Outdoor Air Supply Research Articles

Concept and ventilation performance demonstration of graded ventilation

Advanced air distribution is essential for the energy-efficient provision of thermal comfort and indoor air quality. This study proposes a novel advanced air distribution, i.e., graded ventilation. The airflow pattern of graded ventilation is characterized by a bimodal distribution of vertical air velocity and a unimodal distribution of vertical air temperature. Graded ventilation possesses four mechanisms for high energy-efficient provision of thermal comfort and indoor air quality. First, graded ventilation has a high conditioned air supply efficiency into the occupied zone, particularly the head level, for both thermal comfort and indoor air quality, due to the push-down and pull-down forces of the internal airflow recycling. Second, graded ventilation decouples outdoor fresh air and return air, with high outdoor fresh air supply efficiency for indoor air quality. Third, graded ventilation utilizes higher-quality conditioned air for the zone, which is more critical to thermal comfort and indoor air quality. Fourth, graded ventilation only handles the cooling load of the outdoor fresh air without handling the cooling load of the return air. Case studies demonstrate that compared with mixing ventilation, Type-I stratum ventilation, Type-II stratum ventilation, and interactive cascade ventilation, graded ventilation improves energy efficiency by 49.7%–55.4%, 24.8%–29.1%, 16.3%–23.3%, and 8.4%–12.3% respectively for thermal comfort and indoor air quality. Therefore, this study advances air distribution for low-carbon, thermally comfortable, and healthy buildings.

Exposure assessment during paint spraying and drying using PTR-ToF-MS.

Spraying is a common way to distribute occupational products, but it puts worker's health at risk by exposing them to potentially harmful particles and gases. The objective of this study is to use time-resolved measurements to gain an understanding of spray applications at the process level and to compare them to predictions of exposure models. We used proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) at 1-s time resolution to monitor the gas phase concentration of the solvents acetone, ethanol, butyl acetate, xylene and 1-methoxy-2-propy acetate during outdoor spraying and indoor drying of metal plate under various conditions of outdoor air supply. We found that during spraying, gas-phase exposure was dominated by the more volatile solvents acetone and ethanol, which exhibited strong concentration variations due to the outdoor winds. During drying, exposure strongly depended on the strength of ventilation. Under conditions with high supply of outdoor air, our measurements show a near-exponential decay of the solvent concentrations during drying. Conversely, under conditions without outdoor air supply, the drying process required hours, during which the less volatile solvents passed through a concentration maximum in the gas phase, so that the exposure during drying exceeded the exposure during spraying. The concentrations measured during spraying were then compared for each of the substances individually with the predictions of the exposure models ECETOC TRA, Stoffenmanager, and ART using TREXMO. For these conditions, ECETOC TRA and Stoffenmanager predicted exposures in the measured concentration range, albeit not conservative for all solvents and each application. In contrast, ART largely overestimated the exposure for the more volatile solvents acetone and ethanol and slightly underestimated exposure to 1M2PA for one spraying. ECETOC TRA and ART do not have options to predict exposure during drying. Stoffenmanager has the option to predict drying together with spraying, but not to predict the drying phase independently. Our study demonstrates the importance of considering both the spray cloud and solvent evaporation during the drying process. To improve workplace safety, there is a critical need for enhanced exposure models and comprehensive datasets for calibration and validation covering a broader range of exposure situations.

A new data mining strategy for performance evaluation of a shared energy recovery system integrated with data centres and district heating networks

This study presents a new data mining strategy to discover the performance and operational patterns of a shared energy recovery (SER) system with a data centre and a district heating network. Multidimensional clustering incorporated with a composite performance metric was first used to evaluate the typical performance of the system and reveal the interactions among different performance indicators. Decision tree analysis was then used to identify distinct system performances under different external conditions. Temporal clustering analysis was lastly used to identify the impact of recovered waste heat on the variations in heat supply from the district heating substation. The strategy was evaluated through a case study SER system at a university campus located in Norway. It was found that the most frequent performance accounted for 34 % of the total operational period with the instantaneous waste heat recovery rate of 572.9 kW, the temperature of waste heat of 57.2 °C, and the coefficient of performance of the heat pumps of 2.0. The outdoor air temperature and supply water temperature from the main district heating substation to the campus buildings showed a significant impact on the SER system performance. Moreover, the results showed that the SER system can help reduce the energy use of the district heating networks while increasing the fluctuations of heat supply from the main district heating substation.

