CO2based Demand Controlled Ventilation DCV

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CO2-based Demand Controlled Ventilation (DCV)
04/05/2006 Ryan R. Hoger Commercial Controls
Mgr. Temperature Equipment Corp.
ryan.hoger_at_tecmungo.com
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Benjamin Franklin on Ventilation (c. 1794)

• I considered fresh air an enemy,
• and closed with extreme care
• every crevice in the rooms I inhabited

Experience has convinced me of my error. I now
look upon fresh air as a friend. I even sleep
with an open window
I am persuaded that no common air from without is
so unwholesome as the air within a closed room
that has been often breathed and not changed.
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Comfort Is More Than Just The Right Temperature
Ventilation Control

• Comfort
• Temperature Ventilation

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How is ventilation provided in buildings today?
Ventilation Control

The same way it was in 1930. With Fixed
Ventilation!
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Fixed Ventilation
Building codes require ventilation rates based on
cfm/person (typically 20 cfm/person)
Max Occupancy 25 people 500cfm
Actual Occupancy 5 people 500cfm
Actual Occupancy 1 person 500cfm
Inefficient!
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Ventilation Control
Fixed Ventilation In a Multi-Zone VAV Building
Total cfm Max occupants X 20 cfm
There Is No Control!
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Temperature Control InA Multi-Zone VAV Building

• Measure In Each Zone
• Control Based On Actual Load

What if we did the same thing with ventilation?
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Great Idea!
Delivers The RIGHT Amount of Fresh Air, To The
RIGHT Place, At The RIGHT Time
But How Does It Work?
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Controlling Ventilation
There is a clearly defined relationship between
indoor CO2 levels ventilation rates
established by Indoor CO2 levels are a
measure of ventilation rates (cfm/person) CO2
levels are not a measure of overall IAQ.
CO2 is the control parameter for ventilation!
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CO2 Basics

• CO2 is NOT a contaminant, it is a colorless,
  odorless gas found naturally in the atmosphere
• Outdoor levels are fairly constant at 400 /- 25
  ppm
• Typical indoor levels 400 to 2,500 ppm
• Not harmful unless concentrations reach 30,000
  ppm
• Carbon Monoxide (CO) and Carbon Dioxide are NOT
  the Same

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CO2 Basics
People exhale CO2 at concentrations of 4 (40,000
ppm) Normal room concentrations are in the range
of 400 - 1200 ppm As a gas, CO2 diffuses and
equalizes rapidly throughout a room (like
humidity)
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CO2 and Ventilation Rates

• CO2 production by people is very predictable
  based on activity level
• Doubling the people in a room will double CO2
  production

