intro to energy management

8/9/2019 Intro to Energy Management

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Energy accounting

Energy performance indicators

Energy use prediction


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Energy Accounting: the first step in an energy audit

Performing an energy balance for the building toaccount for all the energy being purchased.

Energy in = Energy out

How do we determine energy in?


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Energy Accounting

Energy in?

With adequate metering, energy input iseasily determined from records of purchased energy (mayneed additional metering)

Energy exchange with the environment may need to be

included (i.e. air infiltration, solar gain, etc.)

How do we determine energy out?


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Energy Accounting

Energy out? A more time consuming analysis including:

The tabulation of electrical devices in the facility, includingnameplate or measured demand and energy consumption,and times of operation

The measurement and calculation of all thermal loads,such as burners in boilers and furnaces, steam or hot waterheater flow, ventilation air flow, fluids to drain, heat lossand gain through the building envelope.


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Energy Accounting ExampleHow many kW-hrs are used by ten 80 W light fixtures whichare on for 8 hours per day, 21 days per month?


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Energy Accounting ExampleHow many kW-hrs are used by ten 80 W light fixtures whichare on for 8 hours per day, 21 days per month?

10*80W*8hr/day*21days =134,00W-hr = 134.4 kW-hr


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Energy Performance IndicatorsUsed to relate consumption to measures of activity,

weather or facility size:

BTU/unit or lbs. of production

BTU/ft2

BTU/degree day

BTU/sales dollar


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Energy Utilization Index

EUI is commonly used in the building sector:

EUI = annual energy use in BTU/conditioned ft2

EUI in BTU/ft2or kWh/m2

EUI relates annual energy use to square feet ofconditioned f loor space.


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Typical EUI values in the US:

Office building 90,500 BTU/ft2

Food sales & service 200,000 BTU/ft2

Health care facilities 175,000 BTU/ft2

u:\pc\win_data\my documents\Courses\Energy Management\DOE Energy Intensity Statistics.htm


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Target values of EUI (BTU/ft2) would vary with whatparameters?


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Target values of EUI would vary with what parameters?

Climate

Construction (age of building)

Building use

Equipment in use


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Energy Conversion Units (p.9)

1 kWh ..3412 BTU

1 ft3 natural gas.1000 BTU

1 therm natural gas.100,000 BTU1 barrel crude oil5,100,000 BTU

1 ton coal.25,000,000 BTU

1 gallon gasoline.125,000 BTU

1 gallon #2 fuel oil.140,000 BTU

1 gallon LP gas95,000 BTU


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Energy Use Index ExampleAn office building has 120,000 square feet ofconditioned space and uses 2.63 million

kWh and 4,800,000 cubic feet of natural gasin one year.

Calculate the EUI (in BTU/ft2) for the building.


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Energy Use Index Example

An office building has 120,000 square feet ofconditioned space and uses 2.63 million kWh and

4,800,000 cubic feet of natural gas in one year.Calculate the EUI for the building.

Answer: EUI = 114,800 BTU/ft2


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8575

202

176

7282

3244

241

10090 87

124

Average EUI Values in kBTU/ft2


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Energy Cost Index, ECI EUI can be limiting because different sources of

energy have different costs.

ECI is simpler and sometimes more meaningful.

ECI = Costs of energy/ ft2of conditioned floor space

Average office building ECI = $1.51/ft2 per year


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Energy Cost Index, ECI

For the last example (using 2.63M kWh ofelectricity and 4.8M ft3of natural gas in120,000ft2), use $0.07 per kWh and $16.93per 1000 ft3of natural gas to determine theECI.


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Energy Cost Index Example

For the last example (using 2.63M kWh of electricityand 4.8M ft3of natural gas in 120,000ft2), use $0.07

per kWh and $16.93 per 1000 ft

3

to determine theECI.

Answer: $2.21/ft2


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Energy Unit Conversions

How many tons of coal will need to be burned to run a3500 kW facility for one month?


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How many tons of coal will need to be burned to run a3500 kW facility for one month?

3500kW *(30days)(24 hr/day) = 2.52 x 106kWh

2.52 x 106kWh (3412BTU/kWh)/(25 x 106BTU/ton)=

343.9 tons of coal


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A 55,000ft2educational facility has an annual energyusage of 1,200,000 kWh of electricity and 7000 thermsof natural gas. Find the EUI and compare to the

average value.

