Natural Night Ventilation Research Articles

Building and system design's impact on thermal resilience to overheating during heatwaves: An uncertainty and sensitivity analysis

Rising heatwaves necessitate thermally resilient buildings to mitigate occupant heat-stress and mortality, ensuring habitable conditions during thermal shocks. This study's aim and novelty is to identify key design parameters affecting three thermal resilience aspects -(i) shock impact or SET-Dh i.e., degree hours above standard effective temperature threshold of 28 °C (ii) absorptivity time (tabs) and (iii) recovery time (trec) across varying degrees of shock intensities (doS-low, medium and high). A reference Belgian apartment is simulated with varying design parameters (building orientation, envelope and glazing properties, glazing percentage, airtightness, operation and control of passive strategies, cooling systems) during three types of heatwaves. Uncertainty analysis quantified the impact of design variations on thermal resilience, while global sensitivity analysis pinpointed key parameters affecting resilience during different shocks. The study shows that while 87 % of design variations remain thermally resilient during shorter shocks, only 21 % do so during longer shocks and that WWR, cooling capacity, and passive strategies (operation of natural night ventilation and solar shading) have twice the impact on thermal resilience compared to building orientation and glazing properties. While tabs is affected by heat build-up factors (e.g., WWR, solar shading), trec is influenced by heat removal factors (e.g., cooling capacity, NNV). Parameters such as heavy thermal mass extend heat absorption but also delays heat dissipation during prolonged heatwaves. This study guides designers and architects to focus on interventions that enhance buildings' thermal resilience during both short and long heatwaves, aiding in climate adaptation and the ability to withstand future extreme heat periods.

Assessing thermal resilience to overheating in a Belgian apartment: impact of building parameters

Globally and in European Union, climate change and heatwaves (HWs) challenges the thermal resilience performance (buildings’ ability to withstand and recover from a shock) of airtight, highly insulated buildings with no cooling strategies. Ensuring thermal resilience in buildings is crucial for maintaining habitability amid climate change uncertainties. This study, under the framework of IEA EBC Annex 80, aims to explore the impact of design parameters (thermal mass, window to wall ratio (WWR), operation of solar shading and natural night ventilation) on the thermal resilience in a Belgian apartment. Although a number of recent studies explored impact of building design on overheating, there is still a lack in the state-of-the-art exploring and varying ranges of the design parameters that impact the thermal resilience performance of apartments during short-term shocks such as heatwaves. In order to reach the aim of this study, building energy simulations were performed. Initially, the default apartment was evaluated during current weather scenario varying the parameters. Results showed overheating risk in default apartment during current weather scenario. Then the worst, improved and, the optimized variation of the building is evaluated against 6 days HW. The apartments’ thermal resilience performance assessment conclude that high window-to-wall ratios (WWR >30%) without solar shading and lighter thermal mass decrease thermal resilience during shocks, highlighting WWR’s significance. For short-term overheating events, heavy thermal mass improves the thermal resilience by pro-longing the absorptivity time (withstanding capability) of the excess heat. However, if excess heat is absorbed by the building (higher WWR resulting in higher solar gains), lighter thermal mass enhances the thermal resilience performance (recovery capability) by flushing out the excess heat. Solar shading and passive cooling strategy like natural night ventilation aids in temperature management, improving the buildings’ thermal resilience performance by prolonging the absorptivity and speeding the recovery from the shock.

Energy efficiency of ecological buildings in Tunisia: Natural fiber composites and passive strategies impact

