Tag Archives: Energy Efficiency

What is Thermal Mass and why should we use it in construction?

thermal mass

Although the term ‘thermal mass’ is not commonly used, there are many examples where we experience it and appreciate its benefits. The most impressive is the ocean: in winter, when there is less sunshine and the average air temperature is low, the water is chilly and only the tough ones might enjoy a swim! In spring, the sun will slowly heat up the water so that finally in summer it will have a comfortable warm temperature. Water has a great capacity of storing heat – it will stay constantly warm during day and night, and even in winter, it can be significantly warmer than its surrounding air temperature due to its ability to absorb solar energy. Water demonstrates the principle of thermal mass. How does it apply to construction?

 

Thermal Mass, Why Is It So Important for Construction?
Thermal mass is the ability of storing and releasing heat to help retain a constant indoor temperature. It is an effective way to improve thermal comfort in a building and plays an essential role in saving energy. Thermal mass inside a building will absorb heat when the surroundings are warmer than the mass, will store the heat and radiate it slowly when the surroundings are cooler. It can actively be used to regulate temperature, therefore, reducing the need for mechanical heating and cooling. Heavy materials, such as concrete and brick have great thermal storage capacity, whereas lightweight construction materials, such as timber and insulation cannot store heat. Generally speaking, the heavier a material the better its ability to store heat.

If you want to know more about thermal mass please also read our further articles about this subject.

Window Energy Rating Scheme

 

Untitled1The Window Energy Rating Scheme (WERS) is a program implemented by the Australian Window Council Inc. (AWC) with the support of the Australian Greenhouse Office. The windows are evaluated with stars, the more stars, the better the performance. If buying windows, always check the label before making a decision.
A single-glazed window with a typical aluminium frame has U-values ranging from 7.9 W/m²K to 5.5 W/m²K (according to the indicative ranges of whole glazing element performance values in the BCA). These U-values will make it hard to reach a good energy rating for a building/ built an energy efficient home.

Keep in mind, the lower the U-value the better performing a window. Double glazing windows with timber framing in Australia usually range between a U-value of 3.8 W/m²K and 2.5 W/m²K.

Sealing and weather-stripping
However, a good U-value is no guarantee for a well performing window. The installation of doors and windows needs to be done according to the manufactures guidelines. All gaps must be sealed and weather-stripped carefully in order to perform to the specified U-value. Unfortunately, the energy rating just states the material U-value of the window and not the end product and common practice often shows incorrect installation leading to thermal bridges around the windows.

 Windows And Double Glazing Overseas
Whereas most countries in Europe require double glazing and even recommend triple glazing, it is not standard in Australia yet. Unfortunately, double glazing is still more expensive than single glazing in Australia, in Europe it’s actually the other way around. Due to the fact that single glazing is not allowed any more, no one is producing it on a large scale making it quite expensive. Double-glazing on the other hand is a standard, and although better performing than common double-glazed windows in Australia, they are available for about a quarter of the price. For instance, the minimum required U-value for windows in Germany is currently 1.1 W/m²K. I trust that with time, double glazing will become more affordable and will become mandatory in Australia to achieve good passive solar design.

Up until then, you, as the client, has to make informed decisions about what glazing you are buying. You can’t just trust a manufacturer stating their glazing is energy efficient. They have to prove the performance to you by showing you the actual u-value of the window system.

What to look for when buying windows?
YES, double glazing is worth its money. It is the best method to reduce heat loss in winter, as long as it is applied, installed and used properly. The window size should respond to the location and the climate, the insulation around the window needs to be snug fit, in order to prevent thermal bridges. Appropriate window frames need to be used and furthermore, adequate internal and or external covers needs to be applied. All these measurements need to work together, otherwise a window is nothing more than a hole in the wall and will be the major contributor for unwanted heat gain and loss, therefore preventing energy efficiency.

Winter heat loss through Windows

Winter heat loss

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Unprotected glazing and single glazing in particular means the surface of the glass is noticeable colder than the warm air in the room. This lowers the room temperature and produces draughts. The Relative Air Velocity ends up too high and occupants will feel winter discomfort. For this reason, all windows require protection from heat loss in winter. To minimise winter heat loss, it is important to trap a layer of insulation still air between the window and the room. This can be achieved for instance by using internal coverings, such as drapes, Holland blinds, Roman blinds or Australian blinds, and thin or lace curtains combined with pelmets.

 Effect of window treatments on winter heat loss
(According to Sustainable Energy Authority Victoria 2002)

  • Unprotected single glazing: 100%
  • Vertical or venetian blinds: 100%
  • Unlined drapes or Holland blinds, no pelmet: 92%
  • Heavy, lined drapes, no pelmet: 87%
  • Unlined drapes or Holland blinds, pelmet: 79%
  • Standard double glazing: 67% (the higher the U-value the less the heat loss can be)
  • Heavy, lined drapes, pelmet: 63%
  • Double glazing with Low-E coating: 57%
  • Double glazing, heavy drapes, pelmet: 46%

Double glazing
The most effective way to protect windows against heat loss in winter is a combination of double glazing and internal window coverings. However, if internal coverings are inappropriate or not desired, for instance in highlight or clerestory windows, in kitchens or simply where unobstructed views are wanted, double glazing is an indispensable measurement in order to prevent heat loss in winter. Yet double glazing won’t prevent sun coming into the building, which means that the windows need to be protected from harsh summer sun by means of external shading.

Window frames
Another, often underestimated roll in the energy efficiency of a window, is the frame itself, as it can effect negatively on the overall performance. As we talked about in the blog “Adequate Insulation”, some materials, such as metal, glass or aluminium, allow heat to pass through them more easily, therefore they shouldn’t be used for windows frames if at all possible. If metal frames are used, such as aluminium, they should have thermal breaks to reduce the heat transfer. Generally speaking, PVC and timber frames perform better than metal frames.

 

Summer heat gain through Windows

heat transfer

It is important to protect windows with external shading devices, through appropriate window sizing and location, in order to minimise heat gain in summer.

