Abstract: The importance of neural network (NN) modelling is evident from its performance benefits in a myriad of applications, where, unlike conventional techniques, NN modeling provides superior performance without relying on complex filtering and/or time-consuming parameter tuning specific to applications and their wider ranges of conditions. In this paper, we employ NN modelling with training data generation based on sensitivity analysis for the prediction of building energy consumption to improve performance and reliability. Unlike our previous work, where insignificant input variables are successively screened out based on their mean impact values (MIVs) during the training process, we use the receiver operating characteristic (ROC) plot to generate reliable data with a conservative or progressive point of view, which overcomes the issue of data insufficiency of the MIV method: By properly setting boundaries for input variables based on the ROC plot and their statistics, instead of completely screening them out as in the MIV-based method, we can generate new training data that maximize true positive and false negative numbers from the partial data set. Then a NN model is constructed and trained with the generated training data using Levenberg–Marquardt back propagation (LM-BP) to perform electricity prediction for commercial buildings. The performance of the proposed data generation methods is compared with that of the MIV method through experiments, whose results show that data generation using successive and cross pattern provides satisfactory performance, following energy consumption trends with good phase. Among the two options in data generation, i.e., successive and two data combination, the successive option shows lower root mean square error (RMSE) than the combination one by around 400~900 kWh (i.e., 30%~75%).
Permalink: https://doi.org/10.3390/pr7100731

Abstract: Energy efficiency and end-to-end delay are two of the major requirements for the monitoring and detection applications based on resource-constrained wireless sensor networks (WSNs). As new advanced technologies for accurate monitoring and detection—such as device-free wireless sensing schemes for human activity and gesture recognition—have been developed, time synchronization accuracy becomes an important requirement for those WSN applications too. Message bundling is considered one of the effective methods to reduce the energy consumption for message transmissions in WSNs, but bundling more messages increases the transmission interval of bundled messages and thereby their end-to-end delays; the end-to-end delays need to be maintained within a certain value for time-sensitive applications like factory monitoring and disaster prevention, while the message transmission interval affects time synchronization accuracy when the bundling includes synchronization messages as well. Taking as an example a novel WSN time synchronization scheme recently proposed for energy efficiency, we investigate an optimal approach for message bundling to reduce the number of message transmissions while maintaining the user-defined requirements on end-to-end delay and time synchronization accuracy. Formulating the optimal message bundling problem as integer linear programming, we compute a set of optimal bundling numbers for the sensor nodes to constrain their link-level delays, thereby achieving and maintaining the required end-to-end delay and synchronization accuracy. Extensive experimental results based on a real WSN testbed using TelosB sensor nodes demonstrate that the proposed optimal bundling could reduce the number of message transmissions about 70% while simultaneously maintaining the required end-to-end delay and time synchronization accuracy.
Permalink: https://doi.org/10.3390/s19184027

Abstract: Computational fluid dynamics (CFD) is an effective analysis method of personalized ventilation (PV) in indoor built environments. As an increasingly important supplement to experimental and theoretical methods, the quality of CFD simulations must be maintained through an adequately controlled numerical modeling process. CFD numerical data can explain PV performance in terms of inhaled air quality, occupants’ thermal comfort, and building energy savings. Therefore, this paper presents state-of-the-art CFD analyses of PV systems in indoor built environments. The results emphasize the importance of accurate thermal boundary conditions for computational thermal manikins (CTMs) to properly analyze the heat exchange between human body and the microenvironment, including both convective and radiative heat exchange. CFD modeling performance is examined in terms of effectiveness of computational grids, convergence criteria, and validation methods. Additionally, indices of PV performance are suggested as system-performance evaluation criteria. A specific utilization of realistic PV air supply diffuser configurations remains a challenging task for further study. Overall, the adaptable airflow characteristics of a PV air supply provide an opportunity to achieve better thermal comfort with lower energy use based on CFD numerical analyses.
Permalink: https://doi.org/10.3390/su11154166

