chapter_2.pdf

05/04/2011 Tarik Al-Shemmeri 1

ENERGY AUDIT FOR BUILDDINGS


Is about the What, Where, and When energy is used

And suggesting how this consumption

can be reduced

Energy Audits


Energy Audit will provide: !  financial, !  operational and !  Environmental

benefits

Energy Audits


!  Financial Benefits - ! Reduced fuel and electricity bills. ! Reduced operation and maintenance costs . ! Reduced capital expenditure.

Energy Audits


!  Operational Benefits - ! Improved comfort levels ! Improved efficiency ! Better informed workers on global issues.

Energy Audits


!   Environmental benefits – ! Reduced consumption of finite resources. ! Reduced Pollution levels. ! Improved public image.

Energy Audits


Assessing current building performance

Two methods of Energy Audit: !  The Regression Method, and !  The NPI Method.



!  The Regression Method A standard method to assess the energy use in buildings, done by plotting the energy consumption each Month against the Degree days for that month.



!  The Regression Method This will show the trend in Energy consumption, is fitted by a linear relation, from this it is possible to predict future consumption.


Month Regression Degree Day Figure

Energy Consumed (GJ)

January 376 185.67 February 359 166.51 March 322 157.56 April 243 124.33 May 162 98.22 June 83 72.6 July 44 56.65 August 48 54.89 September 90 71.66 October 178 103.49 November 275 140.78 December 343 171.62


Regression Method

0

50

100

150

0 100 200 300 400 Degree Day

Ener

gy C

onsu

med

(k

Wh)


NPI Method

The Normalised Performance Indicator (NPI) comparing the building’s energy consumption with similar type buildings.


Calculating the NPI !   Convert Energy Units to KWh !   Find the Energy Used for Space Heating !   Account for Weather !   Account for Exposure !   Add Non-Heating Energy Use !   Account for Hours of Use Factor !   Find Floor Area (Pool Area) (m2) !   Calculate the Normalised Performance

Indicator (NPI).


Calculating the NPI !  Step 1 Collate all energy use, Convert Energy

Units to KWh

1 therm = 29.31 kWh Natural Gas 1 litre = 10.6 kWh Oil 1 tonne = 7600 kWh Coal


Calculating the NPI !  Step 2 Find the Energy Used for Space Heating

eg a sport centre with a swimming pool 65% of the energy is used in heating on average.


Calculating the NPI !  Step 3 Account for Weather

Weather factor = 2462 / annual degree days


Calculating the NPI !  Step 4

Account for Exposure Factor = 1 for urban building

= 1.1 for Sheltered buildings = 0.9 for Exposed buildings


Calculating the NPI !  Step 5 Add Non Space heating energy



Multiply for hours of use

Use factor = standard hours / actual hours in use



Calculate Floor area in square meters



Calculate NPI = corrected energy used / floor area



Compare NPI with tabulated values for similar buildings and hence

find out in which range of performance does your building lie ?


Comparisons of performance indicators

!  Good - generally have good controls and energy management procedures, but further energy savings are often still possible.

!  Fair - reasonable controls and energy management procedures, but significant energy savings should achievable.

!  Poor - unnecessarily high consumption and urgent action should be taken to remedy the situation. Substantial energy savings should result from the introduction of energy efficiency measures.


Performance Yardsticks For Buildings

Energy Efficiency Rating kWh/m2 per year

Type of Facility

Good Fair Poor

Pub <339 339 – 470 >470

Sports centre with swimming Pool.

<570 570 – 840 >840

Theatre <600 600 - 900 >900


Savings 1. By altering the physical

construction of a building to reduce its heat loss

eg double glazing, cavity insulation and loft insulation.


Savings 2. Replacing/upgrading the

equipment and controls to make it more efficient. Time switches, occupancy switches, and Thermostat controls.


Savings 3. Shop around

for the cheapest tariff.


Savings 4.  Continuous monitoring

of Energy consumption.


Savings 5. Using combined heat and power

(CHP) plant to provide electricity and space heating/hot water.

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Tarik Al-Shemmeri 30

Case study

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Month Natural Gas (Therm) Electricity (kWh)

January 1578 5325

February 1400 5220

March 1309 5400

April 1000 5225

May 750 5300

June 503 5425

July 355 5330

August 350 4990

September 500 5250

October 800 5300

November 1150 5400

December 1460 4880

TOTALS 11,155 63,045

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Month Gas (Therm) Gas (GJ) Cost % Cost January 1578 166.5 760.44 14.1 February 1400 147.72 675 12.6 March 1309 138.12 631.32 11.7 April 1000 105.52 483 9 May 750 79.14 363 6.7 June 503 53.07 244.44 4.5 July 355 37.46 173.4 3.2 August 350 36.93 171 3.1 September 500 52.76 243 4.5 October 800 84.41 387 7.2 November 1150 121.34 555 10.3 December 1460 154.05 703.8 13.1 Totals 11,155 1177.03 5390.4 100

Gas Data

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Month Elec. (kWh) Cost % Cost January 5325 429.17 8.4 February 5220 420.77 8.3

March 5400 435.77 8.6 April 5225 42.17 8.3 May 5300 427.17 8.4 June 5425 437.17 8.6 July 5330 429.57 8.5

