ROOM AIR DISTRIBUTION MSYS4480 1 Why Air Distribution? Provide - PDF document

1/21/2019 ROOM AIR DISTRIBUTION MSYS4480 1 Why Air Distribution? ▪ Provide Occupant Thermal Comfort ▪ Provide sufficient ventilation to meet codes ▪ Control Latent loads (Humidity) Satwinder Singh / www.tagengineering.ca 2 2 1

1/21/2019 Comfort Criteria For Occupied zone: ▪ Air temp maintained between 70-76°F ▪ RH maintained between 25-60% ▪ Maximum air motion in the occupied zone ▪ 50 fpm cooling ▪ 25 fpm heating ▪ 1-4 CFM per square foot ▪ Maximum temperature gradient ▪ 1-2° cooling ▪ 4° heating Satwinder Singh / www.tagengineering.ca 3 3 What distributes the air? ▪ Rooftop units, Fan Coil Units ▪ Mixing Boxes, VAV terminals, Water Source Heat Pumps etc ▪ Ductwork ▪ Grilles, Diffusers and other air distribution devices Satwinder Singh / www.tagengineering.ca 4 4 2

1/21/2019 Air Diffusion / Distribution Methods ▪ Mixing Systems ▪ Displacement Ventilation ▪ Localized Ventilation (Make-Up Air) Satwinder Singh / www.tagengineering.ca 5 5 Mixed Ventilation ▪ Most Common Satwinder Singh / www.tagengineering.ca 6 6 3

1/21/2019 Types of Air ▪ Primary Air: ▪ The conditioned air discharged by the supply outlet. This air provides the motive force for room air motion. ▪ Total Air: ▪ The mixture of primary air and entrained room air which is under the influence of supply outlet conditions. ▪ This is commonly considered to be the air within an envelope of 50 fpm [0.25 m/s] (or greater) velocity. The temperature difference between the total air and the room air creates buoyant effects which cause cold supply air to drop and warm air to rise. Satwinder Singh / www.tagengineering.ca 7 7 Why Air Distribution? Satwinder Singh / www.tagengineering.ca 8 8 4

1/21/2019 Why Air Distribution? Satwinder Singh / www.tagengineering.ca 9 9 Room Air Diffusion - Heating Satwinder Singh / www.tagengineering.ca 10 10 5

1/21/2019 Space Air Distribution - THROW THROW • Mass flow • Outlet velocity Satwinder Singh / www.tagengineering.ca 11 11 DROP DROP • Mass flow rate • Bouyancy Satwinder Singh / www.tagengineering.ca 12 12 6

1/21/2019 Terminal Velocity Most catalog throw data is presented for isothermal conditions (i.e., supply air temperature equals room temperature). During cooling the denser supply air will shorten the horizontal throw to approximately 75% of tabulated values (multiply by 0.75), assuming a temperature differential of approximately 15 °F [7.5 °C]. Referring to the catalog page we determine the 50 fpm throw to be : • 0° deflection - 22 ft isothermal or (22 x .75) = 17 ft cooling • 22° deflection - 18 ft isothermal or (18 x .75) = 14 ft cooling • 45° deflection - 11 ft isothermal or (11 x .75) = 8 ft cooling The 22° deflection provides the best coverage and would be the optimum selection. Satwinder Singh / www.tagengineering.ca 13 13 Terminal Velocity Throw is the distance from the center of the outlet face to a point where the velocity of the air stream is reduced to a specified velocity. Usually ▪ 150 fpm [0.75 m/s] ▪ 100 fpm [0.50 m/s] ▪ 50 fpm [0.25 m/s] T150 [T0.75], T100 [T0.50], T50 [T0.25] Satwinder Singh / www.tagengineering.ca 14 14 7

1/21/2019 SPREAD Satwinder Singh / www.tagengineering.ca 15 15 Coanda Effect Satwinder Singh / www.tagengineering.ca 16 16 8

1/21/2019 Occupied Zone 6ft [1.8m] Satwinder Singh / www.tagengineering.ca 17 17 Air Distribution – Performance Factors ▪ Air Pattern ▪ Throw ▪ Drop ▪ Spread ▪ Pressure Drop ▪ Noise Level Satwinder Singh / www.tagengineering.ca 18 18 9

