Relations between structural and dynamic thermal characteristics of building walls

The effect of internal thermal structure on dynamic characteristics of walls is analyzed. The concept of structure factors is introduced and the conditions they impose on response factors are given. Simple examples of multilayer walls, representing different types of thermal resistance and capacity distribution, are analyzed to illustrate general relations between structure factors and response factors. The idea of the ``thermally equivalent wall``, a plane multilayer structure, with dynamic characteristics similar to those of a complex structure, in which three-dimensional heat flow occurs, is presented

Dynamic test method of PCM content in fiberous insulation

Przedstawiono koncepcję metodyki prowadzenia testowych pomiarów zawartości materiału fazowo-zmiennego, w dużych i w założeniu jednorodnych próbkach izolacji z włókna szklanego lub celulozy, z użyciem aparatu płytowego. Podano sposób szacowania stałej czasowej próbki w procesie ustalania się strumienia ciepła po skoku temperatury.Dynamic test method of PCM content in fiberous insulation is considered. Heat balance of a sample of material with PCM is analyzed. Time constants for 7.6 cm thick samples of PCM-Enhanced Cellulose Insulation are estimated

The performance check between whole building thermal performance criteria and exterior wall measured clear wall R-value, thermal bridging, thermal mass, and airtightness

At the last IEA Annex 32 meeting it was proposed that the annex develop the links between level 1 (the whole building performance) and level 2 (the envelope system). This paper provides a case study of just that type of connection. An exterior wall mockup is hot box tested and modeled in the laboratory. Measurements of the steady state and dynamic behavior of this mockup are used as the basis to define the thermal bridging, thermal mass benefit and air tightness of the whole wall system. These level two performance characteristics are related to the whole building performance. They can be analyzed by a finite difference modeling of the wall assembly. An equivalent wall theory is used to convert three dimensional heat flow to one dimensional terms that capture thermal mass effects, which in turn are used in a common whole building simulation model. This paper illustrates a performance check between the thermal performance of a Massive ICF (Insulating Concrete Form) wall system mocked up (level 2) and Whole Building Performance criteria (level 1) such as total space heating and cooling loads (thermal comfort)

Thermal load mitigation and passive cooling in residential attics containing PCM-enhanced insulations

Residential attics has the potential to be one of the most energy efficient building components by combining thermal processes of attic floor insulation, attic air space, ventilation in attics, and solar collecting roof decks. Large amounts of solar energy collected by the roofs in cooling-dominated and mixed climates generate excess cooling loads, which need to be removed from the building by the space conditioning systems. This paper investigates potential ways to improve the thermal design of the residential home attics to minimize the cooling energy consumption in the cooling-dominated and mixed climates. Dynamic thermal characteristics of thick attic floor insulations and blends of phase change materials (PCMs) with insulations are analyzed. Both approaches can provide notable reductions of thermal loads at the attic level. In addition, a significant time shift of peak-hour loads can move a major operation time for air conditioning system from the daytime peak hours to nighttime low demand hours. A reverse heat flow direction can be observed during the day in the case of really thick layers of bulk insulation or PCM-enhanced insulations, compared to the rest of the building envelope components. This effect may provide free passive cooling to the building, and can be very useful in locations of double electrical tariffs with high daytime peak-hour electric energy rates and less-expensive off-peak energy cost. In both of the above cases, an addition of PCM to the bulk insulation brings substantial performance enhancement not available for traditional insulation applications. This paper presents a short overview of dynamic material characteristics and energy performance data necessary for future dynamic applications of different configurations of the attic floor insulation and PCM-insulation blends in residential homes. A series of whole-building scale and material scale numerical simulations were performed on a single story ranch house to analyze potential energy savings and optimize location of PCM within the attic insulation

A new approach for analysis of complex building envelopes in whole building energy simulations

The ability for reduction of whole-building energy consumption depends, in large scales, from correct predictions of building thermal loads with the building's envelope characteristics being one of the most important factors. Since most of today's building envelopes are complex three-dimensional networks of structural, insulation, and finish materials, the potential for correct predictions of their thermal performance depends on availability of acceptable, scientifically valid, consensus procedures for accurately implementing a building's envelope thermal characteristics into whole-building energy simulation programs. This paper is discusses a joint LBNL and Fraunhofer CSE project, focused on the upgrade of the already existing THERM program and its integration with EnergyPlus, a whole-building energy simulation tool. It is expected that these two programs, combined together, will eliminate typical analytical limitations of most of existing whole building energy tools, capable to simulate only simplified one-dimensional envelopes. The main research challenge is the design of an easy to implement upgrade of the THERM numerical tool to allow analysis of complex building envelope structures. The new version of THERM needs to be able to modify thermal characteristics of the complex three-dimensional (3-D) wall assemblies, in a way to enable their use in whole building energy simulation programs. It will be achieved through an application of the unique theoretical procedure, which will allow a generation of the simplified one-dimensional (1-D) wall geometry and material characteristics to fully and accuratly capture the dynamic effects of thermal bridges. At this stage of the project, the research team focuses on development of theoretical bases for necessary changes in the THERM framework. This paper explains the theoretical methodology which is used and presents some results from the series of steady-state and dynamic heat transfer simulations performed on building envelopes architectural components, to illustrate the accuracy limitations associated with thermal calculation methods recommended by building energy codes worldwide

Continuum Dislocation Dynamics: Classical Theory and Contemporary Models

The continuum theory of dislocation fields is discussed in this chapter with an emphasis on the formulations relevant to infinitesimal deformation of single crystals. Both the classical and contemporary developments are concisely outlined. The classical theory of dislocation fields is introduced first for static and dynamic dislocation configurations, followed by a brief discussion of the shortcomings of the classical theory in predicting plasticity of crystals. In this regard, the lack of connection between the evolution of the dislocation field and internal stress state of the crystal is particularly highlighted. The more recent phenomenological and statistically-based formalisms of continuum dislocation dynamics are then introduced. As discussed in the pertinent sections, these formalisms properly connect the evolution of the dislocation fields with the internal stress state in and thus offer frameworks for predicting the plastic behavior of crystals