Thermal modelling of highly glazed spaces.

Within the UK, and elsewhere, there is a growing interest in the Passive Solar Design for dwellings and commercial buildings. The aim is to make greater use of the renewable energy source, the sun, to provide space heating energy and (in commercial buildings) lighting energy. Such buildings often have large equator-facing glazed areas, attached conservatories, or large atria. The trend towards greater areas of glass is, for energy and aesthetic reasons, likely to continue. Thermal simulation models such as ESP, HTB2, and SERI-RES have been used extensively to study the design of highly glazed buildings. However, recent work at De Montfort University Leicester has indicated that approximate methods used to model the glazing, solar distribution, and solar shading can severely compromise the accuracy of the predictions. This was confirmed for both direct-gain spaces and conservatories in early work in this project. To improve the simulation of highly glazed spaces, new algorithms and calculation models for the transmission of solar radiation through windows, and the distribution of the transmitted solar radiation to internal surfaces, have been developed. A new calculation model allows the incidence angle dependent direct transmittance and absorptance, the diffuse transmittance and absorptance, and the effective total solar energy transmittance of glazing systems to be calculated. The main feature of the model is its applicability to any combination of coated or tinted glass, with no limitation on the number or sequence of the layers. The influence of internal or external slat-type blinds can also be simulated. An internal solar distribution model has also been developed which can calculate the time-varying internal solar distribution in a room. It considers radiation transmission through any glazing system, radiation re-transmission through the other windows, backloss of the reflected radiation, and interzonal radiation transfer. The new calculation models were formulated as independent pre-processing programs which produce the necessary input values for thermal simulation programs. The program HTB2 was used to illustrate the different links. The new programs were validated by comparing their predictions with measured values, known analytical solutions, or the results of other reputable programs. Simulation studies examined the thermal consequencesof using the new calculation models rather than applying conventional approximations. It was concluded that the application of all the new simulation aspects leads to a more authentic prediction of the environmental conditions in highly glazed spaces. Finally, the new modelling possibilities were used to produce widely applicable information about the design, energy saving potential, and internal comfort conditions, of domestic conservatories.