August 4990 402.37 7.9 September 5250 423.17 8.3

October 5300 427.17 8.4 November 5400 435.17 8.6 December 4880 393.57 7.7

Totals 63,045 5081.6 100

Electricity Data

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Energy C onsumption

84%

16%

Natural GasElectricity

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Energy C ost

51%49% Natural GasElectricity

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Energy C onsumption

0

50

100

150

200

Jan Feb Mar Apr May Jun Jul Aug Sep O ct Nov Dec

Gas (GJ)Electricity (GJ)

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Energy C ost

0

200

400

600

800

1000

Jan Feb Mar Apr May Jun Jul Aug Sep O ct Nov Dec

Gas (£)Electricity (£)

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Regression data

Month Regression Degree Day Figure

Energy Consumed (GJ)

January 376 185.67

February 359 166.51

March 322 157.56

April 243 124.33

May 162 98.22

June 83 72.6

July 44 56.65

August 48 54.89

September 90 71.66

October 178 103.49

November 275 140.78

December 343 171.62

Totals 1403.99 1228.83

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Regression Equation Graph

0

50

100

150

0 100 200 300 400

Regression Degree Day Figure

Ener

gy C

onsu

med

(G

J)

The equation is given by : E = 0.365(DD) + 38

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1.  Convert your energy use into kWh units

Add your quarterly or monthly use over one year for each fuel and enter below

Natural gas Electricity Total energy use for the year

{ Therms x 29.31 = 11155 x 29.31 =326953 kWh x 1 = 63045 =389998

kWh kWh kWh

A

2.Find your space heating energy use

If you can identify any of the fuels above used only for space heating, enter the total energy use in kWh

Add these to give total 0 kWh B

If you cannot identify these then choose one of the following factors applied to the total energy used.

For light industrial factory building Annual space heating energy Annual non-space heating energy

Space heating factor = 0.80 A x 0.80 = 389998x0.80 = 311998 B or C = 311998 A-D = 389998- 311998= 77999

kWh kWh kWh

C D E

3. Adjust the space heating energy to account for weather

•  Find the Degree Days for the energy data year = 2523 •  The weather correction factor = 2462/2523 = 0.976 •  Adjust the space heating energy to standard conditions = D x G =311998x0.976=304455

kWh F G H

4. Adjust the space heating energy to account for exposure

•  Obtain the exposure factor from this chapter to suit the location of the building = 1 J

•  Adjusted space heating energy = H x J = 304455 x 1 = 304455 kWh K

5. Find normalised annual energy use = E + K = 77999 + 304455 = 382454 kWh L

6. Correct for hours of use of building

•  Obtain standard hours of use = 2000 M

•  Calculate the annual hours of use for your building -= 9x5x48 = 2160 N

•  Hours of use factor M / N =2000/2160 = 0.926 P

•  Annual energy use for standard hours P x L = 0.926x 382454 = 354152 kWh Q

7. Find floor area = 25 x 25 = 625 m2 m2 R

8. Find the Normalised Performance Indicator (NPI) = Q / R = 354152/ 625 = 566 9. Compare with yardstick - [ 180 to 240 kWh/m2 ] Excessive Energy consumption

kWh/m2 POOR

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Calculation of Heat Losses width

height

depth

W W

D

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Element U-value W/m2K

Area m2

Temp. Difference (oC)

Heat loss W

Door 2 18 12.5 450

Windows 5.3 42 12.5 2782

Walls 2.3 360 12.5 10350

Roof 2.6 900 12.5 29250

Floor 0.26 900 12.5 2925

Fabric heat loss = TOTAL ( Doors, Windows, Walls, Roof & Floor)

45757

Ventilation Heat Loss = 0.335 N V ΔT N=1.2

15600

Heat gains from occupants

0

Heat gains from lights 0

Heat gains from machines 0

Net heat transfer for the building 61357

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Energy Efficiency Measures

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Reduction of Fabric Losses Wall Insulation Area = 360 m2 cost of liner board = £8.20/m Cost = 360 * 8.2 = £2952 Roriginal = 1/Uoriginal = 1/2.3 = 0.4348 Rinsulation = x /k = 0.025/0.04 = 0.625 Rnew = Roriginal + Rinsulation = 0.4348 + 0.625 = 1.0598 Unew = 1/1.0598 = 0.9436 AUwall original = 828 W/K AUwall new = 0.9436 * 360 = 339.7 W/K ΔAUwall = ΔAU * 12.5 = 6.104 kW Saving = 6.104 * 65.32 = £3908.71/annum Pay back period = C/F = 2950/398.71 = 7.4 years

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Roof Insulation Area = 900 m2 Cost of Rockwool = £6.40 / m2 Rnew = Rold + Ri = (1/2.6) + ( 0.1/0.04) = 2.5 + 0.3486 = 2.8846 Unew = 1 / 2.8846 = 0.3467 AUroof original = 900 x 2.6 = 2340 W/K AUroof new = 900 x 0.3467 = 312 W/K ΔAU = 2340 - 312 = 2028 W/K ΔQf = ΔAU * 12.5 = 25.35 kW Saving = 25.35 * 65.32 = £1655.84/annum Pay back period = C/F = 5760/1655.84 = 3.48 years

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