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 ft2
Minimally Code Compliant
Building
 Energy
Code Program OK’d with
Envelope
 10
losses 20% above code
Rooftop air conditioners w/EER = 10.0
 On/off
 Night
operation
setback
 Electric
heating
BASELINE BUILDING:
MEASURED CONSUMPTION
350,000 KWH/YR
Other; 313; 0%
Ventilation
fans; 102,165;
27%
Ventilation
27%
Cooling
Cooling;
103,886; 28%
28%
Lighting
21%
Area Lights;
80,248; 21%
End-use
Equipment;
71,332; 19%
Plugs
19%
Heating
5%
Heating;
18,806; 5%
Basic Building Requirements
 Cooling
and Heating for Comfort
 Ventilation
for Healthy Air
 Lighting
 Computers/Printers
 Copiers
 Cooled
Drinking Water
 Heating
 Hot
– Lunch and Coffee
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


Heating: (1 Cup
water)/person/day


Heated from 70ºF to 212ºF
Hot Water-Restrooms: ½
gal/person/day


Cooled from 70ºF to 50ºF
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
 On
Lumens/Watt
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 Limits
Cooling and Heating
 Loads
Electricity
used in space
Occupants
Solar
Ventilation
Heat
power
gain/loss through walls, etc.
Exploring the Limits:
Electricity in Space
Source
Lighting
Computers
Monitors
Printers/Copiers
Water Cooling
Heating Food
Restroom HW
Total
Occupied
(W)
838
147
206
14
4.3
53
31
Unoccupied
(W)
240
0
0
0
0
0
0
1,293 W 240 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
 We
limit is zero
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 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 zero
 Heating
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 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
Incremental” Improvement is
important, BUT
 There is room for
SPECTACULAR progress in
Energy Efficiency!
 Pursue Disruptive Change

??
David Claridge
dclaridge@tamu.edu
Dr. David Claridge
Leland Jordan Professor
Texas A&M University