Night Ventilation Research Articles

Exploration on The Characteristics of Natural Ventilation in Bedrooms and Its Determination Method

In this paper, the CO2 (carbon dioxide) exhaled by indoor occupants was used as the tracer gas, and the variation of indoor CO2 concentration in the whole day was observed. Among the 454 samples, 114 and 345 valid samples were screened out which can be used to calculate the daytime and night ventilation rate by the tracer gas method through the sectioning method. The results indicated that seasonal differences in daytime average ventilation are greater than night average ventilation. The highest daytime- average ventilation was found in autumn, next was summer, there was the lowest ventilation in winter. According to the necessary fresh air rate when sleeping at night, night average ventilation rate of 30.1% of samples met the standard. The ventilation rates of different building characteristics were analyzed, residential location, construction age, living floor, room size, window structure, indoor dampness, and window opening habits were all included. The results revealed that the window opening habits was the most significant factor for natural ventilation. Both daytime and night average ventilation rate are basically in the ratio of 2:1 when the windows are opened and closed. moreover, there was higher impact of outdoor climate on daytime average ventilation when window was closed. Significant impact of window structure and indoor dampness on night average ventilation was observed when window was opened. Present study proposed the measurement and determination methods of ventilation when daytime activities of occupants were happened

Evaluation of mixed mode ventilation cooling energy saving potential in nZEB: A case study in Southern Italy

In recent decades, reducing the energy demand of the building sector has become a major goal of global policies. Proper design of the building-plant system is hence strategic to achieve nearly zero energy building (NZEB) target. This paper reports the results of modeling the building-plant system of an NZEB in Southern Italy. The case study is a multi-family complex of eight dwellings located in Bari, in the Apulia region. The building project originates from the energy refurbishment of a former industrial shed that was demolished and rebuilt for residential use. The planned HVAC system foresees the combined use of primary ventilation with fan-coil units fed by two ground source heat pumps (GSHP) supplied by eight vertical probes. Three hybrid ventilation strategies have been compared to evaluate the potential cooling energy saving: the first one examines an earth-to-air heat exchanger (EAHX), the second one proposes night hybrid ventilation from 10 pm to 6 am, and the last considers the adoption of free cooling in mechanical ventilation. Economic and energy comparisons among these three approaches are reported. Using EAHX, the cooling consumption saving reached about 20.7% The use of night ventilation combined with MVS can reduce the cooling energy demand for 14.4%, while free cooling in MVS produces a less effective decrease in the electricity consumption for cooling of about 7.7%. All three strategies generate major benefits in the middle-season.

Comparative assessment of thermal comfort with Insulation and phase change materials utilizations in building roofs and walls

Present study deals with estimation of thermal comfort of residential buildings for different scenarios. The three scenarios which are analysed for the present study are construction using brick wall and concrete roof, construction by utilization of insulation over walls and roof and construction by utilization of Phase Change Materials (PCM) over walls and roof.A building is simulated in EnergyPlus using conduction finite difference algorithm. The PCM is microencapsulated in plaster boards thereby restricting any chemical reactions with the building material. The assessment is carried out by calculating the hourly average room dry bulb temperature and average room relative humidity. This is then compared with the thermal comfort conditions provided in National Building Code of India 2005 and a percentage of hours within comfort range is worked out. The assessment is carried out between the months of March and October for three cities i.e. Bhubaneshwar, Jodhpur and New Delhi, all under different climatic conditions. The results indicate that PCM is performing comparatively better than insulation in improving the indoor conditions and that its performance can be greatly enhanced if the operating temperature is increased from 27°C to at least 30°C. Combined with the strategy of night ventilation and enhanced heat capacity storage, PCM could greatly enhance the thermal comfort levels. Copyright © 2017 VBRI Press.

