Minimum Ventilation Research Articles

Assessing the impacts of air-sealing on the sizing, operation, and economic feasibility of ground-source heat pumps for electrifying single-family houses in the US

According to recent studies and reports, in single-family houses (SFHs), air-sealing can significantly lower the thermal loads for space heating and cooling. Thus, air-sealing in SFHs could reduce the required size and cost of ground source heat pump (GSHP) systems for electrifying SFHs. This study investigated the costs and benefits of integrating air-sealing with GSHPs for retrofitting existing SFHs when compared with air-source heat pumps. A whole building energy simulation tool integrated with an advanced design tool for modeling ground heat exchangers was used to calculate changes in required GSHP capacity, total borehole length, and building energy consumption with and without air-sealing in SFHs in 16 US climatic regions. The results from this study showed that reducing outdoor air infiltration from 0.8 air changes per hour (ACH) to the minimum ventilation requirement (0.35 ACH) can significantly reduce borehole length (up to 55%), GSHP capacity (up to 48%), and total heating electricity reduction, especially in cold climates (up to 44%). The results also showed that for airtight homes (0.03 ACH infiltration) with a direct outdoor air system, the minimum required borehole length, GSHP capacity, and total heating electricity consumption can be reduced up to 70%, 68%, and 67%, respectively, when compared with SFHs with 0.8 ACH infiltration. Moreover, the life cycle cost analysis showed that air-sealing in conjunction with a GSHP is more profitable than replacing the existing system with an air-source heat pump, even without any incentives for most climatic regions in the US (except for some hot regions).

Reduced Fetuin-A Levels Are Associated With Exercise Intolerance and Predict the Risk of Adverse Outcomes in Patients With Heart Failure: The Role of Cardiac-Hepatic-Peripheral Interaction.

Exercise intolerance in heart failure arises from multifactorial pathophysiological mechanisms. Hepatokines, liver-synthesized molecules, regulate systemic metabolisms in peripheral tissues. We previously identified the hepatokine fetuin-A as being linked to liver hypoperfusion in heart failure. Here, we investigated the role of fetuin-A in connecting cardiac-hepatic-peripheral interaction. We conducted a prospective study involving 202 consecutive hospitalized patients (mean age, 56.8 years; 76.2% men) with heart failure who underwent cardiopulmonary exercise testing. We measured the serum concentration of fetuin-A by ELISA. Correlation analysis revealed a negative association between fetuin-A levels and the ratio of minimum minute ventilation to carbon dioxide production, its slope, and a tendency toward a positive correlation with peak oxygen uptake. Patients with impaired exercise tolerance exhibited lower fetuin-A levels. During a median follow-up of 1045 days, 18.3% experienced cardiac events, including 4 cardiac deaths and 33 cases of worsening heart failure. Classification and regression tree analysis identified a high-risk subgroup with lower fetuin-A (<24.3 mg/L) and impaired exercise tolerance (peak oxygen uptake<14.2 mL/kg per min). Kaplan-Meier analysis revealed that this subgroup had the highest risk of cardiac events. In a multivariable Cox proportional hazard model, the combination of lower fetuin-A and exercise intolerance was independently associated with increased risks of cardiac events. Reduced circulating fetuin-A levels were associated with exercise intolerance in heart failure patients. Fetuin-A could emerge as a target implicated in exercise capacity connecting cardiac-hepatic-peripheral interaction and as a valuable biomarker for predicting prognosis when combined with peak oxygen uptake.

Diffusion characteristics of indoor pollutants from incense sticks combustion in Tibetan Plateau buildings: An experimental study

Incense burning, a common practice among ethnic Tibetans in Qinghai-Tibet Plateau of China, generates pollutants that can impact indoor air quality and, subsequently, human health. In this paper, we investigate the diffusion characteristics of four prevalent pollutants emitted during the burning of local Tibetan incense under low-pressure conditions specific to the plateau region. The diffusion behavior of these incense burning pollutants deviates from that observed under standard atmospheric pressure due to the unique conditions prevailing at high altitudes. The research results reveal that the primary pollutants released during Tibetan incense combustion are carbon dioxide, inhalable PM2.5, and PM10. Furthermore, ambient temperature exerts a substantial influence on the concentration of pollutants emitted during incense burning. A 6 °C increase in ambient temperature results in a 1.17-fold rise in the combustion rate. Consequently, higher temperatures correspond to larger diffusion coefficients, increased gas diffusion rates, and elevated pollutant concentrations at equivalent combustion times. Simultaneously, the low oxygen content characteristic of plateau regions has a notable impact on the diffusion rate of gaseous pollutants. This study of pollutant concentration and diffusion characteristics during incense burning offers valuable insights for determining the minimum ventilation rate in plateau areas.

