Decentralized Ventilation Systems Research Articles

Theoretical studies of the expedient radius of thin pipe insulation

Decentralized ventilation systems with exhaust heat recovery are an energy-efficient solution for organizing and maintaining comfortable microclimate parameters in apartments and individual residential buildings. Such supply and exhaust systems do not require additional space for the distribution network of air ducts and significant intervention in the interior of the premises. One such device is the Vents TwinFresh regenerative installation. Twin Fresh install in the structure of the outer wall. The task of follow-up is to increase the efficiency of its work. Studies of heat exchange processes in the thin channels of the heat regenerator carried out. Channels with different thermophysical properties are studied. Experimental uncertainty decreases with better thermal insulation of the investigational stand. It is confirmed by the decrease in overheating and the heat transfer coefficient of the external surface thermal insulation when its thickness increases. Overcoming the critical diameter of the insulation of the experimental installation allows to minimize the measurement error, which takes into account the influence of heat exchange processes of the outer surface of the insulation with the environment. It is necessary to determine not the critical but the expedient diameter of the insulation. When using the appropriate thickness of thermal insulation, the temperatures on the inner and outer surfaces of the pipe have practically the same value. Thus, it is possible to take temperature readings of thin tubes from the outside, not from the inside, with the same accuracy. Accordingly, the design of the test stands for experimental research is simplified. The scope of application of the appropriate diameter of thermal insulation is not limited only to studies of heat transfer. This concept can used in any systems, equipment, and techniques that require insulating materials.

Heat recovery optimization of a shell and tube bundle heat exchanger with continuous helical baffles for air ventilation systems

We report a numerical evaluation of the impact of continuous helical baffle on the heat recovery efficiency of counterflow tube bundle heat exchangers. The baffle inclination angle has been varied from 11∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$11^{\\circ }$$\\end{document} to 22∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$22^{\\circ }$$\\end{document}. Since the fluid flows over the tube bundle at an angle due to helical flow inside the shell, the heat exchanger operates in cross counter mode. Fluent simulations with the k-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} transition shear stress transport turbulence model have been performed to investigate the thermal-hydraulic parameters of the system in terms of heat recovery efficiency, pressure loss, and overall heat transfer rate. Outside air temperature has been varied to mimic cold and warm weather. Pressure loss has been constrained to be less than 250 Pa, conforming to EU guidelines for energy labeling of residential ventilation units. At the maximum volume flow rate of 40 m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}/h, the device performed with over 80%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$80\\%$$\\end{document} heat recovery efficiency for the considered temperature difference. Continuous helical baffles helped to improve convective heat transfer by reducing cross flow area and increasing velocity. Smaller angles result in greater pressure loss while having no discernible effect on heat recovery efficiency for the considered geometry. The analysis demonstrates the potential of a compact counterflowing recuperative heat exchanger with continuous helical baffles for decentralized ventilation systems and serves as a basis for further optimization.

Numerical analysis, design and application of a decentralized ventilation system with a heat recovery unit adapting to Nordic climates: A case study in Norway

This research investigated the energy efficiency of decentralized ventilation (DV) systems in cold weather conditions in comparison to centralized ventilation (CV) systems, focusing on three locations in Norway. The study found that DV systems with higher heat recovery unit (HRU) efficiency consumed less thermal and fan energy due to shorter air distribution pathways, utilizing a hybrid natural ventilation strategy in mild climates, and simpler space zoning for ventilation. This study proposes to determine a suitable ventilation system for adapting to cold climate. These methodologies are presented in three major parts: 1) ventilation energy demands of DV and CV systems in Norway, 2) performance of the heat recovery unit in the DV system, and 3) numerical analysis of the total ventilation energy demand of the DV system in cold climates using occupant ratio and existing measured data.The results showed specific time periods when it is ideal to use a fan-assisted NV system in cold climates, and in local conditions, 4–20% per year could benefit from a fan-assisted NV system using DV technology. A DV system with 0.7 HRU efficiency can save up to 14.5% of total HVAC energy compared to a CV system. The HRU heating efficiency played a crucial role in thermal ventilation energy demands in cold weather, while the cooling efficiency had no significant effect on energy demands. However, if a hydronic heating and cooling coil is added to the DV system, it consumes more than 9.08% of energy than using a pump. The energy-saving performance of the DV system decreases significantly if its HRU efficiency is below 50%, and there is no real advantage of using the DV system over the CV system in such cases. Nonetheless, the DV system can be utilized in various working conditions to conserve energy, such as different occupancy ratios, individual room space zoning, and indoor air pollution rates.

