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Hyde, a London housing association which owns some 40,000 homes are running a pilot project which examines the possibilities of reducing CO2 in existing homes. The association has taken a 1930's terraced house in South East London and retrofitted it with the aim of reducing its carbon output by 80%, an aim which ties in with Ed Miliband’s recent announcement that the government will now be aiming to reduce emissions by the same amount by 2050.
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The 3 bedroom mid terrace house will be monitored for a period of two years and the data used to identify technology that can be replicated in existing homes to reduce the carbon emissions. The residents of the new home will also enjoy fuel bills reduced by an estimated 65%.
Hyde believes that improving the energy efficiency of the nation’s existing housing stock is crucial in combatting climate change. Our existing stock is typically very inefficient compared to new build housing in terms of energy use, yet less than 20% of existing homes are likely be replaced by 2050.
The external walls are of cavity wall facing brick construction and the original dwelling included suspended timber floors and pitched tiled roofs but no bathroom! Later improvements saw the inclusion of a first floor shower room, the replacement of open fires with a central heating system of gas combination boiler with radiators and the addition of a single-storey rear extension comprising a third bedroom and ensuite bathroom. Poor quality double glazed windows have also been added.
SAP assessments were carried out, and the property was found to already have a rating of 60, well above the national average of 48 and therefore presenting a significant challenge to achieve the 80% reductions. An airtightness test showed a result of – 9.16 m3/hr/m2 @ 50 pascals, which is better than current building regulation requirements. The windows were the source of the worst infiltration with poor seals leaking air badly.
In the retrofit process, heat loss was be addressed though significantly improved insulation to floors, external walls (dry lining of some walls and exterior cladding of the extension) and roofs, replacement high-performance windows and doors, consideration to the dwelling’s air permeability and the installation of a mechanical ventilation system with heat recovery from the extract air.
Triple-glazed windows with warm edge spacers and composite insulated timber frames, as well as insulated front and rear doors were installed. A mechanical ventilation system draws air from the kitchen and bathrooms, reclaiming around 90% of the heat to pre-warm incoming fresh air which is then supplied to the living and bedrooms.
With these measures in place, the space heating requirements at the property are estimated to reduce from 17,238 kWh/yr to 2,410 kWh/yr – a drop of over 86%. With such low levels of heating required, tenant fuel bills will be significantly reduced.
A biomass boiler was ruled out by Hyde as it was thought to place an undue burden on the tenant to source and store a supply of wood pellets, as well as requiring additional space. A decision was made to upgrade the existing gas boiler for a more efficient condensing unit.
The gas condensing boiler will also supply hot water to the property but will be supplemented by solar thermal collectors located on the pitched roof. Two flat plate collectors mounted either side of the ridge will face east and west but will be controlled intelligently to favour the better performing panel as the sun tracks around the house to the south.
LED lighting was fitted throughout, as a way of minimising elctricity for lighting use. Yet despite all the carbon reduction measures described above, the scheme was still estimated to fall short of achieving the 80% target, largely because of its relatively good SAP rating at the outset.
Bridging the shortfall would require the input of renewable electricity micro-generation, with photovoltaics considered the only viable solution. Working with Solar Technologies, proposals for an array of eight panels located on the rear extension roof were developed. A single inverter has been located in the existing ‘electrical’ cupboard and a wall-mounted display will inform the incoming tenants of its electrical contribution.
The insulation measures alone account for a reduction of around a quarter of the original emissions, or a third if the triple glazing is included. The greater efficiency of the condensing boiler then takes the improvement to over 50%, after which the returns on investment are less dramatic. Nevertheless, the introduction of MVHR and airtight construction should contribute a further 15%, with the solar thermal and LED lighting taking our overall reduction to 76%! The photovoltaic contribution allows the refurbishment to easily achieve the target with a built-in contingency for actual performance in use.
The high levels of energy conservation and generation are reflected in the provisional EPC rating of 92, placing the retrifitted property in the highest Band A.
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