The need for heating and cooling in buildings constitutes a considerable part of the total energy use in a country and reducing this need is of outmost importance in order to reach national and international goals for reducing energy use and emissions. One important way of reaching these goals is to increase the proportion of renewable energy used for heating and cooling of buildings. Perhaps the largest obstacle with this is the often occurring mismatch between the availability of renewable energy and the need for heating or cooling, hindering this energy to be used directly. This is one of the problems that can be solved by using thermal energy storage (TES) in order to save the heat or cold from when it is available to when it is needed. This thesis is focusing on the combination of TES techniques and buildings to achieve increased energy efficiency for heating and cooling. Various techniques used for TES as well as the combination of TES in buildings have been investigated and summarized through an extensive literature review. A survey of the Swedish building stock was also performed in order to define building types common in Sweden. Within the scope of this thesis, the survey resulted in the selection of three building types, two single family houses and one office building, out of which the two residential buildings were used in a simulation case study of passive TES with increased thermal mass (both sensible and latent). The second case study presented in the thesis is an evaluation of an existing seasonal borehole storage of solar heat for a residential community. In this case, real measurement data was used in the evaluation and in comparisons with earlier evaluations. The literature reviews showed that using TES opens up potential for reduced energy demand and reduced peak heating and cooling loads as well as possibilities for an increased share of renewable energy to cover the energy demand. By using passive storage through increased thermal mass of a building it is also possible to reduce variations in the indoor temperature and especially reduce excess temperatures during warm periods, which could result in avoiding active cooling in a building that would otherwise need it. The analysis of the combination of TES and building types confirmed that TES has a significant potential for increased energy efficiency in buildings but also highlighted the fact that there is still much research required before some of the technologies can become commercially available. In the simulation case study it was concluded that only a small reduction in heating demand is possible with increased thermal mass, but that the time with indoor temperatures above 24 °C can be reduced by up to 20%. The case study of the borehole storage system showed that although the storage system worked as planned, heat losses in the rest of the system as well as some problems with the system operation resulted in a lower solar fraction than projected. The work presented within this thesis has shown that TES is already used successfully for many building applications (e.g. domestic hot water stores and water tanks for storing solar heat) but that there still is much potential in further use of TES. There are, however, barriers such as a need for more research for some storage technologies as well as storage materials, especially phase change material storage and thermochemical storage. / Behovet av värme och kyla i byggnader utgör en betydande del av ett lands totala energianvändning och att reducera detta behov är av yttersta vikt för att nå nationella samt internationella mål för minskad energianvändning och minskade utsläpp. En viktig väg för att nå dessa mål är att öka andelen förnyelsebar energi för kylning och uppvärmning av byggnader. Det kanske största hindret med detta är det faktum att det ofta råder obalans mellan tillgången på förnyelsebar energi och behovet av värme och kyla, vilket gör att denna energi inte kan utnyttjas direkt. Detta är ett av problemen som kan lösas genom att använda termisk energilagring (TES) för att lagra värme eller kyla från när det finns tillgängligt till dess att det behövs. Denna avhandling fokuserar på kombinationen av TES och byggnader för att nå högre energieffektivitet för uppvärmning och kylning. Olika tekniker för energilagring, samt även kombinationen av TES och byggnader, har undersökts och sammanfattats genom en omfattande litteraturstudie. För att kunna identifiera byggnadstyper vanliga i Sverige gjordes även en kartläggning av det svenska byggnadsbeståndet. Inom ramen för denna avhandling resulterade kartläggningen i valet av tre typbyggnader, två småhus samt en kontorsbyggnad, utav vilka de två småhusen användes i en simuleringsfallstudie av passiv TES genom ökad termisk massa (både sensibel och latent). Den andra fallstudien som presenteras i denna avhandling är en utvärdering av ett existerande borrhålslager för säsongslagring av solvärme i ett bostadsområde. I detta fall användes verkliga mätdata i utvärderingen samt i jämförelser med tidigare utvärderingar. Litteraturstudien visade att användningen av TES öppnar upp möjligheter för minskat energibehov och minskade topplaster för värme och kyla samt även möjligheter till en ökad andel förnyelsebar energi för att täcka energibehovet. Genom att använda passiv lagring genom ökad termisk massa i byggnaden är det även möjligt att minska variationer i inomhustemperaturen och speciellt minska övertemperaturer under varma perioder; något som kan leda till att byggnader som normalt behöver aktiv kylning kan klara sig utan sådan. Analysen av kombinationen av TES och byggnadstyper bekräftade att TES har en betydande potential för ökad energieffektivitet i byggnader, men belyste även det faktum att det fortfarande krävs mycket forskning innan vissa av lagringsteknikerna kan bli kommersiellt tillgängliga. I simuleringsfallstudien drogs slutsatsen att en ökad termisk massa endast kan bidra till en liten minskning i värmebehovet, men att tiden med inomhustemperaturer över 24 °C kan minskas med upp till 20 %. Fallstudien av borrhålslagret visade att även om själva lagringssystemet fungerade som planerat så ledde värmeförluster i resten av systemet, samt vissa problem med driften av systemet, till en lägre solfraktion än beräknat. Arbetet inom denna avhandling har visat att TES redan används med framgång i många byggnadsapplikationer (t.ex. varmvattenberedare eller ackumulatortankar för lagring av solvärme) men att det fortfarande finns en stor potential i en utökad användning av TES. Det finns dock hinder såsom behovet av mer forskning för både vissa lagringstekniker samt lagringsmaterial, i synnerhet för lagring med fasändringsmaterial och termokemisk lagring. / <p>QC 20130225</p>

