In
buildings, glazing plays an important role in influencing energy
demands and lighting requirements. The interrelation between
fenestration design and thermal/visual performance has been receiving
much attentions. As a matter of fact, extensively glazed buildings from
commercial complexes to residences are common in modern architecture
for their lightness and good exterior appearance. But this design trend
intensifies the solar heat gain and therefore the air-conditioning
electricity consumptions. Most buildings in the warm climate are
single glazed, with clear glass offered for residential developments and
absorptive/reflective glass for commercial applications. Alternatively,
ventilated double-glazing with a stream of air flowing through the
glazing cavity can be used. For the warm climate region, solar heat
absorption by the air stream has no direct application value. Instead,
solar heat absorption via a liquid water stream can be readily
transferred to a domestic hot water system. In this study, the system
performance of liquid-filled double glazing integrated with a
water-heater has been investigated. Figure 1 shows the working
principle. The cavity in a double-pane glazing is incorporated with
water inlet and outlet headers at its lower and upper ends. Together
with a water-to-water heat exchanger at the top and the
interconnecting tubing at the side (all are housed in the window
frame), this forms a fully-enclosed water circuit. The heat conversion
to another water stream via the heat exchanger allows the full
utilization of the absorbed solar heat.
Figure 1: Water-flow double-pane window
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Experimental
rigs were designed and constructed for the investigation. At first, a
small experimental unit able to compare directly the solar transmission
and water heat gain of two alternative glazing options was made use of.
The gained experiences then facilitated the production of a full scale
prototype tested at the external wall of a climate chamber, where
thermal and visual comforts were fully investigated, as in Figure 2. A
numerical model validated by the experimental data was incorporated
into the whole-building simulation software for studying the
integrative performance under different conditions of building use,
glazing properties, orientation, occupancy, seasons, and the like.
Solid technical information was gathered on the best use of this
innovative system, and on the energy/cost saving potential of
alternative arrangements. Our results show that the use of absorptive
glass panes can allow better water heat gain. The incorporation of
clear glass pane to a low-emissivity integrated glass unit allows
better visibility and daylight utilization. The economic payback period
is around four years. This makes this innovative technology very good
application potential in the private construction industry, like in
hotels, health clubs, sport centers, swimming pools, elderly
homes, residences, and any domestic commercial complex with a stable hot
water demand. The situation is different from many photovoltaic product
applications which rely heavily on government subsidies as in many
developed countries.
Figure 2: Dr Tin-tai Chow and his PhD student
Chunying Li at the full-scale water-flow window experimental system
Dr Tin-tai CHOW
Division of Building Science
and Technology
City University of Hong Kong
bsttchow@cityu.edu.hk
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