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Testing and Balancing Fume Hood Systems
Published in Samuel C. Sugarman, Testing and Balancing HVAC Air and Water Systems, 2020
To increase face velocities consider using any of the following appropriate methods. Increase the fan speed by increasing motor sheave diameter or decreasing fan sheave pitch diameter. Change belts if needed.If the system is VAV and has a speed or static pressure controller, set the controller for a faster speed or a higher static pressure.Open the volume damper.If the system is VAV, increase the air volume at the air valve.Close the sash on a constant volume conventional hood. If the hood is a constant volume bypass type or the system is VAV, the face velocity should not change. If face velocity does change, investigate and correct where practical.Remove any blockages in the air path. Visually inspect the baffle openings and behind the baffle. Take static pressures in the duct and across the filters and the fan. Visually inspect where possible. Where practical, change ductwork to relieve restrictions and reduce duct friction and dynamic losses.
Studios and their facilities
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
Given that the mass flow rate and density are practically constant for a length of ducting, a reduction in duct area will thus cause the air velocity to increase. Consequently the velocity pressure of the air will also increase for a reduction in duct area although the static pressure will decrease by a greater amount, giving a nett fall in total pressure. In practice, air flow through ductwork is most commonly observed by measuring its pressure and velocity using instruments such as manometers and anemometers, respectively. The designer is able to calculate air delivery rates, pressures and velocities for a given system, and engineers may check these figures using the aforementioned instruments. For this reason air distribution systems are fitted with removable rubber bungs at various strategic points to enable air pressure and velocity to be measured conveniently. This is particularly useful when commissioning an air-conditioning system and also when fault finding. Manometers are often fitted permanently to ducts either side of air filters since they are a useful indicator of how dirty the filter membrane has become. Where it is required to adjust air flow this is most usually by the use of adjustable dampers fitted in the ducts. These devices, normally motor driven, may be set to vary the air flow in the same way as a
Applications
Published in W. P. Jones, Air Conditioning Applications and Design, 2012
Television and broadcasting studios are very special cases indeed. Quite apart from the need to select quiet-running plants, provided with adequate silencers and mounted on properly selected vibration isolators, the air distribution from the supply grilles or diffusers may cause far too much noise. The problem is made worse by the very high lighting loads, 300 W m−2 being common in the UK, and as much as 600 W m−2 in Europe. The studios often have very large floor-to-ceiling heights. There may be a subceiling, acting as a walkway for maintenance and access to the lights supported from it. The space above this can be 5–6 m high and the space in the studio beneath it as much as 12 m. Extreme care must be taken with the design of the air distribution system. Air has been successfully supplied at high level above the suspended walk-way, to spread evenly over it and diffuse downward through it into the studio, giving 20–25 air changes, over its height of 12 m. All supply and extract ducting must be acoustically lined, minimum 50 mm thick, in addition to the silencers required at the plant. A maximum velocity is 2.0 m s−1 through the free area of grilles or slots and velocities in the ductwork must not exceed 3.0 m s−1.
Improving system efficiency for a variable-capacity/variable-blower-speed residential heat-pump system with multizone ductwork
Published in Science and Technology for the Built Environment, 2019
Sreenidhi Krishnamoorthy, Mark P. Modera, Curtis Harrington
The impact of using higher insulation resistances on ductwork has been researched as a solution to address duct heat gain (or heat loss during heating operations) (Jump and Modera 1994); however, implementation of that solution in retrofit applications requires considerable manpower and disruption. Another potential solution to thermal heat gain/loss from ducts would be to reduce duct surface area, which becomes practical when ductwork sections can be removed from the network with zone dampers. One way to think about this is that when the capacity of the equipment is changed, the size of the duct system could be changed by the same amount, resulting in the same fractional energy losses as when the system is operating at full capacity with all ductwork operational.