Optimization of government subsidization strategies for building stock energy refurbishment

The high initial investment required in existing building refurbishment can limit the initiative of the building owners and prevent the full exploitation of a huge energy saving potential. Public incentives can play an essential role in fostering the energy retrofitting of the existing buildings and in increasing the renovation rate of the building stock, effectively reducing the energy final uses, the dependence on the fossil fuels, and helping meet the national efficiency targets. Public subsidization are intended to enhance the economic performance in terms of global cost of the energy efficiency measures for the owner, in order to induce positive actions and move optimality from low to high energy efficient solution. In contrast, the overall economic efficiency is obtained with combinations of interventions, able to achieve a certain energy saving target for the entire building stock at the minimum initial Investment Costs (IC). This paper tries to identify the overall economic efficiency in reducing the energy consumption of the existing stock and compares it with the efficiency of solutions optimal from the owner’s perspective, in order to support more efficient subsidization strategies. Different mixes of three reference building archetypes, representative of the existing buildings, are considered to define different possible stocks, in order to analyse their impact on the efficiency of energy renovation solutions. Four groups of energy efficiency measures (EEMs) dealing with respectively the opaque envelope insulation, the windows substitution, the heat generating system replacement, and the mechanical ventilation introduction are defined and their combinations considered

Internal Versus External Shading Devices Performance in Office Buildings

Abstract In this paper different configurations of an open-space office located in Rome has been simulated with EnergyPlus 8 to compare the performance of outdoor and indoor shading devices concerning the thermal and visual comfort and the overall primary energy use. The standard PMV indices [1] have been calculated considering also the effect of the diffuse and beam solar radiation directly reaching the occupants through the windows. Although the use of shades always improves the thermal comfort, the energy demand could increase as an effect of the internal position of shades in combination with particular orientations and glazing types

Comparison of Different Glare Indices through Metrics for Long Term and Zonal Visual Comfort Assessment

Nowadays different indices are used for the assessment of the visual discomfort related to glare, such as Daylight Glare Index, Daylight Glare Probability, and Vertical Eye illuminance. Regardless of their effectiveness in detecting glare perception, all these indices are intended to be local and instantaneous, not summarizing the long term glare perception through the space (Carlucci et al. 2015). In this work, a set of metrics able to express both the time constancy, i.e. availability, and the spatial uniformity, i.e. usability, has been used for detecting discrepancies and inconsistencies between the glare indices when dealing with time and space distribution. Results confirm that different glare indices can lead to different conclusions not only when considering point and instantaneous values but also when analysing availability and usability. Moreover, the availability and usability representations, indirectly confirm themselves effective in providing a global assessment of the confined space analysed, even when visual comfort is concerned

Impact of occupant behavior on performance optimized building retrofits

In the framework of the recent Directive 844/2018, practitioner often rely on Building Energy Simulation (BES) combined with Multi-Objective Optimization (MOO) to find optimal energy saving measures for building retrofits. However, occupant behaviour is usually oversimplified as a static schedule provided by technical standards mainly developed for energy certification. This can lead to a significant gap between the performance of the optimal designed solution and its actual performance. In this study, we investigate how detailed user-behaviour profiles - e.g. static, probabilistic, and adaptive models - for the operation of windows impact on the optimal retrofit strategy. While the standard and adaptive model use a base ventilation rate like a constraint for indoor air quality (IAQ), the probabilistic models rely solely on the occupant actions on windows. The results demonstrate that the behavioural models result in major differences in indoor comfort conditions. Optimal solutions defined through probabilistic models are likely to be not very robust to the ventilation rate showing the potential for performance gaps. The importance of realistic user behaviour representation is highlighted to raise awareness about its influence on the full potential of retrofitting a building, maybe excluding those solutions that could majorly improve comfort

Energy Performance And Long-Term Evaluation Of Internal Thermal Comfort Of An Office Building With Different Kinds Of Glazing Systems And Window Sizes

Although the presence of large window surfaces could be preferable during the heating season when solar gains through the glazed components can overcome heating losses from the same surfaces, during the cooling season more attention has to be paid in order to limit the inlet of solar radiation which causes the increment of cooling load. Generally the optimal tradeoff for energy optimization, as already underlined in a previous paper by the authors, is using low thermal transmittance and high solar factor glazing, even if higher solar transmittance considerably worsens the cooling performance. However, the choice of glazing type and the design of windows on a façade may depend on comfort consideration besides energetic evaluations. Thermal sensation of an individual is mainly related to the whole thermal balance of the human body. Comfort limits can in this case be expressed by two indexes proposed by Fanger in 1970: the Predicted Mean Vote, PMV, and the correlated Predicted Percentage of Dissatisfied, PPD. The PMV depends on four environmental parameters (air temperature, air humidity, air velocity and mean radiant temperature) and two variables connected with human being (physical activity and clothing). The air temperature, the air humidity and the air velocity inside a building are directly under the system control. In contrast, the mean radiant temperature is strongly conditioned by the envelope surface temperature, and in particular, by the presence of glazed surfaces whose insulating performance is lower than the opaque components one. In this paper the study of heating and cooling energy needs of an open-space office with different windows’ characteristics has been carried out controlling the internal comfort conditions with appropriate setpoint of the system. An office module with windows on a single façade, or on opposite façades, oriented towards 3 different orientations has been simulated, varying the glazed area (2 sizes), the glazing systems (4 types) and considering three localities of central and southern Europe. The PMV have been calculated for each hour of occupation of the whole year assuming two season as regards the setpoint conditions and clothing level. Calculations have then been repeated considering also the effect of the diffuse and beam solar radiation through the windows directly reaching the occupants. The evaluation of the long-term comfort conditions (on seasonal basis) has been conducted considering some statistical indicators of distribution (the median, minimum, maximum and the interquartile range) and the energy performance of the different glazing solution have been compared accounting for the comfort one