Opportunities for passive cooling to mitigate the impact of climate change in Switzerland

Energy systems need to decarbonize rapidly whilst satisfying heating and cooling needs. In Switzerland, residential cooling has so far only a small impact on the national energy demand, but climate change and a larger uptake of cooling devices are expected to lead to future increases. This requires novel approaches for sustainable cooling solutions suitable for implementation at a national scale. Here, we explore the potential of night ventilation and window shading to reduce the buildings cooling demand in a changing climate. A physical bottom-up approach is used to simulate residential space cooling demand and to identify the passive cooling potential whilst considering a detailed representation of the Swiss building stock, featuring building age, construction properties, regional climate, urban layout and occupant behaviour. A supervised building type classification approach is applied to enable up-scaling to the national level. Results show that in 2050, the residential Swiss building stock will require a national cooling demand of around 10.2 TWh for a Representative Concentration Pathway scenario 4.5. Under such future climatic conditions, we simulated a potential to reduce the total cooling demand by 84%, with both passive cooling solutions combined. Individually, window shading could reduce cooling demands by 71% and night ventilation by 38%. We found that newer buildings (built after 2000) already account for about 50% of the total current cooling energy demand. Results demonstrate that night ventilation and window shading have the potential to mitigate the impact of climate change in Switzerland and to improve the sustainability and resilience of residential cooling.

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.

Investigating the effect of summer night ventilation on the urban buildings’ thermal and energy performance using numerical approaches

The present study aims to evaluate by simulation means, the effect of different night ventilations rates on the thermal and energy performance of typical building units, located in dense urban areas in Thessaloniki, Greece, both under thermostatic control and free-floating conditions. The numerical assessment is conducted with the dynamic building energy performance simulation model EnergyPlus. A parametric analysis, involving 4 different air flow rates (i.e., 3 ACH, 5ACH, 10ACH, 15ACH) has been carried out for 8 typical building units, located in 4 different urban areas in the city of Thessaloniki, presenting different morphological characteristics. In all cases, single side ventilation has been considered rather than cross ventilation, to evaluate the less optimal, building configuration scenario. The obtained simulation results revealed the significant effect of night ventilation on improving the thermal and energy performance of all the examined building units. Still, the morphological characteristics of the case study areas in which the examined building units are located, also affected the obtained simulation results and the achieved cooling energy savings.

Indoor environmental assessment: Comparing ventilation scenarios in pre- and post-retrofitted dwellings through test cells

In the next few years, outdoor temperature is expected to increase significantly as a result of climate change, a noticeable phenomenon, especially in the Mediterranean. In this future scenario, ventilation is a low-cost and useful strategy for tackling indoor overheating, mainly in energy-poor housing buildings. This research assesses the influence of different ventilation systems, air rates and schedules on the thermal comfort and indoor air quality of a residential retrofitted space when compared to an un-retrofitted environment, through test cell measurements. To do so, the methodology combines on-site monitoring with numerical models, simultaneously analysing both spaces under the same climate conditions. Results obtained show barely perceptible differences between the implementation of a mechanical ventilation system and a natural one, when it comes to thermal comfort in spaces with low thermal inertia, highlighting the clear advantage of energy and economic savings of the passive system. • The differences between IAQ in pre-/post-retrofitted ventilated spaces are minimal. • Inadequate ventilation periods negatively affect both IAQ and thermal comfort. • Short-term ventilation periods are useful for occasionally reducing high CO 2 . • Long-term ventilation periods are required to maintain IAQ with high occupancy. • Night ventilation is effective if applied under specific thermal conditions.

Performance analysis of a new system for night cooling of buildings on a full scale office room - CFD study

Night natural ventilation systems have been receiving increased attention in recent years because of their energy saving potential and environmental protection when used in passive instead of active cooling. A recently proposed novel system for cooling the building concrete slab is studied numerically in the present work. It consists of a new type of a Suspended Ceiling (SC) with a peripheral gap between it and the walls, combined with the positioning of the air supply and extraction grilles between the ceiling slab and the SC. The system relies only on night ventilation as a means for cooling down the structure of the building. This study focuses on the use of Computational Fluid Dynamics (CFD) to predict the airflow and thermal performance of this strategy and it is applied to a full scale office room. The calculations show that a SC with a gap can reduce the difference between the average temperatures at the end of the heating and the end of the cooling periods by 25% compared with the case of a full covered slab room scenario (tight SC). CFD proved to be a useful and accurate tool to predict indoor conditions in buildings.

