design and control of ventilation systems - seventhwave · march 15 & 16 power quality...

The ‘V’ in HVAC: design and control of

ventilation systems

Presenter: John Murphy

February 16, 2017 in La Crosse

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Course description

Ventilation is critical for making a building safe and

comfortable. This full-day course will begin with a

discussion of ventilation fundamentals, the

requirements of ASHRAE Standard 62.1 and an

overview of the various types of ventilation

systems. Then we will dig deeper into energy

saving ventilation strategies, such as demand

controlled ventilation and exhaust air energy

recovery. Finally, we will discuss the design and

control of dedicated outdoor air systems.

Learning objectives

EXPLAIN the requirements of ASHRAE Standard 62.1 that impact the

design and control of ventilation systems

DESCRIBE how ASHRAE 62.1 relates to meeting LEED prerequisites and

earning credit points

DISCUSS demand controlled ventilation strategies for single zone

systems, dedicated outdoor air systems and multiple zone VAV systems

DESCRIBE how to properly apply exhaust air energy recovery in building

ventilation systems

EXPLAIN how to design and control dedicated outdoor air systems that

balance indoor air quality and energy efficiency

American Institute of Architects

Seventhwave is a Registered Provider with The American Institute of

Architects Continuing Education Systems (AIA/CES). Credit(s) earned

on completion of this program will be reported to AIA/CES for AIA

members. Certificates of Completion for both AIA members and non-

AIA members are available upon request.

This program is registered with 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

addressed at the conclusion of this presentation.

Provider #: G175

Course #: COM346

This course has been registered with

GBCI for CE hours.

REGISTERED

FOR:

BY

NUMBER OF

CE HOURS:

COURSE NAME

PROVIDER NAME

The ‘V’ in HVAC: design and control of ventilation

systems

Seventhwave

6

The 'V' in HVAC:Design and Control of Ventilation Systems

John Murphy, LEED® AP BD+C

Applications Engineer

Trane

Ingersoll Rand

La Crosse, Wisconsin

February 16, 2017

La Crosse, WI

Design and Control of Ventilation Systems2

Design and Control of Ventilation Systems

Learning Objectives

1. Recognize the requirements of ASHRAE Standard 62.1

that impact the design and control of ventilation systems.

2. Understand how ASHRAE 62.1 relates to meeting LEED

prerequisites and earning credit points.

3. Apply various demand-controlled ventilation (DCV)

strategies to single-zone systems, dedicated outdoor-air

systems, and multiple-zone VAV systems.

4. Properly apply exhaust-air energy recovery in building

ventilation systems.

5. Understand how to design and control dedicated outdoor-

air systems that balance indoor air quality and energy use.



Agenda

8:30 – 10:15 Ventilation Fundamentals, ASHRAE 62.1

Break

10:30 – noon Dynamic Ventilation Reset Strategies

Lunch

12:45 – 2:15 Exhaust-Air Energy Recovery

Break

2:30 – 4:00 Dedicated Outdoor-Air Systems


Ventilation Fundamentals and ASHRAE Standard 62.1


ventilation fundamentals and ASHRAE Standard 62.1

Agenda

• Ventilation as part of indoor air quality (IAQ)

• Types of ventilation systems

• ASHRAE Standard 62.1

– General overview

– Ventilation Rate Procedure

• Relationship between ASHRAE 62.1 and LEED


eight objectives

ASHRAE Indoor Air Quality Guide

1. Manage the design and construction

process to achieve good IAQ

2. Control moisture in building assemblies

3. Limit entry of outdoor contaminants

4. Control moisture and contaminants

related to mechanical systems

5. Limit contaminants from indoor sources

6. Capture and exhaust contaminants from

building equipment and activities

7. Reduce contaminant concentrations

through ventilation, filtration, and air cleaning

8. Apply more advanced ventilation approaches



Agenda








zone

Natural Ventilation

No fan is used to deliver OA to the zone

EA OA


zone

Single-Zone Ventilation System

One AHU brings in OA through one intake

and distributes it to a single zone

packagedrooftop unit

EA

OA

RA

RASA


100% Outdoor-Air Ventilation System

One AHU brings in OA through one intake

and distributes only OA to multiple zones

dedicatedOA unit

EA

OA

SA

RAfan-coil

OA OAOA

SA

RA

SA

RA

zone 1 zone 2 zone 3


Multiple-Zone Recirculating System

One AHU brings in OA through one intake, mixes it with

recirculated air (RA), and distributes the mixture to multiple zones

EA

OA

PA PAPARA

VAV VAV VAV

RA RA

RA

zone 1 zone 2 zone 3

VAV air-handling unit



Agenda








The Importance of Standard 62.1

ASHRAE Standard 62.1 is…

• The basis for many building codes

• A prerequisite for LEED certification


ASHRAE Standard 62.1-2013

1. Purpose

2. Scope

3. Definitions

4. Outdoor Air Quality

5. Systems and Equipment

6. Procedures

• Ventilation Rate Procedure

• IAQ Procedure

• Natural Ventilation Procedure

7. Construction and System Start-Up

8. Operations and Maintenance


ASHRAE Standard 62.1, Section 4

Outdoor Air Quality

• 4.1 Regional Air QualityAssess regional air quality compliance with the

National Ambient Air Quality Standard (NAAQS)

• 4.2 Local Air QualityAssess local air quality by checking for local sources

• 4.3 DocumentationReview findings with building owner



System and Equipment Requirements

• Ventilation air distribution

• System controls

• Airstream surfaces

• Outdoor-air intakes

• Filtration

• Moisture management

– Dehumidification

– Drain pans

– Cooling coils and

humidifiers

• Access for cleaning

• Building envelope and

interior surfaces

• Air recirculation

• Exhaust and

combustion air

– Parking garage exhaust

• Environmental tobacco

smoke



Procedures

• Ventilation Rate Procedure (Section 6.2)

– Prescriptive

– Dictates ventilation rates and calculations based on

“typical” spaces

• IAQ Procedure (Section 6.3)

– Performance-based, mass balance analysis

– Must ventilate to achieve specific concentration limits

for all contaminants of concern

• Natural Ventilation (Section 6.4)

– Generally requires a “mixed-mode” system design


ASHRAE Standard 62.1, Section 6.2

Ventilation Rate Procedure

• Outdoor air treatment

• Zone calculations

– Determine breathing-zone outdoor airflow for each zone

• System calculations

– Calculate outdoor-air intake flow for entire system


ASHRAE Standard 62.1, Section 6.2.1

Outdoor Air Treatment

If outdoor air is judged to be unacceptable in accordance

with Section 4.1, each ventilation system shall include:

– MERV 6 filter in locations where the national standard for

particulates < 10 micrometers (PM10) is exceeded

– MERV 11 filter in locations where the national standard for

particulates < 2.5 micrometers (PM2.5) is exceeded

– 40% efficient ozone-removal device in locations where the

average ozone concentration is exceeded

www.epa.gov/green-book


PM10 Non-Attainment Areas


PM2.5 Non-Attainment Areas


Ozone Non-Attainment Areas










ventilation rate procedure

Zone Calculations

1. Calculate breathing-zone outdoor airflow (Vbz)

using Table 6.2.2.1 rates

Vbz = Rp × Pz + Ra × Az

2. Determine zone air-distribution effectiveness (Ez)

Look up Ez in Table 6.2.2.2

3. Calculate zone outdoor airflow (Voz)

Voz = Vbz/Ez


excerpt from Table 6.2.2.1

Minimum Ventilation Rates

Office 5.0 0.06

Conference room 5.0 0.06

Classroom 10.0 0.12

Lecture classroom 7.5 0.06

Retail sales 7.5 0.12

Auditorium 5.0 0.06

Rp Ra

Occupancy category cfm/p cfm/ft²



Zone Calculations




where,

Rp = outdoor airflow rate required per person, cfm/person

Ra = outdoor airflow rate required per unit area, cfm/ft²

Pz = zone population (number of people during typical usage)

Az = zone floor area (net occupiable floor area), ft²



= 5 × 5 + 0.06 × 1000= 25 cfm + 60 cfm

Breathing-Zone Outdoor Airflow

Example: office space

Rp = 5 cfm/person

Ra = 0.06 cfm/ft²

Pz = 5 people

Az = 1000 ft²

breathing zone

Vbz

85 cfm

= 85 cfm



= 5 × 17 + 0.06 × 1000= 85 cfm + 60 cfm

Breathing-Zone Outdoor Airflow

Example: conference room

Rp = 5 cfm/person

Ra = 0.06 cfm/ft²

Pz = 17 people

Az = 1000 ft²

breathing zone

145 cfm

= 145 cfm

Vbz



Zone Calculations







Voz = Vbz/Ez


Ceiling Ceiling or floor Cool 1.0

Ceiling Floor Warm 1.0

Ceiling Ceiling Warm (< Tspace + 15°F) 1.0

Ceiling Ceiling Hot ( Tspace + 15°F) 0.8

Floor Ceiling Cool 1.0

Floor Ceiling Cool (displacement) 1.2

Floor Ceiling Warm 0.7

Floor Floor Warm 1.0

Supply Return SA temperature Ez

Makeup air drawn in,return/exhaust at opposite side of room 0.8

Makeup air drawn in,return/exhaust near supply 0.5

Table 6.2.2.2

Zone Air-Distribution Effectiveness (Ez)


Voz = Vbz / Ez

= 85 / 1.0= 85 cfm

Zone Outdoor Airflow


ceiling supply of cool air

Ez = 1.0

breathing zone

85 cfm

Vbz

Voz

0 cfm

RA

85 cfm


Voz = Vbz / Ez

= 85 / 0.8= 106 cfm

Zone Outdoor Airflow


ceiling supply of hot air

Ez = 0.8

breathing zone

85 cfm

Vbz

Voz

21 cfm

RA

106 cfm



Zone Calculations







Voz = Vbz/Ez











System Calculations

• Single-zone system

– One air-handling unit serving one zone

• 100% outdoor-air system

– One air-handling unit serving many zones

(no recirculation)

• Multiple-zone recirculating system

– One air-handling unit serving many zones

(with recirculation)


system calculations

Single-Zone Systems

Calculate required outdoor-air

intake flow (Vot) for each system:

Vot = Voz

EA

zone 1Voz = 300

zone 3Voz = 500

zone 2Voz = 400

RA RA RA

Vot = 300 cfm

OA

SA

RA

Vot = 400 cfm

OA

SA

RA

Vot = 500 cfm

OA

SA

RA


system calculations

100% Outdoor-Air System


intake flow (Vot) for the system:

Vot = Σ Voz

dedicatedOA unit Vot = 1200 cfm

EA

OA

SA

RAfan-coil

zone 1Voz = 300

zone 3Voz = 500

zone 2Voz = 400

OA OAOA

SA

RA

SA

RA


system calculations



intake flow (Vot) for the system:

Vot = ???

