• Energy Research

This paper is focused on the energy performance of buildings containing massive exterior building envelope components. The effect of mass and insulation location on heating and cooling loads is analyzed for six characteristic wall configurations. Correlations between structural and dynamic thermal characteristics of walls are discussed. A simple one-room model of a building exposed to periodic temperature changes is analyzed to illustrate the effect of material configuration on the ability of a wall to dampen interior temperature swings. Whole-building dynamic modeling using DOE-2.1E is employed for the energy analysis of a one-story residential building with various exterior wall configurations for six different US climates. The best thermal performance is obtained when massive material layers are located at the inner side and directly exposed to the interior space.

Abstract 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.

Abstract A method of derivation of the conduction z-transfer function coefficients from response factors, for three-dimensional wall assemblies, is described. Results of the conduction z-transfer function coefficients calculations are presented for clear walls and separated details which are listed in ASHRAE research project 1145-TRP: “Modeling Two- and Three-Dimensional Heat Transfer Through Composite Wall and Roof Assemblies in Hourly Energy Simulation Programs”. Resistances, three-dimensional response factors and so-called structure factors, have been computed using the finite-difference computer code HEATING 7.2. The z-transfer function coefficients were then derived from a set of linear equations, constituting relationships with the response factors, which were solved using the minimum-error procedure. Test simulations show perfect compatibility of the heat flux calculated using three-dimensional response factors and three-dimensional z-transfer function coefficients, derived from the response factors.

Abstract In most whole building thermal modeling computer programs like DOE-2, BLAST, or ENERGY PLUS simplified, one-dimensional, parallel path, descriptions of building envelope are used. For several structural and material configurations of building envelope components containing high thermal mass and/or two- and three-dimensional thermal bridges, one-dimensional analysis may generate serious errors in building loads estimation. The method of coupling three-dimensional heat transfer modeling and dynamic hot-box tests for complex wall systems with the whole building thermal simulations is presented in this paper. This procedure can increase the accuracy of the whole building thermal modeling. Current thermal modeling and calculation procedures tend to overestimate the actual field thermal performance of today’s popular building envelope designs, which utilize modern building technologies (sometimes highly conductive structural materials) and feature large fenestration areas and floor plans with many exterior wall corners. Some widely used computer codes were calibrated using field data obtained from light weight wood frame buildings. The same codes are used now for thermal modeling of high mass buildings with significant heat accumulation effects. Also, the effects of extensive thermal shorts on the whole building thermal performance is not accurately reflected by the commonly used one-dimensional energy simulations that are the current bases for building envelopes and systems designing.

Abstract Experimental and theoretical analyses have been performed to determine dynamic thermal characteristics of fiber insulations containing microencapsulated phase change material (PCM). It was followed by a series of transient computer simulations to investigate the performance of a wood-framed wall assembly with PCM-enhanced fiber insulation in different climatic conditions. A novel lab-scale testing procedure with use of the heat flow meter apparatus (HFMA) was introduced in 2009 for the analysis of dynamic thermal characteristics of PCM-enhanced materials. Today, test data on these characteristics is necessary for whole-building simulations, energy analysis, and energy code work. The transient characteristics of PCM-enhanced products depend on the PCM content and a quality of the PCM carrier. In the past, the only existing readily-available method of thermal evaluation of PCMs utilized the differential scanning calorimeter (DSC) methodology. Unfortunately, this method required small and relatively uniform test specimens. This requirement is unrealistic in the case of many PCM-enhanced building envelope products. Small specimens are not representative of PCM-based blends, since these materials are not homogeneous. In this paper, dynamic thermal properties of materials, in which phase change processes occur, are analyzed based on a recently-upgraded dynamic experimental procedure: using the conventional HFMA. In order to theoretically analyze performance of these materials, an integral formula for the total heat flow in finite time interval, across the surface of a wall containing the phase change material, was derived. In numerical analysis of the southern-oriented wall the Typical Meteorological Year (TMY) weather data was used for the summer hot period between June 30th and July 3rd. In these simulations the following three climatic locations were used: Warsaw, Poland, Marseille, France, and Cairo, Egypt. It was found that for internal temperature of 24 °C, peak-hour heat gains were reduced by 23–37% for Marseille and 21–25% for Cairo; similar effects were observed for Warsaw.