Implementing Demand Controlled Ventilation to Meet ASHRAE Standard 62.1 - 2010

By Klas C. Haglid, P.E., R.A., CEM

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Klas C. Haglid, P.E., R.A., CEM - Bio• ASHRAE Distinguished Service Award• 2011 ASHRAE Handbook, HVAC Applications and Management, Chapter 37,–

Author, Klas C. Haglid P.E. R.A.• ASHRAE Standard 189.1, Corresponding Member• GPC 32P - Sustainable, High Performance Operations & Maintenance, Voting

Member, Contributing, Co-Author • Technical Committee 5.5 - Air-To-Air Energy Recovery, Handbook Subcommittee

Chairman, Past Chairman• Technical Committee 7.6 - System Energy Utilization, Voting Member• Technical Committee 7.8 - Owning and Operating Costs of Commercial Buildings,

Past Chairman• ASHRAE Standard 84-1991R, Voting Member• Reviewed draft of ASHRAE Standard 84-1991R and provided engineering details for

efficiency calculations.

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Challenge

• Complying with ASHRAE Std. 62.1-2010 to improve IAQ while increasing energy efficiency ASHRAE Std. 90.1 can be accomplished with:– Displacement Ventilation– Demand Controlled Ventilation– Energy Recovery Ventilator– Variable Speed Drives

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ASHRAE Std. 62.1-2010

• Ventilation for Acceptable Indoor Air Quality– How to determine minimum prescriptive

ventilation rates– How to use Demand Side Ventilation to meet

ASHRAE Standard 62.1-2010

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Definitions

• “acceptable indoor air quality: air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.” –ASHRAE Standard 62.1-2010 pg. 3

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6.1.1 Ventilation Rate Procedure

• The following procedure for determining the minimum prescriptive ventilation rates can be used on any zone type.

• 6.1.1 Takes into consideration:– Space type– Number of Occupants– Floor Area– Typical contaminant sources and source strength

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Ventilation Rate Procedure - Breathing Zone Outdoor Airflow

• Vbz = RpPz + RaAz where:

• Az = zone floor area

• Pz = zone population

• Rp = outdoor airflow rate required per person as determined from Table 6-1*.

• Ra = outdoor airflow rate required per unit area as determined from Table 6-1*.

*Table 6-1 from ASHRAE Standard 62.1-20107

Office Example

Vbz = (5x12) + (.06 x 1500) = 60 + 90 = 150 cfm

What is the prescriptive design for outdoor air (cfm) of a 1500 square foot office with 12 occupants?

Eq 6-1 : Vbz = RpPz + RaAz

Design inputs for office space:Pz = 12 peopleAz = 1,500 square feet of floor area

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School Example

Vbz = (10 x 30) + (.12 x 1100) = 300 + 132 = 432 cfm

What is the prescriptive design for outdoor air (cfm) of a 1100 square foot classroom with 30 students?

Eq 6-1 : Vbz = RpPz + RaAz

From Table 6-1:Rp = 10 cfm/personRa = 0.12 cfm/ft2

Design inputs from school classroom project for ventilation: Pz = 30 peopleAz = 1100 square feet

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General Manufacturing Example(Excludes Heavy Industrial and processes using chemicals)

Vbz = (10 x 20) + (.18 x 50000) = 200 + 9,000= 9,200 cfm

What is the prescriptive design for outdoor air (cfm) of a 50,000 square foot coat hanger production facility with 20 machinists?

Eq 6-1 : Vbz = RpPz + RaAz

From Table 6-1:Rp = 10 cfm/personRa = 0.18 cfm/ft2

Production facility input data:Pz = 20 peopleAz = 50,000 square feet of floor area

Notice the Area outdoor air rate (Ra) increased for a manufacturing facility.

Increase

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Ventilation Rate Procedure – Zone Outdoor Airflow

• Voz = Vbz/Ez

• (Ez) The zone air distribution effectiveness shall be determined using ASHRAE Std. 62.1-2010, Table 6-2.

(Partial Table)

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Methods of Providing Outdoor Air to Zone

• Dilution Ventilation

• Displacement Ventilation

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Dilution VentilationIt’s important to design ventilation system to have maximum air distribution. This will help eliminate dead space and short circuiting of air flow

UV is not properly distributing air across classroom

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Dilution Ventilation• Typical in U.S. construction

• Outdoor air is brought into space and dilutes contaminant concentrations in the space.

