Energy Efficient Solar Passive Design
> Thermal Mass
> Quality Glazing
> Draft Proofing
Back in the 60's, we humans discovered the sun!
Before then, the sun and all that it provides for us played very little role in the design of our buildings. Still to this day, there are many architects and designers that design only to reach minimum targets.
So what does the term Solar Passive actually mean? A home that is Solar Passive takes advantage of its surrounding climate to maintain your comfort and reduce energy costs. A truly passive home does not use any means of additional heating or cooling, other than that provided by nature. Imagine what it would mean to our environment (and your mortgage!) if we didn't have to heat and cool our homes!
Heating and cooling represents a high proportion of the average homes energy bill. An ebs design always incorporates the following principles whilst achieving an outcome that suits your needs and your budget:
Generally in Canberra we design to gain the warmth of the sun in the winter when it is lower in the sky, and shade from the sun's hot rays in summer when it is higher in the sky. Orientation is also important in Summer because we design to catch the prevailing night time cool breezes from the East.
First we need to establish True North. Most street directories or maps are oriented with True North to the top of the page. You can also work out True North by using a compass and the following diagram. This shows that, in Canberra True North is approximately 12.5° West of magnetic North.
When designing a solar passive home, the living areas usually take precedence over other rooms in terms of ideal orientation, but we think the more the merrier! In Canberra's winters, the afternoon sun is more reliable because fogs can rob your home of heat-gain in the mornings. If your site is subject to fogs, the ideal orientation for solar gain is within the range of 20°W to 10°E of true or 'solar' north. If above the fog line, then 10°W to 20°E is ideal.
Designing to catch the cool breezes in Summer is also important. Generally we get a lovely cool coastal breeze in the evening which can be used to purge your home of any warm air at night, leaving you to get a peaceful night's sleep, and your home cool for the next day. This can be achieved with Cross Flow Ventilation. Great care must be taken when designing Easterly windows to catch these breezes, as the morning sun in summer has some bite to it, and you may over-heat your home if windows are designed incorrectly.
Service areas such as bathrooms, laundries, or especially garages, should be located to protect the home from harsh weather and the negative impacts of the west sun in particular.
On sites with poor orientation or limited solar access, an energy efficient home is still achievable through careful design. A larger budget may be required though, as the use of advanced glazing systems and shading techniques may be necessary.
Insulation limits the flow of (or forms a barrier to) heat energy. It is essential to keep your home warm in winter and cool in summer. Insulation is the cheapest, most cost effective way to increase your home's performance, and reduce your energy bills.
Without insulative qualities, your building's "skin" soon loses heat in the winter, and gains it in the summer. There is little insulating value in most common construction materials (like brick), so it is usually necessary to install insulation within the skin (or envelope) of the building. There are some exceptions where little or no additional insulation may be required including rendered polystyrene blocks, Straw Bale Construction, and rendered polystyrene sheets.
How do we measure insulation? Insulation is measured in terms of the rate at which heat energy doesn't pass through it, and unless you have a keen interest in building physics, there is no need to understand it in full ! We express the level of insulation as an "R value". The higher the R value, the better the insulation.
How do you know how much insulation you have? If you can't see what type of insulation you have and how thick it is, you can't. An ebs designer can help with this.
Your home loses/gains heat at different rates through the roof, walls, windows and floor of your home.
How much insulation should you have? Generally we recommend as much as possible, in your walls, roof, and floor. There is a diminishing return however, and anything over R4-5 is considered unnecessary. More heat is transferred through the roof, so arguably, this is the most important place for it. Walls and floors also contribute a high percentage of heat transfer through the building skin, so it's important to install insulation in these also.
What type of insulation should you use? There are two general types of insulation; reflective and bulk and you should use both for the best results. Reflective insulation resists radiant heat because of its ability to bounce back and to re-radiate heat. Reflective insulation needs a layer of air of at least 25mm next to the shiny surface for it to work. Without this, it is ineffective. We often use reflective insulation to boost the ability of the buildings skin to reflect heat either in or out (in for the winter and out for the summer). There are some technical points worth knowing when using reflective insulation and an ebs designer can help with this. Reflective insulation is usually shiny foil laminated onto paper or plastic and is available as sheets (sarking), concertina-type batts, "bubble wrap" types, and foam types. Bulk insulation resists the transfer of conducted and convective heat. It does this in the same way your doona does; by trapping pockets of air within its structure. Bulk insulation includes materials such as glasswool, wool, cellulose fibre, polyester and polystyrene.
Thermal Mass is a term used in solar passive design to describe materials that have the ability to absorb and store heat. Concrete, bricks, stone, adobe, pise, and ceramics, and even water, are all common examples of such materials. Solar efficient homes incorporate thermal mass in order to remain warm overnight and through periods of cold or cloudy weather. Appropriate use of thermal mass throughout your home can make a big difference to comfort and heating and cooling bills.
How does Thermal Mass work? Think of thermal mass like a big thermal battery and the sun is your battery charger. During the day, the sun warms up the thermal mass and at night time, the thermal mass releases its' energy back into the home. This process therefore contributes to the warming of the home in the evening when the sun is not around to do it for you.
Also, over the course of winter, the thermal mass decreases in temperature thus having the same effect on a seasonal basis. By the time summer arrives, the thermal mass inside a solar passive home has cooled down, but is also shaded (See orientation above), so it stays cool. This of course helps the whole house to stay cool in summer. Over the course of summer, the thermal mass warms up again, ready for the next winter and so on...
The affect of incorporating sufficient amounts of thermal mass into your home design is a leveling out or moderating of the internal temperatures by averaging day/night (diurnal) extremes. A great example of thermal mass at work is the ocean. Coastal climates always tend to be milder than climates inland. This is because the ocean acts as thermal mass, and helps to even out the temperatures.
