Heating and cooling

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Heating and cooling
Heating and cooling your home can be one of the biggest users of energy. Efficency in this area can
bring great savings. Heating and cooling depend on many contributing factors. The type of heating
and cooling you choose, the design of your home, the spaces that can be closed off, the amount of
glass, draughts, orientation of the house, floor coverings, insulation.
The most efficient and cost effective way to heat a home is to use one or more space heaters or a
zoned central heating natural gas system.
When buying a heating system, carefully consider your household needs. There are a range of heating
systems and fuel sources with different purchase and running costs and energy efficiency levels.
Consider factors such as:
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the size and function of the space to be heated
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how many people use the space
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how often you expect to use the space
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cost of purchase and ongoing maintenance
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energy efficiency requirements
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Where you live – how many days of the year are you likely to need heating?
Choose heaters with:
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the highest energy star rating (the more stars the more efficient and the less it will cost to run)
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a system that can be zoned to only heat the rooms being used
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thermostat controls
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programmable timers
Once you have warmed your home it’s important not to lose that heat or re-heat it too often.
Insulation
Insulation is the top way to increase thermal comfort in a home in most Australian climates. There
are several kinds of insulation, made of different materials. Regardless of what they’re made of, their
effect can be easily compared by the R value.
The R value is a measure of how much a piece of insulation resists heat transfer. The higher the
value, the longer it takes heat to cross the insulation barrier – so the higher, the better. The R value
depends on the thickness of the insulation as well as the material it’s made of, so a polyester batt
that’s thick will have a higher R value than a polyester batt that’s thin.
More technically, the R value is measured in metres squared per degree of temperature difference
(between the two sides of the insulation) per watt of heat flow across the material. It’s the exact
inverse of the U value, which is most often used for measuring how much heat transfers through
windows and similar. The U value describes how many watts of heat transfer through one square
metre of a specified thickness of material for every degree of temperature difference between the
two sides.
Many building codes now specify minimum insulation levels for new houses.
Quick facts on insulation:
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Insulation is the single most effective item you can add to your home to improve its energy
efficiency.
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Installing or topping up insulation in ceilings can save a household over one tonne of
carbon each year.
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For every square metre of floor space, an uninsulated house like this one needs 130W
of heating. Ceiling insulation reduces the power needed for heating to 100W per square
metre, saving them almost a quarter of the power.
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A well insulated, energy efficient home will keep your home up to 10ºC cooler in summer
and 5ºC warmer in winter.
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Insulating a home can save 45-55% of heating and cooling energy
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Uninsulated ceilings, walls and floors can account for 70% of total heat loss from a home.
n Your Home technical manual on insulation
www.greenhouse.gov.au/yourhome/technical/fs16a.htm
n Sustainability Victoria on insulation
www.sustainability.vic.gov.au/www/html/1973-energy-saving-fact-sheets.asp
Thermal mass
Thermal mass refers to the amount of material present that is able to absorb and retain heat.
Metals transfer heat quickly even though they’re heavy, so they count for less thermal mass.
Plastics can absorb heat, but they’re light weight, with little mass to them. Stone, brick,
concrete, earth, sand and water are all substances that tend to provide high thermal mass.
This is why towns by the ocean have less daily variation in temperature than towns inland
– the ocean acts as a moderator.
In general, houses in hot climates are better with less thermal mass, so they can cool down
more quickly overnight. Houses in regions where the temperature goes through big daily
variations are better with more thermal mass, to slow the temperature change inside down
and keep from either heating or cooling too much. Houses in cool climates can benefit from
additional thermal mass in the right places, to maintain warmer conditions inside overnight,
but this can also mean they take longer to warm up inside.
A stud wall has very little thermal mass, so it heats up quickly and cools down quickly – it’s
very environmentally responsive. In contrast, a brick wall absorbs a lot of heat before any
gets passed through, meaning the inside of the house stays cool for longer. And after the
sun’s stopped heating the wall, it will continue to slowly release heat over a long period,
meaning the inside of the house stays warmer at night.
You can retrofit thermal mass in several ways:
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Move books and bookshelves into the room – books are quite heavy for their size
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Place bricks or concrete blocks along the wall
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Put some large sealed containers of water in the room
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Create a Trombe-Michel wall near the windows, using bricks, sealed water containers
such as wine or beer bottles, or containers of damp sand.
n Your Home – thermal mass
www.greenhouse.gov.au/yourhome/technical/fs17.htm
n Sustainability Victoria – thermal mass
www.sustainability.vic.gov.au/resources/documents/Thermal_mass.pdf
Draught proofing
Draughts and air leaks in a house increase the amount of air that needs to be heated and
cooled. Sealing draughts is cheap and simple. Draught proofing typically earns its cost back
within two or three bills.
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Ideally, the air in a house should change, once every two hours at normal atmospheric
pressure to stay sufficiently fresh. Australian houses are typically very leaky. This means they
heat or cool two or three times the amount of air they need to. Common sources of air leaks
include exhaust fans that don’t self-seal, recessed light fittings (particularly gimball fittings
for halogens), gaps between floorboards, gaps around plumbing pipes, windows and door
frames. Even power points and light switches will often contribute tiny air leaks. Ironically,
wall-mounted air conditioners can be a large leak as well.
n Air movement
www.sustainability.vic.gov.au/resources/documents/Air_movement.pdf
Temperature of your heating
Ideally set your winter heating to between 17 – 19 degrees. Every degree above that will cost
you an extra 10 per cent on heating bills .
Use the timer on your heating and turn it off when you leave the house.
Zoning your heating. Modern systems have a way for you to zone your heating. The living
areas are generally set to a little warmer than the bedrooms. Zoning can also be achieved
with older systems by half closing the vents in the bedrooms and leaving them fully open in
the main living areas.
