Daylighting 'energy and comfort' performance in office buildings : sensitivity analysis, metamodel and pareto front.

Daylighting performance is an integral feature of sustainable building design. In this paper, two performance criteria were defined, namely an annual glaring index (AGI) and an annual energy requirement for lighting (AEL). Based on 1900 daylight simulations of an office building located in Montreal (Canada), a sensitivity analysis was performed to identify the most influential building design variables among a list of 15. Two sensitivity analysis techniques were employed. Window-to-wall ratios and the overhang dimension were among the most influential parameters for both AEL and AGI, whereas building orientation and aspect ratio, as well as visible transmittance, were found to have a relatively weak influence. A Pareto front demonstrating the optimal tradeoffs between AEL and AGI was approximated from the simulation sample. Finally, a metamodel is developed to calculate rapidly the daylight performance indices for a given set of the 15 design variable

How managers can use predictive analysis and mathematical models as decision making tools

Cet article propose une mesure simple (un modèle mathématique) évaluant la performance de différentes entités de vente (comme les vendeurs, les territoires de vente, les bureaux de vente régionaux ou l'ensemble des ventes de l'organisation) est proposée. Cette mesure est facile à estimer et elle peut facilement être comprise par les gestionnaires. De fait, elle peut être utilisé pour comparer les performances des différentes entités de vente, en tenant compte des conditions prévalant dans les différents marchés (tels que l'efficacité de la concurrence, la pénétration des ventes, ou les fluctuations du marché local). Les résultats de la mise en oeuvre de cette mesure dans une grande entreprise d'assurance dommage nord-américaine sont présentés

Combined heating and cooling networks with waste heat recovery based on energy hub concept

Waste heat recovery can help reducing operation costs and greenhouse gas emissions. In the present work, an “energy hub” template was employed to design combined heating and cooling networks in which heat pumps can be used to recover heat from the cooling loop and supply it to the heating loop. Heating and cooling loads of the network can be satisfied by natural gas boilers, electric boilers, chillers, and heat pumps. The design of the system and its operation over the year were optimized with respect to cost and greenhouse gas emissions under different combinations of heating and cooling loads. The introduction of 8760-h synthetic loads allowed covering several possible load profiles driving the energy hub. The contribution of each possible energy source and technology and the sizing of the heat pump system are optimized, while ensuring satisfaction of the heating and cooling demands. The optimized hub configurations for scenarios with and without waste heat recovery were compared, showing that heat pumps were beneficial in all scenarios. The optimal capacity of heat pumps to minimize total cost was found to be ∼80% of the maximal possible value from a thermodynamic analysis of the loads. The simultaneous minimization of cost and emissions revealed a relatively sharp transition from gas to electric heating as more emphasis is put on emissions than cost, but in all cases, waste heat recovery with heat pumps was heavily used to satisfy the heating and cooling loads

Numerical modeling of solid-liquid phase change in a closed 2D cavity with density change, elastic wall and natural convection

In this paper, the solidification of water near its density extremum is simulated while taking into account the expansion of the phase change material resulting from the different density of the solid and liquid phases. A thermo-mechanical coupling is achieved through one of the boundaries of the cavity behaving as an elastic wall. A methodology is introduced in which the problem is adapted in order to be solved with commercial CFD software (ANSYS Fluent 17.0). It is shown that when both the density variations and interaction of the phase change material with its boundaries are taken into account, significant differences may be observed in the flow pattern and the thermal behavior of the system, as opposed to an approach where a free ceiling or a constant density would be used. The pressure buildup inside the cavity resulting from the expansion of the phase change material as it pushes against the elastic wall causes the melting temperature to drop, which hinders solidification. It is shown that this effect becomes more pronounced as the spring constant of the elastic wall increases. It is also demonstrated that, with the assumptions made in the present model, the pressure rise may significantly influence the buoyancy forces within the cavity and change the relative size of the two counter rotating convective cells in the liquid phase. In some cases, when the pressure rises very quickly, the density extremum in the cavity disappears which strongly changes the flow pattern, i.e., only a single counter-clockwise convective cell is present in the cavity. This, in turn, changes the shape and position of the solidification front considerably

