Yesterday the Government launched its Energy Efficiency Strategy, and we were particularly interested to see if any mention was given to the role of SAP, the Government’s energy performance assessment tool.
Hockerton Housing Project takes pride in its low-tech, low-cost approach, and the homes consume 15-25% of the energy used by homes built today. But the Government’s energy efficiency measurement assessment tools (SAP and RdSAP) cannot compute the benefit of homes like ours:
- SAP cannot cater for our use of passive solar gain as our main heating system
- Use of thermal mass to reduce heat demand through the year is not recognised (the thermal mass in our homes essentially stores the summer heat and keeps our homes warm in winter)
- SAP assumes that an element of mass thicker than 100mm has no additional thermal capacity is flawed (SAP2009 Table 1e: Heat capacities for some common constructions), contrary to evidence at HHP. As long as the mass is well insulated (externally) the full thickness of the mass will be effective as a heat sink.
- RdSAP does not differentiate between internal and external solid wall insulation, so the benefits of external insulation to “lock in” the mass of the walls, which can then aid summer cooling and winter heating, are not recognised for existing dwellings.
- SAP assumes that thermally separate conservatories are not present, ignoring two benefits:
- The sunspace provides sheltering of the dwelling from the external environment, therefore reducing heat losses.
- The sunspace can be used to harvest passive solar energy which can then be brought into the main dwelling to top-up the heat stored in the thermal mass as required.
All this matters because the Government tells us in the Strategy that it intends to make more policies conditional on energy efficiency. Access to feed-in tariffs and the renewable heat incentive are already affected, and RdSAP or EPC ratings could also be used to introduce differential council tax or stamp duty. All this will mean that energy efficiency improvements will be made to meet whatever measure of energy efficiency is applied. Whilst a policy to drive up the value of energy efficiency in the property market would be very welcome, as this is potentially the simplest way to drive investment in existing homes, this must not be so broad-brush as to drive out innovative approaches and a process for ‘exceptions-handling’ must be incorporated into future policies.
Seeing is believing
On the upside, whatever documents come out of Westminster, here at Hockerton we’re enjoying ‘zero’ energy bills as our investment in additional solar PV starts to pay off and the summer heat stored in our thermal mass continues to keep our homes warm.
If you are interested in homes that are comfortable yet consume only 15-25% of the energy used by homes built today, this time of year is the best time to visit to truly feel the difference. There are some spaces left on the tour this coming Saturday 17 November so book your place on a tour of Hockerton Housing Project here.
The two houses in Newark that we retrofitted in 2010 as part of the Technology Strategy Board’s Retrofit for the Future project have now been re-occupied for over 12 months. As part of the project, the energy use and environmental conditions are being monitored for 2 years following the retrofit, so we’ve done some initial analysis of the first year’s data, and here’s a summary of our findings.
In one house, the tenants are the same retired couple that lived in the house prior to retrofit, so we can compare the past year’s consumption with previous bills as well as the post-retrofit predicted energy use from the SAP calculations.
Prior to the retrofit, the couple’s annual energy use was 15,695kWh. For the first 12 months of occupation post retrofit, Oct 2010 to Oct 2011, their total energy use was 5,305kWh, a reduction of 66.2%. As a part of the retrofit solution, we decided to make an investment in a local community-owned wind turbine, rather than install renewables on the houses (as this was not appropriate for ). Including one house’s share of the annual production of the wind turbine, 1,943kWh, means a net consumption for this house of 3,362kWh, a reduction of 78.6%.
The reduction in annual CO2 emissions is lower at 57.9% due to the fact that all energy use in the house is now electricity, which has higher carbon intensity than gas.
Electricity is also more expensive per kWh than gas, so the reduction in annual fuel bills is also lower at 26.4%, but we have to remember that this is in a climate of rising energy prices, where other consumers would have probably seen their bills rise by an average of 10-15% in the same time period, so in real terms the residents have seen a reduction in energy costs of 35-40%.
The post retrofit SAP calculations predicted an annual energy use of 4,385kWh, but this is only for heating, hot water, ventilation and lighting energy use. We are monitoring 8 individual electrical sub-circuits in the houses, so can compare SAP regulated energy predictions to actual usage. This shows that actual energy use for these regulated elements was only 2,309kWh, 47% less than predicted. Looking at the actual energy use for the sub-elements of the SAP calculation, heating and ventilation energy use were very similar to SAP predictions. The largest reductions were energy for water heating, actual use of 1,186kWh compared to a SAP prediction of 2,696kWh, and lighting, actual use of 62kWh compared to a SAP prediction of 752kWh. The residents clearly use lighting very sparingly! In relation to the hot water disparity, this can probably be explained by the more efficient, HHP designed ‘Hotsi’ hot water system installed, and the fact that SAP assumes a greater occupancy for a property of this size – 2.53 occupants whereas there are only 2.