Comparison of heat gains through different treatments for windows in summer

(According to Sustainable Energy Authority Victoria 2002)

  • Unshaded single-glazed window: 100%
  • Standard double glazing as available in Australia: 90%
  • Vertical blinds/open weave drapes: 76%
  • Internal venetian blinds: 55-85% (Effectiveness is reduced as the colour darkens)
  • Internal drapes or Holland blinds: 55-65%
  • Tinted glass: 46-65%
  • Solar control film/reflective glass: 20-60% (Available in different kind of configuration with varying effectiveness)
  • Trees, full shade: 20-60%
  • 1 metre eave over north wall: 30%
  • Roller shutters: 30%
  • External awnings: 25-30%
  • 2m pergola over north wall covered with deciduous vines or shade cloth: 20%
  • Outside metal blind or miniature louvers, parallel and close to window: 15-20%

External shading devices are an effective way to minimise heat gain through glass in summer and keep a building cool. They provide far better protection from heat gain than internal window covering. However, if external shading is not possible, internal coverings can at least reduce the unwanted heat gains. Shading devices should always enable ventilation outside the window, as shading fitted too closely to a window can trap warm air which can be conducted into the house.

Eaves, verandas or pergolas are commonly a part of the building structure, they are durable and do not require ongoing adjustments. It is essential to have a certain distance between the underside of the shading devise and the top of the window. But these fixed shading devises should only be used over north-facing windows, as they lack flexibility and aren’t adjustable. East and west-facing windows need a flexible shading devise that can be completely retracted in order to let the valuable sun through in winter, but to protect from the harsh summer sun. Adjustable shading includes amongst other things canvas blinds, different types of shutters, angled metal slats, louvers or shadecloth over pergolas. Adjustable shading requires action from the occupants, as they have to respond to climatic conditions.

How to avoid Air Leakage & Thermal Bridges

Imagine it is winter. You wake up in the morning, put on your favourite hand-knitted wool socks and walk to the kitchen to have breakfast. But something is different today, your left toes are cold, you start to shiver  and feel uncomfortable. What happened? The fabric on the toes has worn-out, there is even a little gap. The socks that used to keep your feet warm and cosy have a leakage and they are not able to keep you warm any more.
The same principle applies to a house. The building envelope’s task is to protect its occupants from the environment and to keep them warm. The building envelope needs to be a continuous shell, each little breach will negatively influence the overall performance and reduce the insulation’s potential benefits.
The following will explain where air-leakages in a building usually occur and how to prevent them.

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Air-Leakage And Thermal Bridges
Thermal bridges and air leakages will increase the need of supplementary mechanical cooling and heating, but they will also increase the Relative Air Velocity and the Mean Radiant Temperature which will negatively influence the well-being and the comfort of the residents. By applying the right design features, natural ventilation and cross ventilation can be used to control indoor temperature and therefore reduce energy bills significantly. For these reasons, controlling the air movement is essential.

Draughts + air-leakage
Older style buildings commonly have draughts and air-leakages due to unsealed windows and doors, and unsealed vents and exhausted fans, therefore, heat and air can escape. It is difficult to control the air movement. Other sources for draughts are gaps within or around insulation, vented skylights, gaps between floorboards, open fire places, around air conditioners and heaters, gaps around other wall penetrations, such as down lights, pipes, cables etc. .

Thermal bridges
A thermal bridge is an element or part of a building, which allows heat to travel through it more quickly than through other parts and is therefore responsible for unwanted heat loss or gain. A thermal bridge arises for instance when poor insulative materials touch each other, when gaps occur between insulative materials and structural surfaces, and when materials with different R-values/U-values come in contact with each other. These thermal bridges allow heat transfer from a warmer to a cooler material. The main thermal bridges in a building are located at the junctions of floor to the wall, wall to the roof, balconies and window and door frames.

Draught Proofing
Avoiding gaps and thermal bridges is essential to minimise unwanted heat gain and loss and to utilise the full potential of the insulation. Retrofitting draught-proofing measures is essential to increase the performance, particularly for older homes, such as sealing doors and windows, closing of wall and ceiling vents and installing self-closing exhaust fans.
Most new buildings waive wall and ceiling vents due to different construction methods and use self-closing exhaust fans as a matter of fact. If these measurements are applied correctly the amount of air leakage is reduced enormously.

How to locate draughts?
– Are there any visible gaps? For example is light coming through gaps around windows and doors?
– Are blinds or curtains moving when the windows are closed?
A lit candle can be used to check air movement, such as around windows and doors, vents, floorboards, junctions of floor to wall and wall to roof connections.

Ventilation
Ventilation is the active process of “changing” or replacing air to regulate temperature and moisture. It should always occur under controlled conditions, by opening windows or with ceiling or exhaust fans, NOT through gaps and air-leakage. Ventilation is important to support the ability of thermal mass to absorb and release heat in order to regulate the indoor temperature. It is necessary to ascertain where natural breezes are and to locate the windows accordingly. Landscaping and other buildings can influence and obstruct air flow; therefore it is necessary to visit and check the site before locating windows.  Cool summer breezes in and around Melbourne usually come from south; detailed information can be found from the Bureau of Meteorology (BOM) web site.
The less gaps and air-leakage occur the air-tighter a building gets. Therefore regular ventilation is mandatory to renew oxygen and discharge odours, water vapour, carbon dioxide and other contaminations. For instance, in Germany it’s recommended to cross-ventilate every day for a few minutes, even in winter. If the occupants forget to ventilate regularly, water vapour will be trapped inside and will lead to mildew and mould on the walls and the ceilings.

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Cross-ventilation
Openable windows and external doors should be located on different sides of the home, with less than 8 metres distance between them to allow for adequate and effective air flow. Cooler air enters the building where the breeze is loctated, passes through the building and exits on the other side. The warm air inside gets replaced by fresh and cooler air.

