Measures Taken to Improve Energy Efficiency
Bruce Barbour - July 2019 - Updated February 2020 & August
A brief overview of my house construction and measures taken and
features installed that impact on its thermal efficiency and the
total energy used in the house. For comments on actual
household energy use refer to the Photovoltaic
Site and orientation
There are a couple of reasons I did not choose a larger block which would have allowed full passive design. Firstly larger blocks in the area that I was interested in were more expensive - and I was on a budget. Secondly the larger blocks on the subdivision had minimum house size covenants meaning that I would have had to build a house at least 50% larger than I wanted. This would add considerable expense. The last reason is that I did not want to have to maintain the grounds of a larger block. Refer to the Subdivisions page for further commentary on issues relating to subdivisions.
Given that I had chosen this non ideal block I had to make the
best of it. I located the living rooms to the North facing rear of
the house and the bedrooms and service rooms to the South facing
front of the house. Consequently the house is designed so the
living rooms at the rear of the house benefit from solar access,
and bedrooms etc. at the front of the house getting little direct
See below for reflections on how the design could have been changed to allow solar access to the front bedrooms.
Because the site slopes to the rear two different foundation types are used. The front of the house is constructed on a concrete waffle pad sitting on the ground. The rear of the house is constructed on a suspended concrete slab. It is insulated under the slab with R4 insulation. The floor slab is the main thermal mass in the house.
The walls are a timber framed with rendered 50mm thick Hebel panel veneer. Hebel is manufactured as Autoclaved Aerated Concrete (AAC). It has a lower weight and a higher insulation (R0.5) compared to brick. I also used R2.5 polyester batts between the wall studs bringing the total wall insulation up to approximately R3. The walls are painted a light colour.
Double glazed windows. There is an inert gas (argon) between the panes which adds a bit to the insulation of the windows. Also a low emissivity (Low-e) coating on one of the glass panes. The window frames are Aluminum. The windows and the doors have excellent weather seals on them, lowering infiltration. I have used casement windows where possible which will allow the maximum ventilation rates when opened for summer cooling.
There are two 2.0 metre high by 1.8 metre wide windows / glazed door on the north facing rear wall of the house. These windows are the primary windows for controlled solar access to the house. The windows are under a shade structure designed to allow solar access during winter and to block it during summer.
Three of the east or west facing windows are fitted with roller
shutters to block the sun during summer. No roller shutters on
other windows. Note that there are no eaves on the house.
A note on Low-e window coatings: There are different
formulations of Low-e coating.
(1) Some coatings will lessen emissivity and transmission across a wider section of the electromagnetic spectrum.
(2) Others coatings will mainly lower the emissivity in the infrared section of the radiation spectrum.
If you are using the low-e coating on all windows, including the
north facing windows in a house that uses passive solar principles
the aim is not to block transmission of light on the way
into the house but to block the transmission of infrared radiation
on the way out of the house. So it is the second type of Low-e
coating that is to be preferred in this case - (2) above.
The type (1) coating is sometimes used to lessen solar ingress on East and West windows. However it is not sufficient to do this on its own - East and West windows should be minimised in size and need to be shaded in summer. However I recommend the used of type 2 Low-e glass in all windows rather than trying to mix and match - sure to end in disaster.
Be careful when ordering windows with Low-e coatings - get the
type you need. Even some window retailers don't have a good handle
on Low-e coatings and their uses.
The roof is a light coloured Colorbond corrugated metal roof. The light colour should assist in maintaining cooler temperatures during summer. It is underlain with one layer of reflective foil.
I used two layers of R3 polyester batts (total R6) in the
ceiling, although the contractor that installed them did not do a
very good job meaning that R6 may not be achieved over all of the
ceiling.I will endeavour to fill the gaps but clambering about in
the roof cavity is not easy.
The house itself has an energy rating of 7.2 stars and uses some passive design principles, although full implementation of passive design was restrained by site restrictions, as stated earlier. Effectively the rear of the house uses passive design principles, the front of the house is just well insulated. The floor size is 130 sqm, not including the attached single garage. This is a lot smaller than most new housing which aids in limiting energy usage.