Carbon dioxide guidelines for indoor air quality: a review.

The importance of building ventilation to protect health has been more widely recognized since the COVID-19 pandemic. Outdoor air ventilation in buildings dilutes indoor-generated air pollutants (including bioaerosols) and reduces resulting occupant exposures. Many countries and organizations have advisory guidelines or mandatory standards for minimum ventilation rates (VRs) to maintain indoor air quality (IAQ). Because directly measuring VRs is often difficult, many IAQ guidelines instead specify indoor concentration limits for carbon dioxide (CO2), using CO2 exhaled by building occupants as an indicator of VR. Although indoor CO2 guidelines are common, the evidence basis for the various CO2 limits has not been clear. To review current indoor CO2 guidelines worldwide and the supportive evidence provided. We identified worldwide CO2-based guidelines for IAQ or ventilation, along with any supportive evidence provided. We excluded occupational guidelines for CO2 levels ≥5000 ppm. Among 43 guidelines identified, 35 set single CO2 concentration limits and eight set multi-tiered limits; 16 mentioned no specific human effect to be controlled, 19 specified only odor dissatisfaction, five specified non-infectious health effects, and three specified airborne infectious disease transmission. The most common indoor CO2 limit was 1000 ppm. Thirteen guidelines specified maximum CO2 limits as extended time-weighted averages, none with evidence linking averaged limits to occupant effects. Of only 18 guidelines citing evidence to support limits set, we found this evidence persuasive for eight. Among these eight guidelines, seven set limits to control odor perception. One provided 17 scientifically-based CO2 limits, for specific example space uses and occupancies, to control long-range COVID-19 transmission indoors. Many current indoor carbon dioxide (CO2) guidelines for indoor air quality specified no adverse effects intended for control. Odor dissatisfaction was the effect mentioned most frequently, few mentioned health, and three mentioned control of infectious disease. Only one CO2 guideline was developed from scientific models to control airborne transmission of COVID-19. Most guidelines provided no supportive evidence for specified limits; few provided persuasive evidence. No scientific basis is apparent for setting one CO2 limit for IAQ across all buildings, setting a CO2 limit for IAQ as an extended time-weighted average, or using any arbitraryone-time CO2 measurement to verify a desired VR.

Natural ventilation to improve indoor air quality (IAQ) in existing homes: The development of health-based and context-specific user guidelines

Acceptable indoor air quality (IAQ) is one of the most relevant aspects of a healthy home environment. Despite advances in mechanical and hybrid ventilation systems, natural ventilation still constitutes a crucial intervention to improve IAQ in existing homes; especially in older and/or vulnerable ones. The challenge, however, is optimizing natural ventilation strategies so IAQ is reached while thermal discomfort (and potentially associated energy consumption) is minimized.The complexity of identifying factors that may determine the possibilities of natural ventilation in existing homes has traditionally hindered the efforts from the scientific community to communicate straightforward answers for end-users. This work develops a methodology that, based on real case studies and through a series of simulations, provides simple, context-specific criteria and recommendations in order to reach acceptable IAQ through natural ventilation strategies in existing homes. The use of a minimum ventilation time (MVT) indicator, alongside considerations for different seasons and housing types, are translated into step-by-step guidelines aimed at helping the end-user to (i) gain knowledge regarding the opportunities and limitations for natural ventilation in the dwelling, and (ii) identify which specific actions should be carried out under different conditions to maintain minimum IAQ.The conceptual framework and methodology presented, while illustrated for the case of Barcelona, can be replicated for different cities or regions with differing housing characteristics and climatological conditions, and can easily accommodate other locally relevant factors.

