2:00pm - 2:15pm
Static and dynamic thermal characterization of exterior walls with mineral foam insulation using a Guarded Hot Box apparatus
LafargeHolcim Innovation Center
Reducing heat loss through the envelope of the building had been an efficient way to save on heating and reduce energy consumption of buildings. In Europe, typical exterior walls need to prevent heat loss during cold weather but more and more allow comfortable temperature condition during the hot season. Indoor comfort in hot seasons is dependent on the thermal transmittance and on its dynamic response during hot days. The study presents Guarded Hot Box measurements of exterior walls build with insulating masonry and insulation boards made of innovative mineral foam used as an insulation material. The masonry is a composite system of concrete block filled with mineral foam to reduce the thermal transmittance. Insulation boards are made of mineral foam and are added to achieve the overall thermal transmittance targeted.
Static and dynamic measurements were performed in order to compare U-values and decrement delay. The results are compared with those obtained from a simulation carried out on the performance of the same wall through the application of finite volume software and dynamic thermal characteristics calculations according relevant European standards. Uncertainties of the guarded hot box measurement and calculation methods are discussed. Results shows that with equivalent U-values, the walls with mineral foam offer higher decrement delay compared to a wall using conventional masonry and polystyrene insulation boards.
2:15pm - 2:30pm
Thermal Conductivity of Insulation materials at Different Temperatures
Buildings account for nearly 40% of the global energy consumption, while 85 to 95% of this amount is for the operation of buildings. Using building envelopes with efficient thermal performance conserves energy and consequently less operational energy is required for space cooling in summer and heating in winter. Using insulation in building is considered as a simple yet highly energy efficient approach. Thermal conductivity and heat capacity are among the most essential properties of a building material required in thermal performance calculations. These properties are normally measured in the laboratory at a standard mean temperature of 21oC or 23oC. However, in service, the insulation materials can be exposed to extreme temperatures in the winter and summer periods, and as such, in general, these materials mean temperatures during these periods are much different from that of the standard measurement. This discrepancy can results in under and over estimations of buildings energy uses and the corresponding equipment sizing if one ignores the temperature dependency of these material properties. To obtain more realistic conductivity values of insulation materials, in this paper, thermal conductivity tests at more and broader range of mean temperatures are conducted. For the study five commonly used insulations including Cellulose fiber, Expanded Polystyrene, Extruded Polystyrene, Open Cell Spray Polyurethane, Polyisocyanurate, and Mineral Wool are considered, and their thermal conductivity are measured at six mean temperatures ranging from 5°C to 60°C (5°C, 10°C, 20°C, 24°C, 34°C, 50°C and 60°C). The test results are compared with that of the measurements done following the test conditions set in the ASTM C-518 standard and the findings are reported. According to our results, the thermal conductivity of tested insulations increased with rising temperature.
2:30pm - 2:45pm
Component sequence and thermal mass effects on the transient thermal performance of concrete walls
1Concordia University, Canada; 2National Research Council Canada
The increased requirements of buildings to reduce energy use has highlighted the importance of accounting for all factors that influence energy use in buildings, especially in high-performance buildings. One consideration that requires further study in envelope design of concrete-based wall assemblies is the placement of the thermal mass layer. When considering time-dependent boundary conditions, the placement of this layer within the wall assembly can have a noticeable effect on the rate of heat transfer through, and peak-demand shifting potential of, a thermally massive wall.
In this study, the impact of the thermally massive layer for two different types of concrete wall assemblies is investigated, both of which have the same nominal thermal resistance, specifically: an Insulated Concrete Form (ICF) wall; and a tilt-up wall. The ICF wall consists of a six-inch concrete layer sandwiched between two three-inch layers of insulation; whereas, the tilt-up wall consists of a six-inch insulation layer sandwiched between two three-inch concrete layers. A numerical comparison is made between each wall type for both the total energy used and the potential for peak-demand shifting using COMSOL Multiphysics® by subjecting each wall to the same transient boundary conditions based on hourly weather data for Montreal, Canada.
Preliminary results indicate that, for the transient scenario investigated, the thermal mass effect is more evident for the tilt-up wall, given that for the ICF wall, the exterior insulation layer dampens the magnitudes of temperature fluctuations as compared to the thermally massive sandwiched concrete tilt-up wall. Further investigation into the transient thermal behavior of these walls will lead to a more precise understanding of the effect of component location on the potential for decreasing the energy demand as well as shifting the peak-energy demand on the grid.
2:45pm - 3:00pm
Energy performance analysis of smart wall system with switchable insulation and thermal storage capacity
Oak Ridge National Laboratory, United States of America
The ever-increasing global energy demand and the issues caused by population growth and unsustainable energy resource usages have several environmental and economic impacts. To mitigate these problems the buildings technology research community, need to come up with sustainable and intelligent solutions. The on-demand capability of dynamic wall systems with switchable insulation systems can contribute towards energy efficiency and reduced electric cost using ‘building-as-a battery’. In this paper, the performance of an exterior envelope system that employs a switchable insulation system is investigated. The wall system comprises vinyl siding as cladding, an 8” thick grouted concrete wall, an alternate air- XPS system as switchable insulation on either side of the CMU construction and interior drywall. A COMSOL simulation is used to study the envelope performance under different climate zones, insulation switching cycles. The on and off switching cycle includes insulating or conducting the exterior, interior or both sides of the wall system. To validate the simulation work, an experimental test is conducted using ORNL’s Heat, Air and Moisture climate chamber (HAM chamber) on a 4” X 8” wall system with identical wall components used in the COMSOL simulation. Results show a good agreement between the experiment and simulation results. A further investigation to select an optimal switching cycle for a specific climate and season is underway.
3:00pm - 3:15pm
Evaluation of the intrinsic thermal performance of an envelope in the summer period
1Univ Grenoble Alpes, CEA, LITEN, INES, 73370 LE BOURGET DU LAC, France; 2CSTB, France; 3INES PFE, France
Ensuring the good thermal performance of a building envelope upon receipt of a site is an important step in the life cycle of the building to ensure the good consistency between the design phase and the implementation during the work. This makes it possible to propose corrective actions when necessary. Several methods exist for this and continue to be improved, such as the co-heating, ISABELE, EPILOG, QUB or even SEREINE methods. All these methods have the common point of stressing the building over a given period using a heating system. These measurement protocols measure the dynamic evolution of interior temperatures, thermal power injected into the building and exterior conditions. These data are then used in an algorithm for calibrating RC models to determine, by an inverse method, the parameters of the model and thus to deduce a heat loss value of the Htr, or HLC. These methods require a difference of a few degrees between the interior and the exterior which can be problematic in periods of high heat without risk of damaging the accommodation
The objective of the work presented here is to explore the possibility of determining the intrinsic thermal performance of a building envelope in the summer period via a cooling system and no longer a heating system. This work will be based on an experiment with a small-scale cell (of the order of 1m3) and will explore the capacities and limitations of the method at this scale by varying several stress parameters of the enclosure. Particular focus will be placed on the calibration part in order to demonstrate the feasibility of using the methods developed for the heating mode with the data generated using this experiment in air conditioning mode. Results in cooling mode are also compared to heating mode