Displacement Ventilation Jim Aswegan Chief Engineer
Displacement Ventilation Systems Comfort & Contaminate Control DV Concepts & System Benefits Outlet Types and Air Patterns Example l Space Layouts Displacement & LEED 2
ASHRAE 2011 Application Ch. 57 Fully Stratified Partially Mixed Fully Mixed Displacement Under Floor Air Distribution G.R.D.
Fully Mixed Air Distribution Cold & (Hot) Supply Air 48 58 F F (85 90 F) High Velocity Supply Outside Occupied Zone Minimizes Temp. Variations in Space Uniform Contaminate Concentration 4
Fully Mixed Air Distribution Mixed Air Distribution Mixed Contaminates 5
Fully Stratified Air Distribution Cool Air Supply Only 60 68 Air is Supplied Horizontally across the Floor at Low Velocity (< 70 fpm) Temperature Stratification from Floor to Ceiling (Return) Contaminate Concentration reduced in Occupied Zone 6
Fully Stratified Air Distribution 7
Displacement Ventilation BASIC CONCEPTS & SYSTEM BENEFITS 8
Basic System Concepts Low Energy ( < 0.04 Ps) Air Change Effectiveness (Std. 62.1, Ez = 1.2) Quiet Operation (< 25 NC)
Low Energy Higher equipment efficiency Uses warmer supply air 65 F compared to 55 F Energy consumption is often reduced by raising discharge temperature Extended Economizer Cycle
HVAC System Benefits Heat sources outside the stratification layer are not considered in airflow calculations l Lighting load is designed as equipment load, but not as space load Eff t li l d it b t t i Effects cooling load capacity, but not air distribution capacity
HVAC System Benefits Use 100% outside air overnight to cool Reduced chiller capacity Can be considered a thermal energy storage Can be considered a thermal energy storage system qualifying the owner for utility rebates
Low Energy Lower horsepower fans 004in 0.04 in. pressure is required for proper diffuser performance Results in lower horsepower fans required = Fan Energy egysavings
Improved Ventilation ASHRAE Standard d 62.1 Ventilation for Acceptable Indoor Air Quality Zone Air Distribution Effectiveness, E z Overhead Cooling System = 1.0 Displacement l t Ventilation = 1.2 12 16.7% Less Fresh Air Required
Return Air Outlet located at ceiling level Allows heat tfrom ceiling lights to be returned before it is able to mix with occupied zone Reduced supply volume Reduced supply volume means higher return temperatures
Humidity Issues A potential problem with warmer supply air temperatures is higher humidity Supply system must reduce relative humidity to less than 60% to meet IAQ concerns Condenser water reheat, run around coils, or face & bypass Use of a separate system to dry outside air or the use of desiccant dehumidification f l d f d h df If 55 o F supply air is used for dehumidification, return air can be mixed with supply air to achieve 65 o F air
Perimeter Heating Perimeter heating can not be accomplished with traditional displacement ventilation Separate system required in most applications: UFAD perimeter system Perimeter fan powered systems Ducting of hot or reheated air Baseboard Radiation Rdi Radiant panels Dual Chamber Diffuser 17
Dual Chamber Diffuser Dual chamber diffuser Dual chamber plenum Displacement cooling Mixed-air heating Actuated diverter (24V) Displacement diffuser cooling Linear diffuser heating 18
Application Examples Good applications Room height > 9.0 ft Open Plan Offices Meeting Rooms Casinos Restaurants Theaters, & Auditoriums Schools & Universities 19
Displacement Ventilation Advantages Smaller cooling power for desired room temperature in the occupied area Improved air quality in occupied area Longer periods of free cooling 20
Application Examples Poor Applications Room height < 9 ft Surplus heat tis the main problem not air quality In combination with mixing systems Office/rooms with cubicles Spaces with heavy contaminants 21