EA

OA

PA PAPARA

VAV VAV VAV

RA RA

RA

some excess(unused) OA

leaves building

zone 1Voz = 300Vpz = 1000





multiple-zone recirculating system

System Calculations

1. Zone primary outdoor-air fraction (Zpz)

2. Uncorrected outdoor-air intake (Vou)

3. System ventilation efficiency (Ev)

4. System outdoor-air intake (Vot)


Primary Outdoor-Air Fraction (Zpz)

Zpz = Voz / Vpz

EA

OA

zone 1Voz = 300Vpz = 2600Vpz-min = 650

Zpz = 0.46

PA PAPARA

VAV VAV VAV

RA RA

RA


Zpz = 0.47


Zpz = 0.50

6.2.5.1 Note: For VAV system design purposes,

Vpz is the lowest zone primary airflow value

expected at the design condition analyzed.


highest



System Calculations






Uncorrected Outdoor-Air Intake (Vou)

Vou = D × ∑(Rp × Pz) + ∑(Ra × Az)

where,

D = occupant diversity = Ps / ∑Pz

Ps = peak system population

∑Pz = sum of design zone populations


example

Occupant Diversity (D)

∑Pz = 120

EA

OA

zone 1Pz = 30

PA PAPARA

VAV VAV VAV

RA RA

RA

D = Ps / ΣPz

= 80 / 120 = 0.66

zone 2Pz = 40

zone 3Pz = 50

Ps = 80 people



1 5 × 30 = 150 0.06 × 2500 = 150

2 5 × 40 = 200 0.06 × 3340 = 200

3 5 × 50 = 250 0.06 × 4170 = 250

∑(Rp × Pz) = 600 ∑(Ra × Az) = 600

zone Rp × Pz Ra × Az

Uncorrected Outdoor-Air Intake (Vou)

Vou = D × ∑(Rp × Pz) + ∑(Ra × Az)

= 0.66 × 600 + 600

= 1000 cfm



System Calculations






System Ventilation Efficiency (Ev)

Find system ventilation efficiency (Ev) using either:

Table 6.2.5.2 (“default Ev” method)

or

Appendix A (“calculated Ev” method)


Primary Outdoor-Air Fraction (Zpz)

Zpz = Voz / Vpz

EA

OA


Zpz = 0.46

PA PAPARA

VAV VAV VAV

RA RA

RA


Zpz = 0.47


Zpz = 0.50

6.2.5.1 Note: For VAV system design purposes,

Vpz is the lowest zone primary airflow value

expected at the design condition analyzed.


highest


max Zpz Ev

≤ 0.15 1.0

≤ 0.25 0.9

≤ 0.35 0.8

≤ 0.45 0.7

≤ 0.55 0.6

> 0.55 use Appendix A

Table 6.2.5.2, “default Ev” method


Determine Ev based on the

zone with the highest Zpz

(interpolation is allowed)

max Zpz = 0.50

Ev = 0.65



System Calculations






System Outdoor-Air Intake (Vot)

Calculate required outdoor-air intake flow (Vot) for the system:

Vot = Vou / Ev

= 1000 / 0.65 = 1540 cfm

Vot = 1540 cfm

EA

OA

PA PAPARA

VAV VAV VAV

RA RA

RA

zone 1Voz = 300

zone 2Voz = 400

zone 3Voz = 500




Find system ventilation efficiency (Ev) using either:

Table 6.2.5.2 (“default Ev” method)

or

Appendix A (“calculated Ev” method)


Appendix A, “calculated Ev” method




3. System ventilation efficiency (Ev)a. Average OA fraction (Xs)

Xs = Vou / Vps

b. Zone ventilation efficiency (Evz)Evz = 1 + Xs – Zpz (for single-supply systems)

Evz = (Fa + Xs × Fb – Zpz × Ep × Fc)/Fa (for secondary recirculation systems)

c. System ventilation efficiency (Ev)Ev = smallest Evz



Multiple-Zone Recirculating Systems

• Single-supply system

– All air supplied to each zone is a mixture of outdoor air

and system-level (centralized) recirculated air

Constant-volume reheat system

Single-duct VAV system

Single-fan, dual-duct VAV system

Multizone system

• Secondary recirculation system

– Some (or all) of the air supplied to each zone is

recirculated from other zones, and not directly mixed

with outdoor air

Dual-fan, dual-duct VAV system

Fan-powered VAV system


example: single-path VAV system

Default vs. Calculated Ev Methods

Appendix A generally results in a lower Vot than Table 6.2.5.2

Table 6.2.5.2 1.0 0.50 0.65 1540 cfm

Appendix A 1.0 0.50 0.67 1490 cfm

Ev method Ez Zpz Ev Vot


example: single-path VAV system

Heating vs. Cooling Modes

Table 6.2.5.2 1.0 0.50 0.65 1540 cfm

Appendix A 1.0 0.50 0.67 1490 cfm

Appendix A 0.8 0.63 0.77 1300 cfm

Ev method Ez Zpz Ev Vot

Ez = 0.8 in heating results in larger Zpz, but Xs is higher because Vps is lower,so Ev is actually higher


Tools Available from ASHRAE


example (cooling mode)

Comparison of Ventilation Systems

19% lower Vot than VAV

single zone 1200

100% outdoor air 1200

single-path VAV 1490 0.67(single-supply system)

series FPVAV 1180 0.85(secondary recirculation system)

ventilation system Vot Ev

0.83

0.83



Procedures


– Prescriptive











IAQ Procedure

1. Identify all contaminants of concern, and mixtures of

concern, for the zone.

2. Identify indoor and outdoor sources for each pollutant.

3. Determine emission rate for each pollutant from each

identified source.

4. Specify concentration limit, and exposure time, for each

contaminant, citing an appropriate cognizant authority.

5. Specify limit for perceived IAQ, based on a minimum

percentage of occupants or visitors expressing satisfaction.

6. Using mass balance calculations, determine minimum

breathing zone OA rate (Vbz) to meet concentration limits

established (in step 4) for each contaminant and mixture.

• Can make use of various air cleaning technologies


ASHRAE Standard 62.1, Appendix D

IAQ Procedure: Mass Balance Calculations



IAQ Procedure

7. Conduct a post-occupancy subjective evaluation to ensure

breathing zone OA rate (Vbz) meets the perceived IAQ

criteria (in step 5).

• Can use results from a “substantially similar” zone

8. Set the breathing zone OA rate (Vbz) to the largest of that

determined by mass balance or by subjective evaluation.

9. Calculate system-level outdoor air intake flow (Vot) based

on the breathing zone OA rate found for each zone:

• Single-zone system: Appendix D

• 100% outdoor-air system: Section 6.2.4

• Multiple-zone recirculating system: Section 6.2.5



IAQ Procedure



Procedures


– Prescriptive











Natural Ventilation Procedure

• Naturally ventilated spaces must be permanently open to,

and within minimum distance of, operable wall openings

• Depends on configuration of openings (single-sided or

adjacent walls, cross-ventilation) and ceiling height

• Free, unobstructed area of the openings must be ≥ 4% of

the net occupiable floor area being ventilated

• Operable opening controls

must be readily accessible

to building occupants



Natural Ventilation Procedure

A “mixed-mode” ventilation system is typically required:

…unless either:

• Openings are permanently open or controls prevent closing

during periods of expected occupancy, or

• Zone is not served by heating or cooling equipment

6.4 Natural Ventilation Procedure. Natural ventilation systems shall be

designed in accordance with this section and shall include mechanical

ventilation systems designed in accordance with Section 6.2 (Ventilation

Rate Procedure) and/or Section 6.3 (IAQ Procedure.


ASHRAE Standard 62.1

Further Reading

• American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc.

2011. 62.1-2016 User’s Manual. Atlanta, GA: ASHRAE.

• Ventilation Rate Procedure

– Stanke, D. 2004. “Single-Zone and Dedicated-OA Systems,” ASHRAE Journal

(October): pp. 12-20.

– Stanke, D. 2005. “Single-Path, Multiple-Zone Systems,” ASHRAE Journal

(January): pp. 28-35.

– Stanke, D. 2005. “Dual-Path, Multiple-Zone Systems,” ASHRAE Journal

(May): pp. 20-30.

– Stanke, D. 2008. “Potential ASHRAE Standard Conflicts: Indoor Air Quality

and Energy Standards” Engineers Newsletter (ADM-APN030-EN).

La Crosse, WI: Trane.

– Trane. 2013. “ASHRAE Standard 62.1-2010” Engineers Newsletter Live

program (DVD: APP-CMC047-EN). La Crosse, WI: AVS Group.

• IAQ Procedure

– Stanke, D. 2012. “Minimum Outdoor Airflow Using the IAQ Procedure”

ASHRAE Journal (June): pp. 26-34.



Agenda








Leadership in Energy and Environmental Design

LEED

Voluntary, point-based rating system based on

sustainability goals in the following categories:

Sustainable Sites

Water Efficiency

Energy & Atmosphere

Materials & Resources

Indoor Environmental Quality

Innovation in Design


EQ prerequisite (LEED v4)

Minimum IAQ Performance

Requirements

Mechanically-ventilated spaces

• Meet the minimum requirements of ASHRAE Standard 62.1-2010,

Sections 4 through 7, and

• Determine the minimum outdoor air intake flow (Vot) using the

Ventilation Rate Procedure (Section 6.2) from ASHRAE 62.1-2010

Naturally-ventilated spaces

• Determine the minimum outdoor air opening and space

configuration requirements using the Natural Ventilation Procedure

(Section 6.4) from ASHRAE 62.1-2010

The IAQ Procedure (Section 6.2) defined in ASHRAE 62.1-2010 may

not be used to comply with this prerequisite.


LEED v4 prerequisite changes


ASHRAE 62.1-2007, Sections 4–7

(ASHRAE 170-2008 for healthcare)

• Mechanically ventilated spaces:

• Must use Ventilation Rate

Procedure or local code

• Naturally ventilated spaces:

• Must comply with Section 5.1

• IAQ Procedure not allowed

• Except via pilot prerequisite

• ASHRAE 62.1-2010, Sections 4–7

(ASHRAE 170-2008 for healthcare)

• Mechanically ventilated spaces:

• Use Ventilation Rate Procedure

• Monitor OA intake flow

• Naturally ventilated spaces:

• Use Natural Vent. Procedure

• Monitor NV openings, exhaust

airflow, or CO2 concentrations

• IAQ Procedure not allowed

• Except via pilot prerequisite

LEED v3 (2009) LEED v4




Monitoring

For mechanically ventilated spaces (and for mixed-mode systems when the

mechanical ventilation is activated), monitor outdoor air intake flow as follows:

• For variable air volume systems, provide a direct outdoor airflow

measurement device capable of measuring the minimum outdoor air intake

flow. This device must measure the minimum outdoor air intake flow with an

accuracy of +/–10% of the design minimum outdoor airflow rate, as defined

by the ventilation requirements above. An alarm must indicate when the

outdoor airflow value varies by 15% or more from the outdoor airflow

setpoint.

• For constant-volume systems, balance outdoor airflow to the design

minimum outdoor airflow rate defined by ASHRAE 62.1-2010, or higher.

Install a current transducer on the supply fan, an airflow switch, or similar

monitoring device.




Monitoring

For naturally ventilated spaces (and for mixed-mode systems when the

mechanical ventilation is inactivated), comply with at least one of the following:

• Provide a direct exhaust airflow measurement device capable of

measuring exhaust airflow. This device must measure airflow with an

accuracy of +/–10% of design minimum exhaust airflow. An alarm must

indicate when airflow varies by 15% or more from exhaust airflow setpoint.

• Provide automatic indication devices on all natural ventilation openings

intended to meet the minimum opening requirements. An alarm must

indicate when any one of the openings is closed during occupied hours.

• Monitor carbon dioxide (CO2) concentrations within each thermal zone.

