Room Air Distribution Presented by Randy Zimmerman

Introduction TC 5.03 update Mixed air systems vs. stratified systems Thermal comfort Ventilation effectiveness Diffuser performance Overhead heating Product selection Questions and answers

TC 5.03 Room Air Distribution TC 5.03 Officers Jerry Sipes – Chair Randy Zimmerman – Vice Chair/Research Chair Kevin Gebke – Secretary Fred Lorch - Membership Curtis Peters – Handbook Andrey Livchak - Programs

TC 5.03 Room Air Distribution TC 5.03 Activities RP-1546 – ADPI Update (due 2014) RP-1629 – Energy Performance of Active Beam Systems (just started) SPC 200 – MOT Active Chilled Beams (public review) SPC 130 – MOT Terminal Units (public review) SPC 70 – MOT Air Inlets and Outlets (just formed)

TC 5.03 Room Air Distribution Join TC 5.03 – a large and active committee Chapters in (3) ASHRAE Handbooks Fundamentals Applications Systems and Equipment Subcommittees Room Fan Coils Chilled Beams Underfloor Air Distribution Air Curtains

So Many Choices There’s a Good, Better and Best System for Every Building Old and New Technology Overhead Air Distribution Underfloor Air Distribution Active Chilled Beams Displacement Ventilation Let me assure you that the purpose of this webcast is not to sell displacement ventilation as the best system for every building. We’ll discuss the reasons why certain applications are recommended while others are not, but it’s important to consider displacement ventilation as one more possible solution. I like to think of displacement as one more tool in my toolbox of air distribution systems.

GRD’s Grille Register Diffuser They are all outlets! Outlet similar in size to duct size Register Grille with an integral dampering device Diffuser Outlet that is often larger than duct size Designed to create an air pattern They are all outlets!

The Occupied Zone Occupied Zone 6.0 ft above floor 3.3 ft from outside wall 1.0 ft from interior wall 3.3’ 6.0’ 1.0’

Conventional Mixed-Air System

Fully-Stratified System

Mixed-Air System Concepts Supply air 38-55oF Cold air supplied outside the occupied zone, thoroughly mixes with room air Creates an air pattern on the ceiling and/or walls Picks up heat and pollutants at the ceiling level Creates low velocity room air motion Ideally creates uniform temperature throughout the space and minimizes stratification Displacement systems typically supply 63-68°F air through specially-designed diffusers that are located on low side walls. This cool air discharges at less than 80 fpm from the face of the diffuser and quickly cascades down to the floor. The air continues to move slowly across the room in a layer about 4” deep until it locates a source of heat or an obstruction. In office applications the heat sources in the occupied zone are usually people and equipment. When this slow moving pool of air encounters a heat load, it quickly rises and carries the heat and pollutants towards the ceiling. Internal heat loads and contaminants are then carried away by the return air. We refer to this as a thermal plume.

Fully-Stratified Concepts Supply air 63 - 68oF Cool air supply displaces warm room air at low velocities Uses the natural buoyancy of warm air to provide improved ventilation and comfort Cold air moves slowly across the floor until it reaches a heat source, then rises Improved IAQ Displacement systems typically supply 63-68°F air through specially-designed diffusers that are located on low side walls. This cool air discharges at less than 80 fpm from the face of the diffuser and quickly cascades down to the floor. The air continues to move slowly across the room in a layer about 4” deep until it locates a source of heat or an obstruction. In office applications the heat sources in the occupied zone are usually people and equipment. When this slow moving pool of air encounters a heat load, it quickly rises and carries the heat and pollutants towards the ceiling. Internal heat loads and contaminants are then carried away by the return air. We refer to this as a thermal plume.

Improved Contaminant Removal Stratification creates a single pass Unlike mixed-air, contaminants are not redistributed throughout the room Displacement ventilation can be thought of a single pass system. Unlike a mixed-air system that tends to distribute contaminants more or less evenly throughout the entire room, displacement uses natural buoyancy to collect pollutants at the ceiling where they can exit the room. This action results in lower concentrations in the occupied zone. Displacement Ventilation Overhead System

Improved Ventilation ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality Zone Air Distribution Effectiveness, Ez Best Overhead System (Ez = 1.0) Displacement Ventilation (Ez = 1.2) UFAD also qualifies if T50 is 4.5 ft or less 16.7% Less Fresh Air Required Displacement ventilation is known to be a way to increase comfort through improved ventilation. The goal of any air distribution system should be to efficiently deliver ventilation air to the breathing zone. For this reason, ASHRAE Standard 62.1 rates various types of systems with regard air change effectiveness. These ratings take into account the supply and return locations as well as the discharge pattern and temperature. According to this standard, the very best overhead systems qualify for a rating of 1.0 and other lesser systems could be as low as 0.5. On the other hand, displacement qualifies for the highest possible rating of 1.2. This means that displacement ventilation is 20% more effective than the best overhead system and the minimum fresh air requirement can therefore be reduced by nearly 17%.