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CO2 and Ventilation Rates
CO2 levels will build until an equilibrium level
is reached with outside air entering the space
5 cfm/person
10 cfm/person
15 cfm/person
20 cfm/person
30 cfm/person
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CO2 and Ventilation Rates
Two Sources of CO2 in Buildings are People or
Exhaled CO2 and Outdoor Air Indoor CO2 Levels
Mix of Exhaled CO2 with Outdoor Air Same as
mixing a cup of extremely strong coffee
(breathing) with a bucket of weak coffee (Outdoor
Air) The resulting concentration (Indoor CO2
Level) can be calculated
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CO2 and Ventilation Rates
Vo N/(Cs - Co) Office Space Met Level of 1.2
0.30 L/min (0.0107ft3/min) Outside CO2
concentration is 400 ppm or 0.04 Inside CO2
concentration is 1100 ppm or 0.11 Vo (0.0107
ft3/min)/(0.0011-0.0004) or 15 cfm Cs
Co N/Vo Cs 0.0004 (0.0107 ft3/min/15
ft3/min) 0.0011 or 1100 PPM
Vo Outdoor air flow rate Ve breathing rate N
CO2 generation rate per person Ce CO2
concentration in exhaled breath Cs CO2
concentration in the space Co Co2 concentration
in outdoor space
Source ASHRAE 62-1989 Appendix D
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CO2 and Ventilation Rates
Also can be expressed as... Rp 8,400 X m
CR - COA Where Rp The rate of outdoor air
per person (cfm/person) m The metabolic rate (1
met 58.2 W/m2). The default metabolic rate is
1.2 mets. COA The outdoor air CO2 concentration
(ppm). The default outdoor air CO2 concentration
is 400 ppm. CR The room CO2 concentration (ppm)
measured by
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CO2 and Ventilation Rates
Example 1 Person in an Office
Outdoor Air OA Ventilation Rate 20
cfm/person OA CO2 ppm 400 ppm CO2 Production
by People CO2 Production 0.0106
cfm/person Concentration 1,000,000 ppm
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CO2 and Ventilation Rates
Example
Outdoor Air (20 ft3/min/person _at_ 400 ppm)
What is the CO2 level for one person in the room?
People
People CO2 (0.0106 ft3/min/person _at_ 1,000,000 ppm)
Outdoor Air
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CO2 and Ventilation Rates
What happens with 2 people in the room?
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CO2 and Ventilation Rates
What happens with 100 people in the room?
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CO2 and Ventilation Rates
What is the Control Point for a 15 cfm/person
ventilation rate?
Outdoor Air (15 ft3/min/person _at_ 400 ppm)
People CO2 (0.0106 ft3/min/person _at_ 1,000,000 ppm)
Value Given in ASHRAE 62-1989
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CO2 Equilibrium Levels
CO2 Levels Will Build And Level Off At The Point
Were CO2 Produced By People Is In Equilibrium
With Outside Air Ventilated Into The Space
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Ventilation Control
Actual Occupancy 25 people 500cfm
Actual Occupancy 5 people 100cfm
Actual Occupancy 1 person 20cfm
Ventilation based on actual occupancy!
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With Zone Ventilation Control in a VAV Building
Zone Ventilation Control
Healthy Efficient!
Healthy Efficient!
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Zone Ventilation Control
OK! But How Do We Do It?
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Zone Ventilation Control
Zone level DDC VAV and VVT control systems that
automatically give you the ventilation you need
only when you really need it.
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Zone Ventilation Control
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Numerous Studies Confirm that Correct Ventilation
Zone Ventilation Control

• Increases Productivity
• Improves Occupant/Customer Satisfaction
• Helps Prevent Sick Building Syndrome Health
  Affects

DOE/Lawrence Berkeley Labs Indoor Environment In
Schools Pupils Health Performance In Regard To
CO2 Concentrations A significant correlation was
found between decreased performance and high CO2
levels (lower ventilation rates).
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Numerous Studies Confirm that Correct Ventilation
Zone Ventilation Control

• Increases Productivity
• Improves Occupant/Customer Satisfaction
• Helps Prevent Sick Building Syndrome Health
  Affects

Air Quality and Ventilation ranked very high
(2 of 25) on the list of tenant retention
issues in a recent survey conducted by Real
Estate Information Systems.
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Numerous Studies Confirm that Correct Ventilation
Zone Ventilation Control

• Increases Productivity
• Improves Occupant/Customer Satisfaction
• Helps Prevent Sick Building Syndrome Health
  Affects

Economic Considerations of Air Quality and
Ventilation in Offices (US EPA) Improvements in
the indoor air environment substantially increase
employee morale and productivity.
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Numerous Studies Confirm that Correct Ventilation
Zone Ventilation Control

• Increases Productivity
• Improves Occupant/Customer Satisfaction
• Helps Prevent Sick Building Syndrome Health
  Affects

DOE/Lawrence Berkeley Labs Evaluation of Sick
Leave Statistics vs. Ventilation Rates (3720
employees / 40 buildings) Optimal ventilation
reduces sick time costs. For
every 1 spent on ventilation cost, 2 are
saved in sick time.
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Ventilation Control
Benefits of Ventilation Control