CO2 monitors must be between 3 and 6 feet above the floor and within the

thermal zone. CO2 monitors must have an audible or visual indicator or alert

the building automation system if the sensed CO2 concentration exceeds the

setpoint by more than 10%. Calculate appropriate CO2 setpoints using the

methods in ASHRAE 62.1-2010, Appendix C.


alternate compliance path for EQ prerequisite

EQ Pilot Prerequisite: IAQ Procedure

Requirements

• Meet the minimum requirements of ASHRAE Standard 62.1-2010,

Sections 4 through 7, and

• Determine the minimum outdoor air intake flow (Vot) for mechanical

ventilation systems using the IAQ Procedure (Section 6.3) from

ASHRAE 62.1-2010 (combining the IAQP and VRP is not an

acceptable means of compliance with this pilot prerequisite), and

• Prohibit smoking in the building

www.usgbc.org/pilotcredits


Indoor Environmental Quality (EQ) section (LEED v4)

Credits

Enhanced IAQ Strategies 1-2 points

Low-Emitting Materials 1-3 points

Construction IAQ Management Plan 1 point

IAQ Assessment 1-2 points

Thermal Comfort 1 point

Interior Lighting 1-2 points

Daylight 1-3 points

Quality Views 1-2 points

Acoustic Performance 1-2 points

EQ credit

EQ credit

EQ credit

EQ credit

EQ credit

EQ credit

EQ credit

EQ credit

EQ credit


LEED v4 credit changes

Enhanced IAQ Strategies

Outdoor Air Delivery Monitoring (1 pt)

Increased Ventilation (1 pt)

Indoor Source Control (1 pt)

Enhanced IAQ Strategies (1-2 pts)

• Option 1 (1 pt), implement all:

• Entryway systems, and

• Local exhausts, and

• MERV 13 filtration of outdoor air

• Option 2 (1 pt), choose:

• Prevent pollutants from outside, or

• Increased ventilation, or

• CO2 monitoring, or

• Monitor other contaminants

LEED v3 LEED v4


EQ credit (LEED v4)

Enhanced IAQ Strategies (Option 2)

1.3 × Vbz = 1.3 × (Rp × Pz + Ra × Az)

Increased Ventilation

Increase breathing zone outdoor air ventilation rates (Vbz) to all occupied

spaces by at least 30% above the minimum rates as determined in EQ

Prerequisite, Minimum IAQ Performance.


EQ credit (LEED v4)

Enhanced IAQ Strategies (Option 2)

Carbon Dioxide Monitoring

Monitor CO2 concentrations within all densely occupied spaces. CO2

monitors must be between 3 and 6 feet above the floor. CO2 monitors must

have an audible or visual indicator or alert the building automation system if

the sensed CO2 concentration exceeds the setpoint by more than 10%.

Calculate appropriate CO2 setpoints using methods in ASHRAE 62.1-2010,

Appendix C.

“an area with a design occupant density ≥ 25 people per 1000 ft2”

(LEED Reference Guide for Building Design and Construction, 2013 Edition, page 600)


LEED

Further Reading

• U.S. Green Building Council. 2013. LEED v4 Reference Guide for

Building Design and Construction. Washington, DC: USGBC.

• American Society of Heating, Refrigeration and Air-Conditioning

Engineers, Inc. 2010. ASHRAE Standard 62.1-2010, Ventilation for

Acceptable Indoor Air Quality. Atlanta, GA: ASHRAE.


Engineers, Inc. 2011. 62.1-2010 User’s Manual. Atlanta, GA: ASHRAE.

• Trane. 2014. “LEED v4” Engineers Newsletter Live program

(DVD: APP-CMC050-EN). La Crosse, WI: AVS Group.

Part 1: Ventilation Fundamentals and ASHRAE Standard 62.1

Self-Assessment Quiz

1. Why is it important to be familiar with ASHRAE Standard 62.1?

a. It is the basis for many local building codes.

b. Compliance with it is a prerequisite for LEED certification.

c. All of the above

2. True or False: The Ventilation Rate Procedure of ASHRAE Standard

62.1 is prescriptive in nature, dictating ventilation rates and

calculation procedures given the space and system type.

3. True or False: For many occupancy categories, ASHRAE Standard

62.1 prescribes two ventilation rates; one for people-related

contaminant sources plus one for building-related sources.

4. True or False: The project team can earn a credit point for LEED (v4)

by increasing the ventilation rates above the minimum rates required

by ASHRAE Standard 62.1.



Agenda


Break


Lunch


Break



Dynamic Ventilation Reset Strategies

Dynamic Ventilation Reset Strategies85


Section 6.2.7

Examples mentioned include:

• Variations in zone population

(“demand-controlled ventilation”)

• Variations in ventilation efficiency due to changes in airflow

(“ventilation optimization” or “ventilation reset”)

• Variations in intake airflow due to economizer operation

(“VAV box minimum reset”)

6.2.7 Dynamic Reset. The system may be designed to reset the outdoor

air intake flow (Vot) and/or space or ventilation zone airflow (Voz) as

operating conditions change.


dynamic ventilation reset strategies

Agenda

• Ventilation reset in VAV systems

– VAV box minimum reset

• Demand-controlled ventilation

– Common technologies

– Implementing DCV is various types of systems

• Requirements of ASHRAE Standard 90.1

• Summary of suggestions for cost-effective application

of demand-controlled ventilation


ASHRAE Standard 62.1-2013, Section 6.2.7.2

Ventilation Reset

6.2.7 Dynamic Reset. The system may be designed to reset the outdoor air

intake flow (Vot) and/or space or ventilation zone airflow (Voz) as operating

conditions change.

…

6.2.7.2 Ventilation Efficiency. Variations in the efficiency with which outdoor

air is distributed to the occupants under different ventilation system airflows

and temperatures shall be permitted as an optional basis of dynamic reset.









Ventilation Reset in a VAV System

• Required outdoor airflow (Voz)

• Current primary airflow (Vpz)• Current OA fraction (Zpz)

DDC VAV controllers

SA RA

AHU or rooftop unit withOA flow measurement

• Reset intake airflow (Vot)

Building Automation System

• Find highest OA fraction (Zpz)

• Calculate current systemventilation efficiency (Ev)

• Calculate current system

intake airflow (Vot)


dynamic reset based on

Variations in System Ventilation Efficiency

• Each VAV controller measures current primary airflow (Vpz) and

can calculate that zone’s OA fraction (Zpz = Voz/Vpz)

• BAS polls all VAV controllers to collect current from each:

– Zone outdoor airflow (Voz) and primary airflow (Vpz)

– Zone OA fraction (Zpz)

• BAS solves multiple-zone equations to calculate:

– Current system ventilation efficiency (Ev)

– Current system-level OA intake flow (Vot) required

• BAS communicates new OA intake flow setpoint (Vot)

to AHU or rooftop controller


Zone 1 Zone 2 Zone 3

Zone OA flow Voz 500 600 700 = 1800

Primary airflow Vpz 1500 2000 1500 = 5000

OA fraction Zpz = Voz/Vpz 0.33 0.30 0.47

Avg OA fraction Xs = Vou/Vps = 1800/5000 0.36

Sys vent effic Ev = 1 + Xs – max Zpz = 1 + 0.36 – 0.47 0.89

Sys OA intake Vot = Vou/Ev = 1800/0.89 2020

System

ventilation reset

Example: Operating Condition #1



Zone OA flow Voz 500 600 700 = 1800






System

Compared to

0.89 and 2020 cfm

at condition #1

ventilation reset

Example: Operating Condition #2



Agenda











VAV Box Minimum Reset

6.2.7 Dynamic Reset. The system may be designed to reset the outdoor air

intake flow (Vot) and/or space or ventilation zone airflow (Voz) as operating

conditions change.

…

6.2.7.3 Outdoor Air Fraction. A higher fraction of outdoor air in the air supply

due to intake of additional outdoor air for free cooling [economizing] or

exhaust air makeup shall be permitted as an optional basis of dynamic reset.


VAV box minimums set to avoid overly-high zone OA fractions (Zpz)

ONOFF

Zone 1

ON

Zone 2 Zone 3

Zone OA flow Voz 500 600 700 = 1800


VAV box minimum setting 700 850 1000





Actual OA intake flow (economizing) 2850

VAV box minimum reset

Example: Airside Economizing (Full)

55°F 59°F 60°F

55°F OA

RA

O

F

F 55°F

100% OA


OFF OFF


VAV box minimum reset

Example: Airside Economizing (Full)

55°F 55°F 55°F

55°F OA

RA

O

F

F 55°F

Zone OA flow Voz 500 600 700 = 1800


VAV box minimum setting 500 600 700





Actual OA intake flow (economizing) 2430

allow Zpz as high as 1.0

100% OA

Resetting VAV box minimums downward during airside economizing

reduces both fan and reheat energy use

OFF


dynamic reset based on

Variations in Intake Airflow (Economizing)

• AHU or rooftop controller modulates OA damper for

airside economizing

• When OA damper opens for economizing, the BAS

directs all VAV controllers to lower their minimum

airflow setpoints and allow zone OA fractions (Zpz) to

be as high as the current system OA percentage

(e.g., 100% during full economizing)



Agenda










Demand-Controlled Ventilation

A control strategy that responds to the actual

“demand” (need) for ventilation in a zone by varying

the rate at which outdoor air is delivered to that zone.

cfm required = cfm/person number of peoplelocal code,

ASHRAE 62.1


Purpose of DCV

• DCV is an energy-saving strategy

… it is not an IAQ-improvement strategy.

– The goal of DCV is to reduce ventilation airflow during

periods of reduced occupancy, thereby reducing the

energy needed to condition that ventilation air.

– If the goal was to improve IAQ, you would keep

ventilation airflow high at all times, rather than reducing

it during periods of reduced occupancy.




6.2.7.1 Demand Control Ventilation. DCV shall be permitted as an optional

means of dynamic reset. Exception: CO2 -based DCV shall not be applied in

zones with indoor sources of CO2 other than occupants or with CO2 removal

mechanisms, such as gaseous air cleaners.

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in response to

current occupancy and shall be no less than the building component

(Ra × Az) of the DCV zone. Note: Examples of reset methods or devices

include population counters, carbon dioxide (CO2) sensors, timers, occupancy

schedules, or occupancy sensors.

6.2.7.1.2 The ventilation system shall be controlled such that at steady-state it

provides each zone with no less than the breathing zone outdoor airflow (Vbz)

for the current zone population.

6.2.7.1.3 The current total outdoor air intake flow with respect to the coincident

total exhaust airflow for the building shall comply with Section 5.9.2.


Common DCV Technologies

• Time-of-day schedules

• People counters

• Occupancy (motion) sensors

• Carbon dioxide (CO2) sensors


Time-of-Day (TOD) Schedules

• Scheduling function of the BAS is used to define the

amount of outdoor air required in a zone for each

hour … based on estimated population


0

50

100

150

zo

ne

po

pu

lati

on

, P

z

midnight 6 a.m. noon 6 p.m. midnight

example: high school cafeteria

Occupancy/Ventilation TOD Schedule

200estimated Pz

each hour


0

10

20

30

40

50

60

70

zo

ne

po

pu

lati

on

, P

z

example: university lecture classroom

Occupancy/Ventilation TOD Schedule

80

estimated Pz

each hour

midnight 6 a.m. noon 6 p.m. midnight




• People counters




People Counters




• People counters




Occupancy Sensor / Motion Detector

• Sensor is used to determine if people are present

– Simple, binary input

• When a zone is occupied:

– Zone ventilation setpoint is set to design outdoor airflow

• When a zone is unoccupied:

– Zone ventilation setpoint is set to zero or

an “occupied standby” ventilation setpoint


“occupied standby” mode

Example Conference Room

• Floor area (Az) = 1000 ft2

• Design population (Pz) = 50 people

• Calculate required outdoor airflow at design population

Vbz-design = Rp Pz + Ra Az

= 5 cfm/p 50 people + 0.06 cfm/ft2 1000 ft2

= 310 cfm

• Calculate required outdoor airflow at zero population

Vbz-standby = 5 cfm/p 0 people + 0.06 cfm/ft2 1000 ft2

= 60 cfm

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in response to current

occupancy and shall be no less than the building component (Ra × Az) of the DCV zone.

