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Air Diffusion – Designing for Comfort
Occupant Comfort
Air Diffusion Selection
ADPI Air Diffusion Performance index
Ventilation Effectiveness
Induction – Room Space Induction
Design Criteria ISO7730 ASHRAE 55p
Design & Selection Software
Products
Occupant Comfort
Comfort Limits ASHRAE Standard 55-92 and ISO 7730-94 ADPI Air Diffusion Performance Index / Comfort Index
A person is thermally comfortable when their body heat loss equals their heat production without them sensing any changes in temperature.
When is a person comfortable?
Heat Loss or Gain can occur through:
Conduction – transfer of heat across a bodyConvection – transfer from a body to its surroundingsRadiation – transfer through electromagnetic wavesEvaporation – sweat
Body Heat Loss or Gain
Personal Comfort Variables
- Clothing- Activity- Metabolic rate
Space Comfort Variables
- Dry bulb temperature- Relative humidity- Air velocity- Noise
ASHRAE Definition of ComfortFanger’s comfort index or PMV.
ASHRAE Defines Comfort
ASHRAE Definition of Comfort
ASHRAE/ISO 7730 standard defines comfort as:
- Maintaining a temperature of 22.8 – 25°C- Relative humidity of 25 – 60%
- Maximum velocity within the occupied zone of 0.25 m/s Cooling & 0.15m/s Heating
The percentage of dissatisfied occupants at the Neck Region.Effect of Air Motion on Comfort
The percentage of dissatisfied occupants at the Ankle Region.
Effect of Air Motion on Comfort
• Metabolic Rate – Occupants Physical Activity
• Thermal Resistance of Clothing - Clo Value
• Air Temperature – Optimum Operative Temperature
• Mean Radiant Temperature
• Air Velocity – Mean Space Velocity
• Relative Humidity
Design Criteria ISO7730-ASHRAE 55P-APDI
“Provided there is sufficient heating & cooling to meet the thermal and humidity control requirements, comfort is almost completely a function of the space air distribution.”S.A. Mumma, Ph.D P.E., Fellow ASHRAE
Air Diffusion Selection
Air DistributionAir Diffusion Design & Selection
Defining the Occupied Space
Terminal Velocity
Terminal Velocity – Tv 0.25
.75 m/s .50 m/s .25 m/s
15.6m
11.3 m
7.3 m
Free Expansion
A free jet will expand at 22°.
Zone 1 Zone 2 Zone 3 Zone 4
Exit velocity with initial induction
Laminar, induction increases
Laminar/Turbulent, maximum Room induction
Laminar, induction increases
Hot and Cold Jets
If the supply air is warmer than the room temperature, it will rise.
However if the supply air is cooler than the room air, it will drop.
General Rule: Distance @ T0.25 is effected at 2% per Degree T
Example 50C Delta T Heating
10% T 0.25
General Rule: Distance @T 0.25 is effected at 2% per Degree T
Considerations
With overhead heating, the air slows down and turns upwards at roughly 0.50 to 0.75m/s.
0.5 to 0.75m/s
Furniture against wall
Considerations
Air Diffusion MistakesColliding jets
ADPI Air Diffusion Performance Index
ADPI – Effective Draft Temperature
effective draft temperature (K)
Effective Draft Temperature is calculated by:
local jet dry-bulb temperature (°C)
local jet centreline velocity (m/s)
control room dry-bulb temperature (°C)
( ) ( )
====
---=
x
c
x
xcx
Vtt
where
Vtt
q
q
:
15.08
ADPI & Effective Draft Temperature
An acceptable value for Effective Draft Temperature is within -1.70 and +1.10, with a velocity of less than 0.35m/s
The ADPI is the percentage of locations where measurements are taken which have an:
Acceptable _ Effective Draft Temperature.
Total number of within acceptance
Total number of values measured
q
X 100
ASHRAE Definition of Comfort PMV
Comfort as a function of air velocity and temperature.