Abstract: This paper studies the long-term performance of a Ground Source Heat Pump (GSHP) system and a Water Source Heat Pump (WSHP) system for an office building in Suzhou, which is a hot summer and cold winter climate region of China. The hot summer and cold winter region is the most urbanized region of China and has subtropical monsoon climate, therefore, Heating, Ventilation, and Air Conditioning (HVAC) systems are in great demand. Due to the fact that 42.5% of Suzhou’s total area is covered by lakes and rivers, the city has an abundance of surface water resources. Based on Suzhou’s meteorological data and the thermal characteristics of the building envelope, an office building model was created and the dynamic cooling and heating load was calculated using Transient System Simulation (TRNSYS) simulation software. Two numerical HVAC modeling systems were created: a GSHP system for which the data of an in-situ Thermal Response Test (TRT) was used and a WSHP system for which the Tai Lake water temperature was used. Simulating the performance of both systems over a 20-year period, the two systems were analyzed for their Coefficient of Performance (COP), heat source temperature variation, and energy consumption. The results show that the GSHP system causes ground heat accumulation, which reduces the system’s COP and increases energy consumption. The study also revealed that compared with the GSHP system, the WSHP system has a more stable long-term performance for buildings in Suzhou.
Permalink: https://doi.org/10.3390/su11123282

Abstract: Photovoltaic (PV) techniques are widely used in daily life. In addition to the material characteristics and environmental conditions, maximum power point tracking (MPPT) techniques are an efficient means to maximize the output power and improve the utilization of solar power. However, the conventional fixed step size perturbation and observation (P&O) algorithm results in perturbations and power loss around the maximum power point in steady-state operation. To reduce the power loss in steady-state operation and improve the response speed of MPPT, this study proposes a self-adaptable step size P&O-based MPPT algorithm with infinitesimal perturbations. This algorithm combines four techniques to upgrade the response speed and reduce the power loss: (1) system operation state determination, (2) perturbation direction decision, (3) adaptable step size, and 4) natural oscillation control. The simulation results validate the proposed algorithm and illustrate its performances in operational procedures.
Permalink: https://doi.org/10.3390/en12010092

Abstract: With growing urbanization, it has become necessary to manage this growth smartly. Specifically, increased electrical energy consumption has become a rapid urbanization trend in China. A building model based on a neural network was proposed to overcome the difficulties of analytical modelling. However, increased amounts of data, repetitive computation, and training time become a limitation of this approach. A simplified model can be used instead of the full order model if the performance is acceptable. In order to select effective data, Mean Impact Value (MIV) has been applied to select meaningful data. To verify this neural network method, we used real electricity consumption data of a shopping mall in China as a case study. In this paper, a Bayesian Regularization Neural Network (BRNN) is utilized to avoid overfitting due to the small amount of data. With the simplified data set, the building model showed reasonable performance. The mean of Root Mean Square Error achieved is around 10% with respect to the actual consumption and the standard deviation is low, which reflects the model’s reliability. We also compare the results with our previous approach using the Levenberg–Marquardt back propagation (LM-BP) method. The main difference is the output reliability of the two methods. LM-BP shows higher error than BRNN due to overfitting. BRNN shows reliable prediction results when the simplified neural network model is applied.
Permalink: https://doi.org/10.3390/en12071201

Abstract: This study presents that increases in atmospheric CO₂ levels impact the ventilation and energy in buildings. The most significant impact of ventilation occurs during use, because of the indoor air quality. According to the 2014 IPCC report, observed atmospheric CO₂ levels increased at a rate of 1.9–2.1 ppm per year. This study measured CO₂ levels in a building in an urban area in Shanghai, China, and analyzed existing ventilation performance and energy simulation in relation to the impact of increased atmospheric CO₂ concentrations. As long as the atmospheric CO₂ level increased, the outdoor airflow rate had to increase also to maintain an acceptable indoor CO₂ level. The ventilation rate was also considered in relation to the surrounding environment. In Shanghai, the average value of CO₂ concentrations on an auto road was 550 ± 20 ppm and the average value on a pedestrian road was 435 ± 15 ppm. A building that was surrounded by high traffic roads needed 20–30% more outdoor airflow rate than a building surrounded by pedestrian roads. Accordingly, energy loads in buildings, for heating and cooling were also affected. In order to dilute indoor CO₂ level, the thermal ventilation energy and the ventilation energy uniformly provided a 20% energy load increase during the 12 months, while each monthly energy load varied, depending on the season and/or month. By analyzing indoor CO₂ levels and the rise in atmospheric CO₂ levels, this study determined how these rises impacted the energy consumption of the building, and how to design a new outdoor airflow supply rate to adapt to a changed environmental condition.
Permalink: https://doi.org/10.1016/j.atmosenv.2019.04.015

