Hua Qian

Natural ventilation for reducing airborne infection in hospitals

Abstract High ventilation rate is shown to be effective for reducing cross-infection risk of airborne diseases in hospitals and isolation rooms. Natural ventilation can deliver much higher ventilation rate than mechanical ventilation in an energy-efficient manner. This paper reports a field measurement of naturally ventilated hospital wards in Hong Kong and presents a possibility of using natural ventilation for infection control in hospital wards. Our measurements showed that natural ventilation could achieve high ventilation rates especially when both the windows and the doors were open in a ward. The highest ventilation rate recorded in our study was 69.0 ACH. The airflow pattern and the airflow direction were found to be unstable in some measurements with large openings. Mechanical fans were installed in a ward window to create a negative pressure difference. Measurements showed that the negative pressure difference was negligible with large openings but the overall airflow was controlled in the expected direction. When all the openings were closed and the exhaust fans were turned on, a reasonable negative pressure was created although the air temperature was uncontrolled. The high ventilation rate provided by natural ventilation can reduce cross-infection of airborne diseases, and thus it is recommended for consideration of use in appropriate hospital wards for infection control. Our results also demonstrated a possibility of converting an existing ward using natural ventilation to a temporary isolation room through installing mechanical exhaust fans.

An evaluation of the ventilation performance of new SARS isolation wards in nine hospitals in Hong Kong

In response to the 2003 outbreak of severe acute respiratory syndrome (SARS) the Hong Kong Government promptly constructed 558 new state-of-the-art SARS isolation rooms with more than 1300 beds in 14 hospitals. These were completed by the end of 2003 and some will be available for H5N1 influenza patients, if any human cases occur. We investigated the ventilation of the wards after 18 months of operation and identified the major factors that affect ventilation effectiveness. Negative pressure, airflow path, air change rate and local ventilation effectiveness in selected rooms in 9 major hospitals were measured and their performance assessed against CDC requirements. Testing in 38 rooms found that 97% met the recommended negative pressure difference of 2.5 Pa between corridor and anteroom, 89% of 48 met the same requirement between anteroom and cubicle. No leakage of air to the corridor was found, but 60% of the toilets/bathrooms were operated under positive pressure. Over 90% of corridor-anteroom or anteroom-cubicle doors had bi-directional flow when the door was open. Of 35 tested cubicles, 26% had an air change rate <12 ACH and their ventilation was non-uniform. Despite using state-of-the-art technologies, 28% of the rooms tested still failed to meet the 12 ACH ventilation requirement and 60% had the wrong airflow direction for the toilets/bathrooms, but all satisfied the requirement of no air leakage to the corridor. Regular checks of airflow direction and air change rate are highly recommended together with specific education or training of hospital maintenance engineers and health care workers.

Common cold among pre-school children in China - associations with ambient PM10 and dampness, mould, cats, dogs, rats and cockroaches in the home environment

BACKGROUND There is some evidence that dampness, mould and cockroaches can increase the risk of respiratory infections in children but few studies exist from China on this topic. Aim To study associations between domestic early life exposure to biological indoor factors (dampness, mould, cats, dogs, rats, cockroaches), cleaning habits and common cold among pre-school children across China. METHODS Children aged 3-6years (n=39,782) were recruited from randomly selected day care centres in seven cities in China. Data on common cold and prenatal and postnatal exposure to dampness, mould, windowpane condensation in wintertime (WPC), cats, dogs, cockroaches and rats were assessed by a parentally administered questionnaire. Data on annual ambient temperature and PM10 was assessed on city level. Associations between high frequency (>5 colds per year) and long duration (≥2weeks) of common colds in the past year and exposure were calculated by multilevel logistic regression. RESULTS A total of 9.2% had a high frequency and 11.9% had long duration of common cold. Exposure to mould (OR=1.38, 95% CI 1.24-1.53) and WPC (OR 1.23, 95%CI 1.13-1.33) at birth was associated with frequent common cold. Exposure to dogs at birth was associated with long duration of common cold. (OR=1.22, 95% CI 1.06-1.41). Exposure to mould (OR=1.36, 95% CI 1.22-1.54), WPC (OR=1.27, 95%CI 1.17-1.39) and water leakage (OR 1.34, 95% CI 1.20-1.49) in the current home was associated with frequent common cold. Presence of cockroaches were positively (OR=1.12, 95% CI 1.02-1.24) and presence of rats (OR=0.86, 95% CI 0.77-0.96) negatively associated with high frequency of common cold. Daily cleaning was negatively associated with frequent common cold (OR=0.89, 95% CI 0.81-0.97). Similar associations for mould, WPC, cockroaches and rats were found for long duration. Ambient PM10 (OR=1.21, 95% CI 1.21-1.35 per 10μg/m3) and temperature (OR=1.13, 95% CI 1.06-1.35 °C) on city level were associated with high frequency of common cold. Associations between cat keeping and high frequency of common cold were found only in southern China. Associations with cockroaches were stronger in northern China. Associations with dampness and mould were the same in the north and south. CONCLUSIONS Indoor mould, water damage, windowpane condensation, cockroaches and keeping cats or dogs as pets can be risk factors for common cold while daily cleaning can be protective factor. PM10 and a warmer climate zone can be other risk factors for common cold.

