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!