ULTRATECH ENGINEERING CONSULTANT

ULTRATECH ENGINEERING CONSULTANTBY MARIAPPAN GANESAN

BASICS OF ROOM AIR DISTRIBUTIONAND ADPI.ASHRAE Air Distribution Systems 2007 Applications Handbook, Ch. 56

Local Temp.ElevationElevationLocal Temp.CO2 ConcentrationElevationLocal Temp.CO2 ConcentrationCO2 Concentration

Partially Mixed Room Air Distribution SystemsElevationLocal Temp.CO2 ConcentrationUpper ZoneLower Zoneheight variesFully MixedUpper ZoneLower ZoneUpper ZoneLower ZoneFully MixedPartially MixedFully StratifiedDisplacementUnder Floor Air DistributionG.R.D.ASHRAE Standard 552004 Occupant Comfort Goal Dry Bulb = 73-77 F. Relative Humidity = 25-60%.Local Velocities = Heating < 30 fpm. Cooling < 50 fpm. Clo. Rate 0.5 - 1.1 Met. Rates 1.0 - 2.0 Floor level to 66; < 5.4 F (3 C) Occupied Zone: Floor to 60; except: (Clear, Near, Adjacent) Zone.Occupied Zone for Comfort6'FOccupied Zone1' Floor CeilingUnderfloor PlenumUFAD OutletD.V.Mixed Air OutletFully Mixed Air Distribution Air Patterns Mapping Room Air Motion Vertical Projection ADPI Perimeter HeatingAir Flow Patterns High Sidewall No CeilingHorizontal PatternDeflected (less drop)Spread (shorter throw) High Sidewall with CeilingLonger throw with less drop High Sidewall near CeilingDeflect up for longer throw/less dropSupply Sidewall GrillesAdjustable:Horizontal (spread)

Vertical (deflection)

Duct MountingVelocity & PressureAir PatternsReturn Sidewall GrillesReturnNon Adjustable

Zero Degree Deflection

30-45 Deflection

OtherAir Flow PatternsRadial Air Pattern

Shorter Throw

More InductionRound Pattern DiffusersAir Flow PatternsCross Flow

Longer Throw

Increased DropCross Pattern DiffusersLinear with Plenum or TBar DiffusersWith SpreaderW/O SpreaderLinear PlenumWith SpreadWithout SpreadLinearPlenum Slot DiffusersAir Flow PatternsRadial Pattern - Exposed Duct Air Flow PatternsCross Pattern - Exposed DuctPOORLY ADJUSTED DIFFUSERTHERMOSTATPOOR PATTERN EXAMPLEPROPERLY ADJUSTED DIFFUSERTHERMOSTATGOOD PATTERN EXAMPLEMapping Room Air Motion5-step approachPrimary air

Total air

Convection currents

Room intake

Room airStep 1: Identify the Primary AirPrimary Air - mixture of air supplied to the outlet and induced room air within an envelope of velocities > 150 FPMPrimary air patterns are temperature independent1Catalog Throw:150 100 5010-17 -25Inside WallExposed WallStep 1 Primary AirOutletStep 2: Identify the Total AirTotal Air - mixture of primary air and room air which is under the influence of the outlet conditions

Air has a tendency to scrub surfacesTemperature difference between total air and room air produces a buoyancy effect which cause the cool air to drop and the warm air to riseTotal air has no defined terminal velocity limitStep 2 Total AirStep 3: Identify Natural Convection CurrentsNatural Convection Currents - Caused by difference in temperature between room air and air in contact with a warmor cold surfaceAffects room air motion and affects the comfort in the spaceStep 3 Natural convection currents and stratification zoneStep 4: Identify the Return IntakeReturn Intake - return intake affects only the air motion within its immediate vicinityEven natural convection currents will overcome the draw of the intakeStep 5: Identify the Room AirRoom Air Diagram is complete when remaining room air drifts back towards the primary air and total airLowest air motion is in stratification zoneMost uniform air motion is between stratification zone and total airHighest air motion is in and near the primary and total airMapping ThrowMapping ThrowCoolingADPI & ComfortAir Diffusion Performance IndexStatistically related the space conditions of local or transversed temperature and velocities to occupants thermal comfortADPI >= 80 is considered acceptableEffective draft temperature = (tx-tc) 0.07(Vx-30)% of points where -3