Assessment of the IEQ in Two High Schools by Means of Monitoring, Surveys and Dynamic Simulation

Abstract This work presents an assessment of schools' indoor environmental quality, based on investigations carried out in three Italian classrooms in Treviso, in the North-East of Italy. A first monitoring campaign was performed during the mid season (May-June), a second one during the heating period (January-February). At a first stage, the study was focused on two different approaches, an objective and a subjective one, in order to compare the objective responses with the occupants' subjective sensations. The first method consisted of physical observations and field measurements of thermal environmental parameters, used to calculate Fanger's comfort indices and to apply a comfort adaptive model. The subjective approach was managed by giving students and teachers a survey about their personal judgment concerning the level of comfort perceived. Finally, a simulation model has been built-up and calibrated using the indoor values of air temperature and air humidity trends collected by data loggers. A generic optimization program has been used to calibrate the thermal model. The responses from measurements, surveys and simulations were integrated, analyzed and compared, obtaining a good agreement between the three approaches in assessing the classroom thermal comfort category

Influence Of Building Management On Cost Optimality Definition In Residential Buildings Retrofitting

The enhancement of the existing buildings’ performance requires the choice among a wide selection of energy efficiency measures by means of a cost-optimal approach. Although the cost-optimal analysis represents a useful tool to guide the investment in building renovation, it does not explicitly include the occupant comfort. The retrofit strategy should not only enhance the energy performance of the building in a cost effective way, but also improve, or at least, not deteriorate the indoor thermal comfort during the all year, even when system is off. One of the well-known problems in highly insulated buildings is that, if not correctly managed, they can undergo overheating issues, hampering the indoor environment livability. On the other hand, under discomfort conditions, occupants tend to react, making adjustments (operating the windows and/or the shading devices) in order to improve their thermal comfort, possibly compromising the building energy performance. In this paper the influence of the occupancy behavior on the definition of the cost-optimal level has been investigated on a set of reference buildings, representative of different building typologies, construction periods and windows orientations, located in two typical Italian climates, Milano and Messina, representative of respectively heating and cooling dominated climatic regions. A wide selection of energy efficiency measures has been evaluated, combining a genetic algorithm for the multi-objective optimization and a dynamic simulation code. The search of the best combination of strategies has been conducted optimizing energy efficiency, global costs and the indoor thermal comfort at once. At a first stage, the optimization has been carried out evaluating only the performance of the envelope, without considering the building management operated by the occupants. At a second stage, the optimization has been repeated including the user-operated building management. This allows evaluating the importance of an appropriate management of the building by the occupants, through windows and shading operation, and its impact on the definition of the optimal retrofit strategies. The comparison of the results of the two optimizations also highlights the possible performance gap between asset and tailored rating of refurbished buildings

Evaluation of the Indoor Thermal Quality in high schools buildings: strengths and limits of different assessment methods

Recent studies have pointed out how much the indoor environmental quality in schools\u2019 classrooms is an important factor which could prevent serious adverse effects not only on the students\u2019 comfort sensation, but also on their health and learning potential. However, although standards EN ISO 7726:2001, EN ISO 7730:2005 and EN 10551:2001 give recommendations about how to practically perform objective and subjective measurements, on the evaluation of the level of comfort perceived in buildings, there is the need to define a systematic and standardized way in order to implement the comfort assessment through a methodical and uniform approach. In this work the assessment of the Indoor Thermal Quality of two classrooms in one high school located in Treviso, a town in the North-East of Italy, is presented in order to highlight the strengths and the limits of two different evaluation approaches: field monitoring, survey questionnaires. To reach the aim, two monitoring and surveys campaigns were carried out, one during the spring and one during the heating season. All the four comfort areas were investigated through the questionnaires: the thermal, the visual, the acoustic and the air quality perception.. Afterwards objective and subjective responses on thermal and visual perception have been compared

The Role of Occupant Behavior Models in Multi-Objective Optimization Analysis

Building retrofit design aims at achieving a certain low energy target at a minimum cost. However, these buildings tend to be less comfortable than expected, prone to overheating, poor air quality, and less resilient towards different user profiles. Even when more accurate simulation models are used to calculate the energy demand, occupant behavior is usually oversimplified as a static schedule or rule-based model which often does not depend on comfort conditions and does not represent the actual occupants’ reactions to manage indoor comfort. This can cause a significant gap between the simulated and the measured building performance. To address this gap, we have compared the performance indicators of optimal retrofit solutions obtained through a multi-objective optimization of a reference case and recalculated using different occupant-behavior models for the daily building operation – i.e. opening/closing windows. Recalculations of the optimal solutions have been performed with the generally used static schedules, a rule-based adaptive model, and an innovative probabilistic approach. The results have been analyzed through Pareto difference metrics to quantify the influence of behavioral models on energy consumption, cost, and comfort. Two referent scenarios – in a heating and cooling dominated climate – have been tested to observe the results under different boundary conditions. The findings demonstrate that the performance indicators vary strongly with each behavioral model severely compromising on the competing objectives of energy demand, i.e. cost, indoor air quality, and thermal comfort. The importance of realistic user behavior modeling is highlighted to prevent misleading conclusions on optimal solutions in the assessment of energy efficiency measures. It is pointed out that probabilistic behavior models are highly sensitive to variations of operating conditions, even leading to a positive rebound effect for certain retrofit strategies