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Course Outline

Energy-Saving Strategies for Rooftop VAV Systems

Rooftop variable-air-volume (VAV) systems are used to provide comfort in a wide range of building types and climates. This ENL discusses HVAC system design and operating strategies that can save energy in these systems.

By attending this broadcast, you will be able to: 1. Explain the basic concepts of a rooftop VAV system, including the basic components, its advantages and

disadvantages, and minimum code requirements. 2. Summarize cost-effective strategies to reduce the energy used by rooftop VAV systems. 3. Explain how to analyze the economic benefit of various energy-savings strategies. 4. Summarize system-level control strategies that improve the performance and flexibility of rooftop VAV

systems. Program Outline: 1) Welcome, agenda, introductions 2) Overview of a rooftop VAV system

Basic components Benefits and challenges Minimum code requirements

3) Equipment configuration strategies a) High-efficiency versus standard efficiency equipment (EER, IPLV) b) Air-to-air energy recovery c) Relief fan versus return fan d) Air-cooled or evaporative condensing e) Hot gas bypass f) Fan-Powered VAV g) ECMs on fan-powered VAV boxes

4) System design strategies a) Single-zone VAV (arenas, auditoriums, gymnasiums, sanctuaries) b) Hot gas reheat for unoccupied humidity control c) DOA unit delivering cold OA direct to spaces or dual-duct boxes

5) Optimized system control strategies a) Airside economizing b) Optimum start/stop c) Fan-pressure optimization d) Supply-air temperature reset e) Ventilation optimization: DCV (TOD schedule, occupancy sensor,

CO2 sensor) combined with ventilation reset 6) Example TRACE analysis 7) Operation & Maintenance

a) Proper maintenance b) Balancing and commissioning (ongoing auto-commissioning)

8) Summary

Energy Saving Strategies for Rooftop VAV Systems

Phil Baggett | marketing engineer – large rooftops | Trane

Since starting with Trane in 1968 Phil has served in several roles of increasing responsibility in manufacturing engineering, product marketing, training, product planning, and product management organizations. Phil's primary responsibility as marketing engineer for large rooftop products is to identify and implement product change opportunities, and new product-platform development initiatives. He is also responsible for identifying and assisting in the development of sales and application tools to support those initiatives.

John Murphy | senior applications engineer | Trane

John has been with Trane since 1993. His primary responsibility as an applications engineer is to aid system design engineers and Trane sales personnel in the proper design and application of HVAC systems. His main areas of expertise include dehumidification, air-to-air energy recovery, psychrometry, ventilation, and ASHRAE Standards 15, 62.1, and 90.1. John is the author of numerous Trane application manuals and Engineers Newsletters, and is a frequent presenter on Trane’s Engineers Newsletter Live series of satellite broadcasts. He is also the primary author of the Trane Air Conditioning Clinics, a series of training manuals on HVAC fundamentals. John is a member of ASHRAE, has authored several articles for the ASHRAE Journal, and is a member of that society’s “Moisture Management in Buildings” and “Mechanical Dehumidifiers” technical committees.

Paul Solberg | senior principal applications engineer | Trane

A mechanical engineer from the University of Wisconsin at Platteville, Paul is a 26-year veteran of Trane. He specializes in compressor and refrigeration systems, and has authored numerous Trane publications on these subjects, including application manuals, engineering bulletins, and Engineers Newsletters. Paul served in the technical service and applications engineering areas at various manufacturing locations, where he developed particular expertise supporting split systems, small packaged chillers, rooftop air conditioners, and other unitary products.

Justin Wieman| C.D.S. marketing engineer | Trane

After finishing the Trane Graduate Training Program in 2001, Justin joined the Customer Direct Service (C.D.S.) group as a marketing engineer. Since then he has provided support for various Trane software applications. Presently he is team leader for Trane’s Analysis Software group, and project manager for the Trane Air-Conditioning Economics (TRACE™ 700) product family.

engineers newsletter live Presenter Biographies

a Trane Engineers Newsletter Live online program


© 2010 Trane a business of Ingersoll Rand. All rights reserved

Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

1

Energy-Saving Strategies forRooftop VAV SystemsRooftop VAV Systems

ananEngineers Newsletter Live telecast© 2006 American Standard All rights reserved

Equipment configurations

rooftop VAV systems

Energy-Saving Strategiesrooftop VAV systems

Energy-Saving Strategies Equipment configurations

Alternative system designs

Optimized system controls





2

Ingersoll Rand

Energy-Saving Strategies for Rooftop VAV Systems - Course ID 0090004836

1.5

“Trane” is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members available on request.