Stack-effect
The term “stack-effect” goes back to the chimney. The heat source – in this scenario, the fire – heats up the air. Hot air rises and is discharged through the chimney, as it has a lower density than cold air. This effect can be used to replace air inside a house. For instance, when it’s colder outside the windows can be opened to let in cooler air. Warmer air inside the room will rise towards the ceiling, exiting via high openable windows and skylights. Warm air inside is replaced by fresh and cooler outdoor air.

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Exhaust fans
Exhaust fans should always be self-closing, so that the replacement of air is controlled and not accidental. They are an effective way to replace air, especially in rooms where no natural ventilation is available, or where natural ventilation might not be sufficient, such as kitchens or bathrooms.

Ceiling fans
Ceiling fans are an easy and cost effective way to improve the indoor air quality in summer and also to gain points towards the desired energy rating stars. Ceiling fans provide additional air movement/wind, increasing the Relative Air Velocity (‘wind chill factor’) resulting in the apparent temperature felt on exposed skin to be 3 °C colder than the actual air temperature, thereby reducing the need for additional cooling.

Thermal Bridges And Ventilation Overseas
In Europe, strict regulations are in place to control thermal bridges and air-leakages to minimise the energy needed for heating and cooling. Furthermore, due to the colder climate, a lot of structural damage can occur if heat and vapour is able to ‘travel’ through building materials.

Unlike in Europe, the significance of avoiding gaps and thermal bridges is commonly unknown and not a regulatory requirement in Australia. Common practice often shows that there is barely attention paid to minimising gaps and thermal bridges, leading to unwanted thermal bridges and air-leakages and therefore increases the need for cooling and heating.

Requirements to minimise thermal bridges
Maximum values of heat transfer through thermal bridges are specified and need to get incorporated into the energy ratings. Windows and doors as well as junctions of different building parts and materials require much detailing during the working drawing stage, as well as on the building site. It’s the architect’s/designer’s responsibility to find and draw solutions to overcome thermal bridges, and the builder’s to build accordingly.

Infrared thermal image
In Europe, infrared cameras are often used to locate the misapplication of materials and resulting thermal bridges. The lighter the colour the warmer the materials, the darker the colour the colder the materials. Great differentiation between colours means great temperature difference.
The first picture below shows a typical German home. Although double glazing and thermally improved window frames are used, the windows have a higher U-value than the walls, as the required U-value for the external walls is 0.24 W/(m²K)  and the U-value for the windows 1.30 W/(m²K). Expectedly, the windows present in a lighter colour as they let more heat escape through them than the walls. Determining if a thermal bridge is within the allowed limits requires meticulous measurements and comparison of internal and external material  and air temperatures, humidity levels and following calculations of heat transfer. In this particular case, the thermal bridges occurring due to different U-values are within the allowed limits.

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The third picture shows an obvious thermal bridge where the wall meets the ceiling. The dark colour indicates that there are gaps in the insulation as that corner is significantly darker and therefore colder than the rest of the room. It will require further investigation, if the architect/designer or the builder is liable for this structural damage.

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Conclusion
Although air-leakages and thermal bridges are not accounted for in energy ratings, they can majorly limit the ability and the potential benefits of insulation and other passive solar design solution. Consequently even a house with a 6, 7 or 8 star-energy rating could be draughty in winter. Avoiding air-leakages and thermal bridges means minimising unwanted heat gain or loss and therefore reduces the energy needed to cool or heat a building.

 

101 Building Physics & Condensation or why is it important to open your windows?

Have you ever wondered why there is water running down your window? Or why you have damp spots or even mould in your bathroom or behind the robe? No, it does not come from the outside. (except of course if there is some sort of water leakage somewhere).

The main sources of moisture in a home are cooking, baking, but also all other processes where water is used, like having a shower or a bath, using the toilet, washing your hands or the dishes, using the dishwasher or the washing machine, indoor planting and open water features, like aquariums or indoor ponds and pools. But did you know that one of the main contributors to the moisture in the air and in your home are we humans ourselves?

You might be asking: why, it can’t be that bad. How much moisture, water can there be? Here a little example.

Let’s take a small 3-person household, living in a 100square metres home (While this sounds tiny for most Australians, this is the average home size in Germany!) The indoor temperature is 20° C and 65% relative humidity (which is kind of average). This means there is about 2,8 litres water in the air. In average, this household will produce about 12 litres of water every day.

Between 2-3 litres by breathing, 4 l by showering and washing, about 4 litres for cooking and about 2-3 litres for indoor plants and the like. This 12 litres does not include any extra humidity due to drying clothes inside , which would increase the amount even further.

Summarising this means each household produces each month between 300 and 600 litres of water that is converted into steam. Only a portion of this water will be extracted through ventilation directly. (This is if you open the windows). The rest will be stored initially in the construction elements (walls, ceiling and floor) and furnishings and then later on extracted indirectly. Sufficient fresh air must be provided to exchange the ‘used’ air to allow for the required direct and indirect extraction of the moisture content in the air.

Let’s go one step back. Why is there moisture in the air?

Air is a mixture of different gases. From our school days, we know the air consisting of nitrogen (N), oxygen (O ²) and carbon dioxide (CO ²) as the main constituents.

The absorption of water (H ² O) depends on the temperature of the air. Warm air can hold more water than cold air.

Condensation occurs when air with accumulated moisture content through climate and occupancy cools down.

If the temperature drops, the moisture content of the air remains the same initially, but the maximum capacity to hold water will be reduced. As a consequence the relative humidity is increased. Once it has cooled down to a point where the existing humidity reaches the saturation value condensation takes place. The relative humidity is 100%.

The temperature at which this condition occurs is called the dew point temperature; this depends on the moisture content as well as the temperature of the air.

If temperatures on glazing, walls, ceilings, floors, windows are colder than the room temperature this can lead to condensation on the surface of the materials, which, if not tried out, can lead to mould and fungees. But it is also possible that condensation occurs within the construction, for instance within the insulation. This condensation within the wall components can also be harmful in certain circumstances to the structural integrity of the entire home.

