The influence of VELUX roof windows on the heating energy demand
Publisher
Tisková zpráva
13.12.2013 14:45
Tisková zpráva
13.12.2013 14:45
The following study shows what the impact of the number of roof windows, their orientation to the cardinal directions, and type of glazing is on heating energy demand. A typical object of a family house with a residential attic was chosen for evaluation, which is gradually oriented toward the cardinal directions and assessed with various envelope parameters. For illustration, the study even evaluates unrealizable situations such as the orientation of living spaces to the north or a building without roof windows.
The impact of the number of roof windows on the specific heating energy demand Ea
The selected object, with variable construction parameters (see Table 1), was evaluated for three different NZU defined levels of specific heating energy demand Ea<35 kWh/m²year, Ea<55 kWh/m²year, Ea<70 kWh/m²year. (A house is considered low-energy if it meets Ea<50 kWh/m²year).
The evaluation included three types of glazing: standard insulating double-glazing marked 59, soundproof and overheating double-glazing marked 60, and low-energy triple-glazing marked 66.
Calculations were made for 0 pcs, 2 pcs, and 5 pcs of roof windows for orientations S, J, V, Z.
The following graphs deal with the level of specific heating energy demand Ea<55 kWh/m²year.
The heating energy demand decreases with the increasing number of roof windows with glazing 59 when oriented to the south reduces, remains constant to the east and west, and marginally increases when oriented to the north.
The heating energy demand decreases with the increasing number of roof windows with soundproof and overheating double glazing --60. when oriented to the south, east, and west reduces, and marginally increases when oriented to the north. The ratio between Uw and g (thermal losses and gains) is optimized even for glasses primarily intended to reduce passive solar gains.
The heating energy demand decreases with the increasing number of roof windows with glazing 66 when oriented to the south, east, and west reduces, remains constant when oriented to the north. The ratio between Uw and g (thermal losses and gains) is optimized.
From the perspective of daylight quality in the attic of the given house (for more on the issue of daylight in attics, read here), 5 roof windows are optimal. From the perspective of heating energy demand (when the orientations of living rooms are east-south-west), they also provide a reduction in heating energy demand Ea regardless of the type of glazing.
The aspect of utilizing thermal gains and their potential elimination in the summer period should be considered already at the design stage of roof windows and they should be fitted with external shading accessories.
If we want to financially quantify the energetically most unfavorable variant and compare it with the variant without roof windows, we will compare the variant of five roof windows with double glazing 59 (Ea 61kWh/m2 year) oriented to the north with the variant of a house without roof windows (Ea 60kWh/m² year). Considering the current price of 1 kWh at about 3 CZK (e.g., heating with electricity in the ČEZ distribution territory – the average price of kWh in peak hours is 3.21 crowns, in off-peak hours 2.63 crowns) and with a house size of 111.3m², the financial difference between these variants is 334 CZK per year. It should be noted that this variant of orienting the house to the north is only conceptual and the house with the orientation of living rooms to the north is legislatively unrealizable. At the same time, it is very difficult to financially express the qualitative benefit of daylight with the variant having more windows.
What impact do roof windows have on heating energy demand Ea in houses with a heating energy demand of less than 35 kWh/m²year can be found at www.velux.cz.
Study prepared by:
The entire study is available for download here.
|
|
The impact of the number of roof windows on the specific heating energy demand Ea
The selected object, with variable construction parameters (see Table 1), was evaluated for three different NZU defined levels of specific heating energy demand Ea<35 kWh/m²year, Ea<55 kWh/m²year, Ea<70 kWh/m²year. (A house is considered low-energy if it meets Ea<50 kWh/m²year).
The evaluation included three types of glazing: standard insulating double-glazing marked 59, soundproof and overheating double-glazing marked 60, and low-energy triple-glazing marked 66.
Calculations were made for 0 pcs, 2 pcs, and 5 pcs of roof windows for orientations S, J, V, Z.
The following graphs deal with the level of specific heating energy demand Ea<55 kWh/m²year.
 |
| Tab:1 selected parameters of roof windows |
 |
| Tab:2 selected parameters of the object |
 |
| Graph 1: assessment of specific heating energy demand Ea (level approx. 55 kWh/m2year) depending on the number of roof windows and their orientation to the cardinal directions for standard insulating double glazing --59. |
 |
| Table for Graph 1 |
The heating energy demand decreases with the increasing number of roof windows with glazing 59 when oriented to the south reduces, remains constant to the east and west, and marginally increases when oriented to the north.
 |
| Graph 2: assessment of specific heating energy demand Ea (level approx. 55 kWh/m2year) depending on the number of roof windows and their orientation to the cardinal directions for soundproof and overheating double glazing --60. |
 |
| Table for Graph 2 |
The heating energy demand decreases with the increasing number of roof windows with soundproof and overheating double glazing --60. when oriented to the south, east, and west reduces, and marginally increases when oriented to the north. The ratio between Uw and g (thermal losses and gains) is optimized even for glasses primarily intended to reduce passive solar gains.
 |
| Graph 3: assessment of specific heating energy demand Ea depending on the number of roof windows and their orientation to the cardinal directions for low-energy triple glazing--66. |
 |
| Table for Graph 3 |
The heating energy demand decreases with the increasing number of roof windows with glazing 66 when oriented to the south, east, and west reduces, remains constant when oriented to the north. The ratio between Uw and g (thermal losses and gains) is optimized.
From the perspective of daylight quality in the attic of the given house (for more on the issue of daylight in attics, read here), 5 roof windows are optimal. From the perspective of heating energy demand (when the orientations of living rooms are east-south-west), they also provide a reduction in heating energy demand Ea regardless of the type of glazing.
The aspect of utilizing thermal gains and their potential elimination in the summer period should be considered already at the design stage of roof windows and they should be fitted with external shading accessories.
If we want to financially quantify the energetically most unfavorable variant and compare it with the variant without roof windows, we will compare the variant of five roof windows with double glazing 59 (Ea 61kWh/m2 year) oriented to the north with the variant of a house without roof windows (Ea 60kWh/m² year). Considering the current price of 1 kWh at about 3 CZK (e.g., heating with electricity in the ČEZ distribution territory – the average price of kWh in peak hours is 3.21 crowns, in off-peak hours 2.63 crowns) and with a house size of 111.3m², the financial difference between these variants is 334 CZK per year. It should be noted that this variant of orienting the house to the north is only conceptual and the house with the orientation of living rooms to the north is legislatively unrealizable. At the same time, it is very difficult to financially express the qualitative benefit of daylight with the variant having more windows.
What impact do roof windows have on heating energy demand Ea in houses with a heating energy demand of less than 35 kWh/m²year can be found at www.velux.cz.
Study prepared by:
 |
The entire study is available for download here.
The English translation is powered by AI tool. Switch to Czech to view the original text source.
0 comments
add comment
