High and superinsulation

In recent years attention has been focused towards the use of very thick layers of insulation within the building fabric in order to minimise heat flow. This technique has become known as superinsulation. The use of superinsulation has so far been best demonstrated at the domestic scale. This may be partly due to the problems of overheating experienced in many larger, deeper plan commercial buildings, problems which override the benefits of reduced winter heating requirements. In the future, however, buildings which exhibit less tendency to overheat due to better environmental design may modify the priorities and make superinsulation attractive in all circumstances where buildings experience cold seasons.

Superinsulation is associated with several design features:

• To qualify as superinsulated the building fabric should have U-values that are less than 0.2 W/m2K for all major non-transparent elements and often below 0.1 W/m2K.

• Insulation thickness is often constrained by accepted construction techniques, for instance by allowable cavity widths in cavity wall construction.

• A broader definition of superinsulation is one which specifies a maximum overall building heat loss which permits 'trade-offs' within certain limits, rather than individual component values, for example by an allowance for solar gain.

• In the case of low-energy housing, the typical thickness of insulation material is likely to be of the order of 150 mm in walls and 300 mm in roofs (Figure 6.1); superinsulated walls may have 200-300 mm with 400 mm in the roof (Figure 6.2).

• Achieving a superinsulation standard also requires a high level of air tightness of the building envelope which means that there will need to be trickle ventilation or even mechanical ventilation with heat recovery to reinforce the 'stack effect' in order to provide one to two air changes per hour.

With cavities of 200-300 mm width it is essential to have rigid wall ties of either stainless steel or tough rigid plastic.

The Jaywick Sands development is a social housing project which is designed on sustainability principles. Its 'breathing' walls consist of

Jaywick Green

Figure 6.1

Section, typical low energy construction

Figure 6.1

Section, typical low energy construction

Figure 6.2

Superinsulation in the Autonomous House, Southwell (courtesy of Robert and Brenda Vale)

Warmcel Window

partially prefabricated storey height structural panels (Figure 6.3). They are filled with 170 mm Warmcell insulation and clad with 9 mm sheathing board faced with a breather membrane. The exterior finish is western red cedar boards on battens. The floor is a pot and beam precast concrete slab with 60 mm rigid insulation on the upper surface. It can be argued that the insulation would have been better on the underside of the concrete to allow the slab to provide a degree of thermal mass (the scheme is described in detail in The Architects Journal, 23 November 2000).

M2k Detail

Figure 6.3

Low energy timber panel housing, Jaywick Sands, Essex

Figure 6.3

Low energy timber panel housing, Jaywick Sands, Essex

On mainland Europe solid wall construction is much more common than in the UK. An example is the Zero-energy House at Wadenswil, Switzerland. The structural wall consists of 150 mm dense concrete blocks. These are faced with 180 mm of extruded polystyrene insulation protected by external cladding. The walls have a U-value of 0.15 W/m2K. The roof has 180 mm of mineral fibre insulation giving it a U-value of 0.13 W/m2K.

Timber framed windows are triple glazed with Low-E coatings and an argon gas filled cavity achieving a U-value of 1.2 W/m2K. North facing windows are quadruple glazed achieving a U-value of 0.85 W/m2K.

Air tightness is a prime consideration at this level of energy efficiency. Pressure tested to 50 pascals (Pa) the rate of air change was 0.4 per hour. Polycarbonate honeycomb collectors absorb solar radiation to heat domestic water to 25°C even on cloudy days. Space heating is also supplied by solar collectors and delivered in pipes embedded in the concrete floors. This is supplemented by a heat storage facility and backup liquid petroleum gas (LPG) heater unit. The annual energy consumption is around 14 kWh/m2 excluding solar energy (Figure 6.4).

Figure 6.4

Section of the Wadenswil House

Figure 6.4

Section of the Wadenswil House

Radiation And Energy Inquiry Figures

3 mm bitumous plastic vapour barrier on 12 mm hardboard

.external cladding

-plaster board

-50 mm extruded polystyrene

.15 mm plaster

100 mm mineral fibre

.150 mm dense concrete blocks

180 mm mineral fibre

180 mm extruded polystyrene

3 mm bitumous plastic vapour barrier on 12 mm hardboard

.external cladding

-plaster board

-50 mm extruded polystyrene

.15 mm plaster

100 mm mineral fibre

.150 mm dense concrete blocks

180 mm mineral fibre

180 mm extruded polystyrene

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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