Building high energy efficiency has become a must to reduce carbon emission from the built environment and to meet needs of consumers. Industrialized construction provides an effective way to produce highly insulated and airtight building envelopes to achieve superior building performance, such as Net Zero Energy. However, it is important that as other attributes (e.g., seismic, wind, fire, vibration, etc.) are being addressed, further research is needed to develop well rounded building envelope solutions. Meanwhile, improvement may be made in automated production equipment and software to optimize and monetize these solutions.
Lack of research and design information for the seismic performance of balloon-type CLT shear walls prevents CLT from being used as an acceptable solution to resist seismic loads in balloon-type mass-timber buildings. To quantify the performance of balloon-type CLT structures subjected to lateral loads and create the research background for future code implementation of balloon-type CLT systems in CSA O86 and NBCC, FPInnovations initiated a project to determine the behaviour of balloon-type CLT construction. A series of tests on balloon-type CLT walls and connections used in these walls were conducted. Analytical models were developed based on engineering principles and basic mechanics to predict the deflection and resistance of the balloon-type CLT shear walls. This report covers the work related to development of the analytical models and the tests on balloon-type CLT walls that the models were verified against.
The latest developments in seismic design philosophy have been geared towards developing of so called "resilient" or "low damage" innovative structural systems that can reduce damage to the structure while offering the same or higher levels of safety to occupants. One such innovative structural system is the Pres-Lam system that is a wood-hybrid system that utilizes post-tensioned (PT) mass timber components in both rigid-frame and wall-based buildings along with various types of energy disspators. To help implement the Pres-Lam system in Canada and the US, information about the system performance made with North American engineered wood products is needed. That information can later be used to develop design guidelines for the designers for wider acceptance of the system by the design community. Several components influence the performance of the Pres-Lam systems: the load-deformation properties of the engineered wood products under compression, load-deformation and energy dissipation properties of the dissipators used, placement of the dissiaptors in the system, and the level of post-tensioning force. The influence of all these components on the performance of Pres-Lam wall systems under gravity and lateral loads was investigated in this research project. The research project consisted on two main parts: material tests and system tests.
In the material tests part of the program, a total of 110 compression tests were conducted to determine the load-deformation properties of four different engineered wood products (LVL, LSL, Glulam and CLT) in various directions. The LVL, LSL and Glulam specimens tested under compression parallel to grain had similar linear elastic behaviour with limited ductility. The CLT specimens tested under compression in the major-axis direction had linear elastic behaviour with moderate plasticity. Depending on the type of engineered wood product, typical failure modes included crushing, shear, wedge split and splitting. The compressive strength of the products tested ranged from 42.1 to 53.5 MPa, the global MOE (of the entire specimen under compression) varied between 6390 and 9554 MPa, the local (near the crushing surface) MOE parallel to grain was in the range of 2211 to 5090 MPa, while the local to global MOE ratio ranged from 29.2 to 58.0%, and was higher with the increase in the oven-dry density.
The specimens of the four different engineered wood products tested under compression perpendicular to grain or in the minor-axis direction had elastic-plastic behaviour with a clearly defined plastic plateau. Crushing (densification) of the fibres perpendicular to grain was the main failure mode for all specimens, and was in some cases followed by in-plane shear failure or cracking perpendicular to grain. Compression parallel to grain in the middle layer that was followed by its delamination and buckling was a unique failure mode for CLT specimens tested under compression in the minor strength direction. The compressive strength of the engineered wood products tested were in the range of 4.8 to 27.8 MPa, while the global and local MOE perpendicular to grain were in the range of 244 to 2555 MPa, and 320 to 1726 MPa, respectively. The compressive strength and global MOE perpendicular to grain increased with an increase in the oven-dry density. The results show no well-defined trend for the local MOE perpendicular to grain. The specimens loaded in the centre perpendicular to grain had higher strength, global and local MOE than those loaded at the end.
A convenient and timesaving design for the axial energy dissipators (fuses) was developed by replacing the epoxy in the original design with two half-tubes. Compared to the original design of fuses with epoxy, the new design with two half-tubes had similar necking failure mode and a longer failure displacment, thus providing user-friendly fuses that performed similar or even better than the original design.
In the system tests part of the program, a total of 17 different PT and Pres-Lam CLT walls with six different configurations were tested under monotonic and reversed cyclic loading. The studied parameters included the level of PT force, the position of the fuses, and the number of UFPs. CLT shear walls subjected only to post-tensioning, had non-linear elastic behaviour. The behaviour of the PT walls with and without energy dissipators was relatively similar under monotonic and cyclic loading. The strength degradation observed during the cyclic tests was low in all wall configurations suggesting that very little damage was inflicted upon the structure during the first cycles at any deformation level. Four major failure modes, including yielding and buckling of fuse, crushing and splitting of wood at the end of wall, and buckling of lumber in the exterior-layer of CLT wall, were observed in the tests. The yielding in fuses occurred at the early stage of loading as designed and the other failure modes happened when the lateral drift reached or beyond 2.5%.
