page 1 peng xu, philip haves, james braun, maryann piette january 23, 2004 sponsored by the...
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Page 1
Peng Xu, Philip Haves, James Braun, MaryAnn Piette
January 23, 2004Sponsored by the California Energy Commission and
the California Institute for Energy Efficiency
A Case Study of Precooling with Zone
Temperature Reset in a Commercial Office
Building
Page 2
Outline
• Aim
• Test site description
• Precooling and demand shedding strategies
• Test results
• Utility analysis
• Conclusions and future work
Page 3
Aim
Demonstrate the potential for reducing peak-period electrical demand in a moderate-weight commercial building using building structural mass.
Page 4
Executive Summary
• Precooling and zone temperature reset can shift up to 100% of cooling power from on- to off-peak in a moderate-weight commercial buildings
• Electricity peak demand reduced by as much as 2.3 W/ft2
• Potential for cost savings when combined with Critical Peak Pricing
Page 5
Case Study - Introduction
• Started in August 2003
• Purpose - preliminary study to assess potential and need for further work– Potential demand reduction/load shifting in
moderate-weight buildings– Effectiveness of precooling and zone
temperature reset – Thermal comfort
Page 6
Test Site Description• Medium-sized government building
– Santa Rosa, CA– 80,000 ft2 (40,000 ft2 office + 40,000 ft2 courthouse)– 3 stories
• Relatively low mass building structure– 6 in. concrete floor, 4 in. concrete wall, medium
furniture density, standard commercial carpet
• High window-to-wall ratio – Floor to ceiling glazing on south and north façade
• Typical internal loads • Number of occupants
– ~100 (office side)
Page 7
South Facade
Page 8
North Facade
Page 9
Windows
• Single glazing• Tinted glass• Internal blinds
Page 10
Cooling Plant
• West wing: three 75-ton, 30-year old McQuay air-cooled chillers
• East wing: two 60-ton, 10-year old Carrier air-cooled chillers
• Constant-speed water pumps, one for each chiller
• Two stage compressors
Page 11
HVAC Secondary Systems
Five VAV air handling units (three single duct & two dual duct systems):
• Variable-speed supply and return fans
• 50-60 VAV zones • DDC control (Alerton)• No global rest of zone
temperature
Page 12
Building Operation
• 5 am - 8 am - start up
• 8 am - 5 pm - occupancy
• 2-3 hot/cold calls per month
• No major faults, some modest problems: – One undersized cooling coil– Some air balance problems– Lack of reheat coils in single-duct systems
causes temp control problems
Page 13
Precooling & Zonal Reset Strategies
66
68
70
72
74
76
78
80
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Tem
p (
oF
)
current precooling+zonal reset
extended precooling + zonal reset
unoccupied hours occupied hours unoccupied hours
floating
floating
floatingfloating
floating
zonal reset
precooling
Page 14
Monitoring
• Existing:– Whole building power meters– Chiller power meters– Weather station– HVAC performance data from EMCS
• ~500 data points• 15 minute intervals
• Added:– AHU fans power meters– Operative temperature sensors
Page 15
Operative Temperature & Comfort
Convectiveheat exchange
Radiant heat exchange
RoomRegular temperature sensor
globe
Operative temperature sensor
screen
Page 16
Peak OA Temperature vs. Peak Demand
Whole building power vs Peak OA temp
0
50
100
150
200
250
300
350
400
450
40 50 60 70 80 90 100 110
Outside air peak temperature
wh
ole
bu
ildin
g p
ow
er
(kW
)
-0.2
0.8
1.8
2.8
3.8
4.8
5.8
wh
ole
bu
ildin
g p
ow
er
(kW
/sf)
weekend/holidays
working days
CPP hours
Page 17