Building Materials for Cities and Climate Change – a Material Catalogue with Recommendations

High urban density with heat accumulating materials and sealed surfaces can cause heat stress and reduced nocturnal cooling in summer. Appropriate building materials may contribute to the mitigation of this effect. The research project evaluates building materials for façades and outer surfaces (ground) on the resulting urban microclimate and on factors like glare, acoustics and embedded energy. The present publication focuses on the impact on the microclimate. The analysis comprises the simulation of forty-seven data sets in a microclimatic model with ENVI-met. The results show that during daytime the PET for the whole neighborhood ranges between 30.1 and 36.4 °C. Choosing a bright instead of a dark color can lower the PET between 0.2 and 1.0 K. Dark colored metal sheets may cause turbulences which lead to a reduction of the PET between 2.0 and 3.8 K (compared to a bright metal sheet). However, this effect may not be reproducible under varying boundary conditions. During night-time, the resulting span of ambient temperatures between the materials reaches 21.4 to 22.0 °C (level 1.7 m). The temperature difference between the materials at the level of 10.7 m (for night ventilation) is found to be approx. 0.3 K and can be considered irrelevant.

Thermal storage effect of radiant floor cooling system using phase change materials in the hot and humid climate of Indonesia

We proposed a novel radiant floor cooling system using phase change materials (PCMs) with night ventilation in the hot and humid climate of Indonesia. This study aims to clarify the measures to ensure the thermal storage effect of the proposed cooling system during daytime for a naturally ventilated room within a relatively narrow diurnal temperature range, focusing mainly on the thermal properties of PCMs. We analyzed the relationship between the indoor vertical air temperature distributions and heat flows of the proposed system using an experimental building in Tangerang, Indonesia. The results confirmed that the thermal mass of PCMs and the cooling strategy for the floor structure at night strongly contributed to maintaining a low floor surface temperature during the subsequent daytime. Calm wind conditions and warm nocturnal ambient temperature, which was 0.7–3.2 °C lower than the set-point solidifying temperature and is common in the tropics, prevented PCMs from solidifying in case of natural ventilation for the underfloor space. In contrast, forced ventilation for the underfloor space attaching PCMs was effective in ensuring sufficient solidification. Furthermore, 95% of the thermal storage capacity of PCMs might be utilized when the ambient temperature was 2–3 °C higher than the set-point melting temperature during the daytime. The phase change temperature for PCMs can be determined based on the average ambient temperature, whereas a relatively wide diurnal ambient temperature range, at least 4.7 °C, was required to ensure the latent heat thermal storage effect caused by the supercooling.

Numerical simulation of the effect of bamboo composite building envelope on summer overheating problem

Bamboo is one of the materials that have recently attracted considerable interest in sustainable buildings as they are fast growing, retaining thermal and mechanical properties similar to structural wood products, and considered effective CO2 absorbers. Several studies tried to assess the energy performance of bamboo-structures for residential buildings both experimentally and numerically. This numerical study presents an overview on the overheating problem and thermal comfort of four building envelopes: the original steel-bamboo with thermal transmittance of 0.65 W/m2K developed in China by Li et al. (2017) [22], a modified steel-bamboo with increased insulation with thermal transmittance of 0.22 W/m2K to comply with Hungarian requirements, brick, and bamboo-Expanded Polystyrene (EPS). Therm version 7.7.10 was used to simulate heat-transfer, DesignBuilder version 6 was applied to perform the energy analysis. We found that, if neither shading nor enhanced ventilation are applied, the critical building zone has significant overheating in all building systems, emphasising the importance of efficient shading and night ventilation in Hungarian climate. With shading and natural ventilation, the number of hours at or above 26 °C is over 1000 in the modified steel-bamboo, bamboo-EPS, and brick systems, indicating overheating during the summer. Only the original steel-bamboo building envelope performs well concerning the overheating, as the number of hours at or above 26 °C is only about 200. This is the direct consequence of this structure having the lowest insulation of all cases, and hence it has higher heat loss through transmission and can best cool down during evening. However, the original steel-bamboo has more than 100% higher heating consumption than the modified steel-bamboo, as the former building did not comply with Hungarian regulations.