The initial stiffness of the single-panel PT CLT walls tested ranged from 1.80 to 2.31 kN/mm, the load at the decompression point and 2.5% drift were in the range of 4.2 to 14.9 kN and 32.7 to 45.9 kN, respectively. The initial stiffness of the single-panel Pres-Lam CLT walls tested ranged from 1.69 to 2.44 kN/mm, the load at the decompression point and 2.5% drift were in the range of 21.0 to 30.2 kN and 59.6 to 69.8 kN, respectively. All the mechanical properties increased with an increase in the PT force. The average initial stiffness and the load at 2.5% drift of the coupled-panel Pres-Lam CLT walls tested were 4.59 kN/mm and 151.3 kN, respectively, while the load at the decompression point increased from 58.4 to 69.7 kN by increasing the number of UFP. The test results show that the behaviour of the Pre-Lam CLT shear walls can be de-coupled and a “superposition rule” can be applied to obtain the stiffness and resistance of such system.
The test results gave a valuable insight into the structural behaviour of the PT and Pres-Lam CLT shear wall under in-plane lateral loads. The data from the testing will be used in the future for development of numerical computer models. They will also be used for development of design guidelines for this system. All tests conducted in this study and the analyses in the future modelling research will form the basis for developing future design guidelines for PT and Pres-Lam mass timber systems.
Current forest management policy in many jurisdictions in North America manages excess woody debris by piling and burning it, mainly as a post-harvest fire hazard abatement obligation. This study highlights three key points to consider regarding utilization and disposal of waste wood piles:
1) Allocate most woody debris waste to the biofuels sector in a cost-effective manner;
2) Allocate a small portion of woody debris (e.g. 10-15%) to implement windrow habitats where necessary to maintain mammalian biodiversity on clearcuts;
3) Limit burning of waste wood to those sites near human activity (potential fire hazard) that do not have an opportunity for biofuels or windrow purposes.
This literature review aims to provide a general picture of retrofit needs, markets, and commonly used strategies and measures to reduce building energy consumption, and is primarily focused on energy retrofit of the building envelope. Improving airtightness and thermal performance are the two key aspects for improving energy performance of the building envelope and subsequently reducing the energy required for space heating or cooling. This report focuses on the retrofit of single family houses and wood-frame buildings and covers potential use of wood-based systems in retrofitting the building envelope of concrete and steel buildings.
Air sealing is typically the first step and also one of the most cost-effective measures to improving energy performance of the building envelope. Airtightness can be achieved through sealing gaps in the existing air barrier, such as polyethylene or drywall, depending on the air barrier approach; or often more effectively, through installing a new air barrier, such as an airtight exterior sheathing membrane or continuous exterior insulation during retrofit. Interface detailing is always important to achieve continuity and effectiveness of an air barrier. For an airtight building, mechanical ventilation is needed to ensure good indoor air quality and heat recovery ventilators are typically required for an energy efficient building.
Improving thermal resistance of the building envelope is the other key strategy to improve building energy efficiency during retrofit. This can be achieved by: 1. blowing or injecting insulation into an existing wall or a roof; 2. building extra framing, for example, by creating double-stud exterior walls to accommodate more thermal insulation; or, 3. by installing continuous insulation, typically on the exterior. Adding exterior insulation is a major solution to improving thermal performance of the building envelope, particularly for large buildings. When highly insulated building envelope assemblies are built, more attention is required to ensure good moisture performance. An increased level of thermal insulation generally increases moisture risk due to increased vapour condensation potential but reduced drying ability. Adding exterior insulation can make exterior structural components warmer and consequently reduce vapour condensation risk in a heating climate. However, the vapour permeance of exterior insulation may also affect the drying ability and should be taken into account in design.
Overall energy retrofit remains a tremendous potential market since the majority of existing buildings were built prior to implementation of any energy requirement and have large room available for improving energy performance. However, significant barriers exist, mostly associated with retrofit cost. Improving energy performance of the building envelope typically has a long payback time depending on the building, climate, target performance, and measures taken. Use of wood-based products during energy retrofit also needs to be further identified and developed.
This guide explores how the building industry in British Columbia can meet the challenges of reducing energy use in buildings, in part by effectively accounting for the impact of thermal bridging.
Most practitioners will find PART1 and Appendices A and B to be most useful. PART 1 outlines how to effectively account for thermal bridging. Appendices A and B provide a catalog of common building envelope assemblies and interface details, and their associated thermal performance data.
Researchers and regulators will be interested in PART 2 and PART 3, and Appendices C to E. They contain the cost-benefit analysis, and discussion on significance and further insights, of using this guide to mitigate thermal bridging in buildings.
[Available to the public: http://www.bchydro.com/powersmart/business/programs/new-construction.html?WT.mc_id=rd_construction]
Over the past few years, the constant rise in the price of fuel has prompted the development of new technologies to reduce fuel consumption. To address this concern heavy equipment manufacturers have been introducing new models integrating technologies, such as the diesel-electric hybrid suggesting improved fuel efficiency. In order to validate these claims FPInnovations has developed a methodology aimed at conducting controlled tests to measure fuel consumption. Tests were conducted on three different models of bulldozers of the same power class in order to compare their fuel consumption and energy efficiency. The evaluation of these three bulldozers was carried out on a controlled test track where standardized working conditions were reproduced. This report presents the findings of these tests conducted in Chipman, New Brunswick, in cooperation with J.D. Irving Limited. The test had three main objectives: 1) develop a standardized procedure to measure the fuel consumption of the bulldozers in a controlled environment; 2) compare the fuel consumption of three different models (drive trains) of bulldozers (electric, hydrostatic and standard) for a typical work cycle; and 3) quantify the variation in fuel consumption resulting from the differences between the engine/drive train technologies of the test machines.