Improving the thermal insulation and energy efficiency of building envelopes is a major objective worldwide and has significantly developed in the recent years. This study aims to evaluate the impact of ecological additive and passive strategies on building energy efficiency. An experimental study was carried out to examine the effect of the incorporation of treated Alfa and Posidonia-Oceanica fibers on the thermal properties of cement and gypsum composite samples. The experimental results were then introduced in a numerical study using TRNSYS software to perform a comparison of the energy efficiency and thermal performance of three individual buildings; two ones constructed with our ecological materials and the third one with typical materials is considered as a reference case under the Tunisian climate. The obtained results indicate that the buildings built with Alfa fibers (BAF) and Posidonia-Oceanica fibers (BPOF) are economically effective since they allow a decrease of about 48.20% and 43.48% in heating, 45.71% and 42.77% in cooling, leading to a reduction in CO2 emission of 47.90% and 43.40%, respectively, in comparison with the reference case. The investigation also focuses on the improvement of the ecological building envelope by a storage wall integrated on the south front and shaded by solar movable overhangs during the summer season. The indoor climate results reveal that incorporating passive strategies into the building improves indoor air temperature and preserves a comfortable indoor relative humidity. Heating requirements decrease by 82.82% for BAF and by 79.76% for BPOF. The cooling requirements of the reference building are also reduced by 63.46% for BAF and 60.45% for BPOF by the use of natural night ventilation (4 ACH) and the appropriate shading for Trombe walls and windows. Consequently, the implementation of passive strategies on the ecological buildings led to a net reduction in CO2 emissions by up to 80.55% for BAF, compared to the reference case.

Energy Performance of Vernacular Architecture in Various Desert Climates

Summer 2022 is officially the 2nd hottest summer in France since 1900. It resulted in three episodes of heat waves over a total of thirty-three days. Heat waves are characterized by very high temperatures (exceeding seasonal averages) during the day and night for at least three consecutive days. According to initial estimates, it caused a surplus of more than 11,000 deaths in 2022 in France. In France, despite new thermal standards, the thermal comfort of new housing in hot weather remains very inadequate. Thanks to these empirical developments vernacular architecture has demonstrated its adaptation in particularly harsh climates. The objective of this research is to understand the design strategies of four vernacular houses located in four deserts (Algerian Sahara, Arizona, Libyan desert, and Yemen) to ensure summer comfort in hot environments. The thermal behavior of these four vernacular houses has been studied through dynamic thermal simulations performed with the software ‘ArchiWIZARD’, using the same climate conditions. The results are interpreted in terms of operative temperature and related to building compacity. They show how vernacular architecture, located in desert climates, considered summer thermal comfort with design strategies. The thermal inertia of the four case studies is characterized by the daily thermal damping. The results also show the contribution of natural night ventilation on the energy performance of these four vernacular architectures in hot and arid climates.

Impact of bioclimatism and passive solutions on thermal performance: Feedback from an experimental wood-concrete house in a Mediterranean climate

This article is based on the analysis of the thermal behavior of an experimental house in a Mediterranean climate. This well insulated house presents 3 specificities: inertial elements mainly in the heart of the house with a wood frame envelope, large bay windows, and an interior patio facilitating the safe opening at night. The work focuses on the contribution of passive solutions: the valorization and management of solar gain, natural ventilation at night, thermal inertia and thermal insulation. Dynamic thermal simulations complete the analysis of the measurements. The concept has demonstrated its interest in the summer period with a comfort that can be maintained provided that the available passive solutions are used adequately. The thermal inertia coupled with the natural night ventilation allows to maintain a stable maximum daily indoor temperature lower than the outdoor temperature with a daily thermal amplitude up to 13 °C. The concrete slab of the ground floor exchanges with the indoor air up to 10 W/m2 during the day and up to 25 W/m2 with the natural night ventilation. The flow rate of the latter is estimated at 3.5 to 5.5 vol/h. In winter, the thermal inertia of the slab allows to make better use of solar gains, with for example a thermal flux penetrating the slab that can reach up to 60 W/m2, and represents, cumulated over the day, an energy transferred to the slab up to 300 Wh/m2. This energy is diffused throughout the night with an intensity of about 10 W/m2.