A metamodel-based multi-objective optimization method to balance thermal comfort and energy efficiency in a campus gymnasium

Performing multi-objective optimization for actual public building design has become one of the most challenging subjects in buildings energy efficiency area. Gymnasium is a large energy consumer in public buildings. This study efforts to put forward a novel approach to tackle multi-objective optimization problems for building performance of Qingdao University (QUT) Gymnasium using a new metamodel method. For this purpose, the Nondominated Sorting Genetic Algorithm-II (NSGA-II) was dynamically combined with Multilayer Perception Artificial Neural Network (MLPANN) metamodel, which was previously trained with the co-simulation results conducted using EnergyPlus and Eppy. The new research method also proposes an optimal algorithm coupling Latin Hypercube Sample (LHS) with Principal Component Analysis (PCA) to minimize the total training samples, and guarantees the accuracy of optimization results. The most influential design factors like internal and external wall types, roof types, solar absorptance, windows shading as well as night ventilation (NV) strategy and displacement ventilation (DV) air conditioning system of the gymnasium were considered in three cases of 4×108 possibilities to obtain the optimal trade-off results (Pareto front) between energy consumption and thermal comfort. Finally, a normalized minimum distance decision method was adopted to choose the optimal design configuration from the Pareto front. The optimization results of the study cases showed that reductions were achieved not only in the normalized objectives (88.0% less fh and 85.3% less fc) but also in the sub-objectives: up to 78.2% fewer heating energy and 71.3% fewer cooling energy in air conditioning seasons, and up to 97.7% less heating degree-hours and 99.2% less cooling degree-hours in naturally-ventilated seasons, compared to the original configuration by using optimal design takes simultaneous advantage of NV and DV strategies. The method was confirmed to be an efficient and robust tool for gymnasium design, it could reduce the calculation time of whole optimization process from 10 months to 2 days.

Monitoring and modelling the risk of summertime overheating and passive solutions to avoid active cooling in London care homes

Summertime overheating in care settings has been identified as a key risk and research priority for the health and social care system. This paper examines the current and future risk of summertime overheating in two London-based care homes occupying modern and older buildings. Continuous monitoring of outdoor and indoor temperature in bedrooms, communal areas and offices in summer 2019 helped to establish the prevalence and intensity of overheating. Dynamic thermal simulation (EnergyPlusV8.9) of the two care settings assessed the potential for avoiding active cooling in future climate using passive solutions. In both care settings, indoor temperatures were observed to exceed 30 °C during daytime hours, significantly higher than the recommended 26 °C threshold of Public Health England. Although severity of overheating was lower in the older building, overheating was found to be prevalent and prolonged across both care settings with bedroom temperatures higher than lounges especially at night. Thermal simulation analysis showed that, with regards to temperature reduction and cooling load, nighttime ventilation was the single most effective passive solution for both buildings for the current climate, while a combination of night ventilation, external shading and high-albedo external walls was the most effective package solution. By the 2080s, air-conditioning was the most effective solution for reducing temperature, but also had the highest cooling load, highlighting the importance of balancing passive with active measures to improve thermal comfort and reduce cooling loads.