Study of the Impact of Indoor Environmental Quality in Romanian Schools through an Extensive Experimental Campaign

Decentralized ventilation systems in schools are becoming more important due to the focus on indoor air quality and energy economy. The research aims to explore how these technologies affect classroom air quality, thermal comfort, and noise. The study examined four decentralized ventilation systems in a real-world school using field measurements and data analysis. This included measuring the CO2, temperature, noise, and thermal comfort using the Predicted Mean Vote (PMV) index. All systems greatly improved the air quality, keeping CO2 levels within suggested limits. They failed to control indoor humidity, often lowering it to below optimal levels. Noise surpassed the 35 dB(A) criteria at maximum operation but was acceptable at lower airflows. Noise and air drafts did not bother residents. The study found that decentralized ventilation systems improve air quality and are easy to adapt to, although they need humidity control and noise management at higher operational levels.

Optimization of a ventilation system integrated into a window frame using CFD simulations

A decentralized ventilation system has the potential to decrease the pressure drop in a ventilation system and consequently, increase the efficiency of the system and building skin. Including a decentralized ventilation system in a window cavity allows independent regulation of the fresh air quality in each room and can be easily installed without any additional brickwork. In this study, a novel ventilation system integrated into a window-frame is examined and the most critical region regarding pressure drop is identified using computational fluid dynamic (CFD) simulations. The entire fresh air channel including the optimized section is compared with the original volume regarding system resistance and satisfaction of the required airflow according to Swiss standards. The results suggest a relocation of the restricting control unit and an increased cross-section to decrease the air velocity and the pressure drop. The simulations predicted that the required airflow for sufficient indoor air quality is exceeded using the optimized geometry.

Recent Advancements in Ventilation Systems Used to Decrease Energy Consumption in Buildings—Literature Review

The need for healthy indoor conditions, the energy crisis, and environmental concerns make building ventilation systems very important today. The elements of ventilation systems to reduce energy intensity are constantly the subject of much scientific research. The most recent articles published in the last three years are analyzed in this paper. Publications focused on the topic of reducing energy consumption in ventilation systems were selected and divided into five key research areas: (1) the aspect of the airtightness of buildings and its importance for the energy consumption, (2) the methods and effects of implementing the concept of demand-controlled ventilation in buildings with different functions, (3) the possibilities of the technical application of decentralized ventilation systems, (4) the use of earth-to-air heat exchangers, (5) the efficiency of exchangers in exhaust air heat-recovery systems. The multitude of innovative technologies and rapid technological advances are reflected in articles that appear constantly and prompt a constant updating of knowledge. This review constitutes a relevant contribution to recognizing current advancements in ventilation systems and may be helpful to many scientists in the field.

Parametric optimization of multifunctional integrated climate-responsive opaque and ventilated façades using CFD simulations

The design and application of dynamic façades have gained attention in recent years as new high-performance building façade alternatives. In this study, the optimization of a novel opaque dynamic façade, the MICRO-V (Multifunctional Integrated Climate-responsive Opaque and Ventilated) façade, is investigated. This façade is comprised of different components to regulate the flow of heat, air, and moisture into buildings dynamically with daily and seasonal responses using an integrated ventilation module, phase change materials (PCM), and an adjustable insulation system. This façade acts as a decentralized ventilation system, in which the fresh air is pre-conditioned using the thermal energy storage provided by the PCMs, and the heat recovery inside the ventilation module. The aim of this paper is to optimize the conceptual façade design using parametric simulations by quantifying the performance of the MICRO-V facade. Multiple parameters, among which the geometry, the material properties, and the airspeed were tested. CFD simulations were performed in both the heating and the cooling seasons in a continental climate (Toronto, Canada). The pre-conditioning efficiency of fresh air in the façade was 73% in the summer week and 65% in the winter week. Including the PCMs to condition the air resulted in an average increase of air temperature in the winter by 3 °C, through solar gain storage, and helped to reduce the extreme temperature by 5 °C on extremely hot summer periods. The study showed the thermal resistance in the façade could be increased and decreased as a function of airflow in the façade, which is a potential way to control the overall heat gain and heat loss through the façade annually. The façade-scale simulations showed the necessity of this type of analysis prior to whole-building simulations to accurately represent the façade’s performance.

