Table of Contents

1		Introduction
2		Is it for me?
3		How much does it cost?
4		What are the benefits?
5		Step by step guide
6		Case studies
7		Where can I find out more?

Step by step guide

Bioclimatic elements are classified as passive and active. Active solar systems are directed towards solar energy capture by mechanical and/or electrical systems: solar collectors (for space or water heating) and photovoltaic panels (for producing electric energy). More information about active systems is provided in the RES guide.

Buildings constructed with passive solar design, maximize the benefits from the sun using standard construction features while operating with little or no mechanical assistance. The natural movement of heat and air maintains comfortable temperatures.

Passive systems are explained below.

Passive solar elements: Direct solar gain

Direct solar gain systems are composed of a usually south-facing glazing surface and a large thermal mass placed within the space made by walls, floors and roofs. The most common collecting surfaces are windows, inner courtyards and skylights. In this type of system, sunlight passes through the windows and heat is trapped by the thermal mass in the room. Temperatures reached can be up to 27°C. Figure 1 shows the operating principle of a sun radiation capturing surface.

Figure 1: example of a passive solar surface

Glazing is usually the most important factor in obtaining energy savings. Space heating savings can be even greater than 50% depending on the type and thickness of the chosen glass.

In south-facing buildings with glazing surfaces of 60%, savings due to direct solar gain range between 15% and 40%, depending on the insulating material. However, the same surface demands 55% more air conditioning over summer. This is why building eaves and placing deciduous trees around the building are so important.

Eaves and trees provide shadow in summer and solar gain in winter. Facilitating crossed ventilation is a very important factor (even more than thermal insulation) when trying to avoid air conditioning in the summer.

The colour of the collecting surfaces has a great influence on the final results. Black is the colour with the best solar capturing capacity while white is the worst.

Thermal masses should be made from dense and heavy materials in order to retain heat even in the absence of direct sunlight. For thermal accumulation, floors should be between 5 and 15 cm thick and vertical walls between 5 and 10 cm thick.

Direct solar gain passive elements respond quickly to the sun, making them advisable in buildings used in the morning such as schools. The costs of the additional building work needed to be done is usually low.

Passive solar elements: Indirect solar gain

Indirect solar gain uses the same materials and design principles as direct gain systems, but places the thermal mass between the sun and the space to be heated.

With indirect solar gain passive elements, temperatures up to 70°C can be reached (remember that direct solar gain elements can reach 27°C). These systems are thus great energy storing surfaces. The high temperatures are slowly attained and slowly lost, therefore they are appropriate in buildings with high evening and night occupancy. The thermal delay ranges between 6 and 8 hours. They need between 50% and 90% more thermal mass compared to direct solar gain elements. During the summer period they use eaves to avoid overheating.

These systems affect the global design of the building so they are recommended for predesigned structures.

The most common elements are: Thermal walls with air preheating, Trombe walls, Mass walls, Collectors and Grave Fills.

Thermal walls with air preheating: Cold air passes through a vent made at the bottom of the window to the space between the window and the wall. There the air is preheated and flows into the room.

In order to increase the efficiency, the wall should be dark to improve solar caption. In addition to the heated air there is also heat from conduction through the wall.

Thermal walls are usually built with a thickness of 20-25 cm. The space between the wall and the glass ranges from 5 to 15 cm. The ratio total wall area:vents area is usually 0.01.

Trombe Walls: the principle of operation of trombe walls is very similar to that of thermal walls with preheated air, but without vents in the external glass. In this case, vents are located at the top and bottom of the wall.

Radiation is collected and trapped between the window and the thermal mass, and heats the air which flows into the room to be heated through vents at the top of the wall. Cooled air then moves to take its place from vents at bottom of the wall. The thermal mass continues to absorb and store heat to radiate back into the room after the sun has gone. Dampers can be placed in the vents to prevent warm air from escaping through them at night.

Figure 2: Principle of operation of Trombe walls

Mass Walls: these systems are a kind of Trombe walls without any vents. Heat gains are produced by conduction through the wall.

Collectors and Grave Fills: the collector made from glass surfaces, absorbs sun radiation causing the greenhouse effect. The heat inside the collector is then transferred to the house through ducts and vents.

Grave fills are elements with a high energy storing capacity. They absorb energy from the sun and warm up the air circulating through it. This hot air then flows to the room that needs to be heated. Grave fills can also be used for cooling. Figure 3 shows the principle of operation for collectors and grave fills.

Figure 3: principle of operation of collectors and grave fills

Isolated systems: Sunspaces and atria

Sunspaces for dwellings and atria for larger buildings, represent additional space with attractive architectural qualities. In certain climates they can also offer protection against adverse climate at an acceptable cost.

These systems result from a combination of direct and indirect gain systems. They are made up of a large glazing surface enclosing a thermal mass (greater than the ones in Trombe walls) located between the exterior wall of the building and the glazing surface.

The principle of operation is similar to Trombe walls. In summer, sun spaces should be covered by eaves, trees or other shading elements. If not, the temperatures reached would be unbearable. This effect can be mitigated by making vents in the glass surface allowing the air to circulate. Floors and walls are the storing surface in this case. Depending upon the space and the design of the building, there are different types of atria. They can be attached to the house, be a freestanding structure or be integrated in the building as windows, inner courtyards or galleries. Figure 4 shows the operating principle of atria.

Figure 4: principle of operation of a atria & sunspaces

The ratio of glazing surface:floor area must be between 0,1 and 0,5. If the building is correctly oriented, that is south-facing, the ratio ranges between 0,6 and 1,6. In winter, at night the average temperature in the atria is between 5 and 16°C and during the day about 30°C. On a summer's day, temperature ranges between 15 and 25°C at night and can reach more than 35°C in the daytime. If there were no holes in the glazing surface for air ventilation, temperature could easily exceed 50°C on a summer's day.