8.3 Systems shall be operated such that spaces are ventilated in accordance with

Section 6 when they are expected to be occupied.



“occupied standby” mode

Example Conference Room

Lights on off

Zone cooling setpoint 75°F 77°F

Ventilation setpoint 310 cfm 60 cfm

(Vbz-design) (Vbz-standby)

occupied

mode

occupied standby

mode


“occupied-standby” mode

Change Made to ASHRAE 62.1-2016

6.2.7.1.2 For DCV zones in the occupied mode, breathing zone outdoor airflow

(Vbz) shall not be less than the building component (Ra × Az) for the zone.

Exception: Breathing zone outdoor airflow shall be permitted to be reduced

to zero for zones in occupied-standby mode for the occupancy categories

indicated in Table 6.2.2.1 provided that airflow is restored to Vbz whenever

occupancy is detected.

Section 3. Definitions

occupied mode: when a zone is scheduled to be occupied

occupied-standby mode: when a zone is scheduled to be occupied and

an occupancy sensor indicates zero population within the zone




• People counters




Production of CO2 is

related to the person’s

level of activity.

Therefore, CO2 can be

used as a "tracer gas"

for occupancy.

physical activity level, MET

0 1 2 3 4 5

0.5

0

1.0

1.5

2.0

CO

2p

ro

du

cti

on

, L/

min off

ice w

ork

sle

epin

g

walk

ing

lt m

achin

e w

ork

very light moderatelight

Source: ASHRAE Standard 62.1-2013, Figure C-2


mass balance

CO2-Based DCV

0

200

400

600

800

1000

1200

1400

1600

CO

2con

cen

trati

on

, p

pm

steady state conditions

time

CO2 outdoors

15 cfm/p

20 cfm/p

10 cfm/p

CO2 indoors


mass balance

CO2-Based DCV

0

200

400

600

800

1000

1200

1400

1600

CO

2con

cen

trati

on

, p

pm

time

CO2 indoors

COA = 350 ppm

Cspace = 1050 ppm

Cspace – COA = N / VOA

N = CO2 generation rate, cfm/person VOA = ventilation rate, cfm/person


Setpoints Vary by Application

• CO2 generation rate (N) varies with activity level

– See Appendix C of ASHRAE 62.1

• Ventilation rate (VOA) differs by space type and

cfm/person varies as zone population changes

• Outdoor CO2 concentration (COA) varies by location

– Most designers use a one-time reading from the site or

a conservative value from historical local data

"Unless combustion fumes are present, the outdoor CO2

concentration in most locations seldom varies more than

100 ppm from the nominal value."ASHRAE Transactions, 1998


minimum ventilation rates

ASHRAE Standard 62.1

Office 20 5.0 0.06

Classroom 15 10.0 0.12

Lecture classroom 15 7.5 0.06

Retail sales 0.3 7.5 0.12

Auditorium 15 5.0 0.06

1989-2001 2004-current

Rp Ra Rp Ra

Occupancy category cfm/p cfm/ft² cfm/p cfm/ft²

Beginning with the 2004 version, ASHRAE 62.1

prescribes both per-person and per-area rates


Example: University Lecture Classroom


• Design population (Pz) = 65 people

• Assumed CO2 generation rate (N) = 0.0105 cfm/person

• Outdoor CO2 concentration (COA) = 350 ppm

• Breathing-zone outdoor airflow at design population

Vbz-design = Rp Pz + Ra Az

= 7.5 cfm/p 65 people + 0.06 cfm/ft2 1000 ft2

= 490 cfm + 60 cfm

= 550 cfm

• Breathing-zone outdoor airflow at a population of 20 people

Vbz-min = 7.5 cfm/p 20 people + 0.06 cfm/ft2 1000 ft2

= 150 cfm + 60 cfm

= 210 cfm



10 20

200

400

600

800

1000

zone population, Pz

30 40 50 600

0

1200

Vbz-design = 550 cfm

Vbz-min = 210 cfm

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in response to

current occupancy and shall be no less than the building component (Ra × Az)

of the DCV zone.



for the current zone population.ASHRAE Standard 62.1-2013

bre

ath

ing

-zo

ne o

utd

oo

r air

flo

w (

Vb

z),

cfm

1400



• At design population, VOA-design is 8.5 cfm/person

Vo-design = Vbz-design / Pz-design = 550 cfm / 65 people = 8.5 cfm/person

…and Cs-design is 1600 ppm

Cs-design = COA + N / (Vbz-design/Pz-design)

= 350 ppm + 0.0105 / (550 cfm/65 people) = 1600 ppm

• At a population of 20 people, VOA-min is 10.5 cfm/person

Vo-min = Vbz-min / Pz-min = 210 cfm / 20 people = 10.5 cfm/person

…and Cs-min is 1350 ppm

Cs-min = COA + N / (Vbz-min/Pz-min)

= 350 ppm + 0.0105 / (210 cfm/20 people) = 1350 ppm



10 20

200

400

600

800

1000

zone population, Pz

30 40 50 60

600

800

1000

1200

1400

1600

40000

1200

desire

d s

pace C

O2

co

ncen

tratio

n (C

s ), pp

m

bre

ath

ing

-zo

ne o

utd

oo

r air

flo

w (

Vb

z),

cfm

Cs-min = 1350 ppm

Cs-design = 1600 ppm

18001400


CO2-Based DCV and ASHRAE 62.1

• As zone population (Pz) decreases, cfm/person (VOA)

increases and the desired indoor CO2 concentration

(Cs) decreases…

…so CO2-based DCV is not as easy as setting a

single space CO2 setpoint



Agenda










Implementing DCV in Various Systems


• Dedicated (100%) outdoor-air system



DCV in Single-Zone Systems

SAOA

RAEA

space

CO2

CO2

alternate

unit controller


implementing DCV in single-zone systems

ASHRAE 62.1 User’s Manual (Appendix A)

Example: University lecture classroom


• Peak population (Pz) = 65 people

• CO2 generation rate (N) = 0.0105 cfm/person

(light desk work)

• Outdoor CO2 concentration (COA) = 350 ppm

For this occupancy classification, Table 6-1 of

ASHRAE Standard 62.1 requires:

• Rp = 7.5 cfm/person

• Ra = 0.06 cfm/ft2




1) Calculate breathing-zone outdoor airflow (Vbz)

for both design population and with zero people


Vbz-design = 7.5 × 65 + 0.06 × 1000 = 550 cfm

Vbz-DCVmin = 7.5 × 0 + 0.06 × 1000 = 60 cfm




2) Calculate steady-state indoor CO2 concentration (Cs)

for both design population and with zero people

Cs = COA + N / ( Vbz / Pz )

Cs-design = 350 + 0.0105 / (550 cfm / 65 people) = 1600 ppm

Cs-DCVmin = 350 + 0.0105 / (60 cfm / 0 people) = 350 ppm




Vbz-design = 550 cfm

indoor CO2 concentration, ppm

Vbz-DCVmin = 60 cfm

ou

tdo

or

airflo

w, cfm

set position of OA damper to bring in

Vot-DCVmin when indoor CO2 equals Cs-DCVmin

set position of OA damper to bring in

Vot-design when indoor CO2 equals Cs-design

For single-zone system, Vot = Voz = Vbz/Ez (assumes Ez = 1.0)

Cs-design = 1600 ppmCs-DCVmin = 350 ppm


control coordination issues

DCV in Single-Zone Systems

zone

SAOA

EA RA

CO2

1. Economizer operation should override DCV2. Don’t forget about building pressure control

P



DCV and Building Pressure Control

6.2.7.1 Demand Control Ventilation

…

6.2.7.1.3 The current total outdoor air intake flow with respect to the coincident

total exhaust airflow for the building shall comply with Section 5.9.2.

5.9.2 Exfiltration. For a building, the ventilation system(s) shall be designed

to ensure that the minimum outdoor air intake equals or exceeds the

maximum exhaust airflow.

Exceptions:

1. Where excess exhaust is required by process considerations and approved

by the authority having jurisdiction, such as in certain industrial facilities

2. When outdoor air dry-bulb temperature is below the indoor space dew-point

design temperature







implementing DCV in a dedicated OA system

OA Delivered Directly to Each Zone

SAlocal

HVAC unit

CACA

EA

VAV

dedicatedOA unitOA

VFD

CO2

RA CA

SA

CO2

RA


implementing DCV in a dedicated OA system

OA Delivered to Single-Zone Units

RA

CA CA

SARA

CA

EA

dedicatedOA unitOA

VFD

RA

CO2 CO2

SA

VAV

SA

local

HVAC unit


control coordination issues

DCV in a Dedicated OA Systems

• Requires pressure-independent OA dampers for

any non-DCV zones

• Requires variable airflow at the dedicated OA unit

• Don’t forget about building pressure control







implementing DCV in multiple-zone recirculating systems

CO2 Sensor in Every Zone?

SA

OA

RAEA

space

space

CO2

CO2



CO2 Sensor in Every Zone?

• Requires a CO2 sensor in every zone

– CO2 level doesn’t change much in many of the zones

– Non-critical zones will always be overventilated

– Increases installed cost, maintenance, and risk of energy waste

• Requires BAS to poll all sensors and then determine

required OA damper position

• Requires method to ensure minimum outdoor airflow

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in response

to current occupancy and shall be no less than the building component

(Ra × Az) of the DCV zone.



CO2 Sensor in Common Return-Air Duct?

SAOA

RAEA

space

space

CO2

Under-ventilates some zones while over-ventilating others


implementing DCV in a multiple-zone recirculating system

CO2 Sensor in Common Return Duct?



for the current zone population.ASHRAE Standard 62.1-2013



DCV at Zone Level + Ventilation Reset

lounge restroom

storage office

office conference rm computer roomreception area ele

vato

rs

vestibule corridor

CO2

CO2

OCC

OCC

TOD TOD

building automation system (BAS)


DCV at Zone Level

• Use all zone-level DCV approaches,

each where it best fits

– CO2 sensors: densely-occupied zones with highly-

variable population

– Occupancy sensors: low-density offices or densely-

occupied zones where population varies only minimally

– Time-of-day schedules: zones with predictable patterns


Ventilation Reset at System Level

CO2 OCC

SA RA

CO2TOD TODOCC

• Current required outdoor airflow (Voz)

(TOD schedule, OCC sensor, CO2 sensor)• Current primary airflow (Vpz)

• Current OA fraction (Zpz)

communicating VAV controllers

AHU or rooftop unit withflow-measuring OA damper








DCV at zone level + ventilation reset at system level

Benefits

• Saves energy during partial occupancy

• Lower installed cost, less maintenance, and more

reliable than installing a CO2 sensor in every zone

– Use zone-level DCV approaches where they best fit

(CO2 sensor, occupancy sensor, time-of-day schedule)

– Combine with ventilation reset at the system level

• Earn LEED (v4) EQ credit: Enhanced IAQ Strategies

Carbon Dioxide Monitoring

Monitor CO2 concentrations within all densely occupied spaces. CO2 monitors

must be between 3 and 6 feet above the floor. Calculate appropriate CO2

setpoints using methods in ASHRAE 62.1-2010, Appendix C.