This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.Questions related to specific materials,methods, and services will be addressedat the conclusion of this presentation.





3

Copyrighted MaterialsCopyrighted MaterialsThis presentation is protected by U.S. and international copyright laws. Reproduction, distribution, display, and use of the presentation without written permission of Trane is prohibited.

© 2010 Trane, a business of Ingersoll-Rand. All rights reserved.

AIA continuing education

Learning ObjectivesAIA continuing education

Learning ObjectivesParticipants will learn the following aboutParticipants will learn the following aboutrooftop VAV systems:

Cost-effective strategies to reduce energy use

How to analyze economic impact of various energy-saving strategies





4

Today’s PresentersToday’s Presenters

Justin Wiemanmarketingengineer

Phil Baggettmarketingengineer

Today’s PresentersToday’s Presenters

Paul Solbergapplicationsengineer

John Murphyapplicationsengineer





5

ASHRAE Standard 90.1 and 62.1 Requirementsand 62.1 Requirements

E i Energy-saving strategies for rooftop VAV systems

Rooftop VAV SystemRooftop VAV Systempackaged DXpackaged DXrooftop air conditionerrooftop air conditionerrooftop air conditionerrooftop air conditioner

supplysupplyductworkductwork

returnreturnductworkductwork

supplysupply--airairdiffusersdiffusers

BASBAS

VAVVAVterminalterminal

unitsunits





6

SatisfySatisfy Occupant comfort Occupant comfort

Code (or standard) minimum requirements

ASHRAE 90.1-2004

ASHRAE 62.1-2004

ASHRAE 90.1-2004

Rooftop VAV SystemsASHRAE 90.1-2004

Rooftop VAV Systems Mandatory Prescriptive Mandatory

Equipment efficiency

Controls

Prescriptive

Economizers

Limitation on reheat

Design fan power

Fan control Fan control

Energy recovery

Hot gas bypass





7

packaged rooftop (air-cooled)

Equipment Efficienciespackaged rooftop (air-cooled)

Equipment EfficienciesSize Category Heating

S ti TMinimum Effi iSize Category Section Type Efficiency

<65,000 Btu/h All 12.0 SEER*

≥65,000 Btu/h and

<135,000 Btu/h

Electric ResistanceOther

10.3 EER10.1 EER

≥135,000 Btu/h and

<240,000 Btu/h

Electric ResistanceOther

9.7 EER9.5 EER

≥240,000 Btu/h and

Electric ResistanceOthe

9.5 EER, 9.7 IPLV9 3 EER 9 5 IPLV and

<760,000 Btu/hOther 9.3 EER, 9.5 IPLV

≥760,000 Btu/h Electric ResistanceOther

9.2 EER, 9.4 IPLV9.0 EER, 9.2 IPLV

*NAECA requires 13.0 SEER

Zone Thermostatic ControlsZone Thermostatic Controls

Required for each zone Required for each zone

Perimeter can be treated differently

≥5º F deadband

Dual setpoint or deadband(can be soft a e fo DDC)(can be software for DDC)





8

systems ≥ 15,000 Btu/h

Automatic Shutdownsystems ≥ 15,000 Btu/h

Automatic Shutdown Automatic 7-day/week time clock Automatic 7-day/week time clock

with 10-hour battery backup

Exception: 2-day/week thermostat for residential applications

Occupancy sensor

Manually operated timer(maximum duration: 2 hours)

Security system interlock

systems ≥ 15,000 Btu/h

Setback Controlssystems ≥ 15,000 Btu/h

Setback Controls Climate zones 2-8: Climate zones 2-8:

Lower heating setpoint to 55°F or less

Climate zones 1b, 2b, 3b (hot/dry):Automatically restart, temporarily operate

Raise cooling setpoint to 90°F or higher, or

Prevent high space humidity levels





9

mandatory HVAC provisions

Other Off-Hour Controlsmandatory HVAC provisions

Other Off-Hour Controls Provide optimum start if system Provide optimum start if system

supply-air capacity > 10,000 cfm

Zone isolation:

25,000 ft² maximum zone size on one floor

Isolation devices to shut off outdoor and exhaust airflow

Central systems capable of stable operation

ventilation

High Occupancyventilation

High OccupancyIf outdoor airflow > 3 000 cfm and If outdoor airflow > 3,000 cfm and design occupancy > 100 p/1000 ft²…

