Session 10: Building envelope optimization
2:00pm - 2:15pm
Simplified infinite fin method to model slab edges
National Research Council Canada, Canada
As building codes become more stringent in terms of thermal performance of building envelopes, and higher insulated wall assemblies are becoming more common, the heat flow due to major thermal bridges can contribute to a significant portion of the total heat transfer through a building. Being able to quantify the thermal performance of building façades during the design phase allows enough time for changes or adaptations to be made to mitigate the effects of major thermal bridge. There are different methods being used to quantify the thermal performance of building assemblies, including but not limited to, hand calculations methods, Guarded Hot Box testing, In-Situ testing and computer simulations. The most common method to characterize slab edges is using linear transmittance method. The values are generally developed by using numerical simulation tools and tabulating the results in catalogues to be used by practitioners. The problem with the use of these predetermined values is they can only be used for the exact geometry and materials which are specified in the catalogue. Hence, new numerical simulations will be required for wall assemblies which deviate from the ones from the catalogue. In this study we propose a new method which incorporate the heat transfer portion from the slab edges by modeling them as infinite fins. The Clearfield R-value can be calculated by using other hand calculation methods. Hence, using this method, one do not need to use a numerical simulation software. The initial results have been compared to the simulation results and 1-13 percent deviation have been found which is due to the fact that the lateral heat transfer is being neglected. This method aims to provide a comprehensive approach for designers to quantify the thermal performance of their design.
2:15pm - 2:30pm
Air preheating potential with high Opaque Ventilated Façade under natural and forced convection
Univ. Bretagne Sud, UMR CNRS 6027, IRDL, Lorient, France
Opaque ventilated façades (OVF) are increasingly used in building envelope because of their positive impact on building energy efficiency. Usually, air flow is driven by natural ventilation due to thermal buoyancy and wind forces. Recently, there were some attempt to drive air flow mechanically in view of preheat or precool air in combination with HVAC, Heat pump or Latent Heat Thermal Energy Storage (LHTES) systems. In this framework, an experimental real-scale module of an OVF was built. The OVF is 1.9 m width and 3.5 m height, which is higher than most of the previous studies. In this study, OVF is tested during autumn under natural and under forced convection by means of ventilator placed at cavity outlet. Inlet air flowrate are changed from day to day or during the day. For each test, temperature, air velocity, air flow rate and thermal flux are monitored at different locations of OVF. Their analysis shows collector efficiency and amount of collected energy depend mainly on cavity air flow rate. The measurements are compared to simulation results obtained from two thermal models describing OVF: Trnsys Type 1230 and home-developed pseudo 2D. A good agreement is found for air temperature at cavity outlet while differences are observed in opaque layers due to modelling assumptions. Last, sensitivity analysis on two design parameters is carried out.
2:30pm - 2:45pm
Multifunctional climate-responsive façades coupled with different ventilation modes
Ryerson University, Toronto, Canada
Dynamic building facades are designed to respond to the transient exchange of energy and mass in building enclosures to guarantee better indoor environmental quality (IEQ). In this paper, an opaque climate-responsive façade (OCRF) which aims to dynamically regulate the flow of heat, air, and moisture into buildings with daily and seasonal responses is presented. The façade, inspired by a ventilated cavity Trombe wall, includes thermal energy storage through phase change materials (PCMs), a dynamic insulation system, and an embedded energy recovery unit to pre-condition fresh air. This study aims to investigate the effect of different ventilation modes on the overall performance of the façade. CFD simulations were performed to quantify the interaction of different components within the façade for different airflow mechanisms. The simulation was performed for a south-facing façade scenario in both the heating and the cooling seasons. The ventilation modes tested include: simultaneous supply and exhaust mode, switch between only supply and only exhaust modes, and no ventilation mode. In addition to the ventilation scenarios, the PCM melting temperatures, insulation thermal conductivity, and geometrical parameters were investigated to find the best design configuration and operation scenario. For this, surface and air temperature gradient in the façade, heat and moisture recovery efficiency, dynamic insulation efficiency, and time lag were monitored. The acceptable façade performance range is benchmarked against the building code and Passive House US requirements. The decentralized ventilation designed in the OCRF provides the option to adjust both thermal comfort and ventilation modes in individual indoor spaces. The experimental testing of the OCRF in a full-scale experimental test cell in Toronto is finally described.
