1 Outside Air Nonresidential HVAC Stakeholder Meeting #2 California Statewide Utility Codes and Standards Program Jim Meacham, CTG Energetics
Agenda 2 In Situ Testing Results Reduced Ventilation after Economizing Study Results Recommended changes to Nonresidential Compliance Manual and Acceptance Test Forms Future Code Change
In Situ Testing Results 3 Part 1: Determine best practice for field measurements of outside air flow Part 2: Test existing systems with DCV to compare with Title 24 ventilation rates
Best Practice Method - Approach 4 Conduct research with stakeholders, literature, and industry providers to determine methods to evaluate in the field. Temperature Split Velocity Matrix Traverse Hot Wire Anemometer Traverse Flow Hood Traverse
Best Practice Method Test Matrix 5 Test configurations Exterior Intake Shrouding With/without Measurement Location Interior/Exterior Fan Mode Minimum/Maximum Methodology Velocity Matrix Hot Wire Anemometer Flow Hood Temp. Split Measurement Location Interior Exterior Exterior Interior Exterior Exterior Exterior N/A Intake Shrouded? No Yes No No Yes No No No Fan Mode Number of Tests Minimum 3 3 3 3 3 3 3 3 Maximum 3 3 3 3 3 3 3 3
Best Practice Method - Results 6 Notes: 1) Coefficient of variation = Standard deviation / average 2) Measurement from installed, flow sensing dampers used as reference
Best Practice Method - Conclusions 7 Hot Wire and Velocity Matrix measurements are best performers Velocity matrix not appropriate for flows nominally less than 250 fpm Use hot wire for flows below 250 fpm No significant difference between exterior and interior msmts given above conditions
Best Practice Method - Conclusions 8 Rule out flow hood due to added pressure drop Rule out temperature split due to reliance on large T and error stacking of supply flow measurement
In Situ Testing Systems Description 9 System Type No. Systems No. Total Tested Tests Multi Zone 13 26 Built Up Multi Zone 6 12 OA Control: Fixed Min Damper 5 10 OA Control: Dynamic 1 2 Packaged Multi Zone 7 14 OA Control: Fixed Min Damper 6 12 OA Control: Dynamic 1 2 Single Zone 4 7 OA Control: Fixed Min Damper 4 7 Total 17 33 All systems VAV, test @ both min & max fan mode
In Situ Testing - Results 10 In general, systems are significantly over-ventilating System Type Average % Relative 1 Deviation from Title 24 OA Requirement Average % Absolute 2 Deviation from Title 24 OA Requirement Multi Zone 50% 60% Built Up Multi Zone 84% 89% OA Control: Dynamic 11% 40% OA Control: Fixed Min Damper 98% 99% Packaged Multi Zone 21% 36% OA Control: Dynamic 1% 23% OA Control: Fixed Min Damper 25% 38% Single Zone 108% 138% OA Control: Fixed Min Damper 108% 138% Total 62% 77% 1. Relative deviation includes both under and over performance values from individual tests 2. Absolute deviation considers only the magnitude of the deviation, regardless of whether it is over or under ventilation
In Situ Testing - Results 11 Systems are compliant if measured air flow is within 10% of the Title 24 requirement (per acceptance testing requirements of MECH-2A )
In Situ Testing Dynamic Controls 12 Dynamic controls are effective Only two of 17 VAV units (12%) had dynamic controls
In Situ Testing Dynamic Controls 13 Fixed damper control causes significant over ventilation in max. vent. mode
Reduced Ventilation After Economizing 14 Study the potential for reducing vent rates after economizing Studied potential for energy savings based on CO2 generation rates in worst case climate zones Analyzed on worst case days high ambient temp ramp rates after moderate night temps
15 T-24 Minimum Typical Economizing Range Outside CO 2 concentration Based on office occupancy setting, outdoor CO2 concentration 400ppm, activity level =1.2 Met In normal operating conditions, the space will maintain at a certain ppm above outdoor levels based on the amount of outside air being brought in During Economizing, outside air volumes/person increase to take advantage of free cooling with the side effect of bringing down CO 2 concentration
16 115 Minutes 80 Minutes 44 Minutes 8 Minutes The blue line represents a normal situation where the space will gradually reach its equilibrium offset from outdoor CO2 concentration All other lines represent CO2 concentration given varying starting space concentration. The ventilation system will need to turn on when the space system reaches its equilibrium concentration. A starting space concentration of 400 ppm is likely unobtainable, but represents the theoretical best case scenario
17 115 Minutes 57Minutes 16 Minutes 11 Minutes Based on outdoor CO 2 concentration 400ppm, activity level =1.2 Met, staring CO 2 concentration of 400ppm In higher occupancy spaces, the equilibrium CO 2 concentration does not change, but the time it takes to reach equilibrium decreases with an increase in occupancy
Potential Energy Savings 18 Temp Temp Potential Energy Savings Economizer Shut at 11:08 Hour Ventilation system on to maintain CO 2 levels Economizer Shut at 7:51 Ventilation system on to maintain CO 2 levels Best case climate zone have fast temperature rise after economizing More typical climate zones and days have limited energy savings potential due to mild temperatures after economizing mode is exited Hour
19 On best case day (May 7 th ) in best case climate zone (CZ10), with best case load (office space, starting CO2 ppm = outdoor ppm), a savings of 0.5 btuh/sf is achieved If this savings is applied to every day that the economizer cuttoff is reached, annual energy savings are less than 0.25% for all climate zones.