DCV + VAV Box Reset + Ventilation Reset

CO2

SA RA

CO2TOD TODOCC

• Current required outdoor airflow (Voz)

(TOD schedule, OCC sensor, CO2 sensor)• Current primary airflow (Vpz)

• Current OA fraction (Zpz)

• OA fraction limit (max Zpz)

communicating VAV controllers

AHU or rooftop unit withflow-measuring OA damper







OCC


CO2-Based DCV for Multiple-Zone HVAC Systems

ASHRAE Research Project 1547

• Compares various control sequences

• Further enhances control sequences

and setpoints for multiple-zone

recirculating ventilation systems


Implementation of RP-1547 CO2-Based DCV Control Sequences

ASHRAE Research Project 1747

“Valid logic was developed in Research Project 1547, but it is not readily

implemented in real control systems.”

“This project will develop practical control sequences, then test them in a

real-world building environment with a commercial-grade DDC system.”

RFP for ASHRAE Research Project 1747

• Project began in September 2015

… with expected completion by mid-2017


Seventhwave (2015) field study of DCV in Minnesota

DCV Control Sequences Implemented


Seventhwave (2015) field study of DCV in Minnesota

Measured/Calculated Energy Savings



Agenda










ASHRAE Standard 90.1-2013 (prescriptive requirement)

Ventilation Reset

6.5.3.3 Multiple-Zone VAV System Ventilation Optimization Control.

Multiple-zone VAV systems with DDC of individual zone boxes reporting to a

central control panel shall include means to automatically reduce outdoor air

intake flow (Vot) below design rates in response to changes in system

ventilation efficiency (Ev) as defined by Appendix of ASHRAE Standard 62.1.

Exceptions:

a. VAV systems with zonal transfer fans that recirculate air from other zones

without directly mixing it with outdoor air, dual-duct dual-fan VAV

systems, and VAV systems with fan-powered terminal units.

b. Systems required to have the exhaust air energy recovery complying with

Section 6.5.6.1.

c. Systems where total design exhaust airflow is more than 70% of total

design outdoor air intake flow requirements.


ASHRAE Standard 90.1-2010 (mandatory requirement)


6.4.3.9 Ventilation Controls for High-Occupancy Areas.

Demand control ventilation (DCV) is required for spaces larger than 500 ft2

and with a design occupancy for ventilation of > 40 people per 1000 ft2 of

floor area and served by systems with one or more of the following:

a. an air-side economizer,

b. automatic modulating control of the outdoor air damper,

or

c. a design outdoor airflow > 3000 cfm.

Exceptions:

a. Systems with exhaust air energy recovery complying with Section 6.5.6.1.

b. Multiple-zone systems without DDC of individual zones communicating with a

central control panel.

c. Systems with a design outdoor airflow < 1200 cfm.

d. Spaces where the supply airflow rate minus any makeup or outgoing transfer air

requirement is less than 1200 cfm.


ASHRAE Standard 90.1-2013 (mandatory requirement)


6.4.3.8 Ventilation Controls for High-Occupancy Areas.

Demand control ventilation (DCV) is required for spaces larger than 500 ft2

and with a design occupancy for ventilation of ≥ 25 people per 1000 ft2 of

floor area and served by systems with one or more of the following:

a. an air-side economizer,

b. automatic modulating control of the outdoor air damper,

or

c. a design outdoor airflow > 3000 cfm.

Exceptions:

1. Systems with exhaust air energy recovery complying with Section 6.5.6.1.

2. Multiple-zone systems without DDC of individual zones communicating with a

central control panel.

3. Systems with a design outdoor airflow < 750 cfm.

4. Spaces where > 75% of the space design outdoor airflow is required for

makeup air that is exhausted from the space or transfer air that is required

for makeup air that is exhausted from other space(s).

5. Correctional cells, daycare sickrooms, science labs, beauty and nail salons,

and bowling alley seating.


impact of

90.1-2013

• Correctional waiting room

• Lecture classroom

• Lecture hall

• Multi-use assembly

• Restaurant dining room

• Cafeteria / fast food dining

• Bars, cocktail lounge

• Conference / meeting

• Break room

• Telephone / data entry

• Transportation waiting

• Auditorium seating area

• Place of religious worship

• Courtroom

• Legislative chambers

• Lobby

• Spectator area

• Disco / dance floor

• Gambling casino

• Stage / studio

• Correctional waiting room

• Daycare

• Classroom (ages 5-8)

• Classroom (age 9+)

• Lecture classroom

• Lecture hall

• Computer lab

• Media center

• Music / theater / dance

• Multi-use assembly

• Restaurant dining room

• Cafeteria / fast food dining

• Bars, cocktail lounge

• Conference / meeting

• Lobby / pre-function

• Break room

• Reception area

• Telephone / data entry

• Transportation waiting

• Auditorium seating area

• Place of religious worship

• Courtroom

• Legislative chambers

• Lobby

• Museum / gallery

• Spectator area

• Disco / dance floor

• Health club / aerobics room

• Gambling casino

• Stage / studio

≥ 2

5 p

eo

ple

/ 1

00

0 f

t2

> 4

0 p

eo

ple

/ 1

00

0 f

t2



Agenda











Summary

• ASHRAE Standard 62.1 allows dynamic reset of

ventilation air as operating conditions change

– Ventilation reset in VAV systems

– VAV box minimum reset in VAV systems

– Demand-controlled ventilation in any system

• Consider CO2-based DCV in densely-occupied zones

with widely-varying population

• Use other DCV technologies (occupancy sensors,

time-of-day schedules) where they make sense

• Combine DCV with ventilation reset in a VAV system

to avoid the need to sense CO2 in every zone



Further Reading


2011. 62.1 User’s Manual. Atlanta, GA: ASHRAE.

– Appendix A: CO2-Based Demand-Controlled Ventilation

– Appendix B: Ventilation Reset Control

• Murphy, J. 2008. “CO2-Based Demand-Controlled Ventilation with ASHRAE

Standard 62.1,” HPAC Engineering (Sep): pp. 36-47.

• Seventhwave. 2015. “Energy Savings from Implementing and Energy Savings from

Implementing and Commissioning Demand Control Ventilation.”

• Stanke, D. 2006. “Standard 62.1 System Operation: Dynamic Reset Options”,

ASHRAE Journal (December): pp. 18-32.

• Stanke, D. 2010. “Dynamic Reset for Multiple-Zone Systems,” ASHRAE Journal

(March): pp. 22-35.

• ASHRAE Research Project 1547. CO2-Based Demand-Controlled Ventilation for

Multiple-Zone HVAC Systems.

• ASHRAE Research Project 1747 (in progress). Implementation of

RP-1547 CO2-based DCV for Multiple-Zone Systems in DDC Systems.

Part 2: Dynamic Ventilation Reset Strategies


1. Which of the following are possible technologies for implementing demand-

controlled ventilation? Circle all that apply.

a. Carbon dioxide (CO2) sensors

b. Temperature sensors

c. Time-of-day schedules in a building automation system

d. Occupancy sensors / motion detectors

2. True or False: Demand-controlled ventilation in certain densely-occupied

spaces is a mandatory requirement of ASHRAE Standard 90.1.

3. Which of the following are concerns when implementing demand-controlled

ventilation? Circle all that apply.

a. Allowing the OA damper to open further for economizing, when applicable

b. Sensor inaccuracy and the associated risk to energy use or IAQ

c. Maintaining proper building pressurization

d. Cross-leakage between the exhaust and outdoor air streams

4. True or False: The primary motivation for implementing demand-controlled

ventilation is to improve indoor air quality.



Agenda


Break


Lunch


Break



Exhaust-Air Energy Recovery

Exhaust-Air Energy Recovery163

exhaust-air energy recovery

Agenda

• Psychrometrics of exhaust-air recovery

• Proper control and integration into HVAC systems

• Common technologies

• Requirements of ASHRAE 90.1


of exhaust-air energy recovery



space

SA

RAEA

OA

air-to-airheat exchanger


Example: Total-Energy Wheel


Sensible vs. Total Recovery

• Sensible energy recovery

– Transfers sensible heat

– Changes the dry-bulb temperature of air

• Total energy recovery

– Transfers sensible heat and water vapor (latent heat)

– Changes the dry-bulb temperature and humidity of air


example: coil runaround loop

Sensible-Energy Recovery

EA'

OA

coil loop

7,000 cfm

10,000 cfm

EA

OA'

OA

EA

OA'

92°F DBT,

75°F WBT,

104 gr/lb

78°F DBT,

67 gr/lb

87.4°F DBT,

104 gr/lb

EA

OAOA'

saves 50 MBH (4.2 tons)

sensible-energy recovery • Chicago

EA'

EA' 84.7°F DBT,

67 gr/lb

EA

OA OA'

EA'


OA

EA

OA'

-4°F DBT,

3 gr/lb

70°F DBT,

37 gr/lb,

40°F DPT

20.3°F DBT,

3 gr/lb

EA' 36°F DBT,

31 gr/lb,

100% RH

water vapor condensing

on exhaust-side coil


Frosting

EA

OA

–4°F DBT

70°F DBT

37 gr/lb

40°F DPT

20.3°F DBT

36°F DBT

31 gr/lb

17°F

condensate freezes if the

surface temperature of the

exhaust-side coil is < 32°F


coil runaround loop

Frost Prevention

EA

OA

–4°F DBT

70°F DBT

37 gr/lb

40°F DPT

14.9°F DBT

42°F DBT

37 gr/lb

40°F DPT 39°F

17°F

32°F

3-way mixing valve


EA

OA OA'

saves 205 MBh EA'


OA

EA

OA'

-4°F DBT,

3 gr/lb

70°F DBT,

37 gr/lb,

40°F DPT

14.9°F DBT,

3 gr/lb

EA' 42°F DBT,

37 gr/lb


example: total-energy (enthalpy) wheel

Total-Energy Recovery

total-energy wheel

EA'

OA

7,000 cfm

10,000 cfm

EA

OA'


saves 243 MBh (20.3 tons)

OA'

OA

EA

OA'

92°F DBT,

75°F WBT,

104 gr/lb

78°F DBT,

67 gr/lb

83.6°F DBT,

83 gr/lb

OA

EA

total-energy recovery • Chicago

EA' 90°F DBT,

97 gr/lb

EA'

EAOA'

EA'

total-energy recovery • ChicagoOA

OA

EA

OA'

-4°F DBT,

3 gr/lb

70°F DBT,

37 gr/lb

58°F DBT,

32 gr/lb

EA' 8°F DBT,

100% RH

if EA' reaches 100% RH,

condensation freezes if

the exhaust-side surface

temperature is < 32°F


total-energy wheel

Frost Prevention

Frost prevention options

• Turn wheel off

• Modulate OA

bypass dampers

• Preheat OA

• Preheat EA

OA

EA

OA bypassdampers


EAsaves 452 MBh (sensible)

132 MBh (latent)OA'

EA'PH

total-energy recovery • ChicagoOA

OA

EA

OA'

-4°F DBT,

3 gr/lb

70°F DBT,

37 gr/lb

42°F DBT,

22 gr/lb

EA' 10°F DBT,

9 gr/lb,

97% RH

PH 0°F DBT,

3 gr/lb


cooling plant 50 MBh

reduction (4.2 tons)

heating plant 205 MBh

reduction

cooling plant 243 MBh

reduction (20.3 tons)

heating plant 452 MBh

reduction (latent) (132 MBh)

sensible-energy

recovery

total-energy

recovery

example (Chicago)

Summary of Plant Downsizing



Impact on installed cost

• Cooling and heating plant

downsizing

• Increased fan motor sizes

– Added static pressure of

energy-recovery device

• Additional exhaust ductwork

Impact on operating cost

• Cooling and heating

energy savings

• Increased fan energy use

• Proper control of the device

maximizes energy savings



Other Considerations

• Frost prevention

• Acceptable cross-leakage?