Numerical simulation of a night cooling strategy in an office room

Night natural ventilation systems have been receiving increased attention in recent years because of their energy saving potential and environmental protection when used in passive instead of active cooling. A novel system recently proposed for cooling the building concrete slab is studied numerically in the present work. The system relies only on night ventilation as a means for cooling down the structure of the building. It consists of a new type of suspended ceiling with a peripheral gap between it and the walls combined with the positioning of the air supply and extraction grilles between the ceiling slab and the suspended ceiling. This study focuses on the use of Computational Fluid Dynamics (CFD) to predict the airflow and thermal performance of this strategy for an office room. Ansys-Fluent is used to perform the calculations both for a reduced and a full-scale room. Transient simulations were performed for a period of 24 h and the predictions for the reduced-scale model were validated by experiments under different operating conditions. The results show that the mathematical and numerical models provide satisfactory predictions of the temperature evolution in the reduced-scale model, allowing the analysis to be extended for full scale. The predictions for the office room at full scale confirm the effectiveness of the proposed cooling technique, revealing that the air peak temperature during the day is lower, as well as the temperature of the slab and the temperature of the air in the plenum during the night.

Potential measures towards the reduction of cooling loads of office buildings in Ghana

PurposeGiven the climatic context and economic challenge of Ghana in its developmental strides, energy use of office buildings continues to be a task on the economy. Therefore, the study was about finding measures that could reduce cooling loads in 10 office buildings. The paper presents the outcome of a long-term study of the thermal conditions in a selected number of office buildings in Accra and Kumasi, Ghana.Design/methodology/approachThrough long-term monitoring of environmental data, the buildings were consequently modelled in a simulation application. Thereafter, a validation of the simulation models (using regression coefficients, r2 of 0.53–0.90) was undertaken towards finding measures to reduce cooling loads.FindingsThe results showed various potentials of efficient lighting, thermal mass, night ventilation, insulation to attic floors, efficient glazing, blind deployments, etc. in reducing cooling loads in the range of 2–17.5%. By combining the potential measures to study their synergistic effects on the loads, 35, 39 and 38% improvements were achieved for the low-rise, multi-storey and fully glazed office buildings.Originality/valueThese potential measures ought to be incorporated in the design, specification, construction and operation of Ghanaian office buildings to reduce the burden on the economy and the environment. Now more than ever, there is the need for climatic regions to come up with empirical data that could help relieve the world's economies from the post-pandemic stress.

Simulation and optimization of night cooling with diffuse ceiling ventilation and mixing ventilation in a cold climate

Accurate convective heat transfer coefficient (CHTC) is crucial to assess the night ventilation performance accurately. Previous experimental studies proposed CHTC correlations tailored for night cooling with diffuse ceiling ventilation (DCV) and mixing ventilation (MV). A holistic approach integrating the building energy simulation and optimization method was put forward to validate the experimentally proposed correlations, simulate and optimize the performance of night cooling with DCV and MV. The validation results demonstrated that the proposed correlations predicted the surface temperatures accurately with a maximum mean absolute error of 1.9 °C. For a typical air-conditioned office room, night cooling with DCV saved about 0.2 kWh/m2 total cooling energy per unit floor area (TCEC) more and provided a lower average predicted percentage of dissatisfied during the working hours (aPPD) by up to 3.1% than that with MV. Compared with the validated correlations, the empirical ceiling diffuser convection algorithm overestimated the night energy-saving potential by up to 0.5 kWh/m2 (13.8%) and yielded a maximum difference in the aPPD of 1.5%. Optimization significantly saved TCEC by 1.1 kWh/m2 (29.0%) for DCV and 0.9 kWh/m2 (25.7%) for MV while maintaining the aPPD within 10%, compared to respective base cases.