Automatically reduce outdoor air intake below design requirements when spaces are partially occupied

E tiException:Systems with exhaust-air energy recovery complying with Section 6.5.6.1





10

ASHRAE 90.1-2004

Rooftop VAV systemsASHRAE 90.1-2004

Rooftop VAV systems Mandatory Prescriptive Mandatory

Equipment efficiency

Controls

Prescriptive

Economizers

Limitation on reheat

Design fan power

Fan control Fan control

Energy recovery

Hot gas bypass

System 135,000 Btu/h?Economizer required

Std 90.1 economizer requirements

Exception (a)

4bEconomizerNOT required

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System 65,000 Btu/h?Economizer required

q





11

airside economizer use

Exceptionsairside economizer use

Exceptions(a)(a) Individual fan-cooling units with(a)(a) Individual fan cooling units with

less-than-minimum capacities installed in specific climate zones

(b)(b) Systems with gas-phase outdoor air cleaningto meet ASHRAE Standard 62

(c)(c) Systems with > 25% of supply airserving spaces humidified aboveserving spaces humidified above35°F DP for process needs

(d)(d) Systems with condenser heat recovery

airside economizer use

Exceptionsairside economizer use

Exceptions(e)(e) Residential space systems with capacities(e)(e) Residential space systems with capacities

< 5× limit in Exception (a)

(f)(f) Space sensible cooling load transmission+ infiltration load at 60°F

(g)(g) Systems that operate < 20 hr/wk

(h)(h) Supermarket applications, where outdoor air (h)(h) Supermarket applications, where outdoor air for cooling affects open refrigerated cases

(i)(i) Systems with high mechanical cooling efficiency ( Table 6.3.2 requirements)





12

Simultaneous Heating–CoolingSimultaneous Heating–Cooling

Zone controlsZone controls No reheating No recooling No mixing or

simultaneously supplying mechanically-cooled and ymechanically-heated air

Exceptions based on zone airflow

simultaneous heating–cooling

Exceptionssimultaneous heating–cooling

ExceptionsZone airflow does not exceed Zone airflow does not exceed whichever is largest:

ASHRAE Standard 62 zonerequirements for outdoor air

0.4 cfm/ft²

30% of supply air 30% of supply air

300 cfm

ASHRAE Standard 62 equation





13

simultaneous heating–cooling

Exceptionssimultaneous heating–cooling

Exceptions Zones with special Zones with special

pressurization requirements

Zones with code-required minimum circulation rates

Sit d it Site-recovered or site-solar energy provides ≥ 75% of reheat energy

dehumidification

Exceptions dehumidification

Exceptions Reducing supply airflow to 50% Reducing supply airflow to 50%,

or minimum ventilation rate

Systems < 6.67 tons that can unload at least 50%

Systems smaller than 3.3 tons





14

dehumidification

Exceptionsdehumidification

Exceptions Systems with specific humidity Systems with specific humidity

requirements (museums, surgical suites)

75% of reheat/recool energy is site-recovered or site-solar

Fan Power LimitationFan Power Limitation

Supply air volume Constant volume Variable volume

< 20,000 cfm 1.2 hp/1,000 cfm 1.7 hp/1,000 cfm

≥ 20,000 cfm 1.1 hp/1,000 cfm 1.5 hp/1,000 cfm

Allowable nameplate motor power





15

Air System ControlAir System ControlVAV fan controla co o

Motors ≥ 15 hp require

Variable-speed drive or

Vaneaxial fan with variable-pitch blades or

Design wattage ≤ 30% at 50% air volume

DDC systems must include setpoint reset (fan-pressure optimization)

Airside Energy RecoveryAirside Energy Recovery Required if: Required if:

Supply air capacity ≥ 5,000 cfm

Minimum outdoor air ≥ 70%

Recovery system effectiveness ≥ 50%





16

Maximum HGBP capacity,% f l i

Rated capacityf

Hot Gas BypassHot Gas Bypass

% of total capacityof system

≤ 240,000 Btu/h 50%

> 240,000 Btu/h 25%

Applied in systems with stepped or ti l dicontinuous unloading

Exception: Packaged unitary systems≤ 90,000 Btu/h (7.5 tons)

ASHRAE 62.1

Ventilation RequirementsASHRAE 62.1

Ventilation Requirements Design Operation: Design

Calculate zone ventilation airflow

Determine air distribution effectiveness

Operation:

