Due to an increasing demand for an improvement in environmental conditions for living and a need for energy saving, development of daylight exploitation products has accelerated. The invention of light-pipes which bring natural light indoors where sunlight cannot reach without generating excessive heat is one such example. Mathematical modelling activities aimed at predicting the daylighting performance achievable by light-pipes with various configurations under all weather conditions in the UK are being undertaken. Two models, one for straight light-pipes and the other for elbowed light-pipes are described. The models enable estimation of daylight provision of the light-pipes with a high degree of accuracy i.e., R2 values of 0.95 and 0.97 for regression between predicted and measured illuminance were respectively obtained for the above models. The maximum Mean Bias Error (MBE) and Root Mean Square Error (RMSE) were -2 lux and 27 lux. A design guide for light-pipe assessment is presented that will obviate...

A design guide for performance assessment of solar light-pipes:

As a result of an exponential increase in the application of solar water heating, and more recently solar PV systems, measurement of the available solar radiation resource is gaining rapid momentum. New databases are being created and many of these are being made available via Internet. Up-to-date series of these data are also being sought by architects and building services professionals for better design of buildings. However, in many instances due care is not being exercised with respect to quality control of the measured dataset. Two major activities that utilized large databases of solar radiation, sunshine and cloud-cover have recently been concluded within Europe – the European Solar Radiation Atlas and the Chartered Institution of Building Services Engineers (London) Guide on ‘Weather and Solar Data’. This article provides an account of the research undertaken towards development of robust techniques for identi” cation of erroneous data and their substitution using validated methods for generating...

Quality control of solar radiation and sunshine measurements – lessons learnt from processing worldwide databases

Visual comfort assessment of daylit and sunlit areas: A longitudinal field survey in classrooms in Kashan, Iran

Glazing materials have a significant impact on the energy efficiency of the building interior. Poorly designed skylights, windows and glazed surfaces can create an uncomfortable environment. The effect of heat gain through an un-shaded glass can be 100 times higher compared to the same area of an insulated wall. Currently, various alternative glazings with different performances are being used daily. There are many choices and alternatives to consider, and careful selection is significant to meet the design requirements. The optical features of glazing materials influence daylighting quality, the thermal characteristics and the potential of energy savings. The increasing interest of skylights as an effective strategy among building professionals and building owners implies that they are keen to know about the performance and energy efficiency of various glazing materials used on skylights. The aim of this study is to review the glazing performance and glazing types that are applied in the skylight roofing system. The review targets at two important factors in glazing performance, namely, solar light and solar heat. The review emphasises this general relationship during the design stage to ensure greater visibility in the product selection, also to ensure various other advantages improved comfort in perimeter zones, reduced mechanical loads and improved energy performance.

/pdf/a-review-of-skylight-glazing-materials-in-architectural-9xhy8rlxxr.pdf

A Review of Skylight Glazing Materials in Architectural Designs for a Better Indoor Environment

A novel Building Integrated Concentrating Photovoltaic (BICPV) Smart Window has been designed and developed as a next generation intelligent window system. In response to climatic conditions, the smart window varies solar light transmission into the building for provision of light and heat with the reflection of light to the photovoltaic (PV) for electricity generation. This unique function is realised using an integrated thermotropic layer in conjunction with embedded PVs. As commercial PVs are readily available, the success of this novel BICPV design depends solely on the performance of the thermotropic material. This study aimed to develop a suitable reflective thermotropic layer for the proposed smart Concentrating Photovoltaic (CPV) system. A Hydroxypropyl cellulose (HPC) polymer was tested for its applicability as a potential reflective thermotropic material for this purpose. HPC concentration was systematically varied from 1 wt. % to 6 wt. % in aqueous solution so as to provide insight into the relationship between transmittance/reflectance properties, the concentration of the thermotropic material and their dependence upon the environmental temperature. The degree of hysteresis of light transmittance upon subjecting HPC to heating and cooling cycles was also investigated. Specifically, for the HPC liquid samples the measured threshold temperature/transition temperature (Ts) was observed to be approximately 40 °C for 6 wt. % HPC, increasing to approximately 44 °C for 1 wt. % HPC. No hysteresis was observed upon heating and cooling HPC samples. Reflectance below the Ts was recorded at ~10%, increasing up to ~70% above the Ts for 6 wt. % HPC. Finally, a HPC-based hydrogel membrane sample was developed and exhibited good thermotropic activity therefore demonstrating its suitability for use within the BICPV smart window. This study corroborates that HPC is a suitable thermotropic material in the application of next generation BICPV smart window systems.

Transmittance and Reflectance Studies of Thermotropic Material for a Novel Building Integrated Concentrating Photovoltaic (BICPV) ‘Smart Window’ System

B Norton

Papers

Windows in Buildings: Thermal, Acoustic, Visual and Solar Performance