Ventilation characteristics of an air-conditioned office building in Singapore

The primary functions of mechanical ventilation systems include the delivery of outdoor air to the occupants, the removal of indoor contaminants and the maintenance of thermal comfort conditions in the occupied zones. Air exchange effectiveness can be employed to characterise the ventilation air mixing within a room. This paper presents our findings pertaining to air exchange effectiveness values in a seven-storey office building. Tracer gas analysis, based on concentration decay method, is employed to determine these values. The results indicate air flow patterns in the occupied zones which approximate “perfect mixing”. The measured concentration levels of indoor air pollutants are also found to be within reasonable limits.     

Air Change Effectiveness Measurements in Two Modern Office Buildings

Local age of air and air change effectiveness were determined in two office buildings using tracer gas techniques to study the applicability of the associated measurement procedures in mechanically ventilated office buildings. Measurement issues examined include the establishment of a uniform tracer gas concentration at the start of the test and the relationship of ventilation system configuration and system operation to the test procedure. Air change effectiveness was determined at locations in the occupied space based on the local age of air at that location and the age of air in the corresponding ventilation system return duct. Values of the air change effectiveness in the occupied space were generally close to one, which is consistent with good mixing of the Ventilation air within the occupied space. Deviations from 1.0, on the order of 10%, did occur, but given the limited experience with these measurement procedures in the field it is not clear whether these deviations are significant. These tests provide data on air change effectiveness to supplement the limited database on mechanically ventilated office buildings in the US. In addition, the experience obtained with the measurement procedures will assist in the development of a standardized approach to measuring air change effectiveness in the field.     

Dynamic evaluation of airflow rates for a variable air volume system serving an open-plan office

In a typical air-conditioned office, the thermal comfort and indoor air quality are sustained by delivering the amount of supply air with the correct proportion of outdoor air to the breathing zone. However, in a real office, it is not easy to measure these airflow rates supplied to space, especially when the space is served by a variable air volume (VAV) system. The most accurate method depends on what is being measured, the details of the building and types of ventilation system. The constant concentration tracer gas method as a means to determine ventilation system performance, however, this method becomes more complicated when the air, including the tracer gas is allowed to recirculate. An accurate measurement requires significant resource support in terms of instrumentation set up and also professional interpretation. This method deters regular monitoring of the performance of an airside systems by building managers, and hence the indoor environmental quality, in terms of thermal comfort and indoor air quality, may never be satisfactory. This paper proposes a space zone model for the calculation of all the airflow parameters based on tracer gas measurements, including flow rates of outdoor air, VAV supply, return space, return and exfiltration. Sulphur hexafluoride (SF6) and carbon dioxide (CO2) are used as tracer gases. After using both SF6 and CO2, the corresponding results provide a reference to justify the acceptability of using CO2 as the tracer gas. The validity of using CO2 has the significance that metabolic carbon dioxide can be used as a means to evaluate real time airflow rates. This approach provides a practical protocol for building managers to evaluate the performance of airside systems.     

Ventilation efficiencies of desk-mounted task/ambient conditioning systems

In laboratory experiments, we investigated two task/ambient conditioning systems with air supplied from desk-mounted air outlets to efficiently ventilate the breathing zone of heated manikins seated at desks. In most experiments, the task conditioning systems provided outside air while a conventional ventilation system provided additional space cooling but no outside air. Air change effectiveness (i.e., exhaust air age divided by age of air at the manikin's face) was measured with a tracer gas step-up procedure. Other tracer gases simulated the release of pollutants from nearby occupants and from the floor covering, and the associated pollutant removal efficiencies (i.e., exhaust air concentrations divided by concentrations at manikin's face) were calculated. High values of air change effectiveness (approximately 1.3 to 1.9) and high values of pollutant removal efficiency (approximately 1.2 to 1.6) were measured when these task conditioning systems supplied 100% outdoor air at a flow rate of 7 to 9 L s-1 per occupant. Air change effectiveness was reasonably well correlated with the pollutant removal efficiency. Overall, the experimental data suggest that these task/ambient conditioning systems can be used to improve ventilation and air quality or to save energy while maintaining a typical level of IAQ at the breathing zone.     

