Frequently Asked Questions
What are the “BER” ratings?
BER’s (Building Energy Ratings) indicate how much energy your house is likely to use for heating, hot water, lighting and ventilation during a typical year. The ratings are given in kilowatt hours of primary energy (kWh(P)) per square meter per annum. The groupings used are as follows:
Less than
25
A1
Greater than
25
A2
Greater than
50
A3
Greater than
75
B1
Greater than
100
B2
Greater than
125
B3
Greater than
150
C1
Greater than
175
C2
Greater than
200
C3
Greater than
225
D1
Greater than
260
D2
Greater than
300
E1
Greater than
340
E2
Greater than
380
F
Greater than
450
G
You can see from this that an A rated house can be expected to use less energy than a B rated house…. etc. These figures do not represent the actual amount of energy that will be used because:
a) the actual amount of energy used in any one year depends on actual weather during the year and actual use of the house…. both of which will vary considerably from year to year and family to family; and
b) the energy rating is given in units of primary energy, not units of energy consumed in the house
These ratings are assessed by certified assessors using a standard method called DEAP (Dwellings Energy Assessment Procedure).
Ideally this procedure should be carried out several times during the design of new houses and apartments so that the energy efficiency of the design can be refined with reference to the BER throughout the course of the planning process.
What is the difference between primary & delivered energy?
Primary energy is the term used to describe the energy used to “deliver” useful energy into your house. With oil and gas, for example, energy is used pumping the oil and gas out of the ground and transporting it to your house.
The primary energy factors for oil and gas are 1.1… in other words one unit of energy used in your house involves a total of 1.1 units of primary getting it there (1 unit taken from the oil/gas reserve and 0.1 units getting it there).
Much more primary energy is needed to deliver electricity to the household because of losses in the power stations and from the cables and transformers that carry the electricity from the power stations to the household.
The primary energy factors for electricity is 2.7… in other words one unit of energy used in your house involves a total of 2.7 units of primary getting it there (1 unit taken from the coal/oil/gas reserve and 1.7 units turning it into electricity).
How does insulation work?
Heat energy is transferred from one entity (inside air, for example) to another (outside air, for example) by conduction, convection, draughts and/or radiation. “Insulation” reduces the rate of transfer of heat energy from the inside of the house to the outside. It does this by reducing conduction, convection, draughts and radiation.
Conduction is the transfer of heat from a warmer part of a solid material to a colder part of the same material. The rate at which this occurs depends solely on the thermal properties of the material itself. Materials in which this occurs slowly are described as good insulators. Wood is a better insulator than metal…. for example.
Convection is the transfer of heat within a liquid or gas resulting from movement of the liquid or gas as a result of thermal differences… typically warm liquid or gas rises and cold liquid or gas falls. This is reduced by stopping, or slowing down, the movement of liquid or gas within the material…. typically by filling cavities and attic spaces with material such as glass fibre, rock wool, real wool and so on.
Draughts are similar to convection except that the movement of the gas (air) is also caused by wind-induced pressure differences. These are reduced by sealing gaps, fitting draught proof membranes within walls and roofs and fitting draught proof seals around the edges of doors and windows.
Radiation is the transfer of heat from one material to another where the materials are not in contact. The rate of transfer of heat by radiation is related to the difference in temperature of the two materials, the surface properties of the two materials and the properties of the space between the two materials. The temperature of night sky is extremely low compared with the temperature of the roof of a house… so radiation heat loss from the roof of a house can be very high at night.
A key method to reduce radiation is to change the surface property of the material… typically by making flat roofs and outside walls smooth and “reflective” (silver or white). This is also achieved in low “E” (emissivity) glass by coating the surface of the glass with materials that reflect radiant heat back into the house and/or reduce radiant emissions from the outside of the glass.
What are the most important parts of my house to insulate (new & existing)?
The answer to this question is highly dependent on a lot of variables:
Size of the roof, walls, windows, floors etc.
Orientation, shading, external surface etc.
However, the following is a typical priority scenario:
The roof is probably the most important part of your house to insulate… because it is a large area and it is facing the sky which is very cold at night.
The walls, windows, floor and doors would then follow as the next important parts to insulate.
One recommendation is to get a qualified assessor to carry out a number of full Dwelling Energy Assessment Procedures (DEAP) for your house before taking decisions about insulation and similar procedures.
You could start off with an “as is” assessment and then re-run the procedure with various assumed improvements to see what results can be expected… both in terms of reduced energy consumption and improved energy rating.
How is heat loss measured?
Heat loss is measured in watts per square meter per degree. This is also known as the U-Value. If one square meter of a wall looses one watt of energy when the outside is one degree colder than the inside its U-value is one. The lower the U-value the better.
Single glazed windows have a typical U-value of 5.6.
Double glazed windows have a typical U-value of 2.8.
What are the main tasks involved in installing solar panels?
The first task is a survey to determine if there is a suitable place to put the panels. They need to be placed in an area that is shade free throughout the year, ideally facing due south and sloping towards the south at between 25º and 45°. They can be placed on a sloping roof, a flat roof or on the ground.
The second task is to work out how to hold the panels in place. This can be done using brackets on slated and tiled roofs, clamps on seamed metal roofs, and fixed frames or ballasted buckets on flat roofs and the ground. These are all specially designed products that should be sourced from experienced, competent suppliers. The alternative is to incorporate them into the roof or cladding structure… which is more complex as it involves invasive work on the weathering elements of the building.
The third task it to work out how to connect the system into the household circuits and/or plumbing system.
Solar PV simplifies this task, because this system connects into the existing mains wiring, usually at the distribution board, and is then distributed to existing appliances using the existing wiring.
With a solar thermal system pipes need to be installed running to and from the hot water cylinder and in most cases the hot water cylinder will need to be replaced. As the pipes between the panels and the hot water cylinder need to be as short as possible to prevent excessive losses, it may be necessary to relocate the hot water cylinder and to re-route existing plumbing.
The roof is not suitable for solar panels – what are alternative locations?
The solar panels can be placed in any un-shaded space… on the roof, against a wall, on a garage, on the ground. Solar PV systems can be located remotely as there are very little “line losses” if they are properly designed.