In Europe homes are sealed so tightly that we are taught how important it is to open the windows at least a couple of times a day to exchange the used air. Well, here in Australia most people haven’t heard about it. But when you live in an old ‘typical’ Australian home, this might not be an issue, as there are so many gaps and openings everywhere, that fresh air might get in anyway. But if you live in a new home, or you are thinking about renovating and making your home more energy efficient by sealing your house, this is an entirely different story. Condensation and hence mould can occur internally which can lead to several health issues, like asthma, eczemas, etc., if you do not ventilate your home properly.

However, keeping the rising energy prices in mind and our environment in general, there is nothing more important than making our homes more energy efficient. At least that’s my opinion. In order to do this we have to insulate our houses better, seal it as air tight as possible and also avoid thermal bridges. (I will explain more about thermal bridges in another article).

The better insulated and the more air-tight our homes get, the more we have to convert our thinking. The temperature inside the house, the air’s moisture content as well as the temperature on the surfaces inside the house is fluctuating constantly and depends largely on the usage by its occupants, as well as heating and cooling habits.

It will not be enough anymore to open the window every now and then. You have to exchange the air inside by opening the windows regularly, ideally twice a day for let’s say 5 minutes and create a proper cross-ventilation. Just opening one awning window won’t do it.

 

Humidity levels for typical household processes can be specified as follows:

Emitted amount of water vapour in the household (per person/per day)

Human body – light to medium activity –                   1 to 1,5 litres

Human body – while sleeping –                                     1 litres

Shower                                                                                 1 – 1,5 litres

Bathing                                                                               0.5 – 1 litres

Cooking                                                                              0.5 – 1 litres

Dishwasher (one load)                                                    0,2 litres

Washing machine (one load)                                         from 0.2 to 0.3 litres

Drying tumble dry washing inside (4.5 kg)                 from 1 to 1.5 litres

Drying wet washing/clothing inside (4.5 kg)            2 to 3.5 litres

Flowers                                                                             from 0.5 to 1 litres

Indoor plants from                                                        1 to 1.5 litres

Water features (eg pond, aquarium)                          from 0.8 to 1.3 litres.

 

If you have a really air tight home it is actually recommendable to ventilate the house 4 – 5 times a day properly and perform a complete air exchange.

Now you might think, gosh, that will just increase my heating bills. But, consider this. It’s actually the other way around. Firstly, the higher the humidity inside your house, and inside the wall, the higher the thermal conductivity of the wall, meaning the more heat can the wall store and detract from the room, meaning you have to heat more. But even more critical is, that the insulative properties of the insulation will get reduced significantly. As a rule of thumb you can say that for each 1% moisture increase inside the insulation  value drops by 5%. That’s actually quite a lot, isn’t it?

Summary

It can be stated that a dwelling with insufficient ventilation will most likely have higher heating bills due to the poorer performance of the thermal insulation. It is not recommended to open for instance one awning window the entire day. This will in fact just cool down the house constantly and not exchange the indoor air. Ideally you should open one casement window or door on either side of the house to create a good cross ventilation for about 5 minutes.

Having said all this, this applies for highly energy efficient, highly insulated and well-sealed homes. However, keep in mind even if you home is not that air tight, the humidity is there, even when you can’t see it, and opening the windows should become a daily habit of yours.

BDAV 10 star design Challenge Finalist 2012

 

I still can’t believe that we made it under the 3 finalists of this years 10 star design challenge, this came really unexpected. Especially as I mainly participated to get a certificate that I can design and rate 10 star homes and only spent one Saturday on this. Unbelievable.

Thanks again to the BDAV:

“This contemporary design, with clean lines and clever cantilevers, creates architectural appeal and a well-proportioned building. Innovative non-toxic and renewable building materials were used in combination with triple glazed PVC windows. The building has a small footprint; however, generous room sizes and good use of multi purposes areas create a practical and visual appealing design solution.”

 

 

What is Thermal Mass and why do we need it?

Although the term ‘thermal mass’ is not commonly used, there are many examples where we experience it and appreciate its benefits. The most impressive is the ocean: in winter, when there is less sunshine and the average air temperature is low, the water is chilly and only the tough ones might enjoy a swim! In spring, the sun will slowly heat up the water so that finally in summer it will have a comfortable warm temperature. Water has a great capacity of storing heat – it will stay constantly warm during day and night, and even in winter, it can be significantly warmer than its surrounding air temperature due to its ability to absorb solar energy. Water demonstrates the principle of thermal mass. How does it apply to construction?

Thermal Mass, Why Is It So Important?

Thermal mass is the ability of storing and releasing heat to help retain a constant indoor temperature. It is an effective way to improve thermal comfort in a building and plays an essential role in saving energy. Thermal mass inside a building will absorb heat when the surroundings are warmer than the mass, will store the heat and radiate it slowly when the surroundings are cooler. It can actively be used to regulate temperature, therefore, reducing the need for mechanical heating and cooling. Heavy materials, such as concrete and brick have great thermal storage capacity, whereas lightweight construction materials, such as timber and insulation cannot store heat. Generally speaking, the heavier a material the better its ability to store heat.

Summer benefits
Materials such as concrete and brick are cooler in summer than the surrounding air temperature, so they are able to absorb heat,  which consequently lowers the room temperature and the need for additional cooling. At night the thermal mass will slowly release stored heat. Natural ventilation, via open windows, ceiling or exhaust fans, are an effective way to let cool air in and to let heat – collected during the day – out. In extreme hot periods, when it doesn’t cool down at night, air conditioning may be required to regulate the room temperature. The greater the difference between day and night temperature, the more beneficial the thermal mass.

Winter benefits
In winter, thermal mass works like a heater: it absorbs radiant heat from the sun through north, east and west-facing windows, and also stores heat from mechanical heating. The thermal mass will slowly release the heat which reduces the need for heating. Even when the heaters are turned off, the house will stay warmer for longer. Furthermore, the air and the exposed surfaces have the same temperature (Mean Radiant Temperature), which means there are no unwanted draughts, and the Relative Air Velocity is low; these will increase the thermal comfort of the occupants.

