Indoor air quality assessment in dwellings with different ventilation strategies in Nunavik and impacts on bacterial and fungal microbiota

Indoor air quality is a major issue for public health, particularly in northern communities. In this extreme environment, adequate ventilation is crucial to provide a healthier indoor environment, especially in airtight dwellings. The main objective of the study is to assess the impact of ventilation systems and their optimization on microbial communities in bioaerosols and dust in 54 dwellings in Nunavik. Dwellings with three ventilation strategies (without mechanical ventilators, with heat recovery ventilators, and with energy recovery ventilators) were investigated before and after optimization of the ventilation systems. Indoor environmental conditions (temperature, relative humidity) and microbiological parameters (total bacteria, Aspergillus/Penicillium, endotoxin, and microbial biodiversity) were measured. Dust samples were collected in closed face cassettes with a polycarbonate filter using a micro-vacuum while a volume of 20 m³ of bioaerosols were collected on filters using a SASS3100 (airflow of 300 L/min). In bioaerosols, the median number of copies was 4.01 × 10³ copies/m³ of air for total bacteria and 1.45 × 10¹ copies/m³ for Aspergillus/Penicillium. Median concentrations were 5.13 × 10⁴ copies/mg of dust, 5.07 × 10¹ copies/mg, 9.98 EU/mg for total bacteria, Aspergillus/Penicillium and endotoxin concentrations, respectively. The main microorganisms were associated with human occupancy such as skin-related bacteria or yeasts, regardless of the type of ventilation.     

Thermal storage performance analysis on Chinese kangs

Chinese kangs are widely used as a rural home heating system in Northern China by 175 million people. The main features of Chinese kangs include the effective use of thermal mass in kang plate. In this paper, a thermal and airflow model for an elevated kang is developed with a simply consideration of the heat transfer in building envelope. Approximate analytical formulas are derived to identify the critical parameters that affect the levels and fluctuations of kang plate temperature and indoor air temperature. It can be observed that the increase of the plate time constant and the heat source frequency with continuous firings and equally distributing the firings and adding the number of firing with intermittent firings can effectively decrease the fluctuation of kang plate temperature and indoor air temperature. The results of model analytical solutions can serve engineers for design proposals or check analysis to determine the required thermal capacity of kang plate at the early design stage. An example of heat source-based design process is described to determine the thickness of a kang plate and firing distribution.     

Three dimensional study for evaluating of air flow movements and thermal comfort in a model room: Experimental validation

This paper presents the results of a three dimensional study for evaluating the temperature profiles and air flow movement in a model room with a numerical model based on the Euler equations. Numerical results obtained for two scenarios of ventilation and air conditioning are compared with the predictions of a Navier-Stokes model. These numerical results are validated by experimental results measured in the model room. A comparison of the local thermal comfort indices PMV and PPD obtained experimentally and numerically is also presented. Results show that the Euler model is able to predict adequately total thermal comfort in the model room. Furthermore, the use of Euler equations allows a reduction of computational time in the order of 50% compared to the Navier-Stokes modeling.     

Impact of heat load location and strength on air flow pattern with a passive chilled beam system

A passive chilled beam is a source of natural convection, creating a flow of cold air directly into the occupied zone. Experiments were conducted in a mock-up of an office room to study the air velocities in the occupied spaces. In addition, velocity profiles are registered when underneath heat loads exist and the cool and warm air flows interact. Experimental laboratory study revealed that in the case of the underneath heat gains, even no upward plume was generated and the dummy only acted as a flow obstacle, having a significant effect on the velocity profile. Furthermore, in an actual occupied office environment, the thermal plumes and the supply air diffuser mixed effectively the whole air volume. The maximum air velocity measured was still below 0.25 m/s with the extremely high heat gain of 164 W/m². The results demonstrate that analysis methods were the interaction of convection flow and jet are not taken into account could not accurately describe air movement and draught risk in the occupied room space.     

Study on the performance of a solar assisted air source heat pump system for building heating

This paper proposed a new solar assisted air source heat pump system with flexible operational modes to improve the performance of the heating system. A mathematical model was established on the solar assisted air source heat pump system for building heating with a heating capacity of 10 kW, and an air source heat pump unit was developed to validate the model. The effect of the solar collector area on the performance of the system running in Nanjing was studied. The results showed that the COP of the heat pump unit was enhanced with the increase of the solar radiation density during the typical sunny day in the heating season. In addition, the COP also increased in proportion to the solar collector area. Compared with the case when the solar collector area was 0 m², the COP increase of the heat pump and the energy-saving rate were 11.22% and 24% respectively when the solar collector area was 40 m². Meanwhile, the solar equivalent generation power efficiency could reach 11.8%.     

