Heating, Ventilating, & Air-Conditioning: Diagnostics & Controls to Improve Air-Handling System Performance

1. Heating, Ventilating, & Air-Conditioning: Diagnostics & Controls to ImproveAir-Handling System Performance Craig Wray, P.Eng. Indoor Environment DepartmentLawrence Berkeley National Laboratory Tel: 510-486-4021 Email: CPWray@lbl.gov http://epb.lbl.gov American Physical Society Short CoursePhysics of Sustainable Energy: Using Energy Efficiently and Producing It RenewablyUC Berkeley, 1 March 2008 Energy Performance of Buildings Group

2. Acknowledgments Assistant Secretary for Energy Efficiency and Renewable Energy, Office of the Building Technologies Program, U.S. Department of Energy California Energy Commission PIER Program Max Sherman, Iain Walker, Darryl Dickerhoff (LBNL) Cliff Federspiel (Federspiel Controls) Energy Performance of Buildings Group

3. Overview • Background • Opportunities for improvement • Duct Leakage Diagnosis • Measuring leakage flows using the DeltaQ test • Duct Pressure Diagnosis & Control • Demand-based reset with DDC/non-DDC controls • Ventilation Control • Intermittent ventilation and efficacy Energy Performance of Buildings Group

4. Opportunities for Improvement • Duct Leakage and Operating Pressure • Thousands of field assembled joints • System pressures not uniform or constant; impossibleto know location of each leak and pressure difference across each leak • Unnecessarily closed dampers restrict flow • Large energy savings possible from sealing ducts and optimizing duct static pressures • Ventilation • Standards specify constant ventilation rates • Energy intensive process; sometimes can reduce IAQ • Intermittent ventilation more appropriate in some cases Energy Performance of Buildings Group

5. Overview • Background • Opportunities for improvement • Duct Leakage Diagnosis • Measuring leakage flows using the DeltaQ test • Duct Pressure Diagnosis & Control • Demand-based reset with DDC/non-DDC controls • Ventilation Control • Intermittent ventilation and efficacy Energy Performance of Buildings Group

6. PressurizingAirflow Why Use DeltaQ Duct Leakage Test? • Fast and easy • No register covering (less damage potential) • Coincidentally measures envelope leakage • Uses familiar equipment (blower door) • Self-diagnostic for uncertainty • Can be automated • Accurate • Leaks to outside under operating conditions • BUT… • Need a computer • Need to operate central blower Energy Performance of Buildings Group

7. DeltaQ Airflows and Pressures 10 Pa 10 Pa 30 40 Pa -40 Pa 10 0 60 20 1000 10 Pa Return Supply 10 Pa Air Handler 60 Air Handler OFF 60 Air Handler ON 100 DeltaQ = -80 BuildingEnvelope Blower Door 20 Energy Performance of Buildings Group

8. DeltaQ Test Data • Green = blower on • Red = blower off • Difference = DeltaQ Energy Performance of Buildings Group

9. DeltaQ Model P = Envelope added pressure Ps = Supply Pressure Pr = Return Pressure Cs=Supply leak coefficient Cr=Return leak coefficient Qs=Supply leak flow Qr=Return leak flow DeltaQ(P)=Qon(P)-Qoff(P) Q=C(P)n Qon(P)=Qenv(P) + Cs(P+Ps)ns + Cr(P-Pr)nr Qoff(P)=Qenv(P) + Cs(Pns) + Cr(Pnr) DeltaQ(P)=Cs((P+Ps)ns-Pns) + Cr((P-Pr)nr-Pnr) DeltaQ(P)=Qs((1+P/Ps)ns-(P/Ps)ns) - Qr((1-P/Pr)nr+(P/Pr)nr) Energy Performance of Buildings Group

10. Pressure Scanning Error Surface Solution at lowest error Error For each supply and returnpressure pair, the least squareserror is calculated by comparingthe estimated ΔQ to the measured ΔQ Ps Pr Energy Performance of Buildings Group

11. Duct Flow Resistance Correction Difference between flow throughair handler and flow through ducts Flow through leak Energy Performance of Buildings Group

