The outdoor air ventilation rate in high-rise residences employing room air conditioners

Ventilation is important because it affects indoor environmental conditions, including air pollutant concentrations that may modify the health of the occupants of a building, or their perceptions and comfort. This paper reports, first of all, on field studies monitoring indoor overnight CO₂ levels and outdoor ventilation rates in bedrooms employing room air conditioners (RACs), so the current situation of ventilation in actual high-rise residential buildings in Hong Kong can be appreciated. This is followed by a report of the results of laboratory experiments where two typical RACs were used in an examination of outdoor air ventilation characteristics in rooms employing RACs. The results of field studies showed that the outdoor ventilation rates in the measured bedrooms equipped with RACs in high-rise residential buildings in Hong Kong could not meet the ventilation requirement specified in the ASHRAE standard 62-2001 even if there was only one occupant in a bedroom. Although the use of a window-type air conditioner (WRAC) may provide a higher outdoor ventilation rate than the use of a split-type air conditioner (SARC), this may be ascribed to the fact there is more natural infiltration when a WRAC is used. The ventilation damper currently available in a WRAC does not significantly affect the outdoor ventilation rate. Therefore, such a damper cannot be expected to provide the ventilation rate as required by a ventilation code and its intended function of controlling ventilation is limited. In addition, the air exhausted from indoors to outdoors through the ventilation outlet in a WRAC is air that has just been cooled by the cooling coil (evaporator). This is unreasonable, because exhausting just-cooled and dehumidified air is a waste of energy. Therefore, an improved design for a WRAC has been suggested. Finally, the outdoor ventilation requirement for bedrooms at nighttime, when occupants are asleep, is discussed. A new ventilation rate of 3.0 l/s per person for the sleeping environment in high-rise residential buildings is proposed.     

A questionnaire survey on sleeping thermal environment and bedroom air conditioning in high-rise residences in Hong Kong

This paper reports on the results of a questionnaire survey on sleeping thermal environment and bedroom air conditioning in high-rise residential buildings in Hong Kong. The survey aimed at investigating the current situation of sleeping thermal environment and bedroom air conditioning, in order to gather relevant background information to develop strategies for bedroom air conditioning in the subtropics. It focused on the use patterns and types of bedroom air conditioning systems used, human factors such as the use of bedding and sleepwear during sleep, preference for indoor air temperature settings in bedrooms, ventilation control at nighttime with room air conditioner (RAC) turned on, etc. The results of the survey showed that most of the respondents would prefer a relatively low indoor air temperature at below 24 °C. Most of the respondents might however not be satisfied with the indoor air quality (IAQ) in bedrooms in Hong Kong. On the other hand, 68% of the respondents did not use any ventilation control intentionally during their sleep with their RACs turned on. A lack of knowledge of the ventilation control devices provided on window type room air conditioners (WRACs) indicated an urgent need for user education.     

Residential satisfaction in housing estates: a Hong Kong perspective

Post-occupancy evaluation (POE) has been developed to address the problem of acquiring feedback from the occupants who are, arguably, in the best position to provide information for a future design database. This paper presents a study of the factors (on both physical and social levels), which influence residential satisfaction of a sample of occupants in a chosen residential area in Hong Kong; factor analysis and multiple regression were carried out on the data. A comparison is also made of the perceived factors of dissatisfaction amongst the public and private housing occupants. It is suggested that a wider systematic coverage of the subject through investigative and diagnostic POE should be carried out in Hong Kong.     

An evaluation model for indoor environmental quality (IEQ) acceptance in residential buildings

The indoor environmental quality (IEQ) in residential buildings is examined from the prospect of an occupant's acceptance in four aspects: thermal comfort, indoor air quality, noise level and illumination level. Based on the evaluations by 125 occupants living in 32 typical residential apartments in Hong Kong, this study proposes empirical expressions to approximate the overall IEQ acceptance with respect to four contributors, namely operative temperature, carbon dioxide concentration, equivalent noise level and illumination level, via a multivariate logistic regression model. A range of IEQ acceptances for regular residential conditions is determined and the dependence of the predicted overall IEQ acceptance on the variations of the contributors is discussed. The proposed overall IEQ acceptance can be used as a quantitative assessment criterion for similar residential environments where an occupant's evaluation is expected.     

