This study presents energy-modelling results for a large number of window combinations with window attachments such as shades, blinds, storm window panels and surface applied films in typical residential buildings throughout the United States. It concludes that the use of operable attachments can have a large effect on energy performance.
Key Findings
Overall performance is highly dependent on use of the attachments because more intelligent and responsive use always improves energy performance. Several window attachments provide little to no energy benefit in heating dominated climates and some perform worse than unshaded windows in terms of total energy use.
Further Detail
In order to get results which could faithfully represent the US building stock, a selection of window attachments were systematically modeled for a variety of climates in America. They included: residential building type (with or without basement), shading types (roller, cellular cell, vertical, Venetian, awnings, films, secondary glazing, solar screens and storm panels), glazing types (single and double) and positions resulting in 16,486 energy simulation runs.
In north and largely central climate zones, heating energy use is higher than cooling energy, so a combination of insulation and balanced solar control saves the most energy. Insulating interior window panels, exterior storm panels and cellular shades are most effective in these locations. Other insulating window attachments, such as window quilts and insulating roller shutters, are expected to provide similar level of energy savings, although were not included in this study.
When operable shades are used in a ‘typical’ manner, as investigated in a previous study by the US Department of Energy, some shades provide energy savings in specific climates, but not all operable shades save energy in all climates. The study held the shades fixed in a position – open, half-open or closed – and concluded that depending on the climate, the attachment may save energy or increase the energy use.
The paper suggests efforts are needed to improve manual operation of blinds or development of more cost effective approaches to automating operation is needed. It is expected this would maximize energy savings, as it would keep shades closed, partially open, or open depending on the environmental conditions and state of HVAC.
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