AD Schools

8/11/2019 AD Schools

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Air Distribution Selectionfor Schools


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Air Distribution for Schools

Presented by

Jim Aswegan- Chief Engineer

HVAC Product Design, Development and

Application

ASHRAE TC 5.3, Handbook Liaison

BSUniversity of Texas-Dallas


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Air Distribution for Schools

Question and Answer Panel

Jim Aswegan - Chief Engineer

David Pich P.E., LEED APDirector of Technology

Janis RozenbergsProduct Manager


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Factors Influencing Design

Climate

Local Air Quality

Building Size and UsageBudget Constraints

Maintenance Resources


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HVAC Design Concerns

Thermal Comfort

Ventilation

Acoustics


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HVAC Systems

Fully Mixed Air Distribution

Fully Stratified (DV) Air Distribution

Partially Mixed (UFAD) Air Distribution

Hybrid with DOAS

Other (not detailed in this webinar)


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Codes and Standards

C.H.P.S.: Collaborative for HighPerformance Schools

LEED: Leadership in Energy &

Environmental Design

ASHRAE:

Standard 55(Thermal Comfort)

Standard 62.1(Ventilation)

ANSI S-12.60 (Acoustics)

State & Local


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Thermal Comfort

ASHRAE Standard 55Thermal Environmental Conditionsfor Human Occupancy

Maximum t Ankle to Neck (standing)= 5.4F

Maximum t Ankle to Neck (seated)= 3.6F


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Ventilation Air Requirements

for Classrooms

ASHRAE Standard 62.1 Table 1 120 cfm/1000 sq. ft. of building space.

10 cfm/person @25 people/1000 sq. ft.

15 cfm/person Totalventilation air (370 cfm/1000 ft.).Table 6-2Ventilation/Ez factor = cfm

Fully Mixed CoolingEz = 1.0 (370)

Fully Stratified CoolingEz = 1.2 (309)

Partially Mixed Cooling

T50 < 4.5 AFF = Ez = 1.2 (309)

T50 > 4.5 AFF = Ez = 1.0 (370)


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Acoustic Requirements

for Classrooms

dBA vs. NC vs. RC

ASHRAE Applications Handbook 2011

dBA weighted sound level (loudness), outdoors. NC Loudness & speech interference (63 to 8000 Hz)

RC Loudness & speech interference (sound quality)

ANSI Standard S-12.60

35 dBA recommended for classrooms (25 NC)


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Collaborative for High

Performance Schools

ASHRAE: Standard 55(Thermal Comfort)


Acoustics for Classrooms:

45 dBA required; 40 dBA extra credit

Fully Mixed

4 outlets at NC 18-20 (catalog)

Displacement Ventilation/UFAD

Typically less than NC 25 (catalog)


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LEED-2009 v3

ASHRAE: Standard 55(Thermal Comfort)


Acoustics Classrooms

IEQ p3 45 dBA

IEQ c9 40 dBA


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ASHRAE2011 Application Ch. 57

Fully MixedPartially MixedFully Stratified

Displacement Under Floor Air Distribution G.R.D.


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Air Distribution


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Fully Mixed Air Distribution

Contaminate Control

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Selecting Outlets

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Fully Mixed

ADPI

The grey area

represents

Acceptable

You can vary

temperature

or velocity tomaintain comfort

15 fpm = 1 F


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Plaque

Face

Stamped

Face

ADPI Selection Outlets

Modular

Core

Louvered

Face


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ADPI Selection

OutletType

InletSize

Max.CFM NC ADPI

Min.CFM

Plaque

Face 10 380 15 85 100

Stamped

Face 10 380 18 85 110

ModularCore 10x10 380 19 89 120

Louvered

Face 10 380 20 88 180

ADPI selection based on 1 cfm/sq.ft. Space Load


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Typical Solution

50/50 throw pattern is

the best compromise for

both heating and cooling

Half of the air is always directedin the wrong direction

ASHRAE Std. 62.1-2007

T150to 4-5 AFF

Max t = 15 F


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Auto Changeover Diffuser Solution

Sill

Window

Diffuser

Air flow does not pause inintermittent pattern to causesustained drafts, instant actionof air flow pattern.