ADPI – Effective Draft Temperature
Air Diffusion Performance IndexEffective draft temperature, ( ) ( )15.08 ---= xcx Vttq
tx and Vx
tc
1q100q
100mm
600mm
1100mm
1700mm
ADPI – Air Diffusion Performance Index
Room Temp = 220C30 Test points at 0.1m/s, 20°C35 points at 0.2m/s, 21°C20 points at 0.3m/s, 22°C15 points at 0.4m/s, 22°C ( ) ( )
( ) ( )
22.14.1
6.115.01.08222015.08
4
3
2
1
-=-=-=
-=---=---=
q
q
q
q xcx Vtt
%8585.0
15203530203530
==
=ADPI
Effective draft temperature, ( ) ( )15.08 ---= xcx Vttq
so if 30 points = -1.635 points = -1.420 points = -1.215 points = -2
ADPI = 85
Air Diffusion Performance Index Selection Guide
35-160
Air Diffusion Performance Index Ratio
LT 25.0
Throw distance at terminal velocity 0.25m/s
Characteristic room length
Terminal Velocity – Tv 0.25
.75 m/s
15.6
11.3 m
7.3 m
.25 m/s.50 m/s
Characteristic Room Length LCharacteristic room length for various Air Diffusion Products
Diffuser Type
High Sidewall Register
Circular Ceiling Diffuser& Swirl Diffusers
Sill Grille
Ceiling Slot Diffuser
Light Troffer Diffusers
Perforated, Louvered Ceiling Diffusers
Characteristic Length (L)
Distance to wall perpendicular to jet
Distance to closest wall or intersecting air jet
Length of room in direction of flow
Distance to wall or mid plane between outlets
Distance to mid plane between outlets plus distance from ceiling to top of occupied zone
Distance to wall or mid plane between outlets
ADPI Selection Example
Example Mapping Throw
2.7 m
6 m
A consulting engineer is selecting a diffuser for the room above. The room requires 250 l/s at an NC no greater than 35.
Example Mapping Throw3 m
2.7 m
1.5 m1.5 m
0.4 m 0.4 m
They selected 2 x CFP600/12, with 125l/s for each. Total air quantity 250l/s, with a throw of 2.9m @ 0.25m/s. An NC value of 14.
Will the occupants be comfortable?
Example Using ADPI
3m 1.5m1.5m
2.7m
ADPI range @ 130W/m2 for 80 target - ratio = 0.5 – 1.5
ADPI calculation = 93.15.19.225.0 ==
LT0.4m0.4m
Example Mapping Throw
2.7 m
3m 3m
If our selection 1 x CFP600/24 Radial Swirl diffuser.
Total volume 250l/s - Throw 3.1m @0.25m/s - NC = 26
Will the occupants be comfortable?
Example Using ADPI
2.7 m
3 m 3 m
ADPI calculation = 03.131.325.0 ==
LT
ADPI range @ 130W/m2 for 80 target - ratio = 0.5-1.5
ADPI Selection
LT 25.0
ADPI Selection
LT 25.0
ADPI Selection
ADPI – Design Expectations
High APDI equates to High Air Change Effectiveness (ACE) Value
ADPI method is effective for CAD (as low 50C) “Cold Air Distribution Design Manual” TR-106715 Research Project 3280-39)
ADPI Method is suitable for heating at <100C ΔT
APDI - Ensures proper Selection, Application and Deployment of Air Diffusion Equipment
Ventilation Effectiveness
Ventilation Effectiveness – Air Change Effectiveness (ACE)
ANSI/ASHRAE Standard 129-1997 ASHRAE Fundamentals F25-1997
Principally it is an evaluation of effective mixing of the Supply/Outdoor
with Room/ Space Air
Induction
Induction, High Induction & Induction Ratios
High Induction means High Exit Velocity
High Induction means High Pressure
Higher pressure offsets (CAD) Design Savings
High Induction = Smaller Air flows or more Diffusers or more Noise
Induction, High Induction & Induction Ratio
There is no accepted published method for determining the induction ratio of an
individual diffusion product
Induction Ratio = Primary Air / Induced Air