A study on natural ventilation of dormitories for college students in northeast China during spring: A case of linear-shaped dormitory buildings

This study employed computational fluid dynamics to investigate the natural ventilation efficiency and indoor air temperature changes in different rooms of a linear-shaped dormitory building at a university in northeastern China during the spring season. Using a four-student dormitory in Jilin City as a physical model. Volume ratio of air age curves, depicting indoor air quality, are constructed based on air age values. Due to the dormitory building's symmetry, five wind angles, averaged from 0° to 90° (N - E), are chosen as typical. The results indicate that, following adequate ventilation, the average indoor air temperature (Temstabilize) can be stabilized above 11 °C in rooms located on the leeward side of the dormitory building. Specifically, rooms located on the upwind area at wind angles of 22.5° and 45°, as well as rooms near the environmental air inlets and outlets at wind angles of 67.5° and 90°, can maintain an average air temperature above 15 °C. However, the minimum continuous ventilation time (Tmin) required for these rooms exceeds 1200 s. On the windward side of the dormitory building, rooms near the environmental air inlets and outlets exhibit high ventilation efficiency, but the air temperature in these rooms decreases more rapidly. When the wind angle is 45°, 67.5°, or 90°, the average indoor temperature in these rooms falls below 11 °C. Through normalization analysis, a significant linear relationship is observed between Tmin and Temstabilize data, represented by the numerical relationship Tminnorm=1.0134×Temstabilizenorm. The findings of this study are valuable for assisting students in developing ventilation plans and can also serve as a reference for architects designing dormitory buildings based on prevailing wind directions in the area.

Investigation of Hydrogen-Blended Natural Gas Pipelines in Utility Tunnel Leakage and Development of an Accident Ventilation Strategy for the Worst Leakage Conditions

The development of hydrogen-blended natural gas (HBNG) increases the risk of gas transportation and presents challenges for pipeline security in utility tunnels. The objective of this study is to investigate the diffusion properties of HBNG in utility tunnels and evaluate the effectiveness of various ventilation mechanisms. The numerical simulation software Fluent 2023 R1 is applied to simulate and analyze the leakage of small holes in a HBNG pipeline in the natural gas compartment. By examining the leaking behavior of HBNG through small holes in different circumstances, we aimed to identify the most unfavorable operational situation for leakage. Subsequently, we analyzed the ventilation strategy for sub-high-pressure pipes at various pressure levels in this unfavorable condition. This study’s findings demonstrate that blending hydrogen improves the gas diffusion capacity and increases the likelihood of explosion. The primary factors that influence the pattern of leakage are the size of the leaking holes and the pressure of the pipeline. The gas compartment experiences the most unfavorable working conditions for natural gas pipeline leaks when there are higher pressures, wider leak openings, higher hydrogen blending ratios (HBRs), and leaks in close proximity to an air inlet. When the HBR is 20%, the minimum accident ventilation rates for pressures of 0.4 MPa and 0.8 MPa are 15 air changes per hour and 21 air changes per hour, respectively. The maximum allowable wind speed for accident ventilation is 5 m/s, as regulated by China’s national standard, GB 50838-2015. This regulation makes it difficult to minimize the risk of leakage in a 1.6 MPa gas pipeline. It is recommended to install a safety interlock device to quickly shut off the pipeline in the event of a leak in order to facilitate the dispersion of the substance.

Occupancy schedule development and its effect on OpenStudio prototype college building model

College buildings have unique characteristics compared with school buildings. Therefore, defining the realistic occupancy schedule in a prototype college building has significant research opportunities. In this study, the actual operating schedules of each space type were collected and generated based on the class reservation schedule and compared with the previous reference schedule (primary/secondary school). The schedules were analyzed for their effect on the OpenStudio prototype college building model. The findings highlight that the use of a typical school building schedule in a college building impairs the granularity of information. The analysis shows significant differences between the previous occupancy schedule and the updated occupancy schedule of the college building, leading to a considerable decrease in occupancy density. Furthermore, the effect of these occupancy pattern changes on the prototype building model is examined. The variations were observed in minimum ventilation requirements, the average mechanical ventilation rate, and energy consumption attributed to changes in occupancy density.

The study of the efficiency evaluation of the ventilation system of the poultry house in the summer

