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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Incremental Improvement is important, BUT

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

?? David Claridge

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