Demand control ventilation: maximize savings with practical approaches. Scott Hackel, Senior Energy Engineer May 12, 2015

Transcription

1 Demand control ventilation: maximize savings with practical approaches Scott Hackel, Senior Energy Engineer May 12, 2015

2 Acknowledgement Minnesota Conservation Applied Research and Development (CARD) Grant Program

3 Today s topics Quality DCV design Field study results (Re)commissioning Program recommendations

4 FIELD STUDY Background on DCV OA RA SA VAV Boxes Sensor AHU Central and/or Zone Control Source:

5 Quality DCV design

6 DCV DESIGN Be thorough Choose responsible party Mechanical engineer Controls contractor Be complete: Other (vendor, ) Specific sequence - CO 2 setpoint - Outside airflow lower limit CO 2 sensor location Airflow measurement req.

7 DCV DESIGN Sequence options 1. Direct OA flow control a. Zone CO 2 sensors RA SA Slight potential for imperfect IAQ OA BAS b. Return CO 2 sensor More potential for imperfect IAQ BAS

8 DCV DESIGN Sequence options Ventilation reset Zone outdoor airflow V oz = 1800 Zone primary airflow V pz = 5000 Zone OA fraction Z pz = V oz /V pz Average OA fraction X s = V ou /V ps = 1800/ System vent efficiency E v = 1 + X s max Z pz = System OA intake flow V ot = V ou /E v = 1800/ Figure and table used with permission from Trane, a business of Ingersoll Rand.

9 DCV DESIGN Sequence options Ventilation reset Zone outdoor airflow V oz = 1500 Zone primary airflow V pz = 5000 Zone OA fraction Z pz = V oz /V pz Average OA fraction X s = V ou /V ps = 1500/ System vent efficiency E v = 1 + X s max Z pz = System OA intake flow V ot = V ou /E v = 1500/ Figure and table used with permission from Trane, a business of Ingersoll Rand

10 DCV DESIGN Sequence options 2. Ventilation reset a. OA flow reset BAS b. Zone, then OA flow reset c. Zone, then OA flow reset, with occupancy sensors

11 OA Flow Rate (cfm) DCV DESIGN Elements of sequence Upper limit Freeze protection Mitigates failures Lower limit Save energy Maintain press. Design OA Separation between OA lower limit and Design OA drives energy savings 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00

12 DCV DESIGN Elements of sequence CO 2 setpoint Setpoint(s) per: C R = C OA E Z met R P +R a ( sf p ) Proportional or single setpoint

13 DCV DESIGN CO 2 sensor location Ideally in zone At breathing height (3-6 ft.) Not below a thermostat Common return Limited situations Show on drawings!

14 DCV DESIGN Airflow measurement Use AFMS (not damper position) Careful layout on dwgs: Consider manufacturer requirements If possible: second intake for economizer

15 DCV DESIGN Other considerations Use occupancy sensors! Occ. sensor = VAV savings, aside from DCV Consider OA diversity in sizing DCV: not just a Yes / No choice Control portion of zones Strategically use common return Use 2-way dampers Mix approaches

16 DCV DESIGN Code impacts For MN energy code: DCV has been required in densely occupied spaces New code does NOT change DCV or OA except buildings older than ~8 years The new code could lead to big improvement in compliance. Source:

17 Field study results

18 FIELD STUDY Characterization of approaches 96 systems around Minnesota:

19 FIELD STUDY Characterization of approaches Approaches (sequences): 1a. Direct OA flow control, return sens. 19% 1b. Direct OA flow control 26% 2a. Ventilation reset 15% 2b. Zone box, then ventilation reset 2c. Zone min. reset, w/ occ. sensors 19% 22%

20 FIELD STUDY Results Measured savings per design OA rate (cfm) Occ. + CO 2 sensing With ERV Median = $0.50/cfm High lower limit

21 FIELD STUDY Results We also scaled the results to a Duluth climate Savings per Design OA Flow therms/cfm kwh/cfm $/cfm Median Change from MSP results 27% -34% 18%

22 FIELD STUDY Results Savings are heavily weighted toward heating fuel

23 FIELD STUDY Recommissioning Deficiencies

24 FIELD STUDY Recommissioning results Half the systems saved more, an average of 54%

25 FIELD STUDY Economics

26 (Re)commissioning

27 Cx Virtual performance checks Conduct when hot, or very cold outside CO 2 (ppm) Review OA CO flow 2 (cfm) and OA flow trends: OA flow increases per sequence Find lower limit (also look for upper) CO 2 follows occupancy

28 OA Flow (cfm) Cx Virtual performance checks Determine control: 1) OA damper position vs. 2) OA flow measurement (if available) Check for rogue DCV zones Check CO 2 sensor reading at unoccupied 7000 Office Determine OA damper 6000 schedule OA not directly ctrld. 0 5:00 7:00 9:00 11:00 13:00 15:00 17:00 19:00 = 480 ppm Higher Ed PAC

29 Cx Virtual performance checks Determine control: 1) OA damper position vs. 2) OA flow measurement (if available) Check for rogue DCV zones Check CO 2 sensor reading at unoccupied Determine OA damper schedule Recognize that savings is from heating (gas) - Economizer negates cooling savings Verify economizer operation

30 Cx Spot checks Meet the operator on-site; discuss system operation Validate measured points: Temperatures: SA, MA, RA, OA (brief traverse) Valve positions (visual, temp) OA damper position (visual) Supply fan speed (VFD)

31 Cx Sensors CO 2 sensors Calibrate or replace Auto calibration valid?

32 Cx Sensors Recalculate setpoint per Standard 62.1 Check location of sensor Areas not being sensed? Leave CO 2 logger behind

33 Cx System performance tests Test the AHU 1. Modify CO 2 reading or setpoint a) False full occupancy, AND b) False no occupancy 2. Determine response 3. Await steady-state if possible Test individual VAVs; same method

34 Cx System performance tests: other Test OA damper Visually verify two positions Check for leakage Test occ. sensor impact on VAV box BAS

35 Cx Sequence Optimization Correct deficiencies found in tests Optimize: OA upper / lower limit, CO 2 setpoint, OA schedule

36 OA Flow Rate (cfm) Cx Hand over to operators Report any changes made Add any needed trending Complete handover missed at install Document the sequence Plan for future monitoring Design OA Separation between OA lower limit and Design OA drives energy savings 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00

37 Program recommendations

38 Cx Four opportunities Opportunity #1: New and retrofit DCV systems Incentives per OA flow (see report) Consider more detailed requirements Dependent on heating fuel Opportunity #2: Recommissioning Highly cost-effective for many programs - Recommissioning, retrocommissioning, HVAC tune-up

39 Cx Four opportunities Opportunity #3: Ventilation re-design Code changes Excessive safety factors Poor estimate of occupancy Problem AFMS or dampers OA damper schedule Opportunity #4: Trade allies Awareness Training SOURCE:

40 Cx For more information Sequences Basic: EDR 2007 Ventilation reset: Trane 2005 With occupancy sensors: Taylor Demand control ventilation for multiple zone VAV systems problem solved (from ASHRAE Annual Meeting, Seattle 2014; seminar available for a fee) Code requirements Code Notes 2012 IECC Demand Control Ventilation AFMS: Fisk 2009 CO 2 sensor performance: Shrestha 2009

41 Resources Download the study Stay tuned for a fact sheet and the full report: seventhwave.org/dcv Contact me shackel@seventhwave.org Learn about our work seventhwave.org/buildings