Seasonal variation of window opening behaviors in two naturally ventilated hospital wards

Abstract Natural ventilation enables personal control, and occupant behaviors in window opening play a decisive role on natural ventilation performance, indoor air quality (IAQ), and/or airborne infection risk in a hospital setting. The occupant behaviors differ significantly from different building types with different functions and living habits. Based on a one-year field measurement in two general hospital wards in Nanjing, China, the effects of air quality (i.e. indoor CO2 concentration and outdoor PM2.5 concentration) and the climatic parameters (i.e. indoor/outdoor temperature, relative humidity, and outdoor wind speed, wind direction and rainfall) on window opening/closing behaviors are analyzed. Indoor air temperature or relative humidity is found to be a dominant factor for window opening behaviors. Seasonal differences are observed for the different influences of physical factors. The outdoor temperature is found to be associated with the window opening probability negatively during the cooling season, but positively during the transition and heating seasons. The indoor relative humidity positively affects the window opening probability during the transition season while a negative impact appears during the cooling and heating seasons. Based on the seasonal variation of window opening behaviors, Logistic regression models in different seasons (cooling, transition and heating seasons) are developed to predict the window opening/closing state and are verified to be promisingly adaptable with results of accuracy bigger than 70%.

Associations between Parents’ Perceived Air Quality in Homes and Health among Children in Nanjing, China

The increasing prevalence of respiratory diseases in Chinese children has focused attention on indoor environmental quality. We investigated associations between perceived air quality in domestic environments and children’s allergic diseases with a questionnaire survey study. A total of 4017 children aged 1–8 years old from 23 kindergartens in urban, suburban and industrial areas in Nanjing were randomly recruited for this study. Parents’ perceived odors, including stuffy odor, unpleasant odor, pungent odor, moldy odor, humid air and dry air were found to be associated with asthma, wheeze, dry cough and rhinitis (P < 0.05). Both perceived dry and humid air were found to be positively associated with dampness indices, and we present evidence that the sensation of dryness may not be due to the actual indoor relative humidity, but rather to indoor air irritants. Parents’ perception of odors and relative humidity may be indicators of environment pollutants, which are likely the real factors associated with children’s allergic diseases.

Experimental Assessment on Heat Transfer and Smoke Flow Characteristics of a Typical Elevated Chinese Kang

Chinese kangs are widely used by 175 million people for sleeping and home heating in rural Northern China. However, there are lack of some basic and critical studies on heat transfer and smoke flow characteristics of the kangs, which definitely hinder the development of Chinese kangs. This study presents an experimental assessment on a typically elevated Chinese kang. The heat gain, heat storage, and the heat release performance of the kang body are investigated, respectively, by combining the test data and theoretical analysis. The main results show that the smoke temperature at the inlet face of the kang flue varies within 250°C–600°C as the stove works for the most times. The smoke velocity in the kang flue is about 0.1 m/s–0.4 m/s, and the flow status is determined to be turbulent. The heat exchange between the smoke and the kang plates is mainly by natural convection. The surface temperature of the upper kang plate has significant temporal variation, and its distribution at the center part is reasonably uniform. The radiative heat from the kang plates plays a big role in the total heat release, accounting for 60.6% for the upper plate and 83.3% for the lower plate.

