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