Closing doors. Smaller spaces heat more quickly than larger spaces. Keeping door closed
and areas separated increase the efficiency of heating and you don’t pay to heat areas you
are not using.
Reflection of radiant heat
30% of wall mounted radiator’s heat is lost through the walls and if the units are placed on
an external wall that heat is lost to outside. But it is possible to reflect radiant heat, just like
light, so putting reflective panels behind wall mounted radiators can increase efficiency of the
system overall.
Inside and outside temperatures
An indoor-outdoor thermometer is a cheap way to save on energy bills. It can tell you the
best time to open or close up your home.
If the aim is to keep cool, the house should be shut up once the temperature outside starts
warming up in the morning – curtains pulled, windows and doors closed. In the afternoon,
don’t re-open the house until the temperature outside falls lower than the temperature inside.
As soon as it drops below, opening the house will help it lose any extra heat it’s gained.
If the aim is to keep warm, the reverse applies – have your home open during the day to take
advantage of the sun’s heat and light, but close it up as soon as the temperature outside
drops lower than inside, to conserve your heat.
Window glazing
The amount of heat lost through single glazed windows can be ten to fifteen times greater
than through the wall. Double-glazing puts a sealed air gap between the two panes of glass.
The trapped still air is an insulator hindering heat passing through it. Double glazing can
stop around 35% of heat loss in winter and around 10% of heat gain in summer. These
percentages can be increased by using different special kinds of glass.
Curtains with pelmets can also stop about 25% of heat loss from a window. See the
Windows Fact Sheet.
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Orientation of the house
Orientation of your house should not be underestimated especially if you want to take
advantage of heating from the sun. In most parts of Australia kitchens and living rooms
should be located on the north side of the house with bathrooms and laundries on the west
side, to act as a buffer from the hot afternoon sun. By grouping together rooms with a similar
use, you increase the efficiency of your heating and cooling
Choosing a cooling system
When choosing a cooling system it is important to consider the right system for your home
– think about
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The size of the area you want to cool – is it a small space, a whole room, a few rooms or
the whole house?
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The features of the space – is it draughty or well insulated? How high are the ceilings?
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The frequency and duration of cooling required – does the space need to be cooled all
day, every day or just at particular times?
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Where you live – how many days of the year are you likely to need cooling?
Air Conditioning
Air conditioners can be one of the largest energy users in our homes and have high purchase
and running costs.
In your car, using air conditioning in your car increases your fuel consumption by 5-10%.
At home, typically air conditioning uses between 1000 and 2000 watts to run. Ceiling fans on
the other hand use about 70 watts, about the same as a normal light globe. Ceiling fans are a
far more efficient way to cool a house.
When selecting an air conditioner, look for:
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Programmable timer and thermostat controls. Set your air conditioner at the highest
temperature setting at which you still feel cool enough, 25ºC is usually adequate. Each
1°C increase of the thermostat setting will save about 10% on your energy usage
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Movement sensors, which reduce power and energy usage when the room is unoccupied
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'Set-back' and 'sleep' modes that automatically adjust thermostat settings
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Economy settings
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Multi-speed fans
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Adjustable and rotating louvres
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Remote thermostats and control
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Inverter technology
Search and compare the energy efficiency of air conditioners before you buy –
http://www.energyallstars.gov.au/products/air_conditioners/
Ceiling fans
Ceiling fans are very cheap to run. Many people don’t realise they can be used for both
heating and cooling.
Cooling is obvious – as anyone who’s stood in front of a fan knows, a stiff breeze makes you
feel cooler. It doesn’t actually make anything more cold, but it takes heat away from your skin
faster which helps you cool down more quickly. That’s why fans only need to be on when
you’re in the room, because it’s not actually changing the temperature of anything but
your skin.
Fans can also assist in heating. The blades are designed to draw air upwards, creating
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a draught. The reason it’s upwards is to draw warmer air away from you, so that the air
moving past you is the coolest in the room. If the fan’s direction is reversed, it will create a
draught by pushing air downwards. In winter, this means that warm air that’s collected near
the high ceiling is pushed back down to ground level, keeping the air temperature in the room
more even.
Fans set into high ceilings such as at the Barries’ or McSweeney-Glenwrights may need to be
switched from summer to winter direction by remote-control. They may also need their height
adjusted for the most efficient heating and cooling.
There are many reversible fans available on the market – a net search for “reversible fan” will
give many results.
The heat shifter
Hot air rises and cold air sinks. As hot air rises, it pulls cold air through any gaps around
doors and windows, creating constant cooling. Draught-proofing prevents this. Verne’s
home-made venting system had two flaws. It wasn’t big enough to pull enough warm air
through and it opened out at the kitchen ceiling so the warm air never got down to ground
level. The Cops increased the width of the intake vent and set new outlets into the floors.
The venting system was extended through the ceiling and floor and a ‘summer/winter’ switch
installed. In summer hot air will be vented outside. This hot air will draw cool air up from
below – in this case, from the airspace right below the house creating a cooling effect so the
family won’t need air conditioning. If there is no gap under the house cool air can be drawn
from low down near the ground, from shaded gardens and cool south-facing courtyards, or
from near water features. Air can also be drawn in through pipes buried 20 cm underground,
using the low and stable ground temperature to cool the air before it enters the house.
n Heat shifters – Sustainability Victoria
www.sustainability.vic.gov.au/resources/documents/Heat_shifters.pdf
n Passive cooling and air movement from Your Home
www.greenhouse.gov.au/yourhome/technical/fs152.htm
n Heating and cooling from Your Home, including heat shifters
www.greenhouse.gov.au/yourhome/technical/fs44.htm
© ABC Copyright 2007
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