Abstract: Requirements for measuring the building airtightness have been proposed and included by many countries for national regulations or energy-efficient programs to address the negative effect of poor airtightness on building energy performance, durability and indoor environment. The methods for measuring building airtightness have continuously improved and evolved over a number of years. At present, the well-established and widely accepted method for quantifying the building airtightness is the fan pressurisation method (blower door being the most wellknown), which can be implemented by pressurising the test building to a range of high pressures (usually in steps across 10–60 Pa range) and measuring the corresponding fan flow rate. As an alternative method, the Pulse technique can be utilised to measure building airtightness at low pressures (typically at 4Pa) by rapidly releasing a 1.5-second pulse of air from a pressurised vessel. It is known that the outdoor weather condition and in particular wind velocity can significantly influence building airtightness measurement. For example, ISO 9972 suggests a meteorological wind speed limit of 6m/s and 3m/s at ground level for the fan pressurisation test. However, limited studies have been conducted to evaluate the performance of the Pulse technique under windy conditions. In this study, a series of tests were carried out to measure the building airtightness of a five-bedroom house located at the University of Nottingham, UK using the Pulse technique under various wind conditions. A Pulse unit with a 58.5- litre air tank was employed to measure the building airtightness while an ultrasonic anemometer, located 12 metres away from the building perimeter, was used to obtain the outdoor wind speed at the height of 2.2 metres above ground level. Tests were conducted in March 2019 in a range of wind speed up to 10m/s. Experimental results demonstrate the viability of the Pulse technique for delivering airtightness measurements under certain wind conditions, although analysis has also identified conditions where the test result becomes invalid. This study provides insight into those conditions, which adversely affect the result produced by the Pulse technique and discusses possible areas of improvement to the measurement and calculation process to mitigate such effects. Based on the 423 Pulse tests undertaken, it is recommended that the Pulse tests should be performed when the wind speed is lower than 5m/s (with relative percentage difference of ±10%) in calm conditions and 7.4m/s (with relative percentage difference of ±20%) in windy conditions at the height of 2.2 metres above ground level to minimise the wind impact. If tests are to be carried out when the wind speed is above this limit, multiple Pulse tests should be carried out in order to reduce the wind impact on building airtightness measurement.

Abstract: Building airtightness tests have become very common in several countries, either to comply with minimum requirements of regulations or programs, or to justify input values in calculation methods. This raises increasing concerns for the reliability of those tests. Despite the extensive debates about how the building pressurization test standard ISO 9972 should address sources of uncertainties, no change has been implemented. According to the current standard, the zero-flow pressure shall not exceed 5 Pa for the test to be valid. Consequently, in moderately windy conditions, it may be impossible to perform a pressurization test in accordance with the standard, even using precautions with a careful uncertainty analysis. This study investigates numerically, with the use of a commercial CFD code, the impact of unsteady wind on fan pressurization tests. Two test houses, built in cross-laminatedtimber (CLT), are modelled and used as case study. Various leakage location, fan placement and wind profiles are used as input in a set of Scenarios.

