Energy Efficiency Study on Student Recreation Center

Gang Wang, Ph.D., P.E.

Civil and Architectural Engineering

Texas A&M University - Kingsville

Outline

• Background of Energy Conservation• Studied Facility Information• Purpose• Energy Studies

– Current control sequences– Energy performance– Improvement– Savings estimation– Troubleshooting

• Conclusion

Building Energy System

• Mechanical system– Chilled water (chiller)– Heater (electrical/hot

water)– Fan and pump (motor)

• Lighting and power– Lighting– Office equipment– Motor (chiller, fan and

pump) and electrical heater

Mechanical or HVAC SystemMechanical or HVAC System• Remove impacts

– People (250Btu/h & 0.2lbmv/h)– Lighting and power system– Climate and solar (envelope)

• Create indoor environment– Temperature (75F)– Humidity (50%rh): 55F SAT– Indoor air quality:

• 15CFM (ft3/min) OA or • Indoor CO2=700PPM + OA CO2

• Minimize energy usage– Chilled water (Chiller/electricity.)– Fan and pump (electricity)– Heating (hot water or electricity)

Air

Han

dlin

g U

nit(

AH

U)

Terminal Box (TB)

Computer

Supply air

Return air

Diffuser

Lights

Heating coil (hot water or electrical)

Cooling coil

Supply air fan

Return air fan

Outside air (OA) intake(Hot and humid)

Relief air

People

Supply air temp (SAT=55F)

ChallengesChallenges• DOE: Buildings consume

40% of U.S. energy– HVAC (32%)– lighting and power (37%)

• Electricity consumption– 4.3% per year increase

• Natural gas ($/mmBtu):– $3.0 in 2002 to $14 in 2006.

• TAMUK: $4M/yr

• Improve energy efficiency

• ASHRAE standard 90.1-2010 sets an energy savings target of 30%

Energy Efficiency MeasuresEnergy Efficiency Measures

• Electrical System– Reduce usage– Reduce HVAC load

Energy Efficiency MeasuresEnergy Efficiency Measures

• Electrical System– Reduce usage– Reduce HVAC load

• Indoor Comfort and Health– SAT=55F (humidity control)– Maintain required OA intake

(Annual $1.75 for 1CFM OA)

• Partial Load Operation– Reduce fan speed– Avoid simultaneous cooling

and heating

Air

Han

dlin

g U

nit(

AH

U)

Terminal Box (TB)

Computer

Supply air

Return air

Diffuser

Lights

Heating coil (hot water or electrical)

Cooling coil

Supply air fan

Return air fan

Outside air (OA) intake(Hot and humid)

Relief air

People

Supply air temp (SAT=55F)

Studied Facility Information• Student Recreation

Center, built in 2010• Floor area: 38,000 ft2

– Gym– Weights– Running track– Offices

• Occupancy: – Design: 615 persons. – Actual: < 200 persons

HVAC System Information• Air Handling Unit

– AHU1 (SZ) : Gym– AHU2 (MZ) : Track– AHU3 (SZ) : Weights– AHU4 (SD) : Offices– AHU-OA

• Chilled water• Electrical heating• Siemens APOGEE. • Variable frequency drive

(VFD) on AHU fans

Purposes

• Identify energy efficiency measures– Minimize energy consumption – Improve indoor thermal condition– Increase physical plant cooling capacity

• Develop energy efficiency control

• Estimate cost savings

AHU Schematics

Control Sequencesby Design Engineer

APOGEE PPCL Program by Control Engineer

……00390 C SPEED CONTROL00410 IF("%X%OCC") THEN GOTO 42000412 SET(50,"%X%SVD")00414 GOTO 43000420 TABLE(SECND1,"%X%SVD",0,20,60,100)00430 C DISCHARGE TEMPERATURE CONTROL00450 LOOP(0,"B570.A01RMT","%X