• Proof of Compliance

ASHRAE Standard 62
Using CO2-based ventilation control ensures
compliance to codes and standards
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ASHRAE Interpretation IC 62-1999-33
Ventilation Control

• It is consistent with the Ventilation Rate
  Procedure that demand control be permitted for
  use to reduce the total outdoor air supply during
  periods of less occupancy

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Commentary To The International Mechanical Code
(IMC)Section 403.3.1
Ventilation Control

• The intent of this section is to allow the rate
  of ventilation to modulate in proportion to the
  number of occupants. This can result in
  significant energy savings. Current technology
  can permit the design of ventilation systems that
  are capable of detecting the occupant load of the
  space and automatically adjusting the ventilation
  rate accordingly.
• For example, carbon dioxide (CO2) detectors can
  be used to sense the level of CO2 concentrations
  which are indicative of the number of occupants.
  People emit predictable quantities of CO2 for any
  given activity, and this knowledge can be used to
  estimate the occupant load in a space.

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Chicago Ventilation Code
18-28-403.1.2 Demand ventilation. The amount of
outside air delivered by a mechanical supply
system may be reduced during operation below the
quantities listed in able 18-28-403.3 if the
system is capable of measuring and maintaining
CO2 levels in occupied spaces no greater than
1000 ppm. The system capacity shall be greater
than or equal to the ordinance requirements.
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A Better Operating Building
Zone Ventilation Control

• Ventilate to Actual vs. Assumed Occupancy
• Eliminate Wasteful Over-Ventilation
• Very Attractive ROI/Lower Operating Costs

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DCV Savings
This chart compares ventilation usage throughout
a typical day using purple to represent demand
controlled and green to represent constant.
The difference between the two equates to
significant savings.
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DCV Savings
Average Occupancy Schedule (For Occupied Days)
Relative To Design Occupancy
0 4 8 12 16 20 24
Average occupancy pattern by building type
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Research Findings Demand Control Ventilation
Energy required, DCV control applied
Energy wasted - no DCV
HUGE Savings
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Examples of Potential Energy Savings and ROI
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Zone Ventilation Control Examples
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Red Wing School District, MN
Zone Ventilation Control

• Driver
• Comfort/Productivity
• Need For Quick Response To Complaints
• Results
• Problem areas identified and corrected quickly
• (over and under ventilation).
• Teacher concerns resolved quickly.

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LaSalle Plaza, MN
Zone Ventilation Control

• Driver
• Energy Savings
• Tenant Comfort/Satisfaction
• Results
• Significant reduction in heating and cooling
  costs (200k 1st year)
• 3 month ROI

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Purdue University, IN
Zone Ventilation Control

• Drivers
• Energy Savings
• Productivity/Learning
• Low Maintenance Solution
• Results
• The installation provided a 1 to 2 year payback
  
• (Luci Keazer, Controls Engineer)

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Harley Davidson, WI
Zone Ventilation Control

• Drivers
• Productivity
• Comfort
• Total Quality Environment
• Results
• An Important part of Harleys Quality Program for
  a comfortable and productive work environment.

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Application Stepsfor CO2 Ventilation Control
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Step 1 Determine if CO2 Control is Appropriate

• Factors that may affect the application of CO2
  control are
• Building pressurization
• Ventilation requirements other than ASHRAE 62 or
  the IMC
• Special requirements for control of hazardous
  materials

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Step 1 Determine if CO2 Control is Appropriate
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Step 2 Determine the Design Ventilation
Requirement

• Ventilation required when the building is fully
  occupied
• Ventilation rate used for sizing the HVAC
  equipment
• Outdoor air requirement/damper setting when DCV
  is not used, previously known as minimum
  ventilation

Design Ventilation
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Step 2 Determine the Design Ventilation
Requirement