Cooling

Heating

A i B


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Actuating Between

Cooling and Heating


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Diffuser Tests - ASHRAE 70 Conditions

3 equivalent Diameters, min

Pressure

Measured Air Flow

Discharge VelocitySound

Flow straightener


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Sound Effects

RP-1335 No Damper With OBD

Standard 70 0 1 - 5

3 de 0 - 1 5 - 8

1.5 de 2 - 4 7 - 12

0 de 6 - 9 5 - 10


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Displacement Ventilation


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Basic System Concepts

Low Energy

( < 0.04 Ps)

Air Change

Effectiveness

(Std. 62.1, Ez = 1.2)

Quiet Operation

(< 25 NC)


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Fully Stratified Contaminate Control

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Discharge Air Patterns

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Return Air

Outlet located at ceiling

level

Allows heat from ceiling

lights to be returned before

it is able to mix with

occupied zone

Reduced supply volumemeans higher return

temperatures


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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

If 55oF supply air is used for dehumidification, return air can

be mixed with supply air to achieve 65oF air


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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

Radiant panels

Dual Chamber Diffuser


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Changeover

Heating ModeCooling Mode


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Dual Chamber Diffuser

Dual chamber plenum

Displacement diffuser cooling

Heating

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School Classroom

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Perimeter Wall


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Underfloor Systems

Access Diffusers


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Access Diffusers

for Core Spaces

High induction air flowpattern

Occupant adjustable

damper Actuated version

available

Typical design point is80-100 cfm

Throw between 4-5 ft.

Low NC 37


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Actuated Option

24 VAC Electric

Actuator

Large Spaces

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Typical Perimeter Installation

Low horsepower fan powered terminal unit

ducted to rectangular floor diffuser plenums

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U d fl P i


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Underfloor Passive

Perimeter System

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Perimeter (Cooling Section)

VAV Perimeter Cooling

Linear diffuser 4 length

Variable linear bar diffuser

24V damper actuator

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Transverse Apertures

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Perimeter Cooling Video

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Passive Perimeter Heating

Fin tube perimeter heat system

Self contained heating

No simultaneous cooling and reheat

Per ASHRAE 90.1

3000+ BTUH per 4 ft. plenum

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Passive Perimeter Heating

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Titus Solution for Schools

Displacement, chilled beams

and radiation principles.

Induction Nozzles Tempered and dry primary supply air

delivered at 55F

Induced room air and mix to dischargeair at appropriate temperature

Heat Transfer Coils Room air induced through coils

Sensible load handled by the coil Eliminates separate Heating system


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NozzlesInduction

Plenum

TAO Floor Mounted Active Chilled Beam

Primary SupplyChamber


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CBAF-HC Cooling mode operation

Return Air 100%

Exhausted

Chilled Water

Primary Airflow

(55 to 58F

Room Air

(75 to 78F

Supply Airflow

(65 to 72F

Supply Airflow

(62 to 66 F


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Exhausted

Optional Heat

Recovery

CBAF-HC Heating mode operation

Supply Airflow

(64 to 68F

Primary Supply Airflow

(62 to 66F

Room Air

(70 to 72F

Supply Airflow

(85to 90F


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System Comparison

Description Fully Mixed FullyStratified

PartiallyMixed

Comfort/Temp. Better Average Average

Ventilation Lower Better Avg.-Better

Acoustics Average Better Better

Heating Average Lower Average

Humidity Better Lower Lower

Energy Average Better BetterFirst Cost Better Average Lower

Flexibility Average Lower Better

Rated by C.H.P.S. Vol. II


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Fundamentals Handbook (ASHRAE, 2009) Chapter 8for Sound and Chapter 20 for Room Air Distribution

HVAC Applications Handbook (ASHRAE, 2011) Chapter

47 for Sound and 57 for Room Air Distribution

Selecting Outlets for NC


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Questions?

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The Panel will now answer your questions.


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UFAD Controls

Interior Zones (CAV)

Plenum pressure is maintained by adjusting fancapacity at the air handler

Occupants can make minor changes which are viewed assetup adjustments and not operating adjustment

Perimeter Zones (VAV)

Typically experience load changes greater thaninterior Automatic VAV control is preferred

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