%LOOP","B570.A01RMSP",1000,100,8,1,50,0,100,0)00460 IF("%X%HUMOVRD".EQ. OFF) THEN TABLE("%X%LOOP","%X

%CCV",50,0,100,100)00470 IF("%X%HUMOVRD".EQ. ON) THEN SET(100,"%X%CCV")00480 DBSWIT(1,"%X%LOOP",40,45,"%X%EH1")00490 DBSWIT(1,"%X%LOOP",25,40,"%X%EH2")00500 DBSWIT(1,"%X%LOOP",5,20,"%X%EH3")00510 C DAMPER CONTROL00530 IF("%X%CO2" .LT. 700.0) THEN GOTO 57000540 SET(100,"%X%OAD")00560 GOTO 60000570 LOOP(128,"B570.A02OAF","%X%OALOOP","B570.A02OASP",6,4,1,1,50,0,100,0)00580 TABLE("%X%OALOOP","%X%OAD",0,15,100,100)00600 GOTO 10

Summary of Control Sequences

• OA flow is adjusted based on a design setpoint (615 vs. 200)– OA is fully open if CO2>700ppm

• Space temperature is controlled by cooling coil or electrical heater– Cooling coil is fully opened if space is humid

• Supply fan speed: 100% (no control)

• No supply air temperature control

0

200

400

600

800

1,000

1,200

12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

CO

2(P

PM

)

TSI

0

200

400

600

800

1,000

1,200

12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

CO

2(P

PM

)

TSI

Current Program

Code requirement(ASHRAE62.1)

0

200

400

600

800

1,000

1,200

12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time

CO

2(P

PM

)

TSI

AHU3

AHU4

AHU2

AHU1

Outside Airflow (OA) ControlOutside Airflow (OA) Control

• PerformancePerformance– Low space CO2Low space CO2– Excessive OA intakeExcessive OA intake

• AnalysisAnalysis– Design OA flow setpoint, Design OA flow setpoint,

8,200CFM 8,200CFM – Fault space CO2 setting: Fault space CO2 setting:

700ppm (+OA CO2)700ppm (+OA CO2)– Fault CO2 sensorsFault CO2 sensors

• ImpactImpact– More chilled waterMore chilled water– Disturbance on indoor humidityDisturbance on indoor humidity

Fan Speed ControlFan Speed Control

• Performance:Performance:– Full speed: 24/7Full speed: 24/7

• AnalysisAnalysis– No fan speed controlNo fan speed control

• ImpactImpact– Waste fan powerWaste fan power– Increase cooling loadIncrease cooling load

Space Air Temperature Control Space Air Temperature Control

• PerformancePerformance– Space air temperature Space air temperature

is maintainedis maintained

20

30

40

50

60

70

80

11/5 11/6 11/7 11/8 11/9 11/10 11/11

Time

Tem

per

atu

re(F

)

Space temperature is properly maintained

Heating and Cooling PerformanceHeating and Cooling Performance

• PerformancePerformance– Cooling coil and Cooling coil and

heater is huntingheater is hunting

• AnalysisAnalysis– Single control loop Single control loop

with huge thermal with huge thermal capacitycapacity

• ImpactImpact– Wastes chilled water Wastes chilled water

and electricityand electricity

-150

-100

-50

0

50

100

150

12:00 15:00 18:00 21:00

Time

Hea

tin

g a

nd

co

olin

g c

om

man

ds(

%)

Heating (electricity)

Cooling (Chilled Water)

Supply Air Temperature ControlSupply Air Temperature Control• PerformancePerformance

– Fluctuated SAT(Fluctuated SAT(≠≠55F)55F)– Simultaneous heating Simultaneous heating

and coolingand cooling

• AnalysisAnalysis– No SAT controlNo SAT control– Coil thermal capacityCoil thermal capacity

• ImpactImpact– High space humidityHigh space humidity– Waste chilled water Waste chilled water

and electricityand electricity

45

50

55

60

65

70

75

11/5/10 0:00 11/5/10 6:00 11/5/10 12:00

Time

Tem

per

atu

re(F

)

After cooling coil

After heating coil

Mixing air

Space Humidity ControlSpace Humidity Control

20

30

40

50

60

70

80

11/5 11/6 11/7 11/8 11/9 11/10 11/11

Time

Tem

per

atu

re(F

)