Dynamically calculate system ventilation airflow

In VAV system, fixed damper position does not

Calculate system design ventilation intake airflow

position does not meet requirements





17

Base Rooftop VAV SystemBase Rooftop VAV System Equipment Airside energy Equipment

efficiency

Zone controls

Economizer

Simultaneous heating and cooling

Airside energy recovery

Hot gas bypass

Ventilation

heating and cooling

Design fan power

Fan control

Equipment ConfigurationStrategiesStrategies

Energy-saving strategies for rooftop VAV systems





18

High-Efficiency EquipmentHigh-Efficiency Equipment

Reduced operating Higher first costBenefits Drawbacks

Reduced operating cost

Potential energy rebates

Meet mandated energy codes

Higher first cost

Extended return on investment in some areas

Environmentally intelligent, reduces greenhouse gas emissions

High-Efficiency EquipmentHigh-Efficiency Equipment High-efficiency supply and exhaust High-efficiency supply and exhaust

fan motors

Insist on NEMA Premium rated

Additional evaporator coil rows

Additional condenser coil capacity Additional condenser coil capacity





19

High-Efficiency EquipmentHigh-Efficiency Equipment Standard efficiency rooftop (Alt 1) Standard efficiency rooftop (Alt 1)

9.6 EER

604 gross MBH

High-efficiency rooftop (Alt 2)

10 4 EER 10.4 EER

644 gross MBH

High-Efficiency EquipmentHigh-Efficiency Equipment Example energy savings Example energy savings

Three story 60,000 sq. ft office building

VAV with reheat system

Default settings forbuilding type and exposuresbuilding type and exposures

Alameda, CA weather data and PG&E utility rate





20

System Analyzer™System Analyzer™Alt 1

$ 8 286Alt 2

$18,286$17,300

High-Efficiency EquipmentHigh-Efficiency Equipment Reduced fossil fuel emissions Reduced fossil fuel emissions

CO2 -5,415 lbm/yr SO2 -5,956 gm/yr NOx -8,122 gm/yr





21

Air-to-Air Energy RecoveryAir-to-Air Energy Recovery

total-energywheel

EAEA

OAOA

180

160 h

85

80

wet-bulb temperature, °F

total-energy recovery:

Example in Cooling Mode

140

120

100

80

60

40

um

idity ratio

, grain

s/lb o

f dry

75

70

65

60

5550

45

OA

RA

OA'

2.2 tons1,000 cfm

40

20

0

air

11030 40 50 60 70 80 10090dry-bulb temperature, °F

4035

30

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d

pre-cools andpre-dehumidifies OA





22

180

160 h

85

80

wet-bulb temperature, °F

total-energy recovery:

Example in Heating Mode

140

120

100

80

60

40

um

idity ratio

, grain

s/lb o

f dry

75

70

65

60

5550

45 RA

24 MBh1,000 cfm

40

20

0

air

11030 40 50 60 70 80 10090dry-bulb temperature, °F

4035

30

OA

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serve

d

OA'pre-heats andpre-humidifies OA

DrawbacksBenefits

Air-to-Air Energy RecoveryAir-to-Air Energy Recovery

Reduces cooling, dehumidification, heating, and humidification energy

Allows equipment downsizing

Increases fan energy

Requires exhaust air be routed back to rooftop unit

downsizing





23

Size energy-recovery device for

Air-to-Air Energy RecoveryAir-to-Air Energy Recovery Size energy-recovery device for

minimum outdoor airflow

Strive for balanced airflows

Integrate control with airside economizer operation

How much cross-leakage is acceptable?

Provide a means of capacity control

Building Pressure ControlBuilding Pressure Controlintake airflow

relief airflow

+

+

+

+

+

++

+

+

+





24

control based on RA plenum pressure

Central Return Fancontrol based on RA plenum pressure

Central Return FanRARA

PPreturn fanRLRL RARA

spacespace

PP

PP

return fan

reliefdamper

RLRL

SASA

EAEAspacespaceflow-measuring

damperOAOA

modulated control

Central Relief Fanmodulated control

Central Relief FanRARARLRL

PPRARARLRL

spacespace

relief fanPP

SASA

OAOA

EAEA

spacespaceflow-measuringdamper





25

Return vs. Relief Fan?Return vs. Relief Fan?

