SUSTAINABLE BUILDING DESIGN
SBD Sustainable Building Design consultancy 22 Yamby Rd Strath Creek Vic 3658 Tel 03 5797 0277
Having built physically with his own hands both in Victoria and England, David Halford has a very practical as well as architectural approach to designing.
SIMPLE ELEMENTS OF SUSTAINABLE BUILDING DESIGN
WHY SUSTAINABLE BUILDING DESIGN?
Buildings last a long time so a little thought in their initial design is worth the effort. If we can make buildings more comfortable, cheaper to run, healthy to live in and at the same time less damaging to the planet just by a little thoughtful design why would we choose not to? If you look around you will be amazed to see how many buildings face west into the hottest part of the day so that generations of occupants will suffer discomfort or the expense of air conditioning for years to come. Because there are so many of us, most human activity is bad for the planet. The planet will survive but it might not be suitable for human habitation so we should really do everything we can to minimise the effects of our activities.
Many people assume that sustainable design will add to the capital cost to a building. This can be true in some but it in some cases can also be cheaper. Even where it is true the capital cost is usually very small compared to the savings in running costs. The cost of fuel - whether it is fire wood, electricity, gas or petrol - will inexorably increase so that the pay back on the capital cost of things like insulation, double glazing, solar panels and robust construction methods will become increasingly obvious. If careful design can remove the need for installing expensive artificial heating and cooling systems it will actually reduce the capital cost as well as the running costs. Design has its costs and some builders might charge a premium for “unusual” construction methods but these costs are a very small proportion of the total capital cost and the life time running costs. Sustainable design has nothing to do with “style”, any style of building can be designed to be sustainable.
Sustainable building design can:
Reduce running costs
Provide future proofing against energy price rises
Reduce energy use and carbon emissions
Provide a healthy internal environment
Enhance property value
The techniques used are not magic. Most of them are based on methods used for centuries but enhanced by modern materials. Just careful thought and a little ingenuity are required to ensure that the way they are used is appropriate for the particular internal and external climate of the specific building. Some of the basic elements of sustainable buildings are described below for those who are interested in getting an idea of how buildings can be made more comfortable.
Most of the heat we use comes from the sun but if we get this via fossil fuels we upset the natural balance by releasing carbon from past ages when the oxygen emitted by the trees that produced the fossil fuels has long gone. There are many ways of harnessing the suns energy without using fossil fuels. The simplest and cheapest way is “passive solar gain”.
This just means letting the sun in during cold weather and keeping it out during hot weather. This can be done with shutters if you don’t mind opening and closing them at the appropriate times or by facing the windows towards the midday sun and providing a canopy that shades the window between Spring & Autumn. In SE Australia the sun angle means that the canopy over north facing windows only has to project about a metre but east and west facing windows need shutters or vertical external shading such as deciduous trees. Often there is no additional cost in planning the building so that the main windows face the midday sun.
If materials with high thermal mass are used in internal positions where the sun reaches them in winter, they will absorb the heat while the sun is out and release it when the temperature falls at night, thus maintaining a more even internal temperature. The best places are usually the floor near the windows and internal walls where the sun strikes them in winter.
The “Passivhaus” standard developed in the cold climate of northern Europe has shown that the entire heating and cooling can be provided by a combination of controlled solar gain, controlled heat loss, controlled ventilation/air loss/ heat recovery and thermal mass. Even without attaining the strict Passivhaus standards it is possible to provide most of the heating and cooling requirements of a normal house naturally (see “PASSIVE & ACTIVE SYSTEMS)
“Active” natural heating systems can also be used to top up the heating requirements.
Capturing hot air from under the roof and directing it into the house.
Collecting heat using solar hot water collectors when the sun it out and storing it in a water tank for colder days.
Collecting electricity from the sun using photovoltaic panels and storing it either as electricity in batteries or hot water in a buffer tank to use for heating.
Using wood fired (or other biomass) heaters either for direct heat or indirectly via a water heater or a hot air transfer pipe. Burning wood emits carbon dioxide and other gases but the trees have already absorbed the equivalent carbon dioxide emitted oxygen during their lives.
