Post on 28-Mar-2015
Dr. David ClaridgeLeland Jordan ProfessorTexas 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 AtlantaFebruary 10-12, 2013
ImagineCarbon Neutral Buildings
Assume all energy from renewable sources, e.g.PhotovoltaicsBiomassWindSolar 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 ft2
Minimally Code Compliant Building
Energy Code Program OK’d withEnvelope losses 20% above code
10 Rooftop air conditioners w/EER = 10.0On/off operationNight setbackElectric heating
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:MEASURED CONSUMPTION
350,000 KWH/YR
Ventilation 27%
Cooling 28%
Lighting 21%
Plugs 19%
Heating 5%
Basic Building Requirements
Cooling and Heating for ComfortVentilation for Healthy AirLightingComputers/PrintersCopiersCooled Drinking Water Heating – Lunch and CoffeeHot 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 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 when occupied
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 )
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
1 Cup water or equivalent food per person daily from 70ºF to 212ºF
Carnot heat pump
COPCarnot = 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
COPCarnot = 15.65 for 70ºF to 105ºF
=> 31 W average for building (when occupied)
Exploring The LimitsCooling and Heating
LoadsElectricity used in spaceOccupantsSolarVentilation powerHeat gain/loss through walls, etc.
Exploring the Limits:Electricity in Space
Source Occupied (W)
Unoccupied (W)
Lighting 838 240
Computers 147 0
Monitors 206 0Printers/Copiers
14 0
Water Cooling
4.3 0
Heating Food 53 0
Restroom HW
31 0
Total 1,293 W
240 W
Occupant Gains
ASHRAE: Moderately active office work:73 W/person sensible59 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
AssumePerfect enthalpy recovery device Exhaust air = outside air intake0.02 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 zeroWe assume zero
Exploring the Limits:Cooling and Heating
Assume: “Free” cooling when conditions permitCarnot chiller for cooling otherwiseCarnot heat pump for heating
Exploring the Limits:Chiller Electricity
Assume Houston, TX Weather
Total cooling 40,161 kWhth
Free cooling meets 24,595 kWhth
Chiller provides 15,566 kWhth
Chiller requires 250 kWh Average COP = 62
Exploring the Limits:
Heating
Heating Load is zeroHeating electricity is 0 kWh!
Today’s Buildings vs. “Carnot Limit” Building U.S. average is 82 kBtu/ft2-yr “Carnot Limit ” is 0.73 kBtu/ft2-yr
ESL Building is 50 kBtu/ft2-yra
Today’s Buildings vs. “Carnot Limit” Building U.S. average is 82 kBtu/ft2-yr “Carnot Limit ” is 0.73 kBtu/ft2-yr
ESL Building is 50 kBtu/ft2-yr “Zero Energy” Bullitt Foundation Cascadia
Center is planned for 16 kBtu/ft2-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 summer1.6 kW winter1-2% 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
Incremental” Improvement is important, BUT
There is room for SPECTACULAR progress in Energy Efficiency!
Pursue Disruptive Change
??David Claridge
dclaridge@tamu.edu
Dr. David ClaridgeLeland Jordan ProfessorTexas A&M University