With the onset of cold weather, heat transfer through the walls and especially the roofs of bird rooms, unlike in the summer period, increases significantly, which leads to a sharp decrease in warm indoor air. Therefore, in order to maintain the regulatory conditions of the ventilation system, it is reduced to a transitional mode, and then to a minimum ventilation mode. Low ventilation repeatability limits inside the building determine the minimum volume of air supplied by the ventilation system. The economic and production efficiency of poultry farming is related to the premises and climatic conditions, which can seriously affect the well-being of broilers. Heat stress contributes to behavioral, physiological and biochemical changes in broilers, which leads to economic losses.&#x0D; The purpose of this study is to influence the annual efficiency of the poultry house ventilation system, mainly in summer, in order to evaluate the efficiency during the reconstruction of the cooling system, that is, to improve the ventilation system of the room, as well as to give an economic assessment of waste disposal technology.&#x0D; Energy– and resource-saving, environmentally friendly technologies and technological tools, plastic-type recuperators, a bird droppings removal system, as well as lighting and irrigation processes were taken as the object of the study. In conducting our research, let’s use classical and special methods, including a decomposition method for analyzing the functional use of recycling technology, a logical and linguistic method for assessing the safety of nitrogen during disposal, microclimate technology, nutrition and storage.&#x0D; Based on the mathematical model, a computer research methodology was developed to improve the energy efficiency of the poultry house. Using a computer program, the number of LEDs (α=200, I0=20 cd) for an enclosure measuring 66×12 m is N=273 pieces, and the number of LEDs (α=200, I0=20 cd) for a building measuring 78×18 m is N=259 pieces. The design parameters of the illuminators are justified

Effect of demand-controlled ventilation strategies on indoor air pollutants in a classroom: A Norwegian case study

The choice of the minimum ventilation rate (Vmin) in a demand-controlled ventilation strategy can influence energy demand but also introduce outdoor air pollutants. The latter may have direct health effects, as well as affect indoor chemical reactions. In this paper, we evaluate the effect of ventilation rates and operation hours on the level of CO2, nitrogen dioxide (NO2), and ozone (O3) in a classroom during normal use. We compared the baseline ventilation scenario (S0) with a Vmin of 430 m3/h with S1; Vmin of 150 m3/h for normal ventilation operation time (6:30-17:00) and continuous ventilation for 24h (S2). We found that S1 with reduced Vmin would lower the ozone concentration by 35% during the hours before occupancy compared to S0. Moreover, continuous ventilation during night time with a low Vmin resulted in almost as high O3 concentrations as the baseline ventilation scenario. As O3 reacts easily with certain VOCs to produce secondary organic aerosols, the level of Vmin and the ventilation duration would impact the indoor air quality upon entering the classroom.

Residential Unit Design for Natural Ventilation in Tropical Multi-Family High-Rises With a Double-Loaded Corridor

This research investigates practical methods to improve the efficiency of natural ventilation in residential units of multi-family high-rises without additional areas. Typical studio- and one-bedroom-types of small units were redesigned using: 1) air post, 2) transom window, 3) buffer space with one corridor opening and 4) buffer space with two corridor openings. The simulation study using a CFD program to reveal that the indoor average air velocity coefficient (Cv ) in the best redesigned case (0.46) significantly improves from the base case (0.01). The paper demonstrates an example of application to an actual climate in Bangkok, Thailand. It was found that the proposed redesign using buffer spaces can considerably help upgrade the living conditions of the occupants in terms of both thermal comfort (24 hours vs. 0 hours in the comfort zone per day) and indoor air quality (24 hours vs. 8–17 hours that pass the minimum ventilation requirement per day) in the transitional month of February.

Optimizing demand-controlled ventilation with thermal comfort and CO2 concentrations using long short-term memory and genetic algorithm

Heating, ventilation, and air conditioning systems are the largest consumers of energy in commercial and residential sectors. Minimizing their energy consumption without compromising indoor air quality and thermal comfort would result in environmental and financial benefits. However, most buildings still utilize constant air volume systems with on/off control to meet the thermal loads. Previous studies show that CO2-based demand-controlled ventilation is the most widely used strategy to determine the optimal level of supply air volume. Conventional CO2 mass balanced models, however, do not take the thermal comfort level into account. This paper aims to develop and implement a practical and efficient optimization framework to help office building designers and operators enhance thermal comfort and indoor air quality while minimizing energy costs for ventilation using demand-controlled ventilation. The objective function was constructed to consider thermal comfort indices, indoor air quality, and ventilation power demand. Long Short-Term Memory networks in conjunction with a generic algorithm optimization were utilized to generate the search spaces and solve the objective function. The proposed optimization strategy achieved near-optimal results within approximately 1 h of computation time. The findings indicate a reduction of the average ventilation power by 5.6% compared to the current on/off control approach and a slight increase of 0.25% in ventilation power when compared against the minimum ventilation rate recommended by ASHRAE. Additionally, the optimized approach leads to a saving of 26.9 kg per day of greenhouse gas emissions in terms of carbon dioxide equivalent.