Outdoor thermal condition based-segmented intermittent demand-controlled ventilation for constant-air-volume system

The outdoor air supply is mandatory for healthy built environments but consumes a large amount of building energy. The demand-controlled ventilation method adjusts the outdoor air supply for both indoor air quality and high energy efficiency. However, the conventional demand-controlled ventilation method does not apply to the constant-air-volume ventilation system. Since the constant-air-volume ventilation system is widely used in practice for outdoor air supply, this study proposes a novel demand-controlled ventilation method, i.e., the segmented intermittent demand-controlled ventilation, to improve the energy efficiency of the constant-air-volume ventilation system with indoor air quality. The proposed method intermittently supplies outdoor air to reduce the amount of outdoor air supply for energy saving of ventilation fan while satisfying indoor air quality. Moreover, the proposed method divides the working time into segments and adjusts the outdoor air supply of each segment according to the outdoor weather for cooling/heating energy saving. This study reveals the detailed mechanisms of energy saving of the proposed method and develops an optimization algorithm to maximize the energy saving of the proposed method with indoor air quality. The proposed method is tested for both cooling and heating scenarios in different climate zones. The results show that compared with the conventional methods and the existing intermittent demand-controlled ventilation, the proposed method achieves weekly energy savings of 18.0%–62.4% and 4.3%–6.8% respectively. The proposed method can contribute to the development of low-carbon and healthy built environments.

Unlocking ventilation flexibility of large airport terminals through an optimal CO2-based demand-controlled ventilation strategy

Large airport terminals consume significant energy due to their extensive ventilation demands. Optimizing the operation of ventilation systems is a crucial aspect of achieving greater energy flexibility and efficiency. In this study, we proposed an optimal CO2-based demand-controlled ventilation (DCV) strategy that utilizes the large indoor space of airport terminals to shift ventilation loads, reduce operating cost, and enable demand response (DR) programs. The effect of air infiltration on ventilation demand is considered in the DCV strategy through on-site CO2 measurement. A passenger dwell model is integrated to estimate the occupancy of airport terminal based on flight schedules for dynamic ventilation control. Considering the DR signal and time-of-use tariff, an advanced evolutionary algorithm is employed to locate optimal ventilation solutions that deliver better economic performance and energy flexibility while meeting indoor air quality constraints. Using an airport terminal in Beijing, China, as a testbed, the superior performance of the proposed DCV strategy was demonstrated against a baseline strategy with a fixed outdoor air supply rate under three scenarios. Simulation results showed that the proposed DCV strategy can reduce peak energy consumption by up to 60.9% and operating costs by up to 48.6% in different scenarios. Moreover, the DCV strategy can provide a flexible trade-off between the overall energy efficiency and DR capability in the adjustable DR scenario. This study revealed great opportunities for improving the flexibility of ventilation in large-space buildings and provided an instructive case study.

Characterization of size-differentiated airborne particulate matter collected from indoor environments of childcare facilities

Inhalation of particulate matter (PM) present in indoor atmospheres has been associated with poor health and wellbeing of occupants. Here we report the characteristics of airborne PM collected from twenty-two air-conditioned childcare centres in Singapore. Airborne PM were collected using cascade impactors and characterized for morphology, elemental composition, endotoxin levels, ability to generate abiotic reactive oxygen species, and oxidative stress-dependent cytotoxicity in BEAS-2B cell lines. The mass concentrations of ultrafine particles (PM0.06-1) were more abundant than that of larger particles (PM1-4, PM4-20, and PM20-35 particles). PM20-35 and PM4-20 were irregularly shaped particles, PM1-4 particles had membranous flaky structures and PM0.06-1 particles were pseudo-spherical with the occasional presence of crystalline structures. Carbonaceous matter dominated PM20-35 particles, and the abundance of inorganic salts, iron and sulfur increased with decreasing PM size. Measured endotoxin levels were especially higher in PM4-20 particles. Compared to other particle size fractions, PM0.06-1 particles generated the highest ROS and were also the most potent in generating intracellular ROS in BEAS-2B cell lines. However, total mass concentrations, elemental compositions, abiotic responses, and PM collected from centres with split air-conditioning systems and no active outdoor air supply (SAC) were not statistically different compared with PM collected from centres with air conditioning with mechanical ventilation (ACMV). In conclusion, our study showed obvious distinctions in mass concentrations, morphology, elemental compositions, and cytotoxic potential of different sized particles collected from childcare centres, where the smallest particles (PM0.06-1) exhibited higher hazard potential.

