Technology 4: Energy Efficient Housing

    Introduction
    Site features around residential Buildings
    General Design Features
    Windows and Openings
    Methods of Construction Used to counter the range of climatic conditions
    Heating Systems
    Thermal Insulation
    Economic Considerations
    Conclusion  
    Bibliography



Introduction

No matter where a building is built, some consideration should be placed on trying to increase the use of the sun and wind to heat and cool down the building and its surroundings. To do this site features on the site were the building is to be built such as trees and other vegetation should be used to keep the direct sunlight to a minimum. Another important issue is the buildings orientation and where windows and openings are placed.

The methods and materials of construction used is also paramount as some materials heat or cool quicker, while others may take a long time to heat up but also take a long time to cool down. All of these issues have to be considered not only for the comfort of the buildings occupants but also for their wallets. Every year Households spend hundreds if not thousands of dollars each year that maybe could of been avoided if some of these principles had been thought of when building the house.


Site features around residential buildings

Firstly the use of trees and other vegetation can greatly economise and maximise on the sun as a means of transferring itís heat. Out of all of the types of trees around, the deciduous varieties (or the ones that shed their leaves and growth throughout Autumn and Winter) are ideal as during summer they block out the excesses of heat that we donít want, while during the colder months of the year they have no leaves on them thus allowing the sunlight to come through the trees and heat up the house. In addition trees and creepers can be also used to funnel breezes and winds in order to either stop the cold winter winds and storms or to channel in the cool sea breezes in summer.

Many sites in denser Forest areas are cooler as they have the shading effect of the many trees, but here in W.A. most of these areas lie on granite which increases the temperatures even more due to its lower reflective rate but higher absorption rate of the suns heat.


General Design Features

The first major design consideration is to see what the orientation of the house will be. As a general rule a house should be facing North with an East - West orientation. By keeping the major side away from the direct path of the sun, the heat received is greatly reduced. As the suns path in summer is travelling at a higher angle the suns rays will hit the roof rather than penetrate into the house, while during winter the sun will come in at a lesser angle thus providing much needed light to heat up the building.

Another important design feature to consider is the placement of the eaves. Through different design calculators we as builders can find a pitch of eaves that can maximise the potential of the suns rays (see diagram). As shown below when the suns angle is highest it is summer, so therefore the eaves need to be wide enough to block out itís heat. During the cooler months when the angle decreases more sunlight will be let in to penetrate through windows etc. Where windows are on gable ends or on multi-storey units, Tiled Hoods can provide a feasible means of shading the areas when the temperature is at its hottest.


Windows and Openings

While windows provide the majority of sunlight they also provide a source for letting breeze in if they can open. Some factors affecting which windows should be used are
 
 ·  The number and size of glass areas.
 ·  The type of glass.
 ·  Whether glazing is to be single or double.
 ·  The type of window.
 ·  The ratio of fixed to opening glass.
 ·  Internal and external coverings.
 ·  External shading devices.

All of the above decisions affect the energy efficiency of the house and how hot or cold it will be. Firstly the area of glass compared to the rest of the building is important. If there are too many windows or a large area of glass the building can overheat fast during the day and quickly cool down at night. The reason for this is as the heat enters the house it has little or no mass to absorb the heat therefore heating and cooling a house extremely quickly. A compromise of the area of glass should be achieved to maximise the efficiency of the house.

The type of glass is relevant as some glass reacts different to others. The most common glass used is clear float glass (6mm) and this glass lets in 83% of heat and rays, while cutting out 13%. The double-glazed version of clear float glass lets in 72%, while cutting out 28%. The difference between the two is 11% but double glazing has limited use as these windows are normally fixed and cannot be opened. Heat - absorbing glass (or more commonly tinted glass) cuts out 40% of the suns rays while only allowing 60%. The double-glazed version only allows 49% of the rays in. Finally reflective glass is used where it is hard to directly shade the glass from the sun or where the heat intensity is very high. It is made by applying a thin coat of metallic oxide to the normal glass. This glass is highly effective as it blocks out 51% while only allowing 49% in. The version of using one sheet of metallic glass on the outer side while using float glass on the inside only let in 31% of the suns rays in while blocking out 69% of them.

From the glass type, we can determine what sort of window is required to give us maximum flexibility in allowing both the suns rays and the breeze to enter into the building. The heat performance will not matter if the seal between sashes is tight but the different windows will allow different amounts of breeze into a house.

Firstly a double-hung window has the advantage of allowing the breeze through at both a high and low level. This type of window can be advantageous in winter or when it is raining as the eaves will protect the opening from attracting water.(This is only the case when the top sash is open).

The casement sash window is useful when a direct wind is wished to be trapped and transferred through the house.

Awning windows are good as they shield any rain from coming into the building but they have a disadvantage in not being able to pick up readily available breezes.

Louvres can allow a great source of breeze and direct sunlight in a house but their disadvantage is during winter. With many parts to comprise the louvre there are more gaps and therefore an entrance for the cold winter winds to come in from.

The majority of newer houses use the more common sliding window. These have a high transparency rate and can allow half the opening to be allocated to letting in a breeze.

