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Heating, Ventilating, & Air-Conditioning: Diagnostics & Controls to Improve Air-Handling System Performance. Craig Wray, P.Eng . Indoor Environment Department Lawrence Berkeley National Laboratory Tel: 510-486-4021 Email: CPWray@lbl.gov http://epb.lbl.gov

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slide1

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

acknowledgments
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

overview
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

opportunities for improvement
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

overview1
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

why use deltaq duct leakage test

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

deltaq airflows and pressures
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

slide8
DeltaQ Test Data
  • Green = blower on
  • Red = blower off
  • Difference = DeltaQ

Energy Performance of Buildings Group

deltaq model
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

pressure scanning error surface
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

duct flow resistance correction
Duct Flow Resistance Correction

Difference between flow throughair handler and flow through ducts

Flow through leak

Energy Performance of Buildings Group

overview2
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

variable air volume system schematic
Variable-Air-VolumeSystem Schematic

Energy Performance of Buildings Group

vav system control
VAV System Control

Energy Performance of Buildings Group

duct static pressure r eset issues
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

diagnostic principle
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

diagnostic dual model e stimation
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

haas school of business
Haas School of Business

Energy Performance of Buildings Group

slide19
UCOP

Energy Performance of Buildings Group

county of alameda
County of Alameda

Energy Performance of Buildings Group

overview3
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

intermittent ventilation when steady won t always do
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

what s the problem
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

efficacy is link
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

hyperbolic cotangent
Hyperbolic Cotangent?
  • Nominal Turnover:
  • Fraction of time under-ventilated: flow
  • Recursive equation numerical solution
  • Use efficacy for design

Energy Performance of Buildings Group

efficacy trends
Efficacy Trends

flow

N>>1

N<<1

Energy Performance of Buildings Group

slide29

ε > 90% for region to left and below each curve

Energy Performance of Buildings Group

slide30

Low-Density Spaces

High-Density Spaces

Energy Performance of Buildings Group

questions
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