CO2 concentration as an indicator of indoor ventilation performance to control airborne transmission of SARS-CoV-2

BackgroundThe Wells-Riley equation has been extensively used to quantify the infection risk of airborne transmission indoors. This equation is difficult to apply to actual conditions because it requires measurement of the outdoor air supply rate, which vary with time and are difficult to quantify. The method of determining the fraction of inhaled air that has been exhaled previously by someone in a building using a CO2 concentration measurement can solve the limitations of the existing method. Using this method, the indoor CO2 concentration threshold can be determined to keep the risk of infection below certain conditions. MethodsBased on the calculation of the rebreathed fraction, an appropriate mean indoor CO2 concentration and required air exchange rate to control SARS-CoV-2 airborne transmission was calculated. The number of indoor occupants, ventilation rate, and the deposition and inactivation rates of the virus-laden aerosols were considered. The application of the proposed indoor CO2 concentration-based infection rate control was investigated through case studies in school classrooms and restaurants. ResultsIn a typical school classroom environment with 20–25 occupants and an exposure time of 6–8 h, the average indoor CO2 concentration should be kept below 700 ppm to control the risk of airborne infection indoors. The ASHRAE recommended ventilation rate is sufficient when wearing a mask in classrooms. For a typical restaurant with 50–100 occupants and an exposure time of 2–3 h, the average indoor CO2 concentration should be kept below about 900 ppm. Residence time in the restaurant had a significant effect on the acceptable CO2 concentration. ConclusionGiven the conditions of the occupancy environment, it is possible to determine an indoor CO2 concentration threshold, and keeping the CO2 concentration lower than a certain threshold could help reduce the risk of COVID-19 infection.

Система защиты воздушной среды участка сварочных работ с применением восстановительной вентиляции

The technology is considered related to the protection of the air environment of electric welding areas with the use of restorative ventilation and showering. With the help of it, polluted air is removed from the working area and the conditioned air is supplied instead for meeting the requirements of sanitary norms for the microclimate parameters of working premises and the content of harmful substances in them. The traditional technology of air purification from welding smoke has fundamental disadvantages, the main of which is the inability to clean the air from carbon monoxide and nitrogen dioxide impurities. To normalize the microclimate of working areas, the volumetric air conditioning is used, which requires enormous energy costs. At the same time, the distribution of supply air does not provide for the protection of the welder from intense thermal radiation. The system of harmful substances suction from the welding station limits the freedom of the welder action. Therefore, in some cases, he is forced to raise the suction funnel above his head, as a result of what the welding smoke enters the room. It is proposed to avoid the above shortcomings by improving the system of complex protection of the air environment, containing an exhaust panel, an apparatus for cleaning and heat-moisture treatment of air with its cooling and subsequent return to the welder working area. It is advisable to use an apparatus for wet air treatment made according to the type of a packed scrubber-absorber using water with active additives of permanganate and sodium bicarbonate dissolved in it, which contribute to the dissolution and retention of toxic gases of the welding smoke in water. To increase the efficiency of air purification in this apparatus, it is proposed to use a special irrigated nozzle made of porous plastic plates, in which artificial turbulence of the air flow is carried out, which ensures its intense heat and mass transfer and temperature reduction. The use of such a device allows to implement an energy-saving technology by reducing the performance of the supply units to the minimum required level of outdoor air supply.

