Gordon Sharp Handout
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This document discusses new solutions for controlling outside air to reduce energy usage and carbon footprint while maintaining indoor air quality. It describes multiplexed sensing technology that routes air samples from multiple locations to central sensors, allowing accurate differential measurement and dynamic control of ventilation. Case studies show this approach improved energy efficiency in buildings while keeping indoor pollutant levels low.
Gordon Sharp Handout
- 1. New Outside Air Control Solutions to Cut Your Carbon Footprint & Save Energy Gordon P. Sharp Chairman Aircuity, Inc Case Study Example: Bank of America Tower, NYC
- 2. Session Overview Review of issues concerning outside air control Demand Control Ventilation Multiplexed sensing Differential enthalpy control Lab applications Case studies
- 3. IEQ – Energy Dynamics of Green Buildings Contaminant sources: Human pollutants Non Human Pollutants Outside Air Ventilation: Source dilution Control Approaches: Furnishings selection Green cleaning, etc. Filtration Control Approaches: Demand Control Ventilation (DCV) Economizer control What do current standards and research say about optimum outside air ventilation performance? IEQ & Energy Efficiency Performance
- 4. What do the Guidelines Say About Outside Air? ASHRAE 62.1 – 2004 & 2007 rates versus 2001 Uses area & person component: ~ 5 cfm/person & ~.06 cfm/sq ft Generally lowered O.A rates, sometimes significantly Office rooms changed from 20 to a range of ~14 to 17 cfm/person Conference rooms & classrooms: 15/20 to ~ 5 to 7 cfm/person. From Trane “Co2-Based Demand Controlled Ventilation with ASHRAE Standard 62.1-2004” Engineers Newsletter 34-5
- 5. What do the Guidelines Say About Outside Air? Why did 62.1 reduce O.A. so much for conf. & educ? ASHRAE 62.1 changed: legal code vs. just a guideline Ventilation rates went from “Acceptable” to “Minimum” New criteria used for “minimum” O.A. rates 80% satisfaction of “adapted occupants” vs. “unadapted” (visitors) ASHRAE 62.1 for dense spaces can be problematic Lower ventilation levels will create sensed odors Brief sensed odors: a perception of poor IAQ Complaints and even increased O.A. over prior rates
- 6. What Does the Recent O.A. Research Say? William Fisk, LBNL 2004 ASHRAE Journal article Surveyed results from many studies: 21 CO2 ventilation studies: over 30,000 subjects, over 400 bldgs Consensus of studies indicated that: Occupant health & perceived IAQ worsened w/ <20 cfm /person Unclear whether specifying outside air/person or per area better Most studies were based on cfm/person
- 7. So What Outside Airflow Should be Used? For certain spaces 62.1 min airflows can be too low In other conditions 62.1 allows airflow to be reduced In reality, there is no one best ventilation level! … .The “best” level varies over time, so what can be done? Facilities Env. Health & Safety ASHRAE 62.1-2004 Recent Research
- 8. What about Demand Control Ventilation? Measures the rise of CO2 in the building Measures amount of ventilation CO2 is a good proxy for human pollutants Reduces ventilation when occupancy drops Can save substantial energy when loading varies Even optimizes the ventilation for constant loading Most buildings are designed with more air than normally needed Is DCV a good approach then for saving energy while also improving and validating IEQ?
- 9. Unfortunately, Experience w/ DCV is often poor: DCV CO2 sensors have had problems Sensor drift and loss of accuracy Lack of periodic sensor calibration ASHRAE 62.1 standard: Should check twice annually Accuracy issues w/ differential sensing Indoor to outside air differential measurements Demand Control Ventilation when used, is often disabled!