Thermal Comfort ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy Maximum recommended ∆Thf = 5.4°F ASHRAE Standard 55 is often referred to as the thermal comfort standard. It recommends that for good thermal comfort the temperature difference between the head and foot level of a standing person should not exceed 5.4 °F. If we assume a constant floor-to-ceiling stratification gradient of no more than 1°F per foot, any design that provides comfort for a standing occupant should also work for a seated occupant because a seated occupant would experience no more than a 3.6°F differential. In addition, we need to pay attention to the difference between the supply and exhaust temperatures. As a rule-of-thumb, exhaust temperatures should not be more than 36°F higher than supply temperatures to avoid a sensation of draftiness.

What About Heating? Fully-stratified systems typically use a secondary system for heating Low velocity warm air would short circuit to the ceiling Fin tube perimeter heat is often used

Dual Plenum Diffusers Dual plenum diffusers provide Displacement outlet for cooling Grille for low sidewall heating Internal diverting damper Allows a single system to cool and heat in mild climates

Outlet Performance Tested per ASHRAE 70 SP and TP Area factor, Ak Sound level Throw, drop and spread

Outlet Performance Pressure drop (in wg) Area factor, Ak (ft2) SP measured TP = SP + VP Area factor, Ak (ft2) cfm = Ak x fpm Sound level (dB ref 10-12 w) NC assumes 10 dB room effect

Outlet Performance Throw Drop Spread Terminal velocities T150, T100, T50 Measured from centerline Isothermal (unless specified) Drop Distance below ceiling to center of discharge jet Spread Unbounded jets spread at 11°angle (on each side)

Area Factor vs. Free Area Free area does not govern outlet performance Performance is related to geometry Hole size/shape/number Material depth Curved/angled surfaces Free area may or may not be easy to determine, but it’s not really useful information

ADPI Air Diffusion Performance Index (ADPI) Statistically relates local temperatures and velocities to occupant comfort Ratio of diffuser T50 to characteristic length of the room being served ADPI > 80 is acceptable Currently only applies to cooling applications Soon may be expanded to include more diffuser types and add heating applications

ADPI ASHRAE RP-1546 Conducted at University of Texas at Austin Verify original research Expand the types of outlets Run heating tests Testing will be completed by August, 2014

ADPI Example ADPI Example Results for 24x24 diffusers with 8” necks 200 cfm 20° ∆T 400 ft2 Results for 24x24 diffusers with 8” necks Plaque Face = 93.0 Multi-Cone = 93.0 Perforated = 84.8 It often makes sense to look at typical rather than 100% design conditions…

Overhead Heating Discharge temperature affects minimum ventilation In overhead heating applications, discharge temperatures should never be more than 15°F higher than the desired room temperature and T150 must be within 4.5 ft from the floor (Ez = 1.0) If ΔT > 15°F, then Ez = 0.8 and cfm increases by 25%

Split Pattern Linear 50/50 throw pattern is the best compromise for both heating and cooling Works best when splitting the diffuser length, rather than splitting slots In the cooling mode, 50% of the supply air is directed down the exterior walls – which also wastes energy and causes drafts near the floor… 26

Air Patterns Cross flow Ceiling Longer throw

Air Patterns Round Ceiling Shorter throw

Air Patterns Swirl (floor) Displacement (sidewall) Linear (ceiling) Linear (air curtain) Laminar (OR, clean rooms) Hemispherical (lab, industrial)

Return Grilles Contrary to popular belief – return grille locations generally do not affect room air motion Return grilles merely provide an exit

Surface Effects Discharge jets attach themselves to surfaces Ceilings Walls Glass Obstructions with an angle of incidence greater than 15° can kick the air pattern off the ceiling

Open Ceilings Unless otherwise specified assume Ceiling diffusers were tested with a ceiling Side wall grilles were tested near a ceiling Internal vs. external Coanda pocket Most diffusers need a ceiling for horizontal air pattern Sometimes a small lip can be added to create a ceiling effect Free jets result in a 30% throw reduction due to increased expansion

Temperature Effects T150 is temperature independent – velocity driven Horizontal ceiling throw Cooling decreases throw by 1% per °F Heating inceases throw by 1% per °F Example – Catalog (isothermal) 4-7-9 Cooling 4-6-7 Heating 4-8-11

Active Length Linear diffusers should not have active sections longer than 10 ft Overly long active sections cause problems Extended and unpredictable throw Undulating air patterns Solutions Provide 1-2 ft inactive breaks between sections Alternate throw direction

Acoustics Select diffusers such that they will not be heard Noisy diffusers create a poor communication NC set by in octave bands 4-6 (500, 1000, 2000 Hz) – speech interference bands 10 NC points lower than desired room level, and rarely higher than NC25 unless it’s an industrial application

What Type To Select? The choice can depend on many things Air pattern Performance Appearance Cost Space limitations Installation/ceiling type

Summary Many types of systems and outlets are available, but there’s always a best choice Selecting the right air pattern is critical Be aware of surfaces and ceilings Keep overhead heating temperatures low Select diffusers to be inaudible

Questions and Answers Questions? Thank-you!