EA

total-energy

recovery

sensible-energy

recovery



Agenda









Control During Mild Weather

SA

RA

OA

10,000 cfm

7,000 cfm

30,000 cfm

68°F65°F

70°F

20,000 cfmwheel ON(full capacity)

EA

cooling coil ON(438 MBh)

55°F55°F

RRA




SAOA

10,000 cfm

7,000 cfm

30,000 cfm

65°F55°F

70°F

20,000 cfmwheel OFF

EA


55°F55°F

RRA

RA




SAOA

30,000 cfm

27,000 cfm

30,000 cfm

55°F55°F

70°F

0 cfmwheel OFF

EA

cooling coil OFF(0 MBh)

55°F55°F

RRA

RA

airside economizing



Capacity Control During Heating

SAOA

10,000 cfm

7,000 cfm

18,000 cfm

64°F60°F

70°F

8,000 cfmwheel ON(full capacity)

EA


60°F

(SAT reset)

40°F

RRA

RA




SAOA

10,000 cfm

7,000 cfm

18,000 cfm

53°F40°F

70°F

8,000 cfmwheel OFF

EA

heating coil ON(131 MBh)

60°F

(SAT reset)

40°F

RRA

RA




SAOA

10,000 cfm

7,000 cfm

18,000 cfm

60°F52°F

70°F

8,000 cfmwheel ON(partial capacity)

EA

both coils OFF

60°F

(SAT reset)

40°F

modulate EA bypass dampers

RRA

RA



VAV Mixed-Air System

SA

RAEA

OA

space

EAspace

total-energywheel heating

coilcoolingcoil

VAV terminalunits

bypassdampers

bypassdampers


180

160

140

120

100

80

60

40

20

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rain

s/lb

of d

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ir

11030 40 50 60 70 80 10090

dry-bulb temperature, °F

80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

EA

DBTSA

wheel on (cooling)

bypass dampers closed

wheel off

bypass dampers open

wheel on (heating)

modulate bypass damperto avoid overheating

frost

prevention

468

MinneapolisJacksonville

annual operating hours

1111

496

481

44

wheel on (full cooling)

wheel on (partial heating)

wheel off

0

1585

953

62

0 wheel on (full heating)

wheel on (frost)

14891647 wheel on

mixed-air VAV system



Dedicated Outdoor-Air System

CA

EAEA

OA

space

space

total-energywheel heating

coilcoolingcoil

bypassdampers

bypassdampers

SA

RA

SA

RA


180

160

140

120

100

80

60

40

20

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rain

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of d

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ir

11030 40 50 60 70 80 10090


80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

CA

EA

DPTCA

wheel on (cooling)

bypass dampers closed

wheel off

bypass dampers open

wheel on (heating)

modulate bypass damperto avoid overheating or

over-humidifying

DBTCA

frost

prevention

dedicated OA system



Agenda








Coil Runaround Loop

• 35% – 55% sensible

effectiveness

• 0.2 – 0.7 in. H2O pressure drop

• Very flexible

• No cross-leakage

• Capacity modulation using

variable-speed pump or

mixing valve

• Compact

expansion tank

pump

three-waymixing valve

EA

OA


Heat Pipe


effectiveness



bypass dampers or tilt control

• Very low cross-leakage


Heat Pipe


Fixed-Plate Heat Exchanger

EA

OA


effectiveness



face-and-bypass dampers

• Little or no cross-leakage

• Most susceptible to frosting



fixed-plate heat exchanger


EA

center bypass

face-and-bypass

dampers

OA


Fixed-Membrane Heat Exchanger

• 65% – 75% sensible effectiveness

• 45% – 65% latent effectiveness



external bypass dampers

• Little or no cross-leakage

• Less susceptible to frost

than other technologies

EAOA


Cross-Flow HX Frosting

• Fixed-plate heat exchangers

(sensible-energy recovery)

begin to experience frosting when

entering OA drops below 32°F

• Fixed-membrane heat exchangers

(total-energy recovery) can operate

well below 0°F without frosting


Total-Energy Wheel

• 65% – 80% sensible effectiveness

• 60% – 70% latent effectiveness



bypass dampers

• Some cross-leakage

• Self cleaning (dry particles)

• Less susceptible to frost than

sensible energy-recovery

technologies

bypass dampers


total-energy wheels

Cross-Leakage and Fan Placement


total-energy wheels

Purge Section


comparison of energy-recovery technologies

Typical Performance

effectiveness, %

30 60 805040 70

coil loop

fixed-plateheat exchanger

heat pipe

sensible heat wheel

total-energy wheel

fixed-membraneheat exchanger

sensible

sensible

sensible

sensible

sensiblelatent

sensiblelatent



Typical Performance

airside pressure drop (per side), in. H2O

0.2 0.8 1.20.60.4 1.0

coil loop


heat pipe

sensible heat wheel

total-energy wheel




Typical Frosting Conditions

outdoor temperatures at which frosting typically occurs, °F

-50°F 10°F 50°F-10°F-30°F 30°F

coil loop


heat pipe

sensible heat wheel

total-energy wheel


557 hrs

(1788 hrs)12 hrs

(79 hrs)

7 hrs

(25 hrs)

Chicago, IL6 AM – 6 PM, weekdays

(all hours, all days)


AHRI 1060 Certification

• Industry standard rating and

certification program for air-to-air

energy recovery components

– Rotary heat exchangers (wheels)

– Heat pipes

– Fixed-plate heat exchangers

– Does not cover coil loops

(coils certified by AHRI 410)

• Exhaust-air energy recovery

applications only


AHRI 1060

Certified Rating Points

Summer Winter

Summer Winter

Summer Winter

Summer Winter

Summer Winter

Summer Winter

100%

Rated Flow

75%

Rated Flow

Sensible

Latent

Total

Effectiveness

• Airside pressure drop at all rating points

• Two cross-leakage measurements at three

different deck-to-deck pressures


AHRI 1060

Cross-Leakage Measurements

exhaust-air

transfer rate

EATR

outdoor-air

correction factor

OACF

EA'

OA

EA

OA'


www.ahridirectory.org



Agenda








Section 6.5.6.1

ASHRAE Standard 90.1-1999 thru -2007

6.5.6.1 Exhaust Air Energy Recovery. Individual fan systems that have both

a design supply air capacity of 5000 cfm or greater and have a minimum

outdoor air supply of 70% or greater of the design supply air quantity

shall have an energy recovery system with at least 50% recovery

effectiveness.

Fifty percent energy recovery effectiveness shall mean a change in the

enthalpy of the outdoor air supply equal to 50% of the difference between the

outdoor air and return air at design conditions. Provision shall be made to

bypass or control the heat recovery system to permit air economizer operation

as required by Section 6.5.1.1.


Section 6.5.6.1


6.5.6.1 Exhaust Air Energy Recovery. Each fan system shall have an

energy recovery system when the system’s supply air flow rate exceeds the

value listed in Table 6.5.6.1 based on the climate zone and percentage of

outdoor air flow rate at design conditions.



Section 6.5.6.1


6.5.6.1 Exhaust Air Energy Recovery. Each fan system shall have an

energy recovery system when the system’s supply airflow rate exceeds the

value listed in Tables 6.5.6.1-1 and 6.5.6.1-2, based on the climate zone and

percentage of outdoor airflow rate at design conditions.


Section 6.5.6.1



Section 6.5.6.1

Only Minor Changes to the Exceptions

Standard 90.1-2007 Standards 90.1-2010 and -2013


Section 6.5.6.1

ASHRAE 90.1-2010 and -2013

Energy recovery systems required by this section shall have at least 50%

energy recovery effectiveness. Fifty percent energy recovery effectiveness

shall mean a change in the enthalpy of the outdoor air supply equal to 50% of

the difference between the outdoor air and return air enthalpies at design

conditions.

Provision shall be made to bypass or control the energy recovery system to

permit air economizer operation as required by Section 6.5.1.1.


Energy recovery systems required by this section shall have at least 50%

energy recovery effectiveness. Fifty percent energy recovery effectiveness

shall mean a change in the enthalpy of the outdoor air supply equal to 50% of

the difference between the outdoor air and return air enthalpies at design

conditions.

Section 6.5.6.1


OA

RA

92°F DBT75°F WBT38.4 Btu/lb

78°F DB64°F WB29.2 Btu/lb

hleaving ≤ 33.8 Btu/lb

Be careful of

this term!


defined by ASHRAE Standard 84 and AHRI Standard 1060

Effectiveness

Sensible effectiveness

Total effectiveness

S = (T1 – T2)

(T1 – T3)ṁmin

ṁOA

T = (h1 – h2)

(h1 – h3)ṁmin

ṁOA

ṁmin = smallest of ṁOA or ṁEA

X4 X3

X2X1

ṁOA

ṁEA


Equal Airflows

QT = 4.5 10,000 cfm (38.4 – 32.8 Btu/lb) = 252,000 Btu/hr

T = (38.4 – 32.8)

(38.4 – 29.2)10,000 cfm= 61%

10,000 cfm

10,000 cfm

10,000 cfm





Unequal Airflows

QT = 4.5 10,000 cfm (38.4 – 34.0 Btu/lb) = 198,000 Btu/hr

T = (38.4 – 34.0)

(38.4 – 29.2)6,000 cfm

10,000 cfm= 80%

compared to

61% with

equal airflows

compared to

252,000 Btu/hr with

equal airflows

Does not meet

ASHRAE 90.1(h2 ≤ 33.8 Btu/lb)

6,000 cfm

10,000 cfm




samewheel


“As-Applied” vs. “Rated” Effectiveness

• Be careful not to confuse “as-applied” effectiveness

(required by ASHRAE 90.1) with “rated” effectiveness

per AHRI 1060

• Confusing term was replaced in 2016 version of 90.1

• Strive for balanced airflows

– Bring back as much exhaust air as possible

Energy recovery systems required by this section shall result in an

enthalpy recovery ratio of at least 50%. A 50% enthalpy recovery ratio

shall mean a change in the enthalpy of the outdoor air supply equal to

50% of the difference between the outdoor air and entering exhaust air

enthalpies at design conditions.

excerpt from ASHRAE Standard 90.1-2016, Section 6.5.6.1



Using Restroom Exhaust

VFD

Balancing

Damper

SA OA

RA

EAtoilet

EA

RA



Recirculation of Restroom Exhaust

OA

EA

V1 V2

V4 V3

V3-to-2EATR ≤ 10%

Exhaust Air Transfer Ratio (EATR) is defined

by ASHRAE Standard 84 and certified byAHRI Standard 1060

5.16.3.2.5 Class 2 air [which includes restrooms] shall not be recirculated

or transferred to Class 1 spaces.