Natural lighting is closely related to natural heating and avoiding the need for artificial lighting will also reduce running costs.
For cooling, the aim is to keep the temperature below 25 deg C.
Ground pipe cooling:
At a metre or two below the ground the temperature stays at about 10 to 15 deg all year round because it remains at the annual average surface temperature. Taking air or water from the ground below or building and piping it to the building ventilation system can provide a constant source of cooling. In cold climates this can also be used to provide energy for a “ground source heat pump”
Ventilation for cooling:
In general the purpose of ventilation is to replace stale air with fresh air. However it can also be used to contribute towards cooling. Air passing over a damp surface (such as sweaty skin) causes evaporation which uses heat (technically called “the latent heat of vaporisation”) and therefore causes cooling.
Cross ventilation can be encouraged by placing windows or vents to take advantage of prevailing breezes.
Stack effect ventilation can be arranged so that rising hot air escapes at high level, drawing in cool air from low level (e.g. below a building). Passive ventilation systems often use stack effect to induce the air flow.
Night time purging: In climates where the temperature falls at night, the daytime air can be flushed out so that the building starts the day full of cool fresh air. This is particularly useful in reducing the artificial cooling requirements of commercial building where much of the heat comes from internal sources such as occupants and equipment.
Solar powered artificial cooling: Because the sun is strong when there is a need for cooling, photovoltaic (p.v.) panels can provide the power to run a heat pump air conditioner. Air source heat pumps take most of the energy they need from the air and only need about a quarter of the electricity that old fashioned air conditioners needed. They usually need less than a kilowatt of electricity per room which can be generated economically by p.v. panels when the sun is strong.
The thermal capacity of a material is a measure of how much heat it can store. In general heavy (dense) materials have high thermal mass. The common materials of this type used in buildings are water (used in hydronic heating systems), concrete and various types of masonry such as brick, stone, concrete blocks, concrete panels and earth.
Thermal mass simply stores heat by absorbing it. It does not create any heat and it does not prevent heat being transmitted. It can delay heat being transmitted but eventually it will re-radiate whatever it has absorbed. Heat always travels from hot to cold so any material will receive heat when it is colder than the air and lose heat when it is hotter than the air. For thermal mass to be useful in building construction it must be insulated (see INSULATION) from the outside air and exposed to the inside air. The inside air temperature needs to be controlled by other methods (see NATURAL HEATING & COOLING) and the thermal mass will then greatly help to maintain a constant comfortable temperature. This is particularly useful in SE Australia where temperatures regularly fluctuate between 15 and 35 degrees so the thermal mass will naturally average around 25 degrees without any insulation.
However, if thermal mass is used in the wrong place it can store heat then release it when it is not wanted (e.g. it could make a hot night hotter), so careful design is necessary. Because many common building materials have thermal mass, it can easily be provided with little or no extra cost.
The thermal conductivity of a material is a measure of its ability to transmit heat. The thermal resistance (R Value) is the opposite. In general light materials have low conductivity/ high resistance due to trapped air or gas bubbles and are therefore used for insulation. Trapped air is the most common insulator. Sheep’s wool is commonly used for clothes because it traps air and can also be used for buildings although it tends to slump or compact when used in bulk. Wools made of spun glass and other minerals such as rock are the most commonly used insulations in buildings but they need to be thick to have adequate insulation value. Boards made with expanded polystyrene beads provide very similar levels of insulation to wools. Foams made with various chemicals such as polyurethane can provide high levels of insulation in a much thinner layer. The main criteria for choosing insulation are:
If the space available is not restricted: the cost per unit of insulation (R Value)
If space e.g. wall or roof thickness is restricted: the thickness per unit of insulation (R Value)
Are there any physical requirements such as fire resistance of rigidity (e.g. a rigid board that can take external render will eliminate the need for battens and cladding).
High R value rigid foam insulations are still uncommon in Australia but there are circumstances when they can pay for themselves.
