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Lecture Objectives:
• Finish with example modeling problems– Phase change thermal storage materials– Energy and airflow
• Interpret energy simulation results
Example 3 from previous class: Phase change materials
- Next generation of energy efficient building materials- Integrate phase change materials (PCMs) to insulation - Reduce peak heat transfer rates across walls and
ceilings, - Shift peak cooling loads and reduce size of equipment, - Large potential for reduction of energy use,- Use nanotechnology,- Can be used in insulation or any other building material.
You need to evaluate potential for reduction
of energy use with phase change materials
• Howe would you model phase change materials integrated into building materials?
sourcep
qx
T
c
T
2
2
Example 4 (new): natural ventilation
You need to solve energy and airflow
EnergySimulationProgram
Air FlowProgram ACHData:
geometryweathermaterials
Twall, Tsupply,Tair,…
Flow (ACH), hconv
T room
What are the reasons for the energy simulation?
• Design (sizing of different systems)
• Economic benefits
• Impact on environed
• Fuel budget planning
Site Energy vs. Primary Energy
Site (End-use) energy is the energy directly consumed by end users.
Secondary energy is site energy plus the energy consumed in the production and delivery of energy products
Primary energy is site energy plus the energy consumed in the production and delivery of energy products.
Site energy (End use)
Secondary Energy
Primary Energy
SiteEnergy
PrimaryEnergy
HVAC System
HVAC – Heating, Ventilation and Air-Conditioning
Example of Primary and Site Energy
Site Energy Intensity by Source Primary Energy Intensity by Source
Average Annual Energy Consumption in Commercial Buildings
http://www.eia.doe.gov/emeu/consumptionbriefs/cbecs/cbecs_trends/intensity.html
Site Energy vs. Primary Energy
• Electricity, of the major energy sources, has the greatest disparity between site and primary energy.
• Greater amount of energy is used to generate and transmit electricity than in the production and distribution of the other major sources.
• In 1995, steam-electric utility plants were estimated to have used 10,301 Btu of fossil-fuel energy to generate 1 kilowatthour of electricity.– i.e., approximately 3.02 Btu of fossil-fuel energy were used to
generate 1 Btu of electricity.
Electric Energy Generationin Power Plants
Example 1 of primary energy usefurnace v.s. energy efficiency
Gas or
Coalor Nuclear
Power plant
heat
100 kWh
EE
36 kWh
Transportation losses
EE
33 kWh Electric Heater(100%
efficient)
33 kWh
heat
Overall efficiency 33%
Gas furnace
Electric heater
Gas
Chemicalenergy
100 kWh
Transportation losses
95 kWh Furnace
(80%efficient)
~79 kWh
heat
Overall efficiency 79%
Chemicalenergy
Example 2 of heat pump primary energy efficiency
Gas or
Coalor Nuclear
Power plant
heat
100 kWh
EE
36 kWh
Transportation losses
Buildingat
T=75°FEE
33 kWh
Heat pump
Heat from air, soil, …(100kWh at T=45°F)
COP heat pump = 4
133 kWh
heat
Overall efficiency 133%
However, what is the exact saving? how much will it cost? what kind of system wee need?can we use this system everywhere? ….
Energy modeling and life cycle cost analysis
U.S. Total Primary Energy Consumption by
Source and Sector, 2007
http://www.eia.doe.gov/emeu/aer/pecss_diagram.html
29.4
All numbers are in quadrillion (1015) of Btu
11.2
Total: 101 x 1015 Btu
Use of Electricity by Sector, 2007Total site use of electricity : 3,923,814 thousand
megawatthours ~ 13.3 x 1015 Btu
ResidentialCommercialIndustrialTrans-portation
35.5%
37%27.3%
For the reference and approximate calculation : 1 Wh of electric energy is ~ 3 Wh of primary energy
Total Primary Energy Consumption by Source and Sector, 2007
• Total primary energy: 101.4 x 1015 Btu – ( 29,700,000 thousand MWh)
Residential andCommercial
Industrial
Trans-portation28.5%
32.1%
39.4%
~ 21% residential~ 18% commercial
Do we need stronger motivation to improve our buildings and building systems?
Building Energy Use and Green House Emission
http://www.eia.doe.gov/oiaf/1605/ggrpt/flowchart.html
http://www.eia.doe.gov/oiaf/1605/ggrpt/index.html
17.5%
18.6%
35.8%
28.1%
~36%
How to calculate carbon saving? Some useful data
FuelSpecific Carbon Content(kgC / kgfuel)
Specific Energy Content(kWh / kgfuel)
Specific CO2 Emission
(kgCO2 / kWh)
Coal (bituminous/anthracite) 0.75 7.5 0.37
Gasoline 0.9 12.5 0.27
Light Oil 0.7 11.7 0.26
Diesel 0.86 11.8 0.24
Liquid Petroleum Gas 0.82 12.3 0.24
Natural Gas, Methane 0.75 12 0.23
….
Emission of Carbon Dioxide - CO2 – per unit of energy obtained from different types of fuel.
Zero Energy House High Tech - Solar Decathlon Competition
Cost of these prototype houses: from 200$/sf to 1000$/sf
Technische Universität Darmstadt
UT at Austin
Promote development of solartechnology and energy efficient building systems
Residential Buildings
Low Energy Sustainable Houses Low Tech
Nice examples of sustainable houses, but….
Can you use this technology hereand if yes how large is the overall impact
New York Mexico City
Straw bale house Green roofs Integration of various solutions