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Dr. David Claridge Leland Jordan Professor Texas A&M University

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Exploring the Limits of Energy Efficiency and Demand Reduction in Office Buildings David E. Claridge and Oleksandr Tanskyi Mechanical Engineering Dept. and Energy Systems Laboratory Texas A&M University 2013 SEC Symposium Atlanta February 10-12, 2013

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Imagine Carbon Neutral Buildings Assume all energy from renewable sources, e.g. Photovoltaics Biomass Wind Solar Thermal Photo courtesy of: sine.ni.com

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Less Energy Used = Less Energy Production Impact More flexibility in building design/construction May lower life cycle cost Talk about 30% and 50% less energy than code The Carnot Limit to energy needed defines one boundary of energy use/supply tradeoffs

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Exploring a Carnot Limit for Energy Systems Lab Energy Use 25,774 ft 2

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Minimally Code Compliant Building Energy Code Program OKd with Envelope losses 20% above code 10 Rooftop air conditioners w/EER = 10.0 On/off operation Night setback Electric heating

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B ASELINE B UILDING : MEASURED CONSUMPTION 350,000 K W H / YR Ventilation 27% Cooling 28% Lighting 21% Plugs 19% Heating 5%

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Basic Building Requirements Cooling and Heating for Comfort Ventilation for Healthy Air Lighting Computers/Printers Copiers Cooled Drinking Water Heating – Lunch and Coffee Hot Water – Restrooms

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Building Assumptions Comfort – Maintain 73ºF/50% Relative Humidity Ventilation – Meet ASHRAE Ventilation Standard Lighting –IESNA recommended levels Computers – 1/person Monitors – 2/person Printers – 1/person

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ESL Building Assumptions Copiers: 1/60 people (2000 pages/person/yr) Cooled Drinking Water: 1 Qt/person/day Cooled from 70ºF to 50ºF Heating: (1 Cup water)/person/day Heated from 70ºF to 212ºF Hot Water-Restrooms: ½ gal/person/day Heated from 70ºF to 105ºF Occupied 60 hours/week

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Exploring The Limits What are the limits? What is the minimum energy required to meet each of these office building requirements/services?

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Exploring The Limits: Lighting Chose average of Illuminating Engineering Society of NA recommended 20-50 fc 400 – 700 nM radiation from 5800K black body ~250 Lumens/Watt On 6 hr/day weekdays LED LIGHTS

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Exploring The Limits: Lighting 35 foot-candles => 0.13 W/ft 2 when occupied 0.01 W/ft 2 unoccupied 1.7 kW avg. occupied without daylighting 0.85 kW avg. occupied with daylighting 0.24 kW unoccupied

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Exploring The Limits: Computers No obvious physical limit Assume 2.5W for 1 GHz processor (e.g. iPhone ) Hibernate when not in use Assume 30 hr/wk for 128 people => 147 W average when occupied

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Exploring The Limits: Monitors Assume limit is lighting power Two 1.5ft 2 (23-in) monitors per person 250 candela/m 2 @250 Lumens/W=> 1.75 W/monitor Sleep when not active 6 hr/day for 256 monitors 206 W average when occupied

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Exploring The Limits: Printers Physical limit not obvious Ink jet printer is ~0.07 Wh/page 2000 pages per person/year => 7 W average when occupied

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Exploring The Limits: Copiers 2,000 copies/person per year at Energy Systems Lab Use same energy assumptions as printer 7 W average when occupied

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Exploring The Limits: Cooled Drinking Water 1 Qt/day per person from 70ºF to 50ºF Use Carnot refrigerator COP Carnot = 28.3 => 4.3 W average for building (when occupied)

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Exploring The Limits: Heating Food/Water 1 Cup water or equivalent food per person daily from 70ºF to 212ºF Carnot heat pump COP Carnot = 4.66 for 70ºF to 212ºC => 53 W average for building (when occupied)

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Exploring The Limits: Heating Water - Restrooms ½ gal/person per day 70ºF to 105ºF Carnot heat pump COP Carnot = 15.65 for 70ºF to 105ºF => 31 W average for building (when occupied)

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Exploring The Limits Cooling and Heating Loads Electricity used in space Occupants Solar Ventilation power Heat gain/loss through walls, etc.

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Exploring the Limits: Electricity in Space SourceOccupied (W) Unoccupied (W) Lighting838240 Computers1470 Monitors2060 Printers/Copiers 140 Water Cooling4.30 Heating Food530 Restroom HW310 Total1,293 W240 W

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Occupant Gains ASHRAE: Moderately active office work: 73 W/person sensible 59 W/person latent Assume 40 hours/week/person => 6,250 W sensible 5,000 W latent

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Exploring the Limits: Solar Gains Theoretical limit is zero We assume the amount of solar gain corresponding to the amount of daylight => 850 W average occupied gain

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Exploring the Limits: Ventilation Energy ASHRAE Ventilation Standard requires 2,190 cfm outside air when occupied Assume Perfect enthalpy recovery device Exhaust air = outside air intake 0.02 inWG fan pressurization Perfect fan => 5.1 W fan power when occupied is only ventilation energy required

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Exploring the Limits: Wall/Window/ Roof Gains/Losses Theoretical limit is zero We assume zero

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Exploring the Limits: Cooling and Heating Assume: Free cooling when conditions permit Carnot chiller for cooling otherwise Carnot heat pump for heating

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Exploring the Limits: Chiller Electricity Assume Houston, TX Weather Total cooling 40,161 kWh th Free cooling meets 24,595 kWh th Chiller provides 15,566 kWh th Chiller requires 250 kWh Average COP = 62

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Exploring the Limits: Heating Heating Load is zero Heating electricity is 0 kWh!

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Todays Buildings vs. Carnot Limit Building U.S. average is 82 kBtu/ft 2 -yr Carnot Limit is 0.73 kBtu/ft 2 -yr ESL Building is 50 kBtu/ft 2 -yra

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Todays Buildings vs. Carnot Limit Building U.S. average is 82 kBtu/ft 2 -yr Carnot Limit is 0.73 kBtu/ft 2 -yr ESL Building is 50 kBtu/ft 2 -yr Zero Energy Bullitt Foundation Cascadia Center is planned for 16 kBtu/ft 2 -yr a

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What About Peak Demand? ESL Building 138 kW summer 178 kW winter

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What About Peak Demand? ESL Building 138 kW summer 178 kW winter Carnot Limit Bldg 2.2 kW summer 1.6 kW winter 1-2% of ESL Bldg

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What Can We Achieve? This IBM 7094 Had a tiny fraction of the capability of the Iphone

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Incremental Improvement is important, BUT

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There is room for SPECTACULAR progress in Energy Efficiency! Pursue Disruptive Change

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?? David Claridge dclaridge@tamu.edu

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Dr. David Claridge Leland Jordan Professor Texas A&M University

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