Air-exchange

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

Data files on the THERdbASE CD are 1990 Bureau of Census Population Information, California Adult Activity Pattern Study (1987-88), AT T-sponsored National Activity Pattern Study (1985), Chemical Agents from Sources, Chemical Agent Properties, Air Exchange Rates, Information from EPA s TEAM (Total Exposure Assessment Methodology) Studies, Information from EPA s NOPES (NonOccupational Pesticides Exposure Study) Studies, Information from EPA s AIRS (Aerometric Information Retrieval System), and Human Physiological Parameters. 

Absorption, distribution, biotransformation, and excretion of chemical compounds have been discussed as separate phenomena. In reality all these processes occur simultaneously, and are integrated processes, i.e., they all affect each other. In order to understand the movements of chemicals in the body, and for the delineation of the duration of action of a chemical m the organism, it is important to be able to quantify these toxicokinetic phases. For this purpose various models are used, of which the most widely utilized are the one-compartment, two-compartment, and various physiologically based pharmacokinetic models. These models resemble models used in ventilation engineering to characterize air exchange. 

Zhivov, A. M. and Kclina, E. L. 1989. Evaluation of air exchange rate with air supply with inclined jets. In Occupational Safety Technique and Industrial Sanitary Collected Papers of the Occupational Safety Institutes under AUCCTU, Mosciow. Profizdat, pp. 33-38,... 

The air exchange rate, G , required for temperature control in the occupied zone can be calculated from the room heat balance equation ... 

Charleswofth, P. S. 1988. Air Exchange Rate and Airtightness Measurement Techniques An Applications Guide. Air Infiltration and Ventilation Center, Coventry, UK. 

Air exchange efficiency indices can be used for cases where no or little information on sources is available, whereas ventilation efficiency, which concerns workers, can be used where very detailed information is available on sources and activities. 

In order to have effective exchange of air in important locations in a room, the age of the air in those locations should be low. The basis for comparison is the complete mixing scenario. That scenario gives the same age for any air volume selected in the room, identical to the nominal time constant for the ventilation airflow,. A steady-state scenario is assumed. See Sutcliffe for an overview of definitions related to age of air. The various air exchange efficiency indices are presented in Table 8.6. 

In very long rooms, the exhaust should be located at the opposite end of the room. Otherwise, the air exchange in the far end of the room may be small, resulting in an accumulation of contaminants in that part of the room. See Fig. 8.42. 

For supply inlets in rooms some performance measurements exist, such as air exchange and ventilation efficiencies (see Chapter 8). It is usually not possible to use these for local ventilation supply inlets, and for the moment there are no specific measurements to evaluate the influence of an inlet on contaminants. Some trials with comparison indices, which compare inhaled concentrations (or exposures) with and without a supply inlet, have been done. 

Tor a representative summer case, the outdoor air exchange and the room air temperatures in various zones are to be determined. 

Wind-induced pressures. The pressure at a location on the envelope depends on the shape of the building, the shielding of the building, the wind direction, and the wind speed. Air-exchange due to wind turbulence effects is normally not considered. 

As previously outlined, perfect mixing is assumed in the individual zones. The spatial distribution of air velocities, contaminant concentrations, and air temperatures in a zone cannot be determined. Air exchange due to wind turbulence effects is not considered. 

Many natural ventilation problems are related to the thermally driven air exchange in a building. Such cases must be most often treated using combined thermal and ventilation models or thermal models with an integrated natural ventilation model (see Section 11.5). For example, in COMIS, a simple, single-zone thermal model is included for transient single-sided ventilation calculations. 

VOCs are released during chemical cleaning of bonding surfaces. The extract system is designed on the basis of the steady-state concentration determined for maximum source strength and considering the mechanical extract ventilation only and no air-exchange with the assembly hail. Ehis concentration must be kept below the threshold concentration (TVL) which is set to 300 mg/kg in this example. 

In thermal models, the ventilation airflow rates normally arc input parameters, to be defined by the user or to be calculated by the program on the basis of a nominal air exchange or flow rate) and some control parameters (demand-controlled ventilation, variable air volume flow ventilation systems), in airflow models, on the other hand, room air temperatures must be defined in the input (see Fig. 11.49). 

Due to the thermally driven air exchange and the large building masses involved, the problem must be studied using a dynamic thermal building mode) wirh an integrated ventilation model. 

The relationships between air exchange rate and temperature difference were determined using COMB (Fig. 11.51) and then integrated as the ventilation model in the thermal model. The rhermai behavior is modeled with the TRNSYS multizone type, considering the hall and the room below the thick concrete test floor slab. For the hall, a room model with two air temperature nodes (one for the occupied zone and one for the rest of the hall) and geometrically detailed radiation exchange is used. 

Air change rate, outdoor air temp>erature (TJ and room air temperature in the oecupfed, u. n ui-day summer period. Ventilation openings are opened 0-24 hours if T, > T , The moment when T becomes greater than T is highlighted on the first day, with the air exchange dropping to zero. 

Wall ventilator A wall air outlet or inlet with a weatherproof cover to provide air exchange between inside and outside by natural forces. 

The flasks used had narrow mouths, whereas the Laug technique specifies widemouthed beaker flasks. The small opening reduced air exchange and moisture condensed on the insides of the flasks. This condition is not good for flies and probably accounts for the mortality observed in the checks. However, this effect had not shown up 5 hours after the tests were started, and by that time most of the flies in the flasks containing insecticides were down. These tests are qualitative rather than quantitative, but the data indicate that the chemically determined quantities of the various insecticides in the fat extract were nearly equal in toxicity to known samples at the same level. 

Nazaroff, W. W., F. J. Offermann and A. W. Robb, Automated System for Measuring Air-Exchange Rate and Radon Concentration in Houses,... 

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