• Energy Research

Abstract Contrarily to what happens in northern European countries, buildings in the Mediterranean region are prone to overheating. Consequently, it is important to better understand the role that the thermal transmittance of the building envelope elements has on air-conditioning consumptions. This paper analyzes the effect of different U-values on building design in the Mediterranean area. 192 000 residential buildings were randomly generated for sixteen distinct locations and the energy consumption was assessed for each. It was found that in northern Mediterranean locations, as U-values decreased, energy consumption also decreased. However, in warmer climates, low thermal transmittances tended to significantly increase energy consumption. Hence, the lower the latitude, the higher the U-values should be, in order to prevent increasing the cooling demands. Additionally, geometry-based indexes were correlated with the building’s energy performance. For high U-values, it was found that bigger buildings worsen the energy performance and larger windows tended to improve it. For low U-values, bigger north-facing windows were beneficial. There is an adequate interval of values for which the geometry has a lower impact, which is wider and higher for lower latitudes, thus meaning that not only does the building performance improve but architects are also freer to explore alternative designs.

Old buildings refurbishment is essential for the global improvement of building energy indicators. Within this context, the paper focuses on the energy savings that may occur when using electrochromic (EC) windows, an interesting emerging technology alternative to shading devices to control solar gain in buildings located in Mediterranean climates. The EC windows technology is briefly presented and the optical properties adjustments of the glasses are discussed according to the operated range. The EC window dynamic behavior and the different control strategies are modeled and implemented in the ESP-r building simulation program. The EC window impact in the energy needs for heating and cooling is studied, considering different ambient parameters (exterior dry bulb temperature, interior dry bulb temperature and incident radiation) and set points for the EC control. A comparison of several windows solutions (single, double-glazing and EC windows), the type of building, internal gains from occupancy, lighting and equipment and the orientation of windows are considered for discussion through the analysis of the energy needs for heating and cooling. It is concluded that for this climate the best positive results are obtained when the EC are used in the west facade. For the south facade the results show no significant advantages in using EC windows.

Abstract This paper provides an overview on how phase change materials (PCMs) can be used for the thermal regulation of photovoltaic (PV) devices, and describes an experimental apparatus to assess whether the performance of 250 W STC-rated commercial polycrystalline silicon PV panels can be improved by placing movable thermal energy storage (TES) units filled with the free-form PCM RT 22 HC on the panels' back. The outdoor apparatus is located at Coimbra, Portugal. Three identical PV panels were separately installed and individually monitored: one panel was taken as reference; the other two were considered together with a TES unit each with horizontally and vertically oriented cavities, PV/PCM1 and PV/PCM2 systems, respectively. The time evolutions of the temperature of the PV panels were compared with each other to analyse the possible thermal regulation potential of the TES units. The time evolution of the power output was also assessed to compare the efficiency of the different systems. Finally, the energy produced per day by each system was evaluated. The results showed that the PV operating temperature has increased ca. 16–21 °C and 14–18 °C in the PV/PCM1 and PV/PCM2 systems, respectively, in comparison with the reference PV panel (at peak time). Moreover, the daily energy produced by the PV panel of the PV/PCM1 and PV/PCM2 systems was, respectively, 3.3–6.5% and 3.3–6.0% lower than that produced by the reference PV panel during the measured short-term summer operation period. Therefore, it was concluded that the movable TES units have a negative impact on the performance of the PV/PCM systems, and that a PCM with a higher phase change temperature must be chosen for Mediterranean climate.

Abstract High thermal mass construction is commonly used to reduce cooling energy consumption during the summer period as a passive design strategy in the Mediterranean region. Although being a generalized design practice, the benefit to the building performance is not fully consensual within the scientific community. This work explores the influence of thermal transmittance on the energy efficiency of buildings with different thermal mass levels. Hence, a statistical comparison of the buildings’ annual energy consumption for air-conditioning is carried out based on two synthetic datasets with high and low thermal mass and varying thermal transmittance for opaque and transparent elements. In addition to climate location, the results demonstrate that thermal transmittance has varying impact on the contribution of thermal mass. The locations presenting such behavior were Marseille (−0.99% to +3.89%), Istanbul (−0.73% to +4.21%), Valencia (−1.31% to +4.97%), Algiers (−2.32% to +3.81%), Malaga (−3.95% to +6.21%), Casablanca (−5.66% to +6.96%), and Tel Aviv (−1.81% to +5.44%). These findings demonstrate that the influence of thermal mass is more complex than previously thought and levels should be chosen in relation with the thermal transmittance value.

