Outdoor Air Supply Research Articles

Effects of the COVID-19 Pandemic on Indoor Air Quality and Thermal Comfort of Primary Schools in Winter in a Mediterranean Climate

Research studies have shown the potential effects of indoor environmental quality (IEQ) on pupils’ health and academic performance. The COVID-19 pandemic has prompted renewed interest in the assessment of deficient indoor air quality (IAQ) conditions in schools and has become a priority over achieving adequate comfort conditions. Scientific studies confirm aerosols as one of the transmission routes of SARS-CoV-2 so that the possibility of airborne transmission increases in indoor environments with high occupancy, such as classrooms. As a result, international protocols and guidelines have established a requirement for educational buildings to over-ventilate with a fresh outdoor air supply. The main object of this work is to analyse the effects of the COVID-19 pandemic on thermal comfort and indoor air quality, in winter, in two classrooms of southern Spain. Thus, onsite measurements of environmental variables were conducted before and during the pandemic. Both classrooms have mechanical ventilation systems as they are within a recently built primary school (2018). Results shows a decrease of 300 ppm in CO2 weekly average values during the pandemic, when hybrid ventilation is used, and a decrease of 400 ppm when schools are naturally ventilated during all teaching hours. However, the analysis of standards shows that over 60% of hours are thermal discomfort conditions.

Feasibility study of retrofitting VAV system to VAV-DOAS system for outdoor airflow requirement and distribution in multi-zone VAV system

In this paper, we will focus on the retrofit of the ventilation system setup on the premise of reserving the original VAV system. Therefore, a combination of the existing VAV system and the dedicated outdoor air system (VAV-DOAS) is discussed. Here, the VAV system handles the indoor temperature and humidity without outdoor air supply, while the DOAS handles the indoor air quality with full outdoor air supply. The feasibility and economic analysis of this combined system are discussed by comparing it with the conventional VAV system operated in the multiple spaces equation-based strategy (MSE-V). The experimental results indicate that the presented VAV-DOAS can save 16% and 21% of energy consumption under winter and summer conditions in Dalian, respectively. Furthermore, this paper presents an economic evaluation method that can effectively evaluate the economy of a VAV-DOAS system retrofitted from the VAV system with different air conditioning loads and outdoor airflow demands. The economic analysis result shows that the retrofit system is economically feasible while the system is designed to serve for more than 12 years.

Outdoor air supply in winter for large-space airport terminals: Air infiltration vs. mechanical ventilation

Excessive outdoor air supply in winter due to air infiltration is prevailing in large-space airport terminals, leading to high energy consumption for heating, while mechanical ventilation systems rarely operate to supply outdoor air during the heating season. This study applies a simplified model to analyze the strategies to effectively reduce the air infiltration rate and meanwhile fulfill the demand for outdoor air supply in large-space airport terminals during the heating season. The analysis of main influence factors helps to propose practical methods to reduce the air infiltration rate, i.e., adjust bottom openings, adjust upper openings, use radiant floor. The air infiltration rates can be controlled steadily at a low level (0.14–0.23 h−1) during the heating season by all the three methods. The designed outdoor air ventilation rate is averagely 0.22 h−1 in seven airport terminals without a dramatic difference. An analysis of a real airport terminal indicates that its designed outdoor air ventilation rate (0.20 h−1) largely exceeds the actual maximal demand (0.13 h−1) because of the uneven occupant distributions both in time and space. Therefore, even though the three methods are utilized to decrease the air infiltration rate and its corresponding heating load, the demand for outdoor air in large-space airport terminals can still be fulfilled during the heating season without mechanical ventilation.

Intermittent occupancy combined with ventilation: An efficient strategy for the reduction of airborne transmission indoors

It is important that efficient measures to reduce the airborne transmission of respiratory infectious diseases (including COVID-19) should be formulated as soon as possible to ensure a safe easing of lockdown. Ventilation has been widely recognized as an efficient engineering control measure for airborne transmission. Room ventilation with an increased supply of clean outdoor air could dilute the expiratory airborne aerosols to a lower concentration level. However, sufficient increase is beyond the capacity of most of the existing mechanical ventilation systems that were designed to be energy efficient under non-pandemic conditions. We propose an improved control strategy based on source control, which would be achieved by implementing intermittent breaks in room occupancy, specifically that all occupants should leave the room periodically and the room occupancy time should be reduced as much as possible. Under the assumption of good mixing of clean outdoor supply air with room air, the evolution of the concentration in the room of aerosols exhaled by infected person(s) is predicted. The risk of airborne cross-infection is then evaluated by calculating the time-averaged intake fraction. The effectiveness of the strategy is demonstrated for a case study of a typical classroom. This strategy, together with other control measures such as continuous supply of maximum clean air, distancing, face-to-back layout of workstations and reducing activities that increase aerosol generation (e.g., loudly talking and singing), is applicable in classrooms, offices, meeting rooms, conference rooms, etc.

