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David E. Claridge

Director Oleksandr Tanskyi

Graduate Research Assistant Energy Systems Laboratory

Texas A&M University System

BEST 3 Atlanta

April 2-4, 2012

BACKGROUND

Electric Motor Efficiency is Limited to < 100% Air Conditioners are Limited to Carnot COP Perfection is Impossible – But Perfection Provides Useful Limits

HOME OF ENERGY SYSTEMS LAB

25,774 FT2

MINIMALLY CODE COMPLIANT BUILDING

Doors Meet Prescriptive Code Comchek Passed Envelope

Envelope losses 20% above code 10 Packaged CV systems On/off operation Night setback Electric resistance heating EER = 10.0 (COP=2.9)

Area Lights; 80,248; 21%

End-use Equipment;

71,332; 19%

Heating; 18,806; 5%

Cooling; 103,886; 28%

Ventilation fans; 102,165;

27%

Other; 313; 0%

BASELINE BUILDING:

DOE-2 SIMULATION RESULTS

Site energy consumption: 376,750 kWh/yr (14.6 kWh/ft2-yr)

BASIC ESL OFFICE BUILDING REQUIREMENTS

Comfort for Occupants – Cooling and Heating Ventilation for Indoor Air Quality Lighting Computers/Printers Copiers Cooled Drinking Water Heating – Lunch and Coffee Hot Water – Restrooms Computer Servers

ESL OFFICE BUILDING ASSUMPTIONS

Comfort – Maintain 73ºF/50% Relative Humidity Ventilation – Meet ASHRAE Standard 62

5 cfm/person + 0.06cfm/ft2 Lighting –IESNA recommended levels Computers – 1/person Monitors – 2/person (23-inch) Printers – 1/person (2000 pages/yr)

ESL OFFICE BUILDING ASSUMPTIONS

Copiers – 1/30 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 Computer Servers – Outsourced 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? What is the minimum energy required to provide

these services in our office building?

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

EXPLORING THE LIMITS:

LIGHTING

35 foot-candles => 0.13 W/ft2

Occupancy sensors => 0.01 W/ft2 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 4) 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 1.5ft2 (23-in) monitors per person 250 candela/m2@250 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 COPCarnot = 28.3 => 4.3 W average for building (when occupied)

EXPLORING THE LIMITS:

HEATING FOOD/WATER

Assume 1 Cup water or equivalent food per person daily from 70ºF to 212ºF

Assume Carnot heat pump COPCarnot = 4.66 for 70ºF to 212ºC => 53 W average for building (when occupied)

EXPLORING THE LIMITS: HEATING WATER - RESTROOMS

Assume ½ gal/person per day 70ºF to 105ºF Assume Carnot heat pump COPCarnot = 15.65 for 70ºF to 105ºF => 31 W average for building (when occupied)

EXPLORING THE LIMITS

COOLING AND HEATING

Loads Internal Gains Occupants Solar Ventilation Envelope

EXPLORING THE LIMITS:

INTERNAL GAINS Source Occupied

(W) Unoccupied

(W) Lighting 838 240 Computers 147 0 Monitors 206 0 Printers/Copiers 14 0 Water Cooling 4.3 0 Heating Food 53 0 Restroom HW 31 0 Total 1,293 240

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 daylighting => 850 W average occupied gain

EXPLORING THE LIMITS:

VENTILATION ENERGY ASHRAE Standard 62-2007 requires 2,190 cfm

outside air when occupied Assume

12 hours/day weekdays 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:

ENVELOPE GAINS/LOSSES Theoretical limit is zero We assume zero

EXPLORING THE LIMITS:

COOLING AND HEATING

Assume: “Economizer” cooling when conditions permit Carnot chiller for cooling otherwise Carnot heat pump for heating

EXPLORING THE LIMITS:

COOLING LOADS Gains Occupied (W) Annual Total

(kWhth) Internal 1,293 3,883

Occupant - Sens. 6,250 18,757

Occupant – Lat. 5,000 15,006

Solar 838 2,515

Ventilation Load 0 0

Envelope Load 0 0

Total Load 13,371 W 40,161 kWh

EXPLORING THE LIMITS:

CHILLER ELECTRICITY

Assume Houston, TX Weather Total Cooling Load 40,161 kWhth

Economizer meets 24,595 kWhth

Chiller provides 15,566 kWhth

Chiller requires 250 kWh Average COP = 62

EXPLORING THE LIMITS:

HEATING Heating Load is zero Heating electricity is 0 kWh!

ELECTRICITY CONSUMPTION: THEORETICAL LIMIT

SA

ZAZA DOAS

~

QCooling

Q Heating

QCooling

QHeating

W Heating

Internal heat gain

~

~

OA

EA RA

DA

ERV

Energy recovery

ventilation HP HTG

HP CLGDOAS

WLoads

WCooling

WDOAS

Q DOASWater side economizer

Water side economizer

5,262 kWh 15 kWh

0 kWh

250 kWh

0 kWh

HOW DO TODAY’S BUILDINGS COMPARE WITH THEORETICAL LIMIT?

U.S. Office Building average is 82 kBtu/ft2-yr ESL Building 50 kBtu/ft2-yr Bullitt Foundation Cascadia Center is planned for 16 kBtu/ft2-yr Theoretically possible 5,527 kWh => 0.73 kBtu/ft2-yr = 0.21 kWh/ft2-yr!!!

WHAT SHOULD WE TARGET?

Target? Minimum Lighting and Plug Loads 8,484 kWh 5,252 kWh

Fans, Cooling, Heating 9,269 kWh 265 kWh

Total 17,753 kWh 5,527 kWh

(2.35 kBtu/ft2) (0.73 kBtu/ft2)

HOW DOES “TARGET” COMPARE? ESL Building 50 kBtu/ft2-yr Cascadia Center 16 kBtu/ft2-yr Theoretically possible 0.73 kBtu/ft2-yr “TARGET” 2.35 kBtu/ft2-yr

IF WE COULD ACHIEVE TARGET BUILDINGS WORLDWIDE -

We could power U.S. office space/person for every person in the world on the ELECTRICITY used today in U.S. offices!

And ~6.5 ft2 of Photovoltaic cells/occupant would make the TARGET office building NET ZERO!

CAN WE DO IT? This IBM 7094 Had a tiny fraction of the capability of this Iphone

CONCLUSION

There is still room for SPECTACULAR progress in Energy Efficiency!