Comparative assessment of night ventilation performance in a nearly zero-energy office building during heat waves in Brussels

With increasing urbanization, overheating intensifies, resulting in a greater risk of indoor overheating in commercial buildings, which already have high internal gains. The impact of urban climate on the cooling energy needs of buildings has been extensively researched. However, the building performance during extreme heat events needs further investigation to reduce the energy demand from the grid during critical events and to ensure an acceptable indoor thermal environment. Here, a comparative assessment approach for natural and mechanical night ventilation performance to reduce indoor overheating and energy needs of a nearly zero-energy office building in Brussels, Belgium, was evaluated for the heat wave and non-heat wave periods in urban and rural microclimates, using calibrated thermal-energy simulations. The analysis indicated that active cooling with natural night ventilation was more effective during heat waves than other cooling strategies. In addition, natural night ventilation was also effective in maintaining safer levels of heat index values in the reference office compared to other strategies. Natural night ventilation reduced overheating by 0.39 °C in the urban microclimate and 0.50 °C in the rural microclimate relative to the Baseline. Considering the cooling energy use, natural night ventilation had no significant impact. In contrast, mechanical night ventilation increased energy use by 0.54 kWh/m2 in urban microclimate and 0.40 kWh/m2 in rural microclimate due to prolonged ventilation fan operation in the reference office building. The presented findings in the paper lead to the formulation of design guidelines, recommendations for future practices and identifying needs for further research.

Evaluation of thermal resilience to overheating for an educational building in future heatwave scenarios

Airtight and highly insulated buildings are subjected to overheating risks, even in moderate climates, due to unforeseeable events like frequent heatwaves and power outages. Educational buildings share a major portion of building stocks and a large percentage of the energy is expended in maintaining thermal comfort in these buildings. Overheating risks in educational buildings can lead to heat-stress and negatively impact the health conditions and also cognitive performance of the occupants. In the light of increasing severity and longevity of heat waves in future climate scenarios, and associated power outages occurring during the heatwaves, measures to reduce overheating risk while limiting the cooling energy is gaining importance. Since the performance of existing buildings are not guaranteed during events like heatwaves, power outages, it is crucial for these buildings to be resilient to overheating. (Building) resilience is a method to deal with these uncertainties and is stated as ‘an ability of the building to withstand disruptions; and to maintain the capacity to adapt, learn and transform’. The focus of this paper is to evaluate thermal resilience for two test lecture equipped with low-energy cooling strategies like natural night ventilation (NNV) and indirect evaporative cooling (IEC) rooms, by dynamic Building Energy Simulations (BES). To assess the thermal resilience to overheating three different heatwaves (HW) files (intense, severe, and longest) for 3 future scenarios (1) Historical (2010–2020), (2) mid-term (2041–2060) and (3) long-term (2081–2100) and a 24h power outage (PO)scenario was simulated. Benchmarking was done with a base case – Typical Meteorological year(TMY) with no power outage. The heatwave files were developed adopting the methodology proposed by the 'Weather Data Task Force’ of International Energy Agency Energy in Buildings and Communities Programme (IEA EBC) Annex 80 ‘Resilient Cooling of Buildings’. This study shows, IEC has high to moderate recovery capacity in TMY period and low recovery capacity in HW period, for a power outage of 24 h. Recovery capacity is low during HW period, especially during an intense and longer HW period when outdoor temperature influences the cooling capacity of the IEC. The results also demonstrates the impact of the thermal mass on the resilience to overheating. Passive survivability assessment indicates, the lecture room with lighter thermal mass does not violate 30 °C threshold during a power outage in TMY period and additionally,. recovers faster (11% times faster) from peak temperature compared to lecture room with heavy thermal mass. There is a steep increase in unmet degree hours (occupied hours above24 °C threshold) during HW compared to TMY period. This paper gives a directive towards assessment of resilience to overheating and also points out the gap in the existing indicators to assess the resilience.

Impact of heatwaves and system shocks on a nearly zero energy educational building: Is it resilient to overheating?