Optimal Use Of Thermal Mass

How to locate thermal mass
Thermal mass needs to be situated correctly and needs to work in combination with passive solar design and good performing insulation, otherwise it can have negative effects and even increase the need for heating and cooling. Thermal mass should be situated on the interior face of the building envelope and must be thermally separated from the outside via insulative materials.

Thermal mass should be located throughout the building to maintain comfort in summer, but the main focus should be on north-facing rooms. Good solar access is obligatory as the low winter sun needs to be able to enter the building and to strike the thermal mass. The more glass area, the more thermal mass is required.
Thermal mass is extremely important for multi-storey buildings, as warm air rises and therefore the rooms tend to overheat easily. Unfortunately most upper storeys are usually built in lightweight construction, as this is cheaper and easier to build. It is important, however, to incorporate as much thermal mass as possible, for example concrete floors or internal brick walls.

Material and colour selection
Generally speaking, the more thermal mass the better and the heavier a material, the better its ability to store heat. The optimum would be a masonry home with a reverse brick veneer construction and concrete floors. If this option is too expensive use as much thermal mass as possible, concrete slab is preferable. In warmer climates the ground is colder and can help to cool the concrete. Therefore the indoor air temperature will be reduced. In colder climates, however, the concrete slab needs to be insulated from the ground in order to minimise heat loss in winter.
If a timber subfloor is requested, the focus should be at least on internal brick walls to the north which need to be exposed to the winter sun and are therefore able to absorb and release heat. Other materials that have a good thermal conductivity are water, sandstone, rammed earth and earth blocks, mud brick etc.
Moreover, colours and coverings can influence the performance of thermal mass. For example carpets and timber floors will minimise the ability of thermal mass to absorb and release heat as they work as additional insulation. This can lower the required heating in winter, but it will increase the need of additional cooling in summer, as the thermal mass can absorb less heat. On the other hand, hard floor finishes such as tiles, stone or slate on concrete slab can increase the ability to store heat. Dark colours or dark materials also tend to absorb more heat, however, light-coloured walls are more desirable as they maximise natural daylight. Dark walls will increase the need of artificial lighting, as they absorb light and can make rooms appear smaller. In short, material and colour selection can promote or adversely affect the performance of thermal mass.

Examples for wrong location of thermal mass
Brick veneer wall construction has brick to the exterior, studs to the interior with insulation between the studs. In this scenario, brick can’t act as a thermal mass as it can’t store or release heat to the interior space.  Conversely, double brick walls can absorb heat, but due to the fact that there is no thermal separation to the outside, they act as a thermal bridge and release heat to the exterior which will increase the heating needs in winter.

Heating And Thermal Mass
Split systems and ducted heating are the most common heating systems in Australia – they function by pumping hot air into the room. When fan or ducted heaters are turned on, a room will be warm, however, immediately after they are switched off, it is cold again. This is because they use convective heat which warms the air, not the materials in the room. Open fire, gas or hydronic heaters eject radiant heat from their hot surfaces. It takes longer to warm a room as it also warms up the objects and materials, the occupants in turn feel more comfortable, as the Mean Radiant Temperature is well balanced. Even when the heaters are turned off, the thermal mass will release its stored heat slowly and therefore keep the room warm for a longer time, depending on the performance of the insulation.

How Thermal Mass is Used Overseas
In most European countries, thermal mass is used as a matter of course. Although it takes a longer to heat up a house which contains a lot of thermal mass, it also takes a long time to cool down again. The thermal mass releases constant heat to the rooms and therefore heaters only need to be on a low setting or turned off completely. Unlike in Australia, split systems and ducted heating are rarely used overseas as they use convective heat. The main focus lies on radiant heaters as they heat thermal mass.
If thermal mass is combined with effective insulation and has good solar access, the interior is perceived to be comfortable, without the need for additional heating, even if the external temperature is well below 20°C. The combination of thermal mass and well performing insulation is a condition of passive solar design, as well as low and zero-energy housing.

Conclusion
Thermal mass is an effective way to reduce the need for mechanical heating and cooling and to increase the comfort and well-being of the occupants. In order to perform at its best, it needs to be located appropriately and sized adequately, with a careful eye on insulation and thermal bridges.

Why Is Good Window Design So Important?


Is double glazing worth the money? The answer is YES, but ONLY if it is installed correctly without a cold bridge (thermal bridge). A window or a door is essentially a hole in the wall and responsible for most of the unwanted heat loss or gain.

Windows are essential for a house and the comfort and well-being of its habitants, as they let natural light and fresh air into the building and enable views. Appropriate window design, size, location and glazing treatment, combined with shading and internal covers, can significantly reduce the energy required for heating and cooling. Maximum solar access for north-facing windows can reduce winter heating bills up to 25%. External shading can block up to 80% of summer heat gain through windows. Double glazing and internal coverings can reduce heat loss in winter up to 40%.
Glass is the potential weak point of a building in terms of energy efficiency. A single glazed window can gain or lose up to ten times more heat than an insulated wall. The main heat gain through windows is due to thermal radiation. Windows receive direct solar radiation when the sun strikes the glass, but also diffuse radiation reflected from the sky and the ground. Between 30-40% of total radiation to north windows is diffuse, depending on the weather conditions. Radiation from the sun travels through glass to the inside of a house. This radiant heat is absorbed by thermal mass, building elements and furniture, which when warmed up, re-radiates heat to the room air. This re-radiated heat is trapped inside, resulting in convective heat build-up within the room. This process is called ‘glasshouse effect’. In order to hinder direct rays from the sun entering the building in summer, glass needs to be shaded appropriately. On the other hand it is also important to ensure valuable winter sun can shine into the house, as heat gains in winter can reduce the requirements for mechanical heating.