Transformative Technologies Program identifierSeries Energy Efficiency of Advanced Building Systems
The largest source of energy consumption and greenhouse gas emissions in Canada and around the world is buildings. As a consequence, building designers are encouraged to adopt designs that reduce operational energy, through both increasingly stringent energy codes and voluntary green building programs that go beyond code requirements. Among structural building materials, wood has by far the lowest heat conductivity. As a result it is typically easier to meet certain insulation targets (e.g., thermal transmission and effective thermal resistance) with wood-based wall systems when following current construction practices. Good envelopes greatly contribute to energy efficient buildings. However, there are many factors in addition to building envelope insulation levels that affect the operational energy of a building. This study aims to provide designers with information which will assist them to choose energy efficient exterior wall systems by providing energy consumption estimates for an archetypal 6-storey residential building. Comparisons were made among several exterior wall systems including light wood-framing, cross-laminated timber (CLT), steel-stud framing, and window walls, for a range of structural systems including structural steel, light wood-frame, CLT, heavy timber, and concrete. The opaque exterior wall assemblies targeted meeting the minimum thermal requirements based on the National Energy Code of Canada for Buildings (NECB. NRC 2011). A 3-D method was used to calculate effective R-values of these exterior walls by taking into account all thermal bridging, in comparison with a parallel-path flow method in compliance with the NECB. Three glazing ratios, including 30%, 50%, and 70%, and two efficiency levels for Heating, Ventilation, & Air Conditioning (HVAC) systems, termed basic HVAC and advanced HVAC, were also assessed. Whole-building energy consumption was simulated using EnergyPlus. Four climates, from Zone 4 to Zone 7, with cities of Vancouver, Toronto, Ottawa, and Edmonton to represent each climate, were selected in this study. The energy assessment was conducted by Morrison Hershfield.
A comparison of operational energy consumption among these different exterior wall systems for this archetypal 6-storey building has shown that accounting for thermal bridging is critically important for improving thermal performance of building envelopes. Wood-based systems including light wood-frame walls, CLT, and wood-framed infill walls in concrete structures have inherently lower thermal bridging compared with other systems, such as steel-frame walls in steel and concrete structures, or window walls in concrete or timber structures. Conclusions are provided for specific climates and cities in Section 4.2. General conclusions and highlights are summarized as follows:
Building envelope influences only the energy required for space conditioning. The space heating energy consumption ranged between 28% and 49% of the entire building energy consumption, when the basic HVAC type was used, for the four cities assessed in this study. An efficient HVAC system would further reduce the proportion of space heating energy consumption. The rest of the energy is used for hot water and electrical appliances etc.
Compared to the NECB-compliant calculation, the 3-D method showed a greatly reduced effective R-value of the opaque wall assemblies due to thermal bridging. Steel-stud wall assemblies showed much larger reductions in effective R-values than wood-based wall assemblies.
Wood-based walls in a light wood-frame building, or a CLT building, would improve building energy efficiency, with total energy savings ranging from 3% to 9%, compared to a concrete building with steel-stud walls, depending on the HVAC type and the glazing ratio, when the 3-D method was used for calculating thermal resistance. The energy savings were higher in colder climates, such as Toronto, Ottawa, and Edmonton, than in Vancouver.
The use of wood-frame infill wall in concrete structure improved the whole building energy efficiency by up to 6% depending on the climate, relative to the use of steel-stud infill walls, under the same HVAC (basic or efficient type) and glazing ratio (30% or 50%).
Concrete structures typically have much higher glazing ratios than wood buildings. The wood-framed building, with exterior-insulated walls meeting the thermal insulation requirements and at a glazing ratio of 30%, showed whole-building energy savings of about 13-18%, compared to a concrete structure with window walls at a glazing ratio of 70%.
Simply adding insulation (e.g., exterior insulation) in a building envelope while ignoring thermal bridging is not the most effective way to improve building energy efficiency.
The thermal bridging at window transitions greatly reduced the effective R-values of the opaque walls and consequently the whole-building energy efficiency. The higher the glazing ratio was, the larger the impact would be. Window wall with a high glazing ratio would further reduce building energy efficiency, compared with regular windows.
The energy efficiency of the HVAC system used in a building had the largest impact on the whole-building energy efficiency, compared to the impacts caused by exterior wall systems, glazing ratios, or thermal bridging at various details.
The energy efficiency measures studied in this report delivered higher energy savings in colder climates, such as Montreal, than in warmer climates, such as Vancouver.
It is recommended that future effort be put into further developing tools for practitioners to account for thermal bridging more conveniently.