Analysing the breakdown further, non-regulated energy use (cooking and appliances), which is highly influenced by occupancy levels, accounts for 57% of the total energy use. If we also include energy used for water heating, another element highly influenced by occupancy levels, then this percentage increases to 79%, which clearly illustrates the impact occupancy has on energy use in a very energy efficient house.
Annual gas consumption prior to the retrofit was 12,493kWh, which would have been primarily for heating and hot water, aside from a small amount of gas used for the hob. Post retrofit, annual energy use for heating and hot water was 2,061kWh, an 83.5% reduction.
The neighbouring house that was retrofitted as part of the project is occupied by a couple with 4 children (which rose to 5 during 2011 – congratulations!) However, they were not the pre retrofit occupants, so we cannot do a pre and post retrofit comparison of their energy use. Their total energy use for their first year of occupation was 8,522kWh, or net of 6,579kWh after accounting for their house’s share in the community wind turbine. This is almost double that of their neighbours, but there are 6 (now 7) occupants as opposed to 2 next door, and as we’ve seen occupancy has a significant influence on total energy use.
This analysis is based on the first year of occupancy, to Oct 2011, and there are a number of factors that we believe will have caused this 12-month period to have higher energy use than we’d otherwise expect:
- The retrofit design is based on the principals of passive solar design and high thermal mass (like the homes at HHP), but the houses were completed and re-occupied entering the heating season, so were still drying out and had not had chance to build up a store of energy in the mass to help them through the winter;
- The Envirovent MVHR units broke down and/or were replaced on numerous occasions during the first winter (the first house had 4 units in 12 months) leading to significant periods where the occupants had to open windows to ventilate the house, which completely undermines the design and will negatively impact thermal performance and the homes’ comfort;
- The winter of ’10-’11 was extremely harsh.
In relation to point 1, when the first house was re-visited in October 2011, the internal temperature was 24oC on a Sunday evening, and the occupants had not had to start using the electric heaters, whereas 12 months earlier when they first moved in the internal temperature was 19oC and the heaters were already on for a few hours each day.
As we exit the ‘11/’12 winter (hopefully!), which was much milder than the previous year, it looks like energy use is reducing, at least in the first house where occupancy levels are the same. Comparing total energy use in this house for the November – February period with the same period from the previous year, shows a further 25.7% reduction. In the second house, the energy use for the same period compared to the previous year has actually increased by 9.7%, but there is increased occupancy, and as we have seen, and see here at HHP, occupancy level has a significant impact on energy use in very energy efficient homes.
But what do the residents think about their new homes? We’ve not been able to contact the family in the second home, but have spoken to the retired couple. They had occupied the house for 40 years prior to the retrofit, so are well placed to comment on their new home. There have been some issues, most notably the Envirovent MVHR units frequently failing in the first year, and occasionally find the house too hot in summer or too cold in winter, but on the whole they are very happy with their new home.
We always welcome feedback from visitors, but rarely get as full a review as this…
I am in the Oil Industry and a pilot neither, I admit, the greenest of occupations. My Wife and I faced a major renovation and it seemed sensible to come to listen and learn.
What did I learn?
-A Hockerton house is not a ‘magic’ house.
-Don’t stick a B&Q windmill on top of your house
-It is highly unlikely many of us could achieve what Hockerton has, but, we can all do something.
-the first step is to insulate, don’t waste energy.
What do I know?
-conventional energy cost are going to rise.
-If I had the last barrel of crude oil in the world , I would not just burn it.
-If we don’t do something about carbon, its going to get hot and whilst it probably won’t affect conceited (very lucky) little me it is going to hurt those most in need. Millions of them.
-There are positive things we can do and very simple behaviours we can adopt that help; just that little bit.
So what did we do?
-Insulate! Get the house up to modern standards and prevent the energy haemorrhage.
-Build ‘airlocks’ and adopt the rule of Arctic living; we don’t open one airlock door until we have closed the other.
-Underfloor heat. Small delta T over a very large area is very efficient. Reduce to a minimum heating in areas not in use. [Here delta T is the temperature difference across two surfaces, how does it work]
-Build a conservatory to capture the heat from the sun. Isolate it in Winter or when there is no sun.
-Install GSHP: We yet to have long term use stats but advertised efficiency of 1:4 seems common sense. (Although at HHP our experience has not been so good, find out here.
-install a modern woodburner and have it ‘shared’ between two rooms by a little clever design. How can something so simple be so efficient?
-configure the kitchen to make the most of recycling so that it overcomes lazy human nature
-install a quooker; ie boil exactly what you use. No waste. (again…not sure of the stats over the long term but we will see)
-compost, harvest rainwater , grow our own and keep chickens. In terms of cost time and effort , no it is not effective but, it is a pleasure, tastes great (eggs and food, not the compost) and helps just that little bit.
-develop a ‘stingey’ attitude and aim to use and re-use everything. After a short while it becomes a habit.
A visit to Hockerton is inspirational and motivational. We are doing a little bit as a result.
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 …