Flame interactions and smoke containment by downward displacement ventilation

Smoke contamination even from small fires of sensitive components in telephone central offices (TCO) and semiconductor clean rooms has caused disastrous disruptions in services and excessive financial repercussions. Containment and removal of smoke can be achieved by downward displacement ventilation, also used for other purposes in large floor area semiconductor facilities. Downward ventilation reverses the upward flow from the fire and removes the smoke and other combustion products through the floor. Small-scale model experiments under turbulent fire plume conditions investigate the physical parameters such as downward velocity, ceiling clearance, and size of the fire that control the extent of the smoke containment around the fire. The extent of smoke contamination is mapped by measuring the temperatures in several locations on the vertical axis and in the space around the fire. The downward velocities cause oscillation of the fire plume and the flames around the vertical axis. By combining the experimental data with similarity analysis, a characteristic length scale and nondimensional relations are deduced for the extent of the smoke containment and the onset of plume oscillations. These relations allow design of displacement ventilation effective to contain the smoke but not cause fire spread owing to the leaning of the flames. Previously reported discrepancies in the apparent width and behavior of the plume are resolved by examining the experimental data and assessing the suitability of steady state computational fluid dynamics to model the present flow.     

Investigations into the functioning of a supply air window in relation to solar energy as determined by experiment and simulation

‘Supply air windows’ under optimum flow conditions function as an efficient heat reclaim device. Heat escaping from the room, through the inner glass pane, is entrained in the air flow between the inner and outer sashes and returned to the room. A low-E coating to the inner glass acts as a barrier to radiation heat loss across the window so very low U-values can be achieved. These same characteristics enable the window to function as a passive solar component. Its efficiency is inferior to that of a dedicated passive solar device due to its transparency, but even so at modest levels of incident solar gain a worthwhile proportion is entrained into the air flow and supplied to the rooms as pre-heated ventilation air supply. These characteristics have been established by laboratory, test cell investigations, and simulations using computational fluid dynamics and ESP-r, a whole building dynamic thermal modelling tool.     

暖通设计常见问题与对策

通过对采暖设计中存在的集气、热网水平失调和垂直失调等问题进行分析,及对通风设计中气流组织与风口布置、风管设计和风机选型中存在的一些问题进行分析,总结了一些设计中解决问题的方法。     

Investigation of different approaches to reduce allergens in asthmatic children's homes--the Breath of Fresh Air Project, Cornwall, United Kingdom

During 2001 to 2004, a study was conducted to assess the indoor environmental and health impact of installing allergen-reducing interventions in the homes of asthmatic children. Based on the results of a pilot study, to determine an intervention that would provide improved symptom scores and a reduction in house dust mite allergen (Der p 1), mechanical ventilation and heat recovery (MVHR) systems were installed in 16 homes. Environmental and respiratory health assessments were conducted before and after the installation of the MVHR systems. The results indicated that the installation of MVHR systems reduced Der p 1 concentrations in living room carpets and mattresses. There were significant reductions in symptom scores for breathlessness during exercise, wheezing, and coughing during the day and night. Although, there was not a parallel control group for the main study, the lack of change in the pilot study control group (who did not receive an intervention), indicated that the changes in symptom scores were in part to do with the intervention. Larger scale trials are needed to determine the efficacy of MVHR systems in homes to improve indoor air quality and reduce asthma symptoms.     

Evaluating of air flow movements and thermal comfort in a model room with Euler equation: Two dimensional study

This paper presents the results of a study that consists of estimating the temperature distribution 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 heating are compared with the predictions of a Navier–Stokes model, as well as with experimental results. 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 capable of properly estimating the temperature distribution, the air movement and the comfort indices in the room. Furthermore, the use of Euler equations allows a reduction of computational time in the order of 30% compared to the Navier–Stokes modeling.     

