Every 3 – 4 months we read our 50 power and water meters to check how we are doing in terms of consumption, generation and export.
Each household pays for their share of consumption relative to use, with any income from the export of renewable energy shared equally between us.
The resultant figures help us remain aware of our use, not least because we see it relative to (or in competition with?!) our neighbours. It also reminds us how well these houses perform. This can become easy to forget when the house is your home – until heatwaves like this week, when we could feel the difference as the thermal mass soaked up any heat that made it through shaded windows.
* Our average daily energy use was around 23% of a standard house (per house, not incl the garages).
* We exported 38% of what we generated, compared with 48% in the winter
* We earn around 4p for a kWh exported but pay on average 7.5p per kWh we use, so over the last 4 months we’ve missed out on energy worth £145.
* In the last 4 months we’ve generated the equivalent of 95% of our total household use (not including our shares in our community-owned wind turbine of course).
* And we are using 260 litres of water a day per house on average. Potable: non-potable is 1:11. This is a similar ratio to that in the first quarter but an increase overall. Average usage per person is 82 litres, compared with Code for Sustainable Homes Level 5 and 6 target of 80 litres – perhaps due to higher number of washes during peak vegetable gardening season!
This week we popped in to one of the homes that we retrofitted in 2010/11 as part of a Government-funded project, Retrofit for the Future, to find out how it was performing.
The headline finding is that the house is now using 9% of the energy it previously used for space and water heating; down from 12493kWh to 1133kWh. Overall energy use has been reduced by 75%, with the carbon emissions from the remaining use offset by a cost-effective investment in off-site renewables.
We visited after one year and found that actual energy use was 47% less than that predicted by SAP. There has been a further significant fall since then. Over the intervening years, the average energy use has been 30% of the use originally predicted for space and water heating, ventilation and lighting; and total average use has been 50% of use in that first year.
We expect heat usage to remain steady at this lower level (for the current occupancy patterns) as the fall can be attributed to one-off factors in that first year:
- the building was drying out
- the thermal mass had no heat stored as the build completed in early autumn
- the winter of 2010/11 was particularly cold
Use of energy for appliances and cooking remains the largest influence on energy use, forming two-thirds of annual use on average. As highlighted in previous posts this is very dependent on working patterns and the number of residents. The final 3% of energy use is by the metering system itself – with metering on 8 rings in the house to enable this analysis.
Last, but certainly not least, was the residents’ feedback. The most notable problem was a rain sensor on the automated Velux windows in the sunspace, but that has been repaired quickly enough, and the occupants continue to enjoy the comfort of their old but cheaper-to-heat home.
The tenants of one house have now been back in their home for 2 weeks, and we’ve taken a look at their energy use over that period.
Their total energy consumption is averaging at 11.93kWh/day. At that rate, their annual consumption will be 4,356kWh. However, the heaters are on at the moment – averaging 2.27kWh/day (pretty low!) – so we’re hoping the annual use will be lower than this, as these will not be on all year. It will also probably require more heating this winter as the house has been a building site for 6 months, and not able to build up a store of solar energy from the summer.
So how does this compare to their previous energy use? Well, looking at 18 months of bills prior to the retrofit, they were averaging 3,241kWh/yr of electricity and 18,972kWh/yr of gas.
So down from an annual energy consumption of 22,213kWh to 4,356kWh – not a bad start; long may it continue …
We have now completed the retrofit of the houses, and hopefully you’ll agree they’re looking great.
Front of the completed properties
The rear of the completed properties
The existing tenants of number 30, Mr & Mrs Morton, have already moved back in and are enjoying their new home. Newark and Sherwood Homes are advertising for tenants for number 28, which was previously void.
The houses will now be monitored for 2 years to see how they really perform. The monitoring includes:
- Temperature and relative humidity in 3 rooms of the house (sitting room, bedroom 1 & bedroom 2)
- External temperature
- CO2 level in the sitting room
- Total water and electricity consumption
- Electricity consumption on 8 individual sub-circuits
All this data is being monitored automatically and transmitted to a central database at 5 minute intervals, and we can view it real-time via a website.
We are also hoping to do additional monitoring on the properties, and are in discussion with a couple of universities about the possibiliity of collaborating on this.
Meters, meters and more meters!
We hope you’ve enjoyed our blog so far, and watch this space for more news of post occupancy evaluation …