Links to foam board insulation suppliers:
Foil or multilayer insulations use the fact that every time heat has to move from one material to another there is a surface resistance. The more layers it has to pass through the more resistance there is. Shiny reflective materials have greater surface resistance than dull materials. Dull black materials have the greatest absorption which is why they look dull and black. Many rigid insulation boards have a foil face to further increase their R value.
To avoid having to provide a lot of heating or cooling to stay comfortable, insulation is essential. In general it is the most cost effective element of a comfortable building. The regulations for conservation of energy in Europe have led to the need for high levels of insulation in buildings. The idea of using the insulation to construct the building rather than just adding it to the structure has grown out of this. The result is known as structural insulated panels (see SIPs).
Double glazing uses air or Argon gas as the insulation layer between the 2 sealed panes of glass. It can also have an internal (low E) coating which makes it harder for the glass to emit heat from it surface. There are also many “solar control” glasses available. These do not insulate but reduce sun penetration, however proper shading is usually cheaper and more effective. The value of double glazing was recognised in Europe many decades ago but unfortunately it is only recently becoming main stream in Australia. It has now become economical but if budget is the issue, shopping around is essential since some products are 3 times the price of others.
Links to window manufacturers:
Construction methods that help with sustainable design
OVERVIEW OF ROBUST, LOW ENERGY, FIRE RESISTANT WALL CONSTRUCTIONS AVAILABLE IN AUSTRALIA
BASIC REQUIREMENTS: Structural strength, insulation, fire resistance, thermal mass, external and internal surface finishes.
Internal walls can contribute to thermal mass if heavy materials are used and are simple to construct because no insulation is required. Heavy constructions are normally load bearing by their nature so additional framing is not normally necessary.
External walls can also contribute to thermal mass but the most important consideration is insulation. Any thermal mass that the external walls provide must be inside the insulated envelope. The insulation must either be inherently non flammable/ non-toxic in fire (e.g. mineral fibre and PIR) or be completely sealed within a fire resistant construction. A simple way of achieving this is by using a basic concrete block or brick wall lined externally with insulation which is then covered with cladding or render. There are many rendered insulation systems available (such as Foamular www.foamular.com.au ). There are interlocking block systems such as Benex Block (www.benexblock.com.au) which require less skilled labour. Straw bale construction uses a similar method of applying render to fire and weatherproof an insulating core but is generally not load bearing.
There are also a number of pre-cast and in-situ insulated concrete systems which achieve the same result. These companies generally provide a complete building installation service using the building designers drawings and specifications. Forma-Tech (www.formatech.com.au ) is an insulated in-situ concrete system that also incorporates an integral rendered finish. Thermomass is an insulated precast concrete sandwich panel system. Insulated rammed earth is essentially the same a concrete sandwich panel and although it is more labour intensive it provides an integral finish both internally and externally that eliminates several processes. Hemp-lime construction is a poured alternative to rammed earth that also uses materials with low embodied energy and insulating properties. However it is not load bearing and needs an additional lime render finish or other cladding both sides. It is now available premixed in Australia from Hempcrete (www.hempcrete.com.au ).
Structural Insulated Panels (SIPs) provide load bearing walls made of insulation bonded to a structural skin. The most common form used for walls in Europe & America have a foam core with faces of OSB (orientated strand board similar to plywood). These are just becoming available in Australia but are not as common as SIPs with metal faces which can be used for walling and roofing (see SIPs roof panels suppliers). Green Energy Bricks (www.greenenergybricks.com.au) are a SIPs panel with a PIR core and Magnesium board faces cut into large block sizes which interlock and are glued together for ease of construction.
SIPs for roofs are very common on commercial and industrial buildings in Europe and are also available in Australia. They usually consist of a standard metal roof sheet and a metal ceiling panel bonded to an insulating foam core. Because they can span long distances they need little or no additional structure. They can therefore provide the roof structure, the roof covering, the insulation and the ceiling in a single sheet.