自然通风环境下办公建筑中庭空间热舒适性模糊优化研究

：随着绿色建筑设计理念深入人心,办 公建筑的中庭空间因其特有空间特质受到越来 越多的关注。通常办公中庭空间中的节能性与热 舒适性是一对矛盾体,而自然通风作为被动节能 技术之一,不仅能够促进中庭空间的内外空气 循环,改善室内空气质量,而且降低能耗和提升 热舒适性,较好地解决这一矛盾。以江雅园办公 楼中庭空间为案例进行研究,从中庭屋顶形态、 中庭高度及进风口开启方式三个变量因素出发, 引用模糊评估方法寻找出中庭空间自然通风热 舒适性最佳方案,结论显示在多个组合方案中 斜屋顶形态+进风口全部开启的方案热舒适性最 佳,同时也证明屋顶形态与通风方式的变化对自 然通风舒适性的影响较大,而中庭空间高度的变化对自然通风舒适性影响较小。本研究希望建立一套以风速和温度为评价指标的模糊体系,为自 然通风的热舒适性的评价提供一种客观的评估手段,从而为方案阶段的中庭空间设计提供一种 有效的优化方法。     

The Ventilation Rate of 344 Oslo Residences

Abstract The ventilation in Norwegian residences was studied with respect to the effect of new standards, construction techniques adopted, and energy conservation measures implemented. This was compared to residential ventilation performance in other countries with a similar climate. The effective total air change rate (h^?1) in 344 residences was measured with a passive tracer gas method known as the perfluorocarbon tracer gas method (PFT-method). The measurements were performed over a 14-day integrated sampling period. Overall, 36% of all residences had lower air change rates than the national building code requirement of 0.5 h^?1. In spite of similar construction techniques and building codes in the Nordic countries, Norwegian residences seem to be better ventilated in general than residences in other Nordic countries. However, the common belief of a gradual reduction of ventilation rates in Norwegian buildings as the date of construction becomes more recent is supported by our findings which show a linear reduction (slope β=?0.002, P < 0.05) of ventilation until the revision of the national building codes in 1987. Consequently, our results provide evidence supporting the hypothesis that the introduction of new building standards and construction techniques, and the implementation of energy conservation measures, have decreased the effective total air change rates in Norwegian residences until 1987.     

Contaminant levels,source strengths,and ventilation rates in California retail stores

This field study measured ventilation rates and indoor air quality in 21 visits to retail stores in California. Three types of stores, such as grocery, furniture/hardware stores, and apparel, were sampled. Ventilation rates measured using a tracer gas decay method exceeded the minimum requirement of California's Title 24 Standard in all but one store. Concentrations of volatile organic compounds (VOCs), ozone, and carbon dioxide measured indoors and outdoors were analyzed. Even though there was adequate ventilation according to standard, concentrations of formaldehyde and acetaldehyde exceeded the most stringent chronic health guidelines in many of the sampled stores. The whole‐building emission rates of VOCs were estimated from the measured ventilation rates and the concentrations measured indoor and outdoor. Estimated formaldehyde emission rates suggest that retail stores would need to ventilate at levels far exceeding the current Title 24 requirement to lower indoor concentrations below California's stringent formaldehyde reference level. Given the high costs of providing ventilation, effective source control is an attractive alternative.     

Relationships Between Ventilation and Indoor Air Quality: A Review

Abstract Adjustment of ventilation rates in buildings is widely practised, both to provide good air quality on a proactive basis and to mitigate air quality problems associated with occupant complaints. However, both cross-sectional and experimental epidemiological studies have reported mixed results and have for the most part failed to establish definitive relationships between ventilation rates and symptom prevalence or dissatisfaction with air quality. The difficulties involved in establishing such relationships may be due to a variety of confounding factors which include limitations in study design and interaction effects; difficulties in controlling ventilation rates in experimental studies; inadequate mixing of supply air in occupied spaces; high source strengths for some contaminants; dynamic interactions between sources and ventilation rates that result in increased contaminant emissions; contaminant dose-response sensory effects which are log-linear; potential contaminant generation within ventilation systems themselves; and multifactorial genesis of sick building symptoms. There is limited evidence to suggest that ventilation rate increases up to 10 L/s person may be effective in reducing symptom prevalence and occupant dissatisfaction with air quality and that higher ventilation rates are not effective. Because of complex relationships between ventilation rates, contaminant levels, and building-related health complaints/dissatisfaction with air quality, the use of ventilation as a mitigation measure for air quality problems should be tempered with an understanding of factors which may limit its effectiveness.     

Ventilation performance measurement using constant concentration dosing strategy

Air change performances of an office with variable air volume (VAV) mechanical ventilation system and a domestic apartment with natural ventilation were evaluated using tracer gas techniques. Both the constant concentration and the decay method were utilized. Experimental results showed that the domestic apartment with opened windows performed better than the VAV system in terms of air-exchange efficiency, and maintained the highest air change rate. However, poor air change rate and air-exchange efficiency were resulted when the windows were closed in the home. By comparing the measurement results from the two tracer gas methods, it is found that the results obtained by the constant concentration dosing method were compatible with that obtained from the widely adopted tracer decay method. Several recommendations for conducting constant concentration dosing test were also discussed in this article.     

