Peng Xu, Philip Haves, James Braun, MaryAnn Piette

1
A Case Study of Precooling with Zone Temperature
Reset in a Commercial Office Building

• Peng Xu, Philip Haves, James Braun, MaryAnn
  Piette
• January 23, 2004
• Sponsored by the California Energy Commission and
  the California Institute for Energy Efficiency

2
Outline

• Aim
• Test site description
• Precooling and demand shedding strategies
• Test results
• Utility analysis
• Conclusions and future work

3
Aim

• Demonstrate the potential for reducing
  peak-period electrical demand in a
  moderate-weight commercial building using
  building structural mass.

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

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

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)

7
South Facade
8
North Facade
9
Windows

• Single glazing
• Tinted glass
• Internal blinds

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

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

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

13
Precooling Zonal Reset Strategies
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

15
Operative Temperature Comfort
Room
Regular temperature sensor
Radiant heat exchange
screen
Convective heat exchange
Operative temperature sensor
globe
16
Peak OA Temperature vs. Peak Demand
17
Classification of Weather Conditions
Hot days
Warm days
Cool days
18
Comparison of Baseline Test Conditions
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Tests Performed
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Cool Days Limited Precooling
21
Warm Day Limited Precooling
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Extended Limited Precooling
23
Hot days Extended Precooling
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Chiller Power Limited Precooling
0.7 W/sf shed
25
Results Fan Power
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Results Zone Temp
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Critical Peak Pricing (1 of 3)

• Operating time
• CPP high price 300pm 6pm
• CPP moderate price 1200pm 300pm
• CPP days (12 days 5/1 10/31)
• Average of maximum outside air temperatures in
  San Francisco, San Jose, Sacramento and Fresno gt
  98 oF

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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, (830 am-12 pm)
• CPP Day Rate
• Moderate price, 0.24/kWh (12 pm 3 pm)
• High price, 0.82/kWh, (3 pm-6 pm)

29
Critical Peak Pricing (3 of 3)
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Market Potential Cooling in Office Buildings

• State-wide peak demand 50GW
• Commercial cooling - largest contributor 15,
  7.5 GW

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