Numerical simulation of air distribution and CO2 concentration in different air supply locations in winter classroom

In winter, temperature difference between indoor and outdoor is large, and the concentration of indoor CO2 exceeds standard in the closed classroom. In order to achieve better ventilation effect, different outdoor air supply modes are explored to make up for the shortcoming of existing equipment. In this paper, by using FLUENT software, numerical simulation method is used to simulate the temperature field, velocity field changes and differences of classrooms under different air outlets. Also the concentration of CO2 distribution under this condition is simulated, and the best outlet position is obtained through simulation. With the in-depth study of airflow organization, the fresh air system will provide a more comfortable living condition for human beings and serve production and life.

Proxy zone-level energy use estimation in a commercial building with a variable air volume system

The usefulness of zone level sensors is contentious in the context of commercial building controls. Few building owners are willing to increase capital costs with conflicting information about the most valuable sensors to owners and operators. Few studies have systematically explored this topic in a practical manner. This study compared zone-level sensors of 27 rooms of an institutional building for their ability to estimate energy use indirectly using a novel methodology. Notable sensors in this study include hydronic flow meters, room level lighting and plug load current transducers, window contacts, and ceiling illuminance at three interior depths. Data was collected at 5-min sample intervals over four months total. Sensors were scored and ranked by energy use using mean bias error to infer estimation accuracy over the validation period (half the measurement period) with artificial neural network models. A hierarchy of sensor value for each energy end use was generated. It was found that outdoor air temperature sensors provide the most usefulness for energy use estimation in the building studied (where heating and cooling loads dominated due to the high outdoor air supply ratio). Hydronic flow meter data was also useful for energy use estimation.

The Development of a Live Air Cleaner as Indoor Garden for an Unventilated Air Conditioned Room

Urban temperatures continue to increase due to urban heat island and global warming. Air temperatures in warm, humid tropical cities have exceeded 32 o C. To achieve thermal comfort in buildings, people adopted air conditioners (ACs) that can consume more than 40% of the building's electrical energy. Air conditioning is often not accompanied by a supply of fresh outdoor air to minimize heat gain from the warm outdoor air. In that unventilated room, the CO 2 concentration easily exceeds 1,000 ppm and causes discomfort. Plants such as Dracaena sanderiana require CO 2 for photosynthesis. At the same time, they produce O 2 . Dracaena sanderiana has the potential to keep CO 2 concentrations in the room for not exceeding the comfort limit. That plant can be integrated into architectural elements, both interior and exterior (combined with windows or facades), in the form of a living air purifier or Live Air Cleaner (LAC). This research developed a LAC in the form of an interior garden that can be used as an interior architectural element. The application of LAC helps to save the electrical energy of unventilated air-conditioned rooms while preventing the room CO 2 concentration from reaching the maximum limit of indoor CO 2 level acceptable to humans . The research adopted experimental methods using three experiment chambers to measure the Dracaena sanderiana ’s CO 2 absorption efficiency. The experiments found that Dracaena sanderiana had a unique performance, which should be considered when it is used as a live air cleaner. Though this plant absorbs CO 2 , its efficiency is low. Sufficient volume of Dracaena sanderiana is needed if it is to reduce indoor CO 2 concentration. Keywords: Live Air Cleaner, Air conditioning, Indoor garden, CO2 absorption

A Integrated Dedicated Outdoor Air System to Optimize Energy Saving

Outdoor air supply is required to maintain good indoor air quality (IAQ). For tropical or subtropical regions, warm and humid outdoor air would cause excess air-conditioning energy use. This study has proposed an integrated dedicated outdoor air system (IDOAS), which integrates the enthalpy exchange and outdoor air cooling into a unitary system. IDOAS could operate independently of central air-conditioning systems thus saving tremendous piping cost and energy needed to deliver chilled water to outdoor air unit in a conventional centralized system. An experimental unit of IDOAS was built to prove this novel concept. Enthalpy exchange efficiency was tested to be about 44%. The test results show that about 44% of energy needed to condition the outdoor air can be saved. A reverse Rankine refrigeration cycle was integrated to cool the outdoor air. Due to this integrated configuration, the air passing through the condenser would be at a lower temperature. The consequent lower refrigerant condensing temperature would improve the cooling cycle efficiency. The cooling coefficient of performance (COP) was improved by about 46%. In addition, the outdoor air could be conditioned to a lower humidity before being supplied to space, which would improve the thermal comfort. The test results of this novel IDOAS show that it could provide good air quality at lower energy use.

