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

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

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 5.5 -Air-To-Air Energy Recovery, Handbook Subcommittee Chairman, Past Chairman Technical Committee System Energy Utilization, Voting Member Technical Committee 7.8 -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. 2

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 3

4 ASHRAE Std 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 5

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 6

7 6.1.1 Ventilation Rate Procedure The following procedure for determining the minimum prescriptive ventilation rates can be used on any zone type Takes into consideration: Space type Number of Occupants Floor Area Typical contaminant sources and source strength 7

8 Ventilation Rate Procedure Breathing Zone (bz) Outdoor Airflow (OA) V bz = R p P z + R a A z where: R p = outdoor airflow rate required per person as determined from Table 6-1*. P z = zone population R a = outdoor airflow rate required per unit area as determined from Table 6-1*. A z = zone floor area *Table 6-1 from ASHRAE Standard

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

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

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

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

13 Office Example What is the prescriptive design for outdoor air (cfm) of a 1500 square foot office with 12 occupants? Eq6-1 : 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) = = 150 cfm 13

14 School Example What is the prescriptive design for outdoor air (cfm) of a 1100 square foot classroom with 30 students? Eq6-1 : V bz = R p P z + R a A z From Table 6-1: R p = 10 cfm/person R a = 0.12 cfm/ft 2 Design inputs from school classroom project for ventilation: P z = 30 people A z = 1100 square feet V bz = (10 x 30) + (.12 x 1100) = = 432 cfm 14

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? Eq6-1 : V bz = R p P z + R a A z From Table 6-1: R p = 10 cfm/person R a = 0.18 cfm/ft 2 Increase Production facility input data: P z = 20 people A z = 50,000 square feet of floor area V bz = (10 x 20) + (.18 x 50000) = ,000= 9,200 cfm Notice the Area outdoor air rate (Ra) increased for a manufacturing facility. 15

16 Ventilation Rate Procedure Zone Outdoor Airflow V oz = V bz /E z (E z ) The zone air distribution effectiveness shall be determined using ASHRAE Std , Table 6-2. (Partial Table) 16

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

18 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 18

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

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 20

21 Displacement Ventilation (DV) Uses natural convection to provide Buoyancyassisted 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 21

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) 22

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 23

24 Example of DCV Methods Fan Relays ERV EA SOA 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 24

25 DCV CO 2 concentrations in outdoor air generally range from 300 to 500 ppm ASHRAE std 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 2 Demand Controlled Ventilation properly engineered and installed will keep CO 2 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. 25

26 Fan Affinity Laws Assuming fan diameter and air density are constant Eq(1) : Eq(2) : Eq(3) : 26

27 Fan Affinity Laws Eq(1) : rpm rpm 27

28 Fan Affinity Laws Eq (2) : rpm rpm Pressure is squared rpm rpm 28

29 Fan Affinity Laws Eq (3) : rpm rpm Energy Expended is Cubed BHP BHP 29

30 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 =

31 Example Continued Rearranging Eq(2): RPM 2 = SP 2 /SP 1 x RPM 1 RPM 2 = 1.5/1 x 1000 = 1225 Eq(3): BHP 2 = BHP 1 x ( RPM 2 /RPM 1 ) 3 BHP 2 = 5x ( 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 31

32 Not All ERVs Are the Same ERV Features to Compare: Airflow Arrangement Thermal Effectiveness Pressure Drop Fan Efficiency Maintenance Sound Levels 32

33 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. 33

34 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. EER = BTUs Recovered Watts of Fan Power 34

Thermal Efficiency vs. Overall Efficiency 160 140 120 100 80 60 40 20 0 Effectiveness (%) Fan Power (W) EER (BTU/W) High Eff.

35 Thermal Efficiency vs. Overall Efficiency Effectiveness (%) Fan Power (W) EER (BTU/W) High Eff. ERV Typical ERV 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 35

36 Efficiency = Payback A short term savings in build cost is outweighed by sustainable gains over present consumption. 36

37 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 37

38 Tools to Meet ASHRAE Std and Improve IAQ While Increasing Energy Efficiency, ASHRAE Std 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 38

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DISPLACEMENT VENTILATION

DISPLACEMENT VENTILATION D3 OVERVIEW The fundamental approach to displacement ventilation utilizes the natural buoyancy forces created by the convective flows from heat sources in the space. As supply