Designing cool buildings in a warming world

Passivhaus design is more often associated with heating a building as a means to improving internal comfort when outside temperatures are low but the design is also incredibly effective at countering warmer outside temperatures with cooler comfort inside.

As we face up to a warmer world being the primary effect of climate change, the challenges to ensure we reduce fossil fuel derived energy sources in buildings is at the core of net carbon reduction strategy but with the upward increase of summer temperatures, strategies for keeping buildings cooler passively must be integrated into how we design or modify the built environment.

Topography & Shading

Using the natural (& not so natural) elements around us can help to reduce overheating in Summer months. Very often this will come in the form of trees and foliage in summer months reducing direct sunlight to windows and openings within a building. In urban environments this can prove more challenging.

Awnings & Blinds (integrated or not) are perfect ways to reduce solar gain and these can easily be retrofitted to existing buildings. When designing new buildings, the best design (& architects) will include this in the specification for glazing.

Windows & Insulation

Triple-glazed windows are a major element of Passivhaus design to ensure the comfort and temperature regulation all year round within a building. Any form of higher performing glazing or insulation can lead to overheating in summer if not installed with a broader thermal strategy integrated into all elements of the design. Without adequate shading windows can overperform and overheat a building on hot summer days. The position, size and quantity of glazing facing southward as well as the topographical integration and building overhang designs are also integral to the thermo-regulation strategy of a building.

Passive building design uses triple-glazed windows as a means to capitalise on low u-values (thermal conductivity) to reduce heat loss from inside to outside and conversely on the solar thermal gain in cooler periods. The g-value (solar heat gain) is the significant factor for heat gain in summer months. When selecting windows the closer this value is to 100% the higher the heat gain, so in Passivhaus windows, this is generally around 50%. By comparison, most double-glazed units, as per building regulations, will have g-values around 70% and existing single pane windows may exceed 80%, which in most cases will lead to substantial overheating in warmer months.

Ventilation

One of the many myths of Passivhaus buildings is that opening windows negates the thermal performance of the design. Purge ventilation is a very successful strategy to reduce overheating and should be used regularly, particularly with roof glazing, more effectively removing warmer air as it rises.

Mechanical ventilation with fresh incoming air & removal of exhaust air (MVHR) is another integral principle to Passivhaus design. The advantages of heat or thermal recovery is that internal “cool” can also be recovered in summer versus internal heat in winter.

Renewable heating & cooling strategies

Sustainable and renewable energy strategies like solar thermal or photovoltaic, and air source heat pumps are highly successful in the summer months for heating water, cooling, and storage of electricity, in conjunction with appropriate battery cells.

KNX systems are smart controls which adapt, increase or decrease power to applications to reduce the energy required within a building to heat, cool or light, which auto-adjust shading, air conditioning and lighting.

In our changing world, we have the tools to make the necessary changes to mitigate the impact of climate change, today, if we all do our part.

The author is the founder of Passivhaus Build, Ecohomebuild & The Property Fixer