• For Constant Volume Systems
• Same as current method
• Multiply the per person ventilation rate
  (required by codes) by the number of design
  occupants
• For example if an office space is designed for
  100 people
• Design Ventilation 20 cfm/person 100 people
• 2,000 cfm

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Step 2 Determine the Design Ventilation
Requirement

• For Multiple Zone VAV Systems
• When using CO2 Control, the Multiple Space or
  Critical Space equation is NOT required.
• CO2 control ensures the correct ventilation to
  each zone
• Calculate design ventilation the same as a
  constant volume system

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Step 3 Calculate the Base Ventilation Rate

• Base ventilation establishes the lowest outdoor
  air rate during times when the building is
  sparsely occupied
• Must be adequate to
• Balance supply, exhaust, and building
  pressurization requirements
• Dilute any non-occupant related contaminants

Design Ventilation
Base Ventilation
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Step 3 Calculate the Base Ventilation Rate

• Typical base ventilation is between 20 - 30 of
  design
• Retail and new buildings may want to use 40 of
  design due to higher concentrations of
  non-occupant related contaminants

Design Ventilation
Base Ventilation
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Step 3 Calculate the Base Ventilation Rate

• For VAV Systems
• To ensure the base ventilation rate is delivered
  at light loads
• Set all zone dampers to their base ventilation
  rate
• Ensure the unit is maintaining the design static
  pressure
• Set the outside air damper to bring in the
  buildings base ventilation

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Step 4 Choose the Control Strategy
Determine the CO2 Control Point

• CO2 Control Point Depends on
• Outdoor CO2 Level (typically 400 ppm)
• Required cfm/person ventilation rate
• If OA CO2 is 400 ppm
• 20 cfm/person 930 ppm CO2
• 15 cfm/person 1,100 ppm CO2
• 10 cfm/person 1,450 ppm CO2

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Step 4 Choose the Control Strategy

• Set Point (Relay) Control
• Simplest control strategy (two position damper)
• When the CO2 level reaches the Control Point,
  outside air delivery Increases from the base to
  the design level
• When the CO2 level drops 200 ppm below the
  Control Point, outside air drops back to the base
  level
• Use in high occupant density applications that
  reach peak levels quickly (i.e. classrooms)
• Use only where one air handler serves a single
  zone.

Design Ventilation
Base Ventilation
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Step 4 Choose the Control Strategy

• Proportional Control
• Dampers open as the CO2 level rises
• Set minimum damper position to 20-30 of design,
  start modulation at 100 ppm over outside levels
  (500 ppm). When CO2 level reaches the control
  point, the outdoor air system brings in design
  ventilation levels
• Responds quicker to small changes in occupancy or
  CO2

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Step 4 Choose the Control Strategy

• Proportional-Integral Control
• Ventilation system responds to both the CO2
  level and rate of change
• Best performance from both a comfort and total
  energy savings perspective
• Works well in all applications

CO2 Control Point
Increased CO2 Levels
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Step 5 Locating CO2 Sensors

• Use duct sensors only when one HVAC unit serves
  one occupancy zone
• Locating Wall-Mounted Sensors
• Similar to Tstat
• Centrally located in the space
• Away from doors and windows
• Avoid putting next to where people congregate
  (water coolers)
• 4 feet and higher on the wall
• A wall-mounted CO2 sensor can cover up to 5,000
  ft2 of open space
• For VAV systems, locate at least one CO2 sensor
  in each occupancy zone

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Step 5 Locating CO2 Sensors
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ApplyingCO2 Ventilation Control
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Applying CO2 Sensors

• Most economizer controls accept a CO2 (or IAQ)
  input
• Most HVAC manufacturers have incorporated CO2
  ventilation control into their rooftops
• Most building management systems also can utilize
  CO2 control

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OEM Rooftop Equipment

• Many factory mounted rooftop controllers/
  economizers can accept a CO2 sensor input
  directly.
• In many cases the logic to modulate the dampers
  (including economizer overrides) is built
  in.consult manufacturers literature for
  details.
• If not present, an economizer or motorized damper
  is required.

