Retrofit & Replicate - Hyde Housing Association

More documents

Recommendations

Info

The Retrofit Proposals: The ‘Retrofit and Replicate’ strategy focuses on carrying out the most straightforward improvements to reach the 80% target . . . and on doing them well. The priorities are to minimise heat losses from the building fabric; to install an easily replicable, efficient form of space and water heating; to reduce the energy requirements for lighting; and to utilise the most appropriate renewable forms of micro-generation in reducing CO2 emissions associated to the property. Heat loss will be addressed though significantly improved insulation to floors, external walls 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. In the choice of insulation material, thermal performance and ease of installation has been favoured over embodied energy and material source considerations, although minimal GWP and ZODP credentials were pre-requisites. U-value targets for the various envelope build-ups were set as follows: · Suspended timber floor – 0.2 W/m2K · External walls – 0.15 W/m2K · Pitched or flat roofs – 0.1 W/m2K mechanical ventilation unit, therefore access and available headroom were important factors, as was the poor condition of the existing roofing felt. Simultaneously, we were concerned about achieving good airtightness when recessed light fittings were introduced to the ceiling below. A combination of insulation products were therefore selected – Kingspan Thermapitch, laid on an airtight vapour barrier over the existing ceiling joists, and Web Dynamics’ TLX Gold multi-foil lining the existing rafters and party walls. The rigid boards are laid to the depth of an existing central bearer (170mm), thus allowing a floating floor deck to pass freely across the loft area. TLX Gold is the world’s first breathable multi-foil and the Court Farm Road project will be used as a case study and test-bed for both its ease of installation and performance in operation. This material will also allow the retention of the existing roofing felt and tiles by providing a secondary waterproof layer, as well as minimising the impact on headroom in the loft and reducing summer heat gains due to its reflective gold inner layer. to perform as a low-carbon dwelling. To ensure a reasonably airtight envelope, Mears will keep a log and photographic record of all service penetrations through the external walls and roofs to ensure they are sealed effectively. To provide controlled ventilation, a Vaillant recoVAIR 275 mechanical ventilation system is being retrofitted into the property. Mounted on the party wall in the loft space, the unit will extract 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. In summer mode, a bypass extracts the air direct to outside. Phenolic foam insulation offers the best performance of any readily available panel and therefore has less impact on internal room dimensions where dry-lining is concerned – an important consideration for Hyde. Kingspan’s Kooltherm phenolic range was therefore selected for both suspended floors and external walls. For the main body of the house, insulation-backed K17 plasterboard dry-lining panels were specified, whilst for the rear extension external K5 wallboards with a silicone render finish provides the best solution. This element of the works was supplied and installed by Wetherby Building Solutions. For the rear extension roof Kingspan Thermapitch rigid polyurethane boards (220mm) were preferred, in conjunction with Knauf Carbon Zero glasswool in the eaves location. For the pitched roof element, a number of other factors came into play rather then straightforward thermal performance. The loft is to be used for locating plant such as the proposed thermal store and The existing double-glazed windows were shown to be the weakest building element during the airtightness test: they will be replaced with aluminium-clad NorDan Ntech Passive windows, which are triple-glazed with warm edge spacers and composite insulated timber frames, achieving an overall Uw-value of 0.7 W/m2K. Front and rear doors will also be replaced with insulated replacements with a Uw-value of 1.0 W/m2K. Details have been considered in terms of the abutment of insulation, avoidance of thermal bridging and continuity of the air barrier. As well as communicating installation requirements on 1:5 detail drawings, ECD held a workshop on site with Mears site team to explain the importance of their workmanship to these issues, together with background on how the building is intended - 3 -
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. Capital cost, ease of retrofitting and ongoing maintenance requirements therefore become the most important driver in the choice of fuel source. Ground source heat pumps are relatively expensive to install and need to be located in a substantial, and preferably soundproofed, cupboard. Furthermore, to operate efficiently they work best in conjunction with an underfloor heating system, which in itself has inherent problems in a retrofit situation. The feasibility for underfloor heating was explored by ECD and Mears and found to be technically possible but only with a reduction in underfloor insulation levels and an increase in installation time and cost. When further confronted with a solid concrete floor in the kitchen, the concept was rejected in favour of a conventional wet radiator system. Heat pumps require electricity to operate, which in the UK is particularly carbon intensive – more than twice the kgCO 2 /kWh than mains gas. Therefore to produce carbon reductions in comparison with an efficient gas condensing boiler, heat pumps need to achieve a Coefficient of Performance greater than 2.5 measured across the whole year – the recent trials at the Barratt EcoSmart show properties recorded a CoP of 2.6. Air source heat pumps are unlikely to improve upon these results at present and would also require underfloor heating. A biomass boiler was also 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, and would again require additional plant space. With these considerations in mind, the decision was made to upgrade the existing gas boiler for a more efficient condensing unit and the Vaillant ecoTEC system was selected, with low NOx emissions and programmable controls. This was relocated to a hall cupboard since the existing flue outlet position contravened modern guidelines. 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. The system is to be supplied and installed by Kingspan Renewables in conjunction with a twin-coil 250l Range Tribune thermal store located in the loft space. 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. It is hoped that 50- 60% of the tenant’s hot water needs will be met by this system. All connecting pipework between boiler and thermal store will be well insulated to prevent heat transfer to the internal environment. A significant proportion of the property’s electricity load will be for lighting therefore the retrofit proposals will seek to minimise this component. Other major demands for electricity, eg for household appliance and entertainment use, are typically beyond the control of any RSL refurbishment scheme and down to tenant behaviour. The ‘Retrofit and Replicate’ exemplar project therefore concentrates on minimising electrical lighting loads through the installation of low energy lighting to every room. However, unlike typical low energy lighting solutions, the use of compact fluorescents will be avoided in favour of the latest in LED technology. Unlike CFLs, LED lamps contain no contaminants such as mercury or phosphor and can be safely disposed of or recycled. Although they are much more expensive currently, they are very robust and offer 50,000 hours of use (compared to 10,000 for CFLs or 3,000 for halogens) meaning no need to change then for at least 20 years! In this way, energy use is significantly reduced without the customary start-up delays and only a small reduction in efficacy. ECD have worked with Gloucestershire-based specialist GreenLED to develop the layouts and specifications. GreenLED will supply 3.7W Antares GU10 lamps for installation by Mears into standard recessed fittings. - 4 -
Page 1 and 2: Retrofit & Replicate Mottingham, So
Page 3: Design Team: ECD Architects are lea
Page 7: Materials specifications generally

Retrofit & Replicate - Hyde Housing Association

Create successful ePaper yourself

Delete template?

Save as template?