P ti l t ti l d S l f t b Relief FanReturn Fan

Partial static placed on return fanUse in systems with high RA pressure drop

Supply fan must be sized for entire static

Two continuous motors to provide ventilation air

Intermittent relief fan operationReduced operating cost

(+) Pressurized diverting plenumRA leakage out relief dampers

(-) Pressurized diverting plenumOA leakage in relief dampers

Air-Cooled CondenserAir-Cooled Condenser

llpropellerfanfan

OAOA

finned-tubecondenser coils

OAOA





26

Evaporative CondenserEvaporative Condenserfanfan

condenser condenser coilcoil

sumpsump pumppump

condensing

Air-Cooled vs. Evaporativecondensing

Air-Cooled vs. Evaporative

pre

ssu

re

expansion

air-cooledcondenser

evaporativecondenser

enthalpy

evaporator compressor





27

Avoid Hot Gas BypassAvoid Hot Gas Bypass Purpose Purpose

Frost prevention

Stabilize discharge temperature

HGBP

One step greater capacity One step greater capacity

poor energy efficiency

Avoid Hot Gas BypassAvoid Hot Gas Bypass Choose units that maximize the Choose units that maximize the

stages of compression

Use intertwined coils

Don’t oversize rooftop tonnage… maximizes suction temperature

Use frost control

Remember that the average air condition is what is important





28

parallel

Fan-Powered VAVparallel

Fan-Powered VAV

cool primary airfrom rooftop unit

i i l d

heating coil(second stage of heat)

warm air recirculatedfrom ceiling plenum(first stage of heat)

ECM Fan-Powered BoxesECM Fan-Powered BoxesDrawbacksBenefits

Reduces VAV terminal fan energy





29

ECM EfficiencyECM Efficiency0.6

gy i

np

ut,

kW

/cf

m

0.5

0.4

0.3

0.2

permanent splitcapacitor (PSC) motor

500 1000 15000 25002000

airflow, cfm

en

erg 0.1

0

electrically-commutatedmotor (ECM)

ECM Fan-Powered BoxesECM Fan-Powered BoxesDrawbacksBenefits

Reduces VAV terminal fan energy

Higher first cost

Greater airflow range

Capability for self-balancing

Potential for disruptive harmonic currents

g

Less-annoying sound levels





30

Equipment Configuration StrategiesEquipment Configuration Strategies High efficiency Avoid hot gas High efficiency

Energy recovery

Exhaust fan

Evaporative condenser

Avoid hot gas bypass

Fan-powered boxes

Electronically commutated motors

Alternative System DesignsSystem Designs






31

Single-Zone VAVSingle-Zone VAV

spacespaceTT

RARAEAEA

TT

SASAOAOA

single-zone VAV

Benefitssingle-zone VAV

Benefits Lower operating cost Lower operating cost…

Reduces fan speed at part load

Reduced sound levels… Reduces fan-generated noise at part load

Improved dehumidification…Continues to supply cool, dry air at part load

Simple controls and standard equipment





32

single-zone VAVApplication Considerationssingle-zone VAVApplication Considerations Large zones should have Large zones should have

uniform loads

Design air distribution system for variable airflow

Short, symmetrical ducts

Size for low-to-medium duct velocities

Diffusers that prevent “dumping”

Consider need for zone heating

Prevent overcooling the zone

single-zone VAVApplication Considerationssingle-zone VAVApplication Considerations Prevent overcooling the zone…

SA temperature reset

Employ CO2-based DCV





33

single-zone VAV

CO2-Based DCVsingle-zone VAV

CO2-Based DCV

spacespace

CO2CO2TT

RARAEAEA

flow-measuringdamper

TT

SASAOAOA

humidity control

Unoccupied Modehumidity control

Unoccupied Mode

spacespace

RHRHreheat

RA

SASA

spacespacedehumidification





34

unoccupied humidity control

Hot Gas Reheatunoccupied humidity control

Hot Gas Reheatevaporatorairflow

reheatcoil

condenser

airflow

reheatvalve

compressor

Dedicated OA SystemDedicated OA Systemdedicatedoutdoor-air unit

VAV rooftop(recirculating)

SA RA CA

OA

outdoor-air unit(recirculating)

dual-ductVAV terminals





35

Alternative System DesignsAlternative System Designs Single-zone VAV Single-zone VAV