Effect of Outdoor Temperature on Performance of All-air Wall Induction Unit in a Four-bed Hospital Ward

The prototype all-air wall induction unit (IU) has the characteristics of displacement ventilation (DV) and windless air supply, which is considered ideal for hospital ward usage. The outdoor temperature, however, will affect its ventilation and thermal performance. This study conducted a full-scale experiment. IUs are vertically installed in the four corners of the experiment room, which is furnished as a Japanese hospital ward. An outdoor climate simulation chamber (OCSC) is installed on one side of the room to simulate the external window and sill under different outdoor temperature conditions. CO2 is generated from the room’s one point, representing pollutants emitted by a patient. The room’s steady-state temperature and CO2 concentration distribution are analyzed under different outdoor temperatures (in OCSC) and air supply conditions. The IU maintained a comfortable thermal environment under all experimental conditions. In terms of ventilation performance, downward airflow undermines concentration stratification in midwinter. The DV stabilizes when the temperature difference between inside and outside air becomes less than 10 °C while using the double-pane window in winter. Conversely, upward airflow strengthens the DV in the summer. In addition, a sufficient supply rate is recommended to keep concentrations and temperatures above the patients’ breathing zone.

Association of indoor temperature and air quality in classrooms based on field and intervention measurements

To investigate the variation of classroom environment during typical lecture hours, repeated field measurements and intervention experiments for indoor temperature were carried out in a typical class (95 min in duration, 0.32–0.39 person/m2 of occupants density) in a spring semester of a university in Beijing. Environmental data were recorded every 5 min, including indoor temperature, relative humidity and carbon dioxide (CO2) concentration. Additionally, volatile organic compounds (VOCs) were sampled and indoor air quality (IAQ) were evaluated repeatedly. The results of field measurements showed the average air temperature in the classroom ranged from 21.2 ± 0.8 °C to 26.8 ± 0.7 °C, relative humidity ranged from 23.1 ± 1.8% to 57.5 ± 0.2%, and the average concentrations of CO2 and total volatile organic compounds (TVOC) were 1,291–1,833 ppmv and 159-1,178 ppbm respectively. The subjective evaluations collected during intervention experiments showed that perceived odor intensity by visitors upon entering the room increased significantly, meanwhile the satisfaction and acceptability of air quality reduced considerably at the indoor temperature of 27 °C than that at 24 °C. Present results suggest when the indoor temperature rises, it is necessary to increase the outdoor air supply rate to ensure air freshness in classrooms. Subsequently, the calculated CO2 emission rate by students increased by 0.54 L/h per person for every 1 °C rise in indoor temperature. Corresponding to the control target of indoor CO2 concentration of 1,000 ppmv, the outdoor air ventilation rate required to eliminate occupant-generated pollution needs to be increased by 0.25 L/s per person.

Integrated system of exhaust air heat pump and advanced air distribution for energy-efficient provision of outdoor air.

A large outdoor air supply is required to control the airborne infection risk of respiratory diseases (e.g., COVID 19) but causes a high energy penalty. This study proposes a novel integrated system of the exhaust air heat pump and advanced air distribution to energy-efficiently provide outdoor air. The system energy performances are evaluated by the experimentally validated thermodynamic model of heat pump and heat removal efficiency model of advanced air distribution. Results show the exhaust air heat pump with advanced air distribution can save energy because of three mechanisms. First, the exhaust air heat pump reuses the exhaust air to reduce the condensation temperature, thereby improving the coefficient of performance. Second, advanced air distribution reduces ventilation load. Third, advanced air distribution reduces the condensation temperature and enhances the evaporation temperature, thereby improving the coefficient of performance. The exhaust air heat pump saves energy by 18%, advanced air distribution saves energy by 36%, and the integrated system of the exhaust air heat pump and advanced air distribution can save energy by 45%. As a specific application, compared with the conventional system (i.e., the outdoor air heat pump with mixing ventilation), the exhaust air heat pump with stratum ventilation saves energy by 21% − 35% under various outdoor air ratios and outdoor air temperatures. The proposed integrated system of the exhaust air heat pump and advanced air distribution contributes to the development of low-carbon and healthy buildings.

