1. By Klas C. Haglid, P.E., R.A., CEM
Implementing Demand Controlled Ventilation to Meet ASHRAE Standard
By Klas C. Haglid, P.E., R.A., CEM

2. 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 Air-To-Air Energy Recovery, Handbook Subcommittee Chairman, Past Chairman
Technical Committee System Energy Utilization, Voting Member
Technical Committee Owning and Operating Costs of Commercial Buildings, Past Chairman
ASHRAE Standard R, Voting Member
Reviewed draft of ASHRAE Standard R and provided engineering details for efficiency calculations.

3. Objectives
Complying with ASHRAE Std to improve IAQ while increasing energy efficiency ASHRAE Std can be accomplished with:
Displacement Ventilation
Demand Controlled Ventilation
Energy Recovery Ventilators
Variable Speed Drives

4. 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

5. 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 pg. 3

6. Definitions
Demand Control Ventilation (DCV): any means by which the breathing zone (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 Standard pg. 4

7. 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

8. Ventilation Rate Procedure Breathing Zone (bz) Outdoor Airflow (OA)
Vbz = RpPz + RaAz where:
Rp = outdoor airflow rate required per person as determined from Table 6-1*.
Pz = zone population
Ra = outdoor airflow rate required per unit area as determined from Table 6-1*.
Az = zone floor area
*Table 6-1 from ASHRAE Standard

9. Two Parts to the Formula
Type and size of space?
How many people?

10. First Part of the Equation
Rate Per Person Rp
Zone Pop Pz
cfm for people
ASHRAE Std

11. Second Part Zone Rate Per Person cfm for People Pop Rp Pz Zone
Rate Per Area Ra
Zone
Area Az
cfm for Area

12. Vbz cfm for People cfm for Area Combined Breathing Zone
Outdoor Airflow

13. Office Example
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 people
Az = 1,500 square feet of floor area
Vbz = (5x12) + (.06 x 1500) = = 150 cfm

14. School Example
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/person
Ra = 0.12 cfm/ft2
Design inputs from school classroom project for ventilation:
Pz = 30 people
Az = 1100 square feet
Vbz = (10 x 30) + (.12 x 1100) = = 432 cfm

15. General Manufacturing Example
(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 : Vbz = RpPz + RaAz
From Table 6-1:
Rp = 10 cfm/person
Ra = 0.18 cfm/ft2
Production facility input data:
Pz = 20 people
Az = 50,000 square feet of floor area
Increase
Vbz = (10 x 20) + (.18 x 50000) = ,000= 9,200 cfm
Notice the Area outdoor air rate (Ra) increased for a manufacturing facility.

16. Ventilation Rate Procedure – Zone Outdoor Airflow
Voz = Vbz/Ez
(Ez) The zone air distribution effectiveness shall be determined using ASHRAE Std , Table 6-2.
(Partial Table)

17. Methods of Providing Outdoor Air to Zone
Dilution Ventilation
Displacement Ventilation

18. Poor distribution of air across classroom breathing zone
Dilution Ventilation
It’s important to design ventilation system to have maximum air distribution. This will help eliminate dead space and short circuiting of air flow
Poor distribution of air across classroom breathing zone

19. Dilution Ventilation Typical in U.S. construction
Outdoor air is brought into space and dilutes contaminant concentrations in the space.
Adequate air mixing

20. Air Mass Exchange
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 by displacing room temperature air across a Breathing Zone

21. Displacement Ventilation (DV)
Uses natural convection to provide “Buoyancy-assisted forced ventilation”
Effectively removes contaminants from people and objects locally
ASHRAE Std 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

22. 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)

23. 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 pg. 4

24. Example of DCV Methods EA ERV SOA Fan Relays
CO2 Sensor comes on over 700 ppm and turns off under 600 ppm
ERV- Energy Recovery
Ventilator
EA- Exhaust Air
SOA- Supply Outside Air
People

25. DCV
CO2 concentrations in outdoor air generally range from 300 to 500 ppm
ASHRAE std 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.

