Building Re-Tuning (BRT) Lesson 4: SOI Air-Handling Unit Part II
Lesson 4: Sections Review of last class (0:20) Section 1: AHU: Discharge air temperature control (0:45) Break (0:10) Section 2: AHU: Heating & cooling control (0:45) Section 3: Your final project (0:60) 2
Review of last class Minimum Outdoor Air Operation For ventilation. Even less when unoccupied. Damper fully closed during unoccupied and pre-occupancy start-up OAF (%) = ((Return-Mixed)/(Return-Outside))*100 Use to find % of outside air Air-side Economizer Operation Packaged rooftop units with economizers are often neglected, hard to access, or installed poorly. Static Pressure Control Like discharge-air temperature, discharge static should follow the real load conditions. Static Pressure Re-set - Power Laws. 3
For each SOI, we will focus on: For Each SOI Step #2: Building Walk Down: Identify common operational issues. Step #3: Data Collection: Establish baseline through trend-log data ( before BRT ). Step #4: Data Visualization & Interpretation: Create graphs & interpret data. 4
Check Your Understanding 1. What are some potential issues to identify for incorrect economizer operation? Incorrect control strategy Failed actuator What else? 2. A 20% OA damper position means 20% outdoor air. True False 3. Ideally VAV dampers should run in what range? 5
Homework: What have you found during the week? Questions on reading? AHU Discharge Air Control AHU Heating and Cooling Control Watch ECAM Webinar: Part II ECAM Basics Part III Creating & Analyzing Retuning Charts Issues with completing your Project Report? Complete the SOI Section What SOI(s) are you investigating? What observations and findings so far? 6
Section 1 Time Spent on this Section (45 Minutes) AHU: DISCHARGE AIR TEMPERATURE CONTROL 7
Air Handling Unit For the AHU SOI, we will consider: Minimum Outdoor Air Operation Air-side Economizer Operation Static Pressure Control Discharge Air Temperature Control AHU Heating + Cooling Control 8
Discharge-Air Temperature Control Discharge temperature is the single most important variable in a HVAC system. Low discharge-air temperature will cause: Overcooling Reheating in cooler zones Portable heaters in offices Drafts and cold complaints Extra load on the cooling plant Excess discharge-air pressure Excess energy in reheating the overcooled zones 9
Discharge-Air Temperature Control Step #2. Building Walk Down: Identify issues as you walk around, such as: Are people too cold (air-conditioning)? Do they have sweaters or heaters at their desks? Are air diffusers closed or covered over? Do some rooms have much higher or different loads than others in the same zone? 10
Discharge-Air Temperature Control Step #3. Data Collection: Discharge-air temperature (DAT) Discharge-air temperature set point (DATSP) Outdoor-air temperature (OAT) Zone reheat valve signal 11
Discharge-Air Temperature Control Step #4. Data Visualization & Interpretation: Trends to look for in the data: Is reset being used to control the discharge-air set point? Is the discharge-air temperature meeting the set point, or do deviations occur? Is the discharge-air temperature too cool (<55 F) or too warm (>70 F)? Does the discharge-air temperature remain relatively stable? 12
Discharge-Air Temperature Control Step #4. Data Visualization & Interpretation: Is reset being used to control the discharge-air set point? 13
Discharge-Air Temperature Control Step #4. Data Visualization & Interpretation: Are setback and resets being used? 14
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is the discharge-air temperature meeting the set point, or do deviations occur? 15
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is the discharge-air temperature meeting the set point, or do deviations occur? 16
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is the discharge-air temperature too cool (<55 F) or too warm (>70 F)? 17
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Does the discharge-air temperature remain relatively stable? 18
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is this a good or bad operation? 19
Let s Talk about Your Building! What is driving your current discharge temp set point? How is it impacting energy cost? Set it low enough to handle the peak cooling load: Summer weather peak Interior load peak Staffing peak 1% - 2% of operating hours are at peak yet most systems run 100% of the time at this set point. Reheat makes up for all areas that are too cold from a lower than needed discharge temperature. 20
Addressing Issues: Discharge-Air Temperature Discharge-air temperature can run as high as possible and still meet the cooling needs: VAV boxes can run at higher air flows Return air can be warmer and help heat building Reheats will run a lot less Staff complaints go down due to less cold drafts Building is ventilated better 21
Zones & Discharge-Air Static Pressure Dynamic Reset Does your discharge set point vary with some input signals? > 55 o F < 70 o F Set up a discharge-air set point reset schedule based on the personality of the zones it feeds. Examples: Warmest 3 zones averaged Number of reheats running Coolest perimeter zone Outdoor air temperature 22
Potential Problem Indicators Indicator Many occupant complaints. Trended data is flat or rarely varies. Trended data shows sharply falling temperatures well below set point at chiller system start, and remain well below set point. Trended data shows sharply rising temperatures well above set point at boiler/reheat system start, and remain well above set point. Potential Problem Precursor to an improperly working (or non-functioning) discharge temperature control scheme. Non-functioning discharge temperature reset control. Failed (leaking) cooling control valve. Failed (leaking) heating control valve. 23
Trends for Discharge Air Temperature Trended data for discharge temperature reset control that is properly working should show temperature set points that vary. As the building wakes up, becomes occupied, and changes in outdoor ambient temperatures and solar loading. This can vary as much as 10-15 o F over the course of the day. Does your DDC system calculate: warmest, lowest, and average zone temperatures? Does your DDC system currently reset the discharge temperature set point using either outside-air temperature or return-air temperature? 24
