Passive Environmental Design

In our blog entitled ‘Introduction to Passive Environmental Design‘, we explain the principle differences between Passive and Active Environmental Design. In this blog we concentrate on Passive Environmental Design.

What do we mean by Passive Environmental Design?

Passive environmental design maximises the use of natural sources – for heating, cooling and ventilation, to create comfortable living and working conditions inside buildings. Harnessing environmental conditions such as solar radiation, cool night air and air pressure difference to manage building environments. Passive measures do not involve mechanical or electrical systems.

Passive environmental design uses layout, fabric and form to reduce or remove mechanical cooling, heating, ventilation and lighting demand. Examples of passive environmental design include:

• Optimising spatial planning and orientation to control solar gains and maximise daylighting
• Manipulating the building form and fabric to enable natural ventilation and
• Making effective use of thermal mass to help reduce peak internal temperatures

What methodology will Prime Meridian employ?

As designers our aim is to adapt the thermal characteristics of buildings so that they moderate external environmental conditions and maintain internal conditions, using the minimum resources of material and fuel. Our passive environmental design can reduce capital costs and should reduce the energy consumed by the building.

Our passive environmental design will normally consider the following;

• Location
• Climate
• Landscape
• Orientation
• Massing
• Shading
• Material selection
• Thermal mass
• Insulation
• Internal layout and
• The positioning of openings to allow the penetration of solar radiation, visible light and ventilation.

In its simplest form, a shallow building orientated perpendicular to the prevailing wind with openings on both sides, will allow daylight to penetrate into the middle of the building and will enable cross ventilation. This can be expected to reduce the need for artificial lighting and may even mean that cooling systems and mechanical ventilation are not required.

In taller buildings, stack ventilation can be used to draw fresh air upwards through a building, and in deeper buildings atriums or courtyards can be introduced to allow light and ventilation into the centre of the floor plan.

However, difficulties can arise, when, for example buildings have cellular spaces that block the passage of solar radiation and air, or windows that cannot be opened because of noise or air quality issues. We may need in such instances need to consider the introduction of more complex passive measures, such as solar chimneys (or thermal chimneys), solar stacks and acoustic louvres.

Arriving at the correct passive environmental design can be further complicated by different climates, changing seasons, and the transition from day to night. Typically, these variations can be dealt by measures such as shading, shutters, overhangs and louvres that allow low-level winter sun to penetrate into the building, but block the higher summer sun.

Thermal mass can be used to heat during the day and then to release the heat back into the building at night. Even deciduous trees can be beneficial, their leaves shading buildings from summer sun, but then allowing the solar radiation to penetrate through their bare branches during the winter.

Additional complexities can be introduced by internal heat loads such as people and IT equipment and by occupancy patterns.

Is a passive environmental design sustainable?

Whilst it’s expected to create buildings that consume less energy, they do not always produce buildings that might be considered sustainable. A common view of sustainable or green buildings is that they should be designed and operated to reduce the overall impact of the built environment on human health and the natural environment. This can be achieved by:

• The efficient use of energy, water, and other resources
• Protecting occupant health and
• Reducing waste, pollution and environmental degradation
• Reducing embodied carbon and water

What is the role of a building’s occupants?

Passive design measures will require occupant involvement, for example to open windows, turn out lights, adjust louvres, and many more. This requires education so that occupants are able to understand the building and to operate it efficiently. These systems can be automated, but they will require energy to operate them.