ZEMCH 2019 International Conference Proceedings April.2020 | Page 145
1. Introduction
Buildings are responsible for consuming approximately 40% of energy and emitting 36% of CO2
in the EU [1]. Reducing energy consumption in buildings is one of the main areas that require energy
efficient interventions for reducing their carbon footprint and achieving the emission targets as set in
the Paris Agreement [2]. Thermally insulating building envelopes can help in reducing the space
heating energy consumption and achieving energy efficiency in buildings. Windows are often the
thermally poor performing element in the building envelope and can have heat transfer coefficients (U‐
value) up to 10 times high in comparison of an insulated roof [3]. Window thermal shutters can be used
to reduce heat loss, solar shading and glare [4]. Thermal shutters can improve the thermal performance
of a double‐glazed window by 25%‐30% [5] and can be a non‐intrusive option for internally upgrading
windows of historic buildings without any change in the external façade. Thermal performance of
timber‐framed sash windows can be improved cost effectively using thermal shutters instead of
replacing it with standard double glazing. Heat loss through windows can be reduced up to 60% by
using window shutters insulated with conventional thermal insulation materials [6]. Further decreases
in heat loss would need greater thickness of a shutter’s thermal insulation material, which may not be
aesthetically desirable nor ideal for achieving smart windows. To address this issue, alternative
materials are required to be employed.
Previously, Phase Change Materials (PCMs) have been investigated as one of the options in
external window shutter application in summer climatic conditions and was found to have reduced the
heat gain through windows by 23.29% [7]. Use of PCM in an aluminum hollow blade internal window
shutter was investigated by Silva et al. [8] and found to have reduced the heat flux by 10W/m2 in the
measurement chamber in summer climate conditions in a Mediterranean region. Vacuum Insulation
Panels (VIPs), an advanced thermal insulation material, have been suggested to improve the
performance of thermal window shutters relative to PCMs(?) without any effect on overall thickness
[9,10]. VIPs have a thermal conductivity that is potentially 5‐8 times lower compared to that of a
conventional thermal insulation material [11,12,13]. VIP insulation is a suitable window shutter
application due to its low thermal conductivity, thinner section and damage protection inside the outer
cover of thermal shutter. However, the issue of thermal bridging for VIP insulated thermal window
shutters has been highlighted to have significant impact on the overall window thermal performance
[9]. This paper further investigates the effects of thermal bridging and air gap/cavity between the
window and the shutter and presence of shutter trickle vent on thermal performance of VIP insulated
window shutter.
2. Methodology
Static thermal simulations were conducted in VOLTRA, which is a thermal analysis software used
for simulating three‐dimensional transient heat transfer [14]. A 1000 x1000 mm double‐glazed window
with 50 mm aluminum frame and an overall U‐value of 1.4 W/m2K was modelled. The simulations
were done for a VIP window shutter, with a thermal conductivity of 0.006 W/mK, for the following
combination scenarios:
Geometry:
Air gap size:
Bare window (without thermal shutter)
50 mm
Window and internal shutter with VIP
100 mm
insulation
150 mm
200 mm
Ventilation:
No ventilation/trickle vent
Walling construction:
Trickle ventilation (500mm)
Typical cavity insulated wall
Adiabatic walls
Thermal Performance of Vacuum Insulated Window Shutter Systems
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