Abstract: The Energy Performance Certificate (EPC) allows building users to be informed and aware of the quality of the buildings in terms of energy needs. Additionally, the EPC includes a future for existing buildings, which is the incorporation of a Recommendation list of Measures (RLMs) to improve their energy performance in a cost-effective way. Which have risen the question if this tool can provide trustful Cost-effective recommendations due despite the uses of standardized inputs. This study focuses on estimating the impact of using measure ventilation rate, heating set point and airtightness on the profitability of the recommendations. The study is based on common dwelling in Norway, comparing results obtained with a Building Performance Simulation Software, following the Norwegian standard for energy certification and with the uses of measured ventilation rate, airtightness and real heating set points. The results show that the performance gap can be reduced significantly just by adopting these inputs, increasing the confidence on the RLMs and reducing the uncertainty of the investment.
Permalink: https://doi.org/10.1088/1757-899X/609/3/032053

Abstract: The aim of this study is to investigate whether children’s bioeffluent generation rate is proportional to their carbon dioxide (CO₂) generation rate. Consequently, to assess if there is a need to differentiate the CO₂-setpoint for different user groups, focusing on children. Perceived air quality (PAQ) and odour intensity (OI) were assessed in three classrooms in Oslo, Norway. Two second-grade classes (7-8 years old) were compared with one eighth-grade class (13-14 years old). An untrained test panel consisting of 16 people visited each classroom twice and were asked to evaluate PAQ and OI upon entering the classrooms. The CO₂ levels in the classrooms were kept constant at either 600 ppm or 1100 ppm during each visitation. The results showed that average PAQ-score was significantly worse in the second-grade classrooms compared to the eighth-grade classroom. For perceived odour intensity, the average score indicated that the odour was stronger in the second-grade classrooms compared to the eighth-grade classroom, however, this difference in score was not significant. Our results indicate a need for differentiation of setpoints for CO₂-DCV based on user groups, especially for children.
Permalink: https://doi.org/10.1088/1757-899X/609/4/042062

Abstract: The aim of this paper is to assess whether reducing the minimum ventilation airflow rate (Vmin) has any negative impacts on perceived air quality (PAQ) upon entering an unoccupied room. Seventeen healthy young adults were asked to assess PAQ in 18 unoccupied classrooms upon entry. Extra pollution sources were introduced in two classrooms, while three other classrooms were not cleaned. The ventilation rate in each classroom was set in a random order to off, low (0.9/1.1 l/s per m2), medium (1.3 l/s per m2) and high (2.0 l/s per m2). Increasing the ventilation rate resulted in a significant improvement of the PAQ-score, with highest PAQ-score when Vmin is set to high and lowest when the ventilation is off. However, most of this increase occurred when increasing ventilation to the low rate. Classrooms that were not cleaned for two days of normal use prior to the test only showed a marked reduced PAQ at all ventilation rates.
Permalink: https://doi.org/10.1088/1757-899X/609/4/042038

Abstract: Retrofitting of existing buildings offers significant opportunities to reduce global energy use and greenhouse gas emissions. Therefore, it is considered as one of the main approaches to achieve sustainability in the built environment at a relatively low cost. Although there is a wide range of retrofitting technologies available, methods to identify the most costeffective measures for each project remain a major technical challenge. Numerous projects have been developed worldwide to face this challenge with different approaches; however, many of the tools meet only local objectives, which is why they are unknown in the international arena, showing a limited transfer of knowledge. This review organizes the results under three categories: renovation assessment, financial assessment, and transfer of knowledge. The tools focusing on promoting the renovation of buildings differ in the type of user, for example, the owners, politicians, or investors. The tools dealing with financial assessment suggest different methods to evaluate and calculate the cost savings, construction costs, and return forecasts through retrofit interventions. Other tools comply with the policies that seek to register, evaluate, and characterize the existing buildings. This review provides researchers, construction professionals, and politicians with a better understanding of the advances made to effectively design building retrofitting measures and promote energy conservation as well as the assessment of the building stock for the development of policies. The review shows that many tools have the potential of joining their capabilities, which can create many opportunities for innovation in the retrofitting area.
Permalink: https://doi.org/10.1088/1755-1315/294/1/012035