Exception: When using any energy recovery device, recirculation from

leakage, carryover, or transfer from the exhaust side of the energy

recovery device is permitted. Recirculated Class 2 air shall not exceed

10% of the outdoor air intake flow.



Agenda









Summary

• Total-energy recovery transfers both sensible heat and

water vapor (latent heat)

– Allows for larger reductions in cooling plant capacity

– Less susceptible to frost (greater heating energy savings)

• Maximize energy recovery effectiveness

– Centralize exhaust to better balance airflows and

maximize recovery

– Minimize cross-leakage with proper fan placement

– Proper control is very important (integrate with airside

economizer, modulate capacity to prevent over-heating,

frost prevention)

• Specify AHRI-certified components



Further Reading


Engineers, Inc. (ASHRAE). 2012. ASHRAE Handbook–HVAC

Systems and Equipment (Chapter 26, “Air-to-Air Energy

Recovery Equipment”). Atlanta, GA: ASHRAE.

• Mumma, S. 2001. Dedicated outdoor air-dual wheel system

control requirements. ASHRAE Transactions 107(1). Atlanta, GA:

ASHRAE.

• Murphy, J. and Bradley, B. 2011. Air-to-Air Energy Recovery in

HVAC Systems (SYS-APM003-EN). La Crosse, WI: Trane.

• Murphy, J. March 2012. “Total Energy Wheel Control in a

Dedicated OA System.” ASHRAE Journal 54(3): 46-58.

Part 3: Exhaust-Air Energy Recovery


1. True or False: A total-energy recovery device (such as an enthalpy

wheel) transfers both sensible heat and water vapor (latent heat)

between two airstreams.

2. During cold weather, frosting can occur on the exhaust-air energy

recovery device. On which side of the device does it occur?

a. supply side (through which outdoor air enters the building)

b. exhaust side (through which exhaust air leaves the building)

3. True or False: A total-energy wheel should be controlled to rotate

whenever the supply fan is on.

4. True or False: Sensible-energy recovery devices begin to

experience frosting at higher ambient temperatures than total-

energy recovery devices.



Agenda


Break


Lunch


Break



Dedicated Outdoor-Air Systems

Dedicated Outdoor-Air Systems232

AHRI Standard 920

What is a Dedicated OA System?

“[A dedicated OA unit] operates in combination

with a separate sensible cooling system to

satisfy the entire building humidity load. The

system is sized to maintain a prescribed

ventilation rate under any load condition. The

ventilation rate can be constant or varied based

on the building operation or occupancy schedule

or in response to the actual occupancy.

It may pre-condition outdoor air by containing an enthalpy wheel,

sensible wheel, desiccant wheel, plate heat exchanger, heat pipes

or other heat or mass transfer apparatus. It may reheat the

ventilation air by containing a reheat refrigerant circuit, sensible

wheel, heat pipe, or other heat or mass transfer apparatus.”


dedicatedOA unit

CA

SA CA

EA

OADelivers prescribed

(typically minimum)

ventilation rate Satisfies entire building

humidity (latent) load

May reheat dehumidified

ventilation air

May pre-condition

outdoor air using

air-to-air energy recovery

SA

RA

RA

CA

CA

Operates in combination

with a separate sensible

cooling/heating system

What is a Dedicated OA System?


dedicated outdoor-air systems

Agenda

• Determining the required leaving-air dew point

• Cold versus neutral air

• Optimized control strategies

• Common methods for delivering conditioned OA

• Requirements of ASHRAE 90.1 related to dedicated

OA systems


of dedicated outdoor-air systems


180

160

140

120

100

80

60

40

20

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mid

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rain

s/lb

of d

ry a

ir

11030 40 50 60 70 80 10090


80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

CA

dry enough toremove spacelatent load

OA

space

Determining Required Leaving-Air DPT


180

160

140

120

100

80

60

40

20

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mid

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rain

s/lb

of d

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ir

11030 40 50 60 70 80 10090


80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

CA

OA

space


Wca

Wspace

Qspace,latent

Qspace,latent = 0.69 × Voz × (Wspace – Wca)



1. Calculate outdoor airflow required for each zone (Voz)

2. Define target space humidity level (Wspace)

50% RH, 55%, 60%, 65%, other?

3. Determine latent load for each zone (Qspace,latent)

People, infiltration, indoor moisture sources

4. Calculate required humidity ratio of the

conditioned OA delivered to each zone (Wca):

Qspace,latent = 0.69 × Voz × (Wspace – Wca)


Example Wing of K-12 Classrooms

Classroom

101

Classroom

102

Classroom

103

Classroom

104

Wspace

(75°F, 50% RH,

55°F DPT)

64.7 gr/lb 64.7 gr/lb 64.7 gr/lb 64.7 gr/lb

Qspace,latent 5250 Btu/hr 5470 Btu/hr 5700 Btu/hr 5250 Btu/hr

Voz 450 cfm 450 cfm 480 cfm 435 cfm

Wca 47.7 gr/lb 47.0 gr/lb 47.4 gr/lb 47.2 gr/lb


Calculate Wca for Each Space

Qspace,latent = 0.69 Voz (Wspace – Wca)

For Classroom 102:

Qspace,latent = 5,470 Btu/hr

Voz = 450 cfm

Wspace = 64.7 gr/lb (75°F DBT, 50% RH, 55°F DPT)

5,470 Btu/hr = 0.69 450 cfm (64.7 gr/lb – Wca)

Wca = 47.0 gr/lb (~47°F DPT)


Impact of Wspace

Classroom 102 60% RH 55% RH 50% RH

Wspace

(75°F DBT)

77.8 gr/lb 71.2 gr/lb 64.7 gr/lb

Wca 60.2 gr/lb 53.6 gr/lb 47.0 gr/lb

DPTca 53°F 50°F 47°F



Agenda






OA systems




180

160

140

120

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60

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20

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ir

11030 40 50 60 70 80 10090


80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

CA

OA

RA/spaceSA

dedicated OA system(“neutral” air)

OA 95°F DB78°F WB

CA 70°F DB47°F DPT(450 cfm)

RA 75°F DB50% RH55°F DPT

SA 60°F DB(1500 cfm)

local unit

local unit:

1500 cfm, 2.0 tons


180

160

140

120

100

80

60

40

20

hu

mid

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tio, g

rain

s/lb

of d

ry a

ir

11030 40 50 60 70 80 10090


80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

CA

OA

deh

um

idific

atio

nsensible cooling

space

wasted cooling

dedicated OA system(“neutral” air)


180

160

140

120

100

80

60

40

20

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rain

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of d

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ir

11030 40 50 60 70 80 10090


80

70

50

40

30

60

30

40

50

55

60

65

70

75

80

de

w p

oin

t tem

pe

ratu

re, °F

CA

OA

RA/spaceSA

dedicated OA system(“cold” air)

OA 95°F DB78°F WB

CA 48°F DB47°F DPT(450 cfm)

RA 75°F DB50% RH55°F DPT

SA 60°F DB(840 cfm)

local unit

local unit:

840 cfm, 1.1 tons


1950 cfm

CA

1500 cfm at 60°F

450 cfm at 70°F

neutral air delivereddirect to space

CA SARA

SA

1290 cfm

CA

840 cfm at 60°F

RA

cold air delivereddirect to space

CA

450 cfm at 48°F

840 cfm

1500cfm


Cold vs. Neutral

• Less overall cooling capacity

– Sensible cooling provided by cold conditioned OA

reduces required cooling capacity of local HVAC units

– Cooling (dehumidification) capacity of the dedicated

OA unit is the same in either case

• Less overall cooling energy

– Sensible cooling provided by cold conditioned OA

reduces cooling required from local HVAC units


SA

1290 cfm

CA

840 cfm at 60°F

450 cfmat 48°F

RA

cold air delivereddirect to space

CA

1500 cfm

1500 cfm at 60°F

cold air deliveredto local HVAC unit

SARA

CA

450 cfm at 48°F

840 cfm

1050 cfm


Cold vs. Neutral

• Less overall fan energy, if OA is delivered cold

directly to spaces

– Cold conditioned OA removes some of the space

sensible cooling load, which reduces the airflow

needed from local HVAC units

– Airflow delivered by the dedicated OA unit is the same

in either case


Cold vs. Neutral

dedicated OA unit

cooling capacity, tons 3.9 3.9 3.9

reheat capacity, MBh 11.4 0 0

fan airflow, cfm 450 450 450

local HVAC unit

cooling capacity, tons 2.0 1.1 1.1

fan airflow, cfm 1500 840 1500

cold tospace

neutral tospace/unit

cold tolocal unit


Won’t Cold OA Overcool the Space?

Qsens,space = 26,780 Btu/h (design load)

Qsens,ca = 1.085 450 cfm (75°F – 48°F)

= 13,180 Btu/h

Space sensible cooling load

must be < 50% of design

before overcooling will occur!


When Should OA Be Reheated?

• Applications where space sensible cooling loads

differ greatly at any given time (e.g., hotels, dorms)

• Applications requiring lower-than-normal dew points

(ex. engineer may want to reheat 48°F air to 55°F)

• To avoid condensation when conditioned OA is

delivered to the ceiling plenum

• To avoid overcooling zones at part-load conditions


to avoid overcooling


RA

SA

dedicatedOA unit

CA

EACA

local HVAC units

CA

RA

SA

VAV

CO2 CO2



Activate Heat in Local Unit

RA

SA

dedicatedOA unit

CA

EACA

• only a few zones?• WSHPs

CA

RA

SA



Reheating Dehumidified OA

RA

SA

dedicatedOA unit

CA

EACA

local HVAC units

CA

RA

SA

T



Reheating Dehumidified OA

RA

SA

dedicatedOA unit

CA

EACA

CA

RA

SAT T

BAS


When Should OA Be Reheated?