Demand-controlled ventilation

Humidity control

Dedicated outdoor-air unit in j ti ith ftconjunction with rooftop

Optimized System ControlsSystem Controls






36

Airside EconomizerAirside Economizermech

coolingheatingintegrated

econmodulated

econ coolingheating econ

outdoorair

econ

inta

ke f

low

, %

100

mech clg

heatingcapacity

0

OA

i

OA temperaturecold hot

min

mech clgcapacity

High-Limit ShutoffHigh-Limit ShutoffDisable econDisable econ Enable econEnable econ(minimum OA)(minimum OA) (up to 100% OA)(up to 100% OA)(minimum OA)(minimum OA) (up to 100% OA)(up to 100% OA)

Control typeControl type when OA is:when OA is: when OA is:when OA is:

Fixed dry bulb Warmer than Cooler thanfixed setting fixed setting

Fixed enthalpy Higher enthalpy Lower enthalpy than fixed setting than fixed setting

Differential Higher enthalpy Lower enthalpyenthalpy than RA than RA





37

VAV system (Cincinnati, Ohio)

Energy ComparisonVAV system (Cincinnati, Ohio)

Energy Comparison,

100

10%9%11%

en

erg

y c

on

sum

pti

on

,%

of

base

85

90

95

none 65°Ffixed DB

28Btu/lbfixed h

differentialenthalpy

HV

AC

e

75

80

Optimal StartOptimal Start

systemon

systemoff

occupied hours

occupiedheating

setpoint

unoccupied

optimalstart

6 AM noon 6 PMmid mid

occupied hoursunoccupiedheating

setpoint





38

Optimal StopOptimal Stop

systemon

systemoff

occupied hours

optimalstop

drift below

occupiedheating

setpoint

unoccupied

6 AM noon 6 PMmid mid

occupied hours drift belowoccupiedsetpoint

unoccupiedheating

setpoint

Supply Fan ControlSupply Fan Control

supplyfan

~2/3 distancedown main duct PP

VAV boxes





39

static

Fan Pressure OptimizationFan Pressure Optimization

VAV boxes

pressuresensor

PPsupplyfan

communicating BAS

VAV boxes

Part-Load Energy SavingsPart-Load Energy Savings

tati

c p

ress

ure

duct static pressure control

airflow

st

fan-pressure optimization





40

Reduced Risk of Fan SurgeReduced Risk of Fan Surgeta

tic

pre

ssu

re

duct static pressure control

surge

airflow

st

fan-pressure optimization

SA Temperature ResetSA Temperature Reset Decreases compressor energy Decreases compressor energy

Higher suction pressure

More hours of modulated economizing

Decreases reheat energy

I f Increases fan energy

Raises humidity level in the zones





41

To Reset or Not to ResetTo Reset or Not to Reset Mild climates Hot climates or Mild climates

(many hours when OADB < 60°F)

Minimum VAV airflow settings > 30%

Efficient air

Hot climates or humid climates(few hours when OADB < 60°F)

Efficient part-load fan modulation

Inefficient air Efficient air distribution system

Interior zones with varying cooling loads

Inefficient air distribution system

Zones with near-constant cooling loads

SAT reset based on OA temperature

ExampleSAT reset based on OA temperature

Example

°F 61

mp

era

ture

setp

oin

t, 61

60

59

58

57

56

55 60 6550 807570outdoor dry-bulb temperature, °F

SA

tem 56

55





42

SAT reset based on “critical” zone

ExampleSAT reset based on “critical” zone

ExampleBAS

lounge restroom

storage office

vestibule corridor

TT

TTTT

TTTTTT

office conference rm computer roomreception area elev

ators TTTTTTTT

SAT reset Application ConsiderationsSAT reset Application Considerations Design zones with nearly-constant g y

cooling loads for warmer (reset) SAT

May require larger VAV terminals and ductwork

Allows SAT reset while still providing needed cooling to these zones

Design an efficient air distribution system

Employ fan-pressure optimization





43

SAT resetApplication ConsiderationsSAT resetApplication Considerations Analyze the systemy y

Will compressor and reheat energy savings outweigh additional fan energy?