- 10. LBNL* CO 2 Field Sensor Study Paper Results 10% Dead 81% Read High (avg. 39%!) 9% Low (½ by 50%) No trends observed with 44 sensors vs site, mfg, or age! * Lawrence Berkeley National Laboratory Paper, recently presented at ASHRAE 2009 Winter Conference
- 11. Typical DCV Performance Based on LBNL Outside Air CFM Error % of Required 64% 27% 7%
- 12. CO2 Sensor Study Results from Iowa Energy Center
- 13. Traditional Sensors Not Up to DCV Task Differential sensing needed due to outside air changes Using two sensors doubles error on smaller diff. signal ± 75PPM + ±75PPM = ±150PPM ASHRAE says: Ventilation control needs differential CO 2 measurement Return Air Outside Air Even w/calibrated sensors, avg outside air can be 67% high! Result: Significant energy penalty 400 600 500
- 14. Unfortunately Conventional DCV is Also Flawed DCV only solves half of the problem DCV varies O.A. based only on number of people in bldg DCV does not react to non-human pollutants Odors, particles, CO, and formaldehyde As a result: DCV can create complaints Nonhuman pollutants can rise when DCV reduces O.A. New bldg, recent renovation, cleaning materials, vacuuming Typical response: Disable DCV & increase O.A. RESULT: Increased Energy Costs
- 15. Solution: Multi-parameter DCV or “Healthy” DCV The goal is dilution of all pollutants in building: Human based pollutants (odors, virus, bacteria, etc.) Non human pollutants (TVOC’s, particles, CO, etc.) Control O.A. based on multiple parameters: Use CO2 as a proxy for human based pollutants EPA & LEED specify levels for non-human pollutants TVOC’s, particles, & carbon monoxide Sensing humidity also helpful to prevent mold Vary outside air rates based on actual air cleanliness!
- 16. ASHRAE Support of Sensing More Than CO2: ASHRAE Emerging Technologies Article on DCV, 7/2003: “ Although CO2 levels tend to correlate well with human occupancy and human-generated pollutants, they do not reflect the buildup of pollutants not related to occupancy…, “ Currently, most buildings do not use DCV because of concerns about nonhuman indoor pollutants mentioned previously.” ASHRAE’s Standard 62.1 User Manual: The contaminants in indoor spaces that ventilation is intended to dilute are generated primarily by two types of sources: Occupants (bioeffluents) and their activities … Off-gassing from building materials and furnishings. “ There is little doubt or controversy about the existence of these two sources...”
- 17. Benefits of Varying Outside Air based on IEQ Doesn’t dilute clean air w/ clean air Provides better IEQ Increases fresh air when needed Maximizes energy savings Operates at lowest possible O.A. Effectively validates bldg IEQ Measures multiple air parameters (not just CO2) Sounds great, but can it be done cost effectively?
- 18. Conventional Sensing with Many Sensors Disadvantages High first cost High maintenance costs Lack of accuracy, particularly differential measurements
- 19. A New Approach: Multiplexed Sensing Routes multiplexed air samples to central sensors Multiplex one set of sensors over 20 locations Environmental data sent to BMS for control & to web to view Room 101 Room 102 AHU 2 -1 Sensor Suite BMS Web based data access
- 20. Multiplexed Sensing Operation Room 101 Room 102 Room 103 Outdoor Air Probe Web Based User Interface Sensor Suite Air Data Router Room Sensor Vacuum Pump Connectivity Server
- 21. Benefits of Multiplexed Sensing Concept Better total first cost Sensor cost spread over many locations Single point digital integration w/ BMS Lower operating costs Drastically reduced calibration cost One high quality sensor vs. many low cost units Sensors more accessible, can be swapped out Improved Accuracy Provides “true” differential sensing Sensor errors cancel since one sensor used Reduces impact of RH & barometric pressure Cost effective, accurate bldg data for ventilation control
