Method of calculating gas volume and its travel direction in a sewer

Summary

In the process of operating deep sewers some problems arise such as corrosion of reinforced concrete structures of the sewerage network, saturation of the gas phase of the underground space with corrosive toxic substances, accidental emissions of these gases from the network into the atmosphere. Solving these problems is possible by arranging air exchange between the sewerage network and atmosphere. The available methods of calculating the amount of gas travelling in the sewerage network do not take into account the gas density, dynamic viscosity and other parameters that depend on the chemical composition of the gas phase. The lack of the recommendations does not allow estimating the network ventilation in relation to providing the required gas exchange rate. Consequently determining, estimating and substantiating the required capacity of the ventilation equipment are not possible. Possible flow redistribution is not considered either; and, hence, adjusting the gas exchange systems to the definite network parameters is not possible. A method of calculating gas amount and flow direction induced by fluid entraining capacity and natural draft with account of the physical and hydraulic parameters of wastewater and gas, network design features, daylight surface temperature is presented. The method provides for making calculations at the design stage with account of retrofitting ventilation units, filters and vent pipes. The following parameters are determined: the amount and direction of gas flow in the network, gas exchange rate, anticipated background concentration of corrosive gases at the preset gas exchange rate, network corrosion rate, overhaul period.

Key words

collector , sewerage network , calculation method , ventilation , gas exchange , corrosive toxic substances

DOI 10.35776/VST.2021.02.06
UDC 697.92

Agafonova V. V., Skibin Aleksandr, Volkov Vasilii

Modeling air exchange in office premises using a microperforated fabric air duct

Summary

The issues of improving the quality of the internal environment of an office building using an advanced air dispersion device – a fabric air duct with micro-orifices are considered. The advantage of this device is supplying the incoming air by jets with a low impulse allowing to locate the devices near the working space in offices eliminating the risk of drafts at the working places. The purpose of the work is a comparative numerical calculation of the efficiency of arranging the air exchange in an office building with two air supply schemes: through supply grilles and through a fabric air duct with microperforation. Modeling was carried out using the commercial STAR-CCM + software package. The system of Reynolds equations with closure using the k-ω SST turbulence model (Mentor) is used to describe the air movement. As part of the study, data on the nature of the change in temperature and air speed along the height of the working area of the office were obtained. It has been determined that while air is supplied through the supply grilles, the temperature (23.3–27.2 °C) and air speed (0.06–0.22 m/s) meet the permissible microclimate standards (GOST 30494-2011); while arranging the air exchange with the use of a microperforated air duct they correspond to the optimal parameters (temperature 23.1–25.4 °С, air speed 0.09–0.13 m/s) that are comfortable for the human body. Thus, the use of a microperforated air duct enhances the efficiency of heat surplus assimilation in comparison with traditional air distribution devices (ventilation grilles).

Key words

numerical simulation , ventilation , control volume approach CFD , air distribution , heat-mass exchange , microperforated fabric air duct

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UDC 628.23

Vasilyev V. M., Malkov A. V., PANKOVA G. A., Klementyev M. N.

Detecting the places of corrosive gas emissions from sewers to the surface and conditions of their formation

Summary

Corrosive gas emissions from sewers to the surface happen because of the excess pressure increase in the underroof and shaft space of the sewer. The causes of the pressure increase in the shaft space are considered. The gas amount changing during entering the shaft and removed from it depends on the wastewater flow rate, sewer filling (the height of the gas flow), hydraulic gradient of the sewer, formation of stagnation zones (sludge sedimentation), and temperature. Variation of these parameters and thus the location of corrosive gas emissions to the surface depend on a number of factors that can be divided into several groups: construction, hydraulic, geodesic, operation, random, climatic. Reducing the gas emissions from sewers is possible by: introduction of construction solutions for gaseous medium redistribution; elimination of air blocks, installation of purification filters; avoiding deviations from the design solutions arising during the construction of deep sewers; proper management of wastewater flow at elevation differences; improvement of the sewer operation rules, severization of the requirements to the operating personnel qualification.

Key words

collector , sewerage network , joint movement of liquid and gas , gas emission , excess pressure , ventilation

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UDC 697.92

Agafonova V. V.

Indoor air quality assessment in office buildings

Summary

The assessment of indoor air quality in an office building is given. The analysis of the results of reviewing Russian and foreign authors on this topic showed that at CO₂ concentration of 600–800 ppm and higher the well-being of people worsens, which leads to impaired productivity and increased fatigue. Prolonged exposure to carbon dioxide in humans can lead to chronic diseases. The results of an experimental study of the change in carbon dioxide concentration in an office of a public building with an area of 30 m² with continuing presence of five people are presented. The CO₂ concentration was measured using MT 8057 portable carbon dioxide detector during 24 hours. According to the measurement results a graph of CO2 concentration is plotted against the time. It was concluded that the air quality was not satisfactory during certain periods of the working day (from 10:40 to 13:30 and from 14:45 to 19:00 the CO₂ concentration exceeded 1000 ppm) which indicates problems with the ventilation system and excessive sealing of the room (because of plastic windows). The necessity of taking measures to improve the efficiency of inflow exhaust ventilation has been substantiated.

Key words

carbon dioxide , ventilation , personalized air terminal device , air quality , air exchange , public buildings , sick building syndrome,

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UDC 628.21/.23:696.133.2

Vasilyev V. M., Malkov A. V., Klementyev M. N.

Example of air exchange arrangement and its calculation
for a sewerage network section under design

Summary

The method of calculating the volume and direction of gas travel in the sewerage network induced by the fluid carrying capacity and natural draft with account of different physical, hydraulic parameters of wastewater and gas, network design values, daylight surface temperature is presented. The method provides for making calculations at the design stage and determining the following parameters: the volume and direction of gas travel in the network, gas exchange rate, network corrosion rate, expected background concentration of corrosive gases at the assigned gas exchange rate, network corrosion rate, overhaul period. Herewith commissioning ventilation installations, filters and vent pipes is taken into account. To obtain the regularities for calculating and designing air exchange facilities in the operating urban tunnel sewers numerous experimental studies were carried out. Herewith the basic calculation formulas of the joint travel of fluid and air were obtained and the calculation method of determining the basic parameters of air exchange systems was developed. This method was used in the process of designing the Ufa wastewater disposal system expansion. The conducted economic comparison takes into account the basic technical and economic parameters of the ventilation system operating parameters; provides for assessing approximately different ventilation options and carrying out their comparison and calculating the economic effect.

Key words

collector , sewerage network , ventilation , gas exchange , air exchange calculation method

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