• Adequate air mixing

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Displacement VentilationDiagram shows good air circulation providing fresh air on one end of room and exhaust pulling air out on the other end to maximize removing contaminant concentrations

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Displacement Ventilation (DV)• Uses natural convection to provide “Buoyancy-

assisted forced ventilation”

• Effectively removes contaminants from people and objects locally

• ASHRAE Std. 62.1-2010 Table 6-2 recognizes DV to be 1.2 times more effective than traditional dilution ventilation

• Some applications measured DV to be 2 to 2.5 more effective than traditional dilution ventilation

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Displacement Ventilation

• Using displacement ventilation and then measuring air quality of the space is an effective way to improve IAQ

• Often times, balancing airflow according to how effective the displacement ventilation system is can reduce required airflow by 50%– This saves energy and reduces latent loads– Can be achieved with Variable Speed Drives (VSD)

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Demand Controlled Ventilation (DCV)

• “any means by which the breathing zone outdoor airflow (Vbz) can be varied to the occupied space or spaces based on the actual or estimated number of occupants and/or ventilation requirements of the occupied zone.” – ASHRAE Std. 62.1-2010 pg. 4

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Example of DCV Methods

ERV

CO2 Sensor comes on over 700 ppm and turns off under 600 ppm

SOA

EA

People

Fan Relays

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ERV- Energy RecoveryVentilator

EA- Exhaust Air

SOA- Supply Outside Air

DCV• CO2 concentrations in outdoor air generally range from 300 to 500 ppm

• ASHRAE std. 62.1 2007 and 2010 recognize 700 ppm of CO2 above outdoor ambient levels or 1000 to 1200 ppm to be acceptable air quality for an indoor space. Reference page 37 of Appendix C

• Displacement Ventilation with CO2 Demand Controlled Ventilation properly engineered and installed will keep CO2 levels well below 1000 ppm

• DCV can reduce runtime from 168 hours per week to 30 hours per week for a classroom. That is an 82% reduction in runtime.

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Summary of Ventilation Rates• Determine prescriptive design ventilation rate for zone

by using Ventilation Rate Procedure

• Determine Method of Ventilation– Dilution– Displacement – up to 2.5 times more effective

• Choose appropriate method to control the ventilation system and monitor the contaminants of concern– CO2 sensor– VSD – Variable Speed Drive to reduce fan speed to balance

and optimize ERV efficiency

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Not All ERVs Are the Same• ERV Features to Compare:

– Airflow Arrangement• Thermal Effectiveness

– Pressure Drop– Fan Efficiency– Maintenance– Sound Levels

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Heat Exchanger Airflow Arrangement

ASHRAE states:• Counter-flow heat exchangers are theoretically capable of achieving 100% Sensible Effectiveness* • Parallel Flow heat exchangers: 50% (Max)

• Cross-flow heat exchangers and Enthalpy Wheels: 50-75% (Max)

*Note: Source: 2012 ASHRAE Handbook – HVAC Systems and Equipment, Chapter 26: Air-to-Air Energy Recovery Equipment.

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Fan Affinity Laws

• Assuming fan diameter and air density are constant

• Eq (1) : • Eq (2) : • Eq (3) :

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Example

• What is the percent difference in BHP required to run a ventilation system if alternative 2 has a 50% increase in static pressure from alternative 1?

• Altenative 1 Conditions:– CFM = 8,000– SP = 1” in wg– BHP = 5– RPM = 1000

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Example Continued• Rearranging Eq (2):

– RPM2 = x RPM1

– RPM2 = x 1000 = 1225

Eq (3):BHP2 = BHP1 x ( RPM2/RPM1)3

BHP2 = 5 x ( 1225/1000)3 = 9.2 BHP

9.2-5/5 = 84% Increase

A 50% increase in static pressure results in an 84% increase in power consumption

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High Efficiency Fans

• Typical fan efficiency can range from 5 to 10 W/cfm

• A high efficiency fan can be expected to be approximately 0.2 W/cfm

• The EER of an ERV is formulated by the BTUs recovered divided by the watts of power consumed from the fan energy

BTUs RecoveredWatts of Fan PowerEER =

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Efficiency is Essential

Effectiveness (%) Fan Power (W) EER (BTU/W)0

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40

60

80

100

120

140

160

High Eff. ERVTypical ERV

Combining premium Efficiency fans with High efficiency ERVs and a low static pressure system can yield great energy savings

Typical ERV has an EER of around 10. High efficiency ERV can be well above 120.

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Maintenance Costs are Essential

• There’s more to a product than its initial costs and efficiency – Maintenance costs can make or break your bottom line

• Look for :• Corrosion resistant equipment• Minimal moving parts• Low static pressure

• Use appropriate filter type for equipment

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Tools to Meet ASHRAE Std. 62.1 and Improve IAQ While Increasing Energy Efficiency, ASHRAE Std. 90.1

• Displacement Ventilation• Demand Controlled Ventilation

– CO2 controls or other contaminant monitoring sensors

• ERV– Counter flow heat exchanger– Low Pressure Drops– High efficiency fans

• Variable Speed Drives– Air balancing– Better control

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