Page 1 Peng Xu, Philip Haves, James Braun, MaryAnn Piette January 23, 2004 Sponsored 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/ft 2 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 ft 2 (40,000 ft 2 office + 40,000 ft 2 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 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
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 Convective heat exchange Radiant heat exchange Room Regular temperature sensor globe Operative temperature sensor screen
Page 16 Peak OA Temperature vs. Peak Demand
Page 17 Classification of Weather Conditions Hot days Warm days Cool days
Page 18 Comparison of Baseline & Test Conditions
Page 19 Tests Performed
Page 20 Cool Days – Limited Precooling
Page 21 Warm Day – Limited Precooling
Page 22 Extended & Limited Precooling
Page 23 Hot days – Extended Precooling
Page 24 Chiller Power: Limited Precooling 0.7 W/sf shed
Page 25 Results – Fan Power
Page 26 Results – Zone 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 o F
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)
Page 30 Market Potential – Cooling in Office Buildings State-wide peak demand ~50GW Commercial cooling - largest contributor: 15%, ~7.5 GW
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 o F) Benefits of nocturnal precooling are unclear Economic savings can be made if combined with CPP or similar DR programs Extended Precooling + DL Hot days Time (hour) Whole Building power W/sqft Extended precooling 1baseline 2.3 W/sf shed