The effect of air-conditioning parameters and deposition dust on microbial growth in supply air ducts

To investigate the effect of air-conditioning parameters (including temperature, relative humidity and air velocity) and deposition dust on microbial growth in supply air duct, a complete test facility according to ASHRAE Standard 62.1-2007 was constructed. A series of experiments for testing microbial concentration (including bacteria and fungus) were conducted under different working conditions (such as different temperatures and relative humidity). The air velocity was constantly kept at 2.0 m/s. Orthogonal design was employed for the analysis of test data. The results indicated that air velocity attenuation down the direction of the supply air affected dust distribution at the bottom of duct, to some extent, and the number of microorganisms was positively correlated with the quantity of dust. In the range of temperature 22-32 °C and relative humidity (RH) 40-90%, microbial growth significantly accelerated with higher temperature and RH increasing. The organic compounds composing the dust also had great impact on microbial growth. The basic researches are contributed to control the growth of microorganism and improve the indoor microenvironment in the air-conditioning room.     

Experimental study of the effects of a thermal plume entrainment mode on the flow structure: Application to fire

The aim of this work is to experimentally simulate two heat sources of fire, one placed at ground level, the other at a height above the ground, in order to determine the effect of source air entrainment on the resulting flow structure. The development of a free thermal plume was examined by generating a plume produced from an electrically heated disk at a constant temperature. We first studied the behavior of a thermal plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the plume. The analysis of the average fields as well as the axial evolution of velocity and temperature showed an important widening of the profiles that encouraged a faster spread of the plume. We then determined the structure of the thermal plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting plume.     

Effects of turbulent air on human thermal sensations in a warm isothermal environment

Air movement can provide desirable cooling in "warm" conditions, but it can also cause discomfort. This study focuses on the effects of turbulent air movements on human thermal sensations through investigating the preferred air velocity within the temperature range of 26 degrees C and 30.5 degrees C at two relative humidity levels of 35% and 65%. Subjects in an environmental chamber were allowed to adjust air movement as they liked while answering a series of questions about their thermal comfort and draft sensation. The results show that operative temperature, turbulent intensity and relative humidity have significant effects on preferred velocities, and that there is a wide variation among subjects in their thermal comfort votes. Most subjects can achieve thermal comfort under the experimental conditions after adjusting the air velocity as they like, except at the relative high temperature of 30.5 degrees C. The results also indicate that turbulence may reduce draft risk in neutral-to-warm conditions. The annoying effect caused by the air pressure and its drying effect at higher velocities should not be ignored. A new model of Percentage Dissatisfied at Preferred Velocities (PDV) is presented to predict the percentage of feeling draft in warm isothermal conditions.     

The effects of changes in cadmium and lead air pollution on cancer incidence in children

This article presents the results of research on the effects of air pollution on cancer incidence in children in the region of Silesia (Poland), which has undergone one of the most profound anthropogenic transformations in Europe. The main objective of the research was to specify the impact of changes in cadmium and lead pollution in the years 1990-2005 on the incidence of cancers reported in children. Lead concentration ranged from 0 to 1490 · 10^-9 G m⁻²/year, and cadmium concentration ranged from 0 to 33.7 · 10^-9 G  m⁻²/year. There was no strong significant correlation (max 0.3) between air pollution and incidence rate (IR) in the general population of children in any particular year. Alongside the cartographic presentation of dependences, correlation coefficients between the variables in question were calculated. This made it possible to determine the relationship between the pollution levels and incidence rates in the area. There was a significant reduction in the level of pollution during the investigated period. The study of the relationship between the number of cancers reported and the condition of the natural environment revealed increased sensitivity to toxins in boys (correlation coefficient 0.3). In addition, the spatial distribution of the number of cases reported in boys suggests a correlation with the spatial distribution of the coefficients for the entire group of children included in the study. The yearly average IR of childhood cancer in specific districts ranged from 0 to 61.48/100,000 children under 18 years of age during the 1995-2004 period.     