Comparative Numerical Energy Analysis of Decentralized Ventilation Adapting to Local Norway Climates

The present work evaluates the performance of different decentralized ventilation control strategies in the local Norway climate. Evaluation is performed using a monthly time-step energy analysis and the IDA-ICE simulation tool for a comparative primary energy analysis on the strategy combinations. Primary energy comparison is conducted with respect to a centralized constant air volume system for comparative analysis. The evaluation results show that the representative decentralized ventilation (DV) system has the most significant energy performance. The lower heat recovery efficiency significantly impacts on the ventilation energy of DV system in the cold climate, and the low specific fan power can efficiently be used for zone cooling in summer.

Design and implementation of an occupant-centered self-learning controller for decentralized residential ventilation systems

Mechanical ventilation systems acquired relevance in the past decades as a solution to guarantee air exchange in residential energy retrofit. The individualization of the control strategies to the user preferences could enhance the acceptance of innovative technologies and meet the energy efficiency targets for buildings. In this publication, a novel occupant-centered self-learning control strategy for decentralized ventilation systems is introduced. The controller has a standard-based default control profile, which learns the occupants’ preferences using a classification algorithm. The proposed controller is first simulated and compared to other available mechanical ventilation control strategies. A stochastic model for the manual operation of ventilation systems based on artificial comfort profiles is implemented in the simulation model. Results show that the proposed controller improves the indoor environmental conditions (measured with the relative humidity and CO2 concentration) without disregarding energy efficiency. The self-learning controller can successfully adapt itself to these profiles. The proposed solution was implemented in a real apartment. Measurements were carried out for three months, where two occupants operated the ventilation devices. The installed ventilation concept succeeded in maintaining an acceptable indoor environment, while the distinctive user profiles were learned in each room. The bedrooms were shifted towards lower air exchange rates, while in the rest of the rooms higher air exchange rates were preferred. This implementation confirms the individualization potential of this controller. Finally, the novel self-learning strategy provides an adaptive solution for residential decentralized ventilation controllers, targeting the occupant preferences regarding comfort, health and energy efficiency.

Radon protection in apartments using a ventilation system wireless-controlled by radon activity concentration

The new German Radiation Protection Act (StrlSchG) of 31 December 2018 established a reference value of 300 Bq m−3 for the annual average radon activity concentration in buildings with recreation and living rooms, as well as in workplaces. It is expected that the reference value will be exceeded in a vast number of buildings throughout Germany and that radon protection measures will become indispensable. A simple and inexpensive radon protection measure for existing buildings is ventilation. In the scope of a joint project, ventilation systems with zone control and heat recovery are to be extended by the control parameter radon activity concentration. A highly sensitive, miniaturized radon monitor will be developed for this purpose, which can be integrated wirelessly into ventilation systems. Radon measurements were carried out in 13 apartments of an unoccupied heated apartment block in Germany over a period of three weeks in the wintertime. High radon activity concentrations were found on all three floors. The maximum values were 14000 Bq m−3 on the first floor, 6000 Bq m−3 on the second floor, and 2000 Bq m−3 on the third floor. Ventilation experiments were carried out in an apartment with high radon activity concentration. Two decentralized ventilation systems with heat recovery were installed in each of the two opposite outside walls. The controlling device of the system was activated wirelessly depending on the radon activity concentration. The radon activity concentration was reduced from 8000 Bq m−3 to 800 Bq m−3 in a first experiment in the living room.

Comparative Modelling Analysis of Air Pollutants, PM2.5 and Energy Efficiency Using Three Ventilation Strategies in a High-Rise Building: A Case Study in Suzhou, China

This study investigated the ventilation efficiency and energy performance of three ventilation strategies—an all-air system (AAS), a radiant panel system with a displacement ventilation system (DPS), and a radiant panel system with a decentralized ventilation system (DVS). The research analyzed the indoor air quality (IAQ) in a high-rise building based on the building’s height, the air handling unit (AHU) location, air infiltration rate, outdoor air pollution rate, seasonal change, and air filter efficiency. The results indicated that the AAS had the best performance in terms of IAQ in the high-rise building in winter; however, the AAS also had the highest annual energy demand. For the same conditions, the DVS consumed less energy but had the worst performance in maintaining a satisfactory IAQ. Considering energy consumption, it is worth developing the DVS further to improve ventilation performance. By applying a double-filter system on the lower floors in a high-rise building, the DVS’s ventilation performance was dramatically improved while at the same time consuming less energy than the original DPS and AAS. The application of DVS can also minimize the negative effect of the infiltration rate on indoor air quality (IAQ) in a building, which means that the DVS can better maintain IAQ within a healthy range for a more extended period. Moreover, it was found that the DVS still had a substantial potential for saving energy during the season when the outdoor air was relatively clean. Hence, it is highly recommended that the DVS is used in high-rise buildings.

