Air supply

Until a few years ago these breakers had been quite common for medium voltages, up to 33 kV. Since they require a powerful blast of air at high pressure and velocity into the arcing region, they require a reliable source of air supply. Air should be clean and dry and at the correct... 

In contrast, variable air volume (VAV) systems condition supply air to a constant temperature and ensure thermal comfort by varying the airflow to occupied spaces. Most early VAV systems did not allow control of the outdoor air quantity, so that a decreasing amount of outdoor air was provided as the flow of supply air was reduced. More recent designs ensure a minimum supply of outdoor air with static... 

Check temperature and/or humidity to see whether the complaint area is in the comfort range Take more than one measurement to account for variability over time and from place to place. Check thermostat operation. Check whether the supply air temperature corresponds to the design criteria. Use a hygrothermograph (if available) to log temperature and humidity changes in the complaint area. 

Diluting contaminants with outdoor air may increase the total quantity of supply air (including outdoor cur) Increase the proportion of outdoor air to total air, and also the improve air distribution. 

Pressure-demand full-faeepieee self-eontained breathing apparatus (SCBA) or supplied-air respirator (SAR)... 

Compliance with the written program can be verified during the walkaround by personal observation and employee interviews. If respirators are required to be worn in the workplace or respirators other than dust masks are worn by voluntary users, a written program is required. An overexposure is not required to cite. Discrepancies between the written program and implemented work practices at the worksite should be cited. Use of a elastomeric or supplied-air respirator, even when voluntary on the part of the employee, will require the employer to include all elements in a written program that will make sure that there is proper use of these respirators so that they do not create a hazard. 

Note Air distribution systems are not ventilation or air conditioning systems. For example, mixing air distribution and displacement air distribution are methods to bring the supply air to the treated space. 

To create unidirectional airflow field over the rootn area by supply air... 

To support flow field created by density differences by replacing the airflow out from the room area with supply air... 

To control air conditions within selected zone m the rooin by the supply air and allow stratification of heat and contaminants in the other room... 

These include equipment for supply air and equipment for exhaust air and gases. Cleaning of supply air is normally called air filtering, when the contaminant concentration upstream from the air filter is less than, e.g. 1-2 mg/ m Also, chemical filtration can be applied for supply air. 

Ventilation noise originates primarily from fans and the air turbulence generated inside ducts and around supply air and exhaust air terminal devices. The appearance of the noise is, of course, affected by factors such as the speed of rotation and the power of the fan, and by how the fan is stabilized or in other ways acoustically insulated. The noise level and the frequency characteristics are also largely derermined by the velocity of the air inside ducts and around terminal devices, where factors such as the dimensions and appearance of the ducts and terminal devices may play a decisive role in the appearance of the noise. 

The noise from the fan is propagated in the duct to the openings inwards or outwards in the premises. The ventilation noise often propagates into the surrounding area from the supply air and exhaust air terminal units in the rooms. The ducts in themselves may also be important sources of noise, particularly if they are poorly insulated or otherwise designed in such a way that noise generation may occur. 

Forced convection or supply air jets introduced into the room by mechanical or natural ventilation systems, or their combination (Section 7.4) ... 

The value of the coefficient of turbulent diffusion, D, depends upon the air change rate in the ventilated space and the method of air supply. Studies by Posokhin show that approximate D values for locations outside supply air jets is equal to 0.025 m-/s. Air disturbance caused by operator or robot movement results in an increase in the D value of at least two times. Studies by Zhivov et al. showed that the D value is affected by the velocity and direction of cross-drafts against the hood face, and the presence of an operator e.g., for a cross-draft directed along the hood face with velocity u = 0.5 m/s with D = 0.15 m-/s (with the presence of an operator), an increase to = 1.0 m/s results in D = 0.3 m-/s. 

The p coefficient value depends upon the supply air method (e.g., p = 0 with displacement and natural ventilation, P = 1 with convective plume dissipating within the occupied zone due to interaction with supply jets, airflows created by moving objects, etc.). 

Supply air jets forced into the room by mechanical systems... 

In rooms where energy is introduced primarily by supply air jets, air distribution methods are referred to as mixing type. With a perfect mixing-type air distribution, airflow pattern and air velocity at any point in the room are... 

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). 

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). 

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