The Influence of Office Furniture,Workstation Layouts,Diffuser Types and Location on Indoor Air Quality and Thermal Comfort Conditions at Workstations

Abstract Many factors affect the airflow patterns, contaminant removal efficiency and the indoor air quality at individual workstations in office buildings. The effects of office furniture design and workstation layouts on ventilation performance, contaminant removal efficiency and thermal comfort conditions at workstations were studied. The range of furniture configurations and environmental parameters investigated included: 1) partition heights, 2) partition gap size, 3) diffuser types, 4) supply air diffuser location relative to the workstation, 5) return air grill location relative to the workstation, 6) heat source locations, 7) presence of furniture, 8) supply air temperatures, 9) adjacent workstations, 10) contaminant source locations, 11) supply air flow rates, and 12) outdoor air flow rates. The tracer gas technique was used to study experimentally the relative impact of these parameters on the air distribution and ventilation performance, as well as contaminant removal efficiency. Thermal environmental parameters such as air velocity and temperature were monitored at several locations to characterize the impact of these parameters on the thermal comfort conditions. The results showed that the outdoor air flow rate had a significant influence on the mean age of air. The air distributions at all the workstations were good even when the supply air flow rate was relatively low (i.e 5 L/s). At the same time, most of the parameters tested had a significant influence on contaminant removal efficiency when there was a contaminant source present somewhere in the office.     

Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County

The prevalence of prefabricated, portable classrooms (portables) for United States public schools has increased; in California, approximately one of three students learn inside portables. Limited research has been conducted on indoor air and environmental quality in American schools, and almost none in portables. Available reports and conference proceedings suggest problems from insufficient ventilation due to poor design, operation, and/or maintenance of heating, ventilation and air conditioning (HVAC) systems; most portables have one mechanical, wall-mounted HVAC system. A pilot assessment was conducted in Los Angeles County, including measurements of integrated ventilation rates based on a perfluorocarbon tracer gas technique and continuous monitoring of temperature (T) and relative humidity (RH). Measured ventilation rates were low [mean school day integrated average 0.8 per hour (range: 0.1-2.9 per hour)]. Compared with relevant standards, results suggested adequate ventilation and associated conditioning of indoor air for occupant comfort were not always provided to these classrooms. Future school studies should include integrated and continuous measurements of T, RH, and ventilation with appropriate tracer gas methods, and other airflow measures. PRACTICAL IMPLICATIONS: Adequate ventilation has the potential to mitigate concentrations of chemical pollutants, particles, carbon dioxide, and odors in portable and traditional classrooms, which should lead to a reduction in reported health outcomes, e.g., symptoms of 'sick building syndrome', allergies, asthma. Investigations of school indoor air and environmental quality should include continuous temperature and relative humidity data with inexpensive instrumentation as indicators of thermal comfort, and techniques to measure ventilation rates.     

自然通风室内热舒适均匀度ADPl研究

《绿色建筑评价标准》中对自然通风时外窗的室内外风压差提出了要求,但并未考虑室内热舒适均匀度的问题.通过结合空气分布特性指标(ADPI)对天津地区过渡季自然通风室内热舒适区的确定,对不同外窗风压、房间进深及门窗组织形式进行了数值模拟计算,发现室内热舒适均匀度与室外风压、房间进深均存在比例关系,室内热舒适均匀度随室外风压的上升而下降,并给出了ADPI在不同房间进深、风压及门窗组织形式下的预测图表,供建筑师参考.     

Experimental performance investigation of natural,mechanical and hybrid ventilation in urban environment

An experimental investigation of the performance of natural, mechanical and hybrid ventilation systems was carried out in an urban measurement campaign during summer period 2002 in Athens, Greece. Three building apartments characterized by different geometry and located in two street canyons with different orientation were studied. The aim was to show the impact of the urban environment on the ventilation efficiency of natural and hybrid systems. The tracer gas decay method has been applied during the experimental procedures with one (N₂O) and two tracer gases (N₂O and SF₆). Based on the results of air-exchange rates using multizone methods from a previous study, a further analysis is performed in the present work for the evaluation of the performance of different ventilation systems in urban conditions, with emphasis on the ventilation efficiency. A methodology to estimate the air-exchange efficiency, on the basis of room mean age of air, in multitracer gas experiments is introduced. In spite of the reduced wind speeds due to the canyon effect, appreciable ventilation rates can be obtained with natural ventilation, especially when cross-ventilation with two or more windows is measured. For single-sided ventilation or under calm conditions, hybrid ventilation has only a slight advantage over natural, either in terms of air-exchange rates or of air-exchange efficiencies.     

