With the background of the global energy crisis and the record-breaking summer experienced earlier this year reminding us of the growing climate crisis, increasing energy efficiency in the built environment has taken on ever-greater importance and come to dominate discussions around both residential and commercial property.
Today, we will be taking a brief dive into the concept of passive design and its potential role in taking real estate to a more sustainable future.
In short, passive design is “design that takes advantage of local climate to minimise the use of active heating and cooling … via the use of passive heating and cooling strategies”. Or rather: while active systems consume energy to heat/cool a building, passive strategies utilise the clever design of a building to help it heat and cool itself, as if on ‘autopilot’; this uses less energy.
Passively designed buildings might utilise thermal energy from the Sun or take advantage of a building’s “thermal mass” – we’ll talk about these below. Note that local climate is a fundamental aspect of passive design – “different passive design strategies suit different climates”.
There are 5 key strategies behind passive design:
Solar gain is the energy acquired through direct sunlight into the building. A passive design will maximize desired light (such as low winter sun) and minimize undesirable light (such as intense summer midday sun) in order to prevent overheating. One such method is designing for a large south-facing (in the Northern Hemisphere) glazed window, with a calculated overhang at the roof.
Thermal mass is the property by which a material absorbs, “holds on to” and releases thermal energy. For example, concrete has a high thermal mass; wood, a low one. This means that the temperature variation within a concrete building – all other factors being equal – will be considerably lower than that within a wooden building. This has implications for energy usage (and bills!), as you don’t need to heat up the building inside as much once it has cooled off. On the other hand, this means less chance of overheating too, as the material itself – instead of the air inside the building – “soaks up” the heat.
“Super insulation” and “Airtightness” utilize high levels of insulation and “thermal bridging” design techniques to minimize thermal leaking. The tighter the “thermal envelope” – i.e., the building lining separating the interior from the exterior – the better managed is the air and temperature inside.
Finally, MVHR is a system that conditions and regulates the air going in and out of a building, maintaining a stable and desired temperature, bringing in fresh air and pumping out stale air.
Source: passivedesign.org Source: Wikipedia (Creative Commons)
The foremost accreditation in the field of passive design is that of the Passivhaus, awarded by the Passivhaus Institut in Darmstadt, Germany. While they might on the surface mean the same thing, a “Passive House” is merely built with passive design in mind, whereas a “Passivhaus” has been constructed, tested, and passed highly stringent performance thresholds, covering metrics such as energy demand, airtightness, and thermal comfort – with others besides.
Pursuing the rigorous design metrics of Passivhaus may not be on everyone’s agenda. However, passive design absolutely could (and, arguably, should) be incorporated into the mainstream of residential and commercial properties. There are numerous environmental and potential financial benefits associated with it.
The environmental benefits are - perhaps – obvious. If less energy is required to maintain a desired temperature inside the building, then less energy is used in a world that is not yet near to a fully renewable energy system. On the other hand, this also means lower energy bills; even if passively designing a building might cost more upfront (and it might not), the idea is that as an investment, passive design could provide financial returns over time, due to lower outgoings.
So, could passive design be the right solution for you?