A Case Study on PV-Aided Net Zero-Energy Building: the Daycare in IKCU

At the core of our growing societies, energy supply stands as one of the major concerns today, and it will be an inevitable challenge for our near future. As the nations are looking to find solutions for the transition from fossil fuels – depleting at a high rate – to alternative energy sources, solar energy through PV cells is getting attention as an affordable and easily implemented option especially for power supply in commercial and residential buildings. This work consists in analyzing the possibility to cover the entire energy needs of a building via PV solar cells for the case of a constructed daycare. In this case study, HVAC energy requirement has been calculated by the TS825 standard. The standard specifies a method for calculating the net heating/ventilation energy need and provides the rules for calculating the maximum allowable temperature in buildings. First, dimensions of the investigated building are taken and characteristics affecting the thermal insulation are assessed. Then, other energy needs, mainly lighting and electrical devices, are computed in the analysis as internal electricity needs. The scope of this work extends to the assessment of indoor air quality for occupants of building, which is an important aspect in our case study where the occupants are children. ASHRAE standards 62.1 is utilized for this purpose. The standard specifies minimum ventilation rates and other measures intended to provide acceptable indoor air quality to human occupants and that minimizes adverse health effects. The results are obtained for monthly varying solar exposition in the specified area where the building is located to provide supply for the determined energy demand via solar energy. Finally, monocrystalline PV panel system has been proposed with proper orientation and adequate power potential. Based on the obtained results, as well as the economical aspect, inferences and suggestions are made for improvements.

Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment

Upper-room ultraviolet germicidal irradiation (UVGI) system is recently in the limelight as a potentially effective method to mitigate the risk of airborne virus infection in indoor environments. However, few studies quantitatively evaluated the relationship between ventilation effectiveness and virus disinfection performance of a UVGI system. The objective of this study is to investigate the effects of ventilation strategy on detailed airflow distributions and UVGI disinfection performance in an occupied classroom. Three-dimensional computational fluid dynamics (CFD) simulations were performed for representative cooling, heating, and ventilation scenarios. The results show that when the ventilation rate is 1.1 h−1 (the minimum ventilation rate based on ASHRAE 62.1), enhancing indoor air circulation with the mixing fan notably improves the UVGI disinfection performance, especially for cooling with displacement ventilation and all-air-heating conditions. However, increasing indoor air mixing yields negligible effect on the disinfection performance for forced-convection cooling condition. The results also reveal that regardless of indoor thermal condition, disinfection effectiveness of a UVGI system increases as ventilation effectiveness is close to unity. Moreover, when the room average air speed is >0.1 m/s, upper-room UVGI system could yield about 90% disinfection effect for the aerosol size of 1 μm–10 μm. The findings of this study imply that upper-room UVGI systems in indoor environments (i.e., classrooms, hospitals) should be designed considering ventilation strategy and occupancy conditions, especially for occupied buildings with insufficient air mixing throughout the space.

Study on multicomponent leakage and diffusion characteristics of hydrogen-blended natural gas in utility tunnels

With the rapid development of utility tunnels and hydrogen energy, hydrogen-blended natural gas (HBNG) enters gas compartments just around the corner. However, all safety requirements for gas compartments in current standards are designed for natural gas, and the applicability to HBNG is unclear. In addition, most of the existing diffusion models assume that the CH4/H2/Air mixture is single-component homogeneous gas, which cannot accurately describe the diffusion behavior differences between CH4 and H2. In this paper, an improved diffusion coefficient model for CH4/H2/Air non-ideal multi-component mixtures is proposed, which considers the interaction between CH4 and H2 components. After that, a 200 m long and narrow three-dimensional utility tunnel model is established to study the HBNG concentration distribution, alarm response time, and explosion hazardous area under different ventilation conditions. The effects of hydrogen blending ratio (HBR), leakage diameter, pipeline operating pressure, leakage location, and ventilation frequency on leakage and diffusion characteristics of utility tunnels are analyzed. The results show that under natural ventilation, the HBNG diffuses symmetrically to both sides with the leak hole as the center and covers the whole compartment after 1500 s. Normal mechanical ventilation reduces the distribution range and HBNG concentration, and the leaked gas covers the compartment downstream within 250 s. With the increase of HBR, the CH4/H2 mixture concentration increase at each monitoring point downstream of the leakage location, which causes the advance of the alarm response time. When the leakage reaches a steady state, the CH4/H2 mixture concentration for HBR of 5%, 10%, 15%, and 20% is 2.15%, 4.14%, 7.76%, and 10.97% higher than that of natural gas. The leakage location affects the hazardous area range, but little affects the CH4/H2 mixture concentration at the final steady state. The larger leakage diameter and the higher pipeline operating pressure can accelerate the HBNG diffusion rate in utility tunnels. When the pipeline operating pressure increases to 1.6 MPa, the current minimum accident ventilation frequency of 12 times/h is insufficient to reduce the CH4/H2 mixture concentration below the lower explosion limit (LEL). Increasing the ventilation frequency can effectively reduce the leaked gas concentration in utility tunnels, so it is recommended to increase the minimum accident ventilation frequency from 12 times/h to 15 times/h. The research results can guide the design and safety management of HBNG pipelines in utility tunnels.