Experimental investigation of a decentralized heat recovery ventilation system

Indoor air quality is an important issue for improving and maintaining the indoor environment because it is directly related to people's health and work performance. These days, in many settlements, the applicability of natural ventilation is limited in the face of the decreasing infiltration loads, increased atmospheric pollution, and the climatic conditions. Therefore, the use of mechanical systems that are designed to ensure proper ventilation is becoming widespread. This paper presents full-scale experimental research of a wall-integrated decentralized ventilation system with heat recovery in the laboratory conditions. The heat recovery unit includes a ceramic block for sensible thermal energy storage. Parametric experimental studies were carried out to obtain the temperature distributions and the thermal capacity of the ceramic block during the supply and exhaust modes of working. In order to simulate the winter and summer conditions, two large scale temperature-controlled rooms are built up. The duration of the ventilation period is varied to be 1, 2, 5, 7.5 and 10-min. Experimental measurements indicate that 2 min of operation time shows the best thermal performance in terms of maintaining a comfortable indoor temperature with the least energy consumption. And some shortcomings were observed about the fan and thermal storage limitations.

Simulation and Measurement of Energetic Performance in Decentralized Regenerative Ventilation Systems

Decentralized regenerative mechanical ventilation systems have acquired relevance in recent years for the retrofit of residential buildings. While manufacturers report heat recovery efficiencies over 90%, research has shown that the efficiencies often vary between 60% and 80%. In order to better understand this mismatch, a test facility is designed and constructed for the experimental characterization and validation of regenerative heat exchanger simulation models. A ceramic honeycomb heat exchanger, typical for decentralized regenerative ventilation devices, is measured in this test facility. The experimental data are used to validate two modeling approaches: a one-dimensional model in Modelica and a computational fluid dynamics (CFD) model built in COMSOL Multiphysics®. The results show an overall acceptable thermal performance of both models, the 1D model having a much lower simulation time and, thus, being suitable for integration in building performance simulations. A test case is designed, where the importance of an appropriate thermal and hydraulic modeling of decentralized ventilation systems is investigated. Therefore, the device is integrated into a multizone building simulation case. The results show that including component-based heat recovery and fan modeling leads to 30% higher heat losses due to ventilation and 10% more fan energy consumption than when assuming constant air exchange rates with ideal heat recovery. These findings contribute to a better understanding of the behavior of a growing technology such as decentralized ventilation and confirm the need for further research on these systems.

Energy consumption decreasing strategy for indoor swimming pools – Decentralized Ventilation system with a heat pump

Energy consumption decreasing strategy for indoor swimming pools – Decentralized Ventilation system with a heat pump

STRATEGIES FOR THE ENERGY RETROFITTING OF SOCIAL HOUSING THROUGHOUT EUROPE

Nobel energy retrofitting strategies for social housing buildings are presented in this paper, which attempt to reduce their energy demand and enable a low carbon footprint consumption. Both passive and active approaches are applied to a building archetype under 7 representative climates and constructive properties in Europe. On the one hand, simulation results show that passive renovation of buildings through high efficiency envelopes and decentralized ventilation systems would lead to savings from the 69% to the 87% of the required heating demand. Additionally, the cooling demand is reduced up to 32%, although it increases slightly in cold climates due to the addition of insulation. On the other hand, the active trigeneration system includes parabolic trough solar collectors, ORC based cogeneration, adsorption chiller, and a biomass boiler as backup, which reaches a maximum efficiency of 59% in the best scenario. Results show that, a join exploitation of proposed strategies, would mean primary energy savings up to 38% in the worst case, and 61% in the best one. Regarding CO2 emissions, up to 85% reductions are achieved in the seven considered European climates. Finally, analyzing the costs, it is shown that even in the worst case, the energy bills would be reduced in 62%. These results reveal that, the strategies proposed in this paper, depict a feasible way to achieve nZEB while, at the same time, tackling the energy poverty problem that residents in social housing suffer along Europe.