Abstract: Low-temperature space heating systems play a prominent role in improving the indoor air quality (IAQ) and thermal comfort of energy efficient buildings in cold-climate countries such as Norway. All-air heating (AAH) systems can be a practical solution because they simplify the space heating system and use low temperature energy sources. However, temperature stratification and deficient air distribution in the occupied part of the room can reduce the AAH performance. This study evaluated the performance of a low-temperature AAH system in an office cubicle designed in accordance with the Norwegian passive house (PH) standard and equipped with an active supply diffuser. Unlike conventional supply diffuser, active supply diffusers have variable slot opening permitting draught-free airflow adjustment with moving plates changing position, so that a constant supply air velocity was achieved. System performance simulations were validated by experimental data and then analysed for various supply and outdoor conditions using thermal comfort indices, IAQ indices, and the Archimedes number (Ar). The results showed that, when negatively buoyant air was supplied, the maximum indoor temperature difference between 0.1 m and 1.1 m above the floor was around 1.5K, which is within the recommended comfort range. Furthermore, the air diffusion performance index (ADPI) analysis showed a relatively high diffusion of air in the occupancy zone for all the scenarios, with the minimum ADPI around 75% for the scenarios with a negative Archimedes number. The active supply diffuser could satisfy the thermal comfort requirement even when the system was operating with the minimum airflow rate.
Permalink: https://doi.org/10.1016/j.buildenv.2019.04.017

Abstract: This work reports analysis of complex shock wave diffraction and longtime behavior of shock-vortex dynamics over splitter geometry encountered in both external and internal compressible flows. The simulation resolved the experimental findings of literature, and the insight of the flow topology is being presented with the probability density functions (PDFs) of various contributing terms of enstrophy transport equation and the invariants of the velocity gradient tensor. We use an artificial viscosity (AV)-based explicit discontinuous spectral element method (DSEM)-based compressible flow solver for this purpose. The numerical scheme utilizes entropy generation-based artificial viscosity and thermal conductivity to simulate the conservative form of the governing compressible flow equations. A shock sensor-based switch is used to reduce the addition of AV coefficients in rotation-dominated regions.
Permalink: https://doi.org/10.1007/978-3-319-91020-8_146

Abstract: Shock-wave propagation through obstacles or internal ducts involves complex shock dynamics, shock-wave shear layer interactions and shock-wave boundary layer interactions arising from the associated diffraction phenomenon. This work addresses the applicability and effectiveness of the high-order numerical scheme for such complex viscous compressible flows. An explicit Discontinuous Spectral Element Method (DSEM) equipped with entropy-generation-based artificial viscosity method was used to solve compressible Navier–Stokes system of equations for this purpose. The shock-dynamics and viscous interactions associated with a planar moving shock-wave through a double-bend duct were resolved by two-dimensional numerical simulations. The shock-wave diffraction patterns, the large-scale structures of the shock-wave-turbulence interactions, agree very well with previous experimental findings. For shock-wave Mach number Ms=1.3466 and reference Reynolds number Re_f=10^6, the predicted pressure signal at the exit section of the duct is in accordance with the literature. The attenuation in terms of overpressure for Ms=1.53 is found to be ≈0.51. Furthermore, the effect of reference Reynolds number is studied to address the importance of viscous interactions. The shock-shear layer and shock-boundary layer dynamics strongly depend on the Re_f while the principal shock-wave patterns are generally independent of Re_f
Permalink: https://doi.org/10.3390/e21090837

Abstract: The turbulent structures and long-time flow dynamics of shock diffraction over 90° convex corner associated with an incident shock Mach number Ms = 1.5 are investigated by large eddy simulation (LES). The average evolution of the core of the primary vortex is in agreement with the previous two dimensional studies. The Type-N wall shock structure is found to be in excellent agreement with the previous experimental data. The turbulent structures are well resolved and resemble those observed in the experimental findings. Subgrid scale dissipation and subgrid scale activity parameter are quantified to demonstrate the effectiveness of the LES. An analysis based on turbulent-nonturbulent interface reveals that locally incompressible regions exhibit the universal teardrop shape of the joint probability density function of the second and third invariants of the velocity gradient tensor. Stable focus stretching (SFS) structures dominate throughout the evolution in these regions. Stable node/saddle/saddle structures are found to be predominant at the early stage in locally compressed regions, and the flow structures evolve to more SFS structures at later stages. On the other hand, the locally expanded regions show a mostly unstable nature. From the turbulent kinetic energy, we found that the pressure dilatation remains important at the early stage, while turbulent diffusion becomes important at the later stage. Furthermore, the analysis of the resolved vorticity transport equation reveals that the stretching of vorticity due to compressibility and stretching of vorticity due to velocity gradients plays an important role compared to diffusion of vorticity due to viscosity as well as the baroclinic term.
Permalink: https://doi.org/10.1063/1.5113976