Impacts of airtightening retrofits on ventilation rates and energy consumption in a manufactured home

A retrofit study was conducted in an unoccupied manufactured house to investigate the impacts of airtightening on ventilation rates and energy consumption. This paper describes the retrofits and the results of the pre- and post-retrofit assessment of building airtightness, ventilation, and energy use. Building envelope and air distribution systems airtightness were measured using fan pressurization. Air change rates were measured continuously using the tracer gas decay technique. Energy consumption associated with heating and cooling was monitored through measurement of gas consumption by the forced-air furnace for heating and electricity use by the air-conditioning system for cooling. The results of the study show that the retrofits reduced building envelope leakage by about 18% and duct leakage by about 80%. The reduction in the house infiltration rates depended on weather conditions and the manner in which the heating and cooling system was controlled, but in general these rates were reduced by about one third. The energy consumption of the house for heating and cooling was reduced by only about 10%, which is relatively small but not totally unexpected given that infiltration only accounts for a portion of the heating and cooling load.     

Ventilation and performance in office work

Outdoor air ventilation rates vary considerably between and within buildings, and may be too low in some spaces. The purpose of this study was to evaluate the potential work performance benefits of increased ventilation. We analyzed the literature relating work performance with ventilation rate and employed statistical analyses with weighting factors to combine the results of different studies. The studies included in the review assessed performance of various tasks in laboratory experiments and measured performance at work in real buildings. Almost all studies found increases in performance with higher ventilation rates. The studies indicated typically a 1-3% improvement in average performance per 10 l/s-person increase in outdoor air ventilation rate. The performance increase per unit increase in ventilation was bigger with ventilation rates below 20 l/s-person and almost negligible with ventilation rates over 45 l/s-person. The performance increase was statistically significant with increased ventilation rates up to 15 l/s-person with 95% CI and up to 17 l/s-person with 90% CI. Practical Implications We have demonstrated a quantitative relationship between work performance and ventilation within a wide range of ventilation rates. The model shows a continuous increase in performance per unit increase in ventilation rate from 6.5 l/s-person to 65 l/s-person. The increase is statistically significant up to 15 l/s-person. This relationship has a high level of uncertainty; however, use of this relationship in ventilation design and feasibility studies may be preferable to the current practice, which ignores the relationship between ventilation and productivity.     

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: (a) conventional air distribution system with ceiling supply and return; (b) conventional air distribution system with ceiling supply and return near the floor; (c) underfloor air distribution system; and (d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the indoor/outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used.     

Changing microbial concentrations are associated with ventilation performance in Taiwan's air-conditioned office buildings

Our study conducted serial environmental measurements in 12 large office buildings with two different ventilation designs to obtain airborne microbial concentrations in typical office buildings, and to examine the effects of occupant density, ventilation type and air exchange efficiency on indoor microbial concentrations. Duplicate samples of airborne fungi and bacteria, a total of 2477 measurements, were collected based on a scheme of conducting sampling three times a day for at least seven consecutive days at every study building. Air change rates (ACHs) were also estimated by tracer gas concentration decay method, and measured by continuous Multi-Gas monitor for each building. Most sampling sites were with total fungal and bacteria concentrations higher than 1000 CFU/m(3), an often-quoted guideline in earlier research. Significantly higher concentrations of fungi and bacteria, as well as higher indoor/outdoor (I/O) ratios across most groups of airborne microbes, were identified in buildings with fan coil unit (FCU) system than those with air-handling unit (AHU) system (Student's t test, P < 0.0001). Older buildings and higher air exchange rates were statistically associated with greater indoor bacteria levels in FCU ventilated buildings (R(2) = 0.452); a pattern not found in AHU buildings. Increasing ACH seemed to be the determinant factor for rising indoor fungal and Cladosporium concentrations in those FCU buildings (R(2) = 0.346; 0.518). Our data indicated that FCU ventilated buildings might have provided more outdoor matters into indoor environments through direct penetration of outdoor air. Results also demonstrated a quantitative association between rising numbers of occupants and increasing indoor levels of yeast in both FCU and AHU ventilated buildings. The regression model identified in this study may be considered a reference value for proposing an optimal ACH, while with adequate filtration of fresh air, as an effective strategy in lowering indoor microbial concentrations in air-conditioned buildings. PRACTICAL IMPLICATIONS: As control of indoor microbial contamination has become an increasing concern around the world, feasibility and effectiveness of adopting ventilation approach has attracted a significant interest. This field investigation demonstrated, quantitatively, critical variables to be taken into consideration while applying such a measure, including the kinds of microbes to be removed and the types of ventilation system already in place.     

