Using the dynamic window-model in Norwegian climate

Student thesis: Master thesis (including HD thesis)

  • Espen Kildebo Jensen
  • Eirik Storvig Jacobsen
“Using the dynamic window-model in Norwegian climate” is a project which studies the possibility of using a dynamic window-model in a Norwegian climate. A dynamic window is primarily intended for use in cases of rehabilitation of buildings not equipped with HVAC systems. The description of a dynamic window is a window which has free or forced ventilation of air between the outer and inner glass surface. The idea is that the air which passes through the window will be preheated by the sun and heat transfer from the inner glass surface. Considering the long cold winters and temperate summers in Norway, the question is how the dynamic window-model will perform in these conditions.
This master thesis is initiated with a literature study to understand the basic on this type of window-model and gain knowledge on how far research has progressed in this general field. To achieve low U-values a dynamic window should consist of three glass layers or more, whereas one of the glass layers should be a low energy glass. Turbulent flow patterns should be avoided as this increases heat-transfer between glass surfaces on each side of the ventilated cavity, turbulent flow patterns is indicated to form in ventilated cavities with depths between 25 and 50 mm. These findings can be reviewed in chapter 2 and 3. Due to the time schedule given to complete this master thesis some limitations considering the width of the project had to be made.
Based on the literature study four dynamic window-models, denoted as A, B, C and D, were designed to be tested for selected simulation days. The simulation days were chosen according to the following criteria; cold clear winter day, overcast winter day, warm clear summer day and overcast summer day. The European simulation software WIS 3.0.1 was used to simulate the selected dynamic window-models and simulation days. WIS is a versatile simulation tool that is able to calculate the properties of complex window systems and components, as well as calculate the temperature development through the dynamic windows. A total of 1032 simulations form the basis for evaluating the dynamic window-models. Chapter 4 includes data on window constructions, weather data, simulation days, calculations and simulations in general.
Data acquired from the simulations were put into spreadsheets and graphs to compare U-values, g-values, inner glass surface temperatures and supply air temperatures. Simulation data were also used to calculate heat gain and -loss considering heat transfer, solar heat gain and ventilation. The results and comparisons are presented in chapter 5.
The results show that U-values are halved by halving the amount of air passing through the windows. The results also show that the lowest U- and g-values is achieved by placing the energy glass on the outer surface facing the outside, as done for window-model A and C.
The supply air temperature is affected the most by solar radiation. Window-model B and D are highly affected by solar radiation and experience the greatest temperature fluctuations during the day. Window B and D also experience the highest inner glass surface temperatures, while the surface temperatures for windows A and C are slightly lower in summer conditions. Window-model A experiences the lowest inner surface temperatures in winter, while this window also has stabile high supply air temperatures in winter and lower supply air temperatures in summer than the other window-models.
Not unexpectedly, using external blinds in summer significantly reduces the g-value and inner glass surface temperature, and in some extent the supply air temperature. Using full or halved air volumes through the windows shows only small differences in combination with use of external blinds in summer conditions considering the inner surface temperature. Considering supply air temperature, variations of air volume through the windows show greater impact on the various windows and simulation days.
The conclusion of this master thesis is that the dynamic window-model can be used in a Norwegian climate with good results. Window-model A and C are considered to be the windows best suited for use in a Norwegian climate, this is based on the results from the simulations. Window A and C show some differences in a winter situation, window A has a lower inner surface temperature than window C, while the situation is opposite considering supply air temperatures. The rate of air passing through the window should be lowered in a winter situation to better the windows preheat ability, while higher air volumes would be preferred in summer. The external blinds reduced heat gain due to solar radiation in summer considerably.
Publication date6 Jun 2011
Number of pages140
Publishing institutionAalborg University
ID: 52798336