Abstract: Energy efficiency in buildings is nowadays considered as an essential step to reduce CO₂ emissions and energy utilization. At the same time, new technologies such as building space heating using active air heating has simplified the heating system without any need for backup heating system. This study investigated the thermal stratification of mixing ventilation system equipped with a radial active supply diffuser for space heating of an office room designed according to the Norwegian passive house standard by using Star-CCM+. Simulations were performed for different supply airflow rates with corresponding slot openings of the active diffuser at different outdoor conditions for winter season. The combined effect of the supply airflow rate and the outdoor air temperature were also described in the form of Archimedes number (Ar). The results showed that adopting active diffuser could avoid the temperature stratification for all the simulated cases by preserving the throw length of supply jet. In addition, the lowest temperature effectiveness of 38% occurred when a high supply temperature was used in the coldest day. Furthermore, with the supply temperature 24 °C, the airflow rate 49.4 l/s at the outdoor temperature -15 °C would result in a favorable average of PMV ⁓ 0.497.
Permalink: https://doi.org/10.1051/e3sconf/201911104033

Abstract: It has been nowadays recognized that addressing energy use in buildings can reduce the fossil fuels usage and CO₂ emission. Trombe wall is a widely applicable passive solar design option that can significantly reduce the fossil fuel consumption in buildings. This paper experimentally dealt with the effect of applying vertical thermal fin on the absorber of Trombe wall with new design. Three types of aluminum, brass and copper fins were investigated. The experiments were carried out at arid climate of Yazd, Iran. The results showed that when the thermal fin is used the performance efficiency of the Trombe wall increases up to 3% in terms of stored energy within the Trombe wall and 6% in terms of natural convection heat transfer rate inside the channel. However, adopting more thermal fins on the absorber could not ensure higher heating efficiency in terms of stored energy for all cases. Furthermore, copper fin led to maximum heating efficiency and highest average room temperature among three fin types.
Permalink: https://doi.org/10.1016/j.est.2019.100796

Abstract: This study reports a Post Occupancy Evaluation performed on a social housing complex consisting of 400 apartments, in which symptoms and damage produced by high moisture levels needed investigation. The resulting knowledge is of special interest for other projects designed to be mass-produced such as social housing. Large costs for repairs can be reduced by applying measures to avoid moisture problems in indoor environments. The evaluation was performed over three stages, indicative, investigative and diagnostic. The process was mapped and the data stored using BIM standards so it can be used by stakeholders to take further actions. In the indicative stage, data was collected through questionnaires and surveys, and a quick evaluation was conducted of the affected units. In the investigative stage, an analysis of the entire building complex was conducted through simulation and tested against the building energy standards. In the diagnostic stage, in-situ and laboratory measurements were made and used for calculations. The results show that many factors were involved in the moisture damage, whose main causes were overcrowded spaces, inadequate thermal regulation for the local climate, poor apartment and complex design, and flaws and inconsistencies in the quality of construction.
Permalink: https://doi.org/10.1016/j.buildenv.2019.05.019