The need for temperature zoning in high-performance residential buildings

The development from poorly insulated and leaky buildings to modern high-performance buildings, such as passive houses, has led to considerable improvements regarding thermal comfort. However, user evaluations of passive houses that solely employ air heating indicate that bathrooms are often perceived as too cold and bedrooms as too warm. Based on these experiences, the functional requirement of providing thermal comfort using only air heating has not been adopted in the Norwegian standard for passive houses. Instead, usually local heat sources are installed in living rooms and bathrooms to facilitate temperature zoning within the dwelling. The questions asked in this study are how well this heating and ventilation concept functions in practice from the occupants’ point of view and whether it provides thermal comfort in the various rooms. Therefore, a questionnaire was distributed to the occupants of a typical multifamily passive house project in Norway. Despite the small sample size, the findings give important insight into the residents’ perception of the thermal conditions and clearly demonstrate the limitations of the heating and ventilation solution. Based on the results, the need for further development and further studies to provide temperature zoning is outlined.     

Bayesian adaptive comfort temperature (BACT) of air-conditioning system in subtropical climate

Indoor thermal climate is an important issue affecting the health and productivity of building occupants. In the designing of commercial air-conditioning systems, it is believed that the conventional fixed temperature set point concept is limited because indoor comfort temperature depends on the business culture, such as the nature of activities and dress code of occupants, etc. Researchers have been interested in investigating adaptive temperature control for a realistic in-situ control of comfort. Unfortunately, those studies put great emphasis on energy saving opportunities and sometimes might result in thermal discomfort to individuals. This study argues that complaints of thermal discomfort from individuals, despite representing only a small portion of the population, should not be ignored and can be used to determine the temperature setting for a population in air-conditioned environment. In particular, findings of a new notion of Bayesian adaptive comfort temperature (BACT) in air-conditioned buildings in a humid and subtropical climate like Hong Kong are reported, and the adaptive interface relationship between occupants’ complaints of thermal discomfort and indoor air temperature is determined. This BACT algorithm is intended to optimise the acceptance of thermal comfort, as determined by physical measurements and subjective surveys.     

Evaluating the influence of openings configuration on natural ventilation performance of residential units in Hong Kong

Natural ventilation performance of a residential dwelling is affected by a combination of internal and external factors. External factors are often subject to constraints beyond the control of site planners and architects. Internal factors include the openings configuration, which site planners and architects are free to design the way they deem proper. However, little information is available in this regard. In this study, a case study was conducted by tracer-gas measurements at a carefully selected residential unit for Computational Fluid Dynamics (CFD) model validation. A hypothetical residential unit was formulated to represent the characteristics of typical residential units in Hong Kong. CFD simulations were performed based on the hypothetical unit to evaluate the influence of different openings configurations on natural ventilation performance using the mean age of air. Openings configuration is defined by many parameters. Among the three studied parameters, evaluation results indicate that natural ventilation performance of residential units was most affected by the relative position of the two window openings groups (i.e. bedroom windows and living room windows), followed by building orientation and doors positions. It was found that better natural ventilation performance could be achieved when the two openings groups were positioned in opposite directions or perpendicular to each other. The combined effect of the three parameters was evaluated. It was found that varying two parameters at the same time offered positive improvements in natural ventilation performance, but varying all three parameters did not result in any improvement because of the counter-effects of changes in doors positions.     

