Experimental study on the in-situ performance of a natural ventilation system with heat recovery (original) (raw)
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Energy and Buildings, 2018
This paper presents the ventilation performance of a Passive Ventilation System with Heat Recovery (PVHR) based on in-situ monitoring in a primary school in London. The study involves long-term (15month) monitoring of temperature, relative humidity and Carbon dioxide (CO 2) concentrations in both the classrooms and the outdoor environment. In addition, short term (1&2 week) observational monitoring was performed in two classrooms at ventilation system level and classroom level, during both the heating and non-heating seasons. Temperatures and air velocities were measured within the PVHR system while instances of window opening and the number of students were noted in daily diaries. Air permeability and infiltration measurements were performed to characterise the spaces. Time-varying ventilation rates were estimated through a form of continuity equation considering CO 2 generation rates by occupants. Preliminary results show that the operation of the ventilation system is more sensitive to changes in wind speed and direction than to buoyancy. When negative pressure was observed on the classrooms" facades the ventilation system was supplying two to three times more air in comparison to instances when positive pressures were observed. The assessment of the ventilation performance of such natural ventilation systems depending solely on wind and buoyancy is complicated as they are dynamic systems that constantly balancing with the surrounding conditions, and the operation is highly correlated to the airtightness of the building"s envelope.
Energies
Under-ventilation and high energy consumption are some of the problems associated with school classrooms. Thus, it is necessary to develop a ventilation strategy that is characterized by high energy-saving and ventilation efficiency. To this end, this study aims to investigate natural ventilation as a possible strategy to improve the indoor environment while reducing ventilation loads and maintaining energy costs during intermediate seasons. Ventilation and cooling load reductions based on the opening and closing of several windows were analyzed. Window flow coefficients and ventilation rates were measured and used for computational fluid dynamics (CFD) simulation to obtain pressure coefficients for 16 wind directions. The results obtained showed that the improved natural ventilation strategy could be used to effectively establish required indoor conditions (26 °C, 60% RH). Additionally, compared with the mechanical ventilation system with variable refrigerant flow, this natural str...
Indoor climate of classrooms with alternative ventilation systems
The paper presents the results of the investigations into the indoor climate in classrooms with different ventilation systems. Carbon dioxide is one of the best indicators of air quality in buildings. Therefore the current study is mostly concentrated on the investigation into CO2 levels in classrooms. There is a certain correlation between the air change rate and the changes of carbon dioxide concentration in rooms. The results of the study show the measured values of the CO2 level and indoor air quality in classrooms with different ventilation systems. A new solution of mechanical ventilation is the arrangement of air change in classrooms with mini air handling units (AHU) with heat recovery. The new arrangement might become as revolutionary technology when considering retrofitting smaller schools.
2007
SUMMARY Within the UK, the importance of providing adequate ventilation in schools has been recognised in a recently adopted document (Building Bulletin 101), which defines the set of performance criteria in relation to ventilation rates and indoor air quality in new school buildings. This paper describes a series of field measurements that investigated the ventilation rates and indoor air quality in three new secondary schools in England with respect to these new criteria. The study also analysed the overall performance of the integrated heating and ventilation systems with regards to comfort. All the schools satisfied the recommended ventilation performance standards during the week that the measurements were undertaken. However, this apparently reassuring message can be misleading unless one takes into account both the original design assumptions and then the actual occupancy of the classrooms and occupant behaviour in general. With regards to comfort, for many rooms the schools ...
Energy Efficiency, Thermal Comfort, and Quality of Natural Ventilation Strategies for Classrooms
IntechOpen eBooks, 2023
Classrooms are long-term environments, in which thermal comfort is essential for a good teaching and learning process. This research presents 16 natural ventilation strategies for classrooms related to energy efficiency, thermal comfort, and the quality of natural ventilation, for regions with a humid subtropical climate, represented by the Brazilian city of Santa Maria. Computer simulations were carried out with the Ansys CFX and EnergyPlus software, in addition to thermal comfort criteria recommended by the adaptive model of ASHRAE 55/2017, where the hours spent in thermal comfort, degree-hours of discomfort, indoor air velocity, air renewal rates, and air humidity were analyzed. The results indicate the most favorable natural ventilation strategies for classrooms located in a developing country in a humid subtropical climate, showing that these can contribute to the improvement of the quality of natural ventilation compared to the conventional constructive solutions used with simple strategies.