A 4.3 kW photovoltaic (PV) system was installed at the start of
March 2019. See the separate article
on the photovoltaic system for further details.
There is no gas connected to the site so all heating, cooling and
cooking is by electricity (or passive solar gains for some
Primarily used batten fix lights for main room lighting. Most contain light emitting diode (LED) light bulbs, although there are some compact fluorescent lights (CFL) in low use rooms.
I did not extensively use downlights. Even though LED downlights were available when I built at that stage they still could not be covered by insulation which meant that there had to be holes in the ceiling insulation around the downlight which would result in heat loss in winter and heat gain in summer. Now there are IC rated LED downlights that can be completely covered by insulation. However I still prefer the look of batten fix lighting.
There is a solar powered "skylight" in the laundry. This has a small PV panel (separate to the main PV system) which powers a square (300mm x 300mm) LED ceiling light. The amount that this is lit depends on the amount of sunlight hitting the dedicated PV panel. It works well and looks like a standard skylight without compromising the ceiling insulation.
Daiken reverse cycle split air conditioner - 900W input energy - was installed. It heats / cools the living room areas. There is no heating or cooling for the bedrooms.
The Daikin reverse cycle system installed was smaller than
recommended by the installation company - who suggested 1.5 kW
input energy. I had done the calculations on the house heating
energy usage and had determined that 900W input energy was a
sufficient size. This has so far proven correct. Of an evening
once the room has reached temperature it operates using between
200 to 300 Watts. Of course due to the coefficient of performance
(COP) of the heat pump air conditioner the amount of heat
delivered into the room may be 3 or 4 times the input energy.
If the house has been unattended for a number of days and the thermal mass (mainly the floor slab) has cooled then the reverse cycle air conditioning system can struggle to bring the room quickly up to temperature - not an issue most of the time. I also only heat the main living area and not the bedrooms - a closed door slows the loss of heat to the rest of the house. I insulated (R1) the walls between the living area and the rest of the house during construction. I set the temperature of the air conditioner to about 20 degrees (winter) in the living area in the evening which is fine for me so long as I have a jacket on, but may be too cool for some. Often I find 18 degrees is adequate in the morning (winter).
During winter on most days I use 3 to 4 kWh hours more than I use during a summer day that requires no cooling. So this is the average amount of energy that is used for heating in winter. Some of that 3 to 4 kWh would come from the PV system if there is some sun during the day. Because it only chugs along at about 300W once the room is up to temperature on most days, even on fairly overcast days, the 4.3kW PV system will be supplying more than that. But in early morning and into the evening the PV does not provide any power and the system is running off grid power.
Up until now (August 2021) I have not had to use any energy for
cooling over a number of years - apart from two hours running when
I turned it on to see that it worked in cooling mode!
Windows are the weak link in a house's thermal performance. Even with double glazing it is likely a window without curtains would have an R value of under 0.4. This compares to a typical wall which in newer houses should have an R value of over 2.0. The R value of may walls would be around 3.0. Even with double glazing the R value of windows is still less than 20% the value of the wall's R rating. This means that the conductive heat flow through a square metre of window would be five times that of a square metre of wall. Adding curtains and pelmets will increase the R value of the window by a couple of points when closed. However while the overall R value will still be substantially less than walls, it is a worthwhile improvement, which can be very cost effective.
pump system from Sanden. For further information on the hot
water system see the Photovoltaic
page. I added additional insulation to the water pipes
running between the heat pump and the tank. I insulated the
pressure relief valve on the tank making sure not to disrupt its
operation (very important).
I added additional insulation to the hot water supply pipes from the tank to the tap, where possible. I have also added more insulation to the tank to lessen the tank's direct heat loss.
The refrigerator I use is a LG 300 litre. It is rated at 4 Stars
with a rated energy use of 279 kWh per year, an average of about
0.75 kWh per day - though I measured a daily consumption of 0.66
kWh with my power meter - that may have been due to the
measurement being taken in winter. It was about 6 months old (at
It is interesting to note that my previous fridge was rated at
over 500 kWh per year and only had a storage volume of 200 litres.
It was over 20 years old when I changed it over. I changed it over
because it seemed to be running nearly continuously and being so
old and inefficient it was not worth getting repaired.