A Graphical Tool to Estimate the Air Change Efficiency in Rooms with Heat Recovery Systems

Indoor air quality in buildings must be guaranteed for the health and comfort of the occupants. In order to assess the ventilation strategy of a considered room, the parameter of the air change efficiency ( ε a ) can be used. The objective of this work is to provide designers with a graphical tool for a reliable estimate of the value of ε a of a room. The temperature gradient between the outdoor air supply and the indoor air is so low that the ventilation flow can be assumed as isothermal when high-efficiency heat recovery systems are used. By means of charts, the optimal location of the openings for a better ε a can be determined during the design process, in order to subsequently apply them. It is concluded that it is very important to consider the ε a in the case of openings located in facing walls given that its range varies between 40% and 65%. In contrast, its use can be obviated in the case of openings located in non-facing walls, as the value of ε a obtained is close to 50%; this means a perfect mixing air flow pattern, which is the reference value for the estimation of the indoor air quality (IAQ) in the different national regulations.

COVID Operation Theatre- Advisory and Position Statement of Indian Society of Anaesthesiologists (ISA National).

COVID Operation Theatre- Advisory and Position Statement of Indian Society of Anaesthesiologists (ISA National).

A holistic performance evaluation of ventilation radiators – An assessment according to EN 442-2 using numerical simulations

This research explored the importance of airflow rate and convector plate design on the operational performance of heating radiators equipped with an air device (ventilation radiators). The radiator was analyzed according to European Norm EN 442-2 using numerical simulations. The largest benefit of using staggered convector plates was the more efficient preheating of the incoming outdoor air supply. With this plate design, the evaluated radiator increased the temperature of the incoming airflow of 10 l/s from -5 °C to 26 °C with water supply/return temperatures of 45 °C/35 °C. With these water temperatures, the radiator was able to cover a room heat loss of 34 W/m2 floor area. However, the design of the convector plate alone was found to have a limited impact on the heat output from the radiator. Neither did the plate design significantly affect the uniformity of heat distribution nor the vertical temperature stratification inside the room. The results also showed that ventilation radiators might cover a building heating load (kW) with a lower supply water temperature but not necessarily give a lower annual energy use (kWh) for the space heating of a building.

Pilot study on the impact of green roofs on ozone levels near building ventilation air supply

Outdoor air is often introduced into commercial buildings from ventilation intakes sited on rooftops where vegetation (a green roof) is increasingly present. Little is known about the impact of green roofs on the quality of building outdoor ventilation air supply. In this study, we investigated the potential for green roofs to impact ozone (O3) levels in ventilation air by parameterizing O3 dry deposition to vegetation and substrate typical of extensive green roofs in field and laboratory studies. Values obtained constrain a 2-D advection-diffusion model of O3 transport and reaction at the rooftop scale. The 10th, 50th, and 90th percentiles for O3 surface resistances measured using flux-gradient methods in field studies were 46 s/m, 155 s/m, and 1700 s/m. Surface resistances measured in laboratory chambers for substrate and green roof samples ranged from 360 s/m to 435 s/m, in the 60th-70th percentile of field measurements. The modeled impact of a green roof on O3 levels in building outdoor ventilation air intake was a reduction ranging from 0.25 to 1.8 μg/m3 for short fetch lengths (1 m) and low vertical mixing to larger fetch lengths (5 m) and stronger vertical mixing, respectively, from ambient O3 levels of 144 μg/m3. Vegetation fetch and vegetation height had the largest impact on modeled O3 reductions, suggesting large, continuous, intensive green roof designs may enhance O3 reductions in building ventilation air.

Formula omitted] concentrations in a multifamily building in Porto, Portugal: Occupants' exposure and differential performance of mechanical ventilation control strategies

Adequate supply of fresh outdoor air is important to create healthy and comfortable indoor building environments. Currently, most of the residential buildings in mild climate European countries, such as Portugal or Spain, remain naturally ventilated. Distinct concerns have emerged in the building community regarding the indoor air quality (IAQ) in these buildings since several studies have shown that they are often poorly ventilated. The main cause has been identified as occupants' different window opening behavior, which can vary notably from one apartment to the next. This work presents a comparative method for evaluating occupants' exposure to CO2 concentration levels in existing buildings based on the comparison of cumulative frequency distribution curves. Indoor CO2 concentration levels recorded over 17 months in the bedrooms and living rooms of eight apartments of a naturally ventilated residential building located in Porto (Portugal) were used as experimental input data for developing the method and to calibrate the IAQ performance of an EnergyPlus building model. The calibrated building model exhibited a good agreement with the recorded data on the apartments, reporting maximum Root Mean Square Errors (RMSE) for the majority of the apartments below 5% and 10% for the living rooms and bedrooms, respectively.