A survey investigation of the associated effect of using air conditioning equipment on children’s health in Nanjing

A questionnaire study was conducted in Nanjing from December 2010 to March 2011 to evaluate the association of children’s health with the use of air conditioning equipment at their homes. The questionnaire was issued to parents of 4017 children aged 1–8 years old studying at 23 kindergartens located all over Nanjing in eight urban districts, two suburban districts and one industrial district. The parents of the children participated in the study filled in the questionnaire to provide information about the children’s health, home characteristics and their use of air conditioning equipment. Most families included in the study have air conditioners (91.7%) installed in their homes. Only 13.4% and 2.2% of families studied have humidifiers and air cleaners, respectively. The use of air conditioner was found to be associated with children that had pneumonia (Adjusted Odds Ratio (AOR): 1.46 (1.08–1.98), P < 0.05). The use of the humidifier was found to be associated with children having diagnosed asthma (AOR: 1.37 (1.01–1.86), P < 0.05) and rhinitis symptoms (AOR: 1.28 (1.06–1.55), P < 0.05). The use of air cleaner was also found to be associated with children having diagnosed asthma (AOR: 1.94 (1.07–3.50), P < 0.05). The use of air conditioning equipment was therefore found to be related to children that had or being experienced allergic respiratory diseases.

The Geothermal Field Analysis of Cooling and Heating Load Imbalance for GSHP

This paper developed a heat transfer model of the underground pipe group to study the effect of cooling and heating load imbalance to geothermal field. The results show that, there are the approximate linear relationship between average soil temperature and the total heat flow provided by GSHP system to the soil during the whole running period. The temperature of soil restoration ratio is less than the heat flux ration in the spring and autumn. Simulation results show that when heating/ cooling load equal to 0.5 and the heating flux for the bore hole are 60w/m and -40w/m in the Summer and Winter respectively, after this system run 12 months and 10 hours every day, the average soil temperature around borehole will increase 0.48°C, and the soil close borehole temperature will increase 1.3°C than the initial soil average temperature with the value of 17.6°C, which make GSHP not be efficiently for long term running. The results is hoped to be useful for GSHP design and long term running.

Surface Temperature Distribution of Chinese Kangs

This study is attempted to improve local thermal comfort of Chinese kang through improving the uniformity of the faceplate temperature distribution using computational fluid dynamics simulations. The faceplate temperature of kangs is determined by the heat input to the kangs, the smoke flows, and the kang body materials. The smoke flow rate and the kang body temperature are coupled. The distribution of the faceplate temperature is determined by the interior structure and smoke flow path design. In addition to a recent experimental study using infrared thermal imaging, this study uses computational fluid dynamics simulations to analyze in detail the heat transfer and smoke flow processes in a typical Chinese kang. Different design methods for improving temperature distribution of the kang faceplate are compared. Our results show that the temperature distribution on the faceplate of kang can be made to be more even using simple variations in its design.

Numerical investigation of airborne infection in naturally ventilated hospital wards with central-corridor type

Natural ventilation is believed to control airborne infection due to high ventilation rates while an undesired flow pattern may cause infection transmission in hospital wards. A computational fluid dynamics simulation was carried out in this study to investigate the impact of airflow pattern on cross infection in a real central-corridor hospital ward with natural ventilation in Nanjing, China. The simulation results demonstrate that the predicted infection risks of the downstream cubicle are up to 10.48% and 11.59% as the index patient is located in the corridor and in the opposite upstream cubicle, respectively. Under this circumstance, the downstream cubicle should be listed on the high-risk list and the central-corridor type is not recommended in a naturally ventilated ward. Measures such as keeping cubicle doors closed should be taken in order to cut off the transmission route. The results not only give direct evidence to strongly support World Health Organization’s recommendation but also suggest required amendment of the Chinese standard GB 51039-2014 to improve ventilation arrangement in general hospital wards in China. Our findings are useful for improving the future design of general hospital wards for airborne infection control.