SIPs for walls usually have timber based facing boards bonded to a foam core. They are still a rare concept in Australia but should become more common as their potential is realised. The panels can be pre-cut including window openings so that buildings or several storeys can be assembled on site incredibly quickly. Because the joints are sealed with expanding glue similar to the foam core, the resulting structure is very stiff and air tight. This kind of SIPs provide the structure and high levels of insulation and board surfaces can have internal and external cladding fixed to them on site. They have no significant thermal mass so this need to be provide by other elements such as the floors and internal walls.
Links to Australian SIP roof panel suppliers:
Distributing heat using piped water is the standard and cheapest method of heating in Europe. In Australia it is still uncommon although its benefits are beginning to be recognised. In relation to solar heating it has the advantage that heat collected on sunny days can be stored in an insulated hot water storage tank for distribution on cold days or nights. Heat is released either from water pumped through pipes buried in concrete floors or from water filled “radiators”. Piped under floor heating systems are very efficient because they use the concrete structure to distribute the heat (metal plates can be added below timber floors to provide the same effect). To provide 25 degrees in a room they can be designed so that the water temperature only has to be about 35 degrees. Because the water tank only has to store the water at fairly low temperatures, the heat losses are small.
In commercial buildings a simple system that provides both heating and cooling is now being used in Europe to replace the usual two systems of heating and ducted air conditioning. It exploits the thermal mass of the normal concrete floor structure by pumping water at 20 degrees in pipes through the structure. Because heat always travels from hot to cold, where the room temperature is higher than 20 degrees, the structure will absorb the excess heat. Where the room temperature is less than 20 degrees, the air will absorb heat from the structure. This distributes heat from hot areas to the cool areas of a building so that there is less need to add or remove heat when the water gets back to the plant room. For commercial buildings this greatly reduces the space normally required and other problems associated with air conditioning systems. For passive solar design the principle can be used to transfer heat from areas that receive sunlight to areas that don’t.
The term “passive” is used for systems that operate themselves without additional energy such as passive solar gain, passive ventilation and passive heat storage in thermal mass. Active systems require some mechanical or electrical addition of energy.
Situations where active systems are appropriate:
While the ideal may be to use totally passive systems, the requirements to make them work might not always be cost effective. Although active systems use energy, this energy can be provided from renewable sources and therefore still be zero carbon. They can provide greater versatility and supplement passive systems where it would be difficult or expensive to be 100% passive. For example it is often a lot simpler to use mechanical fans that can be controlled by air quality sensors, humidity sensors, thermostats or simple switches. Heat that would be lost in the exhausted air can be captured in a heat exchanger and used to pre-heat incoming fresh air, more than offsetting the energy used by the fans.
Although there are established temperature standards for buildings (generally around 21 deg C) what people perceive as hot or cold is very subjective. There is also a psychological satisfaction in the act of switching on a fan and feeling the breeze immediately which can justify active systems.
It is relatively easy and cheap to the majority of heating and cooling by passive methods but relatively difficult and expensive to provide the remainder. From a pragmatic cost-benefit perspective it can be more effective to top up passive systems with active systems.
A totally “passive” building will often require the occupants to be very active in opening vents, shutters etc at appropriate times. Home owners might be prepared to do this but not all occupants will find this practicable or desirable especially in large buildings. Active automated systems can provide an easier building to use. Ventilation fans operated by sensors are relatively cheap but more unusual systems such as electrically operated windows and shutters tend to be expensive and are more likely to go wrong. Ideal passive design uses careful orientation and permanent seasonal shading of windows to avoid the need for operating shutters but site conditions do not always allow this.
The "Passivhaus Standard" is based on the simple concept that the heat losses from a building can be reduced to no more than the free heat gains from occupants, equipment and the sun. Links to information on “Passivhaus” standards.
Our experience covers many aspects of design and construction and as time allows we will be adding pages to this website covering:
Passive, active & mixed mode systems - finding a balance
Low carbon on a low budget - choosing cost effective priorities
Thermal mass - when, where and how it works
Embodied and life cycle energy
Structural insulated panels
Insulated rammed earth
Insulated concrete systems
Insulated render systems
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