Room air

Threshold Eimit Values for Chemical Substances in Work Room Air, American Conference of Government Industrial Hygienists, Cincinnati, Ohio, 1975. 

Oxygen is suppHed quite routinely to patients suffering impaired respiratory function as weU as in other situations where oxygen is deemed to be useflil. The pure oxygen, with humidification, is deHvered via a simple double tube (cannula) to a point just inside the nostrils where the 99.5% gas blends with the room air (21% O2), and is inhaled. The concentration of oxygen that reaches the lungs thus depends on the rate and volume of air inhaled and on the exit flow of oxygen from the cannula, usually one to six L/min. 

Barrier polymers are used for many packagiag and protective applications. As barriers they separate a system, such as an article of food or an electronic component, from an environment. That is, they limit the iatroduction of matter from the environment iato the system or limit the loss of matter from the system or both. In many cases the environment is simply room air, but the environment can be very different, such as ia the case of protecting a submerged system from water. 

Basically, an air-conditioning system consists of a fan unit which forces a mixture of fresh outdoor air and room air through a series of devices which 2LCt upon the air to clean it, to increase or decrease its temperature, and to increase or decrease its water-vapor content or humidity. 

Example 5 Cooling and Dehumidification Find the cooling load per pound of dry air resulting from infiltration of room air at 80 F dry-bulb temperature and 67 F wet-bulb temperature into a cooler maintained at. 30 F dry-bulb and 28 F wet-bulb temperature, where moisture freezes on the coil, which is maintained at 20 F. 

Suppose an interstate highway passes 1 km perpendicular distance from a nuclear power plant control room air intake on which 10 trucks/day pass carrying 10 tons bf chlorine each. Assume the probability of truck accident is constant at l.OE-8/mi, but if an accident occurs, the full cargo is released and the chlorine flashes to a gas. Assume that the winds are isotropically distributed with mean values of 5 mph and Pasquill "F" stability class. What is the probability of exceeding Regulatory Guide 1-78 criteria for chlorine of 45 mg/m (15 ppm). 

This chapter describes the room air conditioning process, including the interaction of different flow elements room air distribution, heating and cooling methods, process sources, and disturbances. Air handling equipment, including toom air heaters, is discussed in the form of black boxes as far as possible. 

Room air conditioning (see Fig. 2.1) systems are used to control the main controlled zone. Systems can be divided into subsystems, e.g. ... 

Typical application (example of a general room air distribution method)... 

A detailed description of the methods for room air conditioning is presented in Chapter 8. Table 2.1 summarizes the strategies. 

As an example of special rooms, air quality requirements in electronics work rooms according to standard lEC 72I-,3-.3 were used. 

If the water temperature is held constant and the water is still, Table 7.7 can be used to evaluate the temperature of the water surface (at room air temperature 20 °C and RH = 70%). When the water is stirred, the surface temperature can be assumed to be equal to the mean water temperature. 

Characteristic length, / in Eq. (7.28), depends on the application e.g., for local exhaust design / equals the characteristic hood dimension, and for room air distribution design with a temperature or contaminant stratification, / equals the room height. 

Kinetic energy from the moving objects, calculated from the body s drag coefficient k, area A, velocity V, percent movement t, and the room air density p ... 

FIGURE 7.7 Schematics of air supply (o) with inclined jets toward the occupied zone (b) with horizontal jets and occupied zone ventilated by reverse flow (c) with vertical jets. Shaded areas show the effect of buoyant forces on airflow pattern when supply air is excessively heated over the room air" ... 

One of the unidirectional flow system modifications is air supply through diffusers located above the occupietl zone. The supply air temperature is lower than the desired room air temperature in the occupied zone, and air velocity is lower compared to a mixing-type air supply, bur higher than for a thennal displacement ventilation. Polluted air of the occupied zone is suppressed by an tiverlying air cushion that displaces the contaminated air toward floor-level exhausts (Fig. ". 12). 

The effect of exhaust performance on room air movement is limited compared to the effect produced by air jets. The distance from the opening to the point where air velocity drops to 10% of the initial velocity value (Fig. 7.14) is approximately equal to one characteristic si2e of the exhaust opening (D for the round duct) and 60 characteristic sizes for the supply outlet (60D for the round nozzle). 

General exhausts typically do not prevent contaminants and heat from mixing with the room air, and thus, theoretically, it does not matter where the exhaust openings are located (Fig, 7.15). 

Ill practice, the air seldom mixes as completely as in theory. The poll no ants spread with the room air, but there may be areas where the concentration is higher than the average for the room. This has to be taken into account in determining the location of the exhaust opening. 

Characteristics of the air jet in the room might be influenced by reverse flows, created by the jet entraining the ambient air. This air jet is called a confined jet. If the temperature of the supplied air is equal to the temperature of the ambient room air, the jet is an isothermal jet. A jet with an initial temperature different from the temperature of the ambient air is called a nonisother-mal jet. The air temperature differential between supplied and ambient room air generates buoyancy forces in the jet, affecting the trajectory of the jet, the location at which the jet attaches and separates from the ceiling/floor, and the throw of the jet. The significance of these effects depends on the relative strength of the thermal buoyancy and inertial forces (characterized by the Archimedes number). 

The only force opposing the downward flow of the heated air or upward flow of the cooled air is a buoyancy force. In their analysis, Helander and Jakowatz also suggested accounting for inertial forces due to the entrainment of room air. However, this suggestion is not in an agreement with a principle of momentum conservation used in most of the existing models for isothermal jets. 

Nottage, H. B. 1951. Ventilation jets in room air distribution. Ph.D. thesis. Case Insritute of Technology. 

Christianson, L. L. 1989. Building Systems Room Air and Air Contaminant Distribution. ASHRAE, Atlanta. 

Miller, P. L. 1971, Room Air Distribution Performance of Four Selected Outlets. ASHRAE Research Report No. 2210 RP-88. Washington, D.C. 

Miller, P. L. 1969. ASHRAE Research Report RP—5,5 No. 2100 Room air distribution with an distributing ceiling— Part 1. ASHRAE Transactions, vol. 75, pp. 118-1 31. 

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