Ten questions concerning the paradox of minimizing airborne transmission of infectious aerosols in densely occupied spaces via sustainable ventilation and other strategies in hot and humid climates

Airborne disease transmission in indoor spaces and resulting cross-contamination has been a topic of broad concern for years – especially recently with the outbreak of COVID-19. Global recommendations on this matter consist of increasing the outdoor air supply in the aim of diluting the indoor air. Nonetheless, a paradoxical relationship has risen between increasing amount of outdoor air and its impact on increased energy consumption – especially densely occupied spaces. The paradox is more critical in hot and humid climates, where large amounts of energy are required for the conditioning of the outdoor air. Therefore, many literature studies investigated new strategies for the mitigation of cross-contamination with little-to-no additional cost of energy. These strategies mainly consist of the dilution and/or the capture and removal of contaminants at the levels of macroenvironment room air and occupant-adjacent microenvironment. On the macroenvironment level, the dilution occurs by the supply of large amounts of outdoor air in a sustainable way using passive cooling systems, and the removal of contaminants happens via filtering. Similarly, the microenvironment of the occupant can be diluted using localized ventilation techniques, and contaminants can be captured and removed by direct exhaust near the source of contamination. Thus, this work answers ten questions that explore the most prevailing technologies from the above-mentioned fronts that are used to mitigate cross-contamination in densely occupied spaces located in hot and humid climates at minimal energy consumption. The paper establishes a basis for future work and insights for new research directives for macro and microenvironment approaches.

Solution of Bullet Proof Wooden Frame Construction Panel with a Built-In Air Duct

The growing terrorism threats across the world play an important role in the design of civil buildings and living areas. The safety of personnel is a top priority in unclassified buildings, especially military buildings. However indoor air quality and thermal comfort has a direct impact on personal productivity and ability to concentrate on duties and affect the decision making in stress conditions. The use of wooden structures is becoming more common in the building construction, and application of wooden frame structures for the construction of new buildings as well as for retrofitting the existing buildings. Prefabricated wooded frame construction perfectly fits need of unclassified buildings, allowing significant reduction of construction time and integration of various active and passive elements, such as a fresh air supply duct. Within the scope of this paper a 12 mm thick ballistic panel made of aramid was tested. Ballistic panel, thermal conductivity, and fire resistance of wooded construction panel with embedded air duct were analyzed for the various modelled exterior wall solutions. The main advantage of the proposed technology is fast and qualitative modular construction of unclassified buildings, providing all modern requirements not only for safety, but also for the energy efficiency and indoor air quality. It was found that bullet proof aramid panels do not reduce overall fire safety in comparison to traditional construction materials. However embedded outdoor air supply ducts significantly reduces construction heat transfer coefficient.

Ventilation status of the residential kitchens in severe cold region and improvement based on simulation: A case of Shenyang, China

ABSTRACT Residents tend to close the doors and windows of their residential kitchens in severe cold conditions, making insufficient outdoor air supply and aggravating indoor air pollution. In order to understand the ventilation and pollution status of the residential kitchens in a severe cold region and improve the ventilation system, this study used questionnaires, on-site tests, and Computational Fluid Dynamics (CFD) simulation to analyze a pollution and ventilation case in Shenyang, China. The method of using ceiling openings to compensate for outdoor air supply was proposed and optimized to improve air distribution in the residential kitchen. The average CO2 concentration in the breathing region, air velocity, and temperature levels in the kitchen, before and after the improvement, were compared. The results indicated that the kitchen pollution in severe cold area of Shenyang is serious, and the ventilation habit has regional characteristics. Furthermore, the overall kitchen environment including air velocity, temperature, pollutant levels, static pressure, CO2 concentration, indoor airflow fluctuation, and cooking fire were obviously improved for the ceiling make-up air cases. These findings provide a basis for improving the reasonable air distribution of residential kitchens in cold regions and for building a thermally comfortable environment. Implications: In order to understand the ventilation and pollution status of the residential kitchens in a severe cold region and improve the ventilation system, this study used questionnaires, on-site tests, and Computational Fluid Dynamics (CFD) simulation to analyze one pollution and ventilation case in Shenyang, China. The method of ceiling openings to compensate for outdoor air supply was proposed and optimized to improve air distribution in the residential kitchen. The average CO2 concentration in the breathing region, air velocity, and temperature levels in the kitchen, both before and after the improvement, were compared. The results indicated that the kitchen’s air velocity, temperature, and pollutant levels are much better for the ceiling make-up air case compared with permeation and opening window cases. The static pressure, CO2 concentration, indoor airflow fluctuation, and cooking fire showed remarkable improvement in the residential kitchens. These findings provide a basis for improving the reasonable air distribution of residential kitchens in cold regions and for building a thermally comfortable environment.

