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|Document Type: ||Thesis or dissertation|
|Title: ||Heat and mass transfer behaviours of building materials and structures|
|Authors: ||Parra Saldivar, Maria Luisa|
|Supervisors: ||Batty, W. J.|
Greenhalgh, Douglas A.
|Issue Date: ||Mar-2005|
|Abstract: ||Heat storage as a means to respond to the requirements for improved energy
efficiency motivated this study. The objective was to evaluate the impact of thermal
energy storage systems in dwellings under Mexican climatic conditions. In the first part
of this work thermal behaviors of adobe traditional architecture is discussed; in the
second part a latent heat storage system using phase change materials (PCMs) is
proposed and assessed.
The high thermal mass structural elements of adobe traditional architecture have been
charactefted as heat wave modulators. Nevertheless, the moisture content in these
structures also plays a significant role as a means for heat storage and potentially
enhancing thermal lag. The objective of this part of the study was to assess the scope
of existing coupled heat and mass transport models regarding water contained latent
heat storage on porous structures.
The significant contribution of latent heat storage recognized in adobe structures, led to
the study of a solar-thermal storage system using (PCMs).
The objective of this part of the study was twofold: 1) Enhance the existing
computational models on the Stephan problem by considering the effect of regional
variations (weather conditions imposed) on the boundary conditions. 2) Evaluate the
impact of the solar-thermal system proposed when applied in dwellings in view of
regional variations under Mexican weather conditions.
Solar-thermal storage systems independent of the structure offer the possibility to be
applied to existing buildings as well as new constructions. The proposal is a storage
element that constitutes internal blinds in windows. The computational model of the
Stephan problem was solved with the enthalpy method. Simulations were run under
different sets of climatic conditions. For the first time the main factors for promoting
system's optimisation, when gathered in a single comparison study, provided a more
general insight on system's performance. Experimental work was also carried out
regarding the charging of the heat storage unit by heat gains other than direct
radiation, and the storage unit's performance as insulator. A large-scale solar simulator
Statistical analysis of experimental results showed interesting findings including: The
important role that internal heat gains play on the charging of the latent heat storage
unit proposed. A larger effect on the discharging ratio was found with lower air
temperatures than with faster air flow rates. The faster discharging rate tests also
released slightly more energy. PCM volume was found to be the most critical factor on
system performance. The importance of providing the means to discharge the total
quantity of heat stored was pointed out. For the cooling mode, elements to enhance
discharging might be required. For system control, thermal insulation was found to be
an effective measure when the discharging is required to occur over a longer period.
The multiple PCM unit was found to be more efficient during the charging process
(storing more energy) than units containing a single PCM. Nevertheless the single PCM
unit performed better for cooling than the multiple PCM unit. The question was raised as
to what extent PCM thermal conductivity actually influences system's performance.
The thermal storage system proposed in this study reduced the heating system energy
consumption requirements for an experimental room by 28.6%.|
|Appears in Collections:||PhD and Masters by research theses (School of Engineering)|
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