Ziva Kristl*, Dr., Asist. Prof., Ales Krainer* Dr. Prof., University of Ljubljana, Faculty of Civil and Geodetic Engineering, Chair for Buildings and Constructional Complexes, Jamova cesta 2, 1000 Ljubljana, P. O.BOX3422, Slovenia, tel: +386 1 4768 609 fax: +386 1 4250 688 e-mail: zkristl@faa. uni-li. si *ISES member

Introduction Thermal and luminous evaluation of a site layout with the help of the quantity of solar radiation as well as the density of urban development should present important starting points for a developer or a planning official. The investigation of architectural concept and its influence on thermal and luminous conditions in a building and its surroundings are essential in the early stages of design. During this time it is still possible to change site layout, building orientation, its form and dimensions. By doing so an energy conscious design with relevant functional zones can be obtained.

When designing a solar layout (or a solar urban quarter) the aim is to make a plan that will assure solar exposure of building facades during certain periods of time [1,2], especially during the cold part of the year when solar heating is desired. On the other hand the solar rights regulations, considering the minimum solar exposures during the year, have to be respected. A design that does not respect the solar rights of each building may cause unacceptable conditions in the building and can be refused by the authorities.

Today exist a number of ways for checking and evaluating of site layouts [5,6,7,8] regarding solar access and solar rights. In this paper we investigated the relevance and accuracy of solar volume method for urban planning and estimating of solar access [9]. This method enables the designer to obtain maximum volume of the building, which will not cast shadows over the chosen limits. The volume in designed with regard to solar incidence angle or solar exposure duration and can be optional (for a town, a neighbourhood or a building). Also we tried to establish if the method could be used in Slovenian solar rights regulations. During the investigation we wanted to answer the next questions:

• Is it possible to obtain long solar exposure of the facades and still keep normal/high urban density?

• What incidence angle is actually acceptable (in the literature 10°-15° elevation angle is recommended)?

• Shall we consider all the buildings equally, regardless of location?

• Is east and west solar exposure checking necessary, bearing in mind summer overheating?

For this reason we checked the method on two levels: on the level of solar rights (on 3 reference days) and on the level of prolonged solar access. We established critical periods in which the solar incidence on the buildings is desired, from which the reference solar incidence angles were determined. The results were compared with the results of the two established methods: sun-on-ground method and the iso­shadow method (Fig. 4,5) [3,12]. We compared accuracy of the methods and analysed differences and level of approach. The first two methods were calculated with the computer programme "SENCE" (Shadows) which was developed at the University of Ljubljana, Faculty of Civil Engineering [4]. The third method was assessed with a newly developed computer tool.