Consider impact on zone humidity

Di bl t h h id t id Disable reset when humid outside

Use a humidity sensor to disable reset when zone humidity gets too high

ASHRAE 62.1-2004

Dynamic Reset of OAASHRAE 62.1-2004

Dynamic Reset of OA May reset OA intake flow or zone OA May reset OA intake flow or zone OA

flow in response to:

Variations in zone population (DCV)

Variations in ventilation efficiency due to changes in airflow (ventilation reset)( )





44

ventilation optimization

Zone Level: DCVventilation optimization

Zone Level: DCVBAS

lounge restroom

storage office

vestibule corridor

CO2

mechroom

OCCAHU

TOD

office conference rm computer roomreception area elev

ators

CO2OCC


System Level: Vent Resetventilation optimization

System Level: Vent Resetrooftop unitwith controls

OA

SA RA

• Reset outdoor airflow (Vot)

CO2 CO2OCC OCC

• Required ventilation (Voz)• Actual primary airflow (Vpz)

DDC/VAV terminalscommunicating BAS• New OA setpoint (Vot)





45


DCV and Vent Resetventilation optimization

DCV and Vent Reset Assures each zone receives proper Assures each zone receives proper

ventilation without requiring a CO2sensor in every zone

Enables documentation of actual ventilation system performance

S t l l til ti t System-level ventilation reset equations are defined by ASHRAE 62

Optimized System ControlsOptimized System Controls Economizer Economizer

Optimal stop and start

Fan pressure optimization

Supply air temperature reset

Demand controlled ventilation and ventilation reset





46

AnalysisAnalysis


Building Analysis ToolsBuilding Analysis ToolsTRACE™ 700TRACE 700HVAC load design and analysis software

Comprehensive energy andeconomic analysis for virtuallyany building





47

rooftop VAV system

Example Analysisrooftop VAV system

Example Analysis“Optimized” Systemp y

Optimal start

SA temperature reset

Ventilation optimization

Fan-pressure optimization

Total-energy wheel Total energy wheel

Comparative enthalpy economizer

Parallel FPVAV (perimeter zones)

rooftop VAV system

HVAC Energy Savingsrooftop VAV system

HVAC Energy Savings100

n,

40

60

80

en

erg

y c

on

sum

pti

on

% o

f b

ase

MinneapolisLos AngelesAtlanta0

20

HV

AC

e

optimized systembase system





48

rooftop VAV system

HVAC Energy Savingsrooftop VAV system

HVAC Energy Savings100

n,

40

60

80

en

erg

y c

on

sum

pti

on

% o

f b

ase

MinneapolisLos AngelesAtlanta0

20

HV

AC

e

optimized systemcomplies with 90.1 and 62

Keep the system working properlyworking properly






49

Proper MaintenanceProper Maintenance Periodic maintenance enhances Periodic maintenance enhances

unit performance Always perform airside maintenance first

Inspect air filters regularly,clean or replace as necessary

0.1 inch of additional static pressure pincreases supply motor kW by 7%

Inspect condensate drains and traps whenever filters are inspected, clean as needed


unit performance Inspect fresh- and return-air

damper mechanisms

Clean blades as necessary

Verify all damper linkages move freelyy p g y

Check supply/relief fan motor and shaft bearings, lubricate, repair, or replace as necessary





50


unit performance Inspect evaporator and condenser coils

for dirt buildup, clean as needed

Make sure that condenser fans rotate freely, check bearings for wear

Verify all condenser fan mountings are secure


unit performance #1: Improper refrigerant charge

Overcharging decreases superheat and increases subcooling

10% overcharge can increase gcompressor kW by approximately 3.5% at design conditions





51


unit performance #1: Improper refrigerant charge

Undercharging increases superheat and decreases subcooling… resulting in capacity loss

Always charge according to manufacturers recommendations, and instructions

Answers toYour QuestionsYour Questions

E i

This concludes theAmerican Institute of Architects Continuing Education System Program

Energy-saving strategies for rooftop VAV systems





52

Energy-efficient rooftop VAV systemsEnergy-efficient rooftop VAV systems

Equipment configuration strategies Equipment configuration strategies

Alternative system designs

Optimized system controls

Analysis

Maintenance

references for this broadcast

Where to Learn Morereferences for this broadcast

Where to Learn More

www.trane.com/engineersnewsletter





53

watch past programs

ENL Archiveswatch past programs

ENL ArchivesInsightful topics on HVAC system design:design:

Chilled-water plants Air distribution Refrigerant-to-air systems Control strategies Industry standards and LEED Energy and the environment Acoustics Ventilation Dehumidification

www.trane.com/ENL

mark your calendar

2007 ENL Broadcastsmark your calendar

2007 ENL Broadcasts Feb 21 Waterside heat recovery Feb 21 Waterside heat recovery

Sep 12 Humidity control

Nov 14 LEED™ case studies

Trane Engineers Newsletter Live program

Bibliography

Industry Standards and Handbooks Energy Saving Strategies for Rooftop VAV Systems

