermal chimney effect. One is an attached north facing sunroom that is vented at the top. Air is drawn from the living space through connecting lower vents to be exhausted through the sunroom upper vents (the upper vents from the sunroom to the living space and any operable windows must be closed and the thermal mass wall of the sunroom must be shaded).

Passive solar design