- 22. Economizers – “Free Cooling” w/ More Outside Air Control Method Dry Bulb Temperature Outside air sensor versus fixed setpoint in design ASHRAE Std 90-2004 has max values from 65-75 Differential Enthalpy Control Same outside air and return air sensor for °F Relative Humidity sensor for outside and return air Need High Quality or Expect Failure
- 23. Diff. Enthalpy Economizer Savings Potential Diff. enthalpy is best, yet is rarely used… Why?? Humidity sensors typically fail in outdoor conditions If economizer fails, energy penalty is high (100% OA) Economizer Savings Study, ASHRAE No. 3200, 1989, P.C. Wacker, P.E. City No Economizer 70º Dry-bulb Single Enthalpy Differential Enthalpy Madison, WI 0% 11% 11% 27% Lake Charles, LA 0% 3% 3% 9% New York, NY 0% 12% 11% 33% Los Angeles, CA 0% 51% 33% 76% Seattle, WA 0% 25% 35% 51% Albuquerque, NM 0% 7% 14% 22%
- 24. ASHRAE Humidity Control Design Guide “ For outdoor use, use a rugged sensor and expect to calibrate frequently” “ Sensors in this location are notoriously inaccurate, because they are easily contaminated by pollutants, particles, condensation, and even frost” “ In general, do not expect these signals will always be reporting within the manufacturers tolerance”
- 25. Multiplexed Dewpoint Sensing for Economizers Use multiplexed sensing for AHU Return & OA sensor Solves problems of high drift from outdoor temp., particles, etc. Sensors are inside and can be protected by HEPA filters Allows economic use of high quality dewpoint/enthalpy sensor Eliminates the high error sensitivity of differential measurement If traditional sensor error is ± 5%, total error of two sensors is ± 10% For a 10% RH difference, measurement error is ± 100% Multiplexed sensing cancels errors by using 1 sensor for both readings
- 26. Case Study – LEED Project One Bryant Place – LEED Platinum Also known as Bank Of America Tower World’s largest & most green skyscraper Goal is platinum certification 2 nd tallest building in NYC – 954’ $1.0 B, 2.1M s.f. building Cost effective IEQ monitoring & DCV Sampling at many points. on each floor plate Total of over 800 locations monitored
- 27. Case Study – LEED & DCV Projects ASHRAE Headquarters Renewal – LEED CI Gold Goal Humidity monitoring, DCV control Sensing for AHU & Enthalpy wheel control Helping ASHRAE realize its living laboratory goal TVOC, particles, CO2, Dewpoint , T sensing throughout
- 28. Case Study: Large Energy Retrofit UBS Financial – Stamford, Connecticut World’s largest securities trading floor (100K sq. ft.) Rapid payback for DCV retrofit funded 95% by CL&P Multiplexed sensing of 6 large AHU’s DCV control: 1.6 Yr Payback Also installed in a nearby office tower renovation
- 29. Multi-parameter DCV Case Study: Arena New Jersey Devils – Prudential Arena, Newark, NJ 100,000 sq. ft. sports arena; $310M budget Multi-parameter DCV control: CO2, CO, particles, & TVOC’s Dewpoint sensing & control for “Best Ice in the NHL”
- 30. CO2 ~ 3 days Concert NHL Hockey Indoor Soccer
- 31. The Controversy Around Air Change Rates Minimum air changes still fixed at 6-12 / 10-20 ACH Far majority of time lab air is “clean” However, there many times when more air is better Dilute vapors from a spill when lab is occupied or unocc. Dilute vapors or particles caused by poor practices Working outside the hood, improper storage No localized exhaust for instruments Improper bedding changing The “human” factor There is no one ventilation rate that is right all the time!
- 32. Impact of Higher Air Changes Test Case– Teaching Lab Acetone at 4 ACH CFD courtesy of Glenn Schuyler’s ASHRAE Presentation Relative contaminant level: 27 PPM (black)
- 33. Impact of Higher Air Changes Test Case– Teaching Lab Acetone at 8 ACH CFD courtesy of Glenn Schuyler’s ASHRAE Presentation Relative contaminant level: 2.5 PPM (light blue): Factor of 10 improvement!