Ventilation rates and thermal comfort assessment in a naturally ventilated classroom
2016
Ventilation systems are meant (i) to guarantee good indoor air quality (IAQ) by providing and distributing fresh air to the occupied/breathing zone and (ii) to dilute and remove pollutants emitted by indoor sources. On the other hand, inadequate ventilation rates can induce discomfort issues and excessive energy consumption. This study focuses on the performance assessment of natural ventilation strategies in university classrooms, which are characterized by a high occupancy level and the necessity to provide high levels of comfort to perform intellectual work. The high occupancy level creates challenging conditions both in terms of internal gains and CO2 concentration. This paper presents an experimental performance assessment of four natural ventilation strategies applied to a university classroom: single side ventilation, cross ventilation, stack ventilation with and without window supply. Each strategy is evaluated in terms of thermal comfort and air change rate measurements. Th...
Energy Efficiency, 2016
Indoor environmental conditions in classrooms, in particular temperature and indoor air quality, influence students' health, attitude and performance. In recent years several studies regarding indoor environmental quality of classrooms were published and natural ventilation proved to have great potential, particularly in southern European climate. This research aimed to evaluate indoor environmental conditions in 8 schools and to assess their improvement potential by simple natural ventilation strategies. Temperature, relative humidity and carbon dioxide concentration were measured in 32 classrooms. Ventilation performance of the classrooms was deeply characterized, first by fan pressurization measurements of the air permeability and later by tracer gas measurements of the air change rate assuming different envelope conditions. A total of 110 tracer gas measurements were made and the results validated ventilation protocols that were tested afterward. The results of the ventilation protocol implementation were encouraging and, overall, a decrease on the CO2 concentration was observed without modifying the comfort conditions.
Energy and Buildings, 2005
Many educational buildings in industrialised countries have poor indoor climate, according to today's knowledge about the impact of indoor climate on well-being and productivity. Budget restrictions and practical limitations such as lack of space for central air handling units and ventilation ducts, have motivated the application of simplified ventilation systems in some schools, such as taking unconditioned supply air directly from the facade. One such school was recently evaluated in Norway. On cold days, thermal comfort in the classroom deteriorated due to cold downdraught from the supply outlet. In addition, moist and fertile conditions for microbiological growth were observed in the air supply ductwork. On the other hand the same pupils are more satisfied with the school and have less sick building syndrome (SBS) symptoms during winter than summer. An improved control strategy with a temperature-compensated CO 2 set-point for controlling the airflow is suggested. This could improve thermal comfort and reduce energy use without compromising perceived air quality (PAQ) during cold weather. Furthermore it could improve indoor air quality (IAQ) during warm weather with only a slight increase of energy use. Further evaluation of an improved solution is needed before such a ventilation concept can be recommended in cold climates.
E3S Web of Conference, 2019
Indoor air quality (IAQ) inside educational institutions is an important topic in the field of building and health research. School absenteeism and educational performance have been linked to poor air quality inside classrooms. A numerical simulation software has been used to test 5 different scenarios of natural ventilation during summer and winter. CO2 levels, air relative humidity, operative temperature and PMV were used as indoor air quality and thermal comfort indicators. Results have shown high CO2 and humidity levels when all windows are closed, and a variable improvement when different natural ventilations strategies are employed. A detailed procedure for the numerical simulation has been presented.
Energy and Buildings, 2008
Air flow and the associated indoor carbon dioxide concentrations have been extensively monitored in 62 classrooms of 27 naturally ventilated schools in Athens, Greece. The specific ventilation patterns as well as the associated carbon dioxide concentrations, before, during and after the teaching period are analysed in detail. During the teaching period, only 23% of the measured classrooms presented a flow rate higher than the recommended value of 8 l/p/s while the mean daily fluctuation was close to 40%. About, 52% of the classrooms presented a mean indoor CO2 concentration higher than 1000 ppm. The specific experimental data have been compared against existing ventilation rates and carbon dioxide concentrations using published information from 287 classrooms of 182 naturally ventilated schools and 900 classrooms from 220 mechanically ventilated schools. The relation between the air flow rates and the corresponding indoor carbon dioxide is analysed and then compared to the existing data from naturally and mechanically ventilated schools. It is found that all three data sets present a CO2 concentration equal to 1000 ppm for air flows around 8 l/p/s. Specific adaptive actions to improve the indoor environmental quality have been recorded and the impact of indoor and ambient temperatures as well as of the carbon dioxide concentration on window opening is analysed in detail. A clear relation is found, between the indoor temperature at which the adapting action takes place and the resulting air flow rate. In parallel, a statistically significant relation between window opening and the indoor–outdoor temperature difference has been established.