High Rise Building Air Pressure, Infiltration & Stack .

High Rise BuildingAir Pressure, Infiltration & Stack EffectTheory and Impact on Indoor Environment2012 Spring Seminar, June 14, 2012By:Mehdi Jalayerian, PE, LEED AP BD CExecutive Vice PresidentEnvironmental Systems Design, Inc. 2012-ESD, Inc.

Learning Objectives Basic Theory of Air Flow Around and In High Rise Building– Wind– Stack-Effect Vertical Compartmentation––––ElevatorsStairsImpact on EnergyImpact on Pressure Smoke Management– Pressurization (Stairs/Space)– Smoke Control Considerations Example Building Air Movement/Pressure Analysis– 16 Story Hotel– Mixed-use Tall Building Summary Guidelines 2012-ESD, Inc.

Air Flow in High Rise Buildings Forced ventilation– Building supply/exhaust air systems– Fully controlled and distributed Natural ventilation– Pressure from wind and/or stack effect– Strategically placed intentional openings Infiltration––––Uncontrolled air leakageUnintentional openings in building envelopeAir leakage through floor/wall openingsDriven by wind force, temperature difference (buoyancy), and/orsystem/appliance induced Space Pressurization– Normal mode pressurization– Fire mode pressurization (fire floor and stairs) for smokemanagement 2012-ESD, Inc.

Basic Theory Air movement into/out of a building iscaused by wind pressure and stackeffect pressure Wind pressure causes air to infiltratesinto the building, or ex-filtrate out ofthe building Stack effect (air buoyancy) pressurecauses air to rise or dropWIND VELOCITYPROFILEEXFILTRATIONCold Weather Air infiltrates into the lower half of thebuilding, rises to upper floors due tostack effect and exfiltrates in theupper half of the building.STACK EFFECTHot Weather Air infiltrates into the upper half of thebuilding, drops to lower floors due tostack effect and exfiltrates in thelower half of the building.NUTRAL PLANEINFILTRATIONAVERAGE SURROUNDING ROOF HEIGHTOR 10M ABOVE GRADE 2012-ESD, Inc.

Basic Theory – Air Flow Around Building 2012-ESD, Inc.

Basic Theory - Wind PressureWind creates a distribution of static pressure on the buildingenvelope, which is dependent on wind direction andlocation on building envelope. Pw C Cp ρ v2/2 PwCCpρv 0.33 in WG wind pressure difference, inches of water unit conversion, 0.0129 surface pressure coefficient, dimensionless air density, lbm/ft3 (about 0.075) wind speed, mphNote: Wind Pressure at top of 60 Story:Upwind 1.32 in. of WaterSides 0.61 in. of WaterDownwind -0.61 in. of WaterWindX15 mph2X 2012-ESD, Inc.

Basic Theory - Stack Effect PressureAir density varies with temperature. In cold weather, lowdensity air infiltrated into a building rises and creates stackeffect pressure. Ps C2 ρi g (h-hNPL)(Ti -To)/To PsC2 ρi ghNPLTi&o pressure difference, inches of water density and gravity constant, 0.01444 height of observation, ft building neutral pressure level absolute temperature, oR inside & outside 0.95 in WGNote: Stack Pressure is approximately 1 in. of waterfor a 60-story building and -10oF outside T 2012-ESD, Inc.

Basic Theory – Overall PressureNatural air movement in a building is due to pressure differencecaused by wind and temperature difference between indoor andoutdoor air (stack effect). P (Po - Pi ) Pw Ps P pressure differencePo outside static pressurePi interior static pressure Pw pressure difference due to wind(depends on orientation) Ps pressure difference due to stack effectOverallAdjusted NeutralStack EffectWind 2012-ESD, Inc.

Basic Theory – Air Flow Through OpeningDynamic air flow through an opening is proportional to squareroot of the pressure difference across the flow path.Q C x Cf x A x (2 P/ρ)QCCfA Pρ Air flow, CFM Unit Conversion, 776 Flow Coefficient, typically 0.6-0.7 Opening Area, ft2 pressure difference, inches of water air density, lbm/ft3 (about 0.075 at standard conditions)Operation of building appliances and mechanical ventilationsystems impact natural air movement. The impact is includedwith outside/inside pressure difference 2012-ESD, Inc.