- 34. Lab Application: Dynamic Control of Lab ACH Lab Multi-parameter DCV: Dynamic control of min. ACH Now all three factors affecting lab airflow can be varied Significantly cuts energy & first cost, while enhancing safety Hoods Thermal Load Ventilation rate (cfm) 2- 4 ACH 6-8 ACH* 6-12 ACH 10-20 ACH* VAV VAV Constant ACH / Dilution Requirement Significant energy waste *vivariums VAV
- 35. Dynamic ACH Control Saves Energy Safely There is no need to dilute clean air w/ clean air 99% of the time the air will be clean, no need to dilute Set min dilution levels per OSHA or as desired For high concern: 4 ACH occupied & 2 ACH unocc. OSHA guidelines have a minimum at 4 ACH (range of 4 to 12) For normal to less severe applications, use 2 ACH as min ASHRAE fresh air min for science lab is .18 cfm/sq ft or 1.2 ACH Set max dilution for 12 to 16 ACH for safest purge System responds to great majority of contaminants with high ACH’s vs. a lower fixed ACH rate
- 36. 2008 Lab IEQ Performance Monitoring Study Largest known study done to date Supersedes smaller 2007 study of 7 sites 18 different sites selected 6 East, 7 Central, 3 West, 2 Canada Over 300 different lab areas Largest site: 67 areas, Smallest site: 2 areas Research: Life sciences, bio, physical chem, etc Almost all low density labs w/ dynamic control 3 animal facility sites
- 37. Lab IEQ Performance Monitoring Study Covers over 1,500,000 lab operating hours Data taken over 2 year period up to Jan. 2009 Amount of data varies by site Approx. 20 million sensor values recorded Lab TVOC’s: Measured with PID type TVOC sensor Values shown are differential measurements vs. supply air Particles: laser based particle counter - .3 to 2.5 u. Values shown are differential measurements vs. supply air CO2: Measured with lab grade NDIR sensor Dewpoint: Lab grade infrared spectrometer
- 38. Average of TVOC Data for All Sites: 1.5M Hrs Using LEED flush-out threshold of 0.18 PPM: Low ACH can be used 99.4% of time Represents 1 hour or ~ 4 events week
- 39. Average TVOC Levels at 18 Different Sites At ~0.2PPM, site value range: ~ .05% to 2.25% Average for all sites Significant savings at all sites
- 40. Average Differential Particle Levels For All Sites Using threshold of 1.0M PCF: Lowest airflow 99.6% On average each lab has 2 particle events per week
- 41. Avg. Differential Particle Levels at 18 Sites At 1M PCF, Site value range: ~ 0% to 1.4% Average Level Data shows significant savings at all sites
- 42. Case Study: Arizona State University Pilot Project for ASU Biodesign Institute Large life sciences retrofit at Biodesign Bldg B One Sensor Suite, 11 lab rooms monitored LEED NC Platinum, R&D 2006 Lab of the Year
- 43. Biodesign B Aircuity Pilot Project
- 44. TVOC Performance Before & With Dynamic ACH Dynamic ACH control saved energy & reduced lab TVOCs!
- 45. Current Status of ASU Project Project has moved forward into full building implementation for both Biodesign Bldgs A &B ASU has estimated savings in excess of $1 million a year 330K gross sq ft total for both bldgs Savings of $3 per gross sq. ft/year Savings of ~$5 per net sq ft/year Savings equivalent to: 4.5 MW solar array ~$31M cost ~ 450,000 sq ft of installed panels
- 46. Multiplexed Facility Sensing Summary Optimizes ventilation: Increased savings & IEQ A building wide sensing infrastructure For new & existing facilities Cost effective LEED points Applicable to many building types Office buildings Classroom & Educational Lab & Vivarium Healthcare Public Assembly & Arenas Data Centers