Impact of urban geometry on outdoor thermal comfort and air quality from field measurements in Curitiba,Brazil

Urban climate can have severe impacts on people who use outdoor spaces within a city. In its essence, urban climate is directly linked to the configuration of street axes, building heights and their attributes. Thus, the role of urban planners can be crucial for guaranteeing outdoor thermal comfort and air quality in open spaces. This paper presents observed and estimated relations between urban morphology and changes in microclimate and air quality within a city center. Two approaches are presented, showing results of field measurements and urban climate simulations using the ENVI-met software suite. From measured microclimatic data and comfort surveys, carried out in downtown Curitiba, Brazil, the impact of street geometry on ambient temperatures and on daytime pedestrian comfort levels was evaluated, using the sky-view factor (SVF) as indicator of the complexity of the urban geometry. The impact of street orientation relative to prevailing winds and the resulting effects of ventilation (air speed and spatial distribution) on the dispersion of traffic-generated air pollutants were additionally analyzed by means of computer simulations. Results show the impact of urban geometry on human thermal comfort in pedestrian streets and on the outcomes of pollutant dispersion scenarios.     

Thermal performance analysis according to wood flooring structure for energy conservation in radiant floor heating systems

The aim of this study was to reduce energy consumption, especially heating, in buildings. Improvements in the thermal conductivity of wood flooring, which was considered to decrease heating between floors and the indoor areas, were investigated. Wood flooring components such as solid-wood, high-density fiberboard (HDF), adhesives and polyethylene generally exhibit low thermal conductivity. The thermal conductivity and transfer performance of 21 replicates of wood flooring materials generally used in Korea were measured. The thermal conductivity was measured by using the guarded hot plate method. The thermal conductivities differed according to the structure of the floorings. Laminate wood flooring exhibited the highest thermal conductivity because of its high density and thin layers compared to the other floorings. The thermal transfer performance differed according to the installation method. The floating installation method exhibited a lower thermal transfer speed than the adhesion installation method because of its air layers and polyethylene form.     

Research on seasonal indoor thermal environment and residents' control behavior of cooling and heating systems in Korea

Indoor thermal environments and residents' control behavior of cooling and heating systems were investigated in Seoul, Korea and compared with the results of previous studies. Twenty-four houses in summer, six houses in autumn and 36 houses in winter were used in this study. The measurement of temperature, humidity and air conditioner usage behavior was carried out. The clo-value, thermal comfort, sensation and basic data of the houses were also investigated. The indoor thermal environment in the summer had a high temperature and a high humidity ratio compare to standard comfort zone. Most of the indoor thermal environments at the time of starting the air conditioner in the summer were out of the comfort zone. Some of the data recorded while the air conditioner was stopped were in the comfort zone, but in many cases the temperature was relatively higher than comfort zone. Most indoor climate distributions in the winter were in the comfort zone and the indoor climate in autumn coincided well with the criteria of the comfort zone. Compared with results of previous studies in these 25 years, indoor ambient average temperature in winter has increased and the comfort temperature has increased in the heating period and decreased in the cooling period. This result indicates that the development of an HVAC system has created an expectation of comfort for residents and has shifted their thermal comfort zone warmer in winter and cooler in summer.     

城市综合体酒店客房空调新风设计探讨

本文结合工程实际和现场情况,对热泵式溶液调湿新风处理机组,转轮式热回收机组,板翅式显热回收机组和三维热管热回收机组的特点进行了比较。详细分析了在设计城市综合体酒店客房的空调新风时,如何合理选择热回收设备,保证系统运行稳定、可靠,节能效果明显,是设计成功的关键。     

Effect of uneven building layout on air flow and pollutant dispersion in non-uniform street canyons

Uneven building layouts and non-uniform street canyons are common in actual urban morphology. To study the effects of building layouts on air flow in non-uniform street canyons, various building arrangements are designed in this study. Simulations are carried out under four cases (i.e., a uniform street canyon as Case 1 and three non-uniform canyons as Cases 2–4) with parameter change of the occupying ratio of high buildings (ORHB) in the computational domain and their bilateral allocation as well as the combinations of stepup and/or stepdown notches. In the three non-uniform canyons, stepup and stepdown notches are separating (with ORHB of 25% for Case 2 and 75% for Case 4) or adjoining (with ORHB of 50% for Case 3). The air flow and pollutant dispersion in these street canyons are investigated using Large-eddy Simulation (LES). The air flow structures in the non-uniform street canyons are more complicated than in the uniform street canyon. Inside the non-uniform street canyons, the tilting, horizontal divergence and convergence of wind streamlines are found. Large-scale air exchanges of air mass inside and above the street canyons are found as well. At the pedestrian level, the concentrations of simulated pollutants (e.g., the mean and maximum concentrations) in the non-uniform street canyons are lower than those in the uniform one, suggesting that uneven building layouts are capable of improving the dispersion of pollutants in urban area. Further studies on Case 2–4 show that the separation of stepup and stepdown notches along the street increases the wind velocities in the vicinity of high buildings, while the adjoining of stepup and stepdown notches decreases the wind velocities. Low concentrations of pollutant at the pedestrian level are found in Case 2 compared to Cases 3 and 4. Thus, the separation of stepup and stepdown notches in non-uniform street canyons might be a good choice for uneven building layout arrangements from the point of view of pollutant dispersion and human health.     