Basic Theory - Air Flow NetworkFlow equations aredeveloped between nodes(pressure & mass balance)AMBIENT NODESQ C x A x (2 P)/ρSPACE NODESSystem of equations aresolved for each calculationtime periodSoftware:NIST CONTAMLBNL COMISe-QuestSTAIR NODESELEVATOR NODESSTAIR/ELEVATORINTERCONNECTIONSPACE NODESINTERCONNECTION 2012-ESD, Inc.

Example High Rise Building Air InfiltrationAssumptions 60-Story Office 200 feet x 100 feet floor plate Average leakage curtain wall Weather-stripped exterior existdoors Revolving doors swing exitdoors at main lobby Standard door on typical floor stair Average leakage elevator doors Exterior condition at -10oF Interior condition at 73oF Wind direction from south (longerwall) Wind speed 15 mph (33 feetabove grade)LOBBYTENANTTENANTNGROUND FLOORTENANTTYPICAL FLOOR 2012-ESD, Inc.

Building Air Infiltration – Effect of Elevators60-Story Office BuildingEffect of Elevator Zones57555351494745434139373533 74% reduction3129272523211917151311975Three loorTwo ZonesElevatorsSingle ltration, scfmSingle ZoneTwo ZonesThree Zones10000#1#2STAIRS150006,357 KW100%LRHRELEVATORS#1#2STAIRSTotal Infiltration Heat Load2,903 KW45.7%LRMR HRELEVATORS#1#2STAIRS1,652 KW25.9% 2012-ESD, Inc.

Elevator Shaft Air Flow60 Story Office BuildingElevator Shaft Air Flow 151311975Three loorTwo ZonesElevatorsSingle 0#1#2STAIRSLRHRELEVATORS#1#2STAIRSLRMR HRELEVATORS#1#2STAIRS15000Air Flow, CFMSingle ZoneTwo ZonesThree Zones 2012-ESD, Inc.

Building Air Infiltration – Effect of Stairs60-Story Office BuildingEffect of Stair Zones (Three Elevator Zones)Single ZonesStairs575553514947454341393735 45% reductionFloor3331292725232119171513119753LRMR 9020004000600080001000012000Infiltration, scfmThree Zones Elevators/Single Zone StairsThree Zones Elevators/Three Zones Stairs14000Three ZonesStairs#1#2STAIRSLRMR HRELEVATORS#1#2STAIRSTotal Infiltration Heat Load1,652 KW909 KW100%55% 2012-ESD, Inc.

60 Story Building – Space Pressure 2012-ESD, Inc.

DownUpAlternate AUpDownUp2'-6"AIR LOCK2'-6"TENANT2'-6"2'-6"Alternate B2'-6"2'-6"DownUpDownAir SeparationTypical Stair Air 81716151413121110987654321LRMR HRELEVATORS#1#2STAIRSTYPICAL FLOOR 2012-ESD, Inc.

60 Story Building – Infiltration Load (Energy) 2012-ESD, Inc.

High Rise Building - Smoke ManagementSystem Objectives Reduce occupant death andinjuries––––Delay smoke accumulationReduce smoke migrationProvide safe escape routeProvide safe refuge area Reduce property loss– Purge smoke– Manage fire impactSystem Approach Design/operate system toprevent smoke entering theunaffected areas Integrate Smoke Control withFire Protection System Allow for operational flexibility Use HVAC system for smokecontrol to improve systemreliability Utilize compartmentation Lobbies 2012-ESD, Inc.

Pressurization – Normal Mode of OperationFloor Pressurization Main building lobby is pressurized Each floor is provided with requiredsupply and exhaust Each zone of building is pressurizedby maintaining differential air flowbetween supply/exhaust to minimizeinfiltration Stair pressurization systems are offLOBBYTENANTTENANTGROUND FLOOR100% SUPPLY and 80-90% EXHAUSTTYPICAL FLOOR 2012-ESD, Inc.

Pressurization – Normal Mode of OperationThree ZonesCentral AHU60-Story Office Building InfiltrationEffect of AHU Pressurization (Normal 312111098765432159575553514947454341393735Building Infiltration LoadReduces by 70%(1652 kW reduced to 506 000Infiltration, scfmAHU - OFFAHU - ON1000015000Three Zones ElevatorSingle Zone 13121110987654321LRMR HRELEVATORS#1#2STAIRS 2012-ESD, Inc.

Pressurization – Fire Mode of OperationFloor Pressurization Main building lobby is pressurized Fire Floor is provided with fullexhaust Floors above and below fire floor isprovided with full supply air All other floors operate normal mode Stairs not pressurizedLOBBYTENANTTENANTGROUND FLOOR100% SUPPLY and NO EXHAUSTABOVE OR BELOW FIRE FLOORNO SUPPLY and 100% EXHAUSTFIRE FLOOR 2012-ESD, Inc.