Energy Efficient Window Design
The total radiation received per window varies according to the time of the year and the orientation. In summer, all windows receive heat gains, in particular those facing east and west. Whereas in winter, only windows facing north, north-west and north-east have a net heat gain, with heat gains outweighing heat losses. Windows facing all other directions will affectively lose more heat than they can gain. However, in the absence of northern solar access, windows to the east and west can provide some winter heat gains.
The most appropriate size of windows in terms of energy efficiency depends on many factors, such as glazing type, orientation of a building and thermal mass located inside the building materials. It is important to consider every room separately, as each room may have different acceptable limits and therefore may need different sized windows. Thinking about the windows early in the design process can save time and money otherwise needed later in the progress, to chase after the required stars to obtain a valid energy rating. We can help determine the effect of variations to window orientations, window sizes, internal glazing, double glazing versus single glazing, shading and internal coverings by using the FirstRate House Energy Rating software. Below are some clues on how and where to place windows.

How to orientate and size windows
Windows should be orientated to the north where possible. If solar access is good, north-facing windows should be large, but the size also depends on the amount of thermal mass in the building. South and east-facing windows should be kept pretty small, and windows to the south need to be positioned to enable cooling summer breezes to pass easily through the rooms. Whereas west-facing windows should be avoided where possible, if needed they should be relatively small and well shaded.
Appropriate window sizing, combined with double glazing, and/or close-fitting internal coverings such as drapes with pelmets, can minimise heat loss in winter. Furthermore, it is important not to overshadow windows in winter by the structure of the building itself, as it will reduce the solar access.

How to respond to poor solar access

Innovative design can overcome problems of poor solar access and overshadowing,  especially in renovations, infill developments, higher density or small allotments with bad orientation, which can cause problems. In these cases, it’s important to use better performing insulation, protect windows, minimise overshadowing and courtyards, and reduce air leakage as much as possible. To compensate for poor solar access, the total window area of a building should be reduced.
Where solar access to north-facing windows is obstructed, clearstory windows are a good option to get solar energy into the building. Another option in responding to bad solar access is raising the sill height, as it will minimise permanent shaded glass areas, as these aren’t able to gain heat in winter and will lose heat instead.
Skylights and roof lights are also a good way to bring light into rooms, if obstructions from other buildings and structures prevent good solar access. Furthermore it’s a great opportunity to overcome overlooking into neighbouring properties, as windows above 1.7m don’t need to be screened. However, it is vital to protect the windows against harsh summer sun. Double glazing is mandatory as well as shading (a combination of external as well as internal shading would be the ideal solution).

How To Reduce Unwanted Heat Transfer

Summer heat gain
It is important to protect windows with external shading devices, through appropriate window sizing and location, in order to minimise heat gain in summer.

Comparison of heat gains through different treatments for windows in summer
(According to Sustainable Energy Authority Victoria 2002)

  • Unshaded single-glazed window: 100%
  • Standard double glazing as available in Australia: 90%
  • Vertical blinds/open weave drapes: 76%
  • Internal venetian blinds: 55-85% (Effectiveness is reduced as the colour darkens)
  • Internal drapes or Holland blinds: 55-65%
  • Tinted glass: 46-65%
  • Solar control film/reflective glass: 20-60% (Available in different kind of configuration with varying effectiveness)
  • Trees, full shade: 20-60%
  • 1 metre eave over north wall: 30%
  • Roller shutters: 30%
  • External awnings: 25-30%
  • 2m pergola over north wall covered with deciduous vines or shade cloth: 20%
  • Outside metal blind or miniature louvers, parallel and close to window: 15-20%

External shading devices are an effective way to minimise heat gain through glass in summer and keep a building cool. They provide far better protection from heat gain than internal window covering. However, if external shading is not possible, internal coverings can at least reduce the unwanted heat gains. Shading devices should always enable ventilation outside the window, as shading fitted too closely to a window can trap warm air which can be conducted into the house.
Eaves, verandas or pergolas are commonly a part of the building structure, they are durable and do not require ongoing adjustments. It is essential to have a certain distance between the underside of the shading devise and the top of the window. But these fixed shading devises should only be used over north-facing windows, as they lack flexibility and aren’t adjustable. East and west-facing windows need a flexible shading devise that can be completely retracted in order to let the valuable sun through in winter, but to protect from the harsh summer sun. Adjustable shading includes amongst other things canvas blinds, different types of shutters, angled metal slats, louvers or shadecloth over pergolas. Adjustable shading requires action from the occupants, as they have to respond to climatic conditions.

Winter heat loss
Unprotected  glazing  and single glazing in particular means the surface of the glass is noticeable colder than the warm air in the room. This lowers the room temperature and produces draughts. The Relative Air Velocity ends up too high and occupants will feel winter discomfort. For this reason, all windows require protection from heat loss in winter. To minimise winter heat loss, it is important to trap a layer of insulation still air between the window and the room. This can be achieved for instance by using internal coverings, such as drapes, Holland blinds, Roman blinds or Australian blinds, and thin or lace curtains combined with pelmets.

Effect of window treatments on winter heat loss
(According to Sustainable Energy Authority Victoria 2002)

  • Unprotected single glazing: 100%
  • Vertical or venetian blinds: 100%
  • Unlined drapes or Holland blinds, no pelmet: 92%
  • Heavy, lined drapes, no pelmet: 87%
  • Unlined drapes or Holland blinds, pelmet: 79%
  • Standard double glazing: 67% (the higher the U-value the less the heat loss can be)
  • Heavy, lined drapes, pelmet: 63%
  • Double glazing with Low-E coating: 57%
  • Double glazing, heavy drapes, pelmet: 46%

Double glazing
The most effective way to protect windows against heat loss in winter is a combination of double glazing and internal window coverings. However, if internal coverings are inappropriate or not desired, for instance in highlight or clerestory windows, in kitchens or simply where unobstructed views are wanted, double glazing is an indispensable measurement in order to prevent heat loss in winter. Yet double glazing won’t prevent sun coming into the building, which means that the windows need to be protected from harsh summer sun by means of external shading.