Classification of Weather Conditions
40
60
80
100
120
10/1 10/6 10/11 10/16 10/21 10/26 10/31
Ou
tsid
e ai
r te
mp
(oF
)
Hot daysWarm daysCool days
Page 18
Comparison of Baseline & Test Conditions
40
60
80
100
120
10/7 10/8 10/9 10/10 10/11
Warm daybaseline
Warm dayprecooling
Cool daybaseline
Cool dayprecooling
10/2310/22
Page 19
Tests Performed
Limited Precooling + zonal reset
Extended Precooling + zonal reset
Cool days 3Warm days 5 1Hot days 2
Page 20
Cool Days – Limited Precooling
Limited precooling (Cool days)
00.5
11.5
22.5
33.5
4
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
Wh
ole
bu
ildin
g p
ow
er
W/s
qft
Limited precooling 1 Limited precooling 2 baseline
1 W/sf shed
Page 21
Warm Day – Limited Precooling
Limited precooling (Warm days)
0
0.5
1
1.5
2
2.5
3
3.5
4
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
Wh
ole
bu
ildin
g p
ow
er
W/S
qft
baseline Limted precooling
1.4 W/sf shed
Page 22
Extended & Limited Precooling
Limited and Extended Precooling (warm days)
00.5
11.5
22.5
33.5
4
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
Wh
ole
bu
ildin
g p
ow
er W
/sq
ft
baseline Limited precooling Extended precooling
1.4 W/sf shed
Page 23
Hot days – Extended Precooling
Extended Precooling (Hot days )
0
1
2
3
4
5
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
Wh
ole
Bu
ildin
g p
ow
er
W/s
qft
Extended precooling 1 Extended precooling 2 baseline
2.3 W/sf shed
Page 24
Chiller Power: Limited Precooling
Chiller power shedding
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
Ch
ille
r p
ow
er
(W/f
t)
precooling+DL_10_8 baseline_10_6
0.7 W/sfshed
Page 25
Results – Fan Power
response of one supply fan
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
fan
po
wer
(kW
)
fan power
1.5 kW shed
precooling zonal reset
Page 26
Results – Zone Temp
zone air temperatures
68
69
70
71
72
73
74
75
76
4:00 8:00 12:00 16:00 20:00 0:00
zon
e t
em
pe
ratu
re (
oF
)
Precooling_Temp_operative Precooling_Temp_DDCPrecooling_Average zone temp baseline_temp
Page 27
Critical Peak Pricing (1 of 3)
• Operating time– CPP high price: 3:00pm –6pm– CPP moderate price: 12:00pm –3:00pm
• CPP days (12 days: 5/1 – 10/31)– Average of maximum outside air
temperatures in San Francisco, San Jose, Sacramento and Fresno > 98 oF
Page 28
Critical Peak Pricing (2 of 3)
• Current tariff: A-10S
• Non CPP Day Rate– On-peak credit, $0.0559/kWh, (12 pm- 6 pm)– Part-peak credit, $0.0050/kWh, (8:30 am-12 pm)
• CPP Day Rate– Moderate price, $0.24/kWh (12 pm – 3 pm)– High price, $0.82/kWh, (3 pm-6 pm)
Page 29
Critical Peak Pricing (3 of 3)
$-
$2,000.00
$4,000.00
$6,000.00
$8,000.00
$10,000.00
$12,000.00
$14,000.00
$16,000.00
$18,000.00
non-CPP dayssavings
CPP days extracost withprecooling
CPP days extracost w/o
precooling
Page 30
Market Potential – Cooling in Office Buildings
• State-wide peak demand ~50GW• Commercial cooling - largest contributor: 15%, ~7.5 GW
Cooling Electricity Breakdown*
Large office (>30,000 sf)
Small office (<30,000 sf)
RetailsCollegeRestraurant
School
Health
Hotel
Others
*CEC 1994 electricity consumption
Page 31
Conclusions• Precooling & zone temp reset can shed up to 80 –100% of
the cooling peak load, without comfort complaints, even in relatively high outside temperature conditions (90 oF)
• Benefits of nocturnal precooling are unclear• Economic savings can be made if combined with CPP or
similar DR programs Extended Precooling + DL Hot days
0
1
2
3
4
5
0 2 4 6 8 10 12 14 16 18 20 22 24
Time (hour)
Wh
ole
Bu
ild
ing
po
wer
W/s
qft
Extended precooling 1 baseline
2.3 W/sf shed
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