Post-occupancy evaluation of residential buildings in Luxembourg with centralized and decentralized ventilation systems, focusing on indoor air quality (IAQ). Assessment by questionnaires and physical measurements

Complete knowledge about habits of the occupants, including their opinions regarding ventilation systems is an important condition for reducing the consumption of natural resources and improving indoor comfort. In addition, uncomforted occupants tend to take measures to improve their situation, which may increase energy consumption. Advanced thermal models for buildings can perhaps predict interactions between the IAQ determinants, e.g. energy consumption, ventilation and comfort, but do not take into account the behavior of residents. By questionnaires and physical measurements this study evaluated dwellings equipped partly with centralized and partly with decentralized ventilation systems with heat recovery. This field study involved two post-occupied residential buildings situated in the city of Esch-sur-Alzette, Luxembourg, during spring season 2015. Thus, both the physical measurements and questionnaires were considered. The results obtained demonstrated that more than 80% of the residents were satisfied and the perceived IAQ was judged “normal”, “good” or even “very good”. Furthermore, the measurements performed detected in some cases malfunction of ventilation devices, wherefore the occupants were unable.

Thermal comfort and indoor air quality in super-insulated housing with natural and decentralized ventilation systems in the south of the UK

ABSTRACTImproved energy performance standards are resulting in better insulated and more airtight building. In such buildings, ventilation can be provided by natural means alone or in conjunction with extract mechanical ventilation or with whole-house mechanical ventilation with or without heat recovery. This paper reports on a study funded by the NHBC Foundation of the indoor environment of eight super-insulated homes with natural and decentralized ventilation systems in the south of the UK. The aim was to examine the effectiveness of such ventilation options. The buildings were monitored for one year in relation to temperature, relative humidity, CO2, CO, NO2, CH2O and TVOC. The building occupants’ feedback and IES building modelling triangulated the site data. The study showed that natural and decentralized ventilation systems provided good air quality in the case-study buildings and allowed users to create comfortable thermally differentiate environments in response to their preferences.

Performance Evaluation of Hybrid Radiant Cooling System Integrated with Decentralized Ventilation System in Hot and Humid Climates

Air-conditioning systems account for nearly one-third of the energy consumption in tropical buildings. In summer, mechanical cooling systems become a must especially in office buildings to keep the indoor environment comfort. In this study, a normal office room is designed to evaluate a novel cooling system based on a hot and humid climate. This novel cooling system is considered to serve such climate, which integrates radiant cooling panel, decentralized ventilation, and an Airbox convector. The Airbox convector is designed to deal with condensation risk and provide additional cooling output. In order to evaluate this novel system, it is compared with conventional all-air system and normal radiant system with decentralized ventilation regarding to the system capacity, energy consumption and thermal comfort. Results show that this novel system is adaptable to such climates and capable to reduce the condensation risk and overall cooling energy consumption.

Experimental Investigation of a Friction Ventilator

Standard decentralized ventilation systems typically consist of two ventilators for inlet and exhaust air and a heat exchanger for the heat recovery. A recently developed device, a so called friction ventilator, combines these three elements into a single functional element. The ventilator consists of circular plates which are rotating centrally in between the inlet and the outlet duct of a ventilation system and generate a countercurrent flow in the two ducts. Furthermore, the discs act as a rotating heat exchanger between the two air flows. To increase understanding of the energy transfer from the rotating discs to the flow an experimental investigation on the effect of different rotor geometries was conducted. The study showed an interesting influence of the hub diameter on the characteristic curves with a higher pressure difference for an increase in diameter. The results of the heat recovery measurement however were only mildly affected by the hub geometry. Here the distance between the discs, the rotational speed of the discs and the volumetric flow seemed to have the greatest effect on heat recovery.

Energy analysis of a decentralized ventilation system compared with centralized ventilation systems in European climates: Based on review of analyses

In this study, the decentralized ventilation (DV) performance of a small air ventilator to replace natural ventilation for use in urban areas is analyzed and compared to conventional centralized ventilation (CV) systems in European climates. Selected European weather conditions were used to determine acceptable conditions for the operation of fan-assisted ventilation systems and to analyze the decentralized ventilation system's cooling and heating loads. Entire fan and pump loads of DV system are numerically calculated based on published data. Compared with a conventional centralized ventilation system, this system has shorter air transport distances and therefore entails lower pressure losses. In a decentralized system, fan speed and airflow rate are adjusted simply and effectively depending on indoor thermal conditions. A radiant panel with decentralized ventilation system (RPDV) is shown to have the lowest heating, ventilation, and air conditioning (HVAC) energy consumption because it not only minimizes supply and exhaust air pressure losses, but can also be operated as a fan-assisted natural ventilation system during periods when outdoor air can be used without additional thermal loads. Based on numerically calculated and measured data, this study newly adds fan and pump energy analysis of decentralized ventilation system compared to centralized ventilation systems. This study shows the fan and pump energy consumption with analysis of fan-assisted DV system considering outdoor weather condition in European climate.