• Applications where space sensible cooling loads

differ greatly at any given time (e.g., hotels, dorms)

• Applications requiring lower-than-normal dew points

• To avoid condensation when conditioned OA is

delivered to the ceiling plenum

• To avoid overcooling zones at part-load conditions

– Implement demand-controlled ventilation to

reduce outdoor airflow as population changes

– Activate heat in the local HVAC unit

(few zones, WSHPs)

– Reheat dehumidified air in dedicated OA unit

(consider using recovered energy)



Agenda






OA systems




common methods for

Delivering Conditioned OA to Zones

1. Direct to each zone

2. To intake of each local unit

3. To supply-side of each local unit

4. To ceiling plenum, near each local unit


Direct to Each Zone

RA

SA

dedicatedOA unit

CA• fan-coils

• WSHPs

• PTAC units

• VRF terminals

• passive chilled beams

• radiant cooling panels

EACA

CA


Direct to Each Zone

Advantages

• Easier to ensure required

outdoor airflow reaches each

zone (separate diffusers)

• Opportunity to cycle off local

fan because OA is not

distributed through it

• Allows dedicated OA system

to operate during

unoccupied periods without

needing to operate local fans

• Opportunity to downsize

local equipment (if OA

delivered at a cold temp)

Drawbacks

• Requires installation of

additional ductwork and

separate diffusers

• May require multiple

diffusers to ensure that

outdoor air is adequately

dispersed throughout the

zone


To Intake of Local Units

• fan-coils

• WSHPs

• small rooftop units

• VRF terminals

• sensible-cooling terminals

SA SARA RA

EACA

dedicatedOA unit


To Intake of Local Units

Advantages

• Helps ensure required OA

reaches each zone (ducted

directly to each unit)

• Avoids cost and space to

install additional ductwork

and separate diffusers

• Easier to ensure that OA is

adequately dispersed

throughout zone because it

is distributed by local fan

Drawbacks

• Measurement and balancing

is more difficult than if OA

delivered directly to zone

• May require field-fabricated

plenum to connect OA duct

• May need to increase OA in

heating mode (Ez < 1.0)

• Local fan must operate

continuously to provide OA

during scheduled occupancy

• Local fan must operate if

dedicated OA system

operates during unoccupied

period


To Supply-Side of Local Units

• fan-coils

• WSHPs

• small rooftop units

• active chilled beams

SARA

EACA

SA

RA

dedicatedOA unit


To Supply-Side of Local Units

Advantages

• Helps ensure required OA

reaches each zone (ducted

directly to each unit)




• Easier to ensure that OA is

adequately dispersed

throughout zone because it

is distributed by local fan

• Opportunity to downsize

local equipment (if OA

delivered at a cold temp)

Drawbacks

• Measurement and balancing

is more difficult than if OA

delivered directly to zone



• Local fan typically must

operate continuously to

provide OA during scheduled

occupancy (unless a

pressure-independent

damper is used)


To Plenum, Near Local Units

• fan-coils

• WSHPs

• VRF terminalsSA SARA RA

EACA

dedicatedOA unit


To Plenum, Near Local Units

Advantages




Drawbacks

• More difficult to ensure

required OA reaches each zone

(not ducted directly)

– Refer to Figure 5-D and 5-E,

ASHRAE 62.1-2010 User’s Manual



• Local fan must operate

continuously to provide OA

during scheduled occupancy

• Conditioned OA not able to be

delivered at a cold temperature

due to concerns about

condensation


conditioned OA delivered to plenum, near local units

Excerpt from 62.1-2010 User’s Manual



Agenda






OA systems





Dedicated OA Systems

• Minimum equipment efficiencies

• Fan power limitation

• Economizer

• Limitation on simultaneous

heating and cooling (reheat)


Section 6.4.1, ASHRAE 90.1-2013

Minimum Equipment Efficiencies

Equipment efficiency levels defined in this section [Section 6.4.1] and Tables

6.8.1-1 through 6.8.1-13 are based on industry rating standards, such as

those of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI).

Although Sections 6.4.1.1 and 6.4.1.2 include many types of HVACR

equipment, not every type of HVACR equipment that might be used in a

project is covered. This section [Section 6.4.1.3] clarifies that the use of

HVACR equipment not covered by these sections does not prohibit

compliance with the Standard. Equipment not covered by these sections is

not regulated by this standard, but may be regulated by other standards,

codes, or federal regulations.

Standard 90.1-2013 User's Manual, pages 6-14 and 6-18




• Until AHRI Standard 920 was published (June 2013)

there was no rating standard for DX dedicated OA

equipment, so ASHRAE 90.1 did not include minimum

efficiency requirements for this class of equipment

• Minimum efficiency requirements were added to

Standard 90.1 in the 2016 version

Dedicated outdoor air systems (DOAS) ... are used in many buildings

covered by ASHRAE 90.1. However, the current ASHRAE 90.1 standard

has no minimum energy efficiency requirements for this equipment.

Through AHRI, manufacturers of DOAS developed Standard 920 to

establish common rating conditions for these products. This proposal

establishes for the first time a product class for DOAS.

addendum CD to ASHRAE Standard 90.1-2013





Section 6.5.3.1.1, ASHRAE 90.1-2013

Fan Power Limitation

6.5.3 Air System Design and Control. Each HVAC system having a total

fan system motor nameplate hp exceeding 5 hp shall meet the provisions of

Sections 6.5.3.1 through 6.5.3.5.

6.5.3.1 Fan System Power and Efficiency

6.5.3.1.1 Each HVAC system at fan system design conditions shall not

exceed the allowable fan system motor nameplate hp (Option 1) or fan

system bhp (Option 2) as shown in Table 6.5.3.1-1. This includes supply

fans, return/relief fans, exhaust fans, and fan-powered terminal units

associated with systems providing heating or cooling capability. Single zone

VAV systems shall comply with the constant volume fan power limitation.

Exceptions:

1. Hospital, vivarium, and laboratory systems that utilize flow control devices

on exhaust and/or return to maintain space pressure relationships

necessary for occupant health and safety or environmental control may

use variable-volume fan power limitation.

2. Individual exhaust fans with motor nameplate horsepower of 1 hp or less.


Section 6.5.3.1.1, ASHRAE 90.1-2013

Fan Power Limitation

What is a “fan system”?

“fan system bhp: the sum of the fan brake horsepower

(bhp) of all fans that are required to operate at fan system

design conditions to supply air from the heating or cooling

source to the conditioned space(s) and return it to the

source or exhaust it to the outdoors” (Section 3.2)


example 6-CCC

User’s Manual for 90.1-2013

QUESTION: A wing of an elementary school building is served by

eight WSHPs, each equipped with a ¾-hp fan motor and serving a

single classroom. Ventilation air is supplied directly to each

classroom by a dedicated outdoor-air system. Each classroom

requires 500 cfm of outdoor air, so the DOAS delivers the total of

4000 cfm of conditioned outdoor air using a 5-hp fan. Does this

system need to comply with section 6.5.3.1?

ANSWER: Each WSHP is a separate fan system because

each has a separate cooling and heating source. The power of

the DOAS fan must be allocated to each heat pump on a

cfm-weighted basis.


example 6-CCC


DOAS delivers 500 cfm to each classroom, so

1/8th (500 cfm / 4000 cfm) of the DOAS fan power is

added to the fan power for each WSHP:

• 1/8th of 5 hp = 5/8 hp

• 3/4 hp (WSHP) + 5/8 hp (allocated DOAS) = 1 3/8 hp

ANSWER [continued]:

…

In this instance, even with the DOAS fan allocated, each heat pump

fan system is less than the 5 hp threshold in Section 6.5.3, so the

system does not need to comply with Section 6.5.3.1.



Economizers

Most notable exceptions:

1. Individual fan-cooling units < 54,000 Btu/hr (4.5 tons)

2. Systems that use non-particulate air treatment as

required by ASHRAE Standard 62.1

4. Systems with condenser heat recovery

5. Residential with cooling capacity < 270,000 Btu/hr

7. Systems that operate < 20 hours/week

9. Install higher-efficiency cooling equipment

6.5.1 Economizers. Each cooling system that has a fan shall include

either an air or water economizer meeting the requirements of

Sections 6.5.1.1 through 6.5.1.6.



Economizers

Climate Zone 1

includes south

Florida, Hawaii,

Guam, Puerto

Rico, and the

Virgin Islands

Economizer required if

individual fan-cooling unit

54,000 Btuh (4.5 tons)

The requirement is based on the [capacity of the] fan-coil unit and

not the capacity of a central chilled-water plant or VRF system

condensing unit capacity.

ASHRAE 90.1-2013 User’s Manual, page 6-57


If an Economizer is Required…

• An airside economizer will likely be difficult to implement

with a dedicated OA system (typically sized for minimum

ventilation only)

• Implement a waterside economizer(fan-coils, WSHPs, chilled beams, radiant cooling)

• Install higher-efficiency cooling equipment (Exception 9)

• Comply using the Energy Cost Budget (Section 10)

method, rather than the prescriptive requirements

6.5.1.1.1 Air economizer systems shall be capable of modulating

outdoor air and return air dampers to provide up to 100% of the

design supply air quantity as outdoor air for cooling.



Simultaneous Heating and Cooling

6.5.2.3 Dehumidification. Where humidity controls are provided, such

controls shall prevent reheating, mixing of hot and cold airstreams, or

other means of simultaneous heating and cooling of the same

airstream.

Exceptions:

1. The system is configured to reduce supply air volume to 50% or

less of the design airflow rate or the minimum outdoor air

ventilation rate specified in ASHRAE Standard 62.1 or other

applicable federal, state, or local code or recognized standard,

whichever is larger, before simultaneous heating and cooling takes

place.

…


example 6-SS


QUESTION: A large 100% outdoor air, constant-volume system

provides minimum ventilation to hotel guest rooms in a Florida

hotel. The system includes a cooling coil and reheat coil

controlled by a supply air dew-point sensor. Does this system

comply with the Standard?

ANSWER: Yes. Exception 1 to Section 6.5.2.3 allows this

system, provided that the supply air rate is equal to the minimum

ventilation rate.



Agenda






OA systems





Summary

• Dehumidify OA to a dew point drier than the space

• Deliver conditioned OA “cold” (not “neutral”), if possible

• Deliver conditioned OA directly to occupied spaces

• Use communicating controls to optimize system

– Reset DBTca to reheat only when necessary

– Reset DPTca based on space humidity

• Consider exhaust-air energy recovery



Further Reading


2017. Dedicated Outdoor Air System Design Guide. Atlanta, GA: ASHRAE.

(available mid-2017)

• Morris, W. 2003. “The ABCs of DOAS: Dedicated Outdoor Air Systems.”

ASHRAE Journal (May).

• Murphy, J. 2006. “Smart Dedicated Outdoor Air Systems.” ASHRAE Journal

(July).

• Murphy, J. and Bradley, B. 2002. Dehumidification in HVAC Systems (SYS-

APM004-EN). La Crosse, WI: Trane.

• Murphy, J. and Harshaw, J. 2002. “AHRI 920: Rating Standard for DX Dedicated

Outdoor-Air Units” (ADM-APN060-EN). La Crosse, WI: Trane.

• Mumma, Stanley A. 2008. “DOAS Supply Air Conditions.” ASHRAE IAQ

Applications 9(2):18–20.

• Shank, K. and S. Mumma. 2001. “Selecting the Supply Air Conditions for a

Dedicated Outdoor Air System Working in Parallel with Distributed Sensible

Cooling Terminal Equipment.” ASHRAE Transactions 107(1).

• Trane. 2012. Dedicated Outdoor Air Systems, SYS-APG001-EN.

Part 4: Dedicated Outdoor-Air Systems


1. True or False: For a dedicated outdoor-air system to remove space latent loads, the

outdoor air must be dehumidified to a dew point that is drier than the desired space dew

point.

2. True or False: ASHRAE Standard 90.1 requires an airside economizer on every dedicated

outdoor-air system.

3. Which of the following are benefits of having the dedicated OA unit deliver the

dehumidified outdoor air cold, rather than reheating it to neutral? Circle all that apply.

a. The cold, dehumidified outdoor air results in better dehumidification than warm, dehumidified air.

b. The cold, dehumidified outdoor air removes more of the space sensible cooling loads, often allowing the local HVAC equipment to be downsized and use less energy.

c. Delivering the dehumidified outdoor air at a cold, rather than neutral, temperature avoids (or reduces)

the need to reheat this air in the dedicated OA unit.

d. Delivering the dehumidified outdoor air at a cold temperature eliminates the concern about

overcooling the spaces.

4. Which of the following impact the required dew point temperature delivered by the

dedicated OA equipment, if the goal is to remove the entire space latent load with the

dehumidified outdoor air? Circle all that apply.

a. The desired space humidity level.

b. The outdoor airflow delivered to the space by the dedicated OA unit.

c. The design space latent load.

d. The design space sensible cooling load.


Thank you for attending

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