2:45pm - 3:00pm
The effect of temperature, humidity and mechanical properties on crack formation on external thin plasters of ETICS
1Tallinn University of Technology, Estonia; 2Smart City Center of Excellence (Finest Twins), Tallinn University of Technology, Ehitajate tee 5, Tallinn, Estonia; 3Łodz University of Technology, Department of Environmental Engineering, ul. Wolczanska 213, 90924 Łodz, Poland
External Thermal Insulation Composite Systems (ETICS) are widely used in the northern hemisphere, both in retrofitted and newly constructed external walls. The outer layer of ETICS is usually a thin layer of plaster, deterioration of which is caused by a wide range of factors that are difficult to quantify, including but not limited to quality and properties of the plaster, outdoor climate loads, quality and conditions of construction work and maintenance. The effects of temperature and humidity on the hygrothermal behaviour and mechanical properties of thin plasters have been quantified by conducting several experiments to determine the possibility of crack formation. Combinations of plasters using four types of binders are tested: mineral, organic, silicate and silicone. Plasters are tested as a system consisting of a base coat, a glass-fibre reinforcement mesh and a finishing coat. The survey of expansion and shrinkage of plasters is mainly focused on changes in temperature and moisture. As a result of this study, the coefficients of expansion are determined for all four plastering systems. Sorption curves of the plasters are determined to gather data for numerical simulations. The modulus of elasticity and tensile strength of four different plasters are measured to enable calculating the crack formation in ETICS and suggest the distances between the deformation joints. The method demonstrated in this paper makes it possible to calculate the crack formation caused by temperature and moisture shrinkage in the external thin plaster of ETICS.
3:00pm - 3:15pm
Status assessment of buildings using existing data and identifying gaps in data from performance indicators
Chalmers University of Technology, Sweden
In the past decades, performance-based planning of maintenance and retrofitting of buildings has undergone considerable advancement. Several performance criteria/indicators have been developed that can be used for maintenance planning. These can be used to assess current status or to predict failures of materials, components and other important building factors like moisture safety. However, performance indicators require data which can be difficult to obtain, especially in case of older buildings. Additionally, different indicators have need for different types of data structured in certain ways to provide useful information. It is therefore of great interest whether it is possible to combine several indicators together obtaining a complete picture of building envelope status (structural, moisture safety etc.). Special emphasis is put on older buildings which often lack readily available documentation.
The aim of this study is to identify data gaps preventing to perform building envelope status assessment and to ascertain whether missing data can be filled by combining in-situ building inspections and non-destructive testing. The first part of the paper summarizes known performance indicators which are related to building envelope and arrange them into three groups: general, hygrothermal and service life performance indicators. The second part is a case study where selected performance indicators are applied to buildings from an in-house database that consists information about 610 buildings in Gothenburg. It was found that the use of performance indicators is limited as the gaps in the available data are present for all types of performance indicators. The composition of material layers in building envelopes was identified as the most substantial gap. This limited the use of hygrothermal performance indicators in 58.5% of the buildings.
3:15pm - 3:30pm
Calibration of DSF model for real-time control
1Politecnico di Torino, Italy; 2EURAC Research, Italy; 3Norwegian University of Science and Technology, NTNU, Norway
Double Skin Facades (DSFs) are adaptive building components used to manage the entering solar radiation and ventilation in buildings, with the aim to reduce the building energy use and maximize the user comfort. Due to the intrinsic high dynamicity of such innovative components, having energy simulation models able to replicate the thermal behavior of the Double Skin Facades is of outermost importance.
The aim of this paper is to present a numerical approach to model the inlet flowrate in ventilated Double Skin Façade. In this contest, the experimental campaign is carried out in an outdoor test-facility of the Politecnico di Torino where a novel concept of Double Skin Façade is placed, which maximizes the flexibility of the level of control over environmental conditions to meet multiple performance requirements. Compared to a traditional Double Skin Façade, this is achieved by the capability of varying also the air-path, additionally to the airflow and controlling the solar shading.
The experimental data was used to calibrate both the reduced thermal model of the DSF in according with the ISO 15099 and the DSF model implemented in EnergyPlus, using the AirFlowWindow module. This module is limited for simulate the natural ventilation because it required as input the inlet mass flowrate, which is strictly dependent from the boundary conditions. For this sake, two different numerical models for the estimation of inlet flowrate have been developed from the experimental campaign: the first is an empirical model based on the linear regression of environmental conditions, the second one is based on the calibration of the ISO 15099. The calibration of the flowrate models reports a small deviation from the measured data and the ISO 15099 model seems to better predict the flowrate, although the empirical calibration is needed.