Exergy analysis of a new spray cooling system-based PV/T and heat recovery with application in sow houses

The uncertain cooling effect and additional huge primary energy consumption caused by humidity regulation are currently the main problems of traditional environmental regulation systems in sow houses. In this study, a new spray cooling system is proposed based on PV/T and heat recovery in sow houses. Meanwhile, the mathematical models are established for its key equipment and their reliability is verified according to literature data. The results show that the maximum error is less than 14.5 % for the models. Based on the above models, the annual operation modes are determined for the new system. Specifically, its annual operation modes mainly include the cooling season, the heating season, the transitional spring and the transitional autumn. Meanwhile, the exergy loss and energy consumption are analyzed for the new system in four seasons through simulation. The results show that in the cooling and heating seasons, the exergy loss first decreases and then increases with the increase of spray power (SP) and mass flow rate of circulating water (MFRW). In the transition season, the exergy loss decreases with the increase of MFRW, while it first decreases and then increases with the increase of SP. However, the annual energy consumption increases with the increase of SP and MFRW. Aim at the minimum exergy loss of new system, its optimal control parameters are obtained in four seasons through optimization. Specifically, when the mass flow rate of supply air is the minimum ventilation rate required by sows, the optimal SP and MFRW are recommended as 40 kW and 12245 kg/h in the cooling and heating seasons, respectively. Meanwhile, they are recommended as 35 kW and 12245 kg/h in the transition season, respectively. The above research can provide guidance for the improvement of traditional spray cooling systems and the performance optimization of new system.

Performance and optimization of a new spray cooling system with PV/T and heat recovery in sow houses: A case study in Nanchang, China

The uncertain cooling effect and additional huge primary energy consumption (EC) caused by humidity regulation are currently the main problems of traditional air-conditioning systems in sow houses. In this paper, a new spray cooling system (NSCS) is developed based on PV/T and heat recovery in sow houses. Compared with traditional spray cooling systems, the cooling efficiency of new system can be significantly improved due to solar dehumidification and its EC can be reduced due to PV/T and heat recovery. Meanwhile, the mathematical models are established for its key equipment and their reliability is verified according to literature data. The results show that the maximum error is less than 7.2 % for the models. Aiming at the maximum utilization rate of cooling and heating equipment, the annual operation modes are determined for NSCS based on the above models. The results show that cooling season is from May 21st to September 25th, heating season is from January 1st to March 16th and from November 1st to December 31st, and the transitional spring and autumn are from March 17th to May 20th and from September 26th to October 31st, respectively. Meanwhile, the optimal spray cooling power (SCP) and mass flow rate of circulating water (MFCW) are obtained by analyzing the operation characteristics of NSCS in cooling and heating seasons. The results show that in cooling and heating seasons, it is suggested to use the minimum ventilation required by sows (42763.5 kg/h) for the ventilation rate of NSCS. Meanwhile, the optimal SCP and MFCW are recommended as 40 kW and 12245 kg/h, respectively. Finally, the matching between exergy efficiency (EE) and EC is analyzed for NSCS in transition season through simulation. The operational control methods are further proposed for NSCS in transition season through optimization. The results show that in transition season, increasing mass flow rate of supply air (MFSA) and reducing equipment power are the operational control methods to obtain the optimal performance and minimum EC of NSCS. Specifically, in the transitional spring, the optimal MFSA, SCP and MFCW are recommended as 47812.0 kg/h, 30 kW and 10245 kg/h, respectively. In the transitional autumn, they are recommended as 55806.3 kg/h, 25 kW and 7245 kg/h, respectively. The above conclusions can provide new ideas for the development of new energy-saving air-conditioning systems in sow houses, and guide the operation control and performance optimization of NSCS.