Recommended Code Changes 20 Eliminate Field Calibration Option for CO2 sensors Add Field Verification of CO2 Sensors to Acceptance Testing Confirm Dynamic Control of Outside Air Confirm Pre-occupancy purge for all system types
Recommended Code Changes 21 Verify proper location of OA ducts in plenum systems Add guidance for measuring OA flow Correct CO2 sensor mounting height in Compliance Manual
Eliminate CO2 Sensor Field Calibration 22 Due to inaccuracy of field calibrations, only allow factory calibrations CO2 sensors are critical control inputs to any DCV system and must be calibrated in order to prevent under or over ventilation. Changes required to MECH-6A and Nonresidential Compliance Manual.
Eliminate CO2 Sensor Field Calibration 23 Changes to MECH-6A, Construction Inspection Block Existing Block Modify language of Item 3 under the Construction Inspection section to read: Documentation of all carbon dioxide control sensor includes factory-calibration certificate (calibration certificate must be attached) Remove field calibration option.
Eliminate CO2 Sensor Field Calibration 24 Changes to Nonresidential Compliance Manual, Section 10.6.13, Construction Inspection CO2 sensor is either factory calibrated or field calibrated. A calibration certificate from the manufacturer will satisfy this requirement. Field calibration of CO2 sensors does not comply with Title 24. In order to perform a field calibration check, follow the calibration procedures provided by the manufacturer. Some sensor manufacturers may require using equipment-specific calibration kits (kits may include trace gas samples and other hand-held devices) whereas others may be calibrated simply by using a pre-calibrated hand-held CO2 measuring device and making proper adjustments through the sensor or ventilation controller.
Add Field Verification of CO2 Sensors 25 Require field verification of factory calibrated sensors CO2 sensors can be unreliable, even with factory calibration Changes required to MECH-6A and Nonresidential Compliance Manual.
Add Field Verification of CO2 Sensors 26 Changes to MECH-6A, Functional Testing Block Existing Block Recommended Block A. Functional Testing Results a. Verify in the field that all CO 2 sensors at both zone and system level are accurate to within +/- 75 PPM. All CO 2 sensors must be verified, no sampling is allowed. Indicate PASS/FAIL for all CO 2 sensors. b. Disable economizer controls c. Outside air CO 2 concentration (select one of the following) Measured dynamically using CO 2 sensor PPM Interior CO 2 concentration setpoint (Outside CO 2 concentration + 600 ppm) PPM
Add Field Verification of CO2 Sensors 27 Changes to MECH-6A, Testing Results Block Existing Block Recommended Block B. Testing Results PASS/FAIL All CO 2 sensors verified to be accurate to within +/- 75 PPM Step 1: Simulate a high CO 2 load (check box complete) Step 2: Simulate a low CO 2 load (check box complete)
Add Field Verification of CO2 Sensors 28 Changes to Nonresidential Compliance Manual Section 10.6.12 Estimated Time to Complete Existing Text Functional testing: 1 to 2 hours (depending on how ambient CO2 concentration levels are manipulated, system response time to variations in CO2) Recommended Text Functional testing: 1 to 2 3 hours (depending on number of CO2 sensors to be verified and how ambient CO2 concentration levels are manipulated, system response time to variations in CO2)
Confirm Dynamic Control of Outside Air 29 Section 10.6.3 of the Compliance Manual indicates that confirmation of dynamic controls is intended to be part of acceptance testing, but this protocol is currently omitted on MECH-2A. Changes required to MECH-2A and Nonresidential Compliance Manual.