Measured Space humidity is out of range

Humidity control range(35-55%) by wooden floor

Lighting ControlLighting Control

• PerformancePerformance– Lights are on during Lights are on during

unoccupied hoursunoccupied hours

• AnalysisAnalysis– Fault scheduleFault schedule

• ImpactImpact– Waste electricityWaste electricity

0

50

100

150

200

250

Friday,November 12,

2010

Saturday,November 13,

2010

Sunday,November 14,

2010

Monday,November 15,

2010

Tuesday,November 16,

2010

Po

wer

(kW

)

Lights on 24/7 during weekday

Improve ControlImprove Control(Lighting)(Lighting)

• Current Control– On during weekday

unoccupied time

• Improved control– Off during unoccupied

time

0

50

100

150

200

250

Friday,November 12,

2010

Saturday,November 13,

2010

Sunday,November 14,

2010

Monday,November 15,

2010

Tuesday,November 16,

2010

Po

wer

(kW

)

Lights on 24/7 during weekday

Improve ControlImprove Control(Outside Air)(Outside Air)

• Current Control– Design OA flow

setpoint, 8,200CFM– Fault space CO2

control: 700ppm

• Troubleshoot– Fault CO2 sensors

• Improved control– OA flow setpoint:

3,000CFM based on actual occupancy

– Space CO2: 1000ppm

• Troubleshoot– Calibrate CO2 sensors

Improve ControlImprove Control((Fan Speed and Temperature)Fan Speed and Temperature)

• Current Control– No supply air

temperature (humidity) control

– No fan speed control– Cooling coil and heater

directly control space temperature

• Improved control– Cooling coil is modulated

to maintain SAT at 55F– Fan speed is modulated

to maintain space temperature.

– Heater is stepped on or off to maintain space temperature if airflow drops to min setpoint.

Estimated Annual SavingsEstimated Annual Savings

  Unit Lighting Fan Heater OA

Electricity kWh 52,000 122,252 239,980 0

Chilled Water(electricity) kWh 13,000 37,046 72,721 136,200

Total savings kWh 65,000 159,298 312,701 136,200

Electricity rate $/kWh 0.054 0.081 0.081 0.081

Cost savings $ 3,510 12,903 25,329 11,032

Total savings $ 52,774

TroubleshootingTroubleshooting(Fault Cooling Coil Valve)(Fault Cooling Coil Valve)

Preliminary ResultsPreliminary Results

• Baseline rate: 96kWBaseline rate: 96kW• Valve fault: 164kWValve fault: 164kW

– $48,180/yr wasted$48,180/yr wasted

• Repair and Repair and preliminary control preliminary control upgrade:90kWupgrade:90kW

• Final upgrade: 55kWFinal upgrade: 55kW– $52,774/yr reduced$52,774/yr reduced

0

50

100

150

200

250

11/16 11/17 11/18 11/19 11/20 11/21

Po

wer

(kW

)

96kW (Normal)

0

50

100

150

200

250

11/16 11/17 11/18 11/19 11/20 11/21

Po

wer

(kW

)

96kW (Normal)

Valve lost control

164kW

0

50

100

150

200

250

11/16 11/17 11/18 11/19 11/20 11/21

Po

wer

(kW

)

96kW (Normal)90kW

Valve lost control

164kW

Valve Repair/Control Upgrade

0

50

100

150

200

250

11/16 11/17 11/18 11/19 11/20 11/21

Po

wer

(kW

)

96kW (Normal)90kW

Valve lost control

164kW

Valve Repair/Control Upgrade

Conclusion• Identify energy efficiency measuresIdentify energy efficiency measures

– Lighting control– Outside air – Integrate fan speed and cooling coil control– Calibrate CO2 sensor and repair cooling coil valve

• Annual savings: $52,774Annual savings: $52,774– Electricity: 414,232kWh or 52%Electricity: 414,232kWh or 52%– Chilled water: 2,955MMBtu or 45%Chilled water: 2,955MMBtu or 45%

• No major retrofitsNo major retrofits

Questions and Comments?Questions and Comments?

Project team also includes Emmanuel Ayala, Joel Wright, Leah M. Emmanuel Ayala, Joel Wright, Leah M. Ayala Ayala fromfrom Department of Civil and Architectural Engineering and Department of Civil and Architectural Engineering and Ricardo Contreras Jr.Ricardo Contreras Jr. from University Facilities. from University Facilities.