Performance investigation of outdoor air supply and indoor environment related to energy consumption in two subway stations

On-site measurements of the outdoor air supply and indoor environment in the public area (hall and platform) in two subway stations have been conducted in cooling season in this study. The result revealed that the outdoor air intake through entrances was enormous and played an important role in outdoor air supply. Influencing factors have been discussed and negative effects of mechanical outdoor air supply and train interval are revealed. The total outdoor air involved in by both infiltration and mechanical ventilation was far greater than the demand of occupants in public area under the normal condition, with indoor CO2 concentration only 399∼670 ppm. Return air alone (RAA) condition for ventilation with no mechanical outdoor air supply was then proposed, utilizing the air infiltration through entrances to meet outdoor air demand and reduce the cooling load in public area. Under the proposed condition, similar indoor thermal performance could be realized, and enough outdoor air could be supplied through entrances even for expected maximum passengers. Electricity consumption of VAC systems reduced by 10%∼20% compared with the normal operation condition in cooling season.

Development of a CFD model for simulating vehicle cabin indoor air quality

As the level of CO2 within the vehicle cabin increases, the risk of accidents as a result of driver drowsiness and a slowing of the reactions also increases. Accordingly, a CFD simulation model was developed in this study to explore the effects of outdoor air ventilation rate on vehicle cabin indoor air quality and the amount of outdoor air required for each person in a vehicle. The results show that using the outdoor air supply rate recommendations of ASHRAE Standard 62.1 (i.e. 2.5 l/s per person) the mean CO2 concentrations in the cabin are around 2850 ppm. The results also show that using the outdoor air supply rate recommendations of 4.0 l/s per person for improved human wellbeing, the corresponding mean CO2 concentrations in the cabin are around 1810 ppm. Moreover, the present study found that an outdoor fresh air flow rate of 9.2 l/s per passenger was sufficient to reduce the carbon dioxide concentration within the cabin to a safe value of 1000 ppm. Furthermore, an outdoor fresh air flow rate of 3.6 l/s per passenger resulted in a carbon dioxide concentration of around 2000 ppm.

An experimental evaluation on air purification performance of Clean-Air Heat Pump (CAHP) air cleaner

The escalation of energy consumption in buildings and heightened concerns about acceptable indoor air quality stimulate interest in the usage of air cleaner as an adjunct for indoor environmental conditioning. A regenerative desiccant wheel integrated into a ventilation system termed Clean-Air Heat Pump (CAHP) can improve the air quality during the process of dehumidification without using additional energy. An experimental study in a field lab was performed to investigate the air cleaning performance of CAHP. Photoacoustic gas analyzer-INNOVA was used to characterize chemical removal of indoor air pollutants by the CAHP. The results revealed that all the detected VOCs were removed effectively by the CAHP with an average single pass efficiency of 82.7% when the regeneration temperature for desiccant wheel was 60 °C. The mass balance between adsorption and desorption of the desiccant wheel was 96.8%, which indicated that the most of gaseous pollutants were not accumulated in the CAHP. The regeneration temperature for the wheel could affect the air purification performance of CAHP. At 70 °C of regeneration temperature, the air-cleaning efficiency reached 96.7%. Up to 70% of the outdoor air ventilation can be saved with the operation of CAHP. The clean air deliver rate (CADR) was over threefold of the outdoor air supply rate when CAHP was in operation.

Air tightness measurements in older Danish single-family houses

This paper reports and discusses the air tightness of the building envelope in existing single-family houses in Denmark. The air tightness of the building envelope depends in particular on the performance of specific construction details. There is a lack of knowledge about the air tightness of the building envelope of older buildings despite the fact that the air tightness has a major influence on the energy use. In connection with renovation of the Danish building stock, the coming years will see increased focus on the air tightness of the building envelope like in other countries.This paper presents the results of measurements in 16 single-family houses built between 1880 and 2007. The air tightness of the building envelope was measured according to EN ISO 9972 using the blower-door technique. The results are compared with measurement results of the average air-change rate in the same houses measured over a period of 1-3 weeks when the houses were in normal use.The measurement results of the air tightness of the building envelope range from 1.1 to 5.8 l/(s·m²) at 50 Pa. The investigated houses are all naturally ventilated. The results of the ventilation measurements showed an outdoor air supply ranging from 0.09 to 0.28 l/(s·m²) per heated floor area, which is below the requirement stipulated in the Danish Building Regulations of 0.3 l/(s·m²).Typically, leaks are observed in connection with penetrations of the envelope, e.g. for electrical installations, exhaust ducts and chimneys. In addition, leaks are observed around older windows and doors and in connection with wooden ceilings and attic hatches. The findings should be taken into account when renovating older single-family houses.

