CIBSE Case Study: 1960s Housing Estate Refurbishment Creates Low Carbon Homes

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Article from the June 2012 edition of the CIBSE Journal written by Mark Downson.

Introduction

The transformation of a hard-to-treat 1960s property into a low carbon home involved the use of some unusual technology, writes Mark Dowson.

The Thamesmead housing estate in south-east London is a key example of the often poorly insulated and undervalued concrete dwellings built in the 1960s. It was featured in the Stanley Kubrick film, A Clockwork Orange, and more recently on television in E4's Misfits. But its other claim to fame is that it is now part of "Retrofit for the Future", a government-funded competition launched by the Technology Strategy Board (TSB) in 2009.

The aim of the competition was to develop innovative, scalable, whole-house refurbishment strategies with potential to reduce 80% of CO2 emissions in low-rise social housing. Following two intense design phases, 86 teams across the UK were shortlisted and awarded £150,000 to implement their strategies with occupied dwellings. The selected properties are now being monitored over a two-year period after refurbishment, with the findings feeding into research papers and nationwide design guidance.

As a shortlisted team, Buro Happold collaborated with Fraser Brown MacKenna Architects, Gallions Housing Association, Martin Arnold Associates surveyors and Axis Europe contractors to super-insulate a pre-cast concrete end-of-terrace house on the Thamesmead estate..

Like millions of buildings across the UK, the estate consists largely of properties with solid walls, single glazing and uninsulated floors/roofs responsible for a significant amount of wasted heat. In its unrefurbished state, the hard-to-treat property suffered from moisture-related problems such as condensation, rising damp and mould growth, made worse by insufficient heating and high rates of fuel poverty. It possessed a mixture of singleglazed and old double-glazed windows, unused ground-floor garages (too narrow for modern cars) and a first-floor walkway.

Transformation

Through extensive retrofit works, the property has been transformed into a "near Passivhaus" six-bedroom house, super-insulated with external cladding, triple glazing throughout and high levels of air tightness. Fresh air is provided by a mechanical ventilation system with heat recovery (MVHR). Ten photovoltaic (PV) panels and a vacuum tube collector on the roof provide renewable electricity and water heating. Expected U-values and other projected performance data are shown in the table below.

A key innovation of the Thamesmead project is a highly-insulated solar-air collector prototype integrated into the external insulation on the south facade. The prototype consists of a cavity containing a black perforated metal sheet to absorb solar radiation and a highly insulated translucent cover, consisting of polycarbonate panels fitted with high-performance granular "aerogel" insulation, to reduce heat losses to the outside.

Aerogel is an emerging material in the UK construction market. This unique nano-porous translucent insulation material has the lowest thermal conductivity of any solid, retaining up to four times as much heat as conventional insulation, whilst being highly transparent to light and solar radiation. It is available commercially as translucent granules encapsulated within glass or multi-wall polycarbonate sheets, or as particles embedded within opaque insulation boards and blankets. The material can be applied to a building in a variety of ways.

Linked to the property's MVHR, extracted air from the kitchen and bathrooms is fed into the solar collector cavity, where it is heated by incoming solar radiation. This heat is then used to provide additional energy indirectly to heat the incoming fresh air supply to the property's living room and bedrooms. Automatic flow and bypass controls maintain comfortable living conditions all year round.

Some promising monitored results have already been observed for this system, indicating that it will play an important role in heating the property during cold-sunny conditions. During a seven-day controlled test in October 2011, the solar collector outlet reached 45C on a cold sunny day, preheating the supply air in the mechanical ventilation system to 30C, enabling the house to maintain comfortable living conditions at 21-22C, without additional heating.

A custom-built "aerogel door" developed by Proctor Group was also integrated into this retrofit. The double leaf plant room door incorporates a 30 mm-thick opaque aerogel blanket, capable of achieving a central U-value as low as 0.39 W/sq m.K, or 0.65 W/sq m.K including the frames. In a separate application, 80 mm of aerogel was also applied to the ground-floor slab in a zone where the floor-to-ceiling height was limited.

Evaluation

Onsite work at the property finished in March this year, and a large family is expected to move in over the next one to two months.

Since last August, and for another 18 months, a package of wireless monitoring equipment is being used to capture important information such as the internal temperature and CO2 levels within the house, power consumption of the MVHR, energy generation of the PV panels and solar water heater, as well as the total consumption of gas, electricity and water.

A roof-mounted solar radiation sensor, combined with temperature and humidity sensors inside the aerogel solar collector cavity and MVHR ductwork, provide a unique insight into this system's performance.

Ultimately, the success of the retrofit will rely heavily on the occupants' comfort and satisfaction levels, combined with how well they engage with new technologies and conserve energy at home. Interviews will be held to facilitate this process. Nevertheless, through this deep retrofit, the expected value of the property will have increased greatly, particularly due the extended living space, new kitchen-diner and additional two bedrooms.

There is scope to retrofit millions of buildings to make deep cuts in CO2 emissions. However, effective implementation is no small task. Solutions must account for the variety in age, size, quality, composition, function, asset value and social value across the existing building stock, as well as the different needs, expectations and budgets of homes owners and occupiers. Understanding which solutions are cost effective and deliver real savings in-use is imperative.

Mark Dowson is a research engineer within Buro Happold's sustainability and physics team, London. Read the full scientific paper on the aerogel solar collector's performance.

Specification

Walls: 300 mm of Permarock EPS insulation to achieve U-value of 0.1 W/sq m.K. Yellow render with aluminium fins

Roof: New roof with airtight membrane, services core and PIR 300mm insulation for U-value of 0.1 W/sq m.K

Windows: Passivhaus-certified Nordan N-tech triple glazing with U-value of 0.8 W/sq m.K and solar G-value of 0.5

Doors: Passivhaus-certified front door. Plant door custom built by Proctor Group with U-value of 0.65 W/sq m.K

Ground floor: U-value of 0.15 W/sq m.K throughout. Spacetherm aerogel insulation used in zone with 80mm space available

Air tightness: Pro Clima airtight tapes, sealants and sleeves used throughout.

Target: 0.6 cu m/sq m/hr @50 Pa.

Best on-site: 3.5 cu m/ sq m/hr @50 Pa

Ventilation: Nuaire MRXBOX95B-WH1 unit with summer bypass. Extract air for heat recovery boosted by aerogel solar collector

Heating: Warm air supplied by MVHR. System boiler with small-zoned radiators for peak winter conditions Hot water: 500 litre cylinder fed by electric immersion and boiler. A 3 sq m vacuum tube collector meets 42% of load

Electricity generation: Ten PV panels generate 2.30 kW peak. Array is ballasted using aluminium frame to avoid piercing insulation.

Lights and appliances: Low energy fittings and light bulbs with A-rated appliances specified throughout property

Predicted CO2 emissions

Baseline: 111 kg CO2/sq m/year

Post retrofit: 14 kg CO2/sq m/year

Predicted saving: 87%

Article from the June 2012 edition of the CIBSE Journal written by Mark Downson