The adaptation of spaces to different usage typologies can be complex in heritage buildings. Facilities were initially planned for a specific type of use that, when changed, require additional measures to ensure a suitable indoor environment. Passive strategies—e.g., free cooling—are commonly used as an alternative without requiring equipment installation. However, its implementation often leads to unsatisfactory conditions. Therefore, it is important to clarify the main barriers to achieving thermal comfort in readapted historic buildings. The present work investigates the thermal comfort conditions reported by workers in office spaces of a historic building in the University of Coimbra. A monitoring campaign was carried out between May and September 2020 to assess indoor conditions’ quality. Due to the current pandemic of COVID-19, offices were not occupied at full capacity. A one-day evaluation of thermal comfort was made using a climate analyzer and six occupants were surveyed on 19 August 2020. The main results highlighted discomfort due to overheating of spaces. The causes were related to the combination of inadequate implementation of the free cooling actions and the building use. Furthermore, it was recommended the installation of HVAC systems in case of full capacity.

Abstract A multi-level allocation problem consists in determining the position and size of spaces on several levels according to the user's requirements and constraints. How levels are connected and how vertical circulation objects are treated may limit the practitioner's preferences or reduce the number of solutions. Literature review has shown that in the multi-level allocation problem very often stairs and elevators are considered as fixed and rigid objects during the search process and sometimes even neglected. This paper presents an approach to deal with multi-levels based on a hybrid evolutionary technique where stairs and elevators are parametric objects, which interact with other spaces during the search process. Three case studies are presented, where the algorithm is tested on handling large and complex problems, how concurrent vertical circulation objects interact, and how several levels are stacked within a building boundary. The algorithm shows to be capable of generating coherent multi-level floor plans.

Abstract Lighting simulation is a useful instrument in predicting lighting conditions in buildings. Modelers can use several matrix methods according to the buildings’ characteristics and the objectives of the analysis. However, it is unknown which methods are the most appropriate for lighting analysis of heritage buildings. The Joanina Library located in the University of Coimbra – a World Heritage building – was used to compare different matrix methods (2PH, 3PH, and 5PH) under several solar models (BRL, DISC, Perez, and Reindl) using Radiance-based simulations. On-site measurements (indoor and outdoor) were used to calculate each method’s accuracy under different solar models. The combination of the 2PH method with the DISC solar model presented the highest accuracy with an average MBEr and RMSEr of 2.8 % and 43.6 %, respectively. Therefore, the 2PH method was the best choice for the case study, even though the 3PH method may also be considered, especially for parametric studies of improving measures.

Abstract During the next decades the refurbishment of old buildings will be an essential way to contribute to the global improvement of buildings energy performance indicators. Within this context, the present paper is focused on the use of electrochromic (EC) windows, an emerging technology alternative to shading devices, to control solar gains in buildings located in Mediterranean climates. The optical properties adjustments of the EC glasses are discussed based on the incident solar radiation. The ESP-r building energy simulation software was used to study the energy savings resulting from the application of electrochromic windows, considering the comparison of several windows solutions (single, double-glazing and EC windows) and windows orientations (East, South and West). In addition, different transition ranges for the optical properties of the EC glasses are assessed through the analysis of the energy needs for space heating and cooling. The main conclusion is that EC technology is an effective option in cooling dominated buildings. The impact of EC windows is highly dependent on facade orientation, being a valid option particularly in the cases of the East and West facades. For these facades, the control set point found to be effective corresponds to an incident solar radiation on the glass of 150 W/m 2 to impose a total coloured state. For the South facade the results show no significant advantage of using EC windows.