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1916 Engineers Handbook
Is Using CO2 to Measure Ventilation a New Idea?
CO2 tests should be used for checking the
renewal of air and its distribution within the
room. the CO2 should NOT exceed 8 or 10
parts in 10,000
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DCV Timeline
VAV
CO2
2004 ASHRAE Standard 62 update adds DCV to body
of standard
2000 Intro of low cost temp/CO2 sensor enabling
affordable zone level DCV
1916 Mechanical Engineers Handbook Explains
relationship between CO2 and ventilation
1929 NY Building code details CO2 levels shall
not be greater than one part in one thousand
1973 Energy crunch introduce VAV system for
commercial buildings

• 1989
• ASHRAE Standard 62-89 increases
• ventilation rates, foundation for DCV and 1000
  PPM rate

1997 Interpretation IC-62-1989-27 clarifies use
of CO2 as a method of controlling ventilation
based on occupancy
1999 ASHRAE 62-99 eliminates 1000 PPM CO2
threshold in/outside differential introduced
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Why Now?

• Digital Control Systems
• Integration of ventilation control
• Increased Ventilation Rates (ASHRAE/IMC)
• Increasing Energy Costs
• Decreasing Sensor Costs (First Life Cycle)
  Increased Sensor Reliability

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Sensor Cost

• Control system integration
• Sensor technology and integration (CO2
  Temp)
• Volume increases

1500
Installed Cost Per Point
500
1992
1997
2003
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Sensor Reliability

• 15 Year design life
• Non-interactive, selective to CO2 only
• Stable - lifetime calibration

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Sensor Technology
Cost Effective Zone Level CO2 Temp Sensor
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Sensor Technology
IR Detector
IR Source

• Target gas absorbs radiation at signature
  wavelength
• Filter isolates wavelength that reaches detector
• More gas in chamber leads to lower signal to
  detector

0 ppm CO2
Wavelength Filter
IR Detector
IR Source
1000 ppm CO2
Wavelength Filter
IR Detector
IR Source
2000 PPM CO2
Wavelength Filter
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Sensor Technology
Long life expectance (15 years) Lifetime
calibration guarantee Selective - no interference
with other gases Stable - does not require
calibration
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Self Calibration of a CO2 Detector

• Automatic Baseline Calibration (ABC Logic)
• Self calibrating algorithm
• Considers lowest CO2 level every 24 hrs
• Looks at long term changes in baseline
• Applies a correction factor for calibration

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Self Calibration of a CO2 Detector
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Sensor Reliability
Self Calibration Over 14 Days
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Long Term Sensor Stability
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Infrared Absorption Of Gases
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Infrared Design

• Current Design Product Of Over 10 years/50,000
  units of Experience
• Infrared source emits energy through the patented
  waveguide
• Optical filter eliminates all but CO2 target
  wavelength
• Detector measures amount of infrared energy and
  sends the signal to
• the microprocessor
• More CO2 in the chamber means less infrared
  energy reaches the detector

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Wall-Mount Ventostat 8001 8002

• Single Channel Sensor w/ and w/o Display
• Utilizes ABC Logic - Requires No Calibration

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1508 Aspiration Box

• Compatible with 8000 9000 Series Sensor
  Platforms

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Duct-Mount Ventostat 8007 8008

• Pitot Sampling Measurement Incorporated into the
  8000 Sensor Platform
• Lower-Cost Alternative to Aspiration Box
• Allows Mounting of Sensor Remote from Duct

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Wall-Mount CO2/Temp Airestat 5010 5011

• Designed Specifically for VAV Applications
• Utilizes ABC LogicTM - Needs No Calibration
• Utilizes 10K Thermistor
• Optional Slide Pot Adjustment