Refrigerator technology has come a long way in twenty years. The
new fridge uses 50% of the power of the old fridge and is 50%
larger. Even considering embodied energy it is probably worthwhile
upgrading if the fridge is old. Financially it should pay back in
under ten years.
I use a front loading washing machine on cold setting. This is
quite efficient. If I used hot water the energy usage would be
many times that of the cold setting. (I did measure it once but
have forgotten the figures.) The machine has an internal
water heating element so the energy usage would be high if I
wanted to have a hot wash.
I try to dry the clothes on the outside clothes line though in winter this sometimes does not dry the clothes 100%. In winter I usually have to hang the clothes up in the living room for a day or two to finish drying. I have a tumble dryer but rarely use it.
I don't have a dishwasher at present. I wash the dishes by hand
in the sink. This would be quite energy efficient as the hot water
used comes from the heat pump hot water system largely powered by
the PV system. Most dishwasher machines I saw when I investigated
this a few years ago had an internal heating element, so bypasses
the heat pump hot water system. If I used the machine on a sunny
day most of the power should come from the PV system (depending on
power draw) which is a bit better but energy use would still be
more than sink washing, even if more water was being used in sink
washing (as claimed by the dishwasher machine manufacturers). I
may still get a dishwasher in the future for the undoubted
convenience. I will see.
A two kilolitre water tank was installed under the rear decking during construction. The tank supplies water to the toilet cisterns and the garden taps, utilising a.small electric pump. Installation of a water tank was mandated by regulation - a new house has to have a gas boosted solar hot water system if the house is in area that has reticulated natural gas. This means that gas usually has to be connected to new housing and often is gas is connected then gas heating and cooking are probably also going to be used, even though they don't have to be. If the owner wants to avoid having natural gas connected, i.e. to have an all electric house, they have to install a minimum 2 kL water tank - which is what I did. This is a very strange regulation as the natural gas connection and having a water tank are totally unrelated.
If the regulation was not in place I may not have opted for the
installation of a water tank - the economics, the pay back period
for water tanks, is really quiet poor. However now that I have a
tank it will save some water and means I will be able to water the
vegetable patch over summer with a clear conscience, while the
tank water lasts. Also as Victoria is running the desalination
plant, which is energy intensive, saving water use will also be
saving overall electricity consumption. If the tank water runs out
it automatically switches over to mains water.
Security system - I had a security system installed in the house. This was a decision made on the run with no investigation into the best system. The house had been broken into during construction and many items taken. Consequently I asked the electrician to install a security system. It was only after installation that I discovered that it uses 18 Watts of power. This would have been fine if it was just using this power while the system was switched on and doing its job of detecting intruders. However it uses 18 Watts 24 hours per day whether on or off. This amounts to 0.43 kWh per day. It is approximately 50% of my total "phantom" load of around 36 Watts. Unfortunately it would be too expensive to replace with a more efficient system or at least one with a lower standby power use. It is disappointing to me that companies are still allowed to sell system with such high standby power loads. It is clear to me that the companies won't address this issue by themselves so there needs to be regulations in place to tell them what to do.
My other phantom loads are from the PV system (using 5W after the sun goes down) and the television, recorder/DVD player and washing machine. Also two security lights on sensors and two hard wired smoke detectors.The total phantom load of 36 Watts amounts to over 0.8 kWh per day which is often greater than 10% of my daily energy usage in winter - 20% in summer and the shoulder seasons - reasonably significant. I will endeavour to address this usage by turning appliances off at the wall where possible. (I can't turn off the security system at the wall socket when it is not needed as it has battery backup and will trigger the alarm if it looses power for a time.)
Heating system - I elected to go with a quite small reverse cycle air conditioner (heat pump) for the living room. While it works OK if I was building again I would probably go for the next size up. A larger unit would heat the area quicker which would be a small advantage if coming back to the house after having been away for a few days. It would also allow me to open the door to the rest of the house and provide some level of heat to the whole house. The other reason is that heat pump heaters are more efficient when they are working at a lower level - just chugging along. (This applies to inverter systems which most air conditioners are these days. Do not buy a non-inverter air conditioner.) So a bigger unit would be working at a lower level for a longer period of time and may therefore be more efficient overall. The cost to go up one size is usually not that great.