严寒地区住宅建筑冬季通风研究

针对严寒地区节能住宅建筑冬季卫生通风不足的问题，本文应用Fluent软件对安装通风装置的示范住宅建筑的室外风场、室内气流组织及温度分布进行模拟研究并实测室内空气温度场。在严寒地区，为保证适当的卫生通风和气流组织，应加强热压的作用，而尽量避免风压的不利影响。对严寒地区典型的建筑住区不同尺度的外部风环境模拟分析结果表明：除建筑住区的迎风面建筑外，整个建筑住区及建筑子区内风场分布较为均匀，符合严寒地区冬季避免冷风侵入耗热量的建筑节能设计。为避免迎风面建筑较高层住宅的背风向房间出现进风口变为排风口的现象，需加强屋顶排风风口处的引风作用；示范性通风建筑室内的进风角度及安装位置、建筑构件、家具的材料以及家具摆放位置等是影响室内热舒适性和室内气流组织的主要原因。     

套室内人体热舒适的研究

借助于通用流场计算软件PHOENICS，在考虑了外界气温、太阳的热辐射条件，家具以及人员等室内微气候影响的情况下，预测了两室一厅套室内气流三维流场和温度场。得到了套室内气流的速度、温度和人体热舒适指数等参数的分布，并经过评定，该套室内的热环境达到了人体的舒适性要求。模拟计算结果对套室的设计及其空调系统的配置具有重要的参考价值，并为套室内人体热舒适的进一步研究和室内空气品质问题的研究奠定了基础。     

Comparison of physical performances of the ventilation systems in low-energy residential houses

The paper presents experimental results of the effect of ventilation systems in modern residential low-energy houses on thermal and humid conditions, heat consumption and perception of thermal comfort and air quality by their residents. Practical projects of modern residential houses with various ventilation systems which realize thermal, humid and psycho-physical comfort were worked out. To analyze the influence of ventilation systems on human comfort, results of questionnaires and comprehensive experimental measurements were taken into account. For measurements, 22 identical residential houses in Germany were chosen where 4 various ventilation systems were installed: gravitational (natural) ventilation, air heating system, mechanical ventilation with in- and out-leading air elements and a function of heat recovery and mechanical ventilation with single ventilators. The following parameters were measured in test units: relative air humidity, concentration of CO₂ in the air, air temperature, consumption of electricity, gas and heat, working time of the window opening, working time of the mechanical ventilation and number of residents. Advantages and disadvantages of ventilation systems were outlined. Experimental results were evaluated. Relationships between ventilation systems and thermal comfort were discussed by taking into account opinions of house residents.     

A study on the characteristics of nighttime bedroom cooling load in tropics and subtropics

In both tropical and subtropical regions, residential air conditioning serves to maintain appropriate indoor thermal environments not only at daytime, but also at nighttime in bedrooms for sleeping. However, the current practices for air conditioning are primarily concerned with the situations in which people are awake at daytime. Therefore, these may not be directly applicable to nighttime bedroom air conditioning. This paper reports on a simulation study on the characteristics of nighttime bedroom cooling load in tropics and subtropics, using a building energy simulation program. The weather conditions of and the typical arrangements of high-rise residential blocks in Hong Kong are used in the simulation study. The simulation results on the cooling load characteristics in bedrooms under three different operating modes of room air conditioners (RACs) at the summer design day, the breakdown of the total cooling load in a bedroom at nighttime operating mode (NOM), indoor air temperature and mean radiant temperature variation at NOM, and the effects of indoor design air temperature on the cooling load characteristics at NOM are presented. The differences in the cooling load characteristics among three different operating modes and the issues related to the sizing of RACs used in bedrooms are discussed.     

