Biomimetics design tool used to develop new components for lower-energy buildings

This thesis was submitted for the degree of Doctor of Engineering in Environmental Technology and awarded by Brunel University.The contributions to knowledge documented in this doctoral thesis are two-fold. The first contribution is in the application of a new biomimetic design tool called BioTRIZ. Its creators claim it can be used to facilitate the transfer of biological principles to solve engineering problems. The core case-study of this thesis documents how this tool was used to frame and systematically explore low-energy solutions to a key technical problem in the underdeveloped field of radiative cooling. Radiative cooling is a passive mechanism through which heat from a building can be rejected to the sky – an abundant but underused natural heat sink. Published in the Journal of Bionic Engineering, the study was the first independent application of BioTRIZ in the academic literature. The second contribution to knowledge is in the design, development and testing of the most promising biomimetic concept to come out of the BioTRIZ radiative cooling study. ‘Heat-selective’ insulation gives a roof mass a cool view of the sky because integrated pathways focus and channel longwave thermal radiation through it. It is biomimetic because it achieves infrared transparency by adding structural hierarchy to the component, rather than manipulating the properties of the material itself. Test panels on a rooftop in central London cooled to between 6 and 13 degrees below ambient temperature on May and April nights. Radiative cooling powers of between 25 and 70 W/m2 were measured when plates were at ambient temperature. Daytime radiative cooling below ambient temperature occurred when clouds blocked direct sunlight. Radiative cooling power was increased by 37% using reflective ‘funnels’. Two additional BioTRIZ analyses are presented as minor case studies. They each attend to a key technical problem in the field of passive thermal energy storage in buildings. They serve to illustrate the type of results that can be expected from using BioTRIZ during low-energy building design

Tests of prototype PCM 'sails' for office cooling

This is the post-print version of the final paper published in Applied Thermal Engineering. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.PCM modules, constructed from a paraffin/LDPE composite, were tested in an occupied London office, in summer. Design variations tested the effect on heat transfer of a black paint or aluminium surface, the effect of different phase transition zones and the effect of discharging heat inside or outside. The modules’ temperatures were monitored along with airflow rate, air temperature and globe temperature. Their small size meant any effect on room temperature was negligible. Using DSC measurements of the PCMs’ thermophysical properties, in conjunction with the environmental measurements, a semi-empirical model of the modules was constructed in FLUENT using an enthalpy-porosity formulation to model phase change. Good validation was obtained for all modules using the temperature measurements with notable divergence when maximum liquid fraction was reached. The model was validated by the temperature measurements and used to generate mean liquid fraction and surface heat transfer rate profiles for performance comparisons. The broad phase transition zones of the PCMs results in wasted latent heat capacity. Black modules transfer heat and exhaust latent storage capacity significantly quicker than aluminium modules, due to radiant exchange. Discharging heat outside leads to an increase in thermal storage capacity and a higher rate of heat absorption.Buro Happold Engineers and the EPSRC

Assessing the number of users who are excluded by domestic heating controls

This is the pre-print version of the Article. This Article is also referred to as: "Assessing the 'Design Exclusion' of Heating Controls at a Low-Cost, Low-Carbon Housing Development". - Copyright @ 2011 Taylor & FrancisSpace heating accounts for almost 60% of the energy delivered to housing which in turn accounts for nearly 27% of the total UK's carbon emissions. This study was conducted to investigate the influence of heating control design on the degree of ‘user exclusion’. This was calculated using the Design Exclusion Calculator, developed by the Engineering Design Centre at the University of Cambridge. To elucidate the capability requirements of the system, a detailed hierarchical task analysis was produced, due to the complexity of the overall task. The Exclusion Calculation found that the current design placed excessive demands upon the capabilities of at least 9.5% of the UK population over 16 years old, particularly in terms of ‘vision’, ‘thinking’ and ‘dexterity’ requirements. This increased to 20.7% for users over 60 years old. The method does not account for the level of numeracy and literacy and so the true exclusion may be higher. Usability testing was conducted to help validate the results which indicated that 66% of users at a low-carbon housing development could not programme their controls as desired. Therefore, more detailed analysis of the cognitive demands placed upon the users is required to understand where problems within the programming process occur. Further research focusing on this cognitive interaction will work towards a solution that may allow users to behave easily in a more sustainable manner

Breathing walls: The design of porous materials for heat exchange and decentralized ventilation

This study demonstrates how to design pores in building materials so that incoming fresh air can be efficiently tempered with low-grade heat while conduction losses are kept to a minimum. Any base material can be used in principle, so long as it can be manufactured with millimeter-scale air channels. The channel-pores are optimized according to the thermal conductivity of the base material, the dimensions of the panel, and the suction pressure sustained by a given fan or a chimney. A water circuit is integrated at the interior surface to ensure direct thermal contact and prevent radiant discomfort. Correlations from the thermal sciences literature were used to optimize the size and distribution of channel-pores in wood, glass, and concrete test panels. The measurements showed good agreement with theory and were presented in a general form so that designers can predict the steady-state performance of any optimal design in sensible heat-transfer mode. Schlieren imaging was used to characterize the different regimes of mixed convection at the interior and exterior surface. The data explain the discrepancy between prediction and measurement in the dynamic insulation literature, and how the integrated water circuit overcomes these problems. Surface heat-flux measurements were correlated in a general form so that designers can account for convection at the interior and exterior surface