Dec 24, 2014: December Results

Energy Positive with Renewable Energy

We’ve been living in and monitoring the Greeny Flat for 8 months now. A basic table of the results so far can be found on our Results Page. Looking at the Results Table you’ll see that we have now exported a total of 836kWh of electricity from the grid and we have exported 2652kWh to the grid. This means that we have put more than three times as much energy into the grid as we have taken out.

Given our original goal of trying to be energy positive this is a fantastic progress report. It seems pretty clear now that by the end of a full year of monitoring we will be way beyond energy positive. It’s exciting to think that we might even have enough excess energy to be able to run our house and charge an electric car and still be energy positive.

Water efficiency

Thanks to a VERY wet month of December we have been able to use a lot more tank water (5468 lt) than town water (1364 lt) this month so our overall usage of tank water and town water for the 8 months so far is almost exactly the same (28382 lt vs 28378 lt).

Our original goal was to try to use at least as much harvested rainwater as town water over the first year so we are exactly on track. We still have an almost full tank so we’re looking good for the moment. As you can see from the Results Table, our usage of tank water and town water varies dramatically from month to month depending entirely on how much rain we get in the month. For example, November was a very dry month so we used much more town water than tank water (the opposite to December). It’s also interesting to note that in the warm, dry months we also use a lot more water altogether. This is because in warm and dry months like October and November this year we had to do a lot more watering of the vegetable gardens and fruit trees. By comparison, in December the rain did a lot of the watering for us so our total water usage was lower.

Water conservation is also an important goal with the Greeny Flat. So far we have used a total of 56,760 litres which works out to an average of 233lt/day. This sounds like an awful lot of water. However, according to this Sydney Water Report from 2013, an average dwelling in our region uses 623lt/day. Unfortunately it proved to be very difficult to find figures on average daily water use per person. Nevertheless, we’re using less than half as much water per day as an average household in our region. And, in fact, we’re taking less than a quarter of the average out of the town water supply because, so far, half of our water has come from the rainwater we have harvested from our roof.

Our water conservation strategy is a combination of low-flow fixtures ( taps, toilet, and shower head), low-water-use appliances (the only water-using appliance we have is an Electolux EWF1074 washing machine with a 4.5 star water use rating and we wash dishes by hand), water-wise landscaping (plants and grass that need very little watering), and good water conservation habits like tapping short showers and not leaving taps running unnecessarily.

Comfort Levels

Over the last month the air temperature outside the Greeny Flat ranged from 7.6degC up to 41.3degC. That’s a swing of 33.7degC! Meanwhile the temperature inside only varied between 18.6degC and 28.5degC, a swing of only 9.9degC. This tells us that the Thermal Mass of the concrete floor is doing it’s job perfectly of moderating temperature fluctuations inside a Passive Solar Home.

Graph showing the indoor and outdoor temperature fluctuations in summer at the Greeny Flat

Graph showing the indoor and outdoor temperature fluctuations in winter at the Greeny Flat

The two graphs above are taken from our weather monitoring equipment which records many factors, including the indoor and outdoor temperature fluctuations. These demonstrate very elegantly the way that the indoor temperature in the Greeny Flat stays comfortably within about a ten degree band both summer and winter despite the fact that the outdoor temperature fluctuates dramatically. This is due to the Thermal Mass effect of the concrete slab floor which is a big part of what helps to keep the house comfortable year round.

In Other News

The Greeny Flat has been honoured with a four-page article in the latest issue of ReNew Magazine. ReNew is published by the Alternative Technology Association and is an excellent resource for anyone interested in sustainability in general and renewable energy systems in particular. Our thanks go to the ReNew team and in particular to the editor, Robyn Deed, for helping us to spread the word about affordable, energy-positive design and construction.