Displacement Ventilation Disadvantagesg Risk of draft due to placement of the diffusers Wall mounted devices often occupy large wall areas Stratified air becomes uncomfortable when cooling load exceeds ~30 Btu/hr ft t 2 Cannot heat with displacement ventilation 22
Thermal Comfort ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy Maximum recommended T hf = 5.4 F Avoid drafts by keeping T es < 36 F
Temperature Gradient Ceiling Height 9 14 50% Rule is applied 62 F 72 F 82 F 10 F 10 F (Displacement ventilation, REHVA)
Temperature Gradient Ceiling Height > 14 33% Rule 33% 67% 65 F 72 F 86 F 7 F 14 F (Displacement ventilation, REHVA)
Displacement Ventilation TYPES OF OUTLETS & DISTRIBUTION PATTERNS 26
Adjacent Zone 27
Discharge Air Patterns 28
Standard Air Patterns Adjusted Air Patterns 29
Rectangular Displacement Diffusers Mounts in wall 1 way pattern 30
Displacement Diffusers Rectangular Rectangular In wall, flush or floor mount 31
Displacement Diffusers Rectangular 3 Way Rectangular In wall, flush or floor mount 3 way pattern 32
Displacement Diffusers Rectangular Curved Face Flush or floor mount 3 way pattern 33
Displacement Diffusers Rectangular Stair Riser Steps, Stair Risers applications Great for auditoriums, concert, arena s, and lecture halls 34
Displacement Diffusers Circular Column l or floor mount 360º discharge 35
Displacement Diffusers Semi Circular 180º Sidewall or column applications 180º pattern 36
Displacement Diffusers U shaped Semi circular i i l w straight ih sides 3 way pattern 37
Displacement Diffusers Corner w/ Curved Face Corner mount applications i 2 way pattern 38
Displacement Diffusers Corner/Flat Face Corner mount applications 2 way pattern 39
Displacement Ventilation EXAMPLE SPACE LAYOUTS 40
Private Perimeter Office Perimeter Wall 41
Open Plan Interior Office 42
Interior Break Room Round Outlets 43
Perimeter Conference Room Outside Wall 44
Elementary School Classroom Perimeter Wall 45
ASHRAE Standards for LEED ASHRAE S 62.1 IEQ Prerequisite 1: Minimum IAQ Performance IEQ Credit 1: Outdoor Air Delivery Monitoring IEQ Credit 2: Increased Ventilation IEQ Credit 6.2: Controllability of Systems: Thermal Comfort (for naturally ventilated spaces) ASHRAE Standard 55 IEQ Credit 6.2: Controllability of Systems: Thermal Comfort IEQ Credit 71 7.1: Thermal Comfort: Design IEQ Credit 7.2: Thermal Comfort: Verification
Displacement & LEED Optimize Energy Performance (EAc1) Minimum IAQ Performance (EQp1) Increased d Ventilation i (Q2) (EQc2) Thermal Comfort: Design (EQc7.1)
Displacement Ventilation & LEED Minimum Energy Performance: EAp2 Optimize Energy Performance: EAc1 Minimum Indoor Air Quality Performance: IEQ p1 Increased Ventilation: IEQc2 Thermal Comfort Design: IEQc7.1 48
Minimum IAQ Performance (EQp1) Minimum IAQ per ASHRAE 62.1 1 2007 EQ Q Prereq 1 Required
Increased Ventilation (EQc2) Increase breathing zone outdoor air ventilation rates to all occupied spaces by at least 30% above the minimum rates required by ASHRAE Standard 62.1 2007 as determined by EQ Prereq. 1 Submit Narrative describing the project s ventilation system, including fresh air intake volume for each zone and confirmation that outdoor air exceeds ASHRAE 62.1 by 30% EQ Credit 2 1 Point
Thermal Comfort (EQc7) Design Comply with ASHRAE Standard 55 2004 Submit Narrative detailing established comfort criteria per ASHRAE Standard 55 2004, the desired quality and occupant satisfactionwithbuildingperformance performance, and supporting documentation showing the system design meetsthese these criteria EQ Credit 71 7.1 1 Point
Publications HVAC Applications Handbook, Chapter 57 (ASHRAE, 2011) Fundamentals Handbook, Chapter 20 (ASHRAE, 2009) System Performance Evaluation and Guidelines for Displacement Ventilation (ASHRAE, 2003) Displacement Ventilation in Non Industrial Premises (REHVA, 2002)
Thank you! Questions? 53