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.