Translucent fences (this is how windows are called in the construction science) are responsible for about 20–30% of total heat losses of the building. Heat flow passes through the window structure as a result of temperature difference outdoors and indoors (we know from school that heat is transferred from a more heated to a less heated body). These heat losses are called transmission losses. Heat energy is also lost to heat the cold air that penetrates through the window leaks and enters the room. These heat losses are called infiltration losses.
To reduce heat loss through the windows and to ensure thermal comfort in the dwellings, we replace old wooden windows with multiple glazed windows. However, this replacement often occurs without consideration of air mode in the premises. Although by reducing air permeability of the multiple glazed windows we can save up to 85% of heat, we should remember that the buildings are designed to ensure sanitary conditions for humans, and organization of proper ventilation in the premises is one of these conditions.
| ATTENTION! Higher concentrations of carbon dioxide produced indoors by people while breathing air have harmful effect on health and well-being. Increased concentration of CO₂ over 0.9 l/m³ (medium and low quality premises) leads to inflammation of the eyes and mucous membranes, lowers attention, causes headaches, fatigue, etc. |
The table below presents requirements to the premises with respect to concentration of carbon dioxide in the air
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Requirements to the premises with respect to CO₂ concentration in the air |
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Type of premises |
СО₂concentration in the air |
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Low quality |
0.2% = 2 l/m³ |
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Medium quality |
0.11% = 1.1 l/m³ |
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High quality |
0.09% = 0.9 l/m³ |
The problem of non-compliance with norms of microclimate indicators indoors can be partially solved with periodical airing, but in this case, along with fresh air, dust and street noise get inside. In addition, one has to open and close the window or window leaf all the time. Therefore, it is recommended to install flap ventilators during window replacement. One such device costs UAH 250–300. Typically, it is equipped with flow control allowing change of intensity and direction of the supply air.
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Installation of the flap ventilator resolves the issues of ventilation and "absolute" sealing of premises, but energy efficiency of the installed structure will be 50% of heat losses of the old window. Reduction of the transmission heat losses through the windows is ensured by use of the energy efficient multiple glazed windows. The state building codes (DBN) in Ukraine set minimum requirements for the windows in the process of construction and reconstruction of housing. In Ukraine, there are two temperature zones, the first zone covers all oblasts of Ukraine except the Autonomous Republic of Crimea, Zaporizhia, Kherson, Mykolaiv, Odesa and Zakarpattya oblasts. According to building codes, the windows with energy efficiency class not lower than A2 should be installed in the first temperature zone. |
Therefore, in most cases the windows which are believed to be energy efficient in Ukraine are not really energy efficient. Energy efficient windows provide penetration of sunlight into the room and passive heating, the required air exchange and reflection and conservation of the radiation heat of the building envelope indoors, and heat savings. Energy saving due to installation of such windows is about 230 kW·h/m² of its surface over the heating period (0.197 Gcal/m² of window).
Unit cost of such window is UAH 1,600–1,800/m².
If there is an opportunity to replace windows, one must approach selection seriously and select not only the material but also glass and fittings, and follow all installation and operation rules.
The table below analyzes advantages and disadvantages of different types of windows
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Types of windows |
Advantages |
Disadvantages |
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WOODEN |
× High heat and acoustic insulation of premises; |
× Humidity permeability; × Necessity of permanent care with special tools; × High inflammability. |
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METAL-PLASTIC |
× Practically unlimited range of sizes, colors and forms; × Long life cycle; × Reliable protection from humidity, cold, heat, noise; × Easy care; × Low inflammability. |
× Poor air permeability; × Seriously damaged parts can rarely be repaired, usually defective elements are replaced; × Meteosensitivity. |
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ALUMINUM |
× Light weight and durability of material; × Not subject to impact of natural factors; × Environmental friendliness; × Long life cycle; × Easy care; × Ideal for glazing of large spaces; × Fire safety |
× High thermal conductivity compared to wood and PVC. × Comparatively high cost.
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In absence of funds for window replacement, one should not forget at least about thorough insulation of the existing windows in the paired or individual wooden transoms. This could also give a significant energy saving effect. But for this purpose, not the stationery Scotch tape should be used but sealing in the form of a woolen cord or foam rubber which can be purchased at the hardware stores. According to the measurements, amount of air infiltration in case of a careful window sealing significantly reduces (by 2–3 times).
Along with decrease of air flow, heat losses for heating of cold air with infiltration reduce.
Amount of air that enters through the window, kg/m² of window
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# |
Window characteristics |
Outdoor air temperature, °С |
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|
-2 |
-10 |
-23 |
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1. |
Window without sealing, gap width - 1 mm |
20 |
24 |
30 |
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2. |
Sealing with semi-woolen cord |
9 |
11 |
14 |
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3. |
Sealing with foam rubber |
6 |
8 |
10 |
Heat losses with infiltration through the window in a wooden transom with double separated rabbet ledges (% of total losses)
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# |
Window characteristics |
Outdoor air temperature , °С |
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|
-2 |
-10 |
-23 |
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1. |
Window without sealing, gap width - 1 mm |
70% |
74% |
78% |
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2. |
Sealing with semi-woolen cord |
51% |
56% |
61% |
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3. |
Sealing with foam rubber |
43% |
49% |
54% |
As you can see, there are many "good and different" windows. You can buy and install new windows but you can also give a second life to your wooden windows. So, the choice is yours!