The characteristic that describes the extent to which buildings and their systems maintain their performance during shocks is called resilience. Building policies in the EU have already addressed the resilience of buildings against possible hazards (i.e., natural disasters, extreme weathers, fires). However, with increasing overheating risks (e.g., climate change) accompanied by their detrimental health and economic impacts, the thermal performance of nearly zero energy buildings (nZEB) is not guaranteed. This study aims to assess the impact of shocks and combinations on the thermal resilience of educational nZEB against heatwaves (HW) and system shocks (SS) including failure of indirect evaporative cooling (IEC), natural night ventilation (NNV) and solar shading failure (SF). A Modelica model of the building was developed and experimentally validated. Shocks were classified and quantified using the novel normalized degree of shock (doS) index. Heatwaves (HWs) had 20 × to 93 × more critical impact than the worst SS (NNV failure). Additionally SS occurring at the start of the operational period is 1.2 × more critical than SS occurring later in the day as it allowed for significant heat build-up in both classrooms. In future climate scenarios a combination of HWs and power outages will become frequent. This study showed that a combination of a full day of cooling strategy and shading failure occurring on the hottest day of a 6-day long HW, is 10% more critical on both lecture rooms than an individual 10-day long HW. Classroom with heavy thermal mass prolongs the absorptivity of the shocks but delays recovery.

Impact of thermal inertia coupled to natural night ventilation. A case study for a high performance building in continental climate

In summer time, thermal inertia appears as a passive solution to improve the thermal comfort in many part of Europe. The objective of this paper is in a first step to generate thermal comfort data from energy efficient houses in summer time with a focus on the impact of thermal inertia and natural night ventilation. In a second step, numerical simulation are run on these configurations to compare their construction systems. This work confirms the positive impact of both thermal inertia and natural night ventilation on the thermal comfort for energy efficient buildings in continental climate. It also allows to quantify the difference of indoor air temperature on this case study and to ensure the reliability of the numerical models. Finally, contrary to what is mentioned in many papers, no significant time lags between the heavy and the light weight envelope have been highlighted.

Thermal resilience to overheating assessment in a Belgian educational building with passive cooling strategies during heatwaves and power outages

Airtight and highly insulated educational buildings are subjected to overheating risks, even in moderate climates, due to unforeseeable events like frequent heatwaves (HWs) and power outages (POs) leading to heat-stress and negative impact on the health conditions and cognitive performance of the students. The focus of this paper is to evaluate thermal resilience for two lecture rooms equipped with the low-energy cooling strategies natural night ventilation (NNV) and indirect evaporative cooling (IEC). To assess the thermal resilience to overheating, the lecture rooms were tested with and without passive cooling strategies for 3 Typical meteorological years (TMYs), 3 severe HWs and those 3 HWs + POs. Results evaluating the existing indicators unmet degree hours, indoor overheating degree (IOD), ambient warmness degree (AWD), and overheating escalation factor (αIOD) demonstrated that with passive cooling strategies the two test lecture rooms have good thermal resilience during TMY and HW periods (except long-term severe HW), with 18% higher unmet degree hours during HWs. Lecture room with heavier thermal mass demonstrated higher thermal resilience to overheating in long-term assessment. Furthermore the need to develop a holistic resilience indicator taking into account building and system parameters was also pointed out in this study.

Phase change material coupled building envelope for thermal comfort and energy-saving: Effect of natural night ventilation under hot climate