Window frames
Another, often underestimated roll in the energy efficiency of a window, is the frame itself, as it can effect negatively on the overall performance. As we talked about in the blog “Adequate Insulation”, some materials, such as metal, glass or aluminium, allow heat to pass through them more easily, therefore they shouldn’t be used for windows frames if at all possible. If metal frames are used, such as aluminium, they should have thermal breaks to reduce the heat transfer. Generally speaking, PVC and timber frames perform better than metal frames.

Comparison of heat loss through different window frames
(According to Sustainable Energy Authority Victoria 2002)

  • Single-glazed industry typical aluminium: 100%
  • Single-glazed thermally improved aluminium: 87%
  • Single-glazed timber or PVC: 82%
  • Double-glazed industry typical aluminium: 72%
  • Double-glazed thermally improved aluminium: 60%
  • Double-glazed timber or PVC: 54%

Sealing and weather-stripping
A good U-value is no guarantee for a well performing window. The installation of doors and windows needs to be done according to the manufactures guidelines. All gaps must be sealed and weather-stripped carefully in order to perform to the specified U-value. Unfortunately, the energy rating just states the material U-value of the window and not the end product and common practice often shows incorrect installation leading to thermal bridges around the windows.

Window Energy Rating Scheme
The Window Energy Rating Scheme (WERS) is a program implemented by the Australian Window Council Inc. (AWC) with the support of the Australian Greenhouse Office. The windows are evaluated with stars, the more stars, the better the performance. If buying windows, always check the label before making a decision.
A single-glazed window with a typical aluminium frame has U-values ranging from 7.9 W/m²K to 5.5 W/m²K (according to the indicative ranges of whole glazing element performance values in the BCA). These U-values will make it hard to reach a good energy rating for a building. Keep in mind, the lower the U-value the better performing a window. Double glazing windows with timber framing in Australia usually range between a U-value of 3.8 W/m²K and 2.5 W/m²K.

Windows And Double Glazing Overseas
Whereas most countries in Europe require double glazing and even recommend triple glazing, it is not standard in Australia yet. Unfortunately, double glazing is still more expensive than single glazing in Australia, in Europe it’s actually the other way around. Due to the fact that single glazing is not allowed any more, no one is producing it on a large scale making it quite expensive. Double-glazing on the other hand is a standard, and although better performing than common double-glazed windows in Australia, they are available for about a quarter of the price. For instance, the minimum required U-value for windows in Germany is currently 1.3 W/m²K. I trust that with time, double glazing will become more affordable and will become mandatory in Australia to achieve good passive solar design.

Conclusion
YES, double glazing is worth its money. It is the best method to reduce heat loss in winter, as long as it is applied, installed and used properly.  The window size should respond to the location and the climate, the insulation around the window needs to be snug fit, in order to prevent thermal bridges. Appropriate window frames need to be used and furthermore, adequate internal and or external covers needs to be applied. All these measurements need to work together, otherwise a window is nothing more than a hole in the wall and will be the major contributor for unwanted heat gain and loss, therefore preventing energy efficiency.

Adequate Insulation

Thermal insulation is a fundamental factor to achieve thermal comfort for occupants. Insulation reduces undesirable heat loss or gain and can lower the energy demand on heating and cooling systems.

The Victorian Government is planning to introduce new regulations for the existing housing market. Originally planned for 2011, then moved to 2012, we’re now in 2016 and it this initiative is still getting postponed further. However, eventually  hopefully it will be a requirement to provide information about energy, water and greenhouse performance to buyers and renters.

Assume two homes are for sale in the same street, both are three bedrooms single storey brick veneer buildings with a double garage on a block of approximately the same size. One has a 2-star energy rating and the other one has 5-stars. Which one is more likely to sell for more?

 

 

 

Insulation, Why Is It So Important?
Insulation is the most effective way to improve the energy efficiency of a building, as it acts as a barrier to heat transfer. It will keep the house warm in winter and will help to stay cool in summer, improves thermal comfort and well-being, and minimises condensation on walls and ceilings. Furthermore, insulation needs to be combined with appropriate shading devices to windows and adequate ventilation possibilities, otherwise heat entering a building through windows will be trapped inside by the insulation and lead to overheating.
Older houses in particular pose a problem: inadequate insulation, poor solar access and air leakages amongst other things lead to unwanted heat gain and loss, and consequently higher energy bills.
Adding insulation to a home can save 45-55% of mechanical heating and cooling needs and as a result, save non-renewable resources and reduce greenhouse gas emissions. With the current energy prices, additional insulation usually pays for itself in around five to six years. With the prospect of rising energy prices it’s more than likely that insulation retrofitting will pay off even quicker.

Different Types Of Insulation
The purpose of thermal insulation in a building is to regulate the internal temperature by minimising or stopping heat transfer through radiation, convection and conduction. Generally speaking, there are two different types of insulation that must work together to prevent heat transfer: Bulk insulation and reflective insulation.

Bulk insulation
Bulk insulation mostly resists the transfer of conducted and convected heat, using millions of tiny pockets filled with still air or other gases within its structure. This air provides the material’s insulating effect, therefore it’s essential not to compress bulk insulation. Bulk insulation is available in different shapes and materials.
-Batts and Blankets (Glasswool/Fibreglass, Rockwool, Natural Wool, Polyester)
-Loose-fill insulation (Cellulose Fibre, Natural Wool, Granulated Rockwool)
-Boards (Extruded Polystyrene, Foil-faced expanded polystyrene, Wood Fibre)

Reflective insulation
Reflective insulation mainly resists radiant heat flow. It is made of thin sheets of highly reflective aluminium foil, which reflects heat from its polished surfaces. The performance relies on the presence of an air layer of at least 25 mm next to the reflecting surface. Keep in mind that dust will greatly reduce the performance. Some examples include:
– Reflective Foil Laminate
– Multi-Cell Reflective Foil Products
– Expandable Concertina-Style Foil
– Foil Bonded to Bulk Insulation
For information about electrical safety checks for householders with foil insulation go to ‘Home Insulation Program’ webpage from the Australian Government.