12. Overview • Background • Opportunities for improvement • Duct Leakage Diagnosis • Measuring leakage flows using the DeltaQ test • Duct Pressure Diagnosis & Control • Demand-based reset with DDC/non-DDC controls • Ventilation Control • Intermittent ventilation and efficacy Energy Performance of Buildings Group

13. Variable-Air-VolumeSystem Schematic Energy Performance of Buildings Group

14. VAV System Control Energy Performance of Buildings Group

15. Duct Static Pressure Reset Issues • DDC systems with reset capability already exist, but suffer from: • Inaccurate, open-loop position measurement • Failures at terminal boxes • Limited bandwidth and limited programming capabilities • Many systems have pneumatic terminal controls • Using total supply airflow signal from airflow station expands reset applicability • Aggregation of terminal box flows makes control more robust to single terminal failure Energy Performance of Buildings Group

16. Diagnostic Principle • Terminal flows are regulated by thermostat,independent of duct static pressure • Test Procedure • Start at high pressure • Incrementally lower pressure • Record flow signal at each step • Complicating Issues • Flow stabilizes slowly • Zone temperatures can change • Noisy measurements • Ducts leak (pressure-dependent) Energy Performance of Buildings Group

17. Diagnostic: Dual-Model Estimation • Model components • Constant component • Time-varying component • Leakage flow • Starved behavior • “In-Control”: • “Starved”: • At critical pressure, both models predict same flow; solve for transition using least squares fit Energy Performance of Buildings Group

18. Haas School of Business Energy Performance of Buildings Group

19. UCOP Energy Performance of Buildings Group

20. County of Alameda Energy Performance of Buildings Group

21. Overview • Background • Opportunities for improvement • Duct Leakage Diagnosis • Measuring leakage flows using the DeltaQ test • Duct Pressure Diagnosis & Control • Demand-based reset with DDC/non-DDC controls • Ventilation Control • Intermittent ventilation and efficacy Energy Performance of Buildings Group

22. Intermittent Ventilation:When Steady Won’t Always Do • Ventilation (for acceptable IAQ) should not always be constant • May be periods of the day when outdoor air (OA) quality is poor and one wishes to reduce amount of OA entering building • Economizer operation can over-ventilate a space from IAQ point of view; energy savings can be achieved by reducing ventilation rates at other times to account for over-ventilation • Demand charges or utility peak loads may make it advantageous to reduce ventilation for certain periods of the day • Some HVAC equipment may make cyclic ventilationmore attractive than steady-state ventilation • Example: residential or small commercial systems that coupleventilation to heating and cooling system operation Energy Performance of Buildings Group

23. What’s The Problem? • Constant target ventilation (Aeq) • Intermittent ventilation with cycle time (Tcycle),over-ventilation (Ahigh) for fractional time fhigh, andunder-ventilation (Alow) for fractional time flow • Equivalency = same dose for constant contaminant source • Sherman & Wilson (1986); Std 136 • Means to demonstrate equivalency not obvious: • Designers want flexibility to use intermittent ventilation, but also want to follow standards & guidelines • Average not always same as constant Energy Performance of Buildings Group

24. Efficacy is Link • Provide calculation method to assess equivalency • Find the temporal ventilation effectiveness (“efficacy”)of a given pattern of ventilation • Definition: • Typical Use: Energy Performance of Buildings Group

25. Hyperbolic Cotangent? • Nominal Turnover: • Fraction of time under-ventilated: flow • Recursive equation numerical solution • Use efficacy for design Energy Performance of Buildings Group

26. Energy Performance of Buildings Group

27. Efficacy Trends flow N>>1 N<<1 Energy Performance of Buildings Group

28. Energy Performance of Buildings Group

29. ε > 90% for region to left and below each curve Energy Performance of Buildings Group

30. Low-Density Spaces High-Density Spaces Energy Performance of Buildings Group

31. Energy Performance of Buildings Group

32. Questions? • Background • Opportunities for improvement • Duct Leakage Diagnosis • Measuring leakage flows using the DeltaQ test • Duct Pressure Diagnosis & Control • Demand-based reset with DDC/non-DDC controls • Ventilation Control • Intermittent ventilation and efficacy Energy Performance of Buildings Group