Indoor velocity

The precision of a thermal anemometer is dependent on the instrument quality and the conditions of use. A general rule is, the lower the measured ve locity, the higher the inaccuracy and vice versa. When measuring very low indoor velocities, around 0.1 m s, the relative error can be as high as 100% and not much lower than 30%. Low velocities are extremely difficult to measure with accuracy. 

A. Melikov, ed. Calibration and requirements for accuracy of Thermal Anemometers for Indoor Velocity Measurements. Report ET-1E9701. Technical University of Denmatk, Laboratory of Indoor Environment and Energy, 1997. 

Eigure 3 shows the winter and summer comfort zones plotted on the coordinates of the ASHRAE psychrometric chart. These zones should provide acceptable conditions for room occupants wearing typical indoor clothing who are at or near sedentary activity. Eigure 3 appHes generally to altitudes from sea level to 2150 m and to the common case for indoor thermal environments where the temperature of the surfaces (/) approximately equals air temperature (/ and the air velocity is less than 0.25 m/s. A wide range of environmental appHcations is covered by ASHRAE Comfort Standard 55 (5). Offices, homes, schools, shops, theaters, and many other appHcations are covered by this specification. 

In industrial ventilation the majority of air velocity measurements are related to different means of controlling indoor conditions, like prediction of thermal comfort contaminant dispersion analysis adjustment of supply airflow patterns, and testing of local exhausts, air curtains, and other devices. In all these applications the nature of the flow is highly turbulent and the velocity has a wide range, from O.l m in the occupied zone to 5-15 m s" in supply jets and up to 30-40 m s in air curtain devices. Furthermore, the flow velocity and direction as well as air temperature often have significant variations in time, which make measurement difficult. 

Indoor climate The actual temperature, moisture content, and air velocity within a space. 

Efficiency of any air cleaner or filter is a function of the particle size present in the indoor air and the velocity and volume ot air flowing through the device. 

Traditionally, residential mechanical equipment has been treated as independent devices that have little or no impact on the rest of the building other than the obvious stated purpose. Bath fans, dryers, and kitchen ranges are assumed to exhaust moisture, lint, and cooking by-products, but to have no impact on the performance of chimneys. Instances have been reported that show that this is not the case in some houses where the fireplaces and other combustion appliances backdraft52 when one or more of the exhaust fans are in operation. Houses have been reported in which the operation of exhaust devices increases the radon concentration.53 Houses have been found in which pressure differences between different rooms of the house caused by HVAC distribution fans have increased energy costs,54 occupant discomfort,54,55 condensation of the building shell,55 and radon concentrations in parts of the houses.29,56 All of these effects are the result of air pressure relationships created by the interaction of equipment, indoor/outdoor temperature differences, wind velocity, and moisture and radon availability. 

Sampling rates for the case of total boundary layer-control can be expected to be nearly independent of temperature, since both the diffusion coefficients in air, and the kinematic viscosity of air are only weak functions of temperature (Shoeib and Harner, 2002). This leaves the air-flow velocity as the major factor that can be responsible for the seasonal differences among sampling rates observed by Ockenden et al. (1998). The absence of large R differences between indoor and outdoor exposures may be indicative of membrane-control, but it may also reflect the efficient damping of high flow velocities by the deployment devices used for SPMD air exposures (Ockenden et al., 2001). 

A number of models have been developed for particles indoors (e.g., Nazaroff and Cass, 1989a Sinclair et al., 1990b Nazaroff et al., 1990a Weschler et al., 1996 Wallace et al., 1996, and references therein). This is a complex problem, given the number of potential sources, different deposition velocities for particles of different sizes (e.g., see Chapter 9.A.3 and Nazaroff and Cass (1989b)), the different particle compositions, and the effects of outdoor concentrations and ventila-... 

Environmental Conditions. The last area of discussion concerns those studies that emphasize environmental factors indoors and their interrelationship with clothing. Fanger s multivariate equation for predicting thermal comfort indoors, which he defines as thermal neutrality, is based on statistical analysis of 1,300 Danish and American subjects and consists of six parameters metabolic activity of occupants, clothing insulative value (clo), air temperature, mean radiant temperature, relative humidity, and air velocity ( 8, TjO An instrument based m these parameters and the statistical analysis is available (Figure 2) a reading for the parameters is integrated and the percent of occupants satisfied with the thermal environment is displayed. 

For the experimental measurement of the detonation velocity in a chemical laboratory (indoors), it is advisable to carry out the detonation experiment in a so-called detonation chamber (Fig. 7.15). Usually, the explosive is filled (pressed or... 

Analysis The body loses heat in sensible and latent forms, and the sensible heat consists of convection and radiation heat transfer. At lovy air velocities, the convection heat transfer coefficient for a standing man is given in Table 13-5 to be 4.0 W/m - C. The radiation heat transfer coefficient at typical indoor conditions is 4.7 W/m "C. Therefore, the surface heat transfer coefficient for a standing person for combined convection and radiation is... 