1/21/2019 Air Distribution – Performance Factors – Air Patterns Satwinder Singh / www.tagengineering.ca 19 19 Air Distribution – Performance Factors – Air Patterns Satwinder Singh / www.tagengineering.ca 20 20 10

1/21/2019 Outlet Classification Group A. Outlets mounted in or near the ceiling that discharge air horizontally. Group B. Outlets mounted in or near the floor that discharge air vertically in a non-spreading jet. Group C. Outlets mounted in or near the floor that discharge air vertically in a spreading jet. Group D. Outlets mounted in or near the floor that discharge air horizontally. Group E. Outlets mounted in or near the ceiling that project primary air vertically. Satwinder Singh / www.tagengineering.ca 21 21 Air Distribution – Performance Factors – Diffusers (Group A) Satwinder Singh / www.tagengineering.ca 22 22 11

1/21/2019 Air Distribution – Performance Factors – Pressure Drop Satwinder Singh / www.tagengineering.ca 23 23 Air Distribution – Performance Factors – Noise Criteria Satwinder Singh / www.tagengineering.ca 24 24 12

1/21/2019 Air Distribution – Performance Factors – Noise Criteria Satwinder Singh / www.tagengineering.ca 25 25 Air Distribution – Performance Factors – Noise Criteria Decibel(dB) is measured against a frequency and averaged into octave bands Both tones are equally loud Satwinder Singh / www.tagengineering.ca 26 26 13

1/21/2019 Air Distribution – Performance Factors – Noise Criteria For HIGH Frequencies • 1 dB not noticeable • 3 dB just perceptible • 5 dB noticeable • 10 dB twice as loud • 20 dB four times as loud For LOW Frequencies • 3 dB noticeable • 5 dB twice as loud • 10 dB four times as loud Satwinder Singh / www.tagengineering.ca 27 27 Air Distribution – Performance Factors – Noise Criteria Calculating NC Level Satwinder Singh / www.tagengineering.ca 28 28 14

1/21/2019 Air Distribution – Performance Factors – Noise Criteria Calculating NC Level Satwinder Singh / www.tagengineering.ca 29 29 Air Distribution – Performance Factors – Noise Criteria Can we add decibels? 80 dB To add decibels, calculate + the difference 76 dB 80 dB ‐ 76 dB 156 dB 6 dB From Chart: Add 1.0 dB to higher Value 80 dB +1 dB = 81 dB Satwinder Singh / www.tagengineering.ca 30 30 15

1/21/2019 Air Distribution – Performance Factors – Noise Criteria Hmmmmm…….?? • Proximity to the source sources is vital Diffuser NC values are based on a 10 dB • Properly selected diffusers shouldn’t room effect deduction in each octave be heard from more than 10 feet away band • Typical medium office with 8‐10 ft • There might be more than one high lay‐in ceiling, commercial diffusers in a room, not more than 1 or carpet, sheetrock walls, and some 2 will be within 10 feet from an office furniture occupant • 10 dB is a reasonable room effect deduction for the critical octave bands • Critical octave bands are 4 th (500 Hz), 5 th (1000 Hz), and 6 th (2000 Hz) Satwinder Singh / www.tagengineering.ca 31 31 Air Distribution – Performance Factors – Noise Criteria • Diffuser NC values are based on a 10 dB room effect deduction in each octave band • Typical medium office with 8‐10 ft high lay‐in ceiling, commercial carpet, sheetrock walls, and some office furniture • 10 dB is a reasonable room effect deduction for the critical octave bands • Critical octave bands are 4 th (500 Hz), 5 th (1000 Hz), and 6 th (2000 Hz) Satwinder Singh / www.tagengineering.ca 32 32 16

1/21/2019 Air Distribution – Noise Criteria - Choosing Diffusers Satwinder Singh / www.tagengineering.ca 33 33 Air Distribution – Noise Criteria - EXAMPLE A Model 520 size 6 in. x 5 in. supply grille operating at 150 cfm has been selected to supply a 10 ft x 15 ft room as shown. What is the best deflection setting of the diffuser blades if conditioned cool air is supplied? For 50 fpm throw: 0° deflection: 22 x .75= 17’ 22° deflection: 18 x .75= 14’ 45° deflection: 11 x .75= 8’ 22° deflection provides the best coverage and would be the optimum selection. Satwinder Singh / www.tagengineering.ca 34 34 17