TOWARDS ENERGY NEUTRAL?
Well the jury is still out but after 8 years of living Off the Grid, I think we're getting close! After a concerted effort to retrofit an inefficient 1930's weatherboard house into a super energy efficient, minimal impact dwelling with zero heating and cooling costs, there is still more to do but the progress so far is worth sharing.
A brief history....
In 2007 we rescued and relocated a weatherboard house from Box Hill that was due to be demolished. The original dwelling had a minimal amount of additions to deal with the Australian climate conditions: ceiling insulation and some external blinds on the west wall but that was pretty much the extent of it.
We had the house trucked up to the property in Heathcote (about 120 kms from Box Hill) and basically plonked on the designated site. The original plan was to have the solar PV array on the house roof so the house was positioned with the front facing East to allow maximum solar gain on the North facing roof throughout the day. This aspect also avoids any direct sun into the bedrooms at the front of the house (except during Sunrise in high summer...which is quite nice to watch while lying in bed!)
As the house was basically cut in half, transported and "reconnected" on site, the house was very drafty in winter and a sauna in summer due to the gaps in the floors and the absence of any roof eaves. Those who visited in the depths of Winter in the early days will well remember shivering in the front of the fire with the wind howling through all the gaps!
The plan was always to make the house as energy neutral as possible aiming to keep the internal temperature at a comfortable 18-22 degrees all year round. Living 'Off the Grid' means energy efficiency is critical. We do not have the luxury of being able to switch on an electric radiator whenever a chill is felt or running a split system heating/AC unit in the middle of a cloudy spell in Winter so a lot of thought went in to making the house 'immune' to fluctuations in outside temperature.
The work begins....
How to achieve an energy neutral house? I'm no expert but there are several key areas that need to be considered and can be divided into 7 main categories.
1. Insulation (walls, ceiling, underfloor)
2. Shading (external windows)
3. Roof air extraction (including eave vents)
4. Draft proofing
5. Internal drapes and pelmets
6. Cross ventilation (for rapid cool down in summer)
7. Smart cooking and heating
1. INSULATION
This is the most obvious thing! Generally when old houses were originally constructed, little thought was given to insulation. At that time, insulation technology was minimal or non existent, energy was cheap and people just dealt with the extremes in the climate. Walls (and floors and ceilings) were never insulated which explains why there was often a fireplace in every room!
Retro-fitting an old house with decent insulation is not for the faint hearted but its possible! Insulating a roof space is a fairly simple (but messy) job but when it comes to walls and underfloor, now that's a different kettle of fish! Fortunately in our case, when the house was relocated, it was jacked up above the (new concrete) stumps for a week or so. This made it (slightly) easier to get under the house and fix the insulation sheets to the bearers. We used FoilBoard panels that are readily available in Australia through their Melbourne supplier. The panels come in various sizes and are easily cut to size with a knife and simply nailed to the bearers using the special fasteners.
Wall insulating can be problematic and difficult. A weatherboard house has the advantage of having a fairly low thermal mass. This can be a positive or a negative depending on how you look at it. A low thermal mass means that the nature of a timber skin and thin plaster/gyprock walls means that the house will "breathe" easily. This can be a good thing when the sun goes down after a hot day but it also means that (without adequate insulation), it will heat up quickly in the summer and become an ice box in the winter.Due to the poor condition of the external paint work on our rescue house, we decided to remove every weatherboard wall by wall, insulate with Earthwool R2.0 wall batts and Ametalin SilverWrap. The hardwood weatherboards were replaced by (mostly) recycled Baltic pine boards sourced from various salvage yards in Heathcote and Melbourne.
These insulation improvements alone have seen a massive reduction in the amount of firewood burned during the winter which translates to less chainsawing, collecting, splitting, stacking etc.
