Energy efficient where possible

New Urbanism is about beautiful, energy efficient cities. This page is down at the micro-scale, and is about individual buildings, and how to build energy-efficient homes and offices.

  1. Passive solar keeps you comfortable while saving energy
  2. Energy efficient design more important than embodied energy in materials
  3. Materials can also help

1. Passive solar keeps you comfortable while saving energy

We can now build comfortable low energy apartments that keep us warm in winter and cool in summer, with much lower or even zero air-conditioning bills! Even the materials we use can improve minimise impact on the environment. But let’s start with the design.

First, let’s design our home or office with our local climate in mind.  Most climates can use thermal mass to store an ambient, comfortable temperature, but but how they do so in each climate will vary according to where we live. There are more guidelines here, as I’m not going to analyse all the options but just want to highlight that local considerations are important.

But what is thermal mass in the first place? As the Australian Government website says:

Thermal mass is the ability of a material to absorb and store heat energy. A lot of heat energy is required to change the temperature of high density materials like concrete, bricks and tiles. They are therefore said to have high thermal mass. Lightweight materials such as timber have low thermal mass. Appropriate use of thermal mass throughout your home can make a big difference to comfort and heating and cooling bills.

The graph below shows how the right materials positioned in the right place store the sun’s heat for later that day. Note how the single unbroken line rises and falls with the outside temperature, but a clever building with good heavy, sun-absorbing materials and insulation can keep your home or office building much more comfortable.

PD-ThermalMass-AirTempTime_fmt

So how does it work? There are special plans for different climates. Tropical plans are all about cooling the house, while sub-tropical areas like Sydney have more thermal mass positioned for heating in winter, and cooling in summer. Remember, while these diagrams show individual homes, we’re actually after eco-designed apartments.

Winter stores heat

Winter

Summer releases heat

63494

Indeed, the whole Your Home site has more detail about environmentally friendly, energy efficient designs and materials than I want to go into right now.  You can download their free 10 page PDF YOURHOME-2-PassiveDesign-9-ThermalMass-(4Dec13) if you’re planning a renovation or want more detail. It covers glass-to-mass ratios for different climates, building for cool temperate and alpine climates and hot dry climates, positioning, materials, foundations and concrete slab work, where to put the termite barriers and even Phase Change Materials (PCM’s) that absorb heat and then release it later at night. It’s a comprehensive site, and has PDF’s on saving water in the home, materialsenergy, and so on. I highly recommend a good browse and downloading some of their PDF’s for later.

See the Passive house wiki.

2. Energy efficient design more important than embodied energy in materials

It’s more important to save energy use over the building’s lifetime than to compromise energy efficiency of the building just to use some trendy new material. If the new material cannot support a passive solar design, short term embodied energy gains are quickly swamped by excessive energy use gains over the building’s lifetime. As the Architectural Review says:-

But, while increased scale improves sequestration, it poses greater challenges for overall energy use, especially for high-rise buildings. Studies in the tropics have shown high-rise buildings typically demand higher energy intensity than medium-rise, findings that correlate with recent analysis by Hilson Moran in the UK to determine the effect of building form on energy consumption and CO2 emissions. Even the energy intensity of Ken Yeang’s bio-climatically designed ‘Menara Mesiniaga’ tower has been calculated as approximately twice that of a Passivhaus building. While energy embodied in materials and construction activities is important, operational energy demand still dominates over a building’s lifetime energy use. Studies show that, in a typical building, total in-use energy could surpass embodied energy after as little five years. Even in a low-energy design, it will potentially dominate after 20 years. The evidence again points toward a more humane scale of building also achieving a more sustainable solution overall.

3. Materials can also help

New or even old traditional building materials can help, as long as the passive solar energy efficient form follows function. We’ll have to find sustainable, scalable materials to house growing populations before that population growth finally stabilises. Wood is one of the main solutions. But we cannot sacrifice energy efficiency to just use some trendy new material. This is why on my Tall Timbers page I emphasised bamboo for paper and fibre replacement — to take the pressure off trees so we can use timber in construction. From what I’ve read so far, the engineers are just not sure how bamboo Cross Laminated Timber would perform. From the Architectural Review again:-

All of this ultimately emphasises the importance of research and evidence informing practice, especially for buildings making grand claims about environmental performance. However, as highlighted by Edge Debate 46 and 54 ‘A New Professionalism?’ the built environment industry currently lacks the culture and practice of genuinely evidence-based design and fails to develop a crucial shared knowledge base, arising from the gaps between professions, between practice and academe, and between design assumptions and how buildings perform in use. In this context, the influence of high-profile practices is enhanced, perhaps artificially so, which comes with added responsibility. ‘Farrells Focus’ brings this conversation to the fore, leading us to ask, is ‘raising’ the profile of bamboo as a building material for high-rise useful or irresponsible?

Architects easily become enamoured with a new material or structural system, especially when a top-flight ‘form giver’ architect pioneers it. This fascination with new forms must not distract us from the need to also recognise that in good design form follows function, and, given that low environmental impact and energy consumption is now one of the most important functions, the forms must be derived from firm evidence.

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