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 System
• Remove impacts
Outside air (OA) intake
(Hot and humid)
Supply air
Air Handling Unit(AHU)
Supply air fan
Terminal Box (TB)
Lights
Supply air temp
(SAT=55F)
Cooling coil
Return air fan
Relief air
Heating coil (hot water or electrical)
Return air
People
Diffuser
– 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
Computer
• Minimize energy usage
– Chilled water (Chiller/electricity.)
– Fan and pump (electricity)
– Heating (hot water or electricity)
Challenges
• 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 90.12010 sets an energy
savings target of 30%
Energy Efficiency Measures
• Electrical System
– Reduce usage
– Reduce HVAC load
Energy Efficiency Measures
• Electrical System
Outside air (OA) intake
(Hot and humid)
Supply air
Air Handling Unit(AHU)
Supply air fan
Terminal Box (TB)
Lights
Supply air temp
(SAT=55F)
Cooling coil
People
Diffuser
– 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
Return air fan
Relief air
Heating coil (hot water or electrical)
Return air
Computer
– Reduce fan speed
– Avoid simultaneous cooling
and heating
Studied Facility Information
• Student Recreation
Center, built in 2010
• Floor area: 38,000 ft2
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–
–
–
Gym
Weights
Running track
Offices
• Occupancy:
– Design: 615 persons.
– Actual: < 200 persons
HVAC System Information
• Air Handling Unit
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–
–
–
–
•
•
•
•
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 Sequences
by Design Engineer
APOGEE PPCL Program
by Control Engineer
00390
00410
00412
00414
00420
00430
00450
00460
00470
00480
00490
00500
00510
00530
00540
00560
00570
00580
00600
……
C SPEED CONTROL
IF("%X%OCC") THEN GOTO 420
SET(50,"%X%SVD")
GOTO 430
TABLE(SECND1,"%X%SVD",0,20,60,100)
C DISCHARGE TEMPERATURE CONTROL
LOOP(0,"B570.A01RMT","%X%LOOP","B570.A01RMSP",1000,100,8,1,50,0,100,0)
IF("%X%HUMOVRD".EQ. OFF) THEN TABLE("%X%LOOP","%X%CCV",50,0,100,100)
IF("%X%HUMOVRD".EQ. ON) THEN SET(100,"%X%CCV")
DBSWIT(1,"%X%LOOP",40,45,"%X%EH1")
DBSWIT(1,"%X%LOOP",25,40,"%X%EH2")
DBSWIT(1,"%X%LOOP",5,20,"%X%EH3")
C DAMPER CONTROL
IF("%X%CO2" .LT. 700.0) THEN GOTO 570
SET(100,"%X%OAD")
GOTO 600
LOOP(128,"B570.A02OAF","%X%OALOOP","B570.A02OASP",6,4,1,1,50,0,100,0)
TABLE("%X%OALOOP","%X%OAD",0,15,100,100)
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
Outside Airflow (OA) Control
• Performance
1,200
Code requirement
(ASHRAE62.1)
1,000
AHU3
AHU4
800
AHU2
CO2(PPM)
Current Program
AHU1
600
TSI
400
200
0
12:00
18:00
0:00
6:00
Tim e
12:00
18:00
0:00
– Low space CO2
– Excessive OA intake
• Analysis
– Design OA flow setpoint,
8,200CFM
– Fault space CO2 setting:
700ppm (+OA CO2)
– Fault CO2 sensors
• Impact
– More chilled water
– Disturbance on indoor humidity
Fan Speed Control
• Performance:
– Full speed: 24/7
• Analysis
– No fan speed control
• Impact
– Waste fan power
– Increase cooling load
Space Air Temperature Control
• Performance
80
– Space air temperature
is maintained
Space temperature is properly maintained
70
Temperature(F)
60
50
40
30
20
11/5
11/6
11/7
11/8
Tim e
11/9
11/10
11/11
Heating and Cooling Performance
• Performance
150
– Cooling coil and
heater is hunting
Heating (electricity)
Heating and cooling commands(%)
100
50
• Analysis
0
– Single control loop
with huge thermal
capacity
-50
-100
Cooling (Chilled Water)
-150
12:00
15:00
18:00
Tim e
21:00
• Impact
– Wastes chilled water
and electricity
Supply Air Temperature Control
75
• Performance
After heating coil
Temperature(F)
70
– Fluctuated SAT(≠55F)
– Simultaneous heating
and cooling
65
Mixing air
60
55
After cooling coil
50
45
11/5/10 0:00
11/5/10 6:00
Time
11/5/10 12:00
• Analysis
– No SAT control
– Coil thermal capacity
• Impact
– High space humidity
– Waste chilled water
and electricity
Space Humidity Control
80
70
Measured Space humidity is out of range
Temperature(F)
60
50
Humidity control range
(35-55%) by wooden floor
40
30
20
11/5
11/6
11/7
11/8
Tim e
11/9
11/10
11/11
Lighting Control
• Performance
– Lights are on during
unoccupied hours
250
Power (kW)
200
• Analysis
150
– Fault schedule
100
• Impact
50
Lights on 24/7 during weekday
0
Friday,
Saturday,
Sunday,
Monday,
Tuesday,
November 12, November 13, November 14, November 15, November 16,
2010
2010
2010
2010
2010
– Waste electricity
Improve Control
(Lighting)
• Current Control
• Improved control
– On during weekday
unoccupied time
– Off during unoccupied
time
250
Power (kW)
200
150
100
50
Lights on 24/7 during weekday
0
Friday,
Saturday,
Sunday,
Monday,
Tuesday,
November 12, November 13, November 14, November 15, November 16,
2010
2010
2010
2010
2010
Improve Control
(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 Control
(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 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
Troubleshooting
(Fault Cooling Coil Valve)
Preliminary Results
• Baseline rate: 96kW
• Valve fault: 164kW
250
Valve lost control
200
164kW
– $48,180/yr wasted
Power (kW)
150
• Repair and
preliminary control
upgrade:90kW
• Final upgrade: 55kW
100
96kW (Normal)
90kW
50
Valve Repair/Control Upgrade
0
11/16
11/17
11/18
11/19
11/20
11/21
– $52,774/yr reduced
Conclusion
• Identify energy efficiency measures
–
–
–
–
Lighting control
Outside air
Integrate fan speed and cooling coil control
Calibrate CO2 sensor and repair cooling coil valve
• Annual savings: $52,774
– Electricity: 414,232kWh or 52%
– Chilled water: 2,955MMBtu or 45%
• No major retrofits
Questions and Comments?
Project team also includes Emmanuel Ayala, Joel Wright, Leah M.
Ayala from Department of Civil and Architectural Engineering and
Ricardo Contreras Jr. from University Facilities.