Pressurization – Fire Mode of OperationNo Stair Pressurization ProvidedExhaust on Fire Floor &Supply Above/Below60-Story Office Building InfiltrationSmoke Condition (Level 28) - Fire Mode ositive Press. (Supply)Negative Press. 00-50000Infiltration, scfmAHU - ONAHU - ON - Smoke 19181716151413121110987654321Single Zone 12019181716151413121110987654321LRMR HRELEVATORS#1#2STAIRS 2012-ESD, Inc.

Pressurization – Fire Mode/Stair ImpactFloor and Stair Pressurization Main building lobby is pressurized Fire Floor is provided with fullexhaust Floors above and below fire floor isprovided with full supply air All other floors operate normal mode Stairs are D FLOOR100% SUPPLY and NO EXHAUSTSTAIRS PRESSURIZEDABOVE OR BELOW FIRE FLOORNO SUPPLY and 100% EXHAUSTSTAIRS PRESSURIZEDFIRE FLOOR 2012-ESD, Inc.

Pressurization – Fire Mode/Stair ImpactStairs Are PressurizedOpen Exit DoorsOpen Exit DoorExhaust on Fire Floor &Supply 6151413121110987654321Single Zone StairsPressurized – doors 121110987654321LRMR HRELEVATORS#1#2STAIRS 2012-ESD, Inc.

Elevator Shaft Air Flow – Fire ModeFloor60 Story Office Building - Elevator Shaft Air Flow (Winter)Smoke Condition on Level 28 (Building and Stairs 21191715131197531-4000Exhaust on Fire Floor & Supply Above/BelowDoors open on fire, above/below and ground floorsOpen Exit Doors-20000200040006000800010000120001400016000Air Flow, CFMOpen Exit DoorThree ZonesThree Zones - FireMode/Pressurized 2012-ESD, Inc.

Stair Air Flow – Fire ModeFloor60 Story Ofice BuildingEffect of Stair Compartment on Pressurized Stair Air Flow - Smoke Condition (Level 31197531-15000Exhaust on Fire Floor & Supply Above/BelowDoors open on fire, above/below and ground floorsOpen Exit Doors-12500-10000-7500-5000-25000250050007500Air Flow, CFMOpen Exit DoorSingle Compartment StairThree Compartment Stair 2012-ESD, Inc.

Stair Pressure – Fire 131197531-0.10MAXIMUM STAIR PRESSURE TO MAINTAIN DOOR FORCEFloor60 Story Ofice BuildingEffect of Stair Compartment on Stair Pressure - Smoke Condition (Level 28)Open Exit Doors0.000.100.200.300.40Exhaust on Fire FloorSupply Above/BelowDoors open on fire floor, floorsabove/below fire floor andground floors0.500.600.700.80Pressure, in WGOpen Exit DoorSingle Compartment StairThree Compartment Stair 2012-ESD, Inc.

Smoke Control Considerations Building envelope design Compartmentation– Building occupancy types– Zones Elevator shafts– design/construction Stair shafts– design/construction Air leakage paths (smokemovement) Local design temperatures Local wind velocities:– Site– Envelope (wind tunnel test) HVAC system:– System zoning– Components design– System Activation/Controls Fire protection, detectionand alarm system– Integration/coordination Firefighters Access:– To site– To manual/remote control ofsystem Exiting plan– Refuge areas– Exit duration Security and access control(door status/control) 2012-ESD, Inc.

16 Story Hotel Example – Space Pressure 2012-ESD, Inc.

Tall Building Example – Infiltration Air Flow 2012-ESD, Inc.

menities - 2Amenities - 1HotelAmenities FrieghtHotel FrieghtBuildin FrieghtResidential FrieghtResidential - High ZoneResidential Low ZoneResidential Parking ShuttlePublic Parking ShuttleHotel ShuttleTall Building Example – Space Pressure 2012-ESD, Inc.

Tall Building Example – Space Pressure 2012-ESD, Inc.

Summary High rise building infiltration can be significantly reduced by verticalcompartmentation of building shafts (elevators, stairs, HVAC risers) Vertical compar

into the building, or ex-filtrate out of the building Stack effect (air buoyancy) pressure causes air to rise or drop Cold Weather Air infiltrates into the lower half of the building, rises to upper floors due to stack effect and exfiltrates in the upper half of the building. STACK EFFECT Hot Weather