Break (10 Minutes) Break Time! 25
Section 2 Time Spent on this Section (45 Minutes) AHU: HEATING & COOLING CONTROL 26
AHU Heating and Cooling Control Step #2. Building Walk Down: Identify issues as you walk around, such as: Zone temperatures Thermostat settings and proximity to heat / cold Blocked registers 27
AHU Heating and Cooling Control Step #3. Data Collection: Outdoor-air temperature (OAT) Cooling-coil-valve-signal (CCV) Heating-coil-valve signal (HCV) 28
AHU Heating and Cooling Control Step #4. Data Visualization & Interpretation: Trends to look for in the data: Are outdoor-air temperature lockout set points for heating and cooling reasonable, do they overlap? Is there simultaneous heating and cooling occurring? 29
AHU Heating and Cooling Control Air handler heating vs. cooling valve positions. 100 90 80 Chilled Water vs Hot Water Valve Signals Hot Water Signal (%) 70 60 50 40 30 20 Bad Worse 10 0 0 10 20 30 40 50 60 70 80 90 100 Chilled Water Signal (%) 30
AHU Heating and Cooling Control Step #4. Data Visualization & Interpretation: Is there simultaneous heating and cooling occurring? 31
AHU Heating and Cooling Control Step #4. Data Visualization & Interpretation: Is there simultaneous heating and cooling occurring? 100 90 80 70 MAU1/HeatingValveAO MAU1/CoolingValve MAU1/OAT 100 90 80 70 Valve Position (%) 60 50 40 60 50 40 Temperature 30 30 20 20 10 10 0 0 8/15 8/16 8/17 8/18 8/19 8/20 8/21 8/22 Data/Time 32
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is this a good or bad operation? Why? 33
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is this a good or bad operation? Why? 34
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is this a good or bad operation? Why? 35
Now you try: Interpret the Data CLASS ACTIVITY Step #4. Data Visualization & Interpretation: Is this a good or bad operation? Why? 36
Let s Talk about Your Building! Are the heating and cooling coils efficient? Clean? Valves not leaking through? Check (touch) coil for temperature of pipes at air-handler penetrations Should be room temperature Loops locked out at some ODA temperature preventing heating and cooling at same time. Balance point of building is critical when setting these lockouts. 37
Pump and Fan Operation Parallel in air-distribution: Know your VAV boxes! Various types of VAV boxes, e.g.: Single duct cooling only Single duct, cooling with reheat Dual duct Fan powered Fan powered 38
Variable-Speed Pumps and Fans Huge power consumption variable. Can you monitor that the speed is varying? Change it to energy units and monetize! Identify sensor that controls modulation. Common causes of failure to modulate: Three-way valves and by-pass type VAV Open by-passes (manual or pressure) 39
Section 3 Time Spent on this Section (60 Minutes) YOUR FINAL PROJECT 40
Final Project Report, page 1 BUILDING OVERVIEW Briefly describe your facility here, including: Approximate floor area (square footage) Type(s) of use Schedule of operations Mechanical systems and major equipment HANDOUT! BUILDING WALK DOWN Walk around building and note potential building issues: Zone temperatures Equipment running Scheduling during unoccupied periods Faulty equipment & components Occupant complaints 41
Final Project Report, page 1 BAS Summarize your BAS system(s): Manufacturer (Siemens, Johnson etc) Software version (Apogee, MetaSys etc) Approximate age If it includes an inter-operable protocol (BACNet, ModBus, LON) List of systems covered by the BAS 42
Final Project Report, page 2 SOI Describe here the SYSTEM-OF-INTEREST that you have selected: Relevant details about it If there is a particular reason for choosing this system, briefly describe why If you have a schematic or have drawn one, attach that to this report FUNCTIONS, BRT MEASURES TO BE INVESTIGATED Describe the specific system functions that you will collect data to investigate. Use the cookbook recipes from BRT Resources to help you with this. BRT SET-UP List the specific sensors that you need and will use for BRT of your initial SOI. Use the cookbook recipes from BRT Resources to help you with this. Indicate whether you have each of the necessary sensors available on your BAS. If you are missing certain sensors, indicate here and address in your Next Steps section. 43
Final Project Report, page 3 PROGRESS TO DATE Describe what you have done thus far to set-up and implement BRT. Include both steps taken with your BAS, as well as within your organization and with other individuals. If you have set up Trend Logs, attach sample plots and discuss any findings and patterns you have noted. PROVIDE BRIEF ANSWERS TO THE FOLLOWING: Has the Intro to BRT training made you think about your BAS system in new ways? Does BRT have promise as a procedural tool for your facility? Do you think BRT can help you identify operating patterns and improve efficiencies? 44
Final Project Report, page 4 BARRIERS ENCOUNTERED Create a numbered list of barriers encountered in setting-up and/or implementing initial BRT: Barriers can be technical or organizational Briefly describe each barrier How did you overcome the barrier? PLANNED NEXT STEPS Briefly describe the NEXT STEPS you are planning. Provide both an overall statement and a numbered list corresponding to the BARRIERS identified in the previous section. 45
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Lesson Summary AHU: Discharge air temperature control: Discharge temperature is the single most important variable in a HVAC system. Set discharge temp set point low enough to handle the peak cooling load. Set up a discharge-air set point reset schedule based on the personality of the zones it feeds. Trended data for discharge temperature reset control that is properly working should show temperature set points that vary. AHU: Heating & cooling control Simultaneous heating and cooling. Heating and cooling coils efficient. 47
Homework READ in ES Modeling: Abstract-Exec Summary-Approach, pages iii xii On your Project Report, complete the sections: Functions, BRT Measures what functions how data acquisition has gone trial graphical plots and interpretations BRT Set-Up Progress to Date Barriers Encountered Planned Next Steps 48