Temperature Measurements of Primary Air, Discharge Air and Induced Air
Room Air Induction Equation
Induction Ratio Q Qx
Qo= C
Vo
Vx
Qx
Where:
= Qo X CVo
Vx
C:
Vo:Vx:
Qo:Qx:
= Supply volume m3/s= Induction volume at Distance= Discharge Velocity m/s= Velocity at distance m/s= Entrainment Coefficient 1.4 for infinite slots and 2.0 for round free axial jets
=
Holyoake Swirl Diffusers – Series CFP
CFP - 600/24Aeff: 0.1110m2Veff: 0.7-3m/sAir Flow: 75-300L/SPa: 2-13NC <10-30
CFP - 600/20Aeff: 0.0925m2Veff: 0.5-3m/sAir Flow: 50-250L/SPa: 6-12NC 12-26
CFP - 600/12Aeff: 0.0555m2Veff: 0.5-3m/sAir Flow: 25-150L/SPa: 2-18NC <10-20
• Flexible Volume range suitable for VAV Systems• High Mixing Turbulent Radial Swirl Air Pattern – Good induction • Low Pressure - Low Noise• High Range VAV – Blade Design and Turbulent Radial Mixing
Induction, Room Induction - Room Induction Ratios Q
Room Induction Ratio Q = 17.28
Air Volume 200L/S = 2.16m/s Exit Velocity
3456 L/S
Swirl Diffuser
(Figure 9)
Room Induction Ratio Q = 21.6
Air Volume100L/S = 1.08m/s Exit Velocity
2160 L/S
Swirl Diffuser
(Figure 10)
Room Induction Ratio Q = 28.8
Air Volume 200L/S = 2.16m/s Exit Velocity
5760 L/S
Swirl Diffuser
(Figure 11)
CFP/600/20
Room Induction Ratio Q = 10.8
Air Volume100L/S = 1.08m/s Exit Velocity
1080 L/S
Swirl Diffuser
(Figure 8)
Design Criteria ISO7730 – ASHRAE 55P
PVM Predicted Mean Vote - PPD
• Metabolic Rate – Occupants Physical Activity
• Thermal Resistance of Clothing - Clo Value
• Air Temperature – Optimum Operative Temperature
• Mean Radiant Temperature
• Air Velocity – Mean Space Velocity
• Relative Humidity
Design Criteria ISO7730-ASHRAE 55P-APDI
Thermal Comfort Considerations & Obligations
Design to a Predetermined PMV-PPD As a function of: Clothing, Metabolic Rate. Air temp, Radiant Temp, Velocity, Humidity<6% PD <10% PD <15% PD
Establish Optimum Operative Temperature Range<6% PD <10% PD <15% PD
Establish the draft rating DR – PD (mean velocity)encompassing: Local Air Temperature, Local air velocity, local turbulence intensity<15% PD <20% PD <25% PD
( )( ) ( )14.337.005.034 62.0--= TuvvtDR a
Thermal Comfort Considerations & Obligations
Determine Ventilation rate for Perceived Indoor Air Quality as a result of Occupant numbers and Building Materials<15% PD <20% PD <30% PD
Establish your Ventilation rate for Air Quality as a result of Occupant numbers and Building Materials<15% PD <20% PD <30% PD
Confirm Design Ventilation EffectivenessGreen Star requires Veff 0.95
Thermal Comfort Considerations & Obligations
Establish and Confirm ADPI Rating >80Effective Draft Temperature : local temperature, room average temperature, local velocity
( ) ( )15.08 ---= Vxtctxq
Establish required Flow Rate for Thermal Designin accordance with optimal operating temperature
Ensure Acoustics meet Environment standards Category (A) Category (B) Category (C)
Calculation for PMV for resultant PPD
Design & Selection Software
Air Distribution Design Program
ADE:5.4
Products
Architectural Louvers
CSDF Fixed Pattern Linear Slot
CSD-P Flangeless Linear
LF1200 Flangeless Extruded Linear Bar Diffuser
Thankyou for Listening
Predicted Mean Vote – Percentage Dissatisfied
P. Ole FangerDirector, Professor, D.Sc. International Centre for Indoor Environment and EnergyTechnical University of Denmark, Building 402DK-2800 Lyngby, Denmark.