CFD study on effect of the air supply location on the performance of the displacement ventilation system

The purpose of this paper is to investigate using a numerical simulation (computational fluid dynamics or CFD) the effect of the air supply location on the design and performance of the displacement ventilation (DV) system. The results are reported in terms of thermal comfort and indoor air quality. The study focuses on the typical Hong Kong office under local thermal and boundary conditions. This includes the high cooling load used in Hong Kong. Several pollutants typically found in the office such as carbon dioxide and volatile organic compounds (VOCs) were investigated. The results indicate that the supply should be located near the center of the room rather than to one side of the room. This will provide a more uniform thermal condition in the office. The DV system was found to be effective in dispersing VOCs within an office environment for all cases studied. The exhaust was found to have minimal effect on the thermal comfort. For a DV system in Hong Kong, it is possible to use 100% fresh air without extra energy consumption.     

空调房间冬季室内致适参数的分析与研究

从人体热舒适感觉和室内空气品质方面分析了空调房间室内舒适性的影响因素,根据测试结果给出了致适范围,提出了工程应用中的注意的问题。     

The effects of bedroom air quality on sleep and next‐day performance

The effects of bedroom air quality on sleep and next‐day performance were examined in two field‐intervention experiments in single‐occupancy student dormitory rooms. The occupants, half of them women, could adjust an electric heater to maintain thermal comfort but they experienced two bedroom ventilation conditions, each maintained for 1 week, in balanced order. In the initial pilot experiment (N = 14), bedroom ventilation was changed by opening a window (the resulting average CO₂ level was 2585 or 660 ppm). In the second experiment (N = 16), an inaudible fan in the air intake vent was either disabled or operated whenever CO₂ levels exceeded 900 ppm (the resulting average CO₂ level was 2395 or 835 ppm). Bedroom air temperatures varied over a wide range but did not differ between ventilation conditions. Sleep was assessed from movement data recorded on wristwatch‐type actigraphs and subjects reported their perceptions and their well‐being each morning using online questionnaires. Two tests of next‐day mental performance were applied. Objectively measured sleep quality and the perceived freshness of bedroom air improved significantly when the CO₂ level was lower, as did next‐day reported sleepiness and ability to concentrate and the subjects' performance of a test of logical thinking.     

Indoor thermal environment of urban residential buildings in China: winter investigation in five major cities

The purposes of this investigation are to look into the actual conditions of urban residential indoor environment in China during the winter season, and to discuss the thermal comfort as well as to understand the possibility of space heating energy conservation. Investigations of indoor thermal environment were carried out in Harbin, Beijing, Xi’an, Shanghai and Hong Kong of China. The results showed that the indoor thermal condition in heating usage zone is good, such as Harbin, Beijing and Xi’an. The indoor thermal comfort is strongly affected by the outdoor climate in non-heating usage zone, such as Shanghai and Hong Kong.     

Occupant Tenability in Single Family Homes: Part II: Impact of Door Control,Vertical Ventilation and Water Application

This paper describes experimental investigations of fire service ventilation and suppression practices in full-scale residential structures, including a one-story, 112 m², 3 bedroom, 1 bathroom house with 8 total rooms and a two-story 297 m², 4 bedroom, 2.5 bathroom house with 12 total rooms. The two-story house featured a modern open floor plan, two-story great room and open foyer. Seventeen experiments were conducted varying fire location, ventilation locations, the size of ventilation openings and suppression techniques. The experimental series was designed to examine the impact of several different tactics on tenability: door control, vertical ventilation size, and exterior suppression. The results of these experiments examine potential occupant and firefighter tenability and provide knowledge the fire service can use to examine their vertical ventilation and exterior suppression standard operating procedures and training content. It was observed that door control performed better at controlling the thermal exposure to occupants than did fully opening the door. Additionally, the impact of increased vertical ventilation area was minimal, and only slightly reduced the thermal exposure to occupants in a few non-fire rooms. In the two-story structure, the non-fire rooms on the second floor consistently had larger thermal fractional effective rate (FER) values (approximately 2.5× the thermal risk to oocupants) than did the non-fire rooms on the first floor. Water application was also shown to reduce the thermal risk to occupants 60 s after water application 1/3rd the original values on second floor rooms of the two-storry structure and by at least 1/5th of the original values on the first floor rooms of both structures. Data also showed that the impact of front door ventilation on the toxic gases exposure was minimal, as the toxic gases FER actually increased after front door ventilation for several experiments. However, after vertical ventilation there was a 30% reduction in the toxic gases exposure rate in two of the one-story structure experiments.     