Comparison of three combustion models for simulating anode baking furnaces

Carbon anode blocks used in the Hall-Héroult process for primary aluminum production have to be baked up to 1100 °C in dedicated furnaces. These furnaces are equipped with burner ramps to heat the air circulating in the flues at 1200 °C, so that the anodes reach the required temperature. It is therefore mandatory to include the heat provided by the burners in a numerical model of an anode baking furnace. In this work, we modeled the heat input at the burners in three ways: the Eddy-Dissipation model, the Mixture Fraction/PDF approach and a simplified approach consisting in injecting an equivalent calorific value at the burners' inlets. Results obtained with the first two models are very similar in terms of anode baking prediction but slightly different in terms of flame temperature prediction. Results obtained with the simplified approach show that the model can replace combustion model to predict anode baking, but calibration of boundary conditions is necessary in order to match more elaborate combustion models. The importance of other elements of the model in the flue channel of the furnace has been verified: radiation (cannot be ignored, large influence on the spatial temperature distribution), heat transfer due to species diffusion (negligible influence on the baking, but slight effect on flame shape and temperature), and buoyancy (no significant effect on the results in the furnace firing sections)

Various ways to take into account density change in solid-liquid phase change models : formulation and consequences

In this paper, a classification of different methods for accommodating volume variations during solid–liquid phase change is presented. The impact of each method is analyzed with the help of a scale analysis. Neglecting fluid velocity at the interface or allowing fluid to enter/exit the domain may result in either local (at the solid–liquid interface) or global (within the system) mass imbalance. This can lead to significant differences in the transient phase change process itself (e.g., 19% more time and 9% more energy to completely solidify a given mass of water with models for which the total mass of the system is conserved). This paper aims at addressing this issue by deriving two new models of thermo-mechanical coupling between the PCM and its container. The first model is that of a PCM bounded by an elastic wall, whereas the second model assumes that a compressible air gap is adjacent to the PCM, which allows the PCM to expand more easily. Analytical expressions are developed for both models and can be used to predict important quantities at equilibrium, such as the position of the solid–liquid interface and the pressure rise within the system. Finally, the two thermo-mechanical coupling models are implemented numerically with a finite volume moving mesh method. Numerical simulations are performed to show the limits of the two models. It is observed that volume variations during phase change can have significant impacts on the evolution of the process

New methodology to design ground coupled heat pump systems based on total cost minimization

This paper introduces a method for designing vertical ground heat exchangers and heat pump systems, by minimizing the total cost of the project. The total cost includes an initial cost composed of drilling, excavation, heat pump and piping network. An operational cost is also included to account for the energy consumed for heating/cooling a building. The procedure allows determining the optimal number of boreholes, their depth and spacing, and the optimal size of the heat pump. The method is tested for different ground conductivity and heat demands. The method can also be used to determine the economical viability of a TRT. For tested cases, results show that the excess cost due to uncertainty on ground thermal conductivity increases with the number of boreholes. Also, a cost sensibility analysis shows that the most influential parameters are the number of boreholes and their depth

Probabilistic window opening model considering occupant behavior diversity : a data-driven case study of Canadian residential buildings

It was found from monitored data from eight dwellings in a case study building in Quebec City (Canada) that there are clear differences in the window opening behavior between different households. This paper aims to develop from data a probabilistic window opening model that accounts for occupant behavior. Logit regression is employed to predict the state (opened/closed) of windows according to indoor and outdoor temperatures environmental and temporal parameters. To replicate the diversity of behavior, normal distribution functions applied to the logit regression coefficients are used so that simulated occupants respond differently to environmental stimuli. It was found that the model offers good prediction for the monitoring by only using the outdoor and indoor temperatures as predictors. The proposed methodology was tested by simulating 10,000 times a full validation year of the case study building and comparing the results with measured data. The agreement was good. The model overestimated slightly the total frequency of window opening in the dwellings and the number of window changes-of-state. A vast range of window opening behavior was generated by the model, showing its ability to reproduce both the aggregated window opening behavior and the diversity of behaviors of the case study building

Comfort and energy consumption of hydronic heating radiant ceilings and walls based on CFD analysis

This article presents the methodology and results of a hybrid numerical optimization study of a heating ceiling and wall hydronic radiant panel system in a typical residential building located in Quebec City, Canada. The comfort and energy consumption of the system are the two figures of merit that are considered in the multiobjective optimization analysis. The main design variables are the position and dimension of the panels, and the fluid inlet temperature. The hybrid numerical method features a 2D CFD model of a typical empty room, coupled with a semi-analytic radiant panel model specially developed for coupling with CFD. This strategy allows considering the real room geometry, while providing at the same time accurate temperature profiles of the radiant panels and detailed temperature and comfort data field in the room. The results show that there is no unique optimal solution but rather a family of optimal designs (Pareto fronts) for which the solutions are trade-offs between the two objectives. When adjusting correctly the fluid inlet temperature, it is also possible to achieve nearly Pareto optimal solutions, even when reducing the total panel surface by 66%. This means that the temperature control of the fluid is the most important parameter for maximizing comfort and minimizing energy consumption of hydronic heating radiant panels