Blinds and shutters can help reduce heating, cooling and lighting costs
Getting the energy balance of a building right requires a holistic approach to building design to ensure products and systems work in harmony to maximise the benefits. Solar shading can help to reduce heating and cooling loads and maximise daylight.
The problem
Most buildings have already been built. It is estimated that 75% of the UK’s existing buildings were constructed before 1980 and only 1-1.5% are replaced every year.
Old energy efficient buildings need high energy inputs to keep the temperature at an optimum.
New highly insulated buildings are prone to overheating.
Existing buildings account for 40% of the overall energy consumption. The UK Government’s pledge to cut 80% of GHG emissions by 2050 is a key driver to substantially improving the energy efficiency of the building stock.
The solution
Using blinds and shutters can help to reduce heat gains in the summer, heat loss in the winter and control light levels and harvest natural light.
You can see further information on the specific pages relating to these topics on this website and in the resources section on this page.
The evidence
Building modelling conducted by the National Energy Foundation using Energy Plus on a model office has highlighted that internal shading by a venetian blind could save 10% of HVAC energy and a screen roller 23%. If fitted externally the savings in HVAC energy were 43% and 47% respectively (see image).
The IEA Technology Roadmap of energy efficient building envelopes individuate in exterior shading a dynamic solar control a standard feature in the future new and existing buildings, and specifically refers to low-cost automated dynamic shading as one of the technologies where the highest potential of return on R&D investments lies (IEA, 2013).
Indeed, shading constitutes a self-financing climate control system in the way it improves insulation, manages solar control and maximise daylighting from increased glazing areas (ES-SO, 2014), as such it represents an investment paid back via the savings in energy use. The influence of five different types of shading on the U- and g-values of six reference glazing units is shown in Table 2. Double glazing can have U-values reduced from 21% to 38% (clear) 25% (low-e), and g-values from 16% to 82% and 13% to 85%, respectively, depending on the shading type used.
Fixed solar shading designed according to the sun peak seasonal angles can reduce solar gains in summer but still permit heat gains from the low angle sun, contributing to reduce space cooling and heating loads. In some cases, internal shading can add thermal resistance to the transparent envelope reducing its thermal energy transmittance i.e. heat loss by transmission. Best-performing products include insulated systems (Baker, 2008) and cellular shades containing multiple air layers in a honeycomb cross-section that are fitted into weather stripped edge tracks. Although less effective, uninsulated shutters kept in in a closed position also reduce heat loss forming an insulating package. This occurs when the system is insulated and kept in a closed position.
In summer conditions, external shading is particularly effective at preventing the solar radiation from reaching the glazed surfaces; internal blinds can also contribute to reducing solar energy especially if a reflective finish is applied on the window-facing side (BBSA, 2015). Shading also decreases the fraction of solar radiation in the short-wave infrared range (780-2500nm) that is absorbed and re-irradiated as thermal (long-wave infrared) radiation and can eliminate the need for mechanical space cooling if coupled with cross-ventilation strategies. The potential for space cooling energy savings in UK houses is detailed in Seguro et al (2015).
In winter conditions, shading can provide night time insulation if fully closed overnight and maximise solar gains if left opened during daylight hours (Hutchins, 2015). A control strategy should be put in place rather than delegate its adjustment to the occupants. The potential impact of advanced solar shading on the reduction of the space heating demand can be found in Hutchins (2015).
The ESCORP/EU25 study (energy saving and CO2 reduction potential from solar shading systems and shutters in the EU-25) quantified at 80 and 31 million tonnes of CO2 respectively the carbon that could be saved if all buildings in the EU were properly solar shaded (Standaert, 2005).
Shading can be an effective energy efficiency measure of the transparent envelope, especially under conservation constraints. In Scotland, the Centre for Research on Indoor Climate & Health at Glasgow Caledonian University tested the performance of secondary glazing, uninsulated and insulated shutters, modern roller blinds with and without low-e plastic films on the window blind-facing side, Victorian style blinds and thermal blinds in the upgrade of a timber single paned sash and casement window (U-value: 4.5 Wm-2K-1) (Baker, 2008). Thermal energy loss was reduced by 51% with timber shutters; 28% with Victorian roller blinds; 22% with the modern roller blinds and 14% with curtains. Combined blinds and shutters led to a window U-value < 2 Wm-2K-1 that is below the Building Regulation Approved Document Part L1A windows in new dwellings.