Installation
Insulation needs to be installed with careful attention to detail, as inappropriate or incorrect application will crucially decrease performance. For instance, failure to butt all ends and edges of batts to give a snug fit could mean that about 5% of the ceiling area is not being covered. This could result in losing up to 50% of the potential insulation benefits.

  • Avoid thermal bridges
  • Eliminate gaps in insulation
  • Do not compress bulk insulation
  • Protect insulation from contact with moisture, provide vapour and moisture barriers to prevent condensation
  • Provide a sealed air space of 25mm adjacent to reflective insulation
  • Allow clearance around appliances and fittings
  • All electrical wiring encased in insulation must conform to AS3000: Electrical installations-buildings, structures and premises. It’s best to keep wiring clear of insulation, e.g. to run wiring on top of ceiling joists.

How Much Insulation Is Needed?

The Building Code of Australia (BCA) identifies eight different climate zones for Australia, but within a zone, there are some locations with slightly different temperature ranges.  There can be significant differences between maximum and minimum temperatures in summer and winter and in length and intensity of heating and cooling periods. The house design, the insulation and construction must respond to these variations in order to be able to perform energy efficient. But keep in mind, the required R-values in the BCA are minimum requirements and NOT best practice!!!!

For simplicity, Victoria is divided in five climate zones, with winter heating as the predominant concern especially in the Temperate Coastal and Cool Inland Zones. Summer cooling is variable but generally less significant. House design in these zones requires attention to better performing insulation, draught proofing, window protection in winter and shading in summer. Likewise, in warmer cities and areas like Mildura supplementary heating is obligatory for thermal comfort.  In these regions, it’s advisable to include extra thermal mass, cross ventilation and summer shading, whereas alpine areas may require constant heating for most of the year and cooling requirements are negligible.  Consequently, a  5-star home inMildura wouldn’t comply with the minimum requirements for a  5-star home in Ballarat.

The higher the R-value the better the performance. Consider what insulation is needed in order to build an energy efficient home in a certain climate zone early in the design process. In particular, it’s important to think about the roof insulation. For example, it would be cheaper to use larger rafters in order to fit in sufficient glasswool to fulfil the desired R-value, instead of using thinner expensive extruded polystyrene. Larger rafters would mean that the overall height of the building rises slightly. This is no problem, if the amendments are done early in the design. However, if a town planning permit has already been granted, it’s not that easy any more. It’s necessary to go back to the council with the changes, which can cost a lot of time and money, therefore in most cases, people choose to use the thinner, more expensive insulation instead.
Adding R1.0 insulation can significantly improve the energy efficiency. For example in Melbourne, adding insulation with a R-value of R3.0 to the ceilings and R1.5 insulation to walls can save 12% on energy bills each year and can ensure a higher level of comfort.

Insulation Regulations Overseas

Thermal bridges
When I started working in Australia, I was puzzled how thin walls can be. For example, a typical timber wall measures 110mm, 90mm for the timber studs, 10mm plasterboard on each side and insulation just between the studs. This construction is not allowed in most European countries, as it creates a structural thermal bridge. The U-value of timber is much higher than the U-value of the insulation, which means that heat can escape through the timber and consequently increases unwanted heat gain or loss. In Europe, the main focus lies on avoiding thermal bridges. A timber construction is usually done as a double stud wall. In this case, there is also a timber stud to the interior, covered with plasterboard and insulation between the studs, but at the outside is another continuous layer of insulation, and then another timber stud, with external plasterboard and again insulation in between. (see diagram below)
In Australia, there are no strict regulations about thermal bridges and also no minimum insulation regulations for concrete slab-on-ground construction, roof or internal walls.

 

Example for an insulation for a typical Australian home compared to a German home

AUSTRALIA (2010) GERMANY
External Wall R-value: 1.3 R-value: 5.0
Roof Not required R-value: 6.6
Ceiling R-value: 2.2 R-value: 3.3
Internal Walls (to garage, bathroom, staircase etc.) Not required R-value: 3.3
Floor R-value: 1.0 R-value: 3.3

Obviously, the average temperature in Germany is much lower than in Australia, therefore it is natural, that the R-values of the insulation need to be higher, but there are also some differences in where the insulation needs to be installed. In Australia, usually just the ceiling gets insulated, although the roof space is ventilated, heat can be trapped inside in summer which can transfer through the ceiling and heat up the rooms below. In Germany, the main focus lies on the roof itself, the whole outside of the building is treated as a continuous shell. Ideally, no heat should be able to transfer into the building at all. There are no wall or roof vents, most of the buildings are even air-tight.
For instance, in winter you can easily distinguish between a good and a bad insulated home in Germany. In a good insulated home snow won’t melt on the roof tiles, as no internal heat can escape the through the insulation which reduces the energy required for heating enormously. Furthermore, it is also a requirement to insulate the ceiling to a roof space and to floors/ceilings between different levels, as well as to place insulation on some internal walls, for instance walls between rooms with different heating requirements, to unheated corridors, garages etc. This is to stop heat ‘traveling’ through a house from room to room.
Furthermore, typical brick veneer constructions, as shown above, are not advisable, as the thermal mass is located on the outside of the building and therefore can’t be used to actively contribute to heating and cooling needs. Brick should be located on the inside. Therefore a better opting would be to use a reverse-brick construction, where the brick is inside the building envelope and consequently is able to store heat and to regulate the indoor temperature.

What can we learn from overseas?
Minimising thermal bridges and heat transfer is mandatory in order to create energy efficient and environmentally friendly buildings. All insulation must be installed snug-fit, there should be no gaps and also thermal bridges should be avoided where possible in order to minimise greenhouse gas emission and to protect the environment.

Conclusion
Neither a 6 or 7-star energy rating nor high R-values are a guarantee for energy efficiency. The building envelope needs to be treated as a delicate continuous shell. Each small gap and leakage will impair the performance of the insulation. It is essential to consider the end product in order to determine how energy efficient a building really is. Even small gaps in the insulation such as around windows or other wall penetrations can halve the potential insulation benefits.  Adding good performing and appropriately installed insulation can save a lot on your energy bill and minimise the greenhouse gas emission.