Experimental analysis of indoor air quality improvement achieved by using a Clean-Air Heat Pump (CAHP) air-cleaner in a ventilation system

This study investigated the air purification effect of a Clean-Air Heat Pump (CAHP) air-cleaner which combined a silica gel rotor with a heat pump to achieve air cleaning, heating and ventilation in buildings. The experiments were conducted in a field laboratory and compared a low outdoor air supply rate with CAHP air purification of recirculated air with three different outdoor air supply rates without recirculation or air cleaning. Sensory assessments of perceived air quality and chemical measurements of TVOC concentration were used to evaluate the air-cleaning performance of the CAHP. The results of the experiment showed that the operation of the CAHP significantly improved the perceived air quality in a room polluted by both human bio-effluents and building materials. At the outdoor airflow rate of 2 L/s per person, the indoor air quality with CAHP was equivalent to what was achieved in the same room with 10 L/s per person of outdoor air ventilation without air cleaning. The percentage dissatisfied was as low as 5.2% with the CAHP in operation, based on adapted perception assessment. The outdoor air supply rate can be reduced by 76% by using CAHP, as the Clean Air Delivery Rate (CADR) was over three times the outdoor air supply rate when the CAHP was in operation. The chemical measurements indicated a single-pass efficiency of over 92% for the removal of indoor air pollutants when the regeneration temperature was 60 °C. No VOC accumulation on the desiccant wheel was observed.

Influencing factors and energy-saving control strategies for indoor fine particles in commercial office buildings in six Chinese cities

Experimental studies on indoor fine particles were performed in actual commercial offices in six Chinese cities: Beijing, Shanghai, Guangzhou, Tianjin, Shijiazhuang and Chengdu. Particle introduced through outdoor air supply (OA) system was the most significant contributor to indoor PM2.5. In most cases, the OA systems of the six office buildings could not provide enough protection for staff. The first reason was the insufficient filtration efficiency of the OA system for PM2.5 due to filter bypass and design shortage. The tested filtration efficiency of the OA system for PM2.5 ranged from 17.0±0.9% to 55.7±2.8%. The gaps between the tested and rated filtration efficiencies ranged from 4.4% to 26.3%. The gaps between the rated and required filtration efficiencies ranged from 7.4% to 64.5%. The second reason was the superfluous outdoor air supply rate. The outdoor air supply rates per staff could reach 7.5L/s to 12.8L/s with the operating OA systems, much higher than the ASHRAE guideline. Five control strategies (including higher level filters, minimum outdoor air supply rates, portable air cleaners and combinations of these options) were proposed for HVAC system to reduce indoor PM2.5 concentration level to 35μg/m3. The reduced indoor PM2.5 exposure per power under strategy 2 (minimum outdoor air supply rate+higher level filters) was the highest in all cases. The total energy consumption of HVAC systems under strategy 2 was only 42%-71% of the current energy consumption.

Energy performance evaluation and application of an air treatment system for conditioning building spaces in tropics

The present study attempts to reduce the supply of outdoor air in conditioning building spaces for energy saving while improving the indoor air quality. A hybrid air treatment system incorporating a cooling system is introduced for tropical climates. The air treatment system (ATS) comprises an ozone-based oxidation process and an air scrubbing device. The air purification process has been experimentally investigated. Experimental results demonstrated the feasibility of the proposed ATS to provide improved indoor air quality. A validated mathematical model has been employed to study the air cooling and dehumidification process through the cooling coil. The reduced outdoor air intake facilitates a higher chilled water supply temperature resulting in an improved chiller performance and reduction of cooling load. The energy consumption performance of the proposed hybrid ATS air-conditioning system has been evaluated for an office building experiencing tropical climatic conditions. The cooling load on a design day has demonstrated that the reduction of outdoor air intake enabled marked energy savings potential in terms of the cooling demand. By analysing the building performance based on tropical climatic data, an annual energy consumption saving of up to 64.6kWh/m2 can be achieved via the hybrid ATS air-conditioning system.