Holographic optical elements: various principles for solar control of conservatories and sunrooms

Abstract

Holographic optical elements (HOE) can be used to reflect the direct (beam) sunlight incident on a window whilst allowing the diffuse light to pass through. This is achieved with a semi-transparent hologram, which enables solar control of a building without reducing the benefit of a window or façade to the occupants. Domestic conservatories represent an interesting potential market for such a product. Conservatories and sunrooms by their very nature have large expanses of glass and so are prone to periods of unacceptably high solar gain during the summer months. Currently, blinds or other opaque shading devices are used to reduce the solar gain but this is at the expense of daylighting. This paper describes the potential application of solar control HOE applied as either a fixed plate or tracked solution. The performance of such systems for the UK climate is predicted using transient thermal analysis simulation of commonly used UK conservatories. The benefit of selective HOE glazing of specific elevations within a conservatory is considered to achieve ‘peak clipping’ of daytime temperatures to an acceptable level. The simulations predict that reductions of up to 17° are possible with fully tracked HOE applied to all the elevations of a typical conservatory design. Selective use of fixed plate HOE glazing, can achieve a temperature reduction of 6.1° when only 62% of the glazing within a conservatory is replaced.