Incorporating phase change material (PCM) into buildings in hot climates is an excellent strategy for better thermal comfort and energy-saving in future smart cities. Nevertheless, PCM elements suffer from adverse temperature behaviour at night due to the dissipation of stored diurnal heat. Night ventilation has been proposed as a promising solution and clean strategy for decreasing indoor building temperature at night and increasing PCM benefits in the following cycle. In this study, the effect of the natural night ventilation (NNV) period on the thermal performance of a room-integrated PCM is investigated experimentally under hot summer conditions in Iraq. Six NNV periods (with 1 h increment) are studied for six consecutive days in terms of average indoor and operative temperature reduction. Moreover, the work is extended to study the average heat gain difference in each day cycle to show the contribution of PCM to energy-saving. The results showed a slight enhancement in the average indoor air temperature of the PCM room compared with another identical no-PCM room regardless of the NNV period due to high outdoor ambient temperature at night. However, NNV for 4 h can reduce the average indoor air temperature by 28.6% compared with 1 h of NNV, whereas a slight extra reduction was achieved for 5 and 6 h. Besides, NNV slightly affected the operative temperature at night against no impact during the day, which was more influenced by the solar radiation and high diurnal ambient temperature. The results further revealed that a total average heat gain difference of 63.1–87.9 W was achieved, in which the roof contributed by more than 44% in each cycle. • A PCM coupled building envelope is studied experimentally under severe hot climate. • The effect of NNV on PCM behaviour is evaluated considering the AITR and OTR. • Four-night hours of NNV could lower the indoor temperature of the PCM room to a limit. • Total AHGD of PCM room decreased by 63.1–87.9 W, and the roof contributed by 44%. • Diurnal ambient temperature and solar radiation had influenced the daily AHGR more than NNV.

Climate adaptive optimization of green roofs and natural night ventilation for lifespan energy performance improvement in office buildings

Green roofs and natural night ventilation are highly coupled and complementary techniques to improve building energy efficiency, but previous studies have not fully explored the synergetic benefits of combining two technologies. Furthermore, the traditional method of design optimization using Typical Meteorological Year (TMY) weather data falls short of providing climate-adaptive designs for new buildings that react differently to weather changes, as well as capturing the applicability and uncertainty of yearly weather variations. Therefore, building long-term performance in practice often deviates significantly from its design expectation. To quantitatively assess the energy savings when integrating green roofs and night ventilation (GR-NV) while taking future long-term weather impacts into account, this study proposes a systematic approach that integrates field testing, sensitivity analysis, building energy simulation, and climate adaptive optimization. The proposed approach is validated and demonstrated in an office building in Chongqing, China. The results show that Chongqing's annual mean air temperature in 2050 would climb by 2.4 °C in comparison to that of TMY. With the global warming effects, the annual night ventilation hours and the amount of sensible heat dissipated by NV increased by 78 h (13.2%) and 15.8 MJ/m2 (18.7%) from 1991 to 2050. The choice of plant species in the GR-NV system would also be impacted by global warming. The optimal design alternative based on FMY could reduce annual energy use by up to 5.07 kWh/m2 (12.2%) in new buildings.

Climate change mitigation: thermal comfort improvement in Mediterranean social dwellings through dynamic test cells modelling

Global warming will lead to adverse consequences for human health and well-being. This research ought to determine whether passive low-cost strategies freely controlled by users (ventilation strategies, solar shadings or window operation) could be applied in low-income dwellings to meet acceptable thermal comfort to retrofit the Mediterranean social housing stock of southern Spain towards climate change. On-site measurements registered in some test cells (controlled environment with no users’ influence) were used to calibrate dynamic energy simulation models. The impact of several future periods, climate zones of southern Spain and orientations on thermal comfort was assessed. The results show that climate change triggers a more significant increase in outdoor temperatures in summer than in winter. Should ventilation be kept to minimum and blinds opened during daytime in winter, higher comfort would be achieved, with great differences between orientations and south reporting the best results. The higher the outdoor temperatures due to climate change, the higher the percentage of comfort hours (i.e. 23–68% in the present and 50–75% in 2080). In summer, natural night ventilation and blinds closed during daytime lead to the best comfort result, with negligible temperature differences between orientations. Future climate change scenarios worsen the percentage of comfort hours (i.e. 96–100% in the present, while up to 17% in 2080). Mechanical ventilation and blind aperture schedules were found to have the highest influence on overheating discomfort. Likewise, mechanical and natural ventilation schedules had the highest impact on undercooling discomfort.

