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Thermal Performance and Needs of Buildings


During wintertime, the issue of heating is often a burden not only draining people’s pockets
but also harms the environment as achieving thermal comfort is usually done through burning
materials like wood, causing deforestation, emissions of toxic substances which leads to
long-term effects on residents health and well being. In order to reduce heat transfer, wall
insulation is often used in cold areas in order to reduce their thermal conductivity value
(U-value), however, the use of appropriate glazing systems is often disregarded resulting in
huge losses and consequently increased heating needs.

According to the second law of thermodynamics, whenever we have a temperature difference
between two systems, heat flows from high to low temperatures, and this heat transfer can
take place in three modes, conduction, convection, and radiation. Since in this article we are
interested in studying the effect of glazing systems we will only consider conduction and
radiation and we will disregard convection that requires a fluid as a medium of transfer.
Single glass has poor insulating properties, in order to overcome this issue static glazing
technologies are one of the cheapest and efficient ways, multiple panes are used separated by
either air, vacuum, or a gas such as argon or krypton. Fenestration systems with multiple
panes showed considerably low thermal conductivity while preserving the visible
transmittance (the part of the light spectrum that can be seen with the naked eye) and SHGC
(solar heat gain coefficient, which represents the radiation that was harvested and transferred
to the building by the glazing system either directly from the sun or through reflections).
Filling the gap with inert, non-toxic gases characterized by low thermal conductivity has been
proven to significantly reduce heat losses, however, it increases the overall cost of the
fenestration system.

Case study:
In order to better understand and to analyze the thermal losses and heating/cooling needs
change with different glazing systems, a simulation was carried out on a 100 m2 house
located in Morocco, more specifically in the city of Ifrane, that is characterized by its harsh
climate recording the lowest temperature registered in Africa (-11 C), the elevation of the city
is 1665 m above sea level. We consider a 100m2 house, south oriented, 15% window area (18
m2). Heat losses due to conduction were calculated using the convection formula: 𝑸𝒄 = 𝑼 ∗
𝑨 ∗ 𝜟𝑻 while radiation heat losses were calculated using the Stefan Boltzmann Law
(Radiation): 𝑸𝒓 = 𝒆 ∗ 𝝈 ∗ 𝑨 ∗ (𝑇 − ). with A the area of the window, U the thermal 4 𝑇𝑐4
transmission coefficient, T the inside temperature, Tc outside temperature, e emissivity, 𝝈
Stefan Boltzmann constant. Later the energy needs of the house for heating and cooling were
estimated using a multizone building model in TRNSYS software.

Four scenarios were taken into consideration in this study, a clear 4 mm glass was used as a
reference and was compared with:
*4 mm, clear glass panes were used in all scenarios.
1-Double glass air filled, total thickness=14mm, u-value=3.009 W/m2.k.
2-Double glass Argon filled, total thickness=24 mm, u-value=1.4 W/m2.k.
3-Double Glass Krypton filled, total thickness= 24 mm,u-value=0.86 W/m2.k.
4-Triple glazing air filled, total thickness=36mm,u-value=1.73 W/m2.k.

Results and discussion :
Heat loss calculation results:

From the graph above, we can notice that heat loss increases with using glazing systems with
high thermal conductivity. In other words, the higher the U-value is, the highest losses are.
The best performance was recorded by fenestration systems with gas filling.

Heating & Cooling Simulation Results:
In order to simulate the energy needed to overcome the heat losses, for heating and cooling
some HVAC parameters were set: Natural air exchange was assumed to be 0.25 changes/h, no
mechanical ventilation was taken into consideration. The inside temperature was fixed at 18
°C day time and 15 °C at night during cold months, and during summer it was set to 26 °C.

We can notice that for heating, moving from single normal 4mm glass to double air-filled, triple, double Argon filled, or double Krypton filled saved 1497.543 KWh (15.62 %), 2198.057 KWh ( 21.66 %), 3127.071 KWh (28 %), 2138.407 KWh (18.62 %) respectively, while for cooling using double-Air filled saved 11,90 % of the power used, using Double Argon filled saved 29.9%, Double Krypton filled 47,86 % and Triple glazing saved around 23.35%.

This project showed that disregarding the use of appropriate glazing systems can result in
huge losses and consequently in high energy bills, the use of static glazing technologies can
help reduce the thermal conductivity of fenestration systems while preserving visual comfort.

Ghadbane Aroune. Supervised by Dr Asmae Khaldoun, (2020). TOWARD SUSTAINABLE
ENGINEERING, Al Akhawayn University . AUI capstone repository .

Editors note:

If you have listened to The Energy Geek  videos about net-zero homes, you may note that this article came to the conclusion that Double Pane Argon filled windows are the most cost effective which seems counter to the advice given on this website to use triple pane windows in net-zero homes. These two conclusions are not, as you might think, mutually exclusive.  Aroune’s work for this article is based on a different climate, and different economic markets. Aroune did not test triple pane Low-e argon windows, and he did not do his tests  in a harsh climate like New England.In the Moroccan climate, and economic system double pane windows offer the best value.  That said, we stand by our conclusion that for the best performance in cold climates, Triple Pane, Low-e, Argon windows are our pick.

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