Understanding Manual Q - Low Pressure, Low Velocity Duct Design in the Real World
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The purpose of this program is to give the student the tools necessary to design a low pressure, low velocity ducted distribution system for a low rise commercial building.
Part 1 (Airflow Basics)
Low pressure, low velocity is defined. Duct systems are classified as to function, path geometry, velocity range, pressure class, construction material and shape. Fan and Duct system performance are evaluated using the sensible heat equation and the total pressure equation. How to measure system pressure is explained using duct traverse, Pitot tube, duct flow equation and velocity pressure equation. Tools and instruments are discussed such as Magnehelic gage, Static pressure tips, Anemometer and Flow hood. Flow through registers and grilles is explained as well as the Ak value.
Part 2 (Fan Performance)
Fan curves, their use and application and the result of fan speed changes are discussed and explained. Duct system curve and Operating point are also considered. Standard air is defined and Correction factors for altitude and temperature are explained. Fan performance as well as fan curve correction, correction for shape and correction for roughness are all considered. Duct system pressure changes resulting from straight sections of duct, duct system fittings, fan inlet and outlet fittings, air side devices and supply outlets and return inlets are discussed and explained.
Part 3 (Fan and Duct System Interface)
Fitting losses and dynamic loss coefficients are explained and calculated. Fan and duct system interfaces such as Effective duct, Fan outlet, System effect losses, Fan discharge into plenum, Fan discharge into elbows, and Fan inlet are all considered. Fans located in plenums or cabinets and inlet obstructions are also discussed. Air side devices such as air filters, dampers, as well as damper linearity and damper pressure drop, louvers and penthouse hoods, coils, supply air outlets and inlets and air distribution devices are all considered.
Part 4 (Creating Comfort Using Manual T)
Occupied Zone is defined and explained. Terminal Velocity, Register Throw, Manufacturer’s Engineering Data, Ak and use in volume formula Register or diffuser Drop and Register Spread are all defined and explained. Spacing of diffusers and registers, Ceiling and Wall Effect, Primary and Secondary Air and Induction (Aspiration) are all considered. Choosing a return air grille using the manufacturer’s engineering data is explained. The Cooling and Heating Factors for determining the volume of air (CFM) to be delivered to a space is explained.
: Air Conditioning Contractors of America (ACCA)