398 research outputs found
Buildings Thermal Insulation Performance Analysis
No full textThe paper reports an overview on the physical basis of the building thermal energy balance finalized to highlight the principal energy flows which can be influenced by the envelope insulation characteristics. With the goal of minimizing the energy need, the building thermal load is clearly defined and its minimization is identified as the driving issue to be pursued in order to reduce the required yearly energy demand. An extensive although simplified analysis on the thermal load components is carried out to identify how they react to an envelope insulation change. The results show in some components different and opposite trends with increasing insulation between heating and cooling seasons, which show that is impossible to assume a generalized response for every building in every context and climatic conditions even on national basis. The general conclusion is that a real building energy optimization requires a yearly energy performance parametric study for this specific building in order to tailor, in the specific context and climate, the full set of governing parameters other than insulation
Annual based performance analysis of buildings thermal insulation
No full textThe paper reports an overview on the physical basis of the building thermal energy balance finalized to make in evidence what are the principal energy flows which can be influenced by the envelope insulation degree. With the goal of minimizing the energy need the building thermal load is clearly defined and its minimization is identified as the driving key to reduce the required yearly energy demand. An extensive although simplified analysis on the thermal load components is carried out to identify how they react to an envelope insulation change. The results show in some components different and opposite trend with increasing insulation between heating and cooling seasons, which make impossible to have a general response for any building in any contest and climatic conditions also on national basis. General conclusion is that a real building energy optimization is requiring a yearly energy performance parametric study for this specific building to tailor on the specific contest and climate the full set of governing parameters other than insulation
Energy Performance And Long-Term Evaluation Of Internal Thermal Comfort Of An Office Building With Different Kinds Of Glazing Systems And Window Sizes
No full textAlthough 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
Convective Heat Transfer at Room Walls: Some Investigations
No full textAs well known, predictions of heating/cooling loads and energy consumption in buildings are significantly affected by the evaluation of convection at room surfaces. In this regard suitable heat transfer coefficients are usually applied: however, sometimes the agreement among the available correlations is quite poor and additionally the presence of particular factors (cold and hot portions of wall, plumes from panels or electric appliances, etc.) give rise to specific conditions, which must be studied as separate cases. In this context “Computational Fluid Dynamics” (CFD) is a very useful tool but it is not still suitable for extensive applications. Therefore, in this paper some correlations are summarised and their results are compared with those obtained by numerical CFD experiments; in doing this, some critical points of CFD (such as the choice of turbulence model and grid spacing) are also discusse
The role of the reference building in the evaluation of energy efficiency measures for large stocks of public buildings
No full textWith the last European Directive 2018/844/EU, EU Member States have to outline effective strategies for the energy renovation of existing buildings, so as to achieve the objectives set respectively for 2030, 2040 and 2050, taking advantage of new financing instruments. In this process, public buildings are identified as important drivers for energy-behavioural changes among citizens and, in addition, they can benefit from encouraging mortgages for certified energy efficient renovations. However, the problem of dealing with existing public buildings is their sample size combined with the current necessity of significant renovations. In this scenario, the reference building acquires a key role as the starting model for the evaluation of primary energy needs and of retrofit measures. In this work, a reference building selected by a previous work is further analyzed, testing selected potential retrofit interventions by means of model simulation. The implemented measures are then evaluated using a cost-optimal approach, in order to integrate their priority with respect to cost-effectiveness. The aim of the work is to test on a building centrotype selected retrofit measures, to be then extended to the other buildings similar for their main geometrical and thermophysical features
- …