Effect of thermal mass, night ventilation and window shading on summer thermal comfort of buildings in a temperate climate

Night ventilation and external blinds are the most commonly used passive methods to protect buildings from overheating during high summer temperatures. Another recommended measure is high thermal inertia of buildings. The aim of the study was to compare the effectiveness of night ventilation, external blinds and thermal mass during a heat wave on the thermal performance of a building during a heat wave in a temperate climate. Increasing the thermal mass of the room from light to very heavy without night ventilation resulted in a reduction of the average peak temperature by 3.7 K in a day and 1.2 K by night. The activation of night ventilation in a light room resulted in a reduction of the average value of the peak temperature by 1.5 K during the day and 5.9 K at night. Increase of thermal mass from light to heavy and night ventilation from 0.6 to 10 ACH led to decrease of average peak temperature by 4.7 K in a day and 4.6 K by night. The simultaneous increase of thermal mass, activation of night ventilation and closing of external blinds resulted in lowering the average peak temperature by 7.4 K in a day and 6.3 K by night. The analysis of the test results indicates that the high thermal mass and the closing of the external blinds reduces the diurnal variations of the indoor temperature, while the activation of nighventilation increases it significantly, especially for lightweight construction.

The Effect of the Thermal Mass of the Building Envelope on Summer Overheating of Dwellings in a Temperate Climate

The main objective of this paper is to demonstrate the effectiveness of increasing the thermal capacity of a residential building by using traditional building materials to reduce the risk of its excessive overheating during intense heat waves in a temperate climate. An additional objective is to show that the use of this single passive measure significantly reduces the risk of overheating in daytime rooms, but also, though to a much lesser extent, in bedrooms. Increasing the thermal mass of the room from light to a medium heavy reduced the average maximum daily temperature by 2.2K during the first heat wave and by 2.6K during the other two heat waves. The use of very heavy construction further reduced the average maximum temperature for the heat waves analyzed by 1.4K, 1.2K and 1.7K, respectively, giving a total possible reduction in maximum daily temperatures in the range of 3.6 °C, 3.8 °C and 4.3 °C. A discussion of the influence of occupant behavior on the use of night ventilation and external blinds was carried out, finding a significant effect on the effectiveness of the use of both methods. The results of the study suggest that in temperate European countries, preserving residential construction methods with heavy envelopes and partitions could significantly reduce the risk of overheating in residential buildings over the next few decades, without the need for night ventilation or external blinds, whose effectiveness is highly dependent on individual occupant behavior.

Simulation of Night Cooling Through Natural cross Ventilation using ANSYS (Fluent)

In this study, we carried out a numerical simulation using CFD code “Fluent 14.0” to quantify night ventilation due to convective and radiative phenomena with well-defined boundary conditions. The configuration is an open square cavity. Top & bottom walls are adiabatic, however, vertical walls represent the left/interior wall and right/external wall provided with a top and a bottom opening, at Tcold & Thot temperatures, respectively. The computational domain is two-dimensional with open boundary conditions of the local Bernoulli type. The fluid is incompressible with Boussinesq's approximation and flow regime is stationary turbulent with k-e RNG model on a 200 * 240 mesh refined near the walls, (ΔT = 10 °C). The obtained results allowed flow dynamics & thermal characterization as well as cooling integral quantities calculation. Introduction of surface emissivity influences heat transfer via active walls and increases (decreases) the lower (upper) passive wall temperature, while no effect was noted on the dynamics.

Long-term functionality of a passive phase-change materials building application after more than a decade of operation

For over two decades, latent heat storage (PCM) systems in building applications have been regarded as a promising technology for preventing overheating in the warm season without increasing cooling energy demand. This study aimed to investigate whether PCM can have a noticeable influence on thermal comfort even after up to 14 years of operation, which has not yet been investigated. For this, we collected PCM material samples in some buildings, which we then examined in the DSC laboratory, and analysed a real building application in southern Germany in detail by collecting measurement data and creating building simulations. The DSC measurements revealed a decrease in performance by 12–26%. However, the simulation results did not show a clear decrease in the performance of the PCM. Instead, they indicated that the paraffin-based PCM still had a positive effect on thermal comfort, reducing room temperatures by a maximum of 1.06 K and in average by 0.34 K during working hours. The PCM also reduced cooling degree hours by 15% during the hot months of July and August. An analysis of the user behaviour showed that there might be potential for improving thermal performance, especially through better use of blinds, windows and night ventilation.