I may also put in a multi-head reverse cycle air conditioner to
allow heating in the bedrooms, if required.
Hot water system - It is interesting that even on days
when I don't use any hot water, the hot water system still uses
between 0.75 and 1 kWh of power during winter. The energy use will
probably be less in summer. The energy use must be due to heat
losses from the tank during the day and night.
In my situation each shower per day adds between 0.75 and 1 kilowatt hour to energy use, so decreasing the amount of hot water used per shower can have a significant effect. I measured (with a bucket and stop watch) the flow rate from the shower head that I am currently (July 2019) using at 6 litres per minute. This is higher than the flow rate at a previous residence, with a different shower head, which I measured at 4.5 litres per minute - and I still got a satisfactory shower. That shower head was a cheap head - at around $20 - from Bunnings. I will try to decrease the flow rate from my current shower head by blocking some of the water delivery nozzles. I am hoping to be able to block at least a quarter of them without adversely effecting the feel of the shower.
Note on shower head rating: Both of these shower heads were
rated that 9 litres per minute - the legal maximum. This rating
relates to the maximum flow rate and not the flow rate at which it
is possible to have a nice shower. I would think that few people
would have a shower with the flow rate set to the maximum - I
certainly don't. Consequently I doubt the usefulness of buying a
7.5 litres per minute rated shower head. These usually sell for
prices much higher than warranted and would not guarantee (unless
they specifically provide the guarantee) that you would end up
using less hot water than a cheaper shower head. However if you
have someone in the family that insists on turning the shower
water flow up to the max. then it would be a worthwhile investment
- if education does not work.
Hot water pipes - during construction the plumber installed a line of hot and cold water pipes down the centre of the house for the whole length of the house and then ran branch line to each of the taps. This approach may be alright for cold water but would have been very wasteful for hot water as the hot water would have to run through many additional metres of pipe to get to the tap. I pointed this out to the plumber and he changed the arrangement. However the layout of the hot water pipes is still not optimal. Ideally the hot water pipe should run to each hot tap by the shortest possible route. And the smallest allowable and practical pipe diameter should be used.
Floor tile colour - the tiles in the living area are light coloured. Ideally for passive design the floor tiles in areas that receive sun light onto the tiles should be black or a dark colour. The dark colour would allow more solar energy directly heating of the concrete slab during the day meaning the slab would be warmer going into the evening. With light colour tile a greater proportion of the light is reflected off the tile. This reflected light would more heat up the room during the day, and less for direct slab heating. This is OK so long as the room does not get too hot. However it means the slab will be cooler going into the evening.
Window frames - the window frames are unbroken aluminum.
Aluminum has high thermal conductivity which is not ideal. I can
feel how cold they are at night during winter. Perhaps I should
have used a broken aluminum or even timber would have been better
(though it requires maintenance over time). However the window
energy rating site (WERS) does
not indicate a large energy efficiency difference between
thermally broken and unbroken windows - so perhaps it is not that
much of an issue.
The window shade structure at the rear of the house was installed lower than I wanted. However because the levels were not documented in the house construction contract document there was nothing I could do about this - without large expense. It means that I lose about 150 mm of solar access through the northern windows during winter which is regrettable but certainly not disastrous.
The roofing material is a light coloured (Classic Cream)
Colorbond corrugated steel. This is good for summer but probably
adversely impacts the house in winter. As Melbourne is primarily a
heating climate it may have been better to go for a darker roof
for better winter performance. It would also have allowed me to
experiment with blowing heat from the roof space on sunny winter
days to warm up the front section of the house. However I do
prefer the look of the light coloured material and is better for
the Earth's albedo (the amount of solar that is reflected).
I chose not to use eaves as I was using other methods to
control sunlight shining directly into the house - the rear shade
structure on the northern windows and light coloured roller
shutters on the east and west windows.
There is a fluorescent tube (36W) in the garage. On
reflection I could have installed batten fix LEDs instead of the
fluorescent tube. This will be overcome when LED replacement tubes
become more widely available.
