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Resistance-Start Induction-Run Motor

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Resistance-Start Induction-Run Motor

The rotating magnetic field of the resistance-start induction-run motor is produced by the out-of-phase currents in the run and start windings. Since the run winding appears more inductive and less resistive than the start winding, the current flow in the run winding will be close to 90 degrees out-of-phase with the applied voltage. The start […]

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Return grille sound requirement

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Return air grilles should be selected for static pressures. These pressures will provide the required NC rating and conform to the return system performance characteristics. Fan sound power is transmitted through the return air system as well as the supply system. Fan silencing may be necessary or desirable in the return side. This is particularly […]

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HVAC Controlling Casing Noise

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Terminal boxes can sometimes be located over noisy areas (corridors, toilet areas or machine equipment rooms), rather than over quiet areas. In quiet areas casing noise can penetrate the suspended ceiling and become objectionable. Enclosures built around the terminal box (such as sheetrock or sheet lead over a glass-fiber blanket wrapped around the box) can […]

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Types of Registers and Grilles

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The spread of an unrestricted air stream is determined by the grille bar deflection. Grilles with vertical face bars at 0° deflection will have a maximum throw value. As the deflection setting of vertical bars is increased, the air stream covers a wider area and the throw decreases. Registers are available with adjustable valves. An […]

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HVAC Air Noise

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High velocities in the duct or diffuser typically generate air noise. The flow turbulence in the duct and the excessive pressure reductions in the duct and diffuser system also generate noise. Such noise is most apparent directly under the diffuser. Room background levels of NC 35 and less provide little masking effect. Any noise source […]

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HVAC Vortex Shedding

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Product research in controlling casing noise has developed a new method of reducing radiated noise. The technique is known as vortex shedding. When applied to terminal boxes, casing radiated noise is dramatically lowered. Casing radiation attenuation (CRA) vortex shedders can be installed in all single- or dual-duct boxes up to 7000 cfm, constant volume or […]

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HVAC Fire and Smoke Dampers

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HVAC Fire and Smoke Dampers

Ventilating, air-conditioning, and heating ducts provide a path for fire and smoke, which can travel throughout a building. The ordinary types of dampers that are often installed in these ducts depend on gravity-close action or spring-and-level mechanisms. When their releases are activated, they are freed to drop inside the duct. A fusible link attachment to […]

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Straight Tube Boilers

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The STRAIGHT-TUBE class of water-tube boilers includes three types: 1. Sectional-header cross drum 2. Box-header cross drum 3. Box-header longitudinal drum In the SECTIONAL-HEADER CROSS DRUM boiler with vertical headers, the headers are steel boxes into which the tubes are rolled. Feedwater enters and passes down through the downcomers (pipes) into the rear sectional headers […]

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Horizontal Return Tubular Boiler

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Horizontal Return Tubular Boiler

A STATIONARY BOILER can be defined as one having a permanent foundation and not easily moved or relocated. A popular type of stationary fire-tube boiler is the HORIZONTAL RETURN TUBULAR (HRT) boiler shown in figure 1-4. The initial cost of the HRT boiler is relatively low and installing it is not too difficult. The boiler […]

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Scotch Marine Boiler

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Scotch Marine Boiler

Figure 1-1 is a portable Scotch marine tire-tube boiler. The portable unit can be moved easily and requires only a minimal amount of foundation work. As a complete self-contained unit. its design includes automatic controls. a steel boiler. and burner equipment. These features are a big advantage because no disassembly is required when you must […]

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