Simulation of passive ventilation strategies towards indoor CO2 concentration reduction for passive houses

Population awareness and economic growth are responsible for the increasing requirements of indoor thermal comfort in buildings. However, the use of active systems to ensure indoor thermal comfort, contributes for the building sector to be responsible for high levels of energy consumption and consequently greenhouse gas emissions. Passive Houses are one step forward towards low energy demand and indoor environmental quality in buildings. Airtightness of the building's envelope is one of the major PH requirements, that in association with the mechanical ventilation system are responsible to assure adequate ventilation levels. These parameters result in additional challenges towards PH applications in Mediterranean and warm subtropical climates due to the overheating risk, providing new opportunities to explore potential night ventilation strategies. This study is focused on the analysis of different passive ventilation strategies towards indoor CO2 concentration reduction preventing overheating risk, thus assuring high levels of indoor environmental quality. The adopted methodology relied on collected data acquired from interviews performed to Passive Houses residents as the starting point, to identify their major expectations as well as complaints and concerns regarding indoor environmental quality. Following the interviews analysis, whole building dynamic simulation was performed using as a case study a PH building constructed in Cyprus (Tseri Passive House). Three different ventilation scenarios were evaluated: original settings (scenario 1); mechanical ventilation active during the day and turned off during the night (scenario 2); natural night ventilation (scenario 3). An ideal scenario, considering night ventilation through window openings, in which indoor CO2 concentration never exceeded the normative limit of 1000 ppm during a summer design week was achieved.

On the Energy Performance of Micro-Encapsulated Phase Change Material Enhanced Spackling with Night Ventilation

Phase change material (PCM) is an attractive solution for improvement of thermal performance in buildings, and have excited a vast amount of research in recent years. There are however practical challenges with ensuring adequate phase transitions of the PCM to exploit the passive heat storage benefits. Night ventilation (NV) with free cooling have surfaced as one of the most promising methods to properly utilize PCMs and maximize energy savings. This work deals with a novel spackling compound enhanced with microencapsulated PCM. The product is intended for use at inner walls and ceiling surfaces of buildings and is suited for new and retrofitting building applications. Ensuing former experimental studies, a validated simulation model is developed and used to study the PCM with natural and hybrid NV strategies in an office building during summer conditions in Oslo, Norway. Cooling load reduction and energy savings are analyzed with varying air flow rates of 0.5–5 air changes per hour (ACH) and 2–4 mm PCM layer thickness. It is shown how increasing air flow rates and PCM thickness greatly enhances energy performance, but at a diminishing rate. Although the NV alone can reduce the cooling load by 11.5% at 1 ACH, 40.2% at 3 ACH and 59.8% at 5 ACH, one can achieve further reduction up to 19.5%, 78.2% and 95.5% for the respective ACHs with 4 mm PCM. The natural NV provides more energy savings compared to the hybrid strategy. As energy requirement by fans increases with the increase of air flow rates in the hybrid strategy, the energy savings eventually start to reduce. The hybrid strategy can save 38% energy at most with 3 ACH, and the savings is increased to 50% with the inclusion of 4 mm PCM. On the other hand, the natural strategy saves 56% of energy at the same air flow rate, and 69% with 4 mm of PCM.

ENERGY-CONSERVATION CONSIDERATIONS THROUGH A NOVEL INTEGRATION OF SUNSPACE AND SOLAR CHIMNEY IN THE TERRACED RURAL DWELLINGS

In the present study, a novel passive solar system— a designed sunspace in combination with solar chimney (SS)—is implied to work out the concerns of energy requirement in the terraced rural dwellings of Iran. Renewable plans for heating need to be implemented before regarding mechanical facilities. Due to the southern orientation of most rural homes moreover, dwelling slope it is likely to use sunlight in most hours of the day. Hence, the SS system with an area of 4 m2 on the southern side of the building is considered. The simulation was performed through the Energyplus software and verified by experimental data. On the basis of the results, applying the SS system in buildings can magnify the amount of heat obtained. This is a practical plan to assist in space heating in cold months. Moreover, natural night ventilation over the SS can reduce the cooling load during hot seasons. The results additionally indicate that the highest energy-saving for heating and cooling observed in January and July respectively. Lastly, the annual economic advantage of the SS system with respect to power conservation will be 14.3% accordingly the increased cost for installing the SS will be retrieved by 8 years generally.