Confirm Dynamic Control of Outside Air 30 Changes to MECH-2A, Construction Inspection Block Existing block does not mention dynamic controls
Confirm Dynamic Control of Outside Air 31 Changes to MECH-2A, Construction Inspection Block Add the following verifications to the VAV portion of Item 2. b. Fixed Minimum Damper Setpoint is NOT being utilized to control OSA. c. One of the following dynamic controls is being utilized to control OSA. Dual Minimum Setpoint Design Energy Balance Method Return Fan Tracking Airflow Measurement of the Entire Outdoor Air Inlet Injection Fan Method Dedicated Minimum Ventilation Damper with Pressure Control Other Active Control, Describe
Confirm Dynamic Control of Outside Air 32 Nonresidential Compliance Manual Section 10.6.2 Purpose of the Test Existing Text This test ensures that adequate outdoor air ventilation is provided through the variable air volume air handling unit at two representative operating conditions. The test consists of measuring outdoor air values at maximum flow and at or near minimum flow. Recommended Text This test ensures that adequate outdoor air ventilation is provided through the variable air volume air handling unit at two representative operating conditions. The test consists of confirming dynamic control methods and measuring outdoor air values at maximum flow and at or near minimum flow.
Confirm Dynamic Control of Outside Air 33 Nonresidential Compliance Manual Section 10.6.2 Acceptance Criteria Add the following acceptance criteria. Variable air volume systems use some form of active controls to modulate outdoor air rates. Fixed minimum damper setpoint CANNOT be used.
Confirm Dynamic Control of Outside Air 34 Nonresidential Compliance Manual Section 10.6.3 Construction Inspection Existing Text There are a number of means to dynamically control minimum OSA. A survey of common methods is presented in Chapter 4 of the Nonresidential Compliance Manual. After validating that the sequence of control will dynamically control outdoor air check the System is designed to dynamically control minimum OSA box in the Construction Inspection section of MECH-2A. Note: check box for confirming dynamic controls does not currently exist on the MECH-2A form
Confirm Dynamic Control of Outside Air 35 Nonresidential Compliance Manual Recommended Text There are a number of means to dynamically control minimum OSA. A survey of common methods is presented in Chapter 4 of the Nonresidential Compliance Manual. After validating that the sequence of control will dynamically control outdoor air check the System is designed to dynamically control minimum OSA box in the Construction Inspection section of MECH-2A. Furthermore, fixed minimum damper setpoint, which is common industry practice, is not compliant with Title 24. After validating that the sequence of control will dynamically control outdoor air check the Fixed Minimum Damper Setpoint is NOT being utilized to control OSA box in the Construction Inspection section of MECH-2A. Also, indicate in this section what type of dynamic control is being used.
Confirm Pre-occupancy Purge for all systems 36 Confirm pre-occupancy purge for all system types as required in 121(c)2. No significant cost to verify schedule Low barriers to adoption Current compliance issues Currently, verification only completed for single zone and unitary systems in NA7.5.2. Modifications needed to the MECH-2A acceptance form and Nonresidential Compliance Manual
Confirm Pre-occupancy Purge for all systems 37 Changes to MECH-2A, Construction Inspection Block Add the following confirmation to the end of the existing block. 3. Programming, check the following: Pre-occupancy purge has been programmed to meet the requirements of Standards Section 121(c)2.
Confirm Pre-occupancy Purge for all systems 38 Changes to Compliance Manual Section 10.6.3 (VAV) AND Section 10.6.5 (CV) Add the following text to the end of the existing Construction Inspection text. Confirm that pre-occupancy purge has been programmed to meet the requirements of Standards Section 121(c)2. This is most easily accomplished by scheduling the unit to start one hour prior to actual occupancy.
