D. Chwieduk

Inst. of Fundamental Technological Research Polish Academy of Sciences, Swietokrzyska 21, Warsaw, Poland
Institute of Heating Engineering, Warsaw University of Technology, Nowowiejska 21/25, Warsaw, Poland

dchwied@ippt. gov. pl

Abstract

Nowadays, attic apartments with inclined external walls and windows (roof) surfaces have become quite “fashionable” in buildings erected in highly densely populated cities. The influence of solar energy and in consequence energy transfer through windows on the energy balance of such rooms is evident. Calculations of solar radiation incident on building surfaces, including attic envelope have been performed. To describe and solve problems of the dynamics of processes in the building envelope and surrounding, a mathematical model of energy transfer phenomena in opaque and transparent elements has been developed. The developed model enables to calculate energy transferred through windows into/out of the room at any time, and other energy balance elements, including heating/cooling energy needs. Selected results of simulation studies of attic rooms are presented. It turns out that overheating in summer due to high solar irradiation and energy transmitted and absorbed in glazing can be a real problem for rooms in attics.

Keywords: energy transfer through windows, energy balance of a room, rooms at attics

1. Introduction

Analysis of solar energy availability and its influence on the energy balance of attic rooms is the subject of this paper. Nowadays, when a building envelope is designed and constructed according to energy savings measures, with high quality of thermal insulation and other building materials, the heat transfer through the opaque external walls is a minor part in the total energy transport between the outdoor and indoor environment. Important elements of the energy balance of a building are the energy transfer through windows and energy needed for ventilation (supplied with or parallel to fresh air), even if recuperation of waste heat (from ventilation) is accomplished. Energy transfer through windows is especially important for rooms in attics.

Nowadays, attic apartments with inclined external walls and windows (roof) surfaces have become quite “fashionable” in buildings erected in highly densely populated cities. In many cities because of the high costs of land, especially in the city centres (downtowns), developers and construction companies construct buildings using every available square meter of land. If it is not possible to build high buildings because of existing spatial management plan of some regions of the city, then very often the last floor, at attics, is used as living space. However, it is against traditional way of the use of buildings. For many years in the past attics were used as stores and buffer zones, but not as apartment spaces. The living comfort at attics is not as good as at rooms located on floors below attics. The living standard can not be comfortable if no extra protection especially against too much solar radiation in summer is implemented. The problem of overheating of rooms at attics with special location (orientation), because of too much energy transfer through windows, is the main topic of this paper and problem to be presented.