Performance analysis of small-scale direct expansion air conditioning system with indirect evaporative cooler as dedicated ventilator

Split-type and window-type air-conditioners are typical small-scale direct expansion air-conditioning (DXAC) system widely-used for household applications. However, lack of controllable ventilation can be a serious problem leading to health problems for such air-conditioning (AC) systems. To improve the indoor air quality of a home space equipped with small-scale DXAC system, an indirect evaporative cooler (IEC) is used as a dedicated ventilator, on one hand, to guarantee proper outdoor air supply and on the other hand, to provide sensible cooling under certain climatic conditions. Validated numerical component models of IEC, DXAC and indoor thermal balance were established and coupled in series to form a closed-loop model of DXAC with IEC ventilator (DXAC-IEC) system. The effects of ambient humidity, ambient temperature, sensible heat ratio and ventilation rate on the system performance were investigated, with comparison to the standalone DXAC system. The results show that the IEC can enhance the system performance under moderate hot and dry ambient conditions (tamb ≤ 33 °C, RHamb ≤ 60%) by reducing the cooling load of DXAC. But it would bring extra moisture from outdoor in humid conditions (tamb ≥ 30 °C, RHamb>50%) for sacrifice of improved indoor air quality. Optimal fresh air ratio exists for the DXAC-IEC system to achieve the maximum coefficient of performance. The findings will be beneficial for the design and optimization of DXAC-IEC system.

Use of Beta Regression to investigate the link between home air infiltration rate and self-reported health

The UK has introduced ambitious legislation for reaching net zero greenhouse gas (GHG) emissions by 2050. Improving the energy efficiency of homes is a key priority in achieving this target and solutions include minimising unwanted heat losses and decarbonising heating and cooling. Making a dwelling more airtight and applying insulation can result in a lower energy demand by reducing unwanted heat loss through fabric and openings. However, the supply of sufficient outdoor air is required to dilute indoor airborne pollutants. This research investigates the relationship between dwelling air infiltration and self-reported health at population neighbourhood level for Greater London. This paper links data from a variety of sources including Energy Performance Certificates (EPCs), the Greater London Authorities’ Large Super Output Area (LSOA) Atlas and the Access to Healthy Assets and Hazards (AHAH) database at LSOA level. Beta regression has been performed to assess the influence of air infiltration rate on self-reported health, whilst controlling for other socioeconomic factors. All factors have been ranked in order of their association with self-reported health. Findings indicate that air infiltration rate has a positive association with the percentage of people reporting themselves to be in “good or very good” health.

Implementation of a Ventilation Protocol for SARS-CoV-2 in a Higher Educational Centre

The most recent research confirms that airborne transmission may be the dominant mode of SARS-CoV-2 virus spread in the interior spaces of buildings. Consequently, based on some prescriptions that implemented natural ventilation during face-to-face lessons in a university centre, an experimental characterization of several complementary options aimed at reinforcing the prevention and safety of the occupants was carried out. The action protocol adopted was based on the combination of mandatory natural ventilation, a maximum contribution of outdoor air supply in the air conditioning system, and the use of filtering devices located inside the classroom. All the strategies were incorporated concomitantly with necessary compliance with the basic conditions of social distance, occupation, use of masks and guidelines for use and cleaning within educational buildings. The suitability of this protocol was further evaluated throughout the teaching day with students and teachers by measuring the CO2 concentration. The results showed that the measures implemented successfully removed the possible pollutants generated inside.

The effects of warmth and CO2 concentration, with and without bioeffluents, on the emission of CO2 by occupants and physiological responses.