26. 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

27. Fan Affinity Laws Assuming fan diameter and air density are constant
Eq (1) : 𝐶𝐹𝑀 2 = 𝑅𝑃𝑀 2 𝑅𝑃𝑀 1 𝑥 𝐶𝐹𝑀 1
Eq (2) : 𝑆𝑃 2 =( 𝑅𝑃𝑀 2 𝑅𝑃𝑀 1 ) 2 𝑥 𝑆𝑃 1
Eq (3) : 𝐵𝐻𝑃 2 =( 𝑅𝑃𝑀 2 𝑅𝑃𝑀 1 ) 3 𝑥 𝐵𝐻𝑃 1

28. Fan Affinity Laws Eq (1) : 𝐶𝐹𝑀 2 = 𝑅𝑃𝑀 2 𝑅𝑃𝑀 1 𝑥 𝐶𝐹𝑀 1 100 cfm 200 cfm@
100 rpm
200 cfm @
200 rpm

29. Fan Affinity Laws Eq (2) : 𝑆𝑃 2 =( 𝑅𝑃𝑀 2 𝑅𝑃𝑀 1 ) 2 𝑥 𝑆𝑃 1 100 cfm @
100 rpm
200 cfm @
200 rpm
Pressure is squared
0.3 WC @
100 rpm
0.9 WC @
200 rpm

30. Fan Affinity Laws Eq (3) : 𝐵𝐻𝑃 2 =( 𝑅𝑃𝑀 2 𝑅𝑃𝑀 1 ) 3 𝑥 𝐵𝐻𝑃 1 0.3” WC @
100 rpm
0.9” WC @
200 rpm
Energy Expended
is Cubed
0.3” WC @
1 BHP
0.9” WC @
8 BHP

31. 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?
Alternative 1 Conditions:
CFM = 8,000
SP = 1” in wg
BHP = 5
RPM = 1000

32. Example Continued Rearranging Eq (2): RPM2 = SP2/SP1 x RPM1
RPM2 = /1 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

33. Not All ERVs Are the Same
ERV Features to Compare:
Airflow Arrangement
Thermal Effectiveness
Pressure Drop
Fan Efficiency
Maintenance
Sound Levels
Cross Contamination

34. 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.

35. 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’s performance is formulated by the BTUs recovered divided by the watts of power consumed from the fan energy.
BTUs Recovered
Watts of Fan Power
EER =

36. Thermal Efficiency vs. Overall Efficiency
Typical ERV has an EER of around 11. High efficiency ERV can be well above 120.
Combining premium Efficiency fans with High efficiency ERVs and a low static pressure system can yield great energy savings

37. Efficiency = Payback
A short term savings in build cost is outweighed by sustainable gains over present consumption .

38. Maintenance Costs are Essential
There’s more to a product than its initial costs and efficiency – Maintenance and efficiency equal long term and continuous ROI
Corrosion resistant equipment
Minimal moving parts
Low static pressure
Appropriate filters and size
Efficient fans
Location/Operation

39. Displacement Ventilation Demand Controlled Ventilation ERV
Tools to Meet ASHRAE Std 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

44. Questions Acceptable IAQ indoor air quality is defined as:
Air in which there are no known contaminants at harmful concentrations.
Conditions determined ASHRAE 62.1
Air with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.”
All of the Above.

45. Questions
Compliance with ASHRAE Standard 62.1 and an Increase in energy efficiency ASHRAE Std.90.1 can be obtained with:
Displacement Ventilation
Variable Speed Drives
Demand Control Ventilation
All of the Above.

46. Questions
The procedure for determining the minimum prescriptive ventilation rates that can be used in any zone type takes into consideration which of the following?
The number of Occupants in the space
Air Class defined by ASHRAE
Linear Feet of Wall space
Both A and B

47. Questions Displacement Ventilation can best be described as:
Outdoor air that is brought into a space in lieu of contaminants
An Improvement of Air Classification
The removal of contaminants with limited air mixing
None of the Above

48. Questions Which calculation best represents the efficiency of an ERV?
Cfm exhaust versus cfm Intake
Apparent Thermal Efficiency
Fan Curve and Efficiency
None of the Above