Add guidance for measuring OA flow 39 Outdoor air flow measurements can be very inaccurate if not done properly Add guidance for Choosing instrumentation Avoiding turbulence Measuring free area Averaging multiple measurements
Add guidance for measuring OA flow 40 Change to Nonresidential Compliance Manual Intent: add mention of multi-point velocity pressure probes (i.e. velocity matrix) Section 10.6.2 - Instrumentation Modify existing list of instrumentation to read: An airflow measurement probe (e.g. hot-wire anemometer or single/multi-point velocity pressure probe)
Add guidance for measuring OA flow 41 Change to Nonres Compliance Manual Add the following text to the end of the existing Verify and Document portion of Section 10.6.3 and Section 10.6.5 Follow the best practice guidelines below in order to increase accuracy of outdoor air flow measurements: Traverse measurements taken in supply, return or outdoor air ducts should be located in an area of steady, laminar flow. If possible, take measurements at least six to eight duct diameters away from turbulence, air intakes, bends, or restrictions.
Add guidance for measuring OA flow 42 If using face velocity measurements to calculate outdoor air flow, care should be taken to accurately measure free area dimensions of intake. If velocity measurements are taken at the plane of the intake between damper blades where flow is restricted (i.e. to achieve faster flows), free area should be measured as the actual open space between dampers and should not include frames or damper blades. Hot wire anemometers are more appropriate than velocity pressure probes for measuring low speed flows (i.e. less than 250 feet per minute). Take multiple measurements and average results in order to minimize affects of fluctuations in system operation and environmental conditions (i.e. wind).
Verify location of OA ducts in plenum systems 43 No significant cost to verify location Low barriers to adoption Need changes to MECH-2A and Nonresidential Compliance Manual
Verify location of OA ducts in plenum systems 44 Changes to MECH-2A Add the following confirmation item 3. Outside air supply (check one of the following) Return air plenum is used to distribute outside air to a zonal heating or cooling unit Check as appropriate: a. Confirm that outside air supply is connected either: Within five ft. of the unit Within 15 ft. of the unit, with the air directed substantially toward the unit, and with a discharge velocity of at least 500 ft. per minute. Return air plenum is used NOT to distribute outside air to a zonal heating or cooling unit.
Verify location of OA ducts in plenum systems 45 Changes to Compliance Manual Section 10.6.3 (VAV) and Section 10.6.5 (CV) Add the following text to the end of the existing Construction Inspection text. For systems where return air plenum is used to distribute outside air to a zonal heating or cooling unit, confirm that outside air supply is connected either: Within five ft. of the unit Within 15 ft. of the unit, with the air directed substantially toward the unit, and with a discharge velocity of at least 500 ft. per minute.
Correct CO2 Sensor Mounting Height 46 Correction needed in Nonresidential Compliance Manual Currently lists 1 foot as the minimum mounting height. Section 10.6.12 Acceptance Criteria, corrected text: Each CO2 sensor is located correctly within the space 1 3 to 6 feet above the floor. Note: The minimum mounting height is reported accurately as 3 feet on the MECH-6A form.
Future Consideration 47 Require dedicated minimum OA intake for systems with economizers Require 300-750 FPM face velocity More accurate flow measurement better dynamic control Easier acceptance testing Further study required to determine net cost benefit Energy savings from more accurate flow measurements
Future Code Change 48 Require dedicated minimum OA intake for systems req d to have economizers Require integrated dynamic control Injection fan Pressure control Direct OA airflow measurement
Future Code Change 49 Further study required Energy performance savings of reduced over ventilation observed in the field Cost, design and space impacts of dedicated flow sensing intake on packaged and built-up units of various sizes Cover all CA climate zones
Energy Savings and Cost Effectiveness for Acceptance Testing Measures 50 Finalizing approach for quantifying savings from improved Acceptance Testing Not expecting significant changes to Acceptance Testing costs o Main impact is time for CO2 sensor calibration verification Estimated completion by mid Jan Results will be disseminated by email to stakeholder group
Next Steps 51 Complete in situ testing (3 sites) Finalize Compliance Manual language Finalize energy savings and cost effectiveness for Acceptance Testing changes Consider future code changes for requiring: o Dedicated minimum outside air dampers o Dynamic minimum outside air flow control