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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• 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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• 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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• “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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• 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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• V bz
= R p
P z
+ R a
A z where:
• A z
• P z
= zone floor area
= zone population
• R p
= outdoor airflow rate required per person as determined from Table 6-1*.
• R a
= outdoor airflow rate required per unit area as determined from Table 6-1*.
*Table 6-1 from ASHRAE Standard 62.1-2010
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What is the prescriptive design for outdoor air (cfm) of a 1500 square foot office with 12 occupants?
Eq 6-1 : V bz
= R p
P z
+ R a
A z
Design inputs for office space:
Pz = 12 people
Az = 1,500 square feet of floor area
V bz
= (5x12) + (.06 x 1500) = 60 + 90 = 150 cfm
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What is the prescriptive design for outdoor air (cfm) of a 1100 square foot classroom with 30 students?
Eq 6-1 : V bz
= R p
P z
+ R a
A z
From Table 6-1:
R p
R a
= 10 cfm/person
= 0.12 cfm/ft 2
Design inputs from school classroom project for ventilation:
P z
A z
= 30 people
= 1100 square feet
V bz
= (10 x 30) + (.12 x 1100) = 300 + 132 = 432 cfm
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(Excludes Heavy Industrial and processes using chemicals)
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 : V bz
= R p
P z
+ R a
A z
From Table 6-1:
R p
R a
= 10 cfm/person
= 0.18 cfm/ft 2
Increase
Production facility input data:
P z
A z
= 20 people
= 50,000 square feet of floor area
V bz
= (10 x 20) + (.18 x 50000) = 200 + 9,000= 9,200 cfm
Notice the Area outdoor air rate (Ra) increased for a manufacturing facility.
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• V oz
= V bz
/E z
• (E z
) The zone air distribution effectiveness shall be determined using ASHRAE Std.
62.1-2010, Table 6-2.
(Partial Table)
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It’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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• 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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Diagram 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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• Uses natural convection to provide “Buoyancyassisted 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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• 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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• “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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Fan
Relays
ERV
CO2 Sensor comes on over
700 ppm and turns off under
600 ppm
People
ERV- Energy Recovery
Ventilator
EA- Exhaust Air
SOA- Supply Outside Air
EA
SOA
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• CO
2 ppm concentrations in outdoor air generally range from 300 to 500
• ASHRAE std. 62.1 2007 and 2010 recognize 700 ppm of CO
2 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 CO
1000 ppm
2
Demand Controlled Ventilation properly engineered and installed will keep CO
2 levels well below
• 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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• 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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• ERV Features to Compare:
– Airflow Arrangement
• Thermal Effectiveness
– Pressure Drop
– Fan Efficiency
– Maintenance
– Sound Levels
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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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• Assuming fan diameter and air density are constant
• Eq (1) : 𝐶𝐹𝑀
2
=
𝑅𝑃𝑀
2
𝑅𝑃𝑀
1 𝑥 𝐶𝐹𝑀
1
• Eq (2) : 𝑆𝑃
2
• Eq (3) : 𝐵𝐻𝑃
= (
𝑅𝑃𝑀
2
𝑅𝑃𝑀
1
) 2 𝑥 𝑆𝑃
1
2
= (
𝑅𝑃𝑀
2
𝑅𝑃𝑀
1
) 3 𝑥 𝐵𝐻𝑃
1
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• 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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• Rearranging Eq (2):
– RPM
2
– RPM
2
= SP
2
/SP
1 x RPM
1
= 1.5/1 x 1000 = 1225
Eq (3):
BHP
2
BHP
2
= BHP
1 x ( RPM
2
/RPM
1
) 3
= 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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• 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
EER =
BTUs Recovered
Watts of Fan Power
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160
140
120
100
80
60
40
20
0
High Eff. ERV
Typical ERV
Typical ERV has an
EER of around 10.
High efficiency ERV can be well above
120.
Effectiveness (%) Fan Power (W) EER (BTU/W)
Combining premium Efficiency fans with High efficiency ERVs and a low static pressure system can yield great energy savings
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• 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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