Finally skylights or Clerestory windows can get sunlight into areas of the house which are otherwise cut off from the outer edges of the buildings. For rooms like this these are an advantage but the drawback from these windows is that little or no ventilation can be accessed.

Another method of controlling temperatures is by using shading devices. These can come in the forms of curtains, blinds, roller shutters or drapes. When placing these, full length curtains are better than ones finishing at the window sill. The longer ones act as a form of insulation, while during the night the shorter ones lose heat. Many new houses are installing roller shutters as a form of control over the sun light. This form of shade has been used in Europe for many years and in my opinion it seems like a good idea as it blocks out the majority of light before it even hits the window.


Methods of Construction used to counter the range of Climatic conditions

Timber-frame Construction responds more quickly than an equivalent brick built house when subjected to hot and cold. Although it heats up quickly during the day it also cools down relatively quick. If thermal insulation is used and the are windows closed and shaded, the heat experienced is similar of that of a brick construction.

In hot-dry climates such as W.A., concrete floors on ground can be excellent if floor tiles are used on them. During the day the slab + tiles will heat up and due to the concrete's heavyweight mass will release the heat slowly therefore keeping the floor warm during the night. If a floor covering such as carpet is used, the floors ability to hold onto the heat will be minimised.

In hot climates it is recommended that roof ventilation be installed either mechanically or manually. If the area is prone to dust then fine mesh should be laid to stop dirt entering the roof space. In cold climates this is not recommended as the cold air will worsen the effect of trying to keep the insides of the house warm. Dealing with the roof space, it is better to have a higher pitched roof as when low ceilings are provided for there is lesser of a gap between the roof and ceiling therefore the heating process is accelerated.

Another construction method to use when trying to make the building more energy efficient is to use lighter colours such as whites and cremes. These colours reflect most of the heat away thus causing slightly cooler temperatures.

In the colder winter periods heat is lost from gaps in doors construction joints and from the floor space if the house has them. Therefore the underspace of the floor should be enclosed and than appropriately ventilated so that the floor members will not rot. When enclosing the sub-floor space 2100 sq.mm air-vents per 1 m length of external wall should be provided for. Other areas such as were pipes penetrate through walls, gaps around doors and windows and other joints between different construction joints should be sealed up to avoid draughts from coming into the house.


Heating Systems

The water heater in the house is a major consumer of the households energy budget. The three main hot water systems that can be used are electric, gas, and solar. Firstly Both electricity and gas are pay as you use resources but solar heating is advantageous in Australia were 2/3 of days have sunlight. With solar heating you pay a one off fee then use the suns rays to provide hot water. In most cases an electric booster is used when there is not enough sunlight to heat the solar panels. In terms of cost electric heating costs most with gas coming in even cheaper. Solar heating cannot really be compared to the other two as the other two you have the ability in being able to instantaneously have hot water while solar heating you rely on nature. Never the less solar heating has a larger outlay but pays back for itself in a matter of years.


Thermal Insulation

There are two types of thermal insulation, Bulk insulation and Reflective insulation. The first relies on its bulk trapping heat particles and stopping conductivity while the latter method relies on the reflective properties that metal based products have. The bulk insulation can either come in batts, Loose blown-in fill and foam. The latter is seldomly used in the building industry.

Traditionally the Batts have been the main source of insulation over the past 20 years, but now the companies of blown-in material such as Cool and Cosy, etc. have a product which is on par if not better than the old product. The blown-in insulation can be made from cellulose fibre, Eel grass, expanded polystyrene, rock wool and even wool from sheep is now being used. The advantage of the blown-in variety is that some places in the roof space that are otherwise inaccessible can be reached with the blowers hose.

Insulation can also be placed in the cavities of the wall to enhance the cavities performance even more. The main consideration when placing insulation in walls is for it not to transfer any moisture through to the inside leaf. Carpet with a thick underlay is considered a good insulator in both timber floors and slab-on-ground construction. In extremely cold climates the perimeter of the slab can be insulated by using foam.


Economic Considerations

It does not matter if a house uses all of the methods and materials explained in this assignment, as in most houses the final decisions come down to the economic of it. If a house was to use double glazed reflective glass windows instead of normal ones, insulated the slab, wall cavities and planted barriers of deciduous trees and shrubs the building would be uneconomical to build.

Other considerations are that Batts are more expensive than the blown in insulation and things like increasing the eaves width and increasing the roof pitch will cost more than conventional methods.

In the end the choices will be made which will affect the house in a particular climate zone and the money they have to spend.


Conclusion

All of the information above will help make a building more energy efficient but as stated earlier the main decision will come down to an economical choice. Most of the suggestions offered in this assignment are mostly dealing with hot temperatures as it is a fact that most of the construction in Western Australia is done in a moderate to high temperature range. Many of the things like planting deciduous trees are not very costly and with a bit of forethought before construction a house can become much more energy efficient.


Bibliography

 Þ Building Code of Australia

 Þ Australian Standards

 Þ Building Construction Vol. 1



Back to Building Information Page