Optimization of passive design features for a naturally ventilated residential building according to the bioclimatic architecture concept and considering the northern Morocco climate

Improving the wellbeing of the occupants is the main challenge in the building design field. This work aims optimizing the design of a free-running residential building located in northern Morocco according to the bioclimatic architecture concept. In the first stage, an analysis of the bioclimatic chart has been done to find the best passive design strategies for the northern Morocco climate. Based on the results of the analysis, a set of passive design parameters has been selected to be considered in a building thermal and lighting energy performance optimization. A case study of a family detached residential building is considered for this purpose. The optimization problem is multi-objective, so the Pareto front approach was used to select the best design solution. Finally, a monthly assessment of the thermal and lighting energy performance of the chosen design solution is presented. The main results show that applying exterior insulation with a thick thermal mass layer is best for thermal performance enhancement. A wider glazed area with small overhang depth is more suitable for the south facade. For the east facade, the best solution is to limit the glazed area and increase the overhang depth. The importance of natural night ventilation for summer cooling has been also confirmed. This study can serve as a reference for building designers in northern Morocco while developing their projects.

Efficiency of night ventilation in limiting the overheating of passive sports hall

It is especially difficult to provide optimal microclimatic conditions in sports facilities during summer time. The internal heat gains and an airtight building insulation, combined with high external temperature can easily lead to overheating and upsetting of the body's thermal balance. This article focuses primarily on the effect of natural night ventilation on the thermal comfort in a passive sports hall building. Based on experimental studies of thermal conditions in the hall, a simulation model was made using the Design Builder program. Through simulation analysis, the program considered thermal conditions that arise in various scenarios of natural and mechanical ventilation. Results presented in this article show that the natural ventilation at night in a large volume building is the most effective and the easiest way to reduce overheating in summer.

Present and future potential of natural night ventilation in nZEBs

The increase in the energy need for cooling is one of the major challenges in nearly Zero Energy Buildings. Recent constructions are characterized by high thermal insulation levels, which can be effective in preventing summer discomfort in combination with accurate control of solar gains through glazed surfaces and discharge of overall gains via ventilation. In addition, urbanization, densification and the global warming trends registered in the last decades can increase the risk and magnitude of overheating effect if an accurate design and use of correct technologies and good practices are not considered. The paper investigates the effects and the potential of natural night ventilation, as a strategy to reduce the energy need for cooling even taking into account the evolution of surrounding urban area with the exacerbation of urban heat island under future weather projections. Among the different tools available for the assessment of the cooling potential in buildings, the research focuses on two methodologies, which are adaptable to the conceptual design phase, where a first approximation of the natural ventilation potential is required. The study is developed on the weather datasets referred to the area of Milan and shows the future evolution of the night cooling potential, highlighting the importance of orienting building design towards greater integration between different passive cooling strategies for the summer period.

Development and thermal performance of wood-HPDE- PCM nanocapsule floor for passive cooling in building

ABSTRACTCooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. This work shows the benefits of PCM when incorporated in wood fiber-polymer composite as floor cooling system using nano-encapsulated PCMs. The wood-plastic-NPCM composites were produced using compression molding process and its mechanical and thermal properties were investigated. Two dynamic simulators were employed to investigate synthesized composites thermal performance. Increasing NPCM content in WPC showed that the fluctuations of the simulator temperature was decreased while the heat fluxes through the floor was increased. The variations of ambient maximum temperature have little effect on the air temperature of the simulator with 40% PCM which indicates that the amount of PCM was enough for studied environmental condition. Field experiments were performed using two medium-scale test houses located on Tehran-Iran. It can be concluded that using NPCM helps to reduce heating and cooling demand. Moreover, the natural night ventilation by opening windows reduced the number of hours that the temperature is above 23°C from 499 h/year in case1 (without opening) to 255 h/year in case 2(with opening). This means that natural night ventilation could help reduce the overheating period to about 50% with the use of NPCM.