The emission rate of carbon dioxide (CO2 ) depends on many factors but mainly on the activity level (metabolic rate) of occupants. In this study, we examined two other factors that may influence the CO2 emission rate, namely the background CO2 concentration and the indoor temperature. Six male volunteers sat one by one in a 1.7m3 chamber for 2.5h and performed light office-type work under five different conditions with two temperature levels (23 vs. 28°C) and three background concentrations of CO2 (800 vs. 1400 vs. 3000ppm). Background CO2 levels were increased either by dosing CO2 from a cylinder or by reducing the outdoor air supply rate. Physiological responses to warmth, added CO2 , and bioeffluents were monitored. The rate of CO2 emission was estimated using a mass-balance equation. The results indicate a higher CO2 emission rate at the higher temperature, at which the subjects were warm, and a lower emission rate in all conditions in which the background CO2 concentration increased. Physiological measurements partially explained the present results but more measurements are needed.

Cabin air quality on non-smoking commercial flights: A review of published data on airborne pollutants.

We reviewed 47 documents published 1967-2019 that reported measurements of volatile organic compounds (VOCs) on commercial aircraft. We compared the measurements with the air quality standards and guidelines for aircraft cabins and in some cases buildings. Average levels of VOCs for which limits exist were lower than the permissible levels except for benzene with average concentration at 5.9±5.5μg/m3 . Toluene, benzene, ethylbenzene, formaldehyde, acetaldehyde, limonene, nonanal, hexanal, decanal, octanal, acetic acid, acetone, ethanol, butanal, acrolein, isoprene and menthol were the most frequently measured compounds. The concentrations of semi-volatile organic compounds (SVOCs) and other contaminants did not exceed standards and guidelines in buildings except for the average NO2 concentration at 12ppb. Although the focus was on VOCs, we also retrieved the data on other parameters characterizing cabin environment. Ozone concentration averaged 38ppb below the upper limit recommended for aircraft. The outdoor air supply rate ranged from 1.7 to 39.5 L/s per person and averaged 6.0±0.8L/s/p (median 5.8L/s/p), higher than the minimum level recommended for commercial aircraft. Carbon dioxide concentration averaged 1315±232ppm, lower than what is permitted in aircraft and close to what is permitted in buildings. Measured temperatures averaged 23.5±0.8°C and were generally within the ranges recommended for avoiding thermal discomfort. Relative humidity averaged 16%±5%, lower than what is recommended in buildings.

A fresh (air) look at ventilation for COVID-19: Estimating the global energy savings potential of coupling natural ventilation with novel radiant cooling strategies

Radiant cooling-assisted natural ventilation is an innovative technical approach that combines new radiant cooling technology with natural ventilation to increase fresh air delivery into buildings year-round with minimal energy cost and improvment of air quality. Currently, the standard paradigm for HVAC (heating, ventilation and air conditioning) is based on central air systems that tie the delivery of heating and cooling to the delivery of fresh air. To prevent heat loss, the delivery of fresh air must be tightly controlled and is often limited through recirculation of already heated or cooled air. Buildings are designed with airtight envelopes, which do not allow for natural ventilation, and depend on energy-intensive central-air systems. As closed environments, buildings have become sites of rapid COVID-19 transmission. In this research, we demonstrate the energy cost of increasing outdoor air supply with standard systems per COVID-19 recommendations and introduce an alternative HVAC paradigm that maximizes the decoupling of ventilation and thermal control. We first consider a novel analysis of the energy costs of increasing the amount of conditioned fresh air using standard HVAC systems to address COVID-19 concerns. We then present an alternative that includes a novel membrane-assisted radiant system we have studied for cooling in humid climates, in place of an air conditioning system. The proposed system can work in conjunction with natural ventilation and thus decreases the risk of indoor spread of infectious diseases and significantly lowers energy consumption in buildings. Our results for modeling HVAC energy in different climates show that increasing outdoor air in standard systems can double cooling costs, while increasing natural ventilation with radiant systems can halve costs. More specifically, it is possible to add up to 100 days’ worth of natural ventilation while saving energy when coupling natural ventilation and radiant systems. This combination decreases energy costs by 10–45% in 60 major cities globally, while increasing fresh air intake.