American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE). ANSI/ASHRAE IESNA Standard 90.1-2004: Energy Standard for Buildings Except Low-Rise Residential Buildings. Available at <http://xp20.ashrae.org/ frame.asp?standards/std90.html>

American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. (ASHRAE). Standard 90.1-2004 User’s Manual. Available at <http://www.ashrae.org>

American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE). ANSI/ASHRAE Standard 62.1-2004: Ventilation for Acceptable Indoor Air Quality. Available at <http://www.realread.com/prst/pageview/browse.cgi?book=1931862672>

American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. (ASHRAE). Standard 62.1-2004 User’s Manual. Available at <http://www.ashrae.org>

Trane Publications Guckelberger, D. “Brushless DC Motors: Setting a New Standard for

Efficiency.” Engineers Newsletter 33-4 (2004). Available at <http://www.trane.com/commercial/library/vol33_4/admapn013en_1204.pdf>

Murphy, J. “CO2-Based Demand-Controlled Ventilation.” Engineers Newsletter 34-5 (2005). Available at <http://www.trane.com/commercial/library/vol34_5/admapn017en_1005.pdf>

Murphy, J. “Energy Saving Control Strategies in Rooftop VAV Systems.” Engineers Newsletter 35-4 (2006). Available at <https://www.trane.com/Commercial/Navigation/Files/Pdf/670/admapn022en_1006.pdf>

Murphy, J. and B. Bradley. Air-to-Air Energy Recovery in HVAC Systems, application manual SYS-APM003-EN, July 2002. Available at <http://www.trane.com/bookstore>

Murphy, J. and B. Bradley. Dehumidification in HVAC Systems, application manual SYS-APM004-EN, July 2002. Available at <http://www.trane.com/bookstore>

Solberg, P. “Hot Gas Bypass: Blessing or Curse?” Engineers Newsletter 32-2 (2003). Available at <http://www.trane.com/commercial/library/vol32_2/ADM_APN007_EN_0503.pdf>

bibliography

http://xp20.ashrae.org/%0Bframe.asp?standards/std90.html

http://xp20.ashrae.org/%0Bframe.asp?standards/std90.html

http://www.ashrae.org/

http://www.realread.com/prst/pageview/browse.cgi?book=1931862672

http://www.realread.com/prst/pageview/browse.cgi?book=1931862672

http://www.ashrae.org/

http://www.trane.com/commercial/library/vol33_4/admapn013en_1204.pdf




https://www.trane.com/Commercial/Navigation/Files/Pdf/670/admapn022en_1006.pdf

https://www.trane.com/Commercial/Navigation/Files/Pdf/670/admapn022en_1006.pdf

http://www.trane.com/bookstore

http://www.trane.com/bookstore

http://www.trane.com/commercial/library/vol32_2/ADM_APN007_EN_0503.pdf


Trane Engineers Newsletter Live satellite broadcast

Bibliography

bibliography

Trane Publications (continued)

Stanke, D. “Commercial Building Pressurization.” Engineers Newsletter 31-2 (2002), Available at <http://www.trane.com/commercial/library/vol31_2/ADM_APN003_EN_040302.pdf>

Stanke, D. “Keeping Cool with Outdoor Air: Airside Economizers.” Engineers Newsletter 35-2 (2006), Available at <http://www.trane.com/Commercial/Navigation/Files/Pdf/6/admapn020en_0406.pdf>

Stanke, D. “VAV System Optimization: Critical Zone Reset.” Engineers Newsletter 20-2 (1991), Available at <http://www.trane.com/commercial/library/EN20-2.pdf>

Trane Analysis Software

Trane Air-Conditioning and Economics (TRACE™ 700), Available at <http://www.trane.com/commercial/equipment/ProductDetails.aspx?prod=150>



http://www.trane.com/Commercial/Navigation/Files/Pdf/6/admapn020en_0406.pdf

http://www.trane.com/Commercial/Navigation/Files/Pdf/6/admapn020en_0406.pdf

http://www.trane.com/commercial/library/EN20-2.pdf

http://www.trane.com/commercial/equipment/ProductDetails.aspx?prod=150

http://www.trane.com/commercial/equipment/ProductDetails.aspx?prod=150

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