EUI = 87,170 BTU/ft2

Compare to 75,000 BTU/ft2.


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Energy Monitoring

Independent variables

Operating hours/occupancy

Production levelClimate (degree days)


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Degree Days

An indicator of how much conditioning is needed in acertain climate.

Heating degree day (HDD)= the difference between theaverage outdoor temperature and a baseline indoor

temperature (65F) summed for all heating days

Cooling degree day (CDD) = the difference between the

average outdoor temperature and a baseline indoortemperature (65F) summed for all cooling days


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Degree

day CalculationCalculate the heating degree-days needed for an average

outdoor temperature of 20F for one week.

(65-20)F* 7days = 315 degree-days


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Heating Degree-Days for Januarysource: EIA

Division Normal 2006 2007

New England 1246 993 1106

Middle Atlantic 1158 874 980

South Atlantic 643 464 509East SouthCentral

820 551 705

East NorthCentral

1302 901 1112

Mountain 951 801 1049


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Calculation of Building Heat Load

Total heat load = heat lost through the walls, roof andfoundation plus heat added through HVAC

q = UA(Ti-To) + mcp (Ti-To)

in BTU/hr


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Calculation of Building Heat Load

q = UA(Ti-To) + mcp (Ti-To) becomes (from your text):

H=(UA +CpNV)(Ti-To)

U= overall heat transfer coefficient for the buildingA= surface area of external surfacesCp = specific heat of airN= number of air changes per time

V= volume of air in the roomT = temperature

H (or q) in BTU/hr


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Calculation of Heat Load

Now divide by (Ti-To) and multiply by degree-days to get:

H= (UA +CpNV)* 24hr/day * degree-days + CNow H is in BTUs.

Takes the form: y = mx + c

Where:

y =H, heat loss

x=degree days (climate)


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Calculation of Heat Load

Now divide by (Ti-To) and multiply by degree-days to get:

H= (UA +CpNV)* 24hr/day * degree-days + CH = m*DD + C

C is a constant representing the no load energy used byoffice equipment, lighting, etc.


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Predicting Energy Performance Previous years data

Regression analysis

Simulation model


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Regression Analysis

Use single or multi-variable regression on previousenergy use data to predict future energy use.

Use Excel.


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Facility Energy Use Data

Month Production Degree-days Energy Use(1000 units) (105kWh)

Jan 1250 316 40.2Feb 1385 388 51.7Mar 1150 201 38.8

Apr 950 22 27.9May 900 67 25.5Jun 1075 224 36.7Jul 1225 316 47.3Aug 1250 294 46.5

Sep 1150 118 35.7Oct 1150 69 32.1Nov 975 198 35.6Dec 1425 257 39.5


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Energy Use versus Degree-days

y = 6213.3x + 3E+06R = 0.8646

0

1000000

2000000

3000000

4000000

5000000

6000000

0 50 100 150 200 250 300 350 400 450

EnergyUse(k

Wh)

Degree-days


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Energy Use versus Production

y = 32.408x + 1E+06R = 0.7174

0

10000000

20000000

30000000

40000000

50000000

60000000

800000 900000 1000000 1100000 1200000 1300000 1400000 1500000

EnergyUse(inkW

h)

Production (units)


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Energy Performance Model

From the Energy Use versus Production plot:

y = 32.4x + 1.402E6

R = 0.717Or:

Energy Use =32.4*(production units) + 1,402,000

This means that we use 32.4 kWh/production unit,and

the baseline energy use (with no production) is1,402,000 kWh.


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Energy Performance Model

From the Energy Use versus Degree-days plot:

y = 6213.3x + 3.0E7

R = 0.8646What does this mean?


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Energy Performance ModelFrom the Energy Use versus Degree-days plot:

y = 6213.3x + 3.0E7

R = 0.8646What does this mean?

Energy Use = 6213.3*(degree-days) + 30,000,000

This means that we use 6213.3kWh per degree-day, and

the baseline energy use (with no heating or cooling) is30,000,000 kWh.

intro to energy management

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