In the bathroom and en-suite I installed those IXL Tastic
combined, light, heat lamp and exhaust fan. These require a
massive hole in the ceiling insulation. For the next house I
would install a separate batten fix LED lights and exhaust fans.
For heating I would install either a wall mounted radiantly bar
heater or radiant panel.
The water tank is currently only connected to two roof
down pipes. It would be relatively easy to connect a third down
pipe. (A fourth down pipe would be more difficult but doable.) If
done this would have no impact on winter water collection - there
is an excess to requirements with only two down pipes - however it
should extend the availability of tank water over summer.
As mentioned the bedrooms at the front of the house do not get any solar access. Consequently in winter they are quite cold, too cold to be used for any length of time during the day. This could have been addressed if I had been willing to consider using a split level design. The site slopes from the front to the back so it could have been possible to have the floor level of the rear of the house at a lower level than at the front. This would have allowed the placement of windows in north facing wall of the raised front of the house. However it would have meant having stairs between the two sections of the house which I wasn't keen on. Another possibility would be the use of clerestory windows for the front section of the house - a feature that again I am not keen on.
Considering that I did not do this, if I want to use these
bedrooms for other than sleeping in winter I would have to install
auxiliary heating - probably a multi-head split reverse cycle air
conditioner. This can still be done post construction though I
have no plans to do it at the moment.
It is highly noticeable the difference in the temperatures
between the rear section of the house that gets passive solar
gains and the front of the house that doesn't. Using passive
design features is worthwhile if an appropriate house block can be
purchased. But these blocks are typically rare and subdivision
developers usually do not consider the needs of passive house
design when land is subdivided.
I learnt a lot from the construction of the house and I am happy
with its performance. However on reflection there are a number of
different choices I would make if I was building again.
So this is what I would do:
There is a lot of concrete used in the construction of my house -
the slab on ground and the suspended slab - and also the Hebel
(Aerated Concrete) wall panels. The production of cement and
concrete has significant carbon dioxide release associated with
it. I would seek to limit the use of concrete, including not using
Hebel panels and not using a concrete floor slab, if I was to
build again. I also find that the concrete slab feel cold in the
front of the house and hard on the feet. Walking around with bare
feet is not as pleasant as on timber floors.
I would construct largely with stud timber walls, clad with timber board as cladding. I would go for 140mm wide studs on external walls instead of the standard 90mm studs. This would allow more insulation in the external walls. The flooring and foundation system would also largely be timber with a lot of bulk insulation. However having some thermal mass is important for passive solar design - at least at present. I would achieve this by having internal dividing walls in rooms that receive solar insolation constructed of recycled brick - painted or hard plastered or left natural depending on owner preference and the quality of the recycled brick. There would have to be some concrete used for the foundation of these walls and cement in the brick mortar. The brick dividing wall could be built on steel stumps with steel cross beams.
I would increase the size of the North facing windows, not by a huge amount but a bit. And if I decreased the amount of thermal mass in the Northern room, as suggested in the paragraph above, then perhaps no increase is necessary. I would decrease the size of the windows on other orientations - again only a marginal decrease in size.
For the windows I might opt for uPVC window frames (or timber). Thermally broken aluminium would also be good but has been very expensive in the past.
The North window shading could have been better built to shade the window in summer and allow the sun in in winter, as previously mentioned.
The utility of thermal mass is interesting. Current passive solar
house design orthodoxy says that thermal mass is vital for an
energy efficient house. However I wonder whether this will remain
the case as the cost of batteries and solar panels falls. Thermal
mass can be expensive and can have a high embodied energy (through
recycled bricks - bricks used in previous now demolished buildings
that would otherwise be wasted - and mud brick would not have high
embodied energy.) At some point, which is probably not now, it may
become more cost effective and energy effective to install (more)
batteries and panels, and have reverse cycle air conditioning to
keep the house cool or warm. Passive design principles would still
be used but mainly aimed at keeping the house warm during the day
- correct orientation and north facing windows would have to be
smaller than typical passive design with thermal mass. The windows
would still be shaded to keep out summer sun. The house would
still be well insulated and weather sealed. However this design is
probably not viable at present.