Keeping the sun off external windows is crucial to maintaining a comfortable internal temperature. If you've ever sat in your car for even a few minutes in the full sun, you will know how quickly the internal temperature rises. Remember as a kid starting fires with a magnifying glass? Windows that have any exposure to the sun need to have a mechanism to stop the suns rays hitting the glass. Of course in winter, the suns rays through a north facing window can help maintain a comfortable internal temperature but a west facing window in full sun in high summer needs to be avoided at all costs. Internal curtains are good for shading the sun but if the sun's rays are hitting the glass then there is a problem.
3. ROOF EXTRACTION
With a well insulated ceiling and roof sarking foil under the roof sheeting, temperatures in the roof cavity can reach 50+ degrees on a hot day. This build up of heat will begin to force its way downward through the ceiling, eventually heating up the rooms below. In tackling this problem, I decided to install a powered roof extraction fan (Edmonds Airomatic) in the apex of the roof. This fan has a built in thermostat that switches the fan on when the roof space temperature reaches 30 degrees. The fan is capable of removing up to 647m3 of hot air per hour on full speed while using only 37 watts! At around $230 it's not cheap but super efficient. For optimum performance, it's recommended to install several vents in the roof eaves to allow cool outside air to be drawn into the roof cavity to replace the extracted hot air. I installed six 30cmx30cm vents in the east, south and west eaves.
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| Airomatic roof extraction fan. |
This is one overlooked area when it comes to energy efficiency, especially in the colder months. Leaky windows and gaps under doors allow cold air to enter rooms which undermines efforts to maintain a constant temperature. Make sure all windows and doors have adequate seals and close any external windows during the day to keep the cold air out in winter and the hot air out in summer. Wooden floors are also a culprit for drafts so underfloor insulation can also help avoid this problem.
5. INTERNAL DRAPES AND PELMETS
Block out drapes and pelmets on internal windows help not only keeping heat in but also providing an insulating layer of air between the glass and the drape or blind. Exposed windows can lose as much as 40% of a rooms heat during winter and in summer can multiply the intensity of the heat by the same amount. There has been a lot of debate about the merits of pelmets but the general consensus is that they are effective. Warm room air is drawn up from floor level behind the drapes and is trapped under the helmet, forming an insulating layer of air between the window and the curtains/drapes.
6. CROSS VENTILATION
One internal modification that we did to the house was to remove a small internal wall that was hindering the North- South flow of air through the house. After a hot day when the cooling breeze starts to come through, its essential to be able to open doors and windows on all sides of the house to allow this breeze to "flush out" accumulated heat and refresh the internal air. Needless to say, adequate fly screens are essential.
7. SMART COOKING AND HEATING
An often overlooked factor in maintaining a comfortable internal temperature is the use of cooking appliances such as ovens and to an extent stoves. Choosing appropriate meals that do not require lighting the oven in summer will assist in keeping the house cool in summer. Conversely, a slow cooking roast or casserole in winter may help keep the house warm. We use a slow combustion wood burning heater to heat the house in winter using salvaged wood from fallen trees in the nearby forest. This heater can also double as a stove to slow cook dishes during winter. Great for curries and casseroles!
CONCLUSION
After two fairly extreme summers and cold winters, we're now getting a picture of the impact all these improvements have made to the 'liveability' of house. There is generally an 10 to 12 deg difference between inside and outside temperatures in winter and summer with the temperature hovering around a comfortable 18-20 degrees most of the year. As can be seen from the photo below, Jan 17th this year was an absolute scorcher with an outside maximum of 42 deg at around 5pm. Notice that the inside temperature remained at 29 deg which is not super comfortable but a lot better than 41.8 deg!
One thing I should mention is that we managed to source from Ebay, a very efficient split system AC unit that only consumes around 480 watts when set at 23 deg with a medium fan speed. In good sun conditions, the solar array will generate more than twice that amount of power and allows us to run the unit on days of extreme weather completely free of charge and with the battery bank still fully charged!
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| The trusty ALDI indoor/outdoor thermometer. |