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Zone Ventilation Control
Whats new in ASHRAE 62-2004
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Zone Ventilation Control
Whats new in ASHRAE 62-2004 As stated in
forward of 2004 standard

• IAQ procedure has been restated to include
  mandatory and enforceable language
• Appendix G has been added as a guideline for
  application and enforcement of the standard
• Requirements have been added to ensure air
  systems are capable of delivering outdoor air to
  occupied spaces
• Air cleaning requirements have been added when
  OA is unacceptable

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Zone Ventilation Control

• Ventilation Rate procedure introduces the
  concept of the Breathing Zone, changes
  calculations for zone and system ventilation
  rates to include area and people related
  components, changes the multiple space equation
  to include components for space air distribution
  and system efficiency
• All tables for ventilation rates are specified
  for non-smoking areas
• Air type and quality classification standards
  have been added

Whats new in ASHRAE 62-2004 As stated in
forward of 2004 standard
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Zone Ventilation Control
Whats new in ASHRAE 62-2004

• CO2 based Demand Controlled Ventilation is now
  specifically stated in the body of the
  standard
• Section 6.2.7 of the Ventilation Rate Procedure
• Dynamic Reset. The system may be designed to
• reset the design outdoor air intake flow (Vot)
  and/or space or
• zone airflow as operating conditions change.
  These conditions
• include but are not limited to
• 1. Variations in occupancy or ventilation airflow
  in one or
• more individual zones for which ventilation
  airflow requirements will
• be reset.
• Note Examples of measures for estimating such
  variations include
• occupancy scheduled by time-of-day, a direct
  count of occupants,
• or an estimate of occupancy or ventilation rate
  per person
• using occupancy sensors such as those based on
• indoor CO2 concentrations.

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Zone Ventilation Control
Whats new in ASHRAE 62-2004

• Calculations for Ventilation Requirements in the
  Breathing Zone now provide for
• Population density based upon Table 6-1 or the
  expected population
• Space ventilation requirements are added to
  people related ventilation requirements based
  upon values in Table 6-1
• Short term conditions (starting and stopping of
  mechanical equipment, highly variable
  occupancy, intermittent OA intake) are
  accounted for in equations 6-9a and 6-9b

This can reduce the design ventilation
requirements
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Zone Ventilation Control
Whats new in ASHRAE 62-2004

• Concerns over new standard
• 15 and 20 CFM per person in the previous
  standard was easily understood and implemented.
  Some say the new standard is more difficult to
  enforce.
• With the 2001 standard, code officials could
  calculate ventilation requirements for zones
  without the use of spreadsheets and engineering
  tools
• It took years for most municipalities to adopt
  the current standards. How quickly will they
  adopt the 2004 standard?
• In many cases, the 2004 Standard design
  ventilation rates are lower than 15 and 20 CFM
  per person, which can be seen as decreasing the
  standard of care in building design
• How is a CO2 setpoint derived for a Dynamic
  Reset control strategy?

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Zone Ventilation Control
Use DCV CO2 Setpoint Calculator
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Zone Ventilation Control
CO2 Setpoint Calculator determines optimum CO2
setpoint for all populations
Fixed Ventilation
DCV
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Zone Ventilation Control

• Ventilate to Actual vs. Assumed Occupancy
• Eliminate Wasteful Over-Ventilation
• Insure Adequate Ventilation
• Very Attractive ROI/Lower Operating Costs

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Benjamin Franklin on Ventilation (c. 1794)

• Who says history does not repeat itself?
• Like Ben, we have learned the error of our ways
  (closing with extreme care every crack and
  crevice).
• IAQ and Sick Building Syndrome have "persuaded"
  us on the "Virtues of Ventilation
• "Zone Ventilation Control" an old idea whos
  time has come!

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CO2-based Demand Controlled Ventilation (DCV)
Thank you! Ryan R. Hoger Commercial Controls
Mgr. Temperature Equipment Corp. 708.418.7901
ryan.hoger_at_tecmungo.com