Factors affecting multiple chemical sensitivity (MCS) in newly constructed apartments of Indonesia

In Indonesia, sick building syndrome (SBS) and related health problems possibly caused by chemicals are suspected among residents in newly constructed urban houses, in which modern building materials are used without sufficient material standards and the minimum ventilation rates. This paper analyzes the causal relationships of factors affecting multiple chemical sensitivity (MCS) in urban houses in Indonesia. The measured IAQ data from three major cities of Indonesia (n = 207) were calibrated, and a structural equation modeling (SEM) was performed to identify the factors affecting MCS from a questionnaire survey in apartments and Kampong (n = 896). The results showed that the respondents living in a higher concentration of either formaldehyde or TVOC tended to have higher MCS risk, especially in the apartments. Overall, the apartments exhibited poor air quality rates, with the average maximum values of 0.172 ppm formaldehyde and 1.64 mg/m3 TVOC, potentially resulting in allergic problems and MCS risk among residents. In Kampongs, the building age was observed to increase the dampness, thereafter possibly causing allergies and MCS among residents. The results of this study implied that higher MCS in the apartments was majorly affected not only by their allergic conditions but also by additional factors concerning building attributes and occupant behavior.

A CFD-based framework to assess airborne infection risk in buildings

The COVID-19 pandemic has prompted huge efforts to further the scientific knowledge of indoor ventilation and its relationship to airborne infection risk. Exhaled infectious aerosols are spread and inhaled as a result of room airflow characteristics. Many calculation methods and assertions on risk assume ‘well-mixed’ flow conditions. However, ventilation in buildings is complex and often not showing well-mixed conditions.Ventilation guidance is typically based on the provision of generic minimum ventilation flow rates for a given space, irrespective of the effectiveness in the delivery of the supply air. Furthermore, the airflow might be heavily affected by the season, the HVAC ventilation, or the opening of windows, which would potentially generate draughts and non-uniform conditions. As a result, fresh air concentration would be variable depending upon a susceptible receptor's position in a room and, therefore, associated airborne infection risk.A computational fluid dynamics (CFD) and dynamic thermal modelling (DTM) framework is proposed to assess the influence of internal airflow characteristics on airborne infection risk. A simple metric is proposed, the hourly airborne infection rate (HAI) which can easily help designers to stress-test the ventilation within a building under several conditions. A case study is presented, and the results clearly demonstrate the importance of understanding detailed indoor airflow characteristics and associated concentration patterns in order to provide detailed design guidance, e.g. occupancy, supply air diffusers and furniture layouts, to reduce airborne infection risk.

Investigation on Minimum Ventilation, Heating, and Energy Consumption of Pig Buildings in China during Winter

Ventilation and heating can be necessary for pig production during winter in China. However, it is challenging to balance the ventilation rate and heat loss due to the ventilation. Therefore, it is essential to design the minimum ventilation and heating load properly in order to reduce energy loss. In this paper, a VBA (Visual Basic for Applications) model based on energy balance is established. Meteorological data, pig body masses, outdoor temperatures, feeding densities, and building envelope thermal insulance factors were involved in the model. A model pig house with a length and width of 110 m × 15 m was used to investigate the ventilation, heating time, load, and power consumption in different climate zones, i.e., Changchun, Beijing, Nanning, Wuhan, and Guiyang, representing five major climate regions in China. Based on the simulation results, the models of minimum ventilation and heating load were fitted. The results showed that there is a logarithmic relationship between the minimum ventilation volume and body mass, R2 = 0.9673. The R2 of heating load models for nursery pigs and fattening pigs were 0.966 and 0.963, respectively, considering the feeding area, the outside temperature, the body masses of the nursery and fattening pigs, and the thermal insulance factor of the enclosure. The heating requirements of commercial pig houses within the same building envelope followed the trend in Changchun &gt; Beijing &gt; Guiyang &gt; Wuhan &gt; Nanning. Increasing the building envelope’s thermal insulance factor or using precision heating could reduce the pig house’s power consumption. The analysis of the heating load and energy consumption of winter pig houses in various climate regions provided a reference for precise environmental control and the selection of building thermal insulance factors in China.