Thermal mass is not a substitute for insulation. In fact, poor use of thermal mass (e.g. without insulating it from external temperatures) can make the extremes of the climate worse and can be a huge energy and comfort liability. It can radiate heat all night during a summer heat wave, or absorb all the heat you produce on a winter night.
Thermal mass stores and re-radiates heat. Insulation stops heat flowing into or out of the building. A high thermal mass material is not going to be a good thermal insulator, so if a supplier out there is telling you their product does both.... then walk away.
To be effective, thermal mass must be integrated with all the other good solar passive design techniques; good orientation of appropriate areas of glazing with appropriate levels of shading, insulation, draft proofing, ventilation etc.
Arguably, the glazed components of your building’s skin have the largest effect on your comfort and reduction of energy costs. Poorly designed glazed elements such as windows, skylights and glazed doors can make your home too hot in summer, and too cold in winter. There is light at the end of the tunnel though, as correctly designed glazing will give you comfort all year, reducing and in some cases eliminating the need for heating and cooling!
In summer, the heat coming through an unshaded window can be 100 times greater than through the same area of insulated wall. One square metre of ordinary glass can let in as much heat as would be produced by a single bar radiator! Can you imagine how silly it would be to turn on 10 single bar radiators in your living room in summer and then turn on the air conditioner to compensate for this?!! This is what you are doing when you have only 3 average sized poor quality unshaded windows in your design.
In winter, heat lost through a window can be 10 times more than through the same area of insulated wall.
Four main design considerations for glazed elements are:
- Locate and size your glazing correctly so that they let the sun in wihen its cold, and exclude the sun when it’s hot;
- Locate glazed elements to allow natural cooling by cross ventilation.
- Provide seals to openings to minimise unwanted draughts.
- Choose appropriate types of glazing.
We always recommend installing the highest quality windows your budget will allow, however they are generally the most expensive component to improve significantly, so careful design of your windows is important. There are some things you can do to improve your choice of window, but to understand these, we must first understand how heat transfers through a window. There are four main ways this happens:
There are literally thousands of types of glass and frames to choose from. They all perform in different ways to deal the different forms of heat transfer and ebs can help you make the right choice. Further reading is also available at www.yourhome.gov.au/technical/ .
There is a complex interaction of many variables to consider when designing your glazed elements. The best way to accurately assess the impact of glazing on your home’s thermal performance is to model it with a sophisticated computer program. ebs uses AccuRate, a piece of software compiled by CSIRO. It can be used to calculate your home’s heat gains and losses, hour by hour, and the resulting levels of thermal comfort achieved. We consider all aspects of the building’s design as well local climatic conditions. AccuRate allows options for each window to be compared to ensure that the best performance is achieved without unnecessary expense.
For optimum passive cooling, design your building to catch the desirable breezes in summer. Desirable breezes can provide a cooling purge at night time, whilst unwelcome hot winds can drive the temperature in your home up very quickly in the day time.
Positioning windows to catch the night breezes is only half the story though. Adequate amounts of windows need to be positioned on the leeward side of the building to allow the breezes to pass right through the building. Cross flow ventilation is about five times as effective as ventilation from a single opening. It is important to balance the need for ventilation in summer against air leakage and winter heat loss.
The path of travel for the air inside the building should remain as open as possible, so try to plan openings in internal walls that are large enough to allow air flow.
Fresh air is good but how much fresh air is enough? For a healthy living environment you need 0.5 – 1.0 air exchanges an hour.
Make your home as air tight as possible
To do your own check of where the drafts are, go around with a lit incense stick. When the smoke is disturbed there is a draft. Here are some ways to fix them:
- Draft proof around doors and windows with draft proofing tape and door strips (there is a draft proofing section in most hardware stores)
- Install ‘draftstopper’ or ‘top hats’ over exhaust fans (http://www.draftstoppa.com.au/)
- Get handy with a caulking gun and seal around your architraves, skirting boards, around power points and gaps through which the breeze doth blow.
- Retrofit down-light covers (such as Isolite http://www.isolite.com.au/ or others) over all of the halogens in your ceiling. This means you with stop the drafts and be able to butt the ceiling insulation right up next to the cover without creating a fire risk. Better still, get rid of the down lights and install wall and pendant lighting.
- Get door snakes for external doors or better still, install door seals such as Raven http://www.raven.com.au/ .
Landscaping can play an enormous roll in improving your building's thermal performance. A poorly considered landscape can severely impede on the your comfort and increase your energy bills. Your landscape is an extension of your home, and the best home designs always flow from inside to out. Al-fresco living is a way of life in Australia, and you can improve your energy efficiency if your landscape is designed well.
Correctly placed deciduous trees work well on the north side because they provide summer shade and let in winter sun. Evergreen trees should only be used where permanent shade is required.
A well designed landscape can channel cooling breezes into your home, and shelter from the nasty winds. Vegetation can also be used as a natural evaporative air cooler providing coolth in summer by cooling those hot daytime winds.
Thanks to some government initiatives, and an extremely long drought, rain water tanks are becoming more prevalent in all residential developments. To get the most out of your tank, make sure you choose an appropriate size. ebs can supply you with a great little calculator to work out your most appropriate sized tank. Contact us if you're interested. Ideally, rain water tanks should be connected to toilets and washing machines as well as the garden.
Grey water recycling is also becoming more popular for use in the garden. Showers and laundry water is the most widely used as other water tends to be "dark grey" or "black water". Care needs to be taken in some soils, particularly when watering some native species, and you need to be particularly careful with the types of soaps and detergents you use. There are many expensive proprietary grey water systems on the market, but before purchasing one of these, I would do some more reading here: http://oasisdesign.net/
Last updated 24 November 2011