A limited number of sink effect studies have been conducted in full-sized environments. Tichenor et al. [20] showed the effect of sinks on indoor concentrations of total VOCs in a test house from the use of a wood stain. Sparks et al. [50] reported on test house studies of several indoor VOC sources (i.e., p-dichlorobenzene moth cakes, clothes dry-cleaned with perchloroethylene, and aerosol perchloroethylene spot remover) and they were compared with computer model simulations. These test house studies indicated that small-chamber-derived sink parameters and kj) may not be applicable to full-scale, complex environments. The re-emission rate (kj) appeared to be much slower in the test house. This result was also reported by other investigators in a later study [51]. New estimates of and were provided,including estimates of fca (or deposition velocity) based on the diffusivity of the VOC molecule [50]. In a test house study reported by Guo et al. [52], ethylbenzene vapor was injected at a constant rate for 72 h to load the sinks. Re-emissions from the sinks were determined over a 50-day period using a mass-balance approach. When compared with concentrations that would have occurred by simple dilution without sinks, the indoor concentrations of ethylbenzene were almost 300 times higher after 2 days and 7 times higher after 50 days. Studies of building bake-out have also included sink evaluations. Offermann et al. [53] reported that formaldehyde and VOC levels were reduced only temporarily by bake-out. They hypothesized that the sinks were depleted by the bake-out and then returned to equilibrium after the post-bake-out ventilation period. Finally, a test house study of latex paint emissions and sink effects again showed that... 

The intent of this paper is to present a methodology for estimating, from available information on concentrations and deposition velocities, the potential effects of anthropogenically derived acidic substances on indoor surfaces. Surface accumulation rates are derived that are applicable to all types of indoor surfaces. The discussion of the possible effects of the accumulated substances will concentrate on zinc and aluminum surfaces because data exists on the behavior of these metals in indoor environments (0. Aluminum forms a passivating oxide which protects against corrosion in most environments, while zinc is expected to corrode at a roughly linear rate over its lifetime. 

For the purposes of this discussion, it is reasonable to assume that the outdoor environment is the source of most of the anthropogenically derived substances (4) that are present in the indoor environment. The accumulation rates of species on indoor surfaces are related to the outdoor concentrations of these substances through the relationships among the indoor and outdoor concentrations and the indoor deposition velocities of these species. A substantial amount of data is available on outdoor concentrations (4-13). Simultaneous measurements of outdoor and indoor concentrations are less numerous. Very few measurements of indoor deposition velocities have been made. Estimated ratios of outdoor to indoor concentrations will be used that are based on field data, where available, or best judgments. From the limited experimental measurements, taking into account the relative variations in outdoor deposition velocities as a function of particle size, indoor deposition velocities will be estimated. Using these approximate indoor/outdoor ratios and deposition velocities, the indoor surface accumulation rates for substances contained in airborne particles can then be estimated from prevailing outdoor concentrations. 

Estimating the deposition velocities of gaseous species is considerably more complex than estimating those for substances in particles, in part due to the uncertainties in the sticking and reaction probabilities. Such estimates have not been made but the potential effects of some of the typical gases can be surmised from available data on surface accumulation rates, e.g. sulfate accumulation on indoor zinc and aluminum surfaces is predominantly a result of particulate sulfate deposition rather than a corrosion reaction involving sulfur dioxide (0. 

In order to obtain surface accumulation rates from the indoor concentrations, indoor deposition velocities are needed. These are expected to be considerably lower than outdoor deposition velocities, primarily because of reduced turbulence. Data from the authors (4) and other sources (16) suggest that indoor deposition velocities for substances associated with particles are approximately a factor of 100 lower than outdoor values this factor has been used to estimate values where experimental data are not available. Values for substances in airborne particles are summarized in Table IV. As discussed above, data are not included for gaseous species. 

Dissipative heating in highly viscous liquids leads to a considerable rise in temperature even at moderate velocities of motion. For example, according to Table 5.3 (according to [427, 487]), the viscosity and the thermal conductivity coefficient of motor oil at indoor temperature (Ts = 20° C) are, respectively, fi = 0.8kg/(m s) and x = 0.15N/(s K). By substituting these values into (5.8.4), we obtain... 

The most widely used badge type sampler for indoor air studies has been the OVM 3500. This is a circular badge with a 1-cm diffusion length containing a charcoal wafer. Desorption of VOCs is carried out within the monitor itself by the addition of carbon disulfide. Exposure periods applied have ranged from 24 h to 3 weeks. The diffusive uptake rates reported by the manufacturer for 8-h exposure periods are about 30 ml/ min, but actual values are compound specific. For the monitoring of hexane in the workplace, the diffusive uptake rate is not significantly affected by ambient air movement, provided that there is a minimum air velocity of about 0.1 m/s (HSE, 1992). 

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