Abstract: Low-temperature space heating systems play a prominent role in improving the indoor air quality (IAQ) and thermal comfort of energy efficient buildings in cold-climate countries such as Norway. All-air heating (AAH) systems can be a practical solution because they simplify the space heating system and use low temperature energy sources. However, temperature stratification and deficient air distribution in the occupied part of the room can reduce the AAH performance. This study evaluated the performance of a low-temperature AAH system in an office cubicle designed in accordance with the Norwegian passive house (PH) standard and equipped with an active supply diffuser. Unlike conventional supply diffuser, active supply diffusers have variable slot opening permitting draught-free airflow adjustment with moving plates changing position, so that a constant supply air velocity was achieved. System performance simulations were validated by experimental data and then analysed for various supply and outdoor conditions using thermal comfort indices, IAQ indices, and the Archimedes number (Ar). The results showed that, when negatively buoyant air was supplied, the maximum indoor temperature difference between 0.1 m and 1.1 m above the floor was around 1.5K, which is within the recommended comfort range. Furthermore, the air diffusion performance index (ADPI) analysis showed a relatively high diffusion of air in the occupancy zone for all the scenarios, with the minimum ADPI around 75% for the scenarios with a negative Archimedes number. The active supply diffuser could satisfy the thermal comfort requirement even when the system was operating with the minimum airflow rate.
Permalink: https://doi.org/10.1016/j.buildenv.2019.04.017

Abstract: This paper is dedicated to numerically appraise the passive cooling performance of the new designed and normal Trombe walls combined with solar chimney and water spraying system (WSS) in a test room under Yazd (Iran) desert climate. The new designed Trombe wall expands the indoor space and decreases the implementation cost of the Trombe wall. Furthermore, it can receive the solar intensity from three directions while the normal Trombe wall can only receive it from one direction. The numerical simulation of the new designed Trombe wall was validated by the previous experimental study. The present numerical results indicate that in the morning the average room temperature in the new designed Trombe wall is lower than the normal type since the new designed Trombe wall generates higher natural air ventilation compared with the normal type. But, in the late hour of the day due to the more expansive area of normal Trombe wall and its higher capability to store the solar thermal energy, the average room temperature decreases to a greater extent in the normal type. Moreover, the cooling efficiency analysis demonstrates that the daily average cooling efficiency of the new designed Trombe wall surpasses the normal type by around 8.63%.
Permalink: https://doi.org/10.1016/j.seta.2019.03.005

Abstract: This study was conducted to assess how different filter types in the ventilation system affect the indoor NO₂ concentrations. Measurements were carried out in two classrooms and air intakes in a primary school located in Oslo, Norway. A regular F7 particle filter and an F7 combination filter with activated charcoal lining were compared. NO₂ concentrations were measured for five weeks during winter 2017 in a cross-over study design to compare: (1) NO₂-levels in classrooms with regular filter (RF) versus combination filter (CF); (2) indoor/outdoor ratio with regular filter versus combination filter. One-hour average concentrations are reported during operating time of the ventilation system (6:00–23:00) and during hours with high (>40 µg/m3) outdoor NO₂ concentrations. The measured average NO₂ concentrations in both classrooms with an RF were significantly higher than with a CF. The median CF/RF ratios for the two classrooms were 0.50 and 0.81 during hours with high NO₂ concentrations, and 0.48 and 1.00 during the period the ventilation system was operational. During hours with high NO₂ concentrations, the median indoor/outdoor ratios for the two classrooms with an RF were above 1.00, while the corresponding ratios with a CF were 0.78 and 0.75. Our results demonstrate that a combination filter is more efficient than a regular filter in reducing NO₂ concentrations in classrooms during hours with high outdoor concentrations.
Permalink: https://doi.org/10.1007/978-3-030-00662-4_77

Abstract: The aim of our study is to investigate whether it is necessary to adjust the ventilation requirements according to different user groups. This study is focusing especially on teenagers, who might have a higher odour load than children due to increased hormone and sweat production during puberty. The odour intensity (OI) and the perceived air quality (PAQ) were evaluated in four classrooms in Oslo, Norway. Two control classrooms of 9–11 years olds (children) were compared with two case classrooms of 12–15 years olds (teenagers). A sensory panel of 18 untrained people visited the four classrooms three times during a three-hour period and were asked to evaluate PAQ and OI upon entering the classrooms. The classrooms were supplied with a constant ventilation rate of 7 l/s per person, with no additional ventilation for building materials. We found that the classroom with children had a significant better PAQ-score than both classrooms with teenagers. Furthermore, although the ventilation rate per person was reduced, the percentage of panellists dissatisfied with OI and PAQ was lower (<20%) than expected. Our results indicate that children and teenagers have different sensory pollution loads, and therefore might need differentiated ventilation rates if the ventilation rates were to be optimised. However, more research is needed.
Permalink: https://doi.org/10.1007/978-3-030-00662-4_73