Neutral temperature in subtropical climates—A field survey in air-conditioned offices

The thermal environment for air-conditioned offices in subtropical climates is examined from the prospect of maintaining an optimum operative temperature for the occupants. In this study, the optimum neutral temperature is evaluated from 422 occupants’ responses towards the perceiving thermal environment in 61 air-conditioned offices and 186 complaints of thermal discomfort in an air-conditioned office building on an electronic questionnaire, using a semantic differential evaluation scale and a dichotomous assessment scale. In particular, physical parameters for the thermal comfort study were measured by an indoor environmental quality (IEQ) logger, and the operative temperature was correlated with the occupants’ thermal responses. The probability of accepting an operative temperature for the thermal comfort of the occupants was correlated with logistic regression curves; the optimum operative temperature was derived in order to maximize the probability of thermal comfort expressed by the occupants. The results showed that the thermal neutral temperatures for air-conditioned offices in subtropical climates were 23.6 and 21.4 °C in summer and winter, respectively. The preferred thermal environment in Hong Kong should be slightly cool, corresponding to about 1 °C below the neutral temperature, in order to satisfy most of the occupants in the office space.     

Towards finding the optimal location of a ventilation inlet in a roof monitor skylight,using visual and thermal performance criteria,for dwellings in a Mediterranean climate

The main aim of this work is to study the influence of a roof monitor skylight on comfort criteria. The roof monitor skylight simultaneously provides lighting and outdoor ventilation air for a living room or a master bedroom in a house with an underfloor heating/cooling system. The air is introduced into the room through an air inlet in the carpentry of the opening in the roof monitor skylight and located – for the purposes of this study – in different positions in the carpentry. To evaluate the comfort variations caused by this change of position, a series of lighting and thermal numerical indicators are applied to a set of simulation models, generating a complete analysis to determine optimal positions for the air inlet. These models are designed for the context of a Mediterranean climate, with extreme calculation conditions (overcast sky in winter and clear sky in summer). The simulation tools Daylight Visualizer 2.5 and Design Builder 2.42 have been selected to generate the models. This work concludes that the optimal position for the air inlet is in the side of the carpentry of the roof monitor skylight opening, ensuring the maximization of both lighting and thermal comfort conditions.     

The characteristics of space cooling load and indoor humidity control for residences in the subtropics

For residential buildings located in the subtropics, it is more challenging and difficult to deal with space latent cooling load than space sensible load, using a room air conditioner (RAC), partly due to hot and humid climates. This paper reports a simulation study on the characteristics of space cooling load and indoor humidity control for residences in the subtropics, using a building energy simulation program. Both the weather conditions and the typical arrangements of high-rise residential blocks in subtropical Hong Kong were used in the simulation study. The simulation results on both the space cooling load characteristics and the hourly application sensible heat ratio (SHR) in the living/dining room and the master bedroom in a selected west-facing apartment under different operating modes of RACs in the summer design day are presented. The problem of indoor humidity control due to the mismatching between an application SHR and an equipment SHR in the two rooms both in the summer design day and during part load operations and the influences of indoor furnishings acting as moisture capacitors on indoor RH level are discussed.     

Survey on the indoor environment of enclosed car parks in Hong Kong

Results of an indoor environment survey of 19 underground car parks in Hong Kong are reported. The indoor air temperature, relative humidity and air speed were measured. Subjective feelings of the occupants and their views on the indoor environment were surveyed by questionnaire. The design and operation of the installed ventilation systems and the number of occupants staying at the car parks were also investigated. It was found that studies of this kind are very important in providing design data. Further, a four-point assessment system is proposed to quantify the indoor thermal environment of the car parks.