Enabling the hybrid use of air conditioning: A prototype on sustainable housing in tropical regions

This paper demonstrates how the use of active or passive means only does not give the appropriate answers to a tropical design when considering housing. The author discusses about the idea of both modes of operation being used simultaneously or in parallel, and how this concept has been developed for one experimental building prototype in tropical areas of Brazil (Northeast region). Quantification is given through extensive parametric simulations which have been conducted using different environmental simulation programmes—TAS (EDSL, UK), ESP-r (ESRU, UK) and photovoltaic (PV)-Design PRO-G (Sandia Labs, USA). Thermal comfort levels along with energy use were assessed and compared, in terms of degree hours of overheating/under heating and cooling energy use. The prototype design has also taken into account the appropriate use of resources through sustainable design features: efficient use of energy, water and materials. The results have demonstrated that for regions such as the warm-humid tropics, the use of a mixed running strategy have optimized energy performance and provided better levels of thermal comfort in a much more effective way. For some cases, cooling energy savings up to 80% were feasible on a hybrid mode, where thermal comfort was improved up to 65%. It has also demonstrated the integration of energy efficiency and a PV grid-connected system, while enabling those daytime electrical needs to be accomplished by the photovoltaic component.     

Eggcrate UV: a whole ceiling upper‐room ultraviolet germicidal irradiation system for air disinfection in occupied rooms

A novel whole ceiling upper‐room ultraviolet germicidal irradiation (UVGI) system [eggcrate ultraviolet (UV)] has been developed that incorporates open‐cell ‘eggcrate’‐suspended ceiling panels and bare UV lamps with a ceiling fan. Upper‐room UVGI is more effective for air disinfection than mechanical ventilation at much lower installation and operating costs. Conventional upper‐room UVGI fixtures employ multiple tightly spaced horizontal louvers to confine UV to the upper‐room. These louvered fixtures protect occupants in the lower‐room from UV‐induced eye and skin irritation, but at a major cost to fixture efficiency. Using a lamp and ballast from a conventional upper‐room UVGI fixture in the eggcrate UV system, the germicidal efficacy was markedly improved even though the UV radiation emitted by the lamp was unchanged. This fundamental change in the application of upper‐room UVGI air disinfection should permit wider, more effective application of UVGI globally to reduce the spread of airborne infection.     

Differential effects of air conditioning type on residential endotoxin levels in a semi‐arid climate

Residential endotoxin exposure is associated with protective and pathogenic health outcomes. Evaporative coolers, an energy‐efficient type of air conditioner used in dry climates, are a potential source of indoor endotoxins; however, this association is largely unstudied. We collected settled dust biannually from four locations in homes with evaporative coolers (n=18) and central air conditioners (n=22) in Utah County, Utah (USA), during winter (Jan‐Apr) and summer (Aug‐Sept), 2014. Dust samples (n=281) were analyzed by the Limulus amebocyte lysate test. Housing factors were measured by survey, and indoor temperature and relative humidity measures were collected during both seasons. Endotoxin concentrations (EU/mg) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons. Endotoxin surface loads (EU/m²) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons and in upholstered furniture during winter. For the nine significant season‐by‐location comparisons, EU/mg and EU/m² were approximately three to six times greater in homes using evaporative coolers. A plausible explanation for these findings is that evaporative coolers serve as a reservoir and distribution system for Gram‐negative bacteria or their cell wall components in homes.     

生土建筑物理环境研究——以豫西陕县天井窑洞为例

不同的生态环境、地理气候条件决定着其区域的建筑形式,豫西天井窑洞是适应黄土高原气候的一种生土建筑.生土建筑的环境问题一直是建筑学关注的重大课题,而其物理环境的研究则是最基本的研究,该文通过对其室内热舒适度的考察、测定、比较采分析其居住的舒适性,希望对改善当地窑居环境和条件提供一些理论数据和建议.     

对集中空调冷却水系统变流量的思考

回顾了《暖通空调》近年来所发表的若干关于集中空调冷却水系统变频节能方面的论文，认为集中空调冷却水系统变流量运行对空调系统的节能具有积极意义，但节能收益有待于深入研究。