Ventilation, temperature, and HVAC characteristics in small and medium commercial buildings in California

This field study of 37 small and medium commercial buildings throughout California obtained information on ventilation rate, temperature, and heating, ventilating, and air-conditioning (HVAC) system characteristics. The study included seven retail establishments; five restaurants; eight offices; two each of gas stations, hair salons, healthcare facilities, grocery stores, dental offices, and fitness centers; and five other buildings. Fourteen (38%) of the buildings either could not or did not provide outdoor air through the HVAC system. The air exchange rate averaged 1.6 (s.d. = 1.7) exchanges per hour and was similar between buildings with and without outdoor air supplied through the HVAC system, indicating that some buildings have significant leakage or ventilation through open windows and doors. Not all buildings had sufficient air exchange to meet ASHRAE 62.1 Standards, including buildings used for fitness centers, hair salons, offices, and retail establishments. The majority of the time, buildings were within the ASHRAE temperature comfort range. Offices were frequently overcooled in the summer. All of the buildings had filters, but over half the buildings had a filter with a minimum efficiency reporting value rating of 4 or lower, which are not very effective for removing fine particles. PRACTICAL IMPLICATIONS: Most U.S. commercial buildings (96%) are small- to medium-sized, using nearly 18% of the country's energy, and sheltering a large population daily. Little is known about the ventilation systems in these buildings. This study found a wide variety of ventilation conditions, with many buildings failing to meet relevant ventilation standards. Regulators may want to consider implementing more complete building inspections at commissioning and point of sale.     

Ventilation and health in non-industrial indoor environments: report from a European multidisciplinary scientific consensus meeting (EUROVEN)

Scientific literature on the effects of ventilation on health, comfort, and productivity in non-industrial indoor environments (offices, schools, homes, etc.) has been reviewed by a multidisciplinary group of European scientists, called EUROVEN, with expertise in medicine, epidemiology, toxicology, and engineering. The group reviewed 105 papers published in peer-reviewed scientific journals and judged 30 as conclusive, providing sufficient information on ventilation, health effects, data processing, and reporting, 14 as providing relevant background information on the issue, 43 as relevant but non-informative or inconclusive, and 18 as irrelevant for the issue discussed. Based on the data in papers judged conclusive, the group agreed that ventilation is strongly associated with comfort (perceived air quality) and health [Sick Building Syndrome (SBS) symptoms, inflammation, infections, asthma, allergy, short-term sick leave], and that an association between ventilation and productivity (performance of office work) is indicated. The group also concluded that increasing outdoor air supply rates in non-industrial environments improves perceived air quality; that outdoor air supply rates below 25 l/s per person increase the risk of SBS symptoms, increase short-term sick leave, and decrease productivity among occupants of office buildings; and that ventilation rates above 0.5 air changes per hour (h-1) in homes reduce infestation of house dust mites in Nordic countries. The group concluded additionally that the literature indicates that in buildings with air-conditioning systems there may be an increased risk of SBS symptoms compared with naturally or mechanically ventilated buildings, and that improper maintenance, design, and functioning of air-conditioning systems contributes to increased prevalence of SBS symptoms.     

Thermal Comfort and Air Quality in Three Mechanically Ventilated Residential Buildings

Abstract Thermal comfort and air quality were studied in three multi-family buildings located in urban environments. Measurements of air velocities close to the supply devices are presented along with measurements of CO, TVOC, NO and NO₂. In addition, particle measurements were carried out to check the filter efficiency in one of the buildings (SI) which is specially designed for people with allergy problems. The total air change rate for this building is higher than for normal residential buildings and three different types of air filter are installed in the ventilation system. The results of the thermal comfort measurements in the buildings vary considerably. For two of the buildings thermal comfort can be regarded as acceptable, but can be further improved. The selection and location of the air inlet devices in the third building are not acceptable. The monitoring of the contaminants outdoors and indoors was carried out for diurnal periods. The measured contaminants outside building S1 show good correlation between each other, and the concentrations of gases and particles were considerably lower in the supply air than in the outdoor air outside the apartment where the measurements were made. The importance of not taking samples over too short a period of time is also shown.