Construction of tunnels and small- to medium-span bridges is a $12 billion per year industry in the United States, with a significant portion going into buried arch structures. Notwithstanding such expenditure, modern arch design and construction, in many cases, is highly conservative. This is because the closed-form solutions used by most designers today do not correctly account for soil-structure interaction. In fact, soil-structure interaction makes a closed form solution impossible. With the advent of high power computers in recent years, some designers have turned to finite element (FE)modeling as the main vehicle of analysis. Such numerical procedures provide an accurate approximation of physical behavior. Practices using FE analysis for buried arch design almost exclusively use two-dimensional models because they are faster to set up and analyze than three-dimensional models and cost substantially less. However, 2-D models fail to account for the stiffness of the structure and spread of discrete loads in the third-dimension. Both the 1996 and 1998 AASHTO-LRFD Bridge Design Specifications address this problem, providing methods of load reduction. Much of the current reduction, however, is based on research done on concrete bridge decks, and does not account for continuous elastic support or the geometry of the structure. This results in a conservative analysis at low fill covers (<10') and/or increasing spans (>20’). This research provides a method to rectify the discrepancy that arises in discrete loading of 2-D FE models of semi-flexible buried concrete arch bridge, culvert, and tunnel systems due to the plane-strain assumption. Rectification is accomplished by providing a correlation between the deflection of a beam-on-elastic-foundation analysis and a distribution length by which the load in 2-D analysis is reduced. Distribution lengths are derived using bending energy ratios. The correlation considers structural geometry, overburden height, and base soil stiffness. Reduction of the 2-D design load by the proposed distribution length results in shear forces and bending moments nearly equivalent to those obtained from 3-D analysis in the plane of discrete load application transverse to the structure. Less conservative results are also obtained for axial forces. These results are intended for use on structures that are four times the span in length, or longer.

In the past, the disagreement of near-threshold fatigue-crack growth (FCG) rate data generated from constant Kmax tests, high load ratio (minimum to maximum load) constant R tests, and ΔKeff based data was a mysterious issue. Because of the disagreement, a variety of test or analysis methods were created to correlate FCG rate data. It was suspected that the ASTM threshold test method using load reduction was inducing remote crack closure due to plastically deformed material, which caused elevated thresholds and slower rates than steady-state behavior. The first goal of this study was the development of a test method to eliminate remote closure during threshold testing. In order to avoid/minimize remote closure effect, compression-precracking methods were used to initiate a crack from a starter notch on compact specimens. Two materials with different fatigue crack surface profiles (flat or very rough) were tested and the results generated from the conventional ASTM precracking method and the compression-precracking test method were compared. In order to understand the disagreement of near-threshold data, crack-opening load measurements were performed from locally (near crack tip) installed strain gages instead of the remote gage (i.e., back face gage). Some careful specimen preparations were performed to avoid out-of-plane bending, to maintain straight crack fronts, and to ensure testing system linearity. It was known that remote gages, such as crack-mouth- opening-displacement-gages were insensitive to measuring load-strain records near threshold. By using local gages, the crack closure effects were clearly observed even in high load ratio (R) tests, like or higher than R = 0.7, and constant Kmax tests, which were believed to be crack closure free. By measuring load-reduced-strain records from local gages, crack-opening loads were able to correlate FCG rate data and showed that ΔKeff-rate data was unique for a wide variety of materials. By comparing (ΔKeff)th values, it may provide reasonable guidance for the material resistance against FCG. Because of “high R crack closure”, some theories considered in the past may need to be reconsidered. First, constant Kmax tests are not entirely crack-closure free. Second, there is no critical load ratio, Rc, to indicate the transition from crack-closure affected to crack-closure free data, and Kmax effects that appear in ΔKth-Kmax relations. Research has shown that the three dominate crack-closure mechanisms (plasticity-, roughness- and debris-induced crack closure) FCG rate behavior in the threshold regime from low to high load ratios.