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Building fabric

• External solar shading

External solar shading is particularly beneficial for reducing cooling demand and increasing thermal comfort. There are two key elements to maximising the energy saving potential of solar shading devices. First, the lower the so-called g-value, the better; a value of 0.1 means that the shading device arrests 90% of the solar energy directed at it. Second is the implementation of an automatic control system that can act to minimise excessive solar gain in the summer regardless of whether residents are present in the dwelling. External solar shading devices have a variety of forms and materials; A few of the major forms are illustrated below.

roller blind	Venetian awning	hood awning

Other forms include fixed louvers and laterally sliding panels, and taken together with the wide variety of materials (fibreglass, wood, textiles, metal), this means that there is the possibility to configure external shading measures to suit almost any type of high-rise building.

Depending on the amount and orientation of glazing on a building, external solar shading measures are capable of reducing interior temperatures by 6 to 8 °C on a hot day, reducing cooling demand by 30 to 50% in warm climates and avoiding the need for air-conditioning altogether in some more moderate climates.

The indicative investment cost per m2 for a commonly available fibreglass fabric roller-blind is about €80 to €100. The level of automation, size, and choice of fabrics may raise or lower the investment cost by about 10 to 20%. Depending on climate, g-values, glazing characteristics and energy prices, external solar shading devices can have a payback period of four to six years.

• Effect of insulation and windows on cooling demand

Petersdorff et al have modelled the effect of insulation including windows on cooling demand in moderate and warm climate countries. A number of important conclusions were drawn:

• Windows’ g-values have a more significant effect on reducing cooling demand than their U-values.
• Ground floor insulation increases cooling demand, but it is generally only in warm climate countries that this increase outweighs the reduction in heating demand.
• It is possible for insulation to increase cooling demand as a result of heat gains being retained in the building more effectively.
• The additional effect of insulation on reducing cooling demand in a given climate is greatest where the heat load has been minimised (e.g. through external solar shading, efficient appliances and effective ventilation).
• With the exception of the roof or top storey, the additional effect of insulation on reducing cooling demand is negligible in moderate climate countries.

Heating/cooling system

• Distribution

Insulation of central heating and domestic hot water distribution pipes is fairly inexpensive. Applying this measure to uninsulated and above all accessible pipes is likely to be highly cost-effective as it improves system efficiency at relatively low cost. However, very little is known about the state of pipe insulation in high-rise buildings across Europe and indeed research to quantify the energy and CO2 benefits has only recently been undertaken, which is why this measure has not been considered quantitatively.

foam pipe insulation

In addition to the installation of balancing valves and TRVs outlined, parallel rather than sequential alignment of radiators can also help ensure even heat distribution within a highrise building and contribute to improved comfort levels.

• Generation

Alternative forms of heat generation can be considered. Combined heat and power systems qualify
as a RUE measure and fulfil the objective of saving energy. Renewable heat generation at the
building level, wood chip and wood pellet boilers in particular, would contribute to the objective
of reducing CO2 emissions.

Cooling

While European ownership of air-conditioning units is still very low – about 0.02 per household – compared to the US, Japan and Australia, the market for cooling technologies is growing very quickly. Data on cooling energy consumption is very poor, but the emphasis in high-rise refurbishment with respect to cooling should be placed firmly on averting or reducing the need for active cooling systems. This is equivalent to priority one measures under the Trias Energica, and would include passive solar design, better thermal performance (see above), appropriate ventilation strategies, heat recovery and utilisation, reducing internal heat loads, day-lighting and increasing building albedo. Priority two measures include using renewable energy-based active cooling technologies – for example solar cooling or ground-source heat cooling. Priority three – where active cooling technologies are present – would involve efficient heat pump designs installations. Minimising cooling demand is a priority, especially but not exclusively in warm climate countries, as climate change poses the credible risk of a vicious cycle wherein rising temperatures increase cooling demand, and increased cooling exacerbates the effects of climate change.

Lighting

During refurbishment, electric lighting in common areas of high-rise buildings can be easily upgraded. In general, all incandescent lighting should be examined, using a variety of more efficient lighting technologies as replacements. Indoor incandescent bulbs in corridors, lobbies, stairwells, laundry rooms and other common areas can be replaced with compact fluorescent bulbs. Outdoors, high pressure sodium fixtures can take the place of incandescent lights, combined with timers or photocells to ensure they are off during daylight hours. Furthermore, replacing incandescent lamps in (fire) exit signs with LEDs will also save energy.

Natural lighting design can help minimise electric lighting requirements. Virtually every aspect of window design has a bearing on sunlight entering the building. Natural lighting strategies should be given due consideration and integrated appropriately with the choice of window replacement and electric lighting.

Ventilation

Improvement of the building fabric and thermal properties of any building will lead to increased air-tightness. Unmitigated, this results in a lower rate of renewal of indoor air, and will lead to an increased incidence of condensation and mould growth, hazardous to the health and wellbeing of residents. Some types of high-rise construction, in particular prefabricated concrete panel constructions with solid concrete floors, can already be inherently very airtight, unless windows are poorly fitted26. In any case any refurbishment must incorporate the installation of appropriate ventilation systems. This of course reduces the energy-saving potential of other measures, but is imperative to safeguard the health and wellbeing of occupants. In the interests of maximising energy savings, heat recovery ventilation – which can potentially reduce ventilation loss by up to 75% – should be installed in colder regions to minimise the ventilation loss.

Natural ventilation systems can provide an important and zero energy means of providing fresh air whilst also reducing cooling demand. Dwelling-based ventilation outlets combined with the use of windows help achieve the required ventilation. Natural ventilation is particularly suitable for high-rise buildings because ventilation stacks with intakes at low or ground level and exhaust vents at the top of the building increase in effectiveness the taller they are. However, given that careful whole-building design is needed to achieve ventilation of the right parts of the building at the desired rate, a limitation of natural ventilation systems is that they can prove difficult to incorporate into the refurbishment of existing high-rise buildings. Nevertheless, natural ventilation in high-rise residential buildings combined with efforts to minimise solar and internal gain, has the potential to as effective as a space cooling system. Its feasibility should thus be carefully assessed, particularly in warm climate countries.