Abstract: Demand-Controlled Ventilation is emerging as a dominant ventilation strategy in non-residential buildings in Norway. The ventilation airflow rate is controlled between pre-set minimum (Vmin) and maximum (Vmax) values, based on the signal from room-sensors. The choice of Vmax is based on current knowledge about necessary airflow rate to reach an acceptable IAQ (indoor air quality) with maximum likely personal load and emission load from building materials. The choice of Vmin has an obvious impact on energy use, but there are few studies about its impact on IAQ. Vmin varies typically from 0.7 to above 2 (l/s)/m2 in Norway. In several buildings, Vmin is set to the upper range of this interval due to technical limitations of the specific equipment used. We have performed blind cross over intervention-studies with an untrained test panel to evaluate PAQ (perceived air quality) when entering 20 PAQ-rooms. All the rooms have low-emitting building materials, but extra pollution sources were introduced in some of the rooms for this study. Supplementary, intervention studies were performed in a dedicated test room to assess the impact of airflow rate on PAQ, performance and well-being during the first 20 min of occupation. We found that increasing Vmin has a significant positive impact on PAQ in rooms with extra pollution sources. This effect was not consistently present in the low-emitting rooms. Airflow rates did not noticeably affect PAQ, performance and well-being during the first 20 min of occupation. This indicates that Vmin above 1 (l/s)/m2 has limited benefit to IAQ in low emitting rooms.
Permalink: https://doi.org/10.1007/978-3-030-00662-4_29

Abstract: To assess how people are influenced by relative humidity (RH) in cold climates, a study was conducted in an open office landscape in Oslo, Norway. The study took place during three cold days in February 2017. Fourteen subjects were blindly exposed to different levels of RH in the order of low (14 ± 1%), high (38 ± 3%), and medium (24 ± 4%). The subjects received emails twice a day (at 12:00 and at 14:30) with a link to a webpage where they were asked to: (1) assess perceived air quality (PAQ), (2) respond to a questionnaire about indoor environment quality and symptoms. The subjects performed normal office activity in between the two sessions. We found no significant impact of the level of RH on PAQ. Nevertheless, there were significantly more complaints about dry air at low RH than at medium and high RH. Furthermore, the air was perceived to be significantly more stuffy and heavier at high RH than at medium RH. There were no significant differences in thermal comfort at different RH, yet more people complained that it was cold on the day with low RH and warm on the day with high RH. Generally, there were few complaints related to symptoms at different RH. There were however significantly more complaints of itching and burning in the eyes at low RH than at medium and high RH.
Permalink: https://doi.org/10.1007/978-3-030-00662-4_76

Abstract: Few field studies have evaluated ventilation strategies, such as temporarily increasing the ventilation rate, to counter the high pollutant-load from off-gassing of volatile compounds from new materials in these buildings. We reviewed longitudinal studies that measured both ventilation rate (i.e. fresh air change rate) and airborne concentration of total volatile organic compounds (TVOC). Rates of emission of TVOC follow a multi-exponential decay trend over time after completion of a building. A tri-exponential trend-was fitted by quantile regression. Although the ventilation rate is key to controlling airborne concentrations, it does not noticeably influence TVOC emission rates. Specifying low-emitting materials, or bake-out before occupancy, both have a significant impact on emission rates . The results can be used to assess and size energy-efficient practical ventilation strategies (such as demand-controlled ventilation) to keep the concentration of TVOCs within acceptable levels during hours of occupancy after completion of a new or renovated building.
Permalink: https://doi.org/10.1080/14733315.2018.1435026