Transient buoyancy-driven ventilation: Part 2. Modelling heat transfer

A new mathematical model for buoyancy-driven ventilation [Sandbach SD, Lane-Serff GF. Transient buoyancy-driven ventilation: Part 1. Modelling advection. Building and Environment, 2011] is modified to include heat transfer at the boundaries. Heat transfers at the ceiling and floor are included, using Newton’s law of cooling to model convective heat transfer between the air and the solid boundaries, Fourier’s law to model conductive heat transfer through the floor and ceiling, and a linear version of the Stefan–Boltzmann law to model radiative heat transfer from the ceiling to the floor. The effectiveness of the model was assessed using experimental results obtained in a full-scale test room. In these experiments, the vertical temperature stratification was measured using an array of T-type thermocouples. Speed measurements were obtained to estimate the ventilation flow rate (for displacement ventilation) and the velocity profile across the doorway (for doorway ventilation). Buoyancy was introduced using a twin-hob (∼2.35 kW) heat source, and in most cases a diffuse two-layer temperature stratification developed. The results from these experiments are compared with the model and existing adiabatic models. Our results indicate that the effect of heat transfer at the boundaries on the final stratification is significant and should not be ignored. Furthermore, direct comparisons between the measured and modelled results are in general very good.     

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.     

The prevalence and incidence of sick building syndrome in Chinese pupils in relation to the school environment: a two-year follow-up study

There are few incidence studies on sick building syndrome (SBS). We studied two-year change of SBS in Chinese pupils in relation to parental asthma/allergy (heredity), own atopy, classroom temperature, relative humidity (RH), absolute humidity (AH), crowdedness, CO?, NO?, and SO?. A total of 1993 participated at baseline, and 1143 stayed in the same classrooms after two years. The prevalence of mucosal and general symptoms was 33% and 28% at baseline and increased during follow-up (P < 0.001). Twenty-seven percent reported at least one symptom improved when away from school. Heredity and own atopy were predictors of SBS at baseline and incidence of SBS. At baseline, SO? was associated with general symptoms (OR=1.10 per 100 μg/m3), mucosal symptoms (OR=1.12 per 100 μg/m3), and skin symptoms (OR=1.16 per 100 μg/m3). NO? was associated with mucosal symptoms (OR=1.13 per 10 μg/m3), and symptoms improved when away from school (OR=1.13 per 10 μg/m3). Temperature, RH, AH, and CO? were negatively associated with prevalence of SBS. Incidence or remission of SBS was not related to any exposure, except a negative association between SO? and new skin symptoms. In conclusion, heredity and atopy are related to incidence and prevalence of SBS, but the role of the measured exposures for SBS is more unclear. PRACTICAL IMPLICATIONS: We found high levels of CO? indicating inadequate ventilation and high levels of SO? and NO?, both indoors and outdoors. All schools had natural ventilation, only. Relying on window opening as a tool for ventilation in China is difficult because increased ventilation will decrease the level of CO? but increase the level of NO? and SO? indoors. Prevalence studies of sick building syndrome (SBS) might not be conclusive for causal relationships, and more longitudinal studies on SBS are needed both in China and other parts of the world. The concept of mechanical ventilation and air filtration should be introduced in the schools, and when planning new schools, locations close to heavily trafficked roads should be avoided.     

Comparing mixing and displacement ventilation in classrooms: pupils' perception and health

Several studies have found that indoor air quality (IAQ) in schools is often poor and may affect the health of the pupils. Building ventilation is a means to reduce pollutants indoors, but different designs should be evaluated for their effectiveness in different environments. In a field experiment performed at four classrooms in one school building, air was supplied either in the mixing or in the displacement mode, and we collected information on exposures, pupils' perception of IAQ and climate, and health symptoms and performed clinical examinations. The room temperature, relative humidity, concentration of CO?, and cat allergen were measured at the breathing height and were similar during each ventilation mode. The children perceived IAQ were similar in the two ventilation regimes, and there were few differences in symptom reports or clinical parameters. However, the pupils reported more eye symptoms during displacement ventilation. PRACTICAL IMPLICATIONS: Both mixing and displacement ventilation may be appropriate in school classrooms as long as the overall design, ventilation rates, and maintenance of systems are satisfactory.     

运用正确的通风手段处理火灾事故

矿山救护队是处理矿井灾害事故的一支专业化的队伍,当矿井发生事故时,救护队必须以第一时间进行抢险救援,该文阐述了矿山救护队在处